Light-emitting devices

Abstract

To provide highly reliable light-emitting devices. [Solution] The device has a first electrode formed on an insulating surface, a second electrode facing the first electrode, and an EL layer located between the first electrode and the second electrode, where one of the first electrode and the second electrode is the anode and the other is the cathode, and the EL layer has a light-emitting layer, a first layer and a second layer, where the first layer and the second layer are located between the light-emitting layer and the cathode, the first layer is located between the first electrode and the second layer, and the second layer is located between the first layer and The light-emitting layer is located between the first electrode and the second electrode, and comprises a first light-emitting material and a second light-emitting material, wherein the first light-emitting material is a material capable of converting triplet excitation energy into light emission, and the second light-emitting material is a fluorescent light-emitting material, and the emission peak wavelength of the first light-emitting material is shorter than the emission peak wavelength of the second light-emitting material, providing a light-emitting device in which the GSP_Slope of the second layer is larger than the GSP_Slope of the first layer.

Description

[Technical Field]

[0001] One aspect of the present invention relates to organic compounds, organic semiconductor elements, light-emitting elements, organic EL elements, photodiodes, display modules, lighting modules, display devices, light-emitting devices, electronic devices, lighting devices, and electronic devices. However, one aspect of the present invention is not limited to the above-mentioned technical field. The technical field of one aspect of the invention disclosed herein relates to a product, a method, or a method of manufacture. Alternatively, one aspect of the present invention relates to a process, a machine, a manufacture, or a composition of matter. More specifically, examples of the technical field of one aspect of the present invention disclosed herein include semiconductor devices, display devices, liquid crystal display devices, light-emitting devices, lighting devices, energy storage devices, memory devices, imaging devices, methods for driving them, or methods for manufacturing them. [Background technology]

[0002] The practical application of light-emitting devices (organic EL elements) that utilize electroluminescence (EL) using organic compounds is progressing. The basic structure of these organic EL elements is an organic compound layer (EL layer) containing a light-emitting material sandwiched between a pair of electrodes. By applying a voltage to this device, carriers are injected, and by utilizing the recombination energy of these carriers, light emission can be obtained from the light-emitting material.

[0003] Because these organic EL elements are self-emissive, using them as pixels in a display offers advantages over liquid crystal displays, such as higher visibility and the elimination of the need for a backlight, making them particularly suitable for flat-panel displays. Another major advantage of displays using such organic EL elements is that they can be manufactured to be thin and lightweight. Furthermore, they are characterized by their extremely fast response speed.

[0004] Furthermore, because these organic EL elements can have their light-emitting layers formed continuously in a planar manner, they can produce light in a planar manner. This is a feature that is difficult to obtain with point light sources such as incandescent bulbs and LEDs, or line light sources such as fluorescent lamps, and therefore has high value as a surface light source that can be applied to lighting and other applications.

[0005] As described above, displays and lighting devices using organic EL elements are suitable for various electronic devices, but research and development are underway to find organic EL elements with even better characteristics. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Hiroshi Noguchi, et al., "Orientational Polarization Phenomena of Polar Molecules and Interface Properties of Organic Thin Film Devices," Journal of the Vacuum Society of Japan, 2015, Vol. 58, No. 3. [Overview of the project] [Problems that the invention aims to solve]

[0007] One aspect of the present invention aims to provide a reliable light-emitting device. Another aspect of the present invention aims to provide a light-emitting device with high luminous efficiency. Furthermore, one aspect of the present invention aims to provide a reliable light-emitting device, electronic device, or display device.

[0008] Alternatively, one aspect of the present invention aims to provide a highly reliable blue light-emitting device. Alternatively, another aspect of the present invention aims to provide a blue light-emitting device with high luminous efficiency.

[0009] Furthermore, the description of these problems does not preclude the existence of other problems. Moreover, one aspect of the present invention does not need to solve all of these problems. Other problems will naturally become apparent from the description in the specification, drawings, and claims, and it is possible to extract other problems from the description in the specification, drawings, and claims. [Means for solving the problem]

[0010] One aspect of the present invention includes a first electrode formed on an insulating surface, a second electrode facing the first electrode, and an EL layer located between the first electrode and the second electrode, wherein the EL layer comprises a light-emitting layer, a hole transport layer, a first electron transport layer, and a second electron transport layer, the first electron transport layer located between the first electrode and the second electron transport layer, the light-emitting layer located between the hole transport layer, the first electron transport layer and the second electron transport layer, and the light-emitting layer comprises a first light-emitting material The device comprises a first electron transport layer and a second electron transport layer, wherein the first electron transport layer is a material capable of converting triplet excitation energy into light emission, the second electron transport layer is a fluorescent material, the peak wavelength in the emission spectrum of the first electron transport layer is shorter than the peak wavelength in the emission spectrum of the second electron transport layer, and the GSP_Slope(mV / nm) of the second electron transport layer is greater than the GSP_Slope(mV / nm) of the first electron transport layer.

[0011] Alternatively, in another aspect of the present invention, in the above configuration, the second electron transport layer is located between the first electron transport layer and the second electrode, and the light-emitting device is such that the GSP_Slope(mV / nm) of the light-emitting layer is greater than the GSP_Slope(mV / nm) of the first electron transport layer.

[0012] Alternatively, another aspect of the present invention is a light-emitting device in which the GSP_Slope(mV / nm) of the light-emitting layer is greater than the GSP_Slope(mV / nm) of the hole transport layer.

[0013] Alternatively, another aspect of the present invention includes a first electrode formed on an insulating surface, a second electrode facing the first electrode, and an EL layer located between the first electrode and the second electrode, wherein the EL layer comprises a light-emitting layer, a hole transport layer, a first electron transport layer, and a second electron transport layer, the first electron transport layer located between the first electrode and the second electron transport layer, the light-emitting layer located between the hole transport layer, the first electron transport layer and the second electron transport layer, and the light-emitting layer comprises a first light-emitting material and a second light-emitting material, the first light-emitting material converts triplet excitation energy into light emission. The present invention relates to a light-emitting device in which the following materials are capable: the second light-emitting material is a fluorescent material, the peak wavelength in the emission spectrum of the first light-emitting material is shorter than the peak wavelength in the emission spectrum of the second light-emitting material, the first electron transport layer has a first organic compound, the second electron transport layer has a second organic compound, the first and second organic compounds have π-electron-deficient heteroaromatic rings, and the GSP_Slope(mV / nm) in the vapor-deposited film of the second organic compound is greater than the GSP_Slope(mV / nm) in the vapor-deposited film of the first organic compound.

[0014] Alternatively, another aspect of the present invention comprises a first electrode formed on an insulating surface, a second electrode facing the first electrode, and an EL layer located between the first electrode and the second electrode, wherein the EL layer comprises a light-emitting layer, a hole transport layer, a first electron transport layer, and a second electron transport layer, the first electron transport layer located between the light-emitting layer and the second electron transport layer, the second electron transport layer located between the first electron transport layer and the second electrode, the light-emitting layer located between the hole transport layer and the first electron transport layer, and the light-emitting layer comprises a first light-emitting material and a second light-emitting material, the first light-emitting material converts triplet excitation energy into light emission. The light-emitting device is a material capable of conversion, the second light-emitting material is a fluorescent material, the peak wavelength in the emission spectrum of the first light-emitting material is shorter than the peak wavelength in the emission spectrum of the second light-emitting material, the first electron transport layer has a first organic compound, the second electron transport layer has a second organic compound and the first material, the first and second organic compounds have π-electron-deficient heteroaromatic rings, and the GSP_Slope(mV / nm) in the vapor-deposited film of the second organic compound is greater than the GSP_Slope(mV / nm) in the vapor-deposited film of the first organic compound.

[0015] Alternatively, another aspect of the present invention comprises a first electrode formed on an insulating surface, a second electrode facing the first electrode, and an EL layer located between the first electrode and the second electrode, wherein the EL layer comprises a light-emitting layer, a hole transport layer, a first electron transport layer, and a second electron transport layer, the first electron transport layer located between the light-emitting layer and the second electron transport layer, the second electron transport layer located between the first electron transport layer and the second electrode, the light-emitting layer located between the hole transport layer and the first electron transport layer, and the light-emitting layer comprises a first light-emitting material and a second light-emitting material, the first light-emitting material being a material capable of converting triplet excitation energy into light emission, and the second light-emitting material being fluorescent The present invention relates to a light-emitting device in which, as a light-emitting material, the peak wavelength in the emission spectrum of the first light-emitting material is shorter than the peak wavelength in the emission spectrum of the second light-emitting material, the first electron transport layer contains a first organic compound, the second electron transport layer contains a second organic compound and a first substance, both the first and second organic compounds have π-electron-deficient heteroaromatic rings, and the mixing ratio of the second organic compound and the first substance in the second electron transport layer is x:y, then the GSP_Slope(mV / nm) in the vapor-deposited film of the second organic compound is greater than (x+y) / x times the GSP_Slope(mV / nm) in the vapor-deposited film of the first organic compound.

[0016] Alternatively, another aspect of the present invention is a light-emitting device in the above configuration in which y is greater than or equal to x.

[0017] Alternatively, in another aspect of the present invention, in the above configuration, the second electron transport layer is located between the first electron transport layer and the second electrode, and the light-emitting layer comprises a host material, wherein the GSP_Slope(mV / nm) in the vapor-deposited film of the host material is greater than the GSP_Slope(mV / nm) in the vapor-deposited film of the first organic compound.

[0018] Alternatively, another aspect of the present invention is a light-emitting device in which, in the above configuration, the GSP_Slope(mV / nm) in the vapor-deposited film of the second organic compound is greater than the GSP_Slope(mV / nm) in the vapor-deposited film of the host material.

[0019] Alternatively, another aspect of the present invention is a light-emitting device in which, in the above configuration, the hole transport layer has a third organic compound, and the GSP_Slope(mV / nm) of the light-emitting layer is equal to or greater than the GSP_Slope(mV / nm) of the vapor-deposited film of the third organic compound.

[0020] Alternatively, another aspect of the present invention is a light-emitting device in which the HOMO level of the host material is lower than the HOMO level of the first light-emitting material.

[0021] Alternatively, another aspect of the present invention is a light-emitting device in which the HOMO level of the first light-emitting material is lower than the HOMO level of the second light-emitting material.

[0022] Alternatively, another aspect of the present invention is a light-emitting device in which, in the above configuration, the hole transport layer has a third organic compound, and the GSP_Slope(mV / nm) in the vapor-deposited film of the host material is greater than or equal to the GSP_Slope(mV / nm) in the vapor-deposited film of the third organic compound.

[0023] Alternatively, another aspect of the present invention is a light-emitting device in which, in the above configuration, the host material is an organic compound comprising a first material and a second material, wherein the first material and the second material form an excited complex in a combination.

[0024] Alternatively, another aspect of the present invention is a light-emitting device in which the HOMO levels of the first material and the second material are lower than the HOMO levels of the first light-emitting material.

[0025] Alternatively, another aspect of the present invention is a light-emitting device in which the HOMO levels of the first material and the second material are lower than the HOMO level of the second light-emitting material.

[0026] Alternatively, another aspect of the present invention is a light-emitting device in which, in the above configuration, the first material is an organic compound having a π-electron-deficient heteroaromatic ring, and the second material is an organic compound having a π-electron-excess heteroaromatic ring or an aromatic amine.

[0027] Alternatively, another aspect of the present invention is a light-emitting device in which the first substance is a metal complex.

[0028] Alternatively, another aspect of the present invention is a light-emitting device in which, in the above configuration, the metal complex is an organic complex having an alkali metal.

[0029] Alternatively, another aspect of the present invention is a light-emitting device in which the first light-emitting material is a phosphorescent material.

[0030] Alternatively, another aspect of the present invention is a light-emitting device in which, in the above configuration, a second light-emitting material emits light when a voltage is applied between the first electrode and the second electrode.

[0031] Alternatively, another aspect of the present invention is a light-emitting device in which, in the above configuration, the peak wavelength of the emission spectrum of the second light-emitting material is 450 nm or more and 520 nm or less.

[0032] Alternatively, another aspect of the present invention is a light-emitting device in which, in the above configuration, the energy difference between the lowest triplet excitation energy level of the first material and the lowest triplet excitation energy level of the second material is 0.20 eV or less.

[0033] Alternatively, in another aspect of the present invention, in the above configuration, the light-emitting device is such that the absorption edge on the long-wavelength side in the absorption spectrum of the second light-emitting material is at a longer wavelength than the emission edge on the short-wavelength side in the emission spectrum of the first light-emitting material. Alternatively, the light-emitting device is such that the absorption edge on the long-wavelength side in the absorption spectrum of the second light-emitting material is at a longer wavelength than the absorption edge on the long-wavelength side in the absorption spectrum of the first light-emitting material. Alternatively, the light-emitting device is such that the emission edge on the short-wavelength side in the phosphorescence spectrum of the first material and the emission edge on the short-wavelength side in the phosphorescence spectrum of the second material are at shorter wavelengths than the emission edge on the short-wavelength side in the emission spectrum of the first light-emitting material.

[0034] Alternatively, another aspect of the present invention is a light-emitting device in which, in the above configuration, the proportion of the first light-emitting material in the light-emitting layer is greater than the proportion of the second light-emitting material.

[0035] Alternatively, in another aspect of the present invention, the second light-emitting material has the above configuration, wherein the second light-emitting material has a luminescent phore and a protecting group, the luminescent phore is a condensed aromatic ring or a condensed heteroaromatic ring, and the protecting group is a light-emitting device having one of the following: an alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, or a trialkylsilyl group having 3 to 10 carbon atoms. Alternatively, the second light-emitting material has a luminescent phore and five or more protecting groups, the luminescent phore is a condensed aromatic ring or a condensed heteroaromatic ring, and the protecting group is independently one of the following: an alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, or a trialkylsilyl group having 3 to 10 carbon atoms.

[0036] Alternatively, in another aspect of the present invention, the first light-emitting material in the above configuration is a light-emitting device having one of the following: an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, or a trialkylsilyl group having 3 to 10 carbon atoms.

[0037] However, in one embodiment of the present invention, GSP_Slope(mV / nm) is expressed as ΔV / Δd when the change in surface potential ΔV(mV) is equal to the change in film thickness Δd(nm). [Effects of the Invention]

[0038] In one aspect of the present invention, a highly reliable light-emitting device can be provided. Alternatively, in another aspect of the present invention, a light-emitting device with high luminous efficiency can be provided. Furthermore, in one aspect of the present invention, a highly reliable light-emitting device, electronic device, or display device can be provided.

[0039] Alternatively, one aspect of the present invention can provide a highly reliable blue light-emitting device. Alternatively, another aspect of the present invention can provide a blue light-emitting device with high luminous efficiency.

[0040] Furthermore, the description of these effects does not preclude the existence of other effects. Moreover, one aspect of the present invention does not necessarily have to possess all of these effects. Other effects will naturally become apparent from the description in the specification, drawings, and claims, and it is possible to extract other effects from the description in the specification, drawings, and claims. [Brief explanation of the drawing]

[0041] [Figure 1] Figures 1(A) and 1(B) illustrate the configuration of a light-emitting device according to an embodiment. [Figure 2] Figures 2(A) and 2(B) illustrate the configuration of a light-emitting device according to an embodiment. [Figure 3] Figures 3(A) and 3(B) are diagrams showing the configuration of the light-emitting layer in a light-emitting device according to one embodiment of the present invention. [Figure 4] Figures 4(A) to 4(D) are diagrams illustrating the conceptual energy transfer between compounds contained in the light-emitting layer of a light-emitting device according to one embodiment of the present invention. [Figure 5]Figure 5 shows the capacitance-voltage characteristics of the measurement device 1. [Figure 6] Figure 6 shows the current density-voltage characteristics of the measuring device 1. [Figure 7] Figures 7(A) and 7(B) illustrate the configuration of a light-emitting device according to an embodiment. [Figure 8] Figures 8(A) and 8(B) are a top view and a cross-sectional view of the light-emitting device. [Figure 9] Figures 9(A) and 9(B) are perspective views showing examples of the display module configuration. [Figure 10] Figures 10(A) and 10(B) are cross-sectional views showing examples of the configuration of a display device. [Figure 11] Figure 11 is a perspective view showing an example of a display device configuration. [Figure 12] Figure 12 is a cross-sectional view showing an example of the configuration of a display device. [Figure 13] Figure 13 is a cross-sectional view showing an example of the configuration of a display device. [Figure 14] Figure 14 is a cross-sectional view showing an example of the configuration of a display device. [Figure 15] Figures 15(A) to 15(D) show examples of electronic devices. [Figure 16] Figures 16(A) to 16(F) show examples of electronic devices. [Figure 17] Figures 17(A) through 17(G) show examples of electronic devices. [Figure 18] Figure 18 shows the absorption and PL spectra of PtON-TBBI and 1,6mmtBuDPhAPrn. [Figure 19] Figure 19 shows the luminance-current density characteristics of light-emitting device 1-1, light-emitting device 1-2, comparative light-emitting device 1-1, comparative light-emitting device 1-2, and comparative light-emitting device 1-3. [Figure 20] Figure 20 shows the luminance-voltage characteristics of light-emitting device 1-1, light-emitting device 1-2, reference light-emitting device 1-1, reference light-emitting device 1-2, and reference light-emitting device 1-3. [Figure 21] Figure 21 shows the current efficiency-current density characteristics of light-emitting device 1-1, light-emitting device 1-2, comparative light-emitting device 1-1, comparative light-emitting device 1-2, and comparative light-emitting device 1-3. [Figure 22] Figure 22 shows the current density-voltage characteristics of light-emitting device 1-1, light-emitting device 1-2, comparative light-emitting device 1-1, comparative light-emitting device 1-2, and comparative light-emitting device 1-3. [Figure 23] Figure 23 shows the external quantum efficiency-current density characteristics of light-emitting device 1-1, light-emitting device 1-2, comparative light-emitting device 1-1, comparative light-emitting device 1-2, and comparative light-emitting device 1-3. [Figure 24] Figure 24 shows the electroluminescence spectra of light-emitting device 1-1, light-emitting device 1-2, reference light-emitting device 1-1, reference light-emitting device 1-2, and reference light-emitting device 1-3. [Figure 25] Figure 25 shows the normalized luminance time-varying characteristics of light-emitting device 1-1, light-emitting device 1-2, comparative light-emitting device 1-1, comparative light-emitting device 1-2, and comparative light-emitting device 1-3. [Figure 26] Figure 26 shows the LT90 times for light-emitting device 1-1, light-emitting device 1-2, reference light-emitting device 1-1, reference light-emitting device 1-2, and reference light-emitting device 1-3. [Figure 27] Figure 27 shows the luminance-current density characteristics of light-emitting device 2 and comparison light-emitting device 2. [Figure 28] Figure 28 shows the luminance-voltage characteristics of light-emitting device 2 and comparison light-emitting device 2. [Figure 29] Figure 29 shows the current efficiency-current density characteristics of light-emitting device 2 and comparative light-emitting device 2. [Figure 30] Figure 30 shows the current density-voltage characteristics of light-emitting device 2 and comparison light-emitting device 2. [Figure 31] Figure 31 shows the blue index-current density characteristics of light-emitting device 2 and comparison light-emitting device 2. [Figure 32] Figure 32 shows the external quantum efficiency-current density characteristics of light-emitting device 2 and comparative light-emitting device 2. [Figure 33] Figure 33 shows the electroluminescence spectra of light-emitting device 2 and comparison light-emitting device 2. [Figure 34] Figure 34 shows the chromaticity diagrams for light-emitting device 2 and comparison light-emitting device 2. [Figure 35] Figure 35 shows the normalized brightness time-varying characteristics of light-emitting device 2 and comparison light-emitting device 2. [Figure 36] Figure 36 shows the absorption and PL spectra of Pt(mmtBubOcz35dm4ppy-d6) and 1,6mmtBuDPhAPrn in solution. [Figure 37] Figures 37(A) and 37(B) show the low-temperature PL measurement results for SiTrzCz2 and PSiCzCz, respectively. [Figure 38] Figure 38 shows the PL spectra of thin films of SiTrzCz2, PSiCzCz, and a 1:1 mixed film of SiTrzCz2 and PSiCzCz. [Figure 39] Figure 39 shows the luminance-current density characteristics of light-emitting device 3 and comparative light-emitting device 3. [Figure 40] Figure 40 shows the luminance-voltage characteristics of light-emitting device 3 and comparison light-emitting device 3. [Figure 41] Figure 41 shows the current efficiency-current density characteristics of light-emitting device 3 and comparative light-emitting device 3. [Figure 42] Figure 42 shows the current density-voltage characteristics of light-emitting device 3 and comparison light-emitting device 3. [Figure 43] Figure 43 shows the blue index-current density characteristics of light-emitting device 3 and comparison light-emitting device 3. [Figure 44] Figure 44 shows the external quantum efficiency-current density characteristics of light-emitting device 3 and comparative light-emitting device 3. [Figure 45]Figure 45 shows the electroluminescence spectra of light-emitting device 3 and comparison light-emitting device 3. [Figure 46] Figure 46 shows the normalized brightness time-varying characteristics of light-emitting device 3 and comparative light-emitting device 3. [Figure 47] Figures 47(A) and 47(B) show the normalized luminance time-varying characteristics of SiTrzCz2-d16 and PSiCzCz-d15, respectively. [Figure 48] Figure 48 shows the PL spectra of thin films of SiTrzCz2-d16, PSiCzCz-d15, and a 1:1 mixed film of SiTrzCz2-d16 and PSiCzCz-d15. [Figure 49] Figure 49 shows the results of transient EL measurements performed on light-emitting device 1-1, comparative light-emitting device 1-3, and light-emitting device 1-3. [Modes for carrying out the invention]

[0042] The embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the following description, and its form and details can be modified in various ways without departing from the spirit and scope of the present invention. Accordingly, the present invention shall not be interpreted as being limited to the contents of the embodiments shown below.

[0043] Please note that the positions, sizes, and ranges of each component shown in the drawings may not represent their actual positions, sizes, and ranges for the sake of ease of understanding. Therefore, the disclosed invention is not necessarily limited to the positions, sizes, and ranges disclosed in the drawings.

[0044] In this specification, the ordinal numbers "first," "second," etc., are used for convenience only and do not limit the number of components or the order of components. The order of components includes, for example, the order of processes or the order of stacking. That is, the ordinal numbers used in the embodiments of this specification may not match the ordinal numbers used in the claims. Also, the ordinal numbers used in the examples of this specification may not match the ordinal numbers used in the claims. Also, the ordinal numbers used in the embodiments of this specification may not match the ordinal numbers used in the examples of this specification.

[0045] Furthermore, in this specification and other documents, when describing the structure of the invention using drawings, reference numerals that refer to the same thing may be used in common across different drawings.

[0046] Furthermore, in this specification, the terms "film" and "layer" are interchangeable. For example, the term "conductive layer" may be changed to "conductive film." Or, for example, the term "insulating film" may be changed to "insulating layer."

[0047] In this specification, a photoluminescence (PL) spectrum refers to a spectrum obtained by fixing the excitation wavelength of the excitation light in fluorescence photometry and spectrally analyzing the emission from a sample irradiated with excitation light at each wavelength, thereby measuring the emission intensity distribution at each wavelength. It may also be called an emission spectrum. An emission spectrum may contain both a fluorescent component and a phosphorescent component. In this specification, an emission spectrum consisting of a fluorescent component may be specifically called a fluorescence spectrum, and an emission spectrum consisting of a phosphorescent component may be specifically called a phosphorescent spectrum.

[0048] (Embodiment 1) In this embodiment, a light-emitting device 10A, which is a light-emitting device according to one aspect of the present invention, and a light-emitting device 10B, which is a light-emitting device according to another aspect of the present invention, will be described with reference to Figures 1(A) and 1(B).

[0049] As shown in Figures 1(A) and 1(B), the light-emitting devices 10A and 10B are each located on the substrate 1000. Each light-emitting device 10A and 10B has a first electrode 101 located on an insulating surface, a second electrode 102 facing the first electrode 101, and an EL layer 103 located between the first electrode 101 and the second electrode 102. Also, as shown in Figures 1(A) and 1(B), the EL layer 103 has at least a light-emitting layer 113, a first electron transport layer 114_1, and a second electron transport layer 114_2. The first electron transport layer 114_1 and the second electron transport layer 114_2 have the function of transporting electrons injected into the EL layer 103 from either the first electrode 101 or the second electrode 102 to the light-emitting layer 113. The first electron transport layer 114_1 is located between the first electrode 101 and the second electron transport layer 114_2.

[0050] Furthermore, as shown in Figures 1(A) and 1(B), in the light-emitting devices 10A and 10B, the first electrode 101 is formed on the substrate 1000. It can also be said that the first electrode 101 is provided between the second electrode 102 and the substrate 1000. That is, the first electrode 101 is an electrode provided before the second electrode 102. When a transistor is provided on the substrate 1000, the first electrode 101 is electrically connected to the transistor via wiring. Alternatively, the first electrode 101 is provided on an insulating layer on which external connection electrodes are provided, such as terminals for attaching FPCs. Alternatively, the ends of the first electrode 101 are covered with an insulating film.

[0051] The light-emitting device 10A shown in Figure 1(A) and the light-emitting device 10B shown in Figure 1(B) differ in the functions of the first electrode 101 and the second electrode 102. In light-emitting device 10A, the first electrode 101 functions as the anode, and the second electrode 102 functions as the cathode. In this specification, etc., a light-emitting device like light-emitting device 10A, in which the first electrode provided on the substrate side functions as the anode, is sometimes referred to as a forward-stacked light-emitting device. On the other hand, in light-emitting device 10B, the first electrode 101 functions as the cathode, and the second electrode 102 functions as the anode. In this specification, etc., a light-emitting device like light-emitting device 10B, in which the first electrode provided on the substrate side functions as the cathode, is sometimes referred to as a reverse-stacked light-emitting device.

[0052] In the sequentially stacked light-emitting device 10A, light is emitted when holes injected from the first electrode 101, which is the anode, into the EL layer 103 and transported by the hole transport layer 112, and electrons injected from the second electrode 102, which is the cathode, into the EL layer 103 and transported by the electron transport layer 114, recombine in the light-emitting layer 113. Therefore, in the light-emitting device 10A, the hole transport layer 112 is located between the first electrode 101 and the light-emitting layer 113, and the electron transport layer 114 is located between the second electrode 102 and the light-emitting layer 113.

[0053] In the inverted stacked light-emitting device 10B, electrons are injected into the EL layer 103 from the first electrode 101, which functions as the cathode, and transported by the electron transport layer 114. These electrons are then injected into the EL layer 103 from the second electrode 102, which functions as the anode, and transported by the hole transport layer 112. These electrons then recombine in the light-emitting layer 113, thereby emitting light. Therefore, in the light-emitting device 10B, the hole transport layer 112 is located between the second electrode 102 and the light-emitting layer 113, and the electron transport layer 114 is located between the first electrode 101 and the light-emitting layer 113.

[0054] In light-emitting devices 10A and 10B, the electron transport layer has a multilayer structure (a stack of the first electron transport layer 114_1 and the second electron transport layer 114_2). The hole transport layer 112 may be a single layer or have a multilayer structure. The first electron transport layer 114_1 and the second electron transport layer 114_2 are sometimes collectively referred to as the electron transport layer 114.

[0055] Furthermore, it is preferable that the light-emitting devices 10A and 10B have a hole transport layer 112 between the anode and the light-emitting layer 113, and it is more preferable that they have a hole injection layer 111 between the anode and the hole transport layer 112. Furthermore, it is more preferable that the light-emitting devices 10A and 10B have an electron injection layer 115 between the cathode and the electron transport layer 114.

[0056] Figure 1(A) shows a forward-stacked light-emitting device 10A, which has a structure in which a hole injection layer 111, a hole transport layer 112, a light-emitting layer 113, an electron transport layer 114, an electron injection layer 115, and a second electrode 102, which functions as a cathode, are sequentially stacked on a first electrode 101, which functions as an anode. Figure 1(B) shows an inverted-stacked light-emitting device 10B, which has a structure in which an electron injection layer 115, an electron transport layer 114, a light-emitting layer 113, a hole transport layer 112, a hole injection layer 111, and a second electrode 102, which functions as an anode, are sequentially stacked on a first electrode 101, which functions as a cathode.

[0057] Note that the configurations of light-emitting devices 10A and 10B are not limited to those shown in Figures 1(A) and 1(B). For example, a configuration with two hole transport layers, or a configuration with three or more layers of either the hole transport layer or the electron transport layer, or both, may be used.

[0058] The present inventors have found that in light-emitting devices 10A and 10B, which include a light-emitting layer containing a material capable of converting triplet excitation energy into light emission and a fluorescent light-emitting material, and in which the electron transport layer has a stacked structure, the reliability of light-emitting devices 10A and 10B can be improved by selecting the materials used for each layer while considering the slope of the giant surface potential (GSP) of the electron transport layer.

[0059] In other words, in a light-emitting device that includes a material capable of converting triplet excitation energy into light emission and a fluorescent material in the light-emitting layer, when the electron transport layer has a stacked structure of a first electron transport layer 114_1 formed earlier and a second electron transport layer 114_2 formed later, a light-emitting device in which the GSP slope (GSP_Slope(mV / nm)) of the second electron transport layer 114_2 is larger than the GSP_Slope of the first electron transport layer 114_1 can be made into a highly reliable light-emitting device.

[0060] Alternatively, in a light-emitting device that includes a material capable of converting triplet excitation energy into light emission and a fluorescent material in the light-emitting layer, when the electron transport layer has a stacked structure of a first electron transport layer 114_1 formed earlier and a second electron transport layer 114_2 formed later, a light-emitting device in which the GSP slope (GSP_Slope(mV / nm)) of the film made of an organic compound having a π-electron-deficient heteroaromatic ring contained in the second electron transport layer 114_2 is greater than the GSP_Slope of the film made of an organic compound having a π-electron-deficient heteroaromatic ring contained in the first electron transport layer 114_1 can be made into a highly reliable light-emitting device.

[0061] Here, GSP refers to a phenomenon caused by spontaneous orientation polarization (SOP), which occurs when the orientation of the permanent electric dipole moment of a deposited film is biased in the direction of film thickness.

[0062] The surface potential of a vapor-deposited film exhibiting GSP changes at a constant rate without saturating as the film thickness increases. For example, a vapor-deposited film of tris(8-quinolinolato)aluminum (abbreviated as Alq3) has a surface potential of approximately 28V at a film thickness of 560nm. This electric field strength is 5 × 10⁻¹⁰ 5 It reaches V / cm, which is about the same magnitude as the electric field strength during operation of a typical light-emitting device.

[0063] The GSP slope (GSP_Slope) is expressed as ΔV / Δd when the change in surface potential is ΔV (mV) for a film in which the GSP changes proportionally to the film thickness, and the change in surface potential is ΔV (mV) for a change in film thickness Δd (nm). Note that a positive GSP_Slope occurs when the surface potential increases with increasing film thickness, and a negative GSP_Slope occurs when the surface potential decreases with increasing film thickness. Alq3 can be described as a material with a positive GSP_Slope. Furthermore, layers with a positive GSP_Slope have a low potential on the substrate side, while layers with a negative GSP_Slope have a high potential on the substrate side.

[0064] As mentioned above, this GSP is a phenomenon caused by SOP resulting from the bias in the orientation of the permanent electric dipole moment in the film thickness direction. That is, in layers where GSP_Slope is positive, it can be considered that a negative polarization charge is induced on the substrate side of that layer and a positive polarization charge is induced on the second electrode side. Similarly, in layers where GSP_Slope is negative, it can be considered that a positive polarization charge is induced on the substrate side of that layer and a negative polarization charge is induced on the second electrode side. The induction of such polarization charges is the origin of GSP. In Figures 1(A) and 1(B), the SOP resulting from the bias in the orientation of the permanent electric dipole moment in the film thickness direction of each layer deposited by vapor deposition is shown using σ+ and σ-. σ+ indicates positive polarization, and σ- indicates negative polarization. Furthermore, in each layer, the more σ values ​​there are near the interface, the greater the spontaneous polarization.

[0065] Deposition films of organic compounds often have a positive GSP_Slope. In this case, when a second layer is deposited in contact with a first layer, the signs of the GSP_Slope of the first and second layers become the same positive, and it can be considered that negative polarization charges are induced on the substrate side of each layer, and positive polarization charges are induced on the electrode side of the second layer. In this case, the negative polarization charge on the first layer side of the second layer cancels out with the positive polarization charge on the second layer side of the first layer, and only the remaining charge can be considered as the interfacial charge (fixed charge) at the interface between the first and second layers. Note that in this specification, the virtual charge that can be considered as an interfacial charge is sometimes called an interfacial charge.

[0066] Figure 1(A) shows a forward-stacked light-emitting device 10A, and Figure 1(B) shows an inverted-stacked light-emitting device 10B. The electron transport layer 114 of the light-emitting device has a laminated structure of a first electron transport layer 114_1 and a second electron transport layer 114_2. The light-emitting layer of the light-emitting device contains a material capable of converting triplet excitation energy into light emission and a fluorescent material. The second electron transport layer 114_2 is provided on the second electrode 102 side of the first electron transport layer 114_1. In one embodiment of the present invention, it is preferable that the GSP_Slope of the second electron transport layer 114_2 is larger than the GSP_Slope of the first electron transport layer 114_1. Alternatively, in a light-emitting device according to one aspect of the present invention, it is preferable that the GSP_Slope of the vapor-deposited film of the second organic compound having a π-electron-deficient heteroaromatic ring contained in the second electron transport layer 114_2 is larger than the GSP_Slope of the vapor-deposited film of the first organic compound having a π-electron-deficient heteroaromatic ring contained in the first electron transport layer 114_1.

[0067] In a light-emitting device according to one aspect of the present invention having such a configuration, a negative interfacial charge is generated at the interface between the second electron transport layer 114_2 and the first electron transport layer 114_1. This suppresses the injection of electrons from the second electrode 102 or electron injection layer 115 into the second electron transport layer 114_2 (in the case of forward stacking, Figure 1(A)), or the injection of electrons from the first electrode 101 or electron injection layer 115 into the first electron transport layer 114_1 (in the case of reverse stacking, Figure 1(B)). This prevents the light-emitting layer 113 from becoming electron-excessive, reduces the bias towards the hole transport layer 112 in the recombination region of the light-emitting layer 113, and reduces the degradation of the light-emitting layer 113 and the hole transport layer 112 (or electron blocking layer). As a result, a light-emitting device according to one aspect of the present invention can be made into a highly reliable light-emitting device.

[0068] In the sequentially stacked light-emitting device 10A shown in Figure 1(A), the second electron transport layer 114_2 may contain a first substance in addition to the second organic compound. The first substance is preferably a metal complex, particularly an organic complex containing an alkali metal. Specifically, examples of alkali metal-containing organic complexes include 8-quinolinolato-lithium (abbreviated as Liq), 8-quinolinolato-sodium (abbreviated as Naq), 8-quinolinolato-potassium (abbreviated as Kq), and their derivatives. When the second electron transport layer 114_2 contains such a substance, it becomes possible to control the electron transport properties in the second electron transport layer 114_2, and furthermore, the reliability of the light-emitting device can be improved by suppressing the bias towards the hole transport layer 112 in the light-emitting layer 113 of the recombination region.

[0069] In this case, if the mixing ratio (weight ratio) of the second organic compound and the first substance in the second electron transport layer 114_2 is x:y, it is preferable that the GSP_Slope (mV / nm) of the film of the second organic compound is greater than (x+y) / x times the GSP_Slope (mV / nm) of the film of the first organic compound. With this configuration, even if the GSP_Slope of the film of the first substance is smaller than the GSP_Slope of the film of the second organic compound, the GSP_Slope (mV / nm) of the second electron transport layer 114_2 will be larger than that of the first electron transport layer 114_1, so a negative interfacial charge is generated and electron injection is suppressed, which is preferable. Also, it is preferable that y is greater than x, as this reduces the proportion of the second organic compound responsible for electron transport and thus reduces electron transport performance.

[0070] Furthermore, in the inverted stacking type light-emitting device 10B shown in Figure 1(B), the first electron transport layer 114_1 may contain a first substance in addition to the first organic compound. The first substance is preferably a metal complex, particularly an organic complex containing an alkali metal. When the first electron transport layer 114_1 contains such a substance, it becomes possible to control the electron transport properties in the first electron transport layer 114_1, and furthermore, the reliability of the light-emitting device can be improved by suppressing the bias towards the hole transport layer 112 in the light-emitting layer 113 of the recombination region.

[0071] Here, the light-emitting layer 113 preferably includes a substance capable of converting triplet excitation energy into light emission and a fluorescent substance, with the fluorescent substance emitting light. Furthermore, it is preferable that the fluorescent substance emits light using a substance capable of converting triplet excitation energy into light emission as an energy donor. It is also preferable that the light-emitting layer 113 further includes a host material.

[0072] By having the light-emitting layer configured as described above, the light-emitting device according to one aspect of the present invention can be made into a more reliable light-emitting device.

[0073] The configuration of the light-emitting layer 113 of a light-emitting device according to one embodiment of the present invention will be described in detail below. Figures 3(A) and 3(B) are examples of schematic cross-sectional views of the light-emitting layer 113 shown in Figures 1(A) and 2(B). The light-emitting layer 113 shown in Figure 3(A) has compound 131, compound 132, compound 133, and compound 134. The light-emitting layer 113 shown in Figure 3(B) has compound 131, compound 133, and compound 134. Compound 131 and compound 132 are substances that function as host materials, respectively. Compound 133 is a substance that can convert triplet excitation energy into light emission. Compound 134 is a fluorescent light-emitting substance. The light-emitting layer 113 can obtain light emission originating from compound 134, which is a fluorescent light-emitting substance.

[0074] <Example of light-emitting layer configuration 1> First, a specific example of the configuration of the light-emitting layer 113 will be described. In this example, the light-emitting layer 113 has compounds 131, 132, 133, and 134, as shown in Figure 3(A). Furthermore, in this example, the case in which compound 133, a substance capable of converting triplet excitation energy into light emission, is a phosphorescent material will be described. The phosphorescent material preferably contains heavy atoms such as Ir, Pt, Os, Ru, and Pd, and is preferably an organometallic complex containing any of these heavy atoms.

[0075] An example of the energy level correlation in the light-emitting layer 113 in this configuration is shown in Figure 4(A). The notation and symbols in Figure 4(A) are as follows. ·Comp(131): Compound 131 ·Comp(132): Compound 132 ·Comp(133): Compound 133 ·Guest(134): Compound 134 ·S C1 : S1 level of compound 131 ·T C1 : T1 level of compound 131 ·S C2 : S1 level of compound 132 ·TC2 : T1 level of Compound 132 ·S E : S1 level of the exciplex ·T E : T1 level of the exciplex ·T C3 : T1 level of Compound 133 ·S G : S1 level of Compound 134 ·T G : T1 level of Compound 134

[0076] The combination of Compound 131 and Compound 132, which each function as a host material, is preferably a combination capable of forming an exciplex. It is more preferable that one is a compound having hole-transporting properties and the other is a compound having electron-transporting properties. In this case, it becomes easier to form a donor-acceptor type exciplex, and the exciplex can be efficiently formed. Further, when the combination of Compound 131 and Compound 132 is a combination of a compound having hole-transporting properties and a compound having electron-transporting properties, the carrier balance can be easily controlled by the mixing ratio. Specifically, the range of a compound having hole-transporting properties: a compound having electron-transporting properties = 1:9 to 9:1 (weight ratio) is preferable. Also, by having this configuration, since the carrier balance can be easily controlled, the control of the carrier recombination region can also be simply performed.

[0077] More specifically, examples of the compound having hole-transporting properties include a compound having either or both of a π-electron-excessive heteroaromatic ring and an aromatic amine skeleton, and more specifically, examples of the compound having electron-transporting properties include a compound having a π-electron-deficient heteroaromatic ring.

[0078] Furthermore, as a combination of host materials that efficiently form excited complexes, it is preferable that the HOMO level of one of compound 131 and compound 132 is higher than the HOMO level of the other, and the LUMO level of one is higher than the LUMO level of the other. Alternatively, the HOMO level of compound 131 may be equivalent to that of compound 132, or the LUMO level of compound 131 may be equivalent to that of compound 132.

[0079] Furthermore, the LUMO and HOMO levels of a compound can be derived from the electrochemical properties (reduction potential and oxidation potential) of the compound, which are measured by methods such as cyclic voltammetry (CV).

[0080] As shown in Figure 4(A), the S1 level of the excited complex formed by compound 131 and compound 132 (S E ) and the T1 level of the excited complex (T E These are adjacent energy levels (see route A1 in Figure 4(A)).

[0081] Excitation energy level of the excited complex formed by compound 131 and compound 132 (S E and T E ) is the S1 level (S C1 and S C2 Because this becomes lower, it becomes possible to form an excited state at a lower excitation energy. This allows for a reduction in the driving voltage of the light-emitting device.

[0082] Furthermore, the correlation between the energy levels of compound 131 and compound 132 is not limited to that shown in Figure 4(A). That is, the singlet excitation energy level of compound 131 (S C1 ) is the singlet excitation energy level (S) of compound 132. C2 It may be higher or lower than ). Also, the triplet excitation energy level (T) of compound 131. C1 ) is the triplet excitation energy level (T) of compound 132. C2 It can be higher or lower than ).

[0083] Since compound 133 is a phosphorescent substance, the S1 level (S) of the excited complex formed by compound 131 and compound 132 E ) and T1 level (T E ) From there, both the singlet excitation energy and the triplet excitation energy are rapidly brought to the T1 level (T C3 Move to (route A2). At this time, T E ≧T C3 It is preferable that this is the case. In route A2, the excited complex functions as an energy donor and compound 133 functions as an energy acceptor. Also, at this time the triplet excitation energy level (T C1 ), and the triplet excitation energy level (T C2 ) is the T1 level (T C3 It is preferable that it is higher than ). More specifically, draw a tangent line at the short-wavelength tail of the phosphorescence spectrum of compound 131, and set the energy of the extrapolation line at the wavelength to T C1 Draw a tangent line at the short-wavelength tail of the phosphorescence spectrum of compound 132, and determine the energy of the extrapolation line at its wavelength as T. C2 Draw a tangent line at the short-wavelength tail of the emission spectrum (phosphorescence spectrum) of compound 133, and determine the energy of the wavelength of the extrapolation line as T. C3 When that happens, T C1 ≧T C3 It is preferable that T C2 ≧T C3 It is preferable that the wavelength of the short-wavelength emission edge in the phosphorescence spectrum of compound 131 and the wavelength of the short-wavelength emission edge in the phosphorescence spectrum of compound 132 are shorter wavelengths than the wavelength of the short-wavelength emission edge in the emission spectrum (phosphorescence spectrum) of compound 133.

[0084] The triplet excitation energy of compound 133 is converted into the excitation energy of compound 134, which is a fluorescent material (roots A3 and A4). At this time, as shown in Figure 4(A), T E ≧T C3 ≥S GThis is preferable because it allows for efficient energy transfer from compound 133 to compound 134. More specifically, a tangent line is drawn at the short-wavelength tail of the phosphorescence spectrum of compound 133, and the energy at the wavelength of the extrapolation line is T C3 Let S be the energy of the wavelength at the absorption edge of the absorption spectrum of compound 134. G When that happens, T C3 ≥S G It is preferable that the wavelength of the absorption edge on the long-wavelength side in the absorption spectrum of compound 134 is longer than the wavelength of the emission edge on the short-wavelength side in the emission spectrum (phosphorescence spectrum) of compound 133. In routes A3 and A4, compound 133 functions as an energy donor and compound 134 functions as an energy acceptor. Alternatively, the energy of the wavelength of the absorption edge in the absorption spectrum of compound 133 is T C3 Let S be the energy of the wavelength at the absorption edge of the absorption spectrum of compound 134. G When that happens, T C3 ≥S G It is preferable that the wavelength of the absorption edge on the long-wavelength side in the absorption spectrum of compound 134 is longer than the wavelength of the absorption edge on the long-wavelength side in the absorption spectrum of compound 133.

[0085] Here, from the triplet excitation energy of compound 133, T G The excitation energy transferred to (the energy transferred via route A4) cannot contribute to luminescence because compound 134 is a fluorescent material. Therefore, when energy transfer occurs via route A4, the luminescence efficiency of the light-emitting device decreases.

[0086] Generally, two mechanisms are known for intermolecular energy transfer: the Förster mechanism (dipole-dipole interaction) and the Dexter mechanism (electron exchange interaction). Since compound 134, the energy acceptor, is a fluorescent material, energy transfer via the Förster mechanism results in route A3, while energy transfer via the Dexter mechanism results in both routes A3 and A4. To suppress route A4, which leads to non-radiative deactivation, it is effective to suppress energy transfer via the Dexter mechanism.

[0087] Energy transfer via the Dexter mechanism is advantageous when the distance between the energy donor compound and the energy acceptor compound is 1 nm or less. Therefore, in order to suppress route A4, it is preferable to increase the distance between the energy donor (compound 133) and the energy acceptor (compound 134) to a degree that makes energy transfer via the Dexter mechanism less likely to occur.

[0088] A common method for increasing the distance between energy donors and energy acceptors is to lower the concentration of energy acceptors in the mixed film. However, lowering the concentration of energy acceptors suppresses not only energy transfer based on the Dexter mechanism from energy donors to energy acceptors, but also energy transfer based on the Förster mechanism. In that case, problems such as a decrease in the luminescence efficiency or reliability of the light-emitting device may occur.

[0089] Here, the T1 level of compound 134, which is the energy acceptor (T G ) is often an energy level derived from the luminescent phosphonate of compound 134. In other words, suppressing route A4 can also be achieved by increasing the distance between the luminescent phosphonate of compound 134 and compound 133.

[0090] Therefore, it is preferable that compound 134, which is the energy acceptor, is a compound having a luminescent phosphatid and a protecting group in part of its structure that has the function of increasing the distance between the luminescent phosphatid and other energy donors. When this compound is used as compound 134 in this configuration, even if the concentration of compound 134 is increased, the distance between compound 133 and compound 134 can be increased, and the energy transfer rate by the Förster mechanism can be increased while suppressing energy transfer by the Dexter mechanism. Therefore, by using this compound as compound 134, the S1 level (S) of compound 134 can be increased from compound 133. G Energy transfer of triplet excitation energy to (root A3) becomes more likely, while energy transfer of triplet excitation energy from compound 133 to the T1 level (T G This makes it less likely for triplet excitation energy to be transferred to (route A4: energy transfer via the Dexter mechanism), thereby suppressing the decrease in luminescence efficiency associated with energy transfer via route A4 and increasing the luminescence efficiency of the light-emitting device. It also improves the reliability of the light-emitting device.

[0091] As mentioned above, the Dexter mechanism is dominant when the distance between the energy donor and energy acceptor is 1 nm or less, and the Förster mechanism is dominant when the distance is between 1 nm and 10 nm. Therefore, the protecting group is preferably a bulky substituent that extends from the luminescent phosphodiester of compound 134 in the range of 1 nm to 10 nm.

[0092] Furthermore, in this configuration example, by increasing the concentration of compound 134, which is the energy acceptor, it is possible to suppress energy transfer by the Dexter mechanism while increasing the energy transfer rate by the Förster mechanism. By increasing the energy transfer rate by the Förster mechanism, the excitation lifetime of the energy acceptor in the light-emitting layer is shortened, thereby improving the reliability of the light-emitting device. Specifically, the concentration of compound 134 in the light-emitting layer 113 is preferably 2 wt% to 50 wt% by weight, more preferably 5 wt% to 30 wt%, and even more preferably 5 wt% to 20 wt%, relative to compound 133, which is the energy donor. Alternatively, the concentration of compound 134 in the light-emitting layer 113 is preferably 2 vol% to 50 vol% by volume, more preferably 5 vol% to 30 vol%, and even more preferably 5 vol% to 20 vol%, relative to compound 133, which is the energy donor.

[0093] <Example of luminescent layer configuration 2> Next, we will describe a specific example of the configuration of the light-emitting layer 113, example 2. In this example, the light-emitting layer 113 has compounds 131, 132, 133, and 134, as shown in Figure 3(A). In this example, we will describe the case where compound 133, a substance capable of converting triplet excitation energy into light emission, is a phosphorescent material, and compound 134, a fluorescent material, is a thermally activated delayed fluorescence (TADF) material. Note that TADF materials are materials that have the function of converting both singlet and triplet excitation energy into light emission. An example of the energy level correlation in the light-emitting layer 113 in this example is shown in Figure 4(B). Note that the notation, symbols, and roots A1 and A2 in Figure 4(B) are the same as in Figure 4(A), so they are omitted from the description.

[0094] As shown in Figure 4(B), the triplet excitation energy transferred from the excited complex formed by compounds 131 and 132 to compound 133 via route A2 is converted to the singlet excitation energy of compound 134, which is a TADF material (route A5). At this time, as shown in Figure 4(B), T E ≧T C3 ≥S G This is preferable because it allows for efficient energy transfer from compound 133 to compound 134. More specifically, a tangent line is drawn at the short-wavelength tail of the phosphorescence spectrum of compound 133, and the energy at the wavelength of the extrapolation line is T C3 Let S be the energy of the wavelength at the absorption edge of the absorption spectrum of compound 134. G When that happens, T C3 ≥S G It is preferable that this be the case.

[0095] Furthermore, in the light-emitting layer 113 of the light-emitting device shown in this example, in addition to the above, the triplet excitation energy of compound 133 is transferred to the T1 level of compound 134 (route A6 in Figure 4(B)). In this example, since compound 134 is a TADF material, it has the function of converting the triplet excitation energy to singlet excitation energy by upconversion. Therefore, the triplet excitation energy converted by route A6 is converted to singlet excitation energy by upconversion (route A7 in Figure 4(B)), exhibiting thermally activated delayed fluorescence. Thus, compound 134 can efficiently exhibit emission from the singlet excited state, and the luminescence efficiency of the light-emitting device can be increased. Note that in routes A5 and A6, compound 133 functions as an energy donor and compound 134 functions as an energy acceptor.

[0096] In Configuration Examples 1 and 2, the light-emitting layer 113 is shown to have four compounds (compound 131, compound 132, compound 133, and compound 134), but the present invention is not limited thereto. In the following Configuration Examples 3 and 4, a configuration in which the light-emitting layer 113 has three compounds (compound 131, compound 133, and compound 134) will be described.

[0097] <Example 3 of the light-emitting layer configuration> A specific example of the configuration of the light-emitting layer 113, example 3, will be described. In this example, the light-emitting layer 113 has compound 131, compound 133, and compound 134, as shown in Figure 3(B). Furthermore, in this example, the case in which compound 133, a substance capable of converting triplet excitation energy into light emission, is a phosphorescent material and compound 134 is a fluorescent material will be described. An example of the energy level correlation in the light-emitting layer 113 in this example is shown in Figure 4(C). The notation and symbols in Figure 4(C) are as follows. ·Comp(131): Compound 131 ·Comp(133): Compound 133 ·Guest(134): Compound 134 ·S C1 : S1 level of compound 131 ·T C1 : T1 level of compound 131 ·T C3 : T1 level of compound 133 ·T G : T1 level of compound 134 ·S G : S1 level of compound 134

[0098] In this configuration example, singlet and triplet excitons are generated primarily by carrier recombination in compound 131. Note that compound 133 is T C3 ≦T C1 By selecting a phosphorescent material having the following relationship, both the singlet and triplet excitation energies generated in compound 131 can be converted to the T of compound 133. C3 It can be moved to the level (Root A in Figure 4(C)). 18 ). Furthermore, some carriers can recombine with compound 133.

[0099] The triplet excitation energy of compound 133 is converted into the excitation energy of compound 134, which is a fluorescent material (Root A 19 and Root A 20). At this time, as shown in Figure 4(C), T C3 ≥S G This is preferable because it allows for efficient energy transfer from compound 133 to compound 134. More specifically, a tangent line is drawn at the short-wavelength tail of the phosphorescence spectrum of compound 133, and the energy at the wavelength of the extrapolation line is T C3 Let S be the energy of the wavelength at the absorption edge of the absorption spectrum of compound 134. G When that happens, T C3 ≥S G It is preferable that this be the case. Note that Route A 19 and Root A 20 In this configuration, compound 133 functions as an energy donor, and compound 134 functions as an energy acceptor.

[0100] Here, from the triplet excitation energy of compound 133, T G The excitation energy transferred to (Root A 20 The energy transferred in this way cannot be used to contribute to luminescence because compound 134 is a fluorescent material. Therefore, route A 20 When energy transfer occurs, the luminous efficiency of the light-emitting device decreases.

[0101] Such energy transfer (Route A 20 In order to suppress ), as explained in the above example configuration 1, it is important that the distance between compound 133 and compound 134, that is, the distance between compound 133 and the luminescent phosphatid of compound 134, is long. For this reason, it is preferable that compound 134, which is an energy acceptor, is a compound that has a luminescent phosphatid and a protecting group in part of its structure that has the function of increasing the distance between the luminescent phosphatid and other energy donors. This allows for the suppression of Root A 20 This makes it possible to suppress energy transfer caused by this process.

[0102] <Example of light-emitting layer configuration 4> In this exemplary configuration, the light-emitting layer 113 in the light-emitting device has Compound 131, Compound 134, and Compound 133 as shown in Fig. 3(B). A case where Compound 133, which is a substance capable of converting triplet excitation energy into light emission, is a TADF material is shown. An example of the correlation of energy levels in the light-emitting layer 113 in this exemplary configuration is as shown in Fig. 4(D). The notations and reference signs in Fig. 4(D) are the same as those shown in Fig. 4(C), and other than that, they are as shown below. ·S C3 : S1 level of Compound 133

[0103] In this exemplary configuration, recombination of carriers mainly occurs with Compound 131, thereby generating singlet excitons and triplet excitons. As Compound 133, by selecting a TADF material having a relationship of C3 S ≤ C1 and C3 T ≤ C1 both the singlet excitation energy and the triplet excitation energy generated by Compound 131 can be transferred to the S C3 and T C3 levels of Compound 133 (Route A in Fig. 4(D) 21 ). Note that some carriers may also recombine with Compound 133.

[0104] Since Compound 133 is a TADF material, it has a function of converting triplet excitation energy into singlet excitation energy by upconversion (Route A in Fig. 4(D) 22 ). Also, the singlet excitation energy possessed by Compound 133 can quickly move to Compound 134 (Route A in Fig. 4(D) 23 ). At this time, it is preferable that C3 S ≥ G . More specifically, a tangent is drawn at the short-wavelength side skirt of the fluorescence spectrum of Compound 133, and the energy of the wavelength of the extrapolated line is defined as S C3 , and the energy of the wavelength at the absorption edge of the absorption spectrum of Compound 134 is defined as S G . When C3 S ≥ GIt is preferable that this be the case.

[0105] Therefore, in the light-emitting layer 113 of the light-emitting device shown in this configuration example, Route A in Figure 4(D) 21 Route A 22 , and Root A 23 By following this pathway, the triplet excitation energy generated in compound 133 can be converted into fluorescence emission in compound 134. Route A 23 In this configuration, compound 133 functions as an energy donor and compound 134 functions as an energy acceptor. However, in the light-emitting layer 113 of the light-emitting device shown in this example, in addition to the above, there is also a pathway through which the triplet excitation energy of compound 133 moves to the T1 level of compound 134 (Route A in Figure 4(D)). 24 ) may also compete with this type of energy transfer (Route A 24 When this occurs, compound 134, which is a fluorescent material, cannot contribute the triplet excitation energy to light emission, thus reducing the luminescence efficiency of the light-emitting device.

[0106] Such energy transfer (Route A 24 In order to suppress this, as explained in Configuration Example 1 above, it is important that the distance between compound 133 and compound 134, that is, the distance between compound 133 and the luminescent phosphopectons of compound 134, is long.

[0107] A compound according to one aspect of the present invention has a luminescent phose and a protecting group in part of its structure, and when it functions as an energy acceptor in the light-emitting layer 113, the protecting group has the function of increasing the distance between other energy donors and the luminescent phose. Therefore, when a compound according to one aspect of the present invention is used as compound 134 in this configuration, even if the concentration of compound 134 is increased, the distance between compound 133 and compound 134 can be increased, and the energy transfer rate by the Förster mechanism can be increased while suppressing energy transfer by the Dexter mechanism. Therefore, by using a compound according to one aspect of the present invention as compound 134, the S1 level (S) of compound 134 can be increased from compound 133. G Energy transfer of triplet excitation energy to (√A23 ) is more likely to occur, while the T1 level (T G Transfer of triplet excitation energy to (Root A 24 This makes it less likely for energy transfer (by the Dexter mechanism) to occur, so Route A 24 This method can increase the luminous efficiency of the light-emitting device while suppressing the decrease in luminous efficiency associated with energy transfer. Furthermore, it can improve the reliability of the light-emitting device.

[0108] In the above-described example 1 and example 2 of the light-emitting layer, in route A2, the excitation complex formed by compound 131 and compound 132 functions as an energy donor, and in route A3 of example 1 and routes A5 and A6 of example 2, compound 133 functions as an energy donor, thereby enabling the creation of a highly efficient light-emitting device. Furthermore, in example 3 of the light-emitting layer, route A 18 In this process, compound 131 functions as an energy donor, and route A 19 In this configuration, compound 133 functions as an energy donor, making it possible to obtain a highly efficient light-emitting device. Also, in the example configuration of the light-emitting layer, root A 21 In this process, compound 131 functions as an energy donor, and route A 23 In this configuration, compound 133 functions as an energy donor, making it possible to obtain a highly efficient light-emitting device.

[0109] Here, it is preferable that at least one, preferably two, and most preferably all, of compounds 131, 132, and 133, which function as energy donors in the light-emitting layer, contain deuterium. This is because the bond dissociation energy of the bond between carbon and deuterium is greater than that of the bond between carbon and light hydrogen, making it stable and difficult to break. Therefore, compounds containing deuterium are more stable and less prone to degradation compared to non-deuterated compounds. By having at least one, preferably two, and most preferably all, of compounds 131, 132, and 133 contain deuterium, the stability of the compounds can be increased, and the degradation of the energy donors can be suppressed. This prevents the energy transfer efficiency to compound 134 from decreasing over time, thereby increasing the reliability of the light-emitting device.

[0110] Furthermore, if compounds 131, 132, and 133 contain deuterium, they may each be compounds containing both hydrogen and deuterium, or compounds that contain deuterium but not hydrogen.

[0111] Furthermore, while compounds 131 and 132 may be deuterated as a whole molecule, it is preferable that the group or skeleton where the lowest triplet excitation energy level is localized is deuterated. This makes it possible to obtain compounds 131 and 132 at a lower cost than deuterating the entire molecule.

[0112] Furthermore, while compound 133 may be deuterated as a whole molecule, it is preferable that relatively easily cleaved groups are deuterated. For example, when compound 133 uses an organometallic complex containing an alkyl group such as a methyl group as at least one of its ligands, it is preferable that the alkyl group is deuterated. This makes it possible to obtain compound 133 at a lower cost than deuterating the entire molecule, thereby improving the reliability of the light-emitting device.

[0113] In this specification, "containing deuterium" means that the proportion of deuterium in the hydrogen and deuterium contained in the compound is significantly higher than the natural abundance of deuterium, specifically by 500 times or more. "Deuterated compound" means a compound in which the proportion of deuterium in the hydrogen and deuterium contained in the compound is significantly higher than the natural abundance of deuterium, specifically by 500 times or more. Furthermore, this proportion is not the proportion per molecule, but the average of multiple target compounds present in a certain area.

[0114] In addition to the above-described configuration, it is even more preferable that compound 134, which functions as an energy acceptor in the light-emitting layer, contains deuterium. As described above, compounds containing deuterium are more stable and less prone to degradation compared to non-deuterated compounds, so the presence of deuterium in compound 134 enhances the stability of the compound. Therefore, the presence of deuterium in compound 134 suppresses the decrease in the luminous efficiency of the light-emitting device over time, thereby improving the reliability of the light-emitting device.

[0115] Compound 134 may be deuterated as a whole molecule, but when using a fluorescent material containing deuterium as compound 134, it is more preferable to use a fluorescent material in which the protecting group is deuterated. This allows for obtaining compound 134 at a lower cost than deuterating the entire molecule, thereby improving the reliability of the light-emitting device. In particular, when the protecting group is an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, or a trialkylsilyl group having 3 to 10 carbon atoms, degradation originating from the hydrogen atoms of these groups can be suppressed.

[0116] Furthermore, another reason why the reliability of the light-emitting device can be enhanced by having at least one, preferably two, and most preferably all, of compounds 131, 132, and 133, which function as energy donors in the light-emitting layer, contain deuterium is that the phosphorescence lifetime or delayed fluorescence lifetime of the deuterated compound becomes longer than that of the non-deuterated compound, thereby improving energy transfer efficiency. This is because the intramolecular vibrations in the lowest triplet excited state (T1 state) of the deuterated compound are suppressed more than those of the non-deuterated compound, and non-radiative transitions from the T1 state to more stable states are suppressed.

[0117] Furthermore, when compound 131 and compound 132 constitute an excited complex, a small energy difference between the T1 levels of compound 131 and compound 132 is preferable because it prevents the excitation energy from being biased towards one of the organic compounds, thus preventing significant degradation of one of them and improving the reliability of the light-emitting device. Specifically, the energy difference between the T1 levels of compound 131 and compound 132 is preferably 0.20 eV or less, more preferably 0.15 eV or less, and more preferably 0.10 eV or less.

[0118] In particular, when compound 131 and compound 132 constitute an excited complex, and both compound 131 and compound 132 contain deuterium, that is, when reliability is improved in relation to the extension of the lifetime of triplet excitons due to the suppression of non-radiative deactivation of triplet excitation energy resulting from the suppression of vibrations by deuteration, the effect of degradation of one of the compounds due to the bias in excitation energy is significant. Therefore, when compound 131 and compound 132 constitute an excited complex, and both compound 131 and compound 132 contain deuterium, it is more preferable that the energy difference between the T1 level of compound 131 and the T1 level of compound 132 be 0.20 eV or less, preferably 0.15 eV or less, and more preferably 0.10 eV or less.

[0119] In organic EL devices, there is a demand for increased efficiency and reliability of blue light-emitting devices. This is because, among highly efficient phosphorescent light-emitting devices, blue phosphorescent light-emitting devices have reliability issues compared to other phosphorescent light-emitting devices. The configuration of the light-emitting layer 113 in this light-emitting device is expected to yield an efficient and highly reliable blue light-emitting device.

[0120] In one embodiment of the present invention, when the fluorescent substance (compound 134) that produces light emission is a blue fluorescent substance, and when considering the efficient utilization of the excitation energy obtained from the energy donor, the substance (compound 133) that can convert the triplet excitation energy that serves as the energy donor into light emission is preferably a substance that emits blue light, particularly blue phosphorescence.

[0121] On the other hand, when a blue phosphorescent material with a high excitation energy level is used in the light-emitting layer 113, the band gap of the host material becomes large, making it difficult to control the carrier balance. As a result, light-emitting devices containing blue phosphorescent materials often have a configuration in which the light-emitting layer 113 tends to have an excess of electrons. Similarly, in the case of a light-emitting layer 113 containing a material capable of converting triplet excitation energy into light and a fluorescent material, if the fluorescent material is a blue light-emitting material, the material capable of converting triplet excitation energy into light is preferably a blue phosphorescent material, and it can be said that this is a light-emitting device that tends to have an excess of electrons, making it difficult to control the carrier balance of the light-emitting layer 113.

[0122] When the light-emitting layer 113 becomes electron-rich, the recombination region tends to form more skewed towards the anode side. As a result, the density of excitons generated after recombination also increases on the anode side, making it easier for exciton interactions and interactions between excitons and holes in the electron-blocking layer to occur, thus easily generating very high-energy excitons or holes. These high-energy excitons or holes accelerate the degradation of the light-emitting layer 113 and the hole transport layer 112 or electron-blocking layer adjacent to the light-emitting layer 113.

[0123] However, in a light-emitting device according to one aspect of the present invention, the GSP_Slope of the second electron transport layer can be made larger than the GSP_Slope of the first electron transport layer, thereby controlling the electron injection properties. By applying this configuration to a light-emitting device having the above-described light-emitting layer 113, it is possible to suppress the light-emitting layer 113 from becoming electron-excessive and to obtain a significant improvement in reliability.

[0124] Furthermore, in the light-emitting layer 113 which includes a substance capable of converting triplet excitation energy into light emission and a fluorescent substance, if the HOMO level of the fluorescent substance is equivalent to or higher than the HOMO level of the substance capable of converting triplet excitation energy into light emission, the light-emitting layer 113 is more prone to electron excess. When the light-emitting layer 113 has such a configuration, the light-emitting device according to one aspect of the present invention can achieve a greater improvement in reliability.

[0125] Examples of materials capable of converting triplet excitation energy into light emission include thermally activated delayed fluorescence (TADF) materials and phosphorescent materials. In this specification, a phosphorescent material refers to a compound that exhibits phosphorescence and does not exhibit fluorescence at any temperature range from low temperature (e.g., 77K) to room temperature (i.e., 77K to 313K). The phosphorescent material preferably contains a metal element with a large spin-orbit interaction, specifically a transition metal element, and in particular preferably a platinum group element (ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), or platinum (Pt)), and among these, the presence of iridium or platinum is preferable because it can increase the transition probability related to the direct transition between the singlet ground state and the triplet excited state.

[0126] Specifically, examples of phosphorescent substances include organic compounds that exhibit blue phosphorescence with emission peaks in the wavelength range of 450 nm to 520 nm, as shown below: (2-{3-[3-(3,5-di-tert-butylphenyl)benzimidazole-1-yl-2-ylidene-κC2]phenoxy-κC2}-9-[5-(methyl-d3)-4-phenyl-2-pyridinyl-κN]carbazole-2,1-diyl-κC)platinum(II) (abbreviation: Pt(mmtBubOcz5m4ppy-d3)), shown by structural formula (400), and (2-{3-[3-(3,5-di-tert-butylphenyl)benzimidazole-1-yl-2-ylidene-κC2], shown by structural formula (401). [C2]phenoxy-κC2}-9-(4-tert-butyl-2-pyridinyl-κN)-6-(5-cyano-2-methylphenyl)carbazole-2,1-diyl-κC)platinum(II) (abbreviation: Pt(mmtBubOm5CPcztBupy)), shown in structural formula (402) {[9-(4-tert-butyl-2-pyridinyl-κN)-[3,9'-bi-9H-carbazole]-2,1-diyl-κC]oxy-9-(4-tert-butyl-2-pyridinyl-κN)carbazole-2,1-diyl-κ Platinum(II) (abbreviation: Pt(cztBucpyOtBucpy)), shown in structural formula (403) {[9-(4-tert-butyl-2-pyridinyl-κN)carbazole-2,1-diyl-κC]oxy-9-(4-tert-butyl-2-pyridinyl-κN)carbazole-2,1-diyl-κC}platinum(II) (abbreviation: Pt(tBucpy2O)), shown in structural formula (404) {[9-(2-pyridinyl-κN)carbazole-2,1-diyl-κC]oxy-9-(2-pyridinyl-κN)carbazole Platinum(II) (abbreviation: PtNON), shown in structural formula (405) (2-{4-methyl-3-[3-(3,5-di-tert-butylphenyl)benzimidazole-1-yl-2-ylidene-κC2]phenoxy-κC2}-9-[3,5-di(methyl-d3)-4-phenyl-2-pyridinyl-κN]carbazole-2,1-diyl-κC)platinum(II) (abbreviation: Pt(Me-mmtBubOcz35dm4ppy-d6)), shown in structural formula (406) {[3-(3,[5-di-tert-butylphenyl)-9-(4-tert-butyl-2-pyridinyl-κN)carbazole-2,1-diyl-κC]oxy-9-(4-tert-butyl-2-pyridinyl-κN)carbazole-2,1-diyl-κC}platinum(II) (abbreviation: Pt(mmtBuptBucpyOtBucpy)), shown in structural formula (407) (2-{3-[3-(3,5-di-tert-butylphenyl)benzimidazole-1-I [2-Ilidene-κC2]phenoxy-κC2}-9-[3,5-di(methyl-d3)-4-phenyl-2-pyridinyl-κN]carbazole-2,1-diyl-κC)platinum(II) (abbreviation: Pt(mmtBubOcz35dm4ppy-d6)), shown by structural formula (408) (2-{5-tert-butyl-3-[3-(3,5-di-tert-butylphenyl)benzimidazole-1-yl-2-ylidene-κC2]phenoxy- {2-(3-{3-[2,6-di(phenyl-d3)phenyl]benzimidazole-1-yl-2-ylidene-κC2}phenoxy-κC2)-9-[3,5-di(methyl-d3)-4-phenyl-2-pyridinyl-κN]carbazole-2,1-diyl-κC)platinum(II) (abbreviation: Pt(tBu-mmtBubOcz35dm4ppy-d6)), shown in structural formula (409), {2-(3-{3-[2,6-di(phenyl-d5)phenyl]benzimidazole-1-yl-2-ylidene-κC2}phenoxy-κC2)-9-[3,5-di(methyl-d3)-4-phenyl [Nyl-2-pyridinyl-κN]carbazole-2,1-diyl-κC1}platinum(II) (abbreviation: Pt(mTPbOcz35dm4ppy-d16)), shown by structural formula (410) (2-{3-[3-(3,5-di-tert-butylphenyl)benzimidazole-1-yl-2-ylidene-κC2]phenoxy-κC2}-9-[4-tert-butylphenyl-3,5-di(methyl-d3)-2-pyridinyl-κN]carbazole-2,Examples include 1-diyl-κC)platinum(II) (abbreviation: Pt(mmtBubOcz35dm4tBuppy-d6)). Also, PtON1 shown in structural formula (411), PtON7 shown in structural formula (412), PtON1-Me shown in structural formula (413), PtON1-tBu shown in structural formula (414), PtON1-NMe2 shown in structural formula (415), PtON6-tBu shown in structural formula (416), PtON7-dtb shown in structural formula (417), PtN1N shown in structural formula (418), and P shown in structural formula (419). Examples include tN1pyCl, PtON7-tBu shown in structural formula (420), Pt(ppzOczpy) shown in structural formula (421), Pt(ppzOczpy-m) shown in structural formula (422), Pt(ppzOczpy-2m) shown in structural formula (423), PdN1N shown in structural formula (424), PdN1N-dm shown in structural formula (425), and PdN6N shown in structural formula (426). Among these, it is preferable that the phosphorescent material that acts as an energy donor has one of the following: an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, or a trialkylsilyl group having 3 to 10 carbon atoms, because this can increase the distance to the fluorescent material that acts as an energy acceptor. When using this phosphorescent material, even if the concentration of the phosphorescent material is increased, the distance to the fluorescent material can be increased, thereby suppressing energy transfer by the Dexter mechanism while increasing the energy transfer rate by the Förster mechanism.

[0127] [ka]

[0128] [ka]

[0129] [ka]

[0130] Other organometallic iridium compounds with a 4H-triazole skeleton include Tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazole-3-yl-κN2]phenyl-κC}iridium(III) (abbreviation: [Ir(mpptz-dmp)3]) and Tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III) (abbreviation: [Ir(Mptz)3]). iridium complexes having a 1H-triazole skeleton, such as tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III) (abbreviation: [Ir(Mptz1-mp)3]), tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III) (abbreviation: [Ir(Prptz1-Me)3]), fac-tris[1-(2,6 [Diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III) (abbreviation: [Ir(iPrpim)3]), Tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenantridinato]iridium(III) (abbreviation: [Ir(dmpimpt-Me)3]), Tris(2-{1-[2,6-bis(1-methylethyl)phenyl]-1H-imidazole-2-yl-κN3}-4-cyano Organometallic iridium complexes having an imidazole skeleton, such as phenyl-κC)iridium(III) (abbreviation: CNImIr), organometallic complexes having a benzimidazolidene skeleton, such as tris[(6-tert-butyl-3-phenyl-2H-imidazo[4,5-b]pyrazine-1-yl-κC2)phenyl-κC]iridium(III) (abbreviation: [Ir(cb)3]), and bis[2-(4',6'-difluorophenyl)pyridinato-N,C 2’ Iridium(III) tetrakis(1-pyrazolyl) borate (abbreviation: FIr6), bis[2-(4',6'-difluorophenyl)pyridinate-N,C 2’ Iridium(III) picolinate (abbreviation: Firpic), bis{2-[3',5'-bis(trifluoromethyl)phenyl]pyridinate-N,C 2’Iridium(III) picolinate (abbreviation: [Ir(CF3ppy)2(pic)]), bis[2-(4',6'-difluorophenyl)pyridinate-N,C 2’ Organometallic iridium complexes using phenylpyridine derivatives having electron-withdrawing groups, such as iridium(III) acetylacetonate (abbreviated as FIracac), as ligands, and platinum complexes such as (2-{3-[3-(3,5-di-tert-butylphenyl)benzimidazole-1-yl-2-ylidene-κC2]phenoxy-κC2}-9-(4-tert-butyl-2-pyridinyl-κN)carbazole-2,1-diyl-κC1)platinum(II) (abbreviated as PtON-TBBI) can be used.

[0131] Furthermore, the phosphorescent material described in Embodiment 2 can also be used as the phosphorescent material.

[0132] Furthermore, TADF materials are examples of materials capable of converting triplet excitation energy into luminescence. TADF materials are materials that have a small energy difference between the S1 and T1 levels and can convert triplet excitation energy to singlet excitation energy through reverse intersystem crossing. Therefore, triplet excitation energy can be upconverted to singlet excitation energy (reverse intersystem crossing) with only a small amount of thermal energy, and a singlet excited state can be efficiently generated. In addition, excitation complexes (also called exciplexes) that form an excited state with two types of materials have an extremely small energy difference between the S1 and T1 levels and function as TADF materials capable of converting triplet excitation energy to singlet excitation energy.

[0133] Furthermore, the phosphorescence spectrum observed at low temperatures (e.g., 10K) can be used as an indicator of the T1 level. For TADF materials, it is preferable that when a tangent is drawn at the short-wavelength tail of the fluorescence spectrum and the energy at the wavelength of the extrapolation is defined as the S1 level, and when a tangent is drawn at the short-wavelength tail of the phosphorescence spectrum and the energy at the wavelength of the extrapolation is defined as the T1 level, the energy difference between the S1 level and the T1 level is 0.2 eV or less.

[0134] Specific examples of TADF materials include 2-(biphenyl-4-yl)-4,6-bis(12-phenylindoro[2,3-a]carbazole-11-yl)-1,3,5-triazine (abbreviation: PIC-TRZ), 2-{4-[3-(N-phenyl-9H-carbazole-3-yl)-9H-carbazole-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn), 2-[4-(10H-phenoxazine-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviation: PXZ-TRZ), Examples include 3-[4-(5-phenyl-5,10-dihydrophenazine-10-yl)phenyl]-4,5-diphenyl-1,2,4-triazole (abbreviated as PPZ-3TPT), 3-(9,9-dimethyl-9H-acridine-10-yl)-9H-xanthene-9-one (abbreviated as ACRXTN), bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (abbreviated as DMAC-DPS), and 10-phenyl-10H,10'H-spiro[acridine-9,9'-anthracene]-10'-one (abbreviated as ACRSA). These heterocyclic compounds are preferred because they have π-electron-rich heteroaromatic rings and π-electron-deficient heteroaromatic rings, resulting in high electron transport and hole transport properties. Among the skeletons having a π-electron-deficient heteroaromatic ring, the diazine skeleton (pyrimidine skeleton, pyrazine skeleton, pyridazine skeleton) or the triazine skeleton is preferred because it is stable and reliable. Furthermore, among the skeletons having a π-electron-rich heteroaromatic ring, the acridine skeleton, phenoxazine skeleton, thiophene skeleton, furan skeleton, and pyrrole skeleton are preferred because they are stable and reliable, and it is preferable to have one or more of these skeletons selected from among them. In particular, the indole skeleton, carbazole skeleton, and 3-(9-phenyl-9H-carbazole-3-yl)-9H-carbazole skeleton are preferred as pyrrole skeletons. Substances in which a π-electron-rich heteroaromatic ring and a π-electron-deficient heteroaromatic ring are directly bonded are particularly preferred because both the donor properties of the π-electron-rich heteroaromatic ring and the acceptor properties of the π-electron-deficient heteroaromatic ring are strong, resulting in a small energy difference between the singlet excitation energy level and the triplet excitation energy level.Furthermore, it is preferable that the TADF material acting as an energy donor has one of the following: an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, or a trialkylsilyl group having 3 to 10 carbon atoms, because this can increase the distance to the fluorescent substance acting as an energy acceptor. When such a TADF material is used, the distance to the fluorescent substance can be increased even when the concentration of the TADF material is increased, thereby suppressing energy transfer by the Dexter mechanism while increasing the energy transfer rate by the Förster mechanism.

[0135] Furthermore, as TADF materials, condensed heteroaromatic compounds containing nitrogen and boron, particularly compounds having a diaza-boranaphtho-anthracene skeleton, are preferred because they produce a narrow emission spectrum and blue emission with good color purity. Specific examples include 5,9-diphenyl-5H,9H-[1,4]benzazaborino[2,3,4-kl]phenazavolin (abbreviated as DABNA-1), 9-(diphenyl-3-yl)-N,N,5,11-tetraphenyl-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracene-3-amine (abbreviated as DABNA-2), and 2,12-di(tert-butyl )-5,9-di(4-tert-butylphenyl)-N,N-diphenyl-5H,9H-[1,4]benzazaborino[2,3,4-kl]phenazavolin-7-amine (abbreviation: DPhA-tBu4DABNA), 2,12-di(tert-butyl)-N,N,5,9-tetra(4-tert-butylphenyl)-5H,9H-[1,4]benzazaborino[2,3,4-kl]phenazavolin Phosphorus-7-amine (abbreviation: tBuDPhA-tBu4DABNA), 2,12-di(tert-butyl)-5,9-di(4-tert-butylphenyl)-7-methyl-5H,9H-[1,4]benzazavolino[2,3,4-kl]phenazavolin (abbreviation: Me-tBu4DABNA), N7,N7,N13,N13,5,9,11,15-octaphenyl-5H,9H,11H,15H Examples include -[1,4]benzazabolino[2,3,4-kl][1,4]benzazabolino[4',3',2':4,5][1,4]benzazabolino[3,2-b]phenazabolin-7,13-diamine (abbreviation: ν-DABNA), 2-(4-tert-butylphenyl)benz[5,6]indro[3,2,1-jk]benzo[b]carbazole (abbreviation: tBuPBibc), etc.

[0136] In addition to these, the TADF material is 9,10,11-tris[3,6-bis(1,1-dimethylethyl)-9H-carbazole-9-yl]-2,5,15,18-tetrakis(1,1-dimethylethyl)indoro[3,2,1-de]indoro[3',2',1':8,1][1,4]benzazavolino[2,3,4-kl]phenazavolin (abbreviation: BBCz-G), 9,1 Compounds having an indole skeleton, such as 1-bis[3,6-bis(1,1-dimethylethyl)-9H-carbazole-9-yl]-2,5,15,18-tetrakis(1,1-dimethylethyl)indoro[3,2,1-de]indoro[3',2',1':8,1][1,4]benzazavolino[2,3,4-kl]phenazavolin (abbreviation: BBCz-Y), can be suitably used.

[0137] TADF materials are materials that have a small energy difference between the triplet excited energy level and the singlet excited energy level, and have the function of converting energy from the triplet excited state to the singlet excited state through reverse intersystem crossing. Therefore, the triplet excited state can be upconverted to the singlet excited state (reverse intersystem crossing) with only a small amount of thermal energy, and emission (fluorescence) from the singlet excited state can be efficiently exhibited. Furthermore, conditions for efficiently obtaining thermally activated delayed fluorescence include the energy difference between the triplet excited energy level and the singlet excited energy level being preferably greater than 0 eV and 0.20 eV or less, and more preferably greater than 0 eV and 0.10 eV or less.

[0138] Furthermore, the TADF materials listed in Embodiment 2 can be used, not limited to those described above.

[0139] Furthermore, nanostructures of transition metal compounds having a perovskite structure are examples of materials capable of converting triplet excitation energy into light emission. Nanostructures of metal halogen perovskites are particularly desirable. Nanoparticles and nanorods are preferred as such nanostructures.

[0140] The fluorescent material is preferably a compound having a luminescent phosphodiolum and a protecting group that has the function of increasing the distance between the luminescent phosphodiolum and other energy donors as part of its structure.

[0141] Here, the term "luminescent phore" refers to the group of atoms (skeleton) that causes luminescence in a fluorescent material. The luminescent phore generally has π bonds and preferably contains aromatic rings, and preferably contains condensed aromatic rings or condensed heteroaromatic rings. In another embodiment, the luminescent phore can be considered as a group of atoms (skeleton) containing aromatic rings in which a transition dipole vector exists on the ring plane. Furthermore, if a fluorescent material has multiple condensed aromatic rings or condensed heteroaromatic rings, the skeleton with the lowest S1 level among these multiple condensed aromatic rings or condensed heteroaromatic rings may be considered the luminescent phore of the fluorescent material. Furthermore, the skeleton with the longest wavelength absorption edge among these multiple condensed aromatic rings or condensed heteroaromatic rings may be considered the luminescent phore of the fluorescent material. In addition, the luminescent phore of the fluorescent material can sometimes be predicted from the shape of the emission spectrum of each of these multiple condensed aromatic rings or condensed heteroaromatic rings.

[0142] Examples of such luminescent phosphodes include phenanthrene skeletons, stilbene skeletons, acridone skeletons, phenoxazine skeletons, phenothiazine skeletons, naphthalene skeletons, anthracene skeletons, fluorene skeletons, chrysene skeletons, triphenylene skeletons, tetracene skeletons, pyrene skeletons, perylene skeletons, coumarin skeletons, quinacridone skeletons, and naphthobisbenzofuran skeletons. Fluorescent materials having naphthalene, anthracene, fluorene, chrysene, triphenylene, tetracene, pyrene, perylene, coumarin, quinacridone, and naphthobisbenzofuran skeletons are particularly preferred due to their high fluorescence quantum yield.

[0143] Furthermore, substituents used as protecting groups must have a triplet excitation energy level higher than the T1 level of the luminescent phosphodiester and the host material. For this reason, saturated hydrocarbon groups are preferable. This is because substituents without π bonds have high triplet excitation energy levels. Also, substituents without π bonds have low carrier (electron or hole) transport capabilities. Therefore, saturated hydrocarbon groups can increase the distance between the luminescent phosphodiester and the host material with little effect on the excited state or carrier transport capabilities of the host material. In addition, in organic compounds that simultaneously have substituents without π bonds and substituents with π-conjugated systems, frontier orbitals {HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital)} often exist on the substituent with the π-conjugated system, and the luminescent phosphodiester, in particular, often has frontier orbitals. As will be described later, the overlap of the energy donor and energy acceptor HOMO, and the overlap of the LUMO are important for energy transfer by the Dexter mechanism. Therefore, by using saturated hydrocarbon groups as protecting groups, the distance between the frontier orbital of the host material, which is the energy donor, and the frontier orbital of the guest material, which is the energy acceptor, can be increased, thereby suppressing energy transfer via the Dexter mechanism.

[0144] Specific examples of protecting groups include alkyl groups having 1 to 10 carbon atoms. Furthermore, since the protecting group needs to increase the distance between the luminescent phosphodiester and the host material, bulky substituents are preferred. Therefore, alkyl groups having 3 to 10 carbon atoms, substituted or unsubstituted cycloalkyl groups having 3 to 10 carbon atoms, and trialkylsilyl groups having 3 to 10 carbon atoms are suitably used. Bulky branched alkyl groups are particularly preferred as alkyl groups. Moreover, substituents having a quaternary carbon atom are particularly preferred because they result in bulkier substituents.

[0145] Furthermore, as mentioned above, it is more preferable that the protecting group is deuterated. When the protecting group has deuterium, suitable examples include alkyl groups having 3 to 10 carbon atoms and containing deuterium, substituted or unsubstituted cycloalkyl groups having 3 to 10 carbon atoms and containing deuterium, and trialkylsilyl groups having 3 to 10 carbon atoms and containing deuterium.

[0146] Furthermore, it is preferable to have five or more protecting groups per luminescent phosphodiolus. This configuration allows the entire luminescent phosphodiolus to be covered with protecting groups, thereby appropriately adjusting the distance between the host material and the luminescent phosphodiolus. It is even more preferable that the protecting groups are not directly bonded to the luminescent phosphodiolus. For example, the protecting groups may be bonded to the luminescent phosphodiolus via divalent or higher substituents such as arylene groups or amino groups. By bonding the protecting groups to the luminescent phosphodiolus via such substituents, the distance between the luminescent phosphodiolus and the host material can be effectively increased. Therefore, when the luminescent phosphodiolus and the protecting groups are not directly bonded, having four or more protecting groups per luminescent phosphodiolus can effectively suppress energy transfer via the Dexter mechanism.

[0147] Specific examples of fluorescent luminescent substances having a luminescent phosphodiolum and a protecting group that has the function of increasing the distance between the luminescent phosphodiolum and other energy donors include N,N'-(2-phenylanthracene-9,10-diyl)-N,N,N',N'-tetrakis(3,5-di-tert-butylphenyl)diamine (abbreviation: 2Ph-mmtBuDPhA2Anth), 2,2',6,6'-tetrakis(3,5-di-tert-butylphenyl)-N,N,N',N'-tetrakis(3,5-di-tert-butylphenyl)-[9,9'-bianthracene]-10,10'-diamine (abbreviation: 22'66'mmtBuPh-mmtBuDPhA2BANT), and N,N'-bis[3,5-bis(1-adamantyl)phenyl]-N,N'-bis(3,5-di-t ert-butylphenyl)-2-phenylanthracene-9,10-diamine (abbreviation: 2Ph-mmAdtBuDPhA2Anth-03), N,N'-bis(3,5-di-tert-butylphenyl)-N,N'-bis{3,5-bis[4-(1-adamantyl)phenyl]phenyl}-2,6-diphenylanthracene-9,10-diamine (abbreviation: 2,6Ph-mmAdPtBuDPhA2Anth), N,N'-bis(3,5-di-tert-butylphenyl)-N,N'-bis{3,5-bis[4-(1-adamantyl)phenyl]phenyl}-2-phenylanthracene-9,10-diamine (abbreviation: 2Ph-mmAdPtBuDPhA2Anth), N,N'-bis{3,5-bis(tricyclo[5.2.1.0 2,6]decane-8-yl)phenyl}-N,N'-bis(3,5-di-tert-butylphenyl)-2-phenylanthracene-9,10-diamine (abbreviation: 2Ph-mmTCDtBuDPhA2Anth), N,N'-bis{3,5-bis(2-bicyclo[2.2.1]heptyl)phenyl}-N,N'-bis(3,5-di-tert-butylphenyl)-2-phenylanthracene-9,10-diamine (abbreviation: 2Ph-mmnbtBuDPhA2Anth), N,N'-bis[3,5-bis(2-adamantyl)phenyl]-N,N'-bis[3,5-bis(3,5-di-tert-butylphenyl)phenyl]-2-phenylanthracene-9,10-diamine (abbreviation: 2Ph-mmAdtBuDPhA2Anth-02), N,N'-bis[3,5 -Bis(2-adamantyl)phenyl]-N,N'-bis(3,5-di-tert-butylphenyl)-2-phenylanthracene-9,10-diamine (abbreviation: 2Ph-mmAdtBuDPhA2Anth), N,N'-(2-trimethylsilylanthracene-9,10-diyl)-N,N,N',N'-tetrakis(3,5-di-tert-butylphenyl)diamine (abbreviation: 2TMS-mmtBuDPhA2Anth), N,N'-(pyrene-1,6-diyl)bis[N-(2-methyl [Phenyl)-6-cyclohexylbenzo[b]naphtho[1,2-d]furan-8-amine] (abbreviation: 1,6oMechBnfAPrn), N,N'-(pyrene-1,6-diyl)bis(N-phenyl-6-trimethylsilylbenzo[b]naphtho[1,2-d]furan-8-amine) (abbreviation: 1,6TMSBnfAPrn), N,N'-(3,8-dicyclohexylpyrene-1,6-diyl)bis[N-phenyl-(6-cyclohexylbenzo[b]naphtho[1,2-d]furan)-8-amine Examples include ](abbreviation: ch-1,6chBnfAPrn), N,N'-bis[9-(3,5-di-tert-butylphenyl)-9H-carbazole-2-yl]-N,N'-diphenyl-naphtho[2,3-b;6,7-b']bisbenzofuran-3,10-diamine (abbreviation: 3,10mmtBuPCA2Nbf(IV)-02), and N,N,N',N'-tetrakis(3,5-di-tert-butylphenyl)pyrene-1,6-diamine (abbreviation: 1,6mmtBuDPhAPrn).

[0148] Furthermore, the fluorescent materials listed in Embodiment 2 can be used, not limited to those mentioned above.

[0149] As shown in Figure 2(A), in a sequential light-emitting device according to one embodiment of the present invention, if the sequential light-emitting device has a hole transport layer 112, it is preferable that the GSP_Slope (mV / nm) of the light-emitting layer 113 is greater than the GSP_Slope (mV / nm) of the hole transport layer or the GSP_Slope (mV / nm) of the vapor-deposited film of the third organic compound having a π-electron-rich heteroaromatic ring or aromatic amine present in the hole transport layer 112. Alternatively, it is preferable that the GSP_Slope (mV / nm) of the vapor-deposited film of the host material is greater than the GSP_Slope (mV / nm) of the vapor-deposited film of the third organic compound having a π-electron-rich heteroaromatic ring or aromatic amine present in the hole transport layer 112.

[0150] Furthermore, as shown in Figure 2(B), if an inverted stacking type light-emitting device according to one embodiment of the present invention has a hole transport layer 112, it is preferable that the GSP_Slope (mV / nm) of the light-emitting layer 113 is smaller than the GSP_Slope (mV / nm) of the hole transport layer or the GSP_Slope (mV / nm) of the vapor-deposited film of the third organic compound having a π-electron-rich heteroaromatic ring or aromatic amine present in the hole transport layer 112. Alternatively, it is preferable that the GSP_Slope (mV / nm) of the vapor-deposited film of the host material is smaller than the GSP_Slope (mV / nm) of the vapor-deposited film of the third organic compound having a π-electron-rich heteroaromatic ring or aromatic amine present in the hole transport layer 112.

[0151] In one embodiment of the present invention having this configuration, hole injection is promoted by the effect of the negative interfacial charge originating from the difference in GSP_Slope of the two contacting layers. As a result, hole injection into the light-emitting layer is also effectively achieved, improving the carrier balance and expanding the recombination region, thereby suppressing the degradation of the light-emitting layer 113 and the hole transport layer 112.

[0152] Furthermore, as shown in Figure 1(A), in a sequential stacking type light-emitting device according to one embodiment of the present invention, it is preferable that the GSP_Slope (mV / nm) of the light-emitting layer 113 is greater than the GSP_Slope (mV / nm) of the first electron transport layer 114_1. Alternatively, it is preferable that the GSP_Slope (mV / nm) of the vapor-deposited film of the host material is greater than the GSP_Slope (mV / nm) of the vapor-deposited film of the first organic compound.

[0153] Furthermore, as shown in Figure 1(B), in an inverted stacking type light-emitting device according to one embodiment of the present invention, it is preferable that the GSP_Slope (mV / nm) of the light-emitting layer 113 is smaller than the GSP_Slope (mV / nm) of the second electron transport layer 114_2. Alternatively, it is preferable that the GSP_Slope (mV / nm) of the vapor-deposited film of the host material is smaller than the GSP_Slope (mV / nm) of the vapor-deposited film of the second organic compound.

[0154] In one embodiment of the present invention having this configuration, the injection of electrons from the second electron transport layer 114_2 to the first electron transport layer 114_1 is promoted due to the influence of the positive interfacial charge originating from the difference in GSP_Slope of the two contacting layers. Therefore, even if the injection of electrons from the first electrode 101 or the electron injection layer 115 to the second electron transport layer 114_2 is suppressed, the light-emitting device of one embodiment of the present invention does not cause a significant increase in the driving voltage, making it possible to produce a light-emitting device with good characteristics.

[0155] Furthermore, as shown in Figure 1(A), in a sequentially stacked light-emitting device according to one embodiment of the present invention, it is preferable that the GSP_Slope (mV / nm) of the second electron transport layer 114_2 is greater than the GSP_Slope (mV / nm) of the light-emitting layer 113. Alternatively, it is preferable that the GSP_Slope (mV / nm) of the vapor-deposited film of the second organic compound is greater than the GSP_Slope (mV / nm) of the vapor-deposited film of the host material.

[0156] Furthermore, as shown in Figure 1(B), in an inverted stacking type light-emitting device according to one embodiment of the present invention, it is preferable that the GSP_Slope (mV / nm) of the first electron transport layer 114_1 is smaller than the GSP_Slope (mV / nm) of the light-emitting layer 113. Alternatively, it is preferable that the GSP_Slope (mV / nm) of the vapor-deposited film of the first organic compound is smaller than the GSP_Slope (mV / nm) of the vapor-deposited film of the host material.

[0157] In one embodiment of the present invention having this configuration, the interfacial charge between the first electron transport layer 114_1 and the second electron transport layer 114_2 is negative and smaller than the interfacial charge between the light-emitting layer 113 and the first electron transport layer 114_1. This effect suppresses electron injection into the light-emitting layer while promoting hole injection into the light-emitting layer, thereby improving the carrier balance, expanding the recombination region, and suppressing the degradation of the light-emitting layer 113 and the hole transport layer 112.

[0158] Furthermore, if the light-emitting layer 113 includes a host material, it is preferable that the host material includes a first material and a second material. By composing the host material with multiple materials, it becomes easier to control the carrier balance, contributing to improved reliability. Alternatively, by forming an excitation complex with the first material and the second material, effects such as improved energy transfer efficiency to the light-emitting substance, lower driving voltage, and improved reliability can be achieved. It is preferable that one of the first and second materials is an organic compound having a π-electron-deficient heteroaromatic ring, and the other is an organic compound having a π-electron-rich heteroaromatic ring or aromatic amine, as this makes it easier to adjust the carrier balance.

[0159] When the host material contains multiple materials, the GSP_Slope(mV / nm) of the host material film can be the GSP_Slope(mV / nm) of a mixed film obtained by co-depositing the first material and the second material in a 1:1 ratio. Alternatively, the GSP_Slope(mV / nm) of the deposited film of the material with the higher mixing ratio among the first and second materials can be considered as the GSP_Slope(mV / nm) of the host material film.

[0160] <How to calculate GSP_Slope> Here, we will explain how to determine the GSP_Slope of a film formed by vacuum deposition of an organic compound.

[0161] The phenomenon in which the surface potential of a deposited film increases in proportion to its thickness is called giant surface potential, as mentioned above. Generally, the slope when the surface potential of a deposited film measured by a Kelvin probe is plotted in the direction of film thickness is discussed as the magnitude of the giant surface potential, i.e., GSP_Slope (mV / nm). However, when two different layers are stacked, the charge density accumulated at their interface (mC / m) is also considered. 2 By utilizing the fact that ) changes in relation to GSP, we can estimate GSP_Slope.

[0162] Non-patent document 1 shows that when organic thin films with different spontaneous polarizations (thin film 1 and thin film 2, where thin film 1 is on the anode side and thin film 2 is on the cathode side, and the anode is located on the substrate side) are stacked and a voltage is applied, the following equation holds true if the carriers accumulated at the interface are holes.

[0163]

number

[0164]

number

[0165] In equation (1), σ acc σ is the accumulated charge density. int V is the interfacial charge density. inj V is the hole injection voltage. th V is the threshold voltage, d2 is the thickness of thin film 2, and ε2 is the dielectric constant of thin film 2. inj , V th This can be estimated from the capacitance-voltage characteristics of the device. Furthermore, the dielectric constant is the refractive index n. o The square of (the value for a wavelength of 633 nm) can be used. In this way, V estimated from the capacitance-voltage characteristicsinj , V th Then, using the dielectric constant ε2 of thin film 2 calculated from the refractive index, and the film thickness d2 of thin film 2, the interfacial charge density σ is calculated using equation (1). int It is possible to find this.

[0166] Next, in equation (2), P n ε is the spontaneous polarization of a thin film n (where n is 1 or 2) in the direction normal to the substrate. n V is the dielectric constant of the thin film n. n d is the potential of the film surface, n is the thickness of the thin film n. And the potential (V) of the film surface. n ) film thickness (d n The GSP_Slope can be calculated from the value obtained by dividing by (1) above. Here, the interface charge density σ int Since this can be determined, the GSP_Slope of thin film 1 can be estimated by using a material with a known GSP_Slope as thin film 2 and adopting an appropriate dielectric constant.

[0167] Therefore, using tris(8-quinolinolato)aluminum (abbreviated as Alq3), which has a known GSP_Slope of (48 (mV / nm)) as thin film 2, a measurement device 1 was fabricated and an example of determining the GSP_Slope of a 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviated as NPB) film is shown below.

[0168] The device structure of measurement device 1 is shown in Table 1. The cathode layer 1_1 of measurement device 1 was formed by vacuum deposition from the anode side, with a substrate temperature of room temperature and a deposition rate of 0.2 nm / s to 0.6 nm / s. Deposition was carried out without stopping the deposition process between layers. In measurement device 1, layer 2_1 corresponds to thin film 1, and layer 3_1 corresponds to thin film 2. OCHD-003 is an organic compound with electron acceptor properties.

[0169] When fabricating the measurement device, the deposition rate of each layer is preferably 3 nm / min to 600 nm / min. Furthermore, the film thickness of each layer in the measurement device is preferably 3 nm to 500 nm, and more preferably 50 nm to 300 nm.

[0170] Furthermore, the capacitance-voltage characteristics of measurement device 1 are shown in Figure 5. The capacitance-voltage characteristics were measured using a potentiometer / galvanostat (SP-300, manufactured by Biologic, France) at a frequency of 10 Hz and at room temperature.

[0171] [Table 1]

[0172] Table 2 shows the Hole injection voltage V of the measuring device 1, which was determined using Figure 5 and equations (1) and (2). inj , threshold voltage V th , interfacial charge density σ int SOP, GSP_Slope, and the refractive index n of each material used in the calculation o The results are shown. The refractive index was measured using a spectroscopic ellipsometer (M-2000U, manufactured by J.A. Woolam Japan Co., Ltd.).

[0173] [Table 2]

[0174] Furthermore, we fabricated a measurement device 2 with almost the same configuration as measurement device 1, except that the Alq3 film thickness was 80 nm, and confirmed that the hole injection voltage shifted to a lower voltage than that of measurement device 1. This suggests that in such a device, holes are injected first, and charge accumulates at the interface with Alq3. We also used measurement device 2 to estimate the GSP_Slope in the same way as measurement device 1 and confirmed that the same results were obtained.

[0175] Furthermore, the threshold voltage V can be obtained from the capacitance-voltage characteristics.th When it is difficult to estimate, the threshold voltage estimated from the current density-voltage characteristics may be adopted.

[0176] The current density-voltage characteristics of the measurement device 1 are shown in FIG. 6.

[0177] V estimated from the current density-voltage characteristics th was 2.0 V, which was the same value as the value estimated from the capacitance-voltage characteristics.

[0178] In this way, a device in which a film of Alq3 with a known GSP_Slope of the film and a film formed of an organic compound for which the GSP_Slope is to be determined are laminated is fabricated, and by measuring the capacitance-voltage characteristics, the GSP_Slope of the organic compound can be estimated.

[0179] In the above description, the method for calculating the GSP_Slope in a configuration where the carriers accumulated at the interface are holes has been described. However, when obtaining the GSP_Slope of an organic film in a configuration where the carriers accumulated at the interface are electrons, it can be calculated in the same manner by using the following formula (3).

[0180]

Equation

[0181] It is preferable to select the organic compounds used for each layer of the light-emitting device in consideration of the GSP_Slope of the vapor-deposited film of the organic compound measured in advance by the above measurement method.

[0182] Note that the configuration shown in the present embodiment can be used in appropriate combination with the configurations shown in other embodiments.

[0183] (Embodiment 2) In the present embodiment, a light-emitting device according to an aspect of the present invention will be described in detail.

[0184] Figures 1(A) to 2(B) are schematic diagrams of a light-emitting device according to one embodiment of the present invention. The light-emitting device has a first electrode 101 provided on an insulating substrate 1000, and an EL layer 103 between the first electrode 101 and a second electrode 102. The EL layer 103 has a light-emitting layer 113, and the light-emitting layer 113 contains a light-emitting material. The light-emitting material emits light when a voltage is applied between the first electrode 101 and the second electrode 102.

[0185] The EL layer 103 has, in addition to the light-emitting layer 113, at least a first electron transport layer 114_1 and a second electron transport layer 114_2, and has the configuration shown in Embodiment 1. A light-emitting device according to one embodiment of the present invention having such a configuration can be a light-emitting device with good characteristics, and in particular, good reliability.

[0186] Furthermore, as shown in Figures 1(A) to 2(B), it is preferable to have other functional layers such as a hole injection layer 111, a hole transport layer 112, and an electron injection layer 115. Note that the EL layer 103 may also include functional layers other than those described above, such as a hole blocking layer, an electron blocking layer, an exciton blocking layer, and a charge generation layer. Conversely, none of the above-mentioned layers may be provided.

[0187] The first electrode 101 and the second electrode 102 are formed as a single-layer structure or a multilayer structure. If a multilayer structure is present, the layer in contact with the EL layer 103 functions as the anode or cathode. When the electrodes have a multilayer structure, there are no constraints on the work function of the layers other than the layer in contact with the EL layer 103, and materials can be selected according to the required properties such as resistance, ease of processing, reflectivity, light transmittance, and stability.

[0188] The anode is preferably formed using a metal, alloy, conductive compound, or mixture thereof with a high work function (specifically, 4.0 eV or higher). Specifically, examples include indium tin oxide (ITO), indium tin silicon oxide (ITSO) containing silicon or silicon oxide, indium zinc oxide, and indium oxide (IWZO) containing tungsten oxide and zinc oxide. These conductive metal oxide films are usually deposited by sputtering, but they may also be fabricated using methods such as the sol-gel method. An example of a fabrication method is to form indium zinc oxide by sputtering using a target to which 1 to 20 wt% zinc oxide is added to indium oxide. Furthermore, indium oxide (IWZO) containing tungsten oxide and zinc oxide can also be formed by sputtering using a target containing 0.5-5 wt% tungsten oxide and 0.1-1 wt% zinc oxide relative to indium oxide. Other materials that can be used as anodes include, for example, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), titanium (Ti), aluminum (Al), or nitrides of metallic materials (e.g., titanium nitride). Alternatively, a layer of these materials can be used as the anode. For example, a film in which Al, Ti, and ITSO are layered on Ti is preferable because it has good reflectivity, is highly efficient, and enables high resolution of several thousand ppi. Alternatively, graphene can also be used as a material for the anode. Furthermore, by using a composite material capable of forming the hole injection layer 111 (described later) as the layer in contact with the anode (typically the hole injection layer), it becomes possible to select the electrode material regardless of the work function.

[0189] The hole injection layer 111 is provided in contact with the anode and has the function of facilitating the injection of holes into the EL layer 103. The hole injection layer 111 can be formed from phthalocyanine compounds such as phthalocyanine (abbreviated as H2Pc) and copper phthalocyanine (abbreviated as CuPc), phthalocyanine-based complex compounds, aromatic amine compounds such as 4,4'-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviated as DPAB) and 4,4'-bis(N-{4-[N'-(3-methylphenyl)-N'-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviated as DNTPD), or polymer compounds such as poly(3,4-ethylenedioxythiophene) / (polystyrene sulfonic acid) (abbreviated as PEDOT / PSS).

[0190] Furthermore, the hole injection layer 111 may be formed from a substance having electron-accepting properties. Examples of substances having electron-accepting properties include organic compounds having electron-withdrawing groups (halogen groups, cyano groups, etc.), such as 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviated as F4-TCNQ), chloranil, 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexazatriphenylene (abbreviated as HAT-CN), 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinodimethane (abbreviated as F6-TCNNQ), and 2-(7-dicyanomethylene-1,3,4,5,6,8,9,10-octafluoro-7H-pyrene-2-ylidene)malononitrile. In particular, compounds in which an electron-withdrawing group is bonded to a condensed aromatic ring having multiple heteroatoms, such as HAT-CN, are thermally stable and preferred. Furthermore, radialene derivatives having an electron-withdrawing group (especially halogen groups such as fluoro groups, cyano groups, etc.) are preferred because they have very high electron-accepting properties. Specific examples include α,α',α''-1,2,3-cyclopropanetriylidenates[4-cyano-2,3,5,6-tetrafluorobenzeneacetonitrile], α,α',α''-1,2,3-cyclopropanetriylidenates[2,6-dichloro-3,5-difluoro-4-(trifluoromethyl)benzeneacetonitrile], and α,α',α''-1,2,3-cyclopropanetriylidenates[2,3,4,5,6-pentafluorobenzeneacetonitrile]. In addition to the organic compounds mentioned above, other acceptor materials that can be used include transition metal oxides such as molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, and manganese oxide.

[0191] Furthermore, it is preferable that the hole injection layer 111 be formed from a composite material containing the acceptor material and an organic compound having hole transport properties.

[0192] Various organic compounds with hole-transporting properties can be used in composite materials, including aromatic amine compounds, heteroaromatic compounds, aromatic hydrocarbons, and polymer compounds (oligomers, dendrimers, polymers, etc.). -6 cm 2 It is preferable that the organic compound has a hole mobility of / Vs or greater. The hole-transporting organic compound used in the composite material is preferably a compound having a condensed aromatic hydrocarbon ring or a π-electron-rich heteroaromatic ring. As the condensed aromatic hydrocarbon ring, anthracene rings, naphthalene rings, etc. are preferred. As the π-electron-rich heteroaromatic ring, a condensed aromatic ring containing at least one of a pyrrole skeleton, a furan skeleton, or a thiophene skeleton is preferred, and specifically, a carbazole ring, a dibenzothiophene ring, or a ring in which an aromatic ring or heteroaromatic ring is further condensed thereon is preferred.

[0193] Organic compounds having such hole-transporting properties more preferably have at least one of the following skeletons: a carbazole skeleton, a dibenzofuran skeleton, a dibenzothiophene skeleton, and an anthracene skeleton. In particular, they may be aromatic amines having substituents including a dibenzofuran ring or a dibenzothiophene ring, aromatic monoamines having a naphthalene ring, or aromatic monoamines in which a 9-fluorenyl group is bonded to the nitrogen of the amine via an arylene group. Furthermore, it is preferable that these hole-transporting organic compounds are substances having an N,N-bis(4-biphenyl)amino group, as this allows for the creation of light-emitting devices with a good lifetime.

[0194] Organic compounds that possess the hole transport properties described above include, specifically, N-(4-biphenyl)-6,N-diphenylbenzo[b]naphtho[1,2-d]furan-8-amine (abbreviation: BnfABP), N,N-bis(4-biphenyl)-6-phenylbenzo[b]naphtho[1,2-d]furan-8-amine (abbreviation: BBABnf), 4,4'-bis(6-phenylbenzo[b]naphtho[1,2-d]furan-8-yl)-4''-phenyltriphenylamine (abbreviation: BnfBB1BP), and N,N-bis(4-biphenyl)benzo[b]naph To[1,2-d]furan-6-amine (abbreviation: BBABnf(6)), N,N-bis(4-biphenyl)benzo[b]naphtho[1,2-d]furan-8-amine (abbreviation: BBABnf(8)), N,N-bis(4-biphenyl)benzo[b]naphtho[2,3-d]furan-4-amine (abbreviation: BBABnf(II)(4)), N,N-bis[4-(dibenzofuran-4-yl)phenyl]-4-amino-p-terphenyl (abbreviation: DBfBB1TP), N-[4-(dibenzothiophen-4-yl)phenyl]-N-phenyl-4-bife Nylamine (abbreviation: ThBA1BP), 4-(2-naphthyl)-4',4''-diphenyltriphenylamine (abbreviation: BBAβNB), 4-[4-(2-naphthyl)phenyl]-4',4''-diphenyltriphenylamine (abbreviation: BBAβNBi), 4,4'-diphenyl-4''-([2,1'-binaphthyl]-6-yl)triphenylamine (abbreviation: BBAαNβNB), 4,4'-diphenyl-4''-([2,1'-binaphthyl]-7-yl)triphenylamine (abbreviation: BBAαNβNB-03), 4,4'-diphenyl -4''-(7-phenyl)naphthyl-2-yltriphenylamine (abbreviation: BBAPβNB-03), 4,4'-diphenyl-4''-([2,2'-binaphthyl]-6-yl)triphenylamine (abbreviation: BBA(βN2)B), 4,4'-diphenyl-4''-([2,2'-binaphthyl]-7-yl)triphenylamine (abbreviation: BBA(βN2)B-03), 4,4'-diphenyl-4''-([1,2'-binaphthyl]-4-yl)triphenylamine (abbreviation: BBAβNαNB), 4,4'-diphenyl-4''-([1,2'-binaphthyl]-5-yl)triphenylamine (abbreviation: BBAβNαNB-02), 4-(4-biphenylyl)-4'-(2-naphthyl)-4''-phenyltriphenylamine (abbreviation: TPBiAβNB), 4-(3-biphenylyl)-4'-[4-(2-naphthyl)phenyl]-4''-phenyltriphenylamine (abbreviation: mTPBiAβNBi), 4-(4-biphenylyl)-4'-[4-(2-naphthyl)phenyl]-4''-phenyl Triphenylamine (abbreviation: TPBiAβNBi), 4-phenyl-4'-(1-naphthyl)triphenylamine (abbreviation: αNBA1BP), 4,4'-bis(1-naphthyl)triphenylamine (abbreviation: αNBB1BP), 4,4'-diphenyl-4''-[4'-(carbazole-9-yl)biphenyl-4-yl]triphenylamine (abbreviation: YGTBi1BP), 4'-[4-(3-phenyl-9H-carbazole-9-yl)phenyl]tris (Biphenyl-4-yl)amine (abbreviation: YGTBi1BP-02), 4-[4'-(carbazole-9-yl)biphenyl-4-yl]-4'-(2-naphthyl)-4''-phenyltriphenylamine (abbreviation: YGTBiβNB), N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]-N-[4-(1-naphthyl)phenyl]-9,9'-spirobio[9H-fluorene]-2-amine (abbreviation: PCBNBSF), N,N-bis( Biphenyl-4-yl)-9,9'-spirobio[9H-fluorene]-2-amine (abbreviation: BBASF), N,N-bis(biphenyl-4-yl)-9,9'-spirobio[9H-fluorene]-4-amine (abbreviation: BBASF(4)), N-(biphenyl-2-yl)-N-(9,9-dimethyl-9H-fluorene-2-yl)-9,9'-spirobio[9H-fluorene]-4-amine (abbreviation: oFBiSF), N-(biphenyl-4-yl)-N-(9,9-dimethyl-9H-fluoren-2-yl)dibenzofuran-4-amine (abbreviation: FrBiF), N-[4-(1-naphthyl)phenyl]-N-[3-(6-phenyldibenzofuran-4-yl)phenyl]-1-naphthylamine (abbreviation: mPDBfBNBN), 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl-3'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-phenyl-4' -[4-(9-phenylfluoren-9-yl)phenyl]triphenylamine (abbreviation: BPAFLBi), 4-phenyl-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4'-diphenyl-4''-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBANB), 4,4'- Di(1-naphthyl)-4''-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBNBB), N-phenyl-N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]-9,9'-spirobi[9H-fluorene]-2-amine (abbreviation: PCBASF), N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]-9,9-dimethyl-9H-fluorene-2-amine (abbreviation: PCBBiF), N,N-bis( Examples include 9,9-dimethyl-9H-fluoren-2-yl)-9,9'-spirobio-9H-fluoren-4-amine, N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9'-spirobio-9H-fluoren-3-amine, N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9'-spirobio-9H-fluoren-2-amine, and N,N-bis(9,9-dimethyl-9H-fluoren-2-yl)-9,9'-spirobio-9H-fluoren-1-amine.

[0195] Furthermore, other aromatic amine compounds such as N,N'-di(p-tolyl)-N,N'-diphenyl-p-phenylenediamine (abbreviated as DTDPPA), 4,4'-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviated as DPAB), 4,4'-bis(N-{4-[N'-(3-methylphenyl)-N'-phenylamino]phenyl}-N-phenylamino)biphenyl (abbreviated as DNTPD), and 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene (abbreviated as DPA3B) can also be used as hole transport materials. Organic compounds shown as general formulas (G1) to (G6) in Embodiment 1 can also be suitably used. When organic compounds shown as general formulas (G1) to (G6) in Embodiment 1 are used, it is possible to obtain a light-emitting device with high luminescence efficiency because the refractive index of the film is low.

[0196] By forming the hole injection layer 111, the hole injection performance is improved, and a light-emitting device with a low driving voltage can be obtained.

[0197] Furthermore, among substances with acceptor properties, organic compounds with acceptor properties are easy to use because they are readily deposited and easy to form films.

[0198] The hole transport layer 112 is formed by including an organic compound having hole-transporting properties. The organic compound having hole-transporting properties is 1 × 10⁻⁶ -6 cm 2 It is preferable that the hole mobility is greater than or equal to / Vs. The hole transport layer 112 may be a single layer or have a laminated structure. Furthermore, it is preferable that the hole transport layer in contact with the light-emitting layer has the function of an electron blocking layer.

[0199] Materials exhibiting the above hole transport properties include 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviated as NPB), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-4,4'-diaminobiphenyl (abbreviated as TPD), N,N'-bis(9,9'-spirobi[9H-fluoren]-2-yl)-N,N'-diphenyl-4,4'-diaminobiphenyl (abbreviated as BSPB), 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviated as BPAFLP), and 4-phenyl-3 '-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-phenyl-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4'-diphenyl-4''-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBANB), 4,4'-di(1-naphthyl)-4''-(9-phenyl Compounds having an aromatic amine skeleton such as 9,9-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine (abbreviation: PCBAF), N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9'-spirobio[9H-fluoren]-2-amine (abbreviation: PCBASF), 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP), 4,4'-di( N-carbazolyl)biphenyl (abbreviated as CBP), 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviated as CzTP), 3,3'-bis(9-phenyl-9H-carbazole) (abbreviated as PCCP), 9,9'-bis(biphenyl-4-yl)-3,3'-bi-9H-carbazole (abbreviated as BisBPCz), 9,9'-bis(biphenyl-3-yl)-3,3'-bi-9H-carbazole (abbreviated as BismBPCz), 9-(biphenyl-3-yl)-9'-(biphenyl-4-yl)-9H,9'H-3,3'-bicarbazole (abbreviation: mBPCCBP), 9-(2-naphthyl)-9'-phenyl-3,3'-bi-9H-carbazole (abbreviation: βNCCP), 9-(3-biphenyl)-9'-(2-naphthyl)-3,3'-bi-9H-carbazole (abbreviation: βNCCmBP), 9-(4-biphenyl)-9'-(2-naphthyl)-3,3'-bi-9H-carbazole (abbreviation: βNCCBP), 9,9'-di-2-naphthyl-3,3'-9H,9'H-bicarbazole (abbreviation: BisβNCz), 9-(2- Naphthyl)-9'-[1,1':4',1”-terphenyl]-3-yl-3,3'-9H,9'H-bicarbazole, 9-(2-naphthyl)-9'-[1,1':3',1”-terphenyl]-3-yl-3,3'-9H,9'H-bicarbazole, 9-(2-naphthyl)-9'-[1,1':3',1”-terphenyl]-5'-yl-3,3'-9H,9'H-bicarbazole, 9-(2-naphthyl)-9'-[1,1':4',1”-terphenyl]-4-yl-3,3'-9H,9'H-bicarbazole Lubazole, 9-(2-naphthyl)-9'-[1,1':3',1”-terphenyl]-4-yl-3,3'-9H,9'H-bicarbazole, 9-(2-naphthyl)-9'-(triphenylene-2-yl)-3,3'-9H,9'H-bicarbazole, 9-phenyl-9'-(triphenylene-2-yl)-3,3'-9H,9'H-bicarbazole (abbreviation: PCCzTp), 9,9'-bis(triphenylene-2-yl)-3,3'-9H,9'H-bicarbazole, 9-(4-biphenyl)-9 Compounds having a carbazole skeleton such as '-(triphenylene-2-yl)-3,3'-9H,9'H-bicarbazole, 9-(triphenylene-2-yl)-9'-[1,1':3',1”-terphenyl]-4-yl-3,3'-9H,9'H-bicarbazole, 9-[3-(triphenylsilyl)phenyl]-3,9'-bi-9H-carbazole (abbreviation: PSiCzCz), 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), 2,Examples include compounds having a thiophene skeleton such as 8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviated as DBTFLP-III) and 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviated as DBTFLP-IV), and compounds having a furan skeleton such as 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviated as DBF3P-II) and 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviated as mmDBFFLBi-II). Among the above, compounds having an aromatic amine skeleton and compounds having a carbazole skeleton are preferred because they have good reliability, high hole transportability, and contribute to reducing the driving voltage. Furthermore, the materials listed as having hole-transporting properties for the composite material of the hole injection layer 111 can also be suitably used as materials constituting the hole transport layer 112. Moreover, the use of organic compounds having an amine skeleton and a fluorene skeleton is even more preferable. Organic compounds having an amine skeleton and a fluorene skeleton are preferable because they have good reliability and high hole-transporting properties, thereby reducing the power consumption of the light-emitting device.

[0200] Furthermore, since the GSP_Slope of the hole transport layer 112 is smaller than the GSP_Slope of the light-emitting layer 113, a negative interfacial charge can be established at at least one of the interfaces between the hole transport layer and the light-emitting layer. This facilitates the injection of holes from the anode or hole injection layer to the vicinity of the light-emitting layer interface, making it possible to create a light-emitting device with a low driving voltage.

[0201] A light-emitting device according to one aspect of the present invention has a light-emitting layer comprising at least a substance capable of converting triplet excitation energy into light emission and a fluorescent substance. A phosphorescent substance is preferred as the substance capable of converting triplet excitation energy into light emission. The fluorescent substance also includes substances that exhibit thermally activated delayed fluorescence (TADF). Light-emitting devices using blue light-emitting substances, particularly blue phosphorescent substances, are prone to electron excess in the light-emitting layer 113, and therefore the present invention can be suitably applied to them.

[0202] Examples of materials that can be used as fluorescent materials in the light-emitting layer include the following. The fluorescent materials listed in Embodiment 1 can also be used. Furthermore, other fluorescent materials can also be used.

[0203] 5,6-Bis[4-(10-phenyl-9-antryl)phenyl]-2,2'-bipyridine (abbreviation: PAP2BPy), 5,6-Bis[4'-(10-phenyl-9-antryl)biphenyl-4-yl]-2,2'-bipyridine (abbreviation: PAPP2BPy), N,N'-Diphenyl-N,N'-Bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]pyren-1,6-diamine (abbreviation: 1,6FLPAPrn), N,N'-Bis(3-methylphenyl)-N,N'-Bis[3-(9-phenyl-9H-fluoren-9-yl )phenyl]pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPrn), N,N'-bis[4-(9H-carbazole-9-yl)phenyl]-N,N'-diphenylstilbene-4,4'-diamine (abbreviation: YGA2S), 4-(9H-carbazole-9-yl)-4'-(10-phenyl-9-anthryl)triphenylamine (abbreviation: YGAPA), 4-(9H-carbazole-9-yl)-4'-(9,10-diphenyl-2-anthryl)triphenylamine (abbreviation: 2YGAPPA), N,9-diphenyl-N-[4-( 10-phenyl-9-anthryl)phenyl]-9H-carbazole-3-amine (abbreviation: PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene (abbreviation: TBP), 4-(10-phenyl-9-anthryl)-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBAPA), N,N''-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis(N,N',N'-triphenyl-1,4-phenylenediamine) (abbreviation: DPABPA), N,9 -Diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole-3-amine (abbreviation: 2PCAPPA), N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPPA), N,N,N',N',N'',N'',N''',N'''-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine (abbreviation: DBC1), coumarin 30, N-(9,10-diphenyl-2-anthryl)-N,9-Diphenyl-9H-carbazole-3-amine (abbreviation: 2PCAPA), N-[9,10-bis(biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazole-3-amine (abbreviation: 2PCABPhA), N-(9,10-diphenyl-2-anthryl)-N,N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPA), N-[9,10-bis(biphenyl-2-yl)-2-anthryl]-N,N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPABPhA) 9,10-bis(biphenyl-2-yl)-N-[4-(9H-carbazole-9-yl)phenyl]-N-phenylanthracene-2-amine (abbreviation: 2YGABPhA), N,N,9-triphenylanthracene-9-amine (abbreviation: DPhAPhA), coumarin 545T, N,N'-diphenylquinacridone (abbreviation: DPQd), rubren, 5,12-bis(biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT), 2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyra n-4-ylidene)propanedinitrile (abbreviation: DCM1), 2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinoridine-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCM2), N,N,N',N'-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation: p-mPhTD), 7,14-diphenyl-N,N,N',N'-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluorantene-3,10-diamine (abbreviation) Name: p-mPhAFD), 2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinoridine-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTI), 2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinoridine-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTB), 2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile (abbreviation: BisDCM), 2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: BisDCJTM), N,N'-diphenyl-N,N'-(1,6-pyrene-diyl)bis[(6-phenylbenzo[b]naphtho[1,2-d]furan)-8-amine] (abbreviation: 1,6BnfAPrn-03), N,N'-diphenyl-N,N'-bis(9-phenyl-9H-carbazol-2-yl)naphtho[2,3-b;6,7-b']bisbenzofuran-3,10-diamine (abbreviation: 3,10PCA2Nbf(IV)-02), 3,10-bis[N-(dibenzofuran-3-yl)-N-phenylamino]naphtho[2,3-b;6,7-b']bisbenzofuran (abbreviation: 3,10FrA2Nbf(IV)-02), and the like. In particular, condensed aromatic diamine compounds typified by pyrene diamine compounds such as 1,6FLPAPrn and 1,6mMemFLPAPrn, 1,6BnfAPrn-03 are preferable because they have high hole trap properties and excellent light emission efficiency or reliability.,

[0204] Also, 5,9-diphenyl-5H,9H-[1,4]benzazaborino[2,3,4-kl]phenazavorin (abbreviation: DABNA-1), 9-(diphenyl-3-yl)-N,N,5,11-tetraphenyl-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracene-3-amine (abbreviation: DABNA-2), 2,12-di(tert-butyl)-5,9-di(4-tert-butylphenyl)-N,N-diphenyl-5H,9H-[1,4]benzazaborino[2,3,4-kl]phenazavorin Phosphorus-7-amine (abbreviation: DPhA-tBu4DABNA), 2,12-di(tert-butyl)-N,N,5,9-tetra(4-tert-butylphenyl)-5H,9H-[1,4]benzazabolino[2,3,4-kl]phenazavolin-7-amine (abbreviation: tBuDPhA-tBu4DABNA), 2,12-di(tert-butyl)-5,9-di(4-tert-butylphenyl)-7-methyl-5H,9H-[1,4]benzazabolino[2,3,4-kl]phenazavolin (abbreviation: Me-tBu4DABNA), N 7 ,N 7 ,N 13 ,N 13 Condensed heteroaromatic compounds containing nitrogen and boron, such as ,5,9,11,15-octaphenyl-5H,9H,11H,15H-[1,4]benzazabolino[2,3,4-kl][1,4]benzazabolino[4',3',2':4,5][1,4]benzazabolino[3,2-b]phenazabolin-7,13-diamine (abbreviation: ν-DABNA) and 2-(4-tert-butylphenyl)benz[5,6]indro[3,2,1-jk]benzo[b]carbazole (abbreviation: tBuPBibc), particularly compounds having a diaza-boranaphtho-anthracene skeleton, can be suitably used because they produce blue emission with a narrow emission spectrum and good color purity.

[0205] In addition to these, there is 9,10,11-tris[3,6-bis(1,1-dimethylethyl)-9H-carbazole-9-yl]-2,5,15,18-tetrakis(1,1-dimethylethyl)indoro[3,2,1-de]indoro[3',2',1':8,1][1,4]benzazavolino[2,3,4-kl]phenazavolin (abbreviation: BBCz-G), 9,11-bis[ Compounds having an indole skeleton, such as 3,6-bis(1,1-dimethylethyl)-9H-carbazole-9-yl]-2,5,15,18-tetrakis(1,1-dimethylethyl)indoro[3,2,1-de]indoro[3',2',1':8,1][1,4]benzazavolino[2,3,4-kl]phenazavolin (abbreviation: BBCz-Y), can be suitably used.

[0206] Examples of phosphorescent materials include the following:

[0207] Organometallic iridium complexes having a 4H-triazole skeleton, such as Tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III) (abbreviation: [Ir(mpptz-dmp)3]) and Tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III) (abbreviation: [Ir(Mptz)3]). , organometallic iridium complexes having a 1H-triazole skeleton such as tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III) (abbreviation: [Ir(Mptz1-mp)3]), tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III) (abbreviation: [Ir(Prptz1-Me)3]), fac-tris[1-(2,6-di Isopropylphenyl)-2-phenyl-1H-imidazole]iridium(III) (abbreviation: [Ir(iPrpim)3]), Tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridine]iridium(III) (abbreviation: [Ir(dmpimpt-Me)3]), Tris(2-{1-[2,6-bis(1-methylethyl)phenyl]-1H-imidazole-2-yl-κN3}-4-cyanoph Organometallic iridium complexes having an imidazole skeleton, such as phenyl-κC)iridium(III) (abbreviation: CNImIr), organometallic complexes having a benzimidazolidene skeleton, such as tris[(6-tert-butyl-3-phenyl-2H-imidazo[4,5-b]pyrazine-1-yl-κC2)phenyl-κC]iridium(III) (abbreviation: [Ir(cb)3]), and bis[2-(4',6'-difluorophenyl)pyridinato-N,C 2’ Iridium(III) tetrakis(1-pyrazolyl) borate (abbreviation: FIr6), bis[2-(4',6'-difluorophenyl)pyridinate-N,C 2’ Iridium(III) picolinate (abbreviation: Firpic), bis{2-[3',5'-bis(trifluoromethyl)phenyl]pyridinate-N,C 2’Iridium(III) picolinate (abbreviation: [Ir(CF3ppy)2(pic)]), bis[2-(4',6'-difluorophenyl)pyridinate-N,C 2’ Examples include organometallic iridium complexes with phenylpyridine derivatives having electron-withdrawing groups, such as iridium(III) acetylacetonate (FIracac), and platinum complexes such as (2-{3-[3-(3,5-di-tert-butylphenyl)benzimidazole-1-yl-2-ylidene-κC2]phenoxy-κC2}-9-(4-tert-butyl-2-pyridinyl-κN)carbazole-2,1-diyl-κC1)platinum(II) (PtON-TBBI). These compounds exhibit blue phosphorescence and have emission peaks in the wavelength range of 450 nm to 520 nm. The phosphorescent substances listed in Embodiment 1 can also be used as blue phosphorescent substances. Furthermore, compounds in which some of the hydrogen atoms in these compounds are replaced with deuterium can also be used.

[0208] Also, tris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)3]), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)3]), (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)2(acac)]), (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]), (acetylacetonato)bis[6-(2-norbornyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: [Ir(nbppm)2(acac)]), (acetylacetonato)bis[5-methyl-6- Organometallic iridium complexes having a pyrimidine skeleton, such as (2-methylphenyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: [Ir(mpmppm)2(acac)]), (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]), organometallic iridium complexes having a pyrazine skeleton, such as (acetylacetonato)bis(3,5-dimethyl-2-phenylpyradinato)iridium(III) (abbreviation: [Ir(mppr-Me)2(acac)]), (acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyradinato)iridium(III) (abbreviation: [Ir(mppr-iPr)2(acac)]), and tris(2-phenylpyrimidinato-N,C 2’ Iridium(III) (abbreviation: [Ir(ppy)3]), bis(2-phenylpyridinate-N,C) 2’ Iridium(III) acetylacetonate (abbreviation: [Ir(ppy)2(acac)]), bis(benzo[h]quinolinate)iridium(III) acetylacetonate (abbreviation: [Ir(bzq)2(acac)]), tris(benzo[h]quinolinate)iridium(III) (abbreviation: [Ir(bzq)3]), tris(2-phenylquinolinate-N,C) 2’ Iridium(III) (abbreviation: [Ir(pq)3]), bis(2-phenylquinolinato-N,C) 2’) Iridium(III) acetylacetonate (abbreviation: [Ir(pq)2(acac)]), [2-d3-methyl-8-(2-pyridinyl-κN)benzoflof[2,3-b]pyridine-κC]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III) (abbreviation: [Ir(5mppy-d3)2(mbfpypy-d3)]), {2- (methyl-d3)-8-[4-(1-methylethyl-1-d)-2-pyridinyl-κN]benzofl[2,3-b]pyridin-7-yl-κC]bis{5-(methyl-d3)-2-[5-(methyl-d3)-2-pyridinyl-κN]phenyl-κC}iridium(III) (abbreviation: Ir(5mtpy-d6)2(mbfpypy-iPr-d4)), [2-(methyl-d3) -8-(2-pyridinyl-κN)benzofloxacin[2,3-b]pyridinyl-κC]bis[2-(2-pyridinyl-κN)phenyl-κC]iridium(III) (abbreviation: Ir(ppy)2(mbfpypy-d3)), [2-(4-methyl-5-phenyl-2-pyridinyl-κN)phenyl-κC]bis[2-(2-pyridinyl-κN)phenyl-κC]iridium(III) (Abbreviation: [Ir(ppy)2(mdppy)]), [2-(4-d3-methyl-5-phenyl-2-pyridinyl-κN2)phenyl-κC]bis[2-(5-d3-methyl-2-pyridinyl-κN2)phenyl-κC]iridium(III) (Abbreviation: [Ir(5mppy-d3)2(mdppy-d3)]), [2-methyl-8-(2-pyridinyl-κN)benzofloxacin[2,In addition to organometallic iridium complexes with a pyridine skeleton such as 3-b]pyridine-κC]bis[2-(2-pyridinyl-κN)phenyl-κC]iridium(III) (abbreviation: Ir(ppy)2(mbfpypy)) and tris{2-[5-(methyl-d3)-4-phenyl-2-pyridinyl-κN]phenyl-κC}iridium(III) (abbreviation: Ir(5m4dppy-d3)3), there are also rare earth metal complexes such as tris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation: [Tb(acac)3(Phen)]), and (2-{1-(5-tert-butylbiphenyl-2-yl)-4-[3-tert Examples of organometallic platinum complexes include [-butyl-5-(4-phenyl-2-pyridinyl-κN)phenyl-κC6]-2-benzimidazolyl-κN3}-4,6-di-tert-butylphenolato-κO)platinum(II) (abbreviation: Pt(tBudppymmtBubiz-tBubp)) and [2-(4-(3,5-di-tert-butylphenyl)-6-{3-[4-(5'-tert-butyl[1,1':3',1''-terphenyl]-2'-yl)-2-pyridinyl-κN]phenyl-κC2}-2-pyridinyl-κN)phenolato-κO]platinum(II) (abbreviation: Pt(4tButpppypyp-mmtBup)). These compounds mainly exhibit green phosphorescence and have emission peaks in the wavelength range from 500 nm to 600 nm. Furthermore, organometallic iridium complexes having a pyrimidine skeleton are particularly preferred due to their outstanding reliability and luminescence efficiency. Compounds in which some of the hydrogen atoms are replaced with deuterium can also be used.

[0209] Furthermore, organometallic iridium complexes having a pyrimidine skeleton, such as (diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III) (abbreviation: [Ir(5mdppm)2(dibm)]), bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: [Ir(5mdppm)2(dpm)]), and bis[4,6-di(naphthalene-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: [Ir(d1npm)2(dpm)]), Organometallic iridium complexes with a pyrazine skeleton, such as (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: [Ir(tppr)2(acac)]), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(tppr)2(dpm)]), and (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: [Ir(Fdpq)2(acac)]), and tris(1-phenylisoquinolinato-N,C) 2’ Iridium(III) (abbreviation: [Ir(piq)3]), bis(1-phenylisoquinolinato-N,C) 2’) Iridium(III) acetylacetonate (abbreviation: [Ir(piq)2(acac)]), (3,7-diethyl-4,6-nonanedionato-κO4,κO6)bis[2,4-dimethyl-6-[7-(1-methylethyl)-1-isoquinolinyl-κN]phenyl-κC]iridium(III), (3,7-diethyl-4,6-nonanedionato-κO4,κO6)bis[2,4-dimethyl-6-[5-(1-methylethyl)-2-quinolinyl-κN]phenyl-κC]iridium(III) are organometallic iridium compounds with a pyridine skeleton. In addition to dinium complexes, other examples include platinum complexes such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (abbreviated as PtOEP), and rare earth metal complexes such as tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviated as [Eu(DBM)3(Phen)]) and tris[1-(2-tenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviated as [Eu(TTA)3(Phen)]). These compounds exhibit red phosphorescence and have emission peaks in the wavelength range of 600 nm to 700 nm. Furthermore, organometallic iridium complexes with a pyrazine skeleton yield red emission with good chromaticity. Compounds in which some of the hydrogen atoms in these compounds are replaced with deuterium can also be used.

[0210] In addition to the phosphorescent compounds described above, other known phosphorescent compounds may be selected and used.

[0211] As TADF materials, fullerenes and their derivatives, acridines and their derivatives, eosin derivatives, etc., can be used. Also, metal-containing porphyrins containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd) can be used. Examples of metal-containing porphyrins include protoporphyrin-tin fluoride complexes (SnF2(Proto IX)), mesoporphyrin-tin fluoride complexes (SnF2(Meso IX)), hematoporphyrin-tin fluoride complexes (SnF2(Hemato IX)), coproporphyrin tetramethyl ester-tin fluoride complexes (SnF2(Copro III-4Me)), octaethylporphyrin-tin fluoride complexes (SnF2(OEP)), etioporphyrin-tin fluoride complexes (SnF2(Etio I)), and octaethylporphyrin-platinum chloride complexes (PtCl2OEP), as shown in the following structural formulas.

[0212] [ka]

[0213] Furthermore, the following structural formulas represent 2-(biphenyl-4-yl)-4,6-bis(12-phenylindoro[2,3-a]carbazol-11-yl)-1,3,5-triazine (abbreviation: PIC-TRZ), 9-(4,6-diphenyl-1,3,5-triazin-2-yl)-9'-phenyl-9H,9'H-3,3'-bicarbazol (abbreviation: PCCzTzn), 2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn), 2-[4-(10H-phenoxazine-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn) Heterocyclic compounds having one or both of a π-electron-rich heteroaromatic ring and a π-electron-deficient heteroaromatic ring can also be used, such as PXZ-TRZ, 3-[4-(5-phenyl-5,10-dihydrophenazine-10-yl)phenyl]-4,5-diphenyl-1,2,4-triazole (abbreviated as PPZ-3TPT), 3-(9,9-dimethyl-9H-acridine-10-yl)-9H-xanthene-9-one (abbreviated as ACRXTN), bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (abbreviated as DMAC-DPS), and 10-phenyl-10H,10'H-spiro[acridine-9,9'-anthracene]-10'-one (abbreviated as ACRSA). The heterocyclic compound is preferred because it has both a π-electron-excess heteroaromatic ring and a π-electron-deficient heteroaromatic ring, resulting in high electron transport and hole transport properties. Among the skeletons having a π-electron-deficient heteroaromatic ring, the pyridine skeleton, diazine skeleton (pyrimidine skeleton, pyrazine skeleton, pyridazine skeleton), and triazine skeleton are preferred because they are stable and reliable. In particular, the benzoflopyrimidine skeleton, benzothienopyrimidine skeleton, benzoflopyrazine skeleton, and benzothienopyrazine skeleton are preferred because they have high acceptability and are reliable. Furthermore, among the skeletons having a π-electron-excess heteroaromatic ring, the acridine skeleton, phenoxazine skeleton, phenothiazine skeleton, furan skeleton, thiophene skeleton, and pyrrole skeleton are preferred because they are stable and reliable, and therefore it is preferable to have at least one of these skeletons.Furthermore, a dibenzofuran skeleton is preferred as the furan skeleton, and a dibenzothiophene skeleton is preferred as the thiophene skeleton. In addition, as the pyrrole skeleton, indole skeleton, carbazole skeleton, indrocarbazole skeleton, bicarbazole skeleton, and 3-(9-phenyl-9H-carbazole-3-yl)-9H-carbazole skeleton are particularly preferred. Substances in which a π-electron-rich heteroaromatic ring and a π-electron-deficient heteroaromatic ring are directly bonded are particularly preferred because both the electron-donating and electron-accepting properties of the π-electron-rich heteroaromatic ring are strengthened, and the energy difference between the S1 and T1 levels is reduced, thus efficiently obtaining thermally activated delayed fluorescence. In addition, an aromatic ring to which an electron-withdrawing group such as a cyano group is bonded may be used instead of the π-electron-deficient heteroaromatic ring. Furthermore, aromatic amine skeletons, phenazine skeletons, etc., can be used as the π-electron-rich skeleton. Furthermore, as π-electron-deficient skeletons, xanthene skeletons, thioxanthene dioxide skeletons, oxadiazole skeletons, triazole skeletons, imidazole skeletons, anthraquinone skeletons, boron-containing skeletons such as phenylborane and volanthrene, aromatic rings having a nitrile group or a cyano group such as benzonitrile or cyanobenzene, heteroaromatic rings, carbonyl skeletons such as benzophenone, phosphine oxide skeletons, sulfone skeletons, etc., can be used. In this way, π-electron-deficient skeletons and π-electron-excess skeletons can be used instead of at least one of π-electron-deficient heteroaromatic rings and π-electron-excess heteroaromatic rings.

[0214] [ka]

[0215] TADF materials are materials that have a small energy difference between the S1 and T1 levels and possess the ability to convert energy from triplet excitation energy to singlet excitation energy through reverse intersystem crossing. Therefore, triplet excitation energy can be upconverted to singlet excitation energy with only a small amount of thermal energy (reverse intersystem crossing), and singlet excited states can be efficiently generated. Furthermore, triplet excitation energy can be converted into luminescence.

[0216] Furthermore, an excited complex (also called an exciplex) that forms an excited state with two types of substances has an extremely small energy difference between the S1 and T1 levels and functions as a TADF material that can convert triplet excitation energy into singlet excitation energy.

[0217] Furthermore, the phosphorescence spectrum observed at low temperatures (e.g., 77K to 10K) can be used as an indicator of the T1 level. For TADF materials, when a tangent is drawn at the short-wavelength tail of the fluorescence spectrum and the energy at the wavelength of the extrapolation is taken as the S1 level, and when a tangent is drawn at the short-wavelength tail of the phosphorescence spectrum and the energy at the wavelength of the extrapolation is taken as the T1 level, it is preferable that the energy difference between the S1 level and the T1 level is 0.3 eV or less, and more preferably 0.2 eV or less.

[0218] Furthermore, when using TADF material as a light-emitting material, it is preferable that the S1 level of the host material is higher than the S1 level of the TADF material. Also, it is preferable that the T1 level of the host material is higher than the T1 level of the TADF material.

[0219] Various carrier transport materials can be used as the host material for the light-emitting layer, such as materials with electron transport properties and / or hole transport properties, and the TADF material mentioned above.

[0220] Preferred materials with hole transport properties include organic compounds having an amine skeleton or a π-electron-rich heteroaromatic ring skeleton. Preferred π-electron-rich heteroaromatic rings are condensed aromatic rings containing at least one of the following: acridine skeleton, phenoxazine skeleton, phenothiazine skeleton, furan skeleton, thiophene skeleton, and pyrrole skeleton. Specifically, carbazole rings, dibenzothiophene rings, or rings obtained by further condensing an aromatic ring or heteroaromatic ring with these are preferred.

[0221] Organic compounds having such hole-transporting properties more preferably have at least one of the following skeletons: a carbazole skeleton, a dibenzofuran skeleton, a dibenzothiophene skeleton, and an anthracene skeleton. In particular, they may be aromatic amines having substituents including a dibenzofuran ring or a dibenzothiophene ring, aromatic monoamines having a naphthalene ring, or aromatic monoamines in which a 9-fluorenyl group is bonded to the nitrogen of the amine via an arylene group. Furthermore, it is preferable that these hole-transporting organic compounds are substances having an N,N-bis(4-biphenyl)amino group, as this allows for the creation of light-emitting devices with a good lifetime.

[0222] Examples of such organic compounds include 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviated as NPB), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-4,4'-diaminobiphenyl (abbreviated as TPD), N,N'-bis(9,9'-spirobi[9H-fluoren]-2-yl)-N,N'-diphenyl-4,4'-diaminobiphenyl (abbreviated as BSPB), 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviated as BPAFLP), and 4-phenyl-3 '-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-phenyl-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4'-diphenyl-4''-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBANB), 4,4'-di(1-naphthyl)-4''-(9-phenyl Compounds having an aromatic amine skeleton such as 9,9-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine (abbreviation: PCBAF), N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9'-spirobio[9H-fluoren]-2-amine (abbreviation: PCBASF), 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP), 4,4'-di( N-carbazolyl)biphenyl (abbreviated as CBP), 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviated as CzTP), 3,3'-bis(9-phenyl-9H-carbazole) (abbreviated as PCCP), 9,9'-bis(biphenyl-4-yl)-3,3'-bi-9H-carbazole (abbreviated as BisBPCz), 9,9'-bis(biphenyl-3-yl)-3,3'-bi-9H-carbazole (abbreviated as BismBPCz), 9-(biphenyl-3-yl)-9'-(biphenyl-4-yl)-9H,9'H-3,3'-bicarbazole (abbreviation: mBPCCBP), 9-(2-naphthyl)-9'-phenyl-3,3'-bi-9H-carbazole (abbreviation: βNCCP), 9-(3-biphenyl)-9'-(2-naphthyl)-3,3'-bi-9H-carbazole (abbreviation: βNCCmBP), 9-(4-biphenyl)-9'-(2-naphthyl)-3,3'-bi-9H-carbazole (abbreviation: βNCCBP), 9,9'-di-2-naphthyl-3,3'-9H,9'H-bicarbazole (abbreviation: BisβNCz), 9-(2- Naphthyl)-9'-[1,1':4',1”-terphenyl]-3-yl-3,3'-9H,9'H-bicarbazole, 9-(2-naphthyl)-9'-[1,1':3',1”-terphenyl]-3-yl-3,3'-9H,9'H-bicarbazole, 9-(2-naphthyl)-9'-[1,1':3',1”-terphenyl]-5'-yl-3,3'-9H,9'H-bicarbazole, 9-(2-naphthyl)-9'-[1,1':4',1”-terphenyl]-4-yl-3,3'-9H,9'H-bicarbazole Lubazole, 9-(2-naphthyl)-9'-[1,1':3',1”-terphenyl]-4-yl-3,3'-9H,9'H-bicarbazole, 9-(2-naphthyl)-9'-(triphenylene-2-yl)-3,3'-9H,9'H-bicarbazole, 9-phenyl-9'-(triphenylene-2-yl)-3,3'-9H,9'H-bicarbazole (abbreviation: PCCzTp), 9,9'-bis(triphenylene-2-yl)-3,3'-9H,9'H-bicarbazole, 9-(4-biphenyl)-9 Compounds having a carbazole skeleton such as '-(triphenylene-2-yl)-3,3'-9H,9'H-bicarbazole, 9-(triphenylene-2-yl)-9'-[1,1':3',1”-terphenyl]-4-yl-3,3'-9H,9'H-bicarbazole, 9-[3-(triphenylsilyl)phenyl]-3,9'-bi-9H-carbazole (abbreviation: PSiCzCz), 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), 2,Examples include compounds having a thiophene skeleton such as 8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviated as DBTFLP-III) and 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviated as DBTFLP-IV), and compounds having a furan skeleton such as 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviated as DBF3P-II) and 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviated as mmDBFFLBi-II). Among the above, compounds having an aromatic amine skeleton or a carbazole skeleton are preferred because they have good reliability, high hole transportability, and contribute to reducing the driving voltage. In addition, organic compounds listed as examples of hole transportable materials in the hole transport layer can also be used. Furthermore, it is more preferable to use organic compounds having an amine skeleton and a fluorene skeleton. Organic compounds having an amine skeleton and a fluorene skeleton are preferred because they have good reliability and high hole transport properties, thus reducing the power consumption of the light-emitting device.

[0223] For materials exhibiting electron transport properties, the electron mobility at which the square root of the electric field strength [V / cm] is 600 is 1 × 10⁻⁶. -7 cm 2 / Vs or more, preferably 1 × 10 -6 cm 2 A material having an electron mobility of / Vs or higher is preferred. However, any material with higher electron transport capabilities than holes can be used.

[0224] Preferred electron-transporting materials include metal complexes such as tris(8-quinolinolato)aluminum (abbreviated as Alq3), bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviated as BeBq2), bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (abbreviated as BAlq), bis(8-quinolinolato)zinc(II) (abbreviated as Znq), bis[2-(2-benzoxazollyl)phenolato]zinc(II) (abbreviated as ZnPBO), and bis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviated as ZnBTZ), as well as organic compounds having a π-electron-deficient heteroaromatic ring. Examples of organic compounds having a π-electron-deficient heteroaromatic ring skeleton include organic compounds containing a heteroaromatic ring having an azole skeleton, organic compounds containing a heteroaromatic ring having a pyridine skeleton, organic compounds containing a heteroaromatic ring having a diazine skeleton, and organic compounds containing a heteroaromatic ring having a triazine skeleton.

[0225] Among these, organic compounds containing heteroaromatic rings having a diazine skeleton (pyrimidine skeleton, pyrazine skeleton, pyridazine skeleton), organic compounds containing heteroaromatic rings having a pyridine skeleton, and organic compounds containing heteroaromatic rings having a triazine skeleton are preferred due to their good reliability. In particular, organic compounds containing heteroaromatic rings having a diazine (pyrimidine or pyrazine) skeleton and organic compounds containing heteroaromatic rings having a triazine skeleton have high electron transport properties and contribute to reducing the driving voltage. Furthermore, benzoflopyrimidine skeletons, benzothienopyrimidine skeletons, benzoflopyrazine skeletons, and benzothienopyrazine skeletons are preferred because they have high acceptability and good reliability.

[0226] Examples of organic compounds having a π-electron-deficient heteroaromatic ring skeleton include 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviated as PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviated as TAZ), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (abbreviated as OXD-7), and 9-[4-(5-phenyl-1,3,4-oxadi Azole-2-yl)phenyl]-9H-carbazole (abbreviation: CO11), 2,2',2''-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI), 2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: mDBTBIm-II), 4,4'-bis(5-methylbenzoxazole-2-yl)stilbene (abbreviation: BzOs), 2-{4-[9,10-di(2-naphthyl)-2-anthryl]phen Organic compounds having an azole skeleton such as 1 / 2-phenyl-1H-benzimidazole (abbreviation: ZADN), 3,5-bis[3-(9H-carbazole-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy), 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB), vasophenanthroline (abbreviation: Bphen), vasocuproin (abbreviation: BCP), 2,9-di(naphthalene-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation: NBphen), 2,2'-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviation: mPPhen2P), 2-[3-(2-triphenylenyl)phenyl]-1,10-phenanthroline (abbreviation: mTpPPhen), 2-phenyl-9-(2-triphenylenyl)-1,10-phenanthroline (abbreviation: Ph-TpPhen), 2-[4-(9-phenanthryl)-1-naphthyl]-1,10-phenanthroline (abbreviation: PnNPhen), 2-[4-(2-triphenylenyl)phenyl]-1,Organic compounds containing heteroaromatic rings with a pyridine skeleton, such as 10-phenanthroline (abbreviation: pTpPPhen), 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 2-[3'-(9H-carbazole-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mCzBPDBq), 2 -[4'-(9-phenyl-9H-carbazole-3-yl)-3,1'-biphenyl-1-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mpPCBPDBq), 2-[4-(3,6-diphenyl-9H-carbazole-9-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2CzPDBq-III), 7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 7mDBTPDBq-II), and 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline Xaline (abbreviation: 6mDBTPDBq-II), 9-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]naphtho[1',2':4,5]flo[2,3-b]pyrazine (abbreviation: 9mDBtBPNfpr), 9-[3'-(dibenzothiophen-4-yl)biphenyl-4-yl]naphtho[1',2':4,5]flo[2,3-b]pyrazine (abbreviation: 9pmDBtBPNfpr), 4,6-bis[3-(phenanthrene-9-yl)phenyl]pyrimidine (abbreviation: 4,6mPnP2Pm), 4,6-bis[3-(dibenzothio [Phen-4-yl)phenyl]pyrimidine (abbreviation: 4,6mDBTP2Pm-II), 4,6-bis[3-(9H-carbazole-9-yl)phenyl]pyrimidine (abbreviation: 4,6mCzP2Pm), 9,9'-[pyrimidine-4,6-diylbis(biphenyl-3,3'-diyl)]bis(9H-carbazole) (abbreviation: 4,6mCzBP2Pm), 8-(biphenyl-4-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzoflo[3,2-d]pyrimidine (abbreviation: 8BP-4mDBtPBfpm), 3,8-Bis[3-(dibenzothiophen-4-yl)phenyl]benzoflo[2,3-b]pyrazine (abbreviation: 3,8mDBtP2Bfpr), 4,8-Bis[3-(dibenzothiophen-4-yl)phenyl]-[1]benzoflo[3,2-d]pyrimidine (abbreviation: 4,8mDBtP2Bfpm), 8-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]naphtho[1',2':4,5]flo[3,2-d]pyrimidine (abbreviation: 8mDBtBPNfpm), 8-([2,2'-binaphthalene]-6-yl)-4-[3-(dibenzo Thiophen-4-yl)phenyl]-[1]benzoflo[3,2-d]pyrimidine (abbreviation: 8(βN2)-4mDBtPBfpm), 2,2'-(pyridine-2,6-diyl)bis(4-phenylbenzo[h]quinazoline) (abbreviation: 2,6(P-Bqn)2Py), 2,2'-(pyridine-2,6-diyl)bis{4-[4-(2-naphthyl)phenyl]-6-phenylpyrimidine} (abbreviation: 2,6(NP-PPm)2Py), 6-(biphenyl-3-yl)-4-[3,5-bis(9H-carbazole-9-yl)phenyl]-2-phenyl Pyrimidine (abbreviation: 6mBP-4Cz2PPm), 2,6-bis(4-naphthalene-1-ylphenyl)-4-[4-(3-pyridyl)phenyl]pyrimidine (abbreviation: 2,4NP-6PyPPm), 4-[3,5-bis(9H-carbazole-9-yl)phenyl]-2-phenyl-6-(biphenyl-4-yl)pyrimidine (abbreviation: 6BP-4Cz2PPm), 8-(biphenyl-4-yl)-4-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]-[1]benzoflo[3,2-d]pyrimidine (abbreviation: 8BP-4mDB) Organic compounds having a diazine skeleton such as tBPBfpm), 8-(p-terphenyl-3-yl)-4-[3-(dibenzothiophen-4-yl)phenyl]-[1]benzofloflo[3,2-d]pyrimidine (abbreviation: 8mpTP-4mDBtPBfpm), 7-[4-(9-phenyl-9H-carbazole-2-yl)quinazoline-2-yl]-7H-dibenzo[c,g]carbazole (abbreviation: PC-cgDBCzQz), 2-(biphenyl-4-yl)-4-phenyl-6-(9,9'-spirobio[9H-fluoren]-2-yl)-1,3,5-triazine (abbreviation: BP-SFTzn), 2-{3-[3-(benzo[b]naphtho[1,2-d]furan-8-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: mBnfBPTzn), 2-{3-[3-(benzo[b]naphtho[1,2-d]furan-6-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: mBnfBPTzn-02), 2-{4-[3-(N-phenyl-9H-carbazole-3-yl)-9H-carbazole-9- [Il]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn), 9-[3-(4,6-diphenyl-1,3,5-triazine-2-yl)phenyl]-9'-phenyl-2,3'-bi-9H-carbazole (abbreviation: mPCCzPTzn-02), 2-[3'-(9,9-dimethyl-9H-fluoren-2-yl)biphenyl-3-yl]-4,6-diphenyl-1,3,5-triazine (abbreviation: mFBPTzn), 5-[3-(4,6-diphenyl-1,3,5-triazine-2 -yl)phenyl]-7,7-dimethyl-5H,7H-indeno[2,1-b]carbazole (abbreviation: mINc(II)PTzn), 2-{3-[3-(dibenzothiophen-4-yl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: mDBtBPTzn), 2,4,6-tris[3'-(pyridine-3-yl)biphenyl-3-yl]-1,3,5-triazine (abbreviation: TmPPPyTz), 2-[3-(2,6-dimethyl-3-pyridinyl)-5-(9-phenanthryl) [phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviation: mPn-mDMePyPTzn), 11-[4-(biphenyl-4-yl)-6-phenyl-1,3,5-triazine-2-yl]-11,12-dihydro-12-phenylindoro[2,3-a]carbazole (abbreviation: BP-Icz(II)Tzn), 2-[3'-(triphenylene-2-yl)biphenyl-3-yl]-4,6-diphenyl-1,3,5-triazine (abbreviation: mTpBPTzn), 3-[9-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-dibenzofuranyl]-9-phenyl-9H-carbazole (abbreviation: PCDBfTzn), 2-(biphenyl-3-yl)-4-phenyl-6-[8-([1,1':4',1''-terphenyl]-4-yl)-1-dibenzofuranyl]-1,3,5-triazin (abbreviation: mBP-TPDBfTzn), 2-(3'',5',5''-tri-t-butyl-[1,1':3',1''-terphenyl]-4-yl)-4,6-diphenyl-1,3,5-triazin (abbreviation: mmtBumTPTzn-04), 2,4,6-tris[3'-(pyridine-3-yl)-5'-tert-butyl-biphenyl-3-yl]-1,3,5-triazin (abbreviation: tBu-Tm Examples of organic compounds containing heteroaromatic rings with a triazine skeleton include PPPyTz), 2,4,6-tris[3'-(pyridine-3-yl)-5'-tert-butyl-biphenyl-4-yl]-1,3,5-triazine (abbreviation: tBu-TmPPPyTz-02), 2-(3'',5',5''-tri-t-butyl-[1,1':3',1''-terphenyl]-5-yl)-4,6-diphenyl-1,3,5-triazine (abbreviation: mmtBumTPTzn-03), and 2-{3-(2,6-dimethylpyridine-3-yl)-5-[(3,5-di-tert-butyl)phenyl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: mmtBuPh-mDMePyPTzn). Furthermore, organic compounds containing heteroaromatic rings having a diazine skeleton, or heteroaromatic rings having a pyridine skeleton, or heteroaromatic rings having a triazine skeleton are preferred due to their good reliability. In particular, organic compounds containing heteroaromatic rings having a diazine (pyrimidine or pyrazine) skeleton, or heteroaromatic rings having a triazine skeleton, have high electron transport properties and contribute to reducing the drive voltage. Among these, 8BP-4mDBtBPBfpm, 4,6mDBTP2Pm-II, 8mpTP-4mDBtPBfpm, TPBI, ZADN, BP-ICz(II)Tzn, mmtBumTPTzn-04, tBu-TmPPPyTz, tBu-TmPPPyTz-02, mmtBumTPTzn-03, mmtBuPh-mDMePyPTzn, and 4,Since 8mDBtP2Bfpm and Alq3 are organic compounds with a large GSP_Slope of the deposited film, they can be suitably used as materials for the second electron transport layer in the light-emitting device of the present invention.

[0227] The TADF materials listed above can be used as host materials. When a TADF material is used as a host material, the triplet excitation energy generated by the TADF material is converted into singlet excitation energy through reverse intersystem crossing, and this energy is then transferred to the light-emitting material, thereby increasing the luminescence efficiency of the light-emitting device. In this case, the TADF material functions as an energy donor, and the light-emitting material functions as an energy acceptor.

[0228] The host material may be a mixture of multiple substances, and when using a mixed host material, it is preferable to mix an electron-transporting material with a hole-transporting material. By mixing an electron-transporting material with a hole-transporting material, the transport properties of the light-emitting layer 113 can be easily adjusted, and the recombination region can also be easily controlled. The weight ratio of the hole-transporting material to the electron-transporting material should be 1:19 to 19:1.

[0229] Furthermore, phosphorescent materials can be used as part of the above-mentioned mixed materials. When a fluorescent material is used as the light-emitting material, the phosphorescent material can be used as an energy donor to supply excitation energy to the fluorescent material.

[0230] Furthermore, these mixed materials may form an excited complex. It is preferable to select a combination that forms an excited complex that exhibits emission overlapping with the wavelength of the lowest-energy absorption band of the luminescent material, as this facilitates smooth energy transfer and efficiently obtains light emission. This configuration is also preferable because it reduces the driving voltage.

[0231] Furthermore, at least one of the materials forming the excitation complex may be a phosphorescent material. This allows for the efficient conversion of the triplet excitation energy to the singlet excitation energy through reverse intersystem crossing.

[0232] For efficient excitation complex formation, it is preferable that the HOMO level of the hole-transporting material is above the HOMO level of the electron-transporting material. Furthermore, it is preferable that the LUMO level of the hole-transporting material is above the LUMO level of the electron-transporting material. The LUMO and HOMO levels of the materials can be derived from the electrochemical properties (reduction potential and oxidation potential) of the materials measured by cyclic voltammetry (CV).

[0233] The formation of excited complexes can be confirmed, for example, by comparing the emission spectra of a hole-transporting material, an electron-transporting material, and a mixed film made by mixing these materials, and observing that the emission spectrum of the mixed film shifts to a longer wavelength than the emission spectra of each individual material (or has a new peak on the longer wavelength side). Alternatively, it can be confirmed by comparing the transient photoluminescence (PL) of a hole-transporting material, the transient PL of an electron-transporting material, and the transient PL of a mixed film made by mixing these materials, and observing differences in the transient response, such as the transient PL lifetime of the mixed film having a longer lifetime component or a larger proportion of the delayed component than the transient PL lifetime of each individual material. Furthermore, the transient PL mentioned above can be replaced with transient electroluminescence (EL). That is, the formation of excited complexes can also be confirmed by comparing the transient EL of a hole-transporting material, the transient EL of an electron-transporting material, and the transient EL of a mixed film made by mixing these materials, and observing the differences in the transient response.

[0234] The electron transport layer 114 is a layer containing an electron-transporting material. The electron-transporting material has an electron mobility of 1 × 10⁻¹⁰ at an electric field strength [V / cm] square root of 600. -7 cm 2 / Vs or more, preferably 1 × 10 -6 cm 2 A substance having an electron mobility of / Vs or higher is preferred. However, any substance that has higher electron transport capacity than holes can be used. As the above organic compound, an organic compound having a π-electron-deficient heteroaromatic ring is preferred. As an organic compound having a π-electron-deficient heteroaromatic ring, it is preferable that it be any or more of the following: an organic compound containing a heteroaromatic ring having an azole skeleton, an organic compound containing a heteroaromatic ring having a pyridine skeleton, an organic compound containing a heteroaromatic ring having a diazine skeleton, and an organic compound containing a heteroaromatic ring having a triazine skeleton.

[0235] As an organic compound having electron-transporting properties that can be used in the electron transport layer 114, the same organic compounds that can be used as an organic compound having electron-transporting properties in the light-emitting layer 113 can be used. Among these, organic compounds containing a heteroaromatic ring having a diazine skeleton, or an organic compound containing a heteroaromatic ring having a pyridine skeleton, or an organic compound containing a heteroaromatic ring having a triazine skeleton are preferred due to their good reliability. In particular, organic compounds containing a heteroaromatic ring having a diazine (pyrimidine or pyrazine) skeleton, or an organic compound containing a heteroaromatic ring having a triazine skeleton, have high electron-transporting properties and contribute to reducing the driving voltage. In particular, organic compounds having a phenanthroline skeleton such as mTpPPhen, PnNPhen, and mPPhen2P are preferred, and organic compounds having a phenanthroline dimer structure such as mPPhen2P are more preferred due to their superior stability.

[0236] The electron transport layer 114 may have a multilayer structure. Furthermore, the layer in contact with the light-emitting layer 113 in the multilayer electron transport layer 114 may function as a hole-blocking layer. When the electron transport layer in contact with the light-emitting layer functions as a hole-blocking layer, it is preferable to use a material whose HOMO level is 0.5 eV or more lower than the HOMO level of the material contained in the light-emitting layer 113.

[0237] The electron injection layer 115 may include a layer containing an alkali metal or alkaline earth metal compound or complex such as 8-quinolinolatolithium (abbreviated as Liq), or 1,1'-pyridine-2,6-diyl-bis(1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) (abbreviated as hpp2Py). The electron injection layer 115 may also be a layer containing an alkali metal or alkaline earth metal or a compound thereof within a layer made of an electron-transporting material.

[0238] Alternatively, a charge generation layer 116 may be provided instead of the electron injection layer 115 (Figure 7(A)). The charge generation layer 116 is a layer that can inject holes into the layer in contact with the cathode side and electrons into the layer in contact with the anode side by applying a potential. The charge generation layer 116 includes at least a p-type layer 117. The p-type layer 117 is preferably formed using a composite material listed above as a material that can constitute the hole injection layer 111. The p-type layer 117 may also be formed by laminating a film containing the acceptor material and a film containing the hole transport material as materials constituting the composite material. By applying a potential to the p-type layer 117, electrons are injected into the electron transport layer 114 and holes into the cathode, and the light-emitting device operates. Furthermore, since the organic compound in one embodiment of the present invention is an organic compound with a low refractive index of the film, by using it in the p-type layer 117, a light-emitting device with good external quantum efficiency can be obtained.

[0239] Furthermore, it is preferable that the charge generation layer 116 includes, in addition to the p-type layer 117, one or both of the electron relay layer 118 and the electron injection buffer layer 119.

[0240] The electron relay layer 118 contains at least an electron-transporting material and has the function of preventing interaction between the electron injection buffer layer 119 and the p-type layer 117, thereby smoothly transferring electrons. The LUMO level of the electron-transporting material contained in the electron relay layer 118 is preferably between the LUMO level of the acceptor material in the p-type layer 117 and the LUMO level of the material contained in the layer in contact with the charge generation layer 116 in the electron transport layer 114. The specific energy level of the LUMO level of the electron-transporting material used in the electron relay layer 118 is preferably -5.0 eV or higher, more preferably -5.0 eV or higher and -3.0 eV or lower. It is preferable to use a phthalocyanine-based material or a metal complex having a metal-oxygen bond and an aromatic ligand as the electron-transporting material used in the electron relay layer 118.

[0241] The electron injection buffer layer 119 can use materials with high electron injection potential, such as alkali metals, alkaline earth metals, rare earth metals, and compounds thereof (alkali metal compounds (including oxides such as lithium oxide, halides, and carbonates such as lithium carbonate and cesium carbonate), alkaline earth metal compounds (including oxides, halides, and carbonates), or rare earth metal compounds (including oxides, halides, and carbonates)).

[0242] Furthermore, if the electron injection buffer layer 119 is formed by including an electron-transporting substance and a donor substance, the donor substance can include alkali metals, alkaline earth metals, rare earth metals, and compounds thereof (alkali metal compounds (including oxides such as lithium oxide, halides, and carbonates such as lithium carbonate and cesium carbonate), alkaline earth metal compounds (including oxides, halides, and carbonates), or rare earth metal compounds (including oxides, halides, and carbonates)), as well as organic compounds such as tetratianaphthalene (abbreviated as TTN), nickerosene, and decamethylnickerosene. The electron-transporting substance can be formed using the same materials as those used to constitute the electron transport layer 114 described above.

[0243] The second electrode 102 is an electrode that includes a cathode. The second electrode 102 may have a layered structure, in which case the layer in contact with the EL layer 103 functions as the cathode. As the material forming the cathode, metals, alloys, electrically conductive compounds, and mixtures thereof with a small work function (specifically 3.8 eV or less) can be used. Specific examples of such cathode materials include alkali metals such as lithium (Li) or cesium (Cs), elements belonging to group 1 or 2 of the periodic table such as magnesium (Mg), calcium (Ca), and strontium (Sr), and alloys (MgAg, AlLi) and compounds (lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF2), etc.) containing these, rare earth metals such as europium (Eu) and ytterbium (Yb), and alloys containing these. However, by providing an electron injection layer 115 or a thin film of a material with a low work function between the second electrode 102 and the electron transport layer, various conductive materials such as Al, Ag, ITO, silicon, or indium oxide-tin oxide containing silicon oxide can be used as the cathode, regardless of the magnitude of the work function.

[0244] Furthermore, if the second electrode 102 is formed from a material that is transparent to visible light, it can be made into a light-emitting device that emits light from the second electrode 102 side.

[0245] These conductive materials can be formed using dry methods such as vacuum deposition or sputtering, inkjet printing, or spin coating. Alternatively, they may be formed using a wet method with a sol-gel process, or using a metal paste.

[0246] Furthermore, various methods can be used to form the EL layer 103, regardless of whether they are dry or wet methods. For example, vacuum deposition, gravure printing, offset printing, screen printing, inkjet printing, or spin coating may be used.

[0247] Furthermore, each electrode or layer described above may be formed using different film deposition methods.

[0248] Next, an embodiment of a light-emitting device (also called a stacked element or tandem element) with a configuration in which multiple light-emitting units are stacked will be described with reference to Figure 7(B). This light-emitting device has multiple light-emitting units between the anode and the cathode. Each light-emitting unit has a configuration substantially similar to the EL layer 103 shown in Figures 1(A) to 2(B). In other words, the light-emitting device shown in Figure 7(B) is a light-emitting device having multiple light-emitting units, while the light-emitting devices shown in Figures 1(A) to 2(B) are light-emitting devices having one light-emitting unit.

[0249] In Figure 7(B), a first light-emitting unit 511 and a second light-emitting unit 512 are stacked between the first electrode 501 and the second electrode 502, and a charge generation layer 513 is provided between the first light-emitting unit 511 and the second light-emitting unit 512. The first electrode 501 and the second electrode 502 correspond to the first electrode 101 and the second electrode 102 in Figures 1(A) to 2(B), respectively, and the same components described in the explanation of Figures 1(A) to 2(B) can be applied. Furthermore, the first light-emitting unit 511 and the second light-emitting unit 512 may have the same configuration or different configurations.

[0250] The charge generation layer 513 has the function of injecting electrons into one light-emitting unit and holes into the other light-emitting unit when a voltage is applied to the first electrode 501 and the second electrode 502. That is, in Figure 7(B), when a voltage is applied such that the potential of the anode is higher than the potential of the cathode, the charge generation layer 513 only needs to inject electrons into the first light-emitting unit 511 and holes into the second light-emitting unit 512.

[0251] The charge generation layer 513 is preferably formed with the same configuration as the charge generation layer 116 described in Figure 7(A). Because the composite material of the organic compound and the metal oxide has excellent carrier implantation and carrier transport properties, it can achieve low voltage drive and low current drive.

[0252] Furthermore, if the anode side of the light-emitting unit is in contact with the charge generation layer 513, the charge generation layer 513 can also serve as the hole injection layer of the light-emitting unit, so the light-emitting unit does not need to have a hole injection layer.

[0253] Furthermore, when an electron injection buffer layer 119 is provided in the charge generation layer 513, the electron injection buffer layer 119 plays the role of an electron injection layer in the anode-side light-emitting unit, so it is not necessarily required to form an electron injection layer in the anode-side light-emitting unit.

[0254] Figure 7(B) illustrates a light-emitting device having two light-emitting units, but the same principles can be applied to light-emitting devices with three or more stacked light-emitting units. As in the light-emitting device according to this embodiment, by arranging multiple light-emitting units separated between a pair of electrodes by a charge generation layer 513, high-brightness light emission can be achieved while maintaining a low current density, and a long-life element can be realized. Furthermore, a light-emitting device that can be driven at a low voltage and consumes little power can be realized.

[0255] Furthermore, by making the light-emitting colors of each light-emitting unit different, it is possible to obtain a desired color of light emission from the entire light-emitting device. For example, in a light-emitting device having two light-emitting units, it is possible to obtain a light-emitting device that emits white light as a whole by obtaining red and green light-emitting colors from the first light-emitting unit and blue light-emitting color from the second light-emitting unit.

[0256] Furthermore, each layer, such as the EL layer 103, the first light-emitting unit 511, the second light-emitting unit 512, and the charge generation layer, as well as the electrodes, can be formed using methods such as vapor deposition (including vacuum deposition), droplet ejection (also known as inkjet printing), coating, and gravure printing. They may also contain low-molecular-weight materials, medium-molecular-weight materials (including oligomers and dendrimers), or polymer materials.

[0257] (Embodiment 3) In this embodiment, an example in which a light-emitting device according to one aspect of the present invention is used as a display element for a display device will be described. In this embodiment, the light-emitting device is shown in a shape formed by photolithography, but it may also be formed by a method using a fine metal mask or the like.

[0258] As illustrated in Figures 8(A) and 8(B), multiple light-emitting devices 130 are formed on the insulating layer 175 to constitute a display device.

[0259] The display device 100 has a pixel section 177 in which a plurality of pixels 178 are arranged in a matrix. The pixels 178 include sub-pixels 110R, sub-pixels 110G, and sub-pixels 110B.

[0260] In this specification, for example, when describing matters common to sub-pixels 110R, 110G, and 110B, they may be referred to simply as sub-pixel 110. Similarly, when describing matters common to other components distinguished by letters, the letters may be omitted and the corresponding symbols used.

[0261] Sub-pixel 110R emits red light, sub-pixel 110G emits green light, and sub-pixel 110B emits blue light. This allows an image to be displayed on the pixel section 177. In this embodiment, three sub-pixels of red (R), green (G), and blue (B) are used as an example, but other combinations of sub-pixels of other colors may be used. Furthermore, the number of sub-pixels is not limited to three, but may be four or more. Examples of four sub-pixels include four sub-pixels of R, G, B, and white (W), four sub-pixels of R, G, B, and yellow (Y), and four sub-pixels of R, G, B, and infrared (IR).

[0262] In this specification and other documents, the row direction is sometimes referred to as the X direction, and the column direction as the Y direction. The X and Y directions intersect, for example, perpendicularly.

[0263] Figure 8(A) shows an example where subpixels of different colors are arranged in the X direction, and subpixels of the same color are arranged in the Y direction. Alternatively, subpixels of different colors may be arranged in the Y direction, and subpixels of the same color may be arranged in the X direction.

[0264] A connecting portion 140 and a region 141 may be provided on the outside of the pixel portion 177. The region 141 is provided between the pixel portion 177 and the connecting portion 140. An EL layer 103 is provided in the region 141. A conductive layer 151C is provided in the connecting portion 140.

[0265] Figure 8(A) shows an example where region 141 and connection portion 140 are located to the right of pixel portion 177, but the positions of region 141 and connection portion 140 are not particularly limited. Also, region 141 and connection portion 140 may be singular or plural.

[0266] Figure 8(B) is an example of a cross-sectional view between the dashed line A1-A2 in Figure 8(A). As shown in Figure 8(B), the display device has an insulating layer 171, a conductive layer 172 on the insulating layer 171, an insulating layer 173 on the insulating layer 171 and on the conductive layer 172, an insulating layer 174 on the insulating layer 173, and an insulating layer 175 on the insulating layer 174. The insulating layer 171 is provided on a substrate (not shown). The insulating layer 175, insulating layer 174, and insulating layer 173 are provided with openings that reach the conductive layer 172, and plugs 176 are provided to fill these openings.

[0267] In the pixel section 177, a light-emitting device 130 is provided on an insulating layer 175 and a plug 176. A protective layer 131 is provided so as to cover the light-emitting device 130. A substrate 120 is bonded to the protective layer 131 by a resin layer 122. Preferably, an inorganic insulating layer 125 and an insulating layer 127 on the inorganic insulating layer 125 are provided between adjacent light-emitting devices 130.

[0268] In Figure 8(B), multiple cross-sections of the inorganic insulating layer 125 and the insulating layer 127 are shown, but when the display device is viewed from above, it is preferable that the inorganic insulating layer 125 and the insulating layer 127 are connected as one unit. In other words, it is preferable that the inorganic insulating layer 125 and the insulating layer 127 are insulating layers having an opening on the first electrode.

[0269] In Figure 8(B), the light-emitting devices 130 are shown as light-emitting devices 130R, 130G, and 130B. Light-emitting devices 130R, 130G, and 130B are assumed to emit different colors from each other. For example, light-emitting device 130R can emit red light, light-emitting device 130G can emit green light, and light-emitting device 130B can emit blue light. In addition, light-emitting devices 130R, 130G, or 130B may emit other visible light or infrared light. Note that in Figure 8(B), light-emitting devices 130R and 130G, and light-emitting devices 130G and 130B can be considered adjacent light-emitting devices.

[0270] One embodiment of the present invention can be a top-emission type, for example, which emits light in the opposite direction to the substrate on which the light-emitting device is formed. Alternatively, one embodiment of the present invention may be a bottom-emission type.

[0271] The light-emitting device 130R is a light-emitting device that exhibits red light emission (phosphorescence is preferred), and preferably has the configuration shown in Embodiment 2. It has a first electrode (pixel electrode) 101R consisting of a conductive layer 151R and a conductive layer 152R, a first layer 135R on the first electrode 101R, a common layer 136 on the first layer 135R, and a second electrode (common electrode) 102 on the common layer 136. The common layer 136 is preferably an electron injection layer.

[0272] The light-emitting device 130G is a light-emitting device that emits green light (phosphorescence is preferred), and preferably has the configuration shown in Embodiment 2. It has a first electrode (pixel electrode) 101G consisting of a conductive layer 151G and a conductive layer 152G, a first layer 135G on the first electrode 101G, a common layer 136 on the first layer 135G, and a second electrode (common electrode) 102 on the common layer 136. The common layer 136 is preferably an electron injection layer.

[0273] The light-emitting device 130B is a light-emitting device that emits blue light (fluorescence is preferred), and preferably has the configuration shown in Embodiment 2. It has a first electrode (pixel electrode) 101B consisting of a conductive layer 151B and a conductive layer 152B, a first layer 135B on the first electrode 101B, a common layer 136 on the first layer 135B, and a second electrode (common electrode) 102 on the common layer 136. The common layer 136 is preferably an electron injection layer.

[0274] Of the pixel electrodes (first electrodes) and common electrodes (second electrodes) of the light-emitting device, one functions as the anode and the other as the cathode. In this embodiment, unless otherwise specified, the pixel electrodes function as the anode and the common electrodes function as the cathode.

[0275] The first layer 135R, the first layer 135G, and the first layer 135B are independent island-like layers for each light-emitting device or for each light-emitting color. Furthermore, it is preferable that the first layer 135R, the first layer 135G, and the first layer 135B do not overlap with each other. Note that the first layers formed on multiple light-emitting devices 130 in the light-emitting device, such as the first layer 135R, the first layer 135G, and the first layer 135B, may be collectively referred to as the first layer group 135A. By providing the first layer group 135A in an island-like manner for each light-emitting device 130, leakage current between adjacent light-emitting devices 130 can be suppressed even in high-definition display devices. This prevents crosstalk and enables the realization of a display device with extremely high contrast. In particular, it enables the realization of a display device with high current efficiency at low brightness.

[0276] The island-like first layer group 135A is formed by depositing an EL film for each emission color and processing the EL film using photolithography.

[0277] Preferably, the first layer 135 is provided so as to cover the top and side surfaces of the first electrode 101 (pixel electrode) of the light-emitting device 130. This makes it easier to increase the aperture ratio of the display device compared to a configuration in which the edges of the first layer 135 are located inward from the edges of the pixel electrode. In addition, by covering the side surfaces of the pixel electrode of the light-emitting device 130 with the first layer 135, contact between the first electrode 101 and the second electrode 102 can be suppressed, thereby suppressing short circuits of the light-emitting device 130.

[0278] Furthermore, in a display device according to one aspect of the present invention, it is preferable that the first electrode 101 (pixel electrode) of the light-emitting device be in a stacked configuration. For example, in the example shown in Figure 8(B), the first electrode 101 of the light-emitting device 130 is in a stacked configuration of a conductive layer 151 provided on the insulating layer 171 side and a conductive layer 152 provided on the organic compound layer side.

[0279] For example, a metallic material can be used as the conductive layer 151. Specifically, metals such as aluminum (Al), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), gallium (Ga), zinc (Zn), indium (In), tin (Sn), molybdenum (Mo), tantalum (Ta), tungsten (W), palladium (Pd), gold (Au), platinum (Pt), silver (Ag), yttrium (Y), neodymium (Nd), and alloys containing these in appropriate combinations can also be used.

[0280] As the conductive layer 152, an oxide having one or more selected from indium, tin, zinc, gallium, titanium, aluminum, and silicon can be used. For example, it is preferable to use a conductive oxide containing one or more of the following: indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, zinc oxide containing gallium, titanium oxide, indium zinc oxide containing gallium, indium zinc oxide containing aluminum, indium tin oxide containing silicon, and indium zinc oxide containing silicon. In particular, indium tin oxide containing silicon has a large work function, for example, a work function of 4.0 eV or more, so it can be suitably used as the conductive layer 152.

[0281] The conductive layer 151 may be a laminated structure of multiple layers having different materials, and the conductive layer 152 may be a laminated structure of multiple layers having different materials. In this case, the conductive layer 151 may have a layer made of a material that can be used for the conductive layer 152, such as a conductive oxide, and the conductive layer 152 may have a layer made of a material that can be used for the conductive layer 151, such as a metallic material. For example, if the conductive layer 151 has a laminated structure of two or more layers, the layer in contact with the conductive layer 152 may be a layer made of a material that can be used for the conductive layer 152.

[0282] Furthermore, it is preferable that the end of the conductive layer 151 has a tapered shape. Specifically, it is preferable that the end of the conductive layer 151 has a tapered shape with a taper angle of less than 90°. In this case, the conductive layer 152 provided along the side surface of the conductive layer 151 also has a tapered shape. By making the side surface of the conductive layer 152 tapered, the coverage of the first layer 135 provided along the side surface of the conductive layer 152 can be improved.

[0283] (Embodiment 4) This embodiment describes a display device according to one aspect of the present invention.

[0284] The display device of this embodiment can be a high-definition display device. Therefore, the display device of this embodiment can be used, for example, as a display unit for information terminals (wearable devices) such as wristwatches and bracelets, and as a display unit for wearable devices that can be worn on the head, such as VR devices such as head-mounted displays (HMDs) and AR devices such as glasses.

[0285] Furthermore, the display device of this embodiment can be a high-resolution display device or a large-screen display device. Therefore, the display device of this embodiment can be used in electronic devices with relatively large screens, such as television equipment, desktop or notebook personal computers, computer monitors, digital signage, and large game machines such as pachinko machines, as well as in the display units of digital cameras, digital video cameras, digital photo frames, mobile phones, portable game consoles, personal information terminals, and audio playback devices.

[0286] [Display Module] Figure 9(A) shows a perspective view of the display module 280. The display module 280 includes a display device 100A and an FPC 290. Note that the display device included in the display module 280 is not limited to display device 100A, but may be any of the display devices 100B to 100E described later.

[0287] The display module 280 has substrates 291 and 292. The display module 280 has a display unit 281. The display unit 281 is an area in the display module 280 that displays an image, and is an area in which light from each pixel provided in the pixel unit 284, which will be described later, can be seen.

[0288] Figure 9(B) shows a schematic perspective view illustrating the configuration of the substrate 291. On the substrate 291, a circuit section 282, a pixel circuit section 283 on the circuit section 282, and a pixel section 284 on the pixel circuit section 283 are stacked. In addition, a terminal section 285 for connecting to the FPC 290 is provided in the portion of the substrate 291 that does not overlap with the pixel section 284. The terminal section 285 and the circuit section 282 are electrically connected by a wiring section 286 composed of multiple wires.

[0289] The pixel section 284 has a plurality of pixels 284a arranged periodically. A magnified view of one pixel 284a is shown on the right side of Figure 9(B). Various configurations described in the previous embodiment can be applied to the pixels 284a. Figure 9(B) shows an example where the pixel 284a has the same configuration as the pixel 178 shown in Figure 8.

[0290] The pixel circuit section 283 has a plurality of pixel circuits 283a arranged periodically.

[0291] One pixel circuit 283a is a circuit that controls the driving of multiple elements that a single pixel 284a has.

[0292] The circuit section 282 has circuits for driving each pixel circuit 283a of the pixel circuit section 283. For example, it is preferable to have one or both of a gate line drive circuit and a source line drive circuit. In addition, it may have at least one of the following: an arithmetic circuit, a memory circuit, and a power supply circuit.

[0293] The FPC290 functions as wiring for supplying video signals or power potential, etc., to the circuit section 282 from an external source. An IC may also be mounted on the FPC290.

[0294] Since the display module 280 can be configured such that one or both of the pixel circuit section 283 and the circuit section 282 are stacked on the lower side of the pixel section 284, the aperture ratio (effective display area ratio) of the display section 281 can be made extremely high.

[0295] Because such a display module 280 is extremely high-resolution, it can be suitably used in VR devices such as HMDs or AR devices such as glasses. For example, even in a configuration where the display part of the display module 280 is viewed through lenses, the display module 280 has an extremely high-resolution display part 281, so even when the display part is magnified with lenses, pixels are not visible, and a highly immersive display can be achieved. Furthermore, the display module 280 is not limited to this and can be suitably used in electronic devices having relatively small display parts.

[0296] [Display device 100A] The display device 100A shown in Figure 10(A) includes a substrate 301, light-emitting devices 130R, 130G, 130B, a capacitor 240, and a transistor 310.

[0297] Substrate 301 corresponds to substrate 291 in Figures 9(A) and 9(B). Transistor 310 is a transistor having a channel formation region in substrate 301. For example, a semiconductor substrate such as a single-crystal silicon substrate can be used as substrate 301. Transistor 310 has a part of substrate 301, a conductive layer 311, a low-resistance region 312, an insulating layer 313, and an insulating layer 314. The conductive layer 311 functions as a gate electrode. The insulating layer 313 is located between substrate 301 and the conductive layer 311 and functions as a gate insulating layer. The low-resistance region 312 is a region of substrate 301 doped with impurities and functions as a source or drain. The insulating layer 314 is provided covering the side surface of the conductive layer 311.

[0298] Furthermore, an element isolation layer 315 is provided between two adjacent transistors 310 so as to be embedded in the substrate 301.

[0299] Furthermore, an insulating layer 261 is provided covering the transistor 310, and a capacitance 240 is provided on the insulating layer 261.

[0300] The capacitor 240 has a conductive layer 241, a conductive layer 245, and an insulating layer 243 located between them. The conductive layer 241 acts as one electrode of the capacitor 240, the conductive layer 245 acts as the other electrode of the capacitor 240, and the insulating layer 243 acts as the dielectric of the capacitor 240.

[0301] The conductive layer 241 is provided on the insulating layer 261 and embedded in the insulating layer 254. The conductive layer 241 is electrically connected to either the source or drain of the transistor 310 by a plug 271 embedded in the insulating layer 261. The insulating layer 243 is provided covering the conductive layer 241. The conductive layer 245 is provided in the region that overlaps with the conductive layer 241 via the insulating layer 243.

[0302] An insulating layer 255 is provided covering the capacitance 240, an insulating layer 174 is provided on the insulating layer 255, and an insulating layer 175 is provided on the insulating layer 174. Light-emitting devices 130R, 130G, and 130B are provided on the insulating layer 175. An insulator is provided in the region between adjacent light-emitting devices.

[0303] An insulating layer 156R is provided so as to have a region that overlaps with the side surface of the conductive layer 151R, an insulating layer 156G is provided so as to have a region that overlaps with the side surface of the conductive layer 151G, and an insulating layer 156B is provided so as to have a region that overlaps with the side surface of the conductive layer 151B. Furthermore, a conductive layer 152R is provided so as to cover the conductive layer 151R and the insulating layer 156R, a conductive layer 152G is provided so as to cover the conductive layer 151G and the insulating layer 156G, and a conductive layer 152B is provided so as to cover the conductive layer 151B and the insulating layer 156B. A sacrificial layer 158R is located on the first layer 135R, a sacrificial layer 158G is located on the first layer 135G, and a sacrificial layer 158B is located on the first layer 135B.

[0304] The conductive layers 151R, 151G, and 151B are electrically connected to either the source or drain of the transistor 310 by the insulating layers 243, 255, 174, and plugs 256 embedded in the insulating layer 175, the conductive layer 241 embedded in the insulating layer 254, and plugs 271 embedded in the insulating layer 261. Various conductive materials can be used for the plugs.

[0305] Furthermore, a protective layer 131 is provided on the light-emitting devices 130R, 130G, and 130B. A substrate 120 is bonded to the protective layer 131 by a resin layer 122. Details of the components from the light-emitting devices 130 to the substrate 120 can be found in Embodiment 3. The substrate 120 corresponds to the substrate 292 in Figure 9(A).

[0306] Figure 10(B) shows a modified version of the display device 100A shown in Figure 10(A). The display device shown in Figure 10(B) has a colored layer 132R, a colored layer 132G, and a colored layer 132B, and the light-emitting device 130 has a region that overlaps with one of the colored layers 132R, 132G, and 132B. In the display device shown in Figure 10(B), the light-emitting device 130 can emit, for example, white light. Also, for example, the colored layer 132R can transmit red light, the colored layer 132G can transmit green light, and the colored layer 132B can transmit blue light.

[0307] [Display device 100B] Figure 11 shows a perspective view of the display device 100B, and Figure 12 shows a cross-sectional view of the display device 100C.

[0308] The display device 100B has a configuration in which substrate 352 and substrate 351 are bonded together. In Figure 11, substrate 352 is shown by a dashed line.

[0309] The display device 100B includes a pixel section 177, a connection section 140, a circuit 356, and wiring 355, etc. Figure 11 shows an example in which IC 354 and FPC 353 are mounted on the display device 100B. Therefore, the configuration shown in Figure 11 can also be called a display module having the display device 100B, an IC (integrated circuit), and an FPC. Here, a display module is a display device on which a connector such as an FPC is attached, or on which an IC is mounted.

[0310] The connection portion 140 is provided on the outside of the pixel portion 177. There may be one or more connection portions 140. The connection portion 140 is electrically connected to the common electrode of the light-emitting device and the conductive layer, and can supply potential to the common electrode.

[0311] For example, a scan line drive circuit can be used as circuit 356.

[0312] The wiring 355 has the function of supplying signals and power to the pixel unit 177 and the circuit 356. These signals and power are input to the wiring 355 from an external source via the FPC 353 or from the IC 354.

[0313] Figure 11 shows an example in which IC 354 is provided on substrate 351 using COG (Chip On Glass) or COF (Chip On Film) methods. IC 354 can be an IC having, for example, a scan line drive circuit or a signal line drive circuit. Note that the display device 100B and the display module may be configured without an IC. Alternatively, the IC may be mounted on an FPC, for example, using the COF method.

[0314] Figure 12 shows an example of a cross-section obtained by cutting a portion of the display device 100C, including the FPC 353, a portion of the circuit 356, a portion of the pixel portion 177, a portion of the connection portion 140, and a portion of the end portion.

[0315] [Display device 100C] The display device 100C shown in Figure 12 has a transistor 201, a transistor 205, a light-emitting device 130R that emits red light, a light-emitting device 130G that emits green light, and a light-emitting device 130B that emits blue light, etc., between substrates 351 and 352.

[0316] Details of the light-emitting devices 130R, 130G, and 130B can be found in Embodiment 1.

[0317] Light-emitting device 130R has a conductive layer 224R, a conductive layer 151R on the conductive layer 224R, and a conductive layer 152R on the conductive layer 151R. Light-emitting device 130G has a conductive layer 224G, a conductive layer 151G on the conductive layer 224G, and a conductive layer 152G on the conductive layer 151G. Light-emitting device 130B has a conductive layer 224B, a conductive layer 151B on the conductive layer 224B, and a conductive layer 152B on the conductive layer 151B.

[0318] The conductive layer 224R is connected to the conductive layer 222b of the transistor 205 through an opening provided in the insulating layer 214. The edge of the conductive layer 151R is located outside the edge of the conductive layer 224R. The insulating layer 156R is provided so as to have a region in contact with the side surface of the conductive layer 151R, and the conductive layer 152R is provided so as to cover the conductive layer 151R and the insulating layer 156R.

[0319] The conductive layers 224G, 151G, 152G, and insulating layer 156G in the light-emitting device 130G, and the conductive layers 224B, 151B, 152B, and insulating layer 156B in the light-emitting device 130B are the same as the conductive layers 224R, 151R, 152R, and insulating layer 156R in the light-emitting device 130R, so a detailed explanation is omitted.

[0320] The conductive layer 224R, conductive layer 224G, and conductive layer 224B have recesses formed to cover the openings provided in the insulating layer 214. Layer 128 is embedded in these recesses.

[0321] Layer 128 has the function of flattening the recesses of conductive layers 224R, 224G, and 224B. Conductive layers 151R, 151G, and 151B are provided on conductive layers 224R, 224G, and 224B and on layer 128, and are electrically connected to conductive layers 224R, 224G, and 224B. Therefore, regions overlapping with the recesses of conductive layers 224R, 224G, and 224B can also be used as light-emitting regions, thereby increasing the aperture ratio of the pixels.

[0322] Layer 128 may be an insulating layer or a conductive layer. Various inorganic insulating materials, organic insulating materials, and conductive materials can be used for layer 128 as appropriate. In particular, it is preferable that layer 128 be formed using an insulating material, and especially preferable that it be formed using an organic insulating material. For example, an organic insulating material that can be used for the insulating layer 127 described above can be applied to layer 128.

[0323] A protective layer 131 is provided on the light-emitting devices 130R, 130G, and 130B. The protective layer 131 and the substrate 352 are bonded via an adhesive layer 142. A light-shielding layer 157 is provided on the substrate 352. A solid encapsulation structure or a hollow encapsulation structure can be applied to encapsulate the light-emitting devices 130. In Figure 12, the space between the substrate 352 and the substrate 351 is filled with the adhesive layer 142, indicating a solid encapsulation structure. Alternatively, the space may be filled with an inert gas (such as nitrogen or argon), indicating a hollow encapsulation structure. In this case, the adhesive layer 142 may be provided in a frame shape so as not to overlap with the light-emitting devices. Furthermore, the space may be filled with a resin different from the adhesive layer 142 provided in a frame shape.

[0324] Figure 12 shows an example in which the connection portion 140 has a conductive layer 224C obtained by processing the same conductive film as conductive layers 224R, 224G, and 224B; a conductive layer 151C obtained by processing the same conductive film as conductive layers 151R, 151G, and 151B; and a conductive layer 152C obtained by processing the same conductive film as conductive layers 152R, 152G, and 152B. Figure 12 also shows an example in which an insulating layer 156C is provided so as to have a region that overlaps with the side surface of conductive layer 151C.

[0325] The display device 100C is a top-emission type. The light emitted by the light-emitting device is emitted towards the substrate 352. It is preferable to use a material with high transmittance to visible light for the substrate 352. If the light-emitting device emits infrared or near-infrared light, it is preferable to use a material with high transmittance to those. The first electrode (pixel electrode) contains a material that reflects visible light, and the second electrode (counter electrode) contains a material that transmits visible light.

[0326] On the substrate 351, insulating layers 211, 213, 215, and 214 are provided in this order. A portion of insulating layer 211 functions as a gate insulating layer for each transistor. A portion of insulating layer 213 functions as a gate insulating layer for each transistor. Insulating layer 215 is provided covering the transistors. Insulating layer 214 is provided covering the transistors and functions as a planarization layer. The number of gate insulating layers and insulating layers covering the transistors are not limited and may be a single layer or two or more layers, respectively.

[0327] It is preferable to use an inorganic insulating film as the insulating layer 211, insulating layer 213, and insulating layer 215.

[0328] An organic insulating layer is preferred for the insulating layer 214, which functions as a planarizing layer.

[0329] Transistors 201 and 205 each have a conductive layer 221 that functions as a gate, an insulating layer 211 that functions as a gate insulating layer, conductive layers 222a and 222b that function as source and drain, a semiconductor layer 231, an insulating layer 213 that functions as a gate insulating layer, and a conductive layer 223 that functions as a gate.

[0330] A connection portion 204 is provided in the region of substrate 351 where substrate 352 does not overlap. At the connection portion 204, the wiring 355 is electrically connected to the FPC 353 via the conductive layer 166 and the connecting layer 242. The conductive layer 166 is shown as an example of a laminated structure consisting of a conductive film obtained by processing the same conductive film as conductive layers 224R, 224G, and 224B, a conductive film obtained by processing the same conductive film as conductive layers 151R, 151G, and 151B, and a conductive film obtained by processing the same conductive film as conductive layers 152R, 152G, and 152B. On the upper surface of the connection portion 204, the conductive layer 166 is exposed. This allows the connection portion 204 and the FPC 353 to be electrically connected via the connecting layer 242.

[0331] It is preferable to provide a light-shielding layer 157 on the surface of the substrate 352 that faces the substrate 351. The light-shielding layer 157 can be provided between adjacent light-emitting devices, at connection points 140, and in circuits 356, etc. In addition, various optical components can be arranged on the outside of the substrate 352.

[0332] Materials that can be used for substrate 120 can be applied to substrate 351 and substrate 352, respectively.

[0333] As the adhesive layer 142, a material that can be used for the resin layer 122 can be applied.

[0334] As the connecting layer 242, an anisotropic conductive film (ACF) or an anisotropic conductive paste (ACP) can be used.

[0335] [Display device 100D] The display device 100D shown in Figure 13 differs from the display device 100C shown in Figure 12 mainly in that it is a bottom-emission type display device.

[0336] The light emitted by the light-emitting device is projected onto the substrate 351. It is preferable to use a material with high transparency to visible light for the substrate 351. On the other hand, the light transmittance of the material used for the substrate 352 is not a requirement.

[0337] It is preferable to form a light-shielding layer 157 between the substrate 351 and the transistor 201, and between the substrate 351 and the transistor 205. Figure 13 shows an example in which a light-shielding layer 157 is provided on the substrate 351, an insulating layer 153 is provided on the light-shielding layer 157, and transistors 201, 205, etc. are provided on the insulating layer 153.

[0338] The light-emitting device 130R includes a conductive layer 112R, a conductive layer 126R on the conductive layer 112R, and a conductive layer 129R on the conductive layer 126R.

[0339] The light-emitting device 130B includes a conductive layer 112B, a conductive layer 126B on the conductive layer 112B, and a conductive layer 129B on the conductive layer 126B.

[0340] The conductive layers 112R, 112B, 126R, 126B, 129R, and 129B are made of materials with high transmittance to visible light. It is preferable to use a material that reflects visible light for the second electrode.

[0341] Although the light-emitting device 130G is not shown in Figure 13, it is also provided.

[0342] Furthermore, while Figure 13 and other figures show an example where the upper surface of layer 128 has a flat portion, the shape of layer 128 is not particularly limited.

[0343] [Display device 100E] The display device 100E shown in Figure 14 is a modified version of the display device 100C shown in Figure 12, and differs from the display device 100C mainly in that it has a colored layer 132R, a colored layer 132G, and a colored layer 132B.

[0344] In the display device 100E, the light-emitting device 130 has a region that overlaps with one of the colored layers 132R, 132G, and 132B. The colored layers 132R, 132G, and 132B can be provided on the substrate 351 side of the substrate 352. The edges of the colored layer 132R, the edges of the colored layer 132G, and the edges of the colored layer 132B can overlap with the light-shielding layer 157.

[0345] In the display device 100E, the light-emitting device 130 can emit, for example, white light. Furthermore, for example, the colored layer 132R can transmit red light, the colored layer 132G can transmit green light, and the colored layer 132B can transmit blue light. The display device 100E may also be configured with the colored layers 132R, 132G, and 132B placed between the protective layer 131 and the adhesive layer 142.

[0346] Figures 12 and 14 show examples where the upper surface of layer 128 has a flat portion, but the shape of layer 128 is not particularly limited.

[0347] This embodiment can be appropriately combined with other embodiments or examples. Furthermore, if multiple configuration examples are shown within a single embodiment in this specification, these configuration examples can be appropriately combined.

[0348] (Embodiment 5) This embodiment describes an electronic device according to one aspect of the present invention.

[0349] The electronic device of this embodiment has a display device according to one aspect of the present invention in its display unit. The display device according to one aspect of the present invention has low power consumption. Therefore, it can be used in the display unit of various electronic devices.

[0350] Examples of electronic devices include television sets, desktop or notebook personal computers, computer monitors, digital signage, large game machines such as pachinko machines, and other electronic devices with relatively large screens, as well as digital cameras, digital video cameras, digital photo frames, mobile phones, portable game consoles, personal digital assistants, and audio playback devices.

[0351] In particular, a display device according to one aspect of the present invention consumes little power and is therefore suitable for use in relatively small electronic devices. Examples of such electronic devices include wristwatch-type and bracelet-type information terminals (wearable devices), as well as wearable devices that can be worn on the head, such as VR devices such as head-mounted displays, AR devices such as glasses, and MR devices.

[0352] The electronic device of this embodiment may have sensors (including those with functions to measure force, displacement, position, velocity, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared radiation).

[0353] An example of a wearable device that can be worn on the head is illustrated using Figures 15(A) to 15(D).

[0354] The electronic device 700A shown in Figure 15(A) and the electronic device 700B shown in Figure 15(B) each include a pair of display panels 751, a pair of housings 721, a communication unit (not shown), a pair of mounting units 723, a control unit (not shown), an imaging unit (not shown), a pair of optical members 753, a frame 757, and a pair of nose pads 758.

[0355] A display device according to one aspect of the present invention can be applied to the display panel 751. Therefore, it is possible to create an electronic device that consumes little power and can be operated for a long time.

[0356] Electronic devices 700A and 700B can project an image displayed on the display panel 751 onto the display area 756 of the optical element 753. Because the optical element 753 is translucent, the user can see the image displayed on the display area superimposed on the transmitted image visible through the optical element 753.

[0357] Electronic devices 700A and 700B may be equipped with cameras capable of capturing images of the area in front of them as imaging units. Furthermore, electronic devices 700A and 700B may each be equipped with acceleration sensors such as gyro sensors to detect the orientation of the user's head and display an image corresponding to that orientation in the display area 756.

[0358] The communications unit has a wireless communication device, which can supply, for example, a video signal. Alternatively, instead of the wireless communication device, or in addition to the wireless communication device, it may be equipped with a connector to which a cable for supplying video signals and power potential can be connected.

[0359] Furthermore, electronic devices 700A and 700B are equipped with batteries that can be charged wirelessly, wired, or both.

[0360] The housing 721 may also be provided with a touch sensor module.

[0361] Various types of touch sensors can be used in the touch sensor module. For example, various methods such as capacitive, resistive, infrared, electromagnetic induction, surface acoustic wave, or optical sensors can be employed. In particular, it is preferable to apply capacitive or optical sensors to the touch sensor module.

[0362] The electronic device 800A shown in Figure 15(C) and the electronic device 800B shown in Figure 15(D) each include a pair of display units 820, a housing 821, a communication unit 822, a pair of mounting units 823, a control unit 824, a pair of imaging units 825, and a pair of lenses 832.

[0363] A display device according to one aspect of the present invention can be applied to the display unit 820. Therefore, it is possible to create an electronic device that consumes little power and can be operated for a long time.

[0364] The display unit 820 is located inside the housing 821, in a position where it can be seen through the lens 832. Furthermore, by displaying different images on a pair of display units 820, a three-dimensional display using parallax can also be performed.

[0365] Preferably, electronic devices 800A and 800B have a mechanism that allows the left and right positions of the lens 832 and the display unit 820 to be in an optimal position according to the user's eye position.

[0366] The attachment part 823 allows the user to attach the electronic device 800A or the electronic device 800B to their head.

[0367] The imaging unit 825 has the function of acquiring external information. The data acquired by the imaging unit 825 can be output to the display unit 820. An image sensor can be used in the imaging unit 825. In addition, multiple cameras may be provided to accommodate multiple angles of view, such as telephoto and wide-angle.

[0368] The electronic device 800A may have a vibration mechanism that functions as a bone conduction earphone.

[0369] Electronic devices 800A and 800B may each have input terminals. Cables can be connected to the input terminals to supply video signals from video output devices, etc., and power for charging batteries provided within the electronic devices.

[0370] An electronic device according to one aspect of the present invention may have a function for wireless communication with an earphone 750.

[0371] Furthermore, the electronic device may have an earphone section. The electronic device 700B shown in Figure 15(B) has an earphone section 727. Some of the wiring connecting the earphone section 727 and the control unit may be located inside the housing 721 or the mounting section 723.

[0372] Similarly, the electronic device 800B shown in Figure 15(D) has an earphone unit 827. For example, the earphone unit 827 and the control unit 824 can be connected to each other by a wire.

[0373] Thus, as one embodiment of the present invention, both eyeglass-type (electronic devices 700A and 700B, etc.) and goggle-type (electronic devices 800A and 800B, etc.) are preferred as electronic devices.

[0374] The electronic device 6500 shown in Figure 16(A) is a portable information terminal that can be used as a smartphone.

[0375] The electronic device 6500 includes a housing 6501, a display unit 6502, a power button 6503, a button 6504, a speaker 6505, a microphone 6506, a camera 6507, and a light source 6508, etc. The display unit 6502 has a touch panel function.

[0376] A display device according to one embodiment of the present invention can be applied to the display unit 6502. Therefore, an electronic device with low power consumption and long operating time can be made.

[0377] Figure 16(B) is a schematic cross-sectional view of the housing 6501 including the end on the microphone 6506 side.

[0378] A light-transmitting protective member 6510 is provided on the display side of the housing 6501, and the display panel 6511, optical member 6512, touch sensor panel 6513, printed circuit board 6517, and battery 6518 are arranged in the space enclosed by the housing 6501 and the protective member 6510.

[0379] The protective member 6510 is fixed to the display panel 6511, the optical member 6512, and the touch sensor panel 6513 by an adhesive layer (not shown).

[0380] In the area outside the display unit 6502, a portion of the display panel 6511 is folded back, and the FPC 6515 is connected to this folded portion. IC 6516 is mounted on the FPC 6515. The FPC 6515 is connected to terminals provided on the printed circuit board 6517.

[0381] A display device according to one embodiment of the present invention can be applied to the display panel 6511. This makes it possible to realize an extremely lightweight electronic device. Furthermore, because the display panel 6511 is extremely thin, it is possible to incorporate a large-capacity battery 6518 while keeping the thickness of the electronic device low. In addition, by folding back a part of the display panel 6511 and placing the connection part with the FPC 6515 on the back of the pixel section, an electronic device with a narrow bezel can be realized.

[0382] Figure 16(C) shows an example of a television system. The television system 7100 has a display unit 7000 incorporated into a housing 7171. Here, the housing 7171 is shown supported by a stand 7173.

[0383] A display device according to one aspect of the present invention can be applied to the display unit 7000. Therefore, an electronic device with low power consumption and long operating time can be obtained.

[0384] The television device 7100 shown in Figure 16(C) can be operated using the operation switches on the housing 7171 and a separate remote control unit 7151.

[0385] Figure 16(D) shows an example of a notebook personal computer. The notebook personal computer 7200 has a casing 7211, a keyboard 7212, a pointing device 7213, and an external connection port 7214, etc. A display unit 7000 is incorporated into the casing 7211.

[0386] A display device according to one aspect of the present invention can be applied to the display unit 7000. Therefore, an electronic device with low power consumption and long operating time can be obtained.

[0387] Figures 16(E) and 16(F) show examples of digital signage.

[0388] The digital signage 7300 shown in Figure 16(E) comprises a housing 7301, a display unit 7000, and a speaker 7303, etc. Furthermore, it may include LED lamps, operation keys (including a power switch or operation switch), connection terminals, various sensors, a microphone, etc.

[0389] Figure 16(F) shows a digital signage 7400 mounted on a cylindrical column 7401. The digital signage 7400 has a display unit 7000 that is provided along the curved surface of the column 7401.

[0390] In Figures 16(E) and 16(F), a display device according to one embodiment of the present invention can be applied to the display unit 7000. Therefore, a highly reliable electronic device can be made.

[0391] The larger the display area 7000, the more information can be provided at once. Furthermore, a larger display area 7000 is more eye-catching, which can, for example, enhance the effectiveness of advertising.

[0392] Furthermore, as shown in Figures 16(E) and 16(F), it is preferable that the digital signage 7300 or digital signage 7400 can be linked wirelessly with an information terminal 7311 or information terminal 7411 such as a smartphone owned by the user.

[0393] The electronic equipment shown in Figures 17(A) to 17(G) includes a housing 9000, a display unit 9001, a speaker 9003, operation keys 9005 (including a power switch or operation switch), connection terminals 9006, sensors 9007 (including functions for measuring force, displacement, position, velocity, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared radiation), a microphone 9008, etc.

[0394] The electronic devices shown in Figures 17(A) to 17(G) have various functions. For example, they may have functions to display various information (still images, videos, text images, etc.) on a display unit, a touch panel function, a function to display a calendar, date or time, a function to control processing by various software (programs), a wireless communication function, a function to read and process programs or data recorded on a recording medium, etc.

[0395] The details of the electronic equipment shown in Figures 17(A) through 17(G) will be explained below.

[0396] Figure 17(A) is a perspective view showing a personal digital information terminal (PDI) 9171. The PDI 9171 can be used, for example, as a smartphone. The PDI 9171 may also be equipped with a speaker 9003, a connection terminal 9006, or a sensor 9007. Furthermore, the PDI 9171 can display text and image information on multiple surfaces. Figure 17(A) shows an example where three icons 9050 are displayed. Information 9051, indicated by a dashed rectangle, can also be displayed on other surfaces of the display unit 9001. Examples of information 9051 include notifications of incoming emails, SNS messages, phone calls, etc., the subject of emails or SNS messages, the sender's name, date and time, time, battery level, signal strength, etc. Alternatively, icons 9050, etc., may be displayed in the position where the information 9051 is displayed.

[0397] Figure 17(B) is a perspective view showing the personal digital assistant (PDA) 9172. The PDA 9172 has the function of displaying information on three or more sides of the display unit 9001. Here, an example is shown in which information 9052, information 9053, and information 9054 are displayed on different sides. For example, a user can check information 9053, which is displayed in a position that can be observed from above the PDA 9172, while the PDA 9172 is stored in the breast pocket of their clothing.

[0398] Figure 17(C) is a perspective view showing the tablet terminal 9173. The tablet terminal 9173 can run various applications, such as mobile phone calls, email, document viewing and creation, music playback, internet communication, and computer games. The tablet terminal 9173 has a display unit 9001, a camera 9002, a microphone 9008, and a speaker 9003 on the front of the housing 9000. Operation keys 9005 are located on the left side of the housing 9000, and connection terminals 9006 are located on the bottom.

[0399] Figure 17(D) is a perspective view showing a wristwatch-type personal information terminal 9200. The personal information terminal 9200 can be used, for example, as a smartwatch (registered trademark). The display unit 9001 has a curved display surface, allowing it to display information along the curved surface. The personal information terminal 9200 can also make hands-free calls by communicating with, for example, a wireless communication headset. Furthermore, the personal information terminal 9200 can transmit data to other information terminals and be charged via the connection terminal 9006. Charging may be performed by wireless power supply.

[0400] Figures 17(E) to 17(G) are perspective views showing a foldable portable information terminal 9201. Figure 17(E) shows the portable information terminal 9201 in an unfolded state, Figure 17(G) shows it in a folded state, and Figure 17(F) shows a state in between, transitioning from one of Figures 17(E) or 17(G) to the other. The portable information terminal 9201 offers excellent portability in its folded state and excellent readability of the display due to its seamless, wide display area in its unfolded state. The display unit 9001 of the portable information terminal 9201 is supported by three housings 9000 connected by hinges 9055. For example, the display unit 9001 can be bent with a radius of curvature of 0.1 mm to 150 mm.

[0401] This embodiment can be appropriately combined with other embodiments or examples. Furthermore, if multiple configuration examples are shown within a single embodiment in this specification, these configuration examples can be appropriately combined. [Examples]

[0402] In this example, the detailed manufacturing methods and characteristics of light-emitting devices 1-1, 1-2, and comparative light-emitting devices 1-1 to 1-3 will be described. The structural formulas of the main compounds used in this example are shown below.

[0403] [ka]

[0404] (Method for fabricating light-emitting device 1-1) First, a film of indium tin oxide (ITSO) containing silicon oxide was deposited on a glass substrate by sputtering to a thickness of 55 nm, forming a first electrode 101 measuring 2 mm x 2 mm. The ITSO functions as an anode.

[0405] Next, as a pretreatment for forming a light-emitting device on the substrate, the substrate surface was washed with water.

[0406] After that, approximately 1 × 10-4 The substrate was introduced into a vacuum deposition apparatus where the internal pressure was reduced to Pa. After vacuum firing at 170°C for 30 minutes in the heating chamber of the vacuum deposition apparatus, the substrate was allowed to cool for approximately 30 minutes.

[0407] Next, the substrate was fixed to a holder provided in the vacuum deposition apparatus so that the surface on which the first electrode 101 was formed was facing downwards. On the first electrode 101, a hole injection layer 111 was formed by co-depositing N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviated as PCBBiF), represented by the above structural formula (i), and an electron acceptor material (OCHD-003) containing fluorine with a molecular weight of 672, in a weight ratio of 1:0.03 (=PCBBiF:OCHD-003) and with a film thickness of 10 nm.

[0408] After depositing PCBBiF onto the hole injection layer 111 to a thickness of 45 nm, a hole transport layer 112 was formed by depositing 9-[3-(triphenylsilyl)phenyl]-3,9′-bi-9H-carbazole (abbreviated as PSiCzCz), represented by the above structural formula (ii), to a thickness of 5 nm. The PSiCzCz layer is an organic compound having a π-electron-rich heteroaromatic ring and also functions as an electron blocking layer.

[0409] Next, on the hole transport layer, 9,9'-{6-[3-(triphenylsilyl)phenyl]-1,3,5-triazine-2,4-diyl}bis(9H-carbazole) (abbreviated as SiTrzCz2), represented by the above structural formula (iii), PSiCzCz, and (2-{3-[3-(3,5-di-tert-butylphenyl)benzimidazole-1-yl-2-ylidene-κC2]phenoxy-κC2}-9-(4-tert-butyl-2-pyridinyl-κN)carbazole- represented by the above structural formula (iv) A light-emitting layer 113 was formed by co-depositing 2,1-diyl-κC1)platinum(II) (abbreviated as PtON-TBBI) and N,N,N',N'-tetrakis(3,5-di-tert-butylphenyl)pyrene-1,6-diamine (abbreviated as 1,6mmtBuDPhAPrn), represented by the above structural formula (v), in a weight ratio of 0.35:0.53:0.12:0.015 (=SiTrzCz2:PSiCzCz:PtON-TBBI:1,6mmtBuDPhAPrn) and with a film thickness of 40 nm.

[0410] PtON-TBBI is an organometallic complex that exhibits blue phosphorescence, while 1,6mmtBuDPhAPrn is an organic compound that exhibits blue fluorescence. Furthermore, PtON-TBBI has a tert-butyl group, which is a C4 alkyl group. 1,6mmtBuDPhAPrn is an organic compound that has a pyrene skeleton, which is a condensed aromatic ring, as its luminescent phosphodiester, and has eight tert-butyl groups, which are C4 alkyl groups.

[0411] Note that SiTrzCz2 is an organic compound having a π-electron-deficient heteroaromatic ring, while PSiCzCz is an organic compound having a π-electron-rich heteroaromatic ring.

[0412] Next, 2-phenyl-4,6-bis[3-(triphenylsilyl)phenyl]-1,3,5-triazine (abbreviated as mSiTrz), represented by the above structural formula (vi), was deposited to a thickness of 5 nm to form a first electron transport layer. Then, 11-[4-(biphenyl-4-yl)-6-phenyl-1,3,5-triazine-2-yl]-11,12-dihydro-12-phenylindoro[2,3-a]carbazole (abbreviated as BP-Icz(II)Tzn), represented by the above structural formula (vii), and 8-quinolinolato-lithium (abbreviated as Liq), represented by the above structural formula (viii), were co-deposited in a weight ratio of 1:4 (=BP-Icz(II)Tzn:Liq) to a thickness of 30 nm to form a second electron transport layer. Furthermore, mSiTrz and BP-Icz(II)Tzn are organic compounds having π-electron-deficient heteroaromatic rings, Liq is an organometallic complex containing an alkali metal, and the first electron transport layer is a layer that also functions as a hole blocking layer.

[0413] After the electron transport layer was formed, lithium fluoride (abbreviated as LiF) was deposited to a thickness of 1 nm to form an electron injection layer 115, and then aluminum (abbreviated as Al) was deposited to a thickness of 200 nm to form a second electrode 102 (cathode).

[0414] Next, in a glove box under a nitrogen atmosphere, the light-emitting device was sealed with a glass substrate to prevent exposure to the atmosphere (applying a UV-curable sealant around the element, irradiating only the sealant with UV light without irradiating the light-emitting device, and heat-treating at 80°C for 1 hour under atmospheric pressure) to form light-emitting device 1-1.

[0415] (Method for fabricating light-emitting devices 1-2) Light-emitting device 1-2 was fabricated in the same manner as light-emitting device 1-1, except that SiTrzCz2 in the light-emitting layer of light-emitting device 1-1 was replaced with 9,9'-{6-[3-(triphenylsilyl)phenyl]-1,3,5-triazine-2,4-diyl}bis(9H-carbazole-1,2,3,4,5,6,7,8,1',2',3',4',5',6',7',8'-d16) (abbreviated as SiTrzCz2-d16), represented by the above structural formula (xi), and PSiCzCz was replaced with 9-[3-(triphenylsilyl)phenyl]-3,9'-(bi-9H-carbazole-d15) (abbreviated as PSiCzCz-d15), represented by the above structural formula (xii).

[0416] (Method for fabricating comparative light-emitting device 1-1) Comparative light-emitting device 1-1 was fabricated in the same manner as light-emitting device 1-1, except that the second electron transport layer was formed of 2,2'-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviated as mPPhen2P) represented by the above structural formula (ix).

[0417] (Method for fabricating comparative light-emitting devices 1-2) Comparative light-emitting device 1-2 was fabricated in the same manner as comparative light-emitting device 1-1, except that the light-emitting layer was formed in a weight ratio of SiTrzCz2:PSiCzCz:PtON-TBBI:1,6mmtBuDPhAPrn=0.35:0.53:0.12:0, i.e., without using 1,6mmtBuDPhAPrn.

[0418] (Method for fabricating comparative light-emitting devices 1-3) Comparative light-emitting device 1-3 was fabricated in the same manner as light-emitting device 1-1, except that the light-emitting layer was formed in the weight ratio of SiTrzCz2:PSiCzCz:PtON-TBBI:1,6mmtBuDPhAPrn=0.35:0.53:0.12:0, i.e., without using 1,6mmtBuDPhAPrn.

[0419] The device structures of light-emitting device 1-1, light-emitting device 1-2, comparative light-emitting device 1-1, comparative light-emitting device 1-2, and comparative light-emitting device 1-3 are shown in the table below.

[0420] [Table 3]

[0421] Figure 19 shows the luminance-current density characteristics, Figure 20 shows the luminance-voltage characteristics, Figure 21 shows the current efficiency-current density characteristics, Figure 22 shows the current density-voltage characteristics, Figure 23 shows the external quantum efficiency-current density characteristics, and Figure 24 shows the field emission spectra for light-emitting devices 1-1, 1-2, 1-1, 1-2, and 1-3. 2 Table 4 shows the main characteristics of the device. A spectroradiometer (Topcon SR-UL1R) was used to measure luminance, CIE chromaticity, and field emission spectrum at room temperature. The external quantum efficiency was calculated using the measured luminance and emission spectrum, assuming a Lambertsian optical distribution pattern.

[0422] The Blue Index (BI) is a value obtained by dividing the current efficiency (cd / A) by the y value of the CIE(x,y) chromaticity, and is one of the indicators that represent the emission characteristics of blue light. Blue light tends to have higher color purity as the chromaticity y value decreases. By using blue light with a small chromaticity y value and high color purity, it becomes possible to express a wide range of blue colors in a display, and the brightness of blue required to express white in the display decreases, resulting in the effect of reducing the power consumption of the display. For this reason, the BI, which is a current efficiency that takes into account the chromaticity y value, one of the indicators of blue purity, is sometimes suitably used as a means of representing the efficiency of blue light emission, and it can be said that light-emitting devices with a high BI are more efficient as blue light-emitting devices used in displays.

[0423] [Table 4]

[0424] Figure 24 shows that the peak wavelength of the electroluminescence spectra of light-emitting device 1-1, light-emitting device 1-2, and comparative light-emitting device 1-1 is 471 nm and the full width at half maximum is 47 nm, while the peak wavelength of the electroluminescence spectra of comparative light-emitting device 1-2 and comparative light-emitting device 1-3 is 463 nm and the full width at half maximum is 45 nm. The emission spectra of light-emitting device 1-1, light-emitting device 1-2, and comparative light-emitting device 1-1 are different from those of comparative light-emitting device 1-2 and comparative light-emitting device 1-3, indicating that light-emitting device 1-1, light-emitting device 1-2, and comparative light-emitting device 1-1 emit light from the fluorescent material 1,6 mmtBuDPhAPrn.

[0425] Furthermore, as shown in Figure 23, despite the fact that light-emitting devices 1-1, 1-2, and comparative light-emitting device 1-1 emit light from the fluorescent material 1,6mmtBuDPhAPrn as described above, they exhibit an external quantum efficiency of over 20% at its maximum. Thus, by using the phosphorescent material PtON-TBBI as an energy donor, light-emitting devices 1-1, 1-2, and comparative light-emitting device 1-1 were made into light-emitting devices that exhibit high efficiency, with an external quantum efficiency exceeding 20%, despite being fluorescent light-emitting devices.

[0426] Next, light-emitting device 1-1, light-emitting device 1-2, comparison light-emitting device 1-1, comparison light-emitting device 1-2, and comparison light-emitting device 1-3 were tested at 10 mA / cm². 2 Figure 25 shows the time-dependent characteristics of the normalized brightness when driven at the specified current density, and Figure 26 shows a graph of the elapsed time (LT90) until the brightness decreased to 90% of the initial brightness for each light-emitting device in this measurement. Note that the time-dependent characteristics of the normalized brightness are shown with the initial brightness set to 100%.

[0427] As shown in Figures 25 and 26, a light-emitting device 1-1 according to one embodiment of the present invention, in which the GSP_Slope of the second electron transport layer is high and the light-emitting layer contains both PtON-TBBI (phosphorescent material) and 1,6mmtBuDPhAPrn (fluorescent material), showed very good characteristics at LT90, approximately 1.7 times better than comparative light-emitting devices 1-1 and 1-3, and approximately 2.5 times better than comparative light-emitting device 1-2. Light-emitting device 1-2 showed very good characteristics, approximately 2.1 times better than comparative light-emitting devices 1-1 and 1-3, and approximately 3.2 times better than comparative light-emitting device 1-2.

[0428] Figure 18 shows the emission spectra (PL spectra) and absorption spectra of PtON-TBBI, a material capable of converting the triplet excitation energy in the fabricated light-emitting device 1 and comparative light-emitting device 1-1 into light emission, and 1,6mm tBuDPhAPrn, a fluorescent material. For PtON-TBBI, the emission spectrum was measured using a spectrofluorometer (FP-8600DS, JASCO Corporation) and the absorption spectrum was measured using a UV-Vis spectrofluorometer (V-770DS, JASCO Corporation) in a dichloromethane solution. For 1,6mm tBuDPhAPrn, the emission spectrum was measured using a fluorometer (FS920, Hamamatsu Photonics Ltd.) and the absorption spectrum was measured using a UV-Vis spectrofluorometer (V-550DS, JASCO Corporation) in a toluene solution.

[0429] As shown in Figure 18, the peak wavelength (456 nm) in the emission spectrum of PtON-TBBI is at a shorter wavelength than the peak wavelength (467 nm) in the emission spectrum of 1,6 mmtBuDPhAPrn. Alternatively, the long-wavelength absorption edge (465 nm) in the absorption spectrum of 1,6 mmtBuDPhAPrn is at a longer wavelength than the short-wavelength emission edge (441 nm) in the emission spectrum of PtON-TBBI. Alternatively, the long-wavelength absorption edge (465 nm) in the absorption spectrum of 1,6 mmtBuDPhAPrn is at a longer wavelength than the long-wavelength absorption edge (457 nm) in the absorption spectrum of PtON-TBBI.

[0430] In the light-emitting device 1 and comparative light-emitting device 1-1 having such a configuration, energy transfer occurs efficiently from PtON-TBBI, a material capable of converting triplet excitation energy into light emission in the light-emitting layer, to the fluorescent material 1,6mmtBuDPhAPrn. This configuration allows for a light-emitting device that exhibits high luminescence efficiency while being composed of a fluorescent material that emits light.

[0431] Furthermore, Figures 37(A) and 37(B) show the results of low-temperature PL measurements of SiTrzCz2 and PSiCzCz, which are host materials for the fabricated light-emitting devices, and Figures 47(A) and 47(B) show the results of low-temperature PL measurements of SiTrzCz2-d16 and PSiCzCz-d15. For the measurements, a LabRAM HR-PL micro-PL system (Horiba, Ltd.) was used, with a measurement temperature of 10K, a He-Cd laser (wavelength 325nm) as the excitation light, and a CCD detector. The measurement samples were thin films, with the target film deposited on a quartz substrate to a thickness of 50nm. Another quartz substrate was then attached to the deposited quartz substrate from the deposition side in a nitrogen atmosphere before being used for measurement.

[0432] As shown in Figures 37(A) and 37(B), the wavelength of the short-wavelength emission edge of the emission spectrum in low-temperature PL measurements is 424 nm for SiTrzCz2 and 418 nm for PSiCzCz. Therefore, the T1 levels of SiTrzCz2 and PSiCzCz are 2.92 eV and 2.97 eV, respectively, with an energy difference of 0.05 eV. When these materials are used as host materials, the energy difference of the T1 levels between host materials is 0.20 eV or less. Thus, the light-emitting device fabricated in this embodiment exhibits a small bias in triplet excitation energy between host materials, making it possible to produce a highly reliable light-emitting device.

[0433] Furthermore, as shown in Figures 47(A) and 47(B), the wavelength of the short-wavelength emission edge of the emission spectrum in low-temperature PL measurements is 423 nm for SiTrzCz2-d16 and 417 nm for PSiCzCz-d15. Therefore, the T1 levels of SiTrzCz2-d16 and PSiCzCz-d15 are 2.93 eV and 2.97 eV, respectively, with an energy difference of 0.05 eV. When these materials are used as host materials, the energy difference of the T1 levels between host materials is 0.20 eV or less. As a result, the light-emitting device fabricated in this embodiment exhibits a small bias in triplet excitation energy between host materials, making it possible to produce a highly reliable light-emitting device. In addition, the light-emitting device in this embodiment uses a deuterated material as the host material. The use of a deuterated material as the host material improves the reliability of the light-emitting device. The improvement in reliability when using a deuterated host material is related to the extension of the lifetime of the triplet excitons in the host material. The extended lifetime of triplet excitons is due to the suppression of non-radiative deactivation of the triplet excitation energy, which results from the suppression of vibrations by deuteration. In this case, the small energy difference between the T1 levels of SiTrzCz2-d16 and PSiCzCz-d15 makes it less likely for the excitation energy to be biased towards one of the organic compounds, preventing significant degradation of one of them, and thus improving the reliability of the light-emitting device, which is preferable.

[0434] Furthermore, as shown in Figure 18, the wavelength of the short-wavelength emission edge of the PtON-TBBI emission spectrum is 441 nm, and the T1 level of PtON-TBBI is estimated to be 2.81 eV. As mentioned above, the T1 levels of the host materials SiTrzCz2 and PSiCzCz are 2.92 eV and 2.97 eV, respectively, so the T1 level of PtON-TBBI is lower than that of SiTrzCz2 and PSiCzCz. The light-emitting device 1-1 and comparative light-emitting devices 1-1 to 1-3 fabricated in this embodiment, having such a configuration, efficiently transfer energy from the host material to a material capable of converting triplet excitation energy into light emission, thus enabling light-emitting devices with high luminescence efficiency and good reliability.

[0435] Furthermore, since the T1 levels of the host materials SiTrzCz2-d16 and PSiCzCz-d15 are 2.93 eV and 2.97 eV, respectively, the T1 level of PtON-TBBI is lower than that of SiTrzCz2-d16 and PSiCzCz-d15. The light-emitting devices 1-2 fabricated in this embodiment, having such a configuration, efficiently transfer energy from the host material to a material capable of converting triplet excitation energy into light emission, thus enabling a light-emitting device with high luminescence efficiency and good reliability.

[0436] Figure 38 also shows the emission spectra (PL spectra) of a mixed film of SiTrzCz2 and PSiCzCz in a 1:1 (weight ratio) ratio, and of the individual films. The measurements were performed using a spectrofluorometer (FP-8600DS, JASCO Corporation). As shown in Figure 38, the mixed film of SiTrzCz2 and PSiCzCz exhibited emission spectra that were shifted to longer wavelengths, different from the emission spectra of either individual film, indicating that SiTrzCz2 and PSiCzCz are a combination that forms an excited complex.

[0437] Furthermore, Figure 48 shows the emission spectra of a 1:1 (weight ratio) mixed film of SiTrzCz2-d16 and PSiCzCz-d15, as well as the individual films. As shown in Figure 48, the mixed film of SiTrzCz2-d16 and PSiCzCz-d15 exhibits emission spectra that are shifted to longer wavelengths and differ from the emission spectra of either individual film. This indicates that SiTrzCz2-d16 and PSiCzCz-d15 are a combination that forms an excited complex.

[0438] Next, Table 5 shows the GSP_Slope of the organic compound having a π-electron-deficient heteroaromatic ring used in the first electron transport layer of light-emitting device 1-1, light-emitting device 1-2, comparative light-emitting device 1-1, comparative light-emitting device 1-2, and comparative light-emitting device 1-3, the organic compound having a π-electron-deficient heteroaromatic ring used in the second electron transport layer, the organic compound having a π-electron-rich heteroaromatic ring or aromatic amine used in the hole transport layer, and the vapor-deposited film of the host material used in the light-emitting layer. Note that in Table 5, the GSP_Slope was measured by the method shown in Embodiment 1.

[0439] [Table 5]

[0440] Thus, in comparative light-emitting devices 1-1 and 1-2, the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the second electron transport layer is smaller than the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the first electron transport layer. In this configuration, electrons are well injected from the electrode or electron injection layer to the interface of the first electron transport layer. On the other hand, in light-emitting devices 1-1, 1-2, and 1-3, the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the second electron transport layer is larger than the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the first electron transport layer. As a result, in light-emitting devices 1 and 1-3, the injection of electrons from the electrode or electron injection layer to the second electron transport layer is suppressed.

[0441] Typically, in emissive layers containing blue phosphorescent material, the HOMO and LUMO levels of the blue phosphorescent material are both higher than those of the host material. This traps holes but not electrons, causing the recombination region to be biased towards the anode side of the emissive layer. When the recombination region is biased towards the anode side, the density of excitons generated after recombination also increases on the anode side of the emissive layer. This makes it easier for exciton interactions and interactions between excitons and holes in the electron blocking layer to occur, leading to the generation of very high-energy excitons or holes. These high-energy excitons or holes accelerate the degradation of the emissive layer and the electron blocking layer adjacent to it.

[0442] In one embodiment of the present invention, as described above, electron injection is suppressed due to the high GSP_Slope of the second electron transport layer. This allows the recombination region, which tends to be biased towards the anode side of the light-emitting layer, to be extended to the cathode side as well, thereby suppressing the degradation of the hole transport layer, which functions as an electron blocking layer. As a result, comparative light-emitting devices 1-3 showed improved reliability compared to comparative light-emitting devices 1-2, and light-emitting device 1 showed improved reliability compared to comparative light-emitting device 1-1.

[0443] In the light-emitting device 1-1, comparative light-emitting device 1-1, comparative light-emitting device 1-2, and comparative light-emitting device 1-3 fabricated in this embodiment, the HOMO level of PSiCzCz used as the host material in the light-emitting layer is -5.7 eV and the LUMO level is -2.06 eV. The HOMO level of SiTrzCz2 is lower than that of PSiCzCz, with a LUMO level of -2.98 eV. The HOMO level of PtON-TBBI, which was added in a small amount (12 wt%) in the light-emitting layer as a blue phosphorescent material, is -5.50 eV and the LUMO level is -2.3 eV. Therefore, the HOMO level of PtON-TBBI is higher than that of the host material, resulting in a configuration that easily traps holes.

[0444] In light-emitting devices 1-2, the HOMO level of PSiCzCz-d16 used as the host material in the light-emitting layer is -5.7eV and the LUMO level is -2.05eV. The HOMO level of SiTrzCz2-d16 is lower than that of PSiCzCz-d16, with a LUMO level of -2.98eV. The HOMO level of PtON-TBBI, which was added in a small amount (12wt%) in the light-emitting layer as a blue phosphorescent material, is -5.50eV and the LUMO level is -2.3eV. Therefore, the HOMO level of PtON-TBBI is higher than that of the host material, resulting in a configuration that easily traps holes.

[0445] Furthermore, since the HOMO level of 1,6mmtBuDPhAPrn added in a trace amount (1.5wt%) as a fluorescent material in light-emitting devices 1-1, 1-2, and comparative light-emitting device 1-1 is -5.30eV, 1,6mmtBuDPhAPrn also easily traps holes. Moreover, since the HOMO level of the fluorescent material is higher than that of the phosphorescent material, and the amount of fluorescent material added is less than the amount of phosphorescent material added, the fluorescent material in the light-emitting layer is configured to further trap holes that have been trapped by the phosphorescent material. Therefore, in the light-emitting layer, holes are easily trapped strongly, and the hole transportability tends to be low. For this reason, by applying the configuration of one aspect of the present invention and suppressing electron injection, the decrease in reliability can be greatly suppressed, and a light-emitting device with good reliability can be obtained.

[0446] The HOMO and LUMO levels were determined by cyclic voltammetry (CV) measurements.

[0447] In cyclic voltammetry (CV) measurements, the HOMO and LUMO levels (E) were calculated based on the oxidation peak potential (Epa) and reduction peak potential (Epc) obtained by changing the potential of the working electrode relative to the reference electrode. The HOMO level was determined from the positive potential scan, and the LUMO level from the negative potential scan. The scan speed was set to 0.1 V / s.

[0448] Specifically, the standard redox potential (Eo) (=(Epa+Epc) / 2) was determined from the oxidation peak potential (Epa) and reduction peak potential (Epc) obtained from the cyclic voltammogram of the material. The values ​​of the HOMO and LUMO levels (E) (=Ex-Eo) were then determined by subtracting this from the potential energy (Ex) of the reference electrode relative to the vacuum level.

[0449] The above describes the case where a reversible redox wave is obtained. However, when an irreversible redox wave is obtained, the HOMO level is calculated by assuming that the reduction peak potential (Epc) is obtained by subtracting a certain value (0.1 eV) from the oxidation peak potential (Epa), and the standard redox potential (Eo) is calculated to one decimal place. Similarly, the LUMO level is calculated by assuming that the oxidation peak potential (Epa) is obtained by adding a certain value (0.1 eV) to the reduction peak potential (Epc), and the standard redox potential (Eo) is calculated to one decimal place.

[0450] Here, we show the results of transient EL measurements of light-emitting device 1-1, comparative light-emitting device 1-3, and light-emitting device 1-3. Light-emitting device 1-3 is a light-emitting device fabricated using N,N,N',N'-tetra(3-methylphenyl)pyrene-1,6-diamine (abbreviation: 1,6mMeDPhAPrn), represented by the following structural formula (xviii), instead of 1,6mmtBuDPhAPrn used in light-emitting device 1-1.

[0451] [ka]

[0452] A picosecond fluorescence lifetime measurement system (Hamamatsu Photonics) was used for the measurement. In this measurement, a rectangular pulse voltage of 101.5 μs was applied to the light-emitting device, and the emission that decayed from the falling edge of the voltage was measured with time resolution using a streak camera. The measurement was performed at room temperature (300 K), and the brightness of the light-emitting device was 2500 cd / m². 2The applied pulse voltage was set to approximately 6.8V to 8.2V to achieve the desired result, with an applied pulse duration of 101.5μs, a negative bias voltage of -5V (when the element drive was OFF), and a measurement time range of 10μs. The measurement results are shown in Figure 49. In Figure 49, the vertical axis represents the intensity normalized by the maximum luminescence intensity, and the horizontal axis represents the elapsed time from the falling edge of the pulse voltage.

[0453] In the decay curve shown in Figure 49, it was found that the luminescence decay times of light-emitting devices 1-1 and 1-3 were shorter than those of comparative light-emitting device 1-3. This was possible because light-emitting devices 1-1 and 1-3 are configured to emit light using fluorescent materials, thus shortening the luminescence decay time.

[0454] In addition to light-emitting device 1-1, light-emitting device 1-2 and comparative light-emitting device 1-1 are also configured to emit light from a fluorescent material. Compared to phosphorescent material, fluorescent material has a faster emission rate constant and a shorter excited state lifetime, resulting in higher stability against degradation. Furthermore, the energy transfer rate when the excitation energy of the phosphorescent material is transferred to the fluorescent material exceeds the emission rate of the phosphorescent material, thus increasing stability against degradation. As a result, comparative light-emitting device 1-1, which is configured to emit light from a fluorescent material, is more reliable than comparative light-emitting device 1-2, and light-emitting device 1-1 is more reliable than comparative light-emitting device 1-3. In addition, light-emitting devices 1-1, 1-2, 1-3, and comparative light-emitting device 1-1 emit light from a fluorescent material through energy transfer from the phosphorescent material. In this case, particularly in light-emitting devices 1-1, 1-2, and comparative light-emitting device 1-1, the presence of a protecting group in the fluorescent material suppresses energy transfer via the Dexter mechanism, leading to a dominance of energy transfer via the Förster mechanism. This suppresses triplet excitation energy transfer from the T1 level of the phosphorescent material to the T1 level (non-luminescent) of the fluorescent material due to energy transfer via the Dexter mechanism, thus preventing a decrease in luminescence efficiency. As a result, despite being a light-emitting device that obtains light from a fluorescent material, it exhibits excellent characteristics with an external quantum efficiency exceeding 20%.

[0455] Here, considering that the LT90 of comparative light-emitting devices 1-1 and 1-3 are approximately 1.5 times that of comparative light-emitting device 1-2, as shown in Figure 26, the improvement in LT90 from increasing the GSP_Slope of the second electron transport layer and from including phosphorescent and fluorescent materials in the light-emitting layer can be estimated to be about 1.5 times, respectively. On the other hand, the LT90 of light-emitting device 1-1 was approximately 1.7 times that of comparative light-emitting devices 1-1 and 1-3. This means that reliability is further improved by having both the configuration with a high GSP_Slope of the second electron transport layer and the configuration with phosphorescent and fluorescent materials in the light-emitting layer, indicating that there is a synergistic effect in this combination of configurations.

[0456] Furthermore, it was found that light-emitting devices 1-2, which used a deuterated material as the host material for the light-emitting layer, exhibited even better reliability. This is because the bond dissociation energy of the carbon-deuterium bond is greater than that of the carbon-pneumatic bond, making it more stable and difficult to break. As a result, compounds containing deuterium are more stable and less prone to degradation compared to non-deuterated compounds.

[0457] Furthermore, in light-emitting devices 1-1, 1-2, and comparative light-emitting device 1-3, the second electron transport layer contains not only an organic compound having a π-electron-deficient heteroaromatic ring, but also Liq, a metal complex containing an alkali metal. When the weight ratio of the organic compound having a π-electron-deficient heteroaromatic ring to Liq in the second electron transport layer is x:y, the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the first electron transport layer multiplied by (x+y) / x is 51.5 (mV / nm). In other words, in light-emitting devices 1-1, 1-2, and comparative light-emitting device 1-3, the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the second electron transport layer is greater than the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the first electron transport layer multiplied by (x+y) / x.

[0458] Thus, when the weight ratio of the organic compound having a π-electron-deficient heteroaromatic ring in the second electron transport layer to Liq is x:y, a reliable light-emitting device can be provided if the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the second electron transport layer is greater than the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the first electron transport layer multiplied by (x+y) / x.

[0459] In the above-described light-emitting device, the GSP_Slope of the host material (SiTrzCz2 and PSiCzCz) film is larger than the GSP_Slope of the first organic compound film. Furthermore, the GSP_Slope of the light-emitting layer is larger than the GSP_Slope of the first electron transport layer.

[0460] This configuration allows a positive interfacial charge to be placed at the interface between the light-emitting layer and the first electron transport layer, thereby suppressing the electron injection barrier from the second electron transport layer to the first electron transport layer in the light-emitting device. As a result, even if electron injection into the second electron transport layer is suppressed, the light-emitting device does not cause a significant increase in the driving voltage, making it possible to create a light-emitting device with good characteristics.

[0461] Furthermore, BP-Icz(II)Tzn, an organic compound having a π-electron-deficient heteroaromatic ring, is included in the second electron transport layer of light-emitting devices 1-1, 1-2, and comparative light-emitting device 1-3, and has a larger GSP_Slope than the host material (SiTrzCz2 and PSiCzCz, etc.). Also, the GSP_Slope of the second electron transport layer is larger than the GSP_Slope of the light-emitting layer.

[0462] As a result, in light-emitting devices 1-1, 1-2, and comparative light-emitting device 1-3, the interface charge between the first electron transport layer and the second electron transport layer is negative and smaller than the interface charge between the light-emitting layer and the first electron transport layer. This effect suppresses the injection of electrons from the second electrode or electron injection layer into the second electron transport layer, and promotes the injection of holes into the light-emitting layer. Consequently, in light-emitting devices using blue phosphorescent materials, the recombination region, which tends to be biased towards the anode side, can be expanded, and the degradation of the hole transport layer, which functions as an electron blocking layer, can be further reduced.

[0463] Furthermore, the above-mentioned light-emitting device has a configuration in which the GSP_Slope of the light-emitting layer (a co-evaporated film of SiTrzCz2, PSiCzCz, PtON-TBBI, and 1,6mmtBuDPhAPrn, or a co-evaporated film of SiTrzCz2-d15, PSiCzCz-d16, PtON-TBBI, and 1,6mmtBuDPhAPrn) or the GSP_Slope of the host material film (a co-evaporated film of SiTrzCz2 and PSiCzCz, or a co-evaporated film of SiTrzCz2-d15 and PSiCzCz-d16) is larger than the GSP_Slope of the hole transport layer (a evaporated film of PCBBiF). Due to this relationship between the GSP_Slopes of the hole transport layer and the light-emitting layer, a negative interfacial charge can be established at at least one of the interfaces present between the hole transport layer and the light-emitting layer. This facilitates the injection of holes from the anode or hole injection layer to the vicinity of the light-emitting layer interface, making it possible to create a light-emitting device with a low driving voltage.

[0464] Thus, a light-emitting device according to one aspect of the present invention can be a light-emitting device with high reliability and good characteristics. [Examples]

[0465] In this example, the detailed manufacturing methods and characteristics of light-emitting device 2 and comparative light-emitting device 2 will be described. The structural formulas of the main compounds used in this example are shown below.

[0466] [ka]

[0467] (Method for fabricating light-emitting device 2) First, indium tin oxide (ITSO) containing silicon dioxide was layered onto a glass substrate by sputtering to a thickness of 55 nm, forming a first electrode 101 measuring 2 mm x 2 mm. The ITSO functions as an anode.

[0468] Next, as a pretreatment for forming a light-emitting device on the substrate, the substrate surface was washed with water.

[0469] After that, approximately 1 × 10 -4 The substrate was introduced into a vacuum deposition apparatus where the internal pressure was reduced to Pa. After vacuum firing at 170°C for 30 minutes in the heating chamber of the vacuum deposition apparatus, the substrate was allowed to cool for approximately 30 minutes.

[0470] Next, the substrate was fixed to a holder provided in the vacuum deposition apparatus so that the surface on which the first electrode 101 was formed was facing downwards. On the first electrode 101, a hole injection layer 111 was formed by co-depositing N-(biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviated as PCBBiF), represented by the above structural formula (i), and an electron acceptor material (OCHD-003) containing fluorine with a molecular weight of 672, in a weight ratio of 1:0.03 (=PCBBiF:OCHD-003) and with a film thickness of 10 nm.

[0471] After depositing PCBBiF onto the hole injection layer 111 to a thickness of 45 nm, a hole transport layer 112 was formed by depositing 9-[3-(triphenylsilyl)phenyl]-3,9′-bi-9H-carbazole (abbreviated as PSiCzCz), represented by the above structural formula (ii), to a thickness of 5 nm. The PSiCzCz layer is an organic compound having a π-electron-rich heteroaromatic ring and also functions as an electron blocking layer.

[0472] Next, on the hole transport layer, 9,9'-{6-[3-(triphenylsilyl)phenyl]-1,3,5-triazine-2,4-diyl}bis(9H-carbazole) (abbreviated as SiTrzCz2), represented by the above structural formula (iii), PSiCzCz, and (2-{3-[3-(3,5-di-tert-butylphenyl)benzimidazole-1-yl-2-ylidene-κC2]phenoxy-κC2}-9-[3,5-di(methyl-d3)-4-phenyl-2-pyridinyl-κN]carbazole-2,1-diyl-κC Platinum(II) (abbreviated as Pt(mmtBubOcz35dm4ppy-d6)) and N,N,N',N'-tetrakis(3,5-di-tert-butylphenyl)pyrene-1,6-diamine (abbreviated as 1,6mmtBuDPhAPrn), represented by the above structural formula (v), were co-deposited in a weight ratio of 0.35:0.53:0.12:0.015 (=SiTrzCz2:PSiCzCz:Pt(mmtBubOcz35dm4ppy-d6):1.6mmtBuDPhAPrn) and with a film thickness of 40 nm to form an emissive layer 113.

[0473] Pt(mmtBubOcz35dm4ppy-d6) is an organometallic complex that exhibits blue phosphorescence, and 1,6mmtBuDPhAPrn is an organic compound that exhibits blue fluorescence. Furthermore, Pt(mmtBubOcz35dm4ppy-d6) has a tert-butyl group, which is a C4 alkyl group. Furthermore, 1,6mmtBuDPhAPrn is an organic compound that has a pyrene skeleton, which is a condensed aromatic ring, as its luminescent phosphodiester, and has eight tert-butyl groups, which are C4 alkyl groups.

[0474] Note that SiTrzCz2 is an organic compound having a π-electron-deficient heteroaromatic ring, while PSiCzCz is an organic compound having a π-electron-rich heteroaromatic ring.

[0475] Next, 2-phenyl-4,6-bis[3-(triphenylsilyl)phenyl]-1,3,5-triazine (abbreviated as mSiTrz), represented by the above structural formula (vi), was deposited to a thickness of 5 nm to form a first electron transport layer. Then, 11-[4-(biphenyl-4-yl)-6-phenyl-1,3,5-triazine-2-yl]-11,12-dihydro-12-phenylindoro[2,3-a]carbazole (abbreviated as BP-Icz(II)Tzn), represented by the above structural formula (vii), and 8-quinolinolato-lithium (abbreviated as Liq), represented by the above structural formula (viii), were co-deposited in a weight ratio of 1:4 (=BP-Icz(II)Tzn:Liq) to a thickness of 30 nm to form a second electron transport layer. Furthermore, mSiTrz and BP-Icz(II)Tzn are organic compounds having π-electron-deficient heteroaromatic rings, Liq is an organometallic complex containing an alkali metal, and the first electron transport layer is a layer that also functions as a hole blocking layer.

[0476] After the electron transport layer was formed, lithium fluoride (abbreviated as LiF) was deposited to a thickness of 1 nm to form an electron injection layer 115, and then aluminum (abbreviated as Al) was deposited to a thickness of 200 nm to form a second electrode 102 (cathode).

[0477] Next, in a glove box under a nitrogen atmosphere, the light-emitting device was sealed with a glass substrate to prevent exposure to the atmosphere (applying a UV-curable sealant around the element, irradiating only the sealant with UV light without irradiating the light-emitting device, and heat-treating at 80°C for 1 hour under atmospheric pressure) to form light-emitting device 2.

[0478] (Method for fabricating comparative light-emitting device 2) Comparative light-emitting device 2 was fabricated in the same manner as light-emitting device 2, except that the second electron transport layer was formed of 2,2'-(1,3-phenylene)bis(9-phenyl-1,10-phenanthroline) (abbreviated as mPPhen2P) represented by the above structural formula (ix).

[0479] The device structures of light-emitting device 2 and comparative light-emitting device 2 are shown in the table below.

[0480] [Table 6]

[0481] Figure 27 shows the luminance-current density characteristics of light-emitting device 2 and comparative light-emitting device 2, Figure 28 shows the luminance-voltage characteristics, Figure 29 shows the current efficiency-current density characteristics, Figure 30 shows the current density-voltage characteristics, Figure 31 shows the blue index-current density characteristics, Figure 32 shows the external quantum efficiency-current density characteristics, and Figure 33 shows the field emission spectrum. Furthermore, the current density is 10 mA / cm². 2 The chromaticity diagram is shown in Figure 34, and the main characteristics are shown in Table 7. A spectroradiometer (Topcon SR-UL1R) was used to measure luminance, CIE chromaticity, and the field emission spectrum at room temperature. The external quantum efficiency was calculated using the measured luminance and emission spectrum, assuming a Lambertsian optical distribution pattern.

[0482] [Table 7]

[0483] Furthermore, as shown in Figure 32, both the light-emitting device 2 and the comparative light-emitting device 2 exhibited an external quantum efficiency exceeding 20% ​​despite the emission of light by the fluorescent material 1,6mmtBuDPhAPrn. Thus, both the light-emitting device 2 and the comparative light-emitting device 2 were able to become light-emitting devices that exhibit high efficiency, with an external quantum efficiency exceeding 20%, despite being fluorescent light-emitting devices, by using the phosphorescent material Pt(mmtBubOcz35dm4ppy-d6) as an energy donor and the fluorescent material 1,6mmtBuDPhAPrn, which has a protecting group, as the light-emitting material, while still being fluorescent light-emitting devices.

[0484] Next, the 10mA / cm² values ​​for light-emitting device 2 and comparison light-emitting device 2. 2Figure 35 shows the time-dependent characteristics of the normalized brightness when driven by [the specified method]. In this measurement, the elapsed time (LT90) until the brightness decreased to 90% of the initial brightness was 54 hours for light-emitting device 2 and 35 hours for comparison light-emitting device 2. Note that the time-dependent characteristics of the normalized brightness are shown with the initial brightness set to 100%.

[0485] Figure 36 shows the emission spectra (PL spectra) and absorption spectra of Pt(mmtBubOcz35dm4ppy-d6), a material capable of converting the triplet excitation energy in the fabricated light-emitting device 2 and the comparative light-emitting device 2 into light emission, and the fluorescent material 1,6mmtBuDPhAPrn. For Pt(mmtBubOcz35dm4ppy-d6), the emission spectrum was measured using a spectrofluorometer (JASCO FP-8600DS) and the absorption spectrum was measured using a UV-Vis spectrofluorometer (JASCO V-770DS) in a dichloromethane solution. For 1,6mmtBuDPhAPrn, the emission spectrum was measured using a fluorometer (Hamamatsu Photonics FS920) and the absorption spectrum was measured using a UV-Vis spectrofluorometer (JASCO V-550DS) in a toluene solution.

[0486] As shown in Figure 36, the peak wavelength (461 nm) in the emission spectrum of Pt(mmtBubOcz35dm4ppy-d6) is at a shorter wavelength than the peak wavelength (467 nm) in the emission spectrum of 1,6mmtBuDPhAPrn. Alternatively, the long-wavelength absorption edge (465 nm) in the absorption spectrum of 1,6mmtBuDPhAPrn is at a longer wavelength than the short-wavelength emission edge (445 nm) in the emission spectrum of Pt(mmtBubOcz35dm4ppy-d6). Alternatively, the long-wavelength absorption edge (465 nm) in the absorption spectrum of 1,6mmtBuDPhAPrn is at a longer wavelength than the long-wavelength absorption edge (463 nm) in the absorption spectrum of Pt(mmtBubOcz35dm4ppy-d6).

[0487] In a light-emitting device 2 and a comparative light-emitting device 2 having such a configuration, energy transfer from Pt(mmtBubOcz35dm4ppy-d6), a material capable of converting triplet excitation energy into light emission in the light-emitting layer, to the fluorescent material 1,6mmtBuDPhAPrn occurs efficiently, resulting in a light-emitting device that exhibits high luminescence efficiency while being configured to emit light from a fluorescent material.

[0488] Furthermore, the results of low-temperature PL measurements of SiTrzCz2 and PSiCzCz, which are the host materials for the fabricated light-emitting devices, are shown in Figures 37(A) and 37(B). For the measurements, a LabRAM HR-PL micro-PL system (Horiba, Ltd.) was used, the measurement temperature was 10K, a He-Cd laser (wavelength 325nm) was used as the excitation light, and a CCD detector was used. The measurement samples were thin films, with the target film to be measured deposited on a quartz substrate to a thickness of 50nm. After the deposited quartz substrate was attached to the deposition side in a nitrogen atmosphere, another quartz substrate was attached to it before use for measurement.

[0489] As shown in Figures 37(A) and 37(B), the wavelength of the short-wavelength emission edge of the emission spectrum in low-temperature PL measurements is 424 nm for SiTrzCz2 and 418 nm for PSiCzCz. Therefore, the T1 levels of SiTrzCz2 and PSiCzCz are 2.92 eV and 2.97 eV, respectively, with an energy difference of 0.05 eV. Since the energy difference of the T1 levels between the host materials is 0.20 eV or less, the light-emitting device fabricated in this embodiment exhibits a small bias in triplet excitation energy between the host materials, making it possible to produce a highly reliable light-emitting device.

[0490] Furthermore, as shown in Figure 36, the wavelength of the short-wavelength emission edge of the emission spectrum of Pt(mmtBubOcz35dm4ppy-d6) is 445 nm, and the T1 level of Pt(mmtBubOcz35dm4ppy-d6) is estimated to be 2.78 eV. As mentioned above, the T1 levels of the host materials SiTrzCz2 and PSiCzCz are 2.92 eV and 2.97 eV, respectively, so the T1 level of Pt(mmtBubOcz35dm4ppy-d6) is lower than that of SiTrzCz2 and PSiCzCz. In this embodiment, the light-emitting device fabricated with such a configuration allows for efficient energy transfer from the host material to a substance capable of converting triplet excitation energy into light emission, resulting in a light-emitting device with high luminescence efficiency and good reliability.

[0491] Figure 38 also shows the emission spectra (PL spectra) of a mixed film of SiTrzCz2 and PSiCzCz in a 1:1 (weight ratio) ratio, and of the individual films. The measurements were performed using a spectrofluorometer (FP-8600DS, JASCO Corporation). As shown in Figure 38, the mixed film of SiTrzCz2 and PSiCzCz exhibited emission spectra that were shifted to longer wavelengths, different from the emission spectra of either individual film, indicating that SiTrzCz2 and PSiCzCz are a combination that forms an excited complex.

[0492] As shown in Figure 35, a light-emitting device 2 according to one embodiment of the present invention, in which the GSP_Slope of the second electron transport layer is high and the light-emitting layer contains both Pt(mmtBubOcz35dm4ppy-d6) (phosphorescent material) and 1,6mmtBuDPhAPrn (fluorescent material), showed better reliability compared to comparative light-emitting device 2.

[0493] Table 8 shows the GSP_Slope of the organic compound having a π-electron-deficient heteroaromatic ring used in the first electron transport layer of light-emitting device 2 and comparative light-emitting device 2, the organic compound having a π-electron-deficient heteroaromatic ring used in the second electron transport layer, the organic compound having a π-electron-rich heteroaromatic ring or aromatic amine used in the hole transport layer, and the deposited film of the host material used in the light-emitting layer. In Table 8, the GSP_Slope was measured by the method shown in Embodiment 1.

[0494] [Table 8]

[0495] Thus, in comparative light-emitting device 2, the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the second electron transport layer is smaller than the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the first electron transport layer. In this configuration, electrons are well injected from the electrode or electron injection layer to the interface of the first electron transport layer. On the other hand, light-emitting device 2 has a configuration in which the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the second electron transport layer is larger than the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the first electron transport layer. As a result, in light-emitting device 2, the injection of electrons from the electrode or electron injection layer to the second electron transport layer is suppressed.

[0496] Typically, in emissive layers containing blue phosphorescent material, the HOMO and LUMO levels of the blue phosphorescent material are both higher than those of the host material. As a result, it traps holes rather than electrons, causing the recombination region to be biased towards the anode side of the emissive layer. When the recombination region is biased towards the anode side, the density of excitons generated after recombination also increases on the anode side of the emissive layer. This makes it easier for interactions between excitons and between excitons and holes in the electron blocking layer to occur, leading to the generation of very high-energy excitons or holes. These high-energy excitons or holes accelerate the degradation of the emissive layer and the electron blocking layer adjacent to it.

[0497] In one embodiment of the present invention, the high GSP_Slope of the second electron transport layer suppresses electron injection, as described above. This allows the recombination region, which tends to be biased towards the anode side of the light-emitting layer, to be extended to the cathode side as well, thereby suppressing the degradation of the hole transport layer, which functions as an electron blocking layer. As a result, the reliability of the light-emitting device 2 is improved compared to the comparative light-emitting device 2.

[0498] In the light-emitting device fabricated in this embodiment, the HOMO level of PSiCzCz used as the host material in the light-emitting layer is -5.7eV and the LUMO level is -2.06eV. The HOMO level of SiTrzCz2 is lower than that of PSiCzCz, with a LUMO level of -2.98eV. The HOMO level of Pt(mmtBubOcz35dm4ppy-d6), which was added in a small amount (12wt%) as a blue phosphorescent material in the light-emitting layer, is -5.50eV and the LUMO level is -2.47eV, making it a configuration that easily traps holes. Furthermore, the HOMO level of 1,6mmtBuDPhAPrn, which was added in a small amount (1.5wt%) as a fluorescent material in light-emitting device 2, is -5.30eV, indicating that 1,6mmtBuDPhAPrn also easily traps holes, similar to the phosphorescent material. Furthermore, since the HOMO level of the fluorescent material is higher than that of the phosphorescent material, and the amount of fluorescent material added is less than the amount of phosphorescent material added, the fluorescent material in the light-emitting layer is configured to further trap the holes that have been trapped by the phosphorescent material. Therefore, in this light-emitting layer, holes are easily trapped strongly, and the hole transportability tends to be low.

[0499] The values ​​of the HOMO and LUMO levels were determined in the same manner as in Example 1.

[0500] Furthermore, the light-emitting device 2 contains not only an organic compound having a π-electron-deficient heteroaromatic ring in its second electron transport layer, but also Liq, a metal complex containing an alkali metal. When the weight ratio of the organic compound having a π-electron-deficient heteroaromatic ring to Liq in the second electron transport layer is x:y, the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the first electron transport layer multiplied by (x+y) / x is 51.5 (mV / nm). In other words, the light-emitting device 2 is configured such that the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the second electron transport layer is greater than the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the first electron transport layer multiplied by (x+y) / x.

[0501] Thus, when the weight ratio of the organic compound having a π-electron-deficient heteroaromatic ring in the second electron transport layer to Liq is x:y, a reliable light-emitting device can be provided if the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the second electron transport layer is greater than the GSP_Slope of the film of the organic compound having a π-electron-deficient heteroaromatic ring contained in the first electron transport layer multiplied by (x+y) / x.

[0502] Furthermore, in the above-mentioned light-emitting device 2 and comparative light-emitting device 2, the GSP_Slope of the host material (SiTrzCz2 and PSiCzCz) film is larger than the GSP_Slope of the first organic compound film. Also, the GSP_Slope of the light-emitting layer is larger than the GSP_Slope of the first electron transport layer.

[0503] This configuration allows a positive interfacial charge to be placed at the interface between the light-emitting layer and the first electron transport layer, thereby suppressing the electron injection barrier from the second electron transport layer to the first electron transport layer in the light-emitting device. As a result, even if electron injection into the second electron transport layer is suppressed, the light-emitting device 2 does not cause a significant increase in the driving voltage, making it possible to produce a light-emitting device with good characteristics.

[0504] Furthermore, BP-Icz(II)Tzn, an organic compound containing a π-electron-deficient heteroaromatic ring in the second electron transport layer of the light-emitting device 2, has a larger GSP_Slope than the host materials (SiTrzCz2 and PSiCzCz). Also, the GSP_Slope of the second electron transport layer is larger than that of the light-emitting layer.

[0505] As a result, in the light-emitting device 2, the interface charge between the first electron transport layer and the second electron transport layer is negative and smaller than the interface charge between the light-emitting layer and the first electron transport layer. This effect suppresses the injection of electrons from the second electrode or electron injection layer into the second electron transport layer, and promotes the injection of holes into the light-emitting layer. Consequently, in the light-emitting layer of light-emitting devices that typically use blue phosphorescent materials, the recombination region, which tends to be biased towards the anode side, can be expanded, and the degradation of the hole transport layer, which functions as an electron blocking layer, can be further reduced.

[0506] Furthermore, the above-mentioned light-emitting device has a configuration in which the GSP_Slope of the light-emitting layer (a co-evaporated film of SiTrzCz2, PSiCzCz, Pt (mmtBubOcz35dm4ppy-d6), and 1,6mmtBuDPhAPrn) or the GSP_Slope of the host material film (a co-evaporated film of SiTrzCz2 and PSiCzCz) is larger than the GSP_Slope of the hole transport layer (a evaporated film of PCBBiF). This relationship between the GSP_Slopes of the hole transport layer and the light-emitting layer allows for the establishment of a negative interfacial charge at at least one of the interfaces between the hole transport layer and the light-emitting layer. This facilitates the injection of holes from the anode or hole injection layer to the vicinity of the light-emitting layer interface, making it possible to create a light-emitting device with a low driving voltage.

[0507] Thus, a light-emitting device according to one aspect of the present invention can be a light-emitting device with high reliability and good characteristics. [Examples]

[0508] In this example, the detailed manufacturing methods and characteristics of the light-emitting device 3 and the comparative light-emitting device 3 will be described. The structural formulas of the ...

Claims

1. A first electrode formed on an insulating surface, A second electrode facing the first electrode, The present invention has an EL layer located between the first electrode and the second electrode, The EL layer comprises a light-emitting layer, a hole transport layer, a first electron transport layer, and a second electron transport layer. The first electron transport layer is located between the first electrode and the second electron transport layer. The light-emitting layer is located between the hole transport layer and the first electron transport layer and the second electron transport layer. The light-emitting layer comprises a first light-emitting material and a second light-emitting material. The first luminescent material is a material capable of converting triplet excitation energy into light emission, The second light-emitting material is a fluorescent material, The peak wavelength in the emission spectrum of the first luminescent material is shorter than the peak wavelength in the emission spectrum of the second luminescent material. A light-emitting device in which the GSP_Slope (mV / nm) of the second electron transport layer is greater than the GSP_Slope (mV / nm) of the first electron transport layer (where GSP_Slope (mV / nm) is expressed as ΔV / Δd when the change in surface potential ΔV (mV) is equal to the change in film thickness Δd (nm)).

2. A first electrode formed on an insulating surface, A second electrode facing the first electrode, The present invention has an EL layer located between the first electrode and the second electrode, The EL layer comprises a light-emitting layer, a hole transport layer, a first electron transport layer, and a second electron transport layer. The first electron transport layer is located between the first electrode and the second electron transport layer. The light-emitting layer is located between the hole transport layer and the first electron transport layer and the second electron transport layer. The light-emitting layer comprises a first light-emitting material and a second light-emitting material. The first luminescent material is a material capable of converting triplet excitation energy into light emission, The second light-emitting material is a fluorescent material, The peak wavelength in the emission spectrum of the first luminescent material is shorter than the peak wavelength in the emission spectrum of the second luminescent material. The first electron transport layer comprises a first organic compound, The second electron transport layer comprises a second organic compound, The first organic compound and the second organic compound have a π-electron-deficient heteroaromatic ring, A light-emitting device in which the GSP_Slope (mV / nm) in the vapor-deposited film of the second organic compound is greater than the GSP_Slope (mV / nm) in the vapor-deposited film of the first organic compound (where GSP_Slope (mV / nm) is expressed as ΔV / Δd when the change in surface potential ΔV (mV) is equal to the change in film thickness Δd (nm)).

3. A first electrode formed on an insulating surface, A second electrode facing the first electrode, The present invention has an EL layer located between the first electrode and the second electrode, The EL layer comprises a light-emitting layer, a hole transport layer, a first electron transport layer, and a second electron transport layer. The first electron transport layer is located between the light-emitting layer and the second electron transport layer. The second electron transport layer is located between the first electron transport layer and the second electrode. The light-emitting layer is located between the hole transport layer and the first electron transport layer. The light-emitting layer comprises a first light-emitting material and a second light-emitting material. The first luminescent material is a material capable of converting triplet excitation energy into light emission, The second light-emitting material is a fluorescent material, The peak wavelength in the emission spectrum of the first luminescent material is shorter than the peak wavelength in the emission spectrum of the second luminescent material. The first electron transport layer comprises a first organic compound, The second electron transport layer comprises a second organic compound and a first substance. The first organic compound and the second organic compound have a π-electron-deficient heteroaromatic ring, A light-emitting device in which the GSP_Slope (mV / nm) in the vapor-deposited film of the second organic compound is greater than the GSP_Slope (mV / nm) in the vapor-deposited film of the first organic compound (where GSP_Slope (mV / nm) is expressed as ΔV / Δd when the change in surface potential ΔV (mV) is equal to the change in film thickness Δd (nm)).

4. A first electrode formed on an insulating surface, A second electrode facing the first electrode, The present invention has an EL layer located between the first electrode and the second electrode, The EL layer comprises a light-emitting layer, a hole transport layer, a first electron transport layer, and a second electron transport layer. The first electron transport layer is located between the light-emitting layer and the second electron transport layer. The second electron transport layer is located between the first electron transport layer and the second electrode. The light-emitting layer is located between the hole transport layer and the first electron transport layer. The light-emitting layer comprises a first light-emitting material and a second light-emitting material. The first luminescent material is a material capable of converting triplet excitation energy into light emission, The second light-emitting material is a fluorescent material, The peak wavelength in the emission spectrum of the first luminescent material is shorter than the peak wavelength in the emission spectrum of the second luminescent material. The first electron transport layer comprises a first organic compound, The second electron transport layer comprises a second organic compound and a first substance. The first organic compound and the second organic compound have a π-electron-deficient heteroaromatic ring, When the mixing ratio of the second organic compound and the first substance in the second electron transport layer is x:y, A light-emitting device in which the GSP_Slope (mV / nm) in the vapor-deposited film of the second organic compound is greater than (x+y) / x times the GSP_Slope (mV / nm) in the vapor-deposited film of the first organic compound (where GSP_Slope (mV / nm) is expressed as ΔV / Δd when the change in surface potential ΔV (mV) is equal to the change in film thickness Δd (nm)).

5. In claim 4, A light-emitting device in which the aforementioned y is greater than or equal to the aforementioned x.

6. In any one of claims 2 to 5, The second electron transport layer is located between the first electron transport layer and the second electrode. The light-emitting layer includes a host material, A light-emitting device in which the GSP_Slope (mV / nm) in the vapor-deposited film of the host material is greater than the GSP_Slope (mV / nm) in the vapor-deposited film of the first organic compound.

7. In claim 6, A light-emitting device in which the GSP_Slope (mV / nm) in the vapor-deposited film of the second organic compound is greater than the GSP_Slope (mV / nm) in the vapor-deposited film of the host material.

8. In claim 6, The hole transport layer has a third organic compound, A light-emitting device in which the GSP_Slope (mV / nm) of the light-emitting layer is equal to or greater than the GSP_Slope (mV / nm) of the vapor-deposited film of the third organic compound.

9. In claim 6, The hole transport layer has a third organic compound, A light-emitting device in which the GSP_Slope (mV / nm) in the vapor-deposited film of the host material is equal to or greater than the GSP_Slope (mV / nm) in the vapor-deposited film of the third organic compound.

10. In claim 6, The host material comprises a first material and a second material, A light-emitting device which is an organic compound in which the first material and the second material form an excited complex.

11. In claim 10, The first material is an organic compound having a π-electron-deficient heteroaromatic ring, A light-emitting device in which the second material is an organic compound having a π-electron-rich heteroaromatic ring or an aromatic amine.

12. In claim 10, A light-emitting device in which the HOMO levels of the first material and the HOMO levels of the second material are lower than the HOMO level of the first light-emitting material.

13. In claim 12, A light-emitting device in which the HOMO levels of the first material and the HOMO levels of the second material are lower than the HOMO levels of the second light-emitting material.

14. In any one of claims 3 to 5, The first material is a metal complex, which is used in this light-emitting device.

15. In claim 14, The aforementioned metal complex is an organic complex containing an alkali metal, which is used as a light-emitting device.

16. In any one of claims 1 to 4, A light-emitting device in which the first light-emitting material is a phosphorescent material.

17. In any one of claims 1 to 4, A light-emitting device in which the second light-emitting material emits light when a voltage is applied between the first electrode and the second electrode.

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