Host material for light-emitting layer, light-emitting element, light-emitting device, lighting device, and electronic device

Abstract

One embodiment of the present invention provides a light-emitting element having a light-emitting material with high luminous efficiency. One embodiment of the present invention is a light-emitting element comprising a host material and a guest material. The host material comprises a first organic compound and a second organic compound. In the first organic compound, the difference between the singlet excitation energy level and the triplet excitation energy level is greater than 0 eV and less than 0.2 eV. One of the first organic compound and the second organic compound has a HOMO energy level higher than the HOMO energy level of the other organic compound and a LUMO energy level higher than the LUMO energy level of the other organic compound. An excited-state complex is formed from the first organic compound and the second organic compound.

Description

Technical Field

[0001] One embodiment of the present invention relates to a light-emitting element or a display device, electronic device, and lighting device including the light-emitting element.

[0002] Note that one embodiment of the present invention is not limited to the above-described technical field. The technical field of one embodiment of the invention disclosed in this specification relates to an object, method, or manufacturing method. Furthermore, one embodiment of the present invention relates to a process, machine, manufacture, or composition of matter. Therefore, more specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include semiconductor devices, display devices, liquid crystal display devices, light-emitting devices, lighting devices, energy storage devices, memory devices, and methods for driving or manufacturing these devices. Prior Technology

[0003] In recent years, research and development of light-emitting elements utilizing electroluminescence (EL) has become increasingly active. The basic structure of these light-emitting elements consists of a layer containing luminescent material (EL layer) sandwiched between a pair of electrodes. By applying a voltage between the electrodes of the element, light emission from the luminescent material can be obtained.

[0004] Because the aforementioned light-emitting element is a self-emissive element, the display device using this element has the following advantages: good visibility; no need for a backlight; and low power consumption. Furthermore, the display device also has the following advantages: it can be manufactured to be thin and light; and it has a fast response time.

[0005] When using a light-emitting element (e.g., an organic EL element) that uses an organic material as the light-emitting material and has an EL layer containing the light-emitting material disposed between a pair of electrodes, current flows through the EL layer by applying a voltage between the pair of electrodes, where electrons and holes are injected from the cathode and anode, respectively. Furthermore, the injected electrons and holes recombine to excite the light-emitting organic material, thereby producing light emission.

[0006] The excited states formed by organic materials include singlet excited states (S*) and triplet excited states (T*). Emission from singlet excited states is called fluorescence, and emission from triplet excited states is called phosphorescence. Furthermore, in this light-emitting element, the statistically significant ratio of singlet excited states to triplet excited states is S*:T* = 1:3. Therefore, light-emitting elements using phosphorescent materials have higher luminous efficiency than those using fluorescent materials. Consequently, in recent years, there has been active development of light-emitting elements using phosphorescent materials capable of converting the energy of triplet excited states into emission (see, for example, Patent Document 1).

[0007] To make the energy required to excite an organic material dependent on the energy of the singlet excited state, in light-emitting elements using phosphorescent organic materials, the triplet excitation energy is converted into luminescence energy. Therefore, when the energy difference between the singlet and triplet excited states formed in the organic material is large, the energy required to excite the organic material must be higher than the luminescence energy; the difference is equivalent to this energy difference. In light-emitting elements, increasing the energy difference between the energy required to excite the organic material and the luminescence energy increases the driving voltage and affects the element characteristics. Therefore, methods to suppress the rise of the driving voltage are being investigated (see Patent Document 2).

[0008] In light-emitting elements using phosphorescent materials, especially those exhibiting blue light emission, the development of stable materials with high triplet excitation energy levels is challenging, thus hindering their practical application. Therefore, efforts are underway to develop light-emitting elements using more stable fluorescent materials and to find methods to improve the luminous efficiency of these elements (fluorescent light-emitting elements).

[0009] Thermally activated delayed fluorescence (TADF) materials are known as materials capable of converting a portion of the energy of a triplet excited state into light emission. In TADF materials, a singlet excited state is generated from a triplet excited state via antisystem crossing, and the singlet excited state is converted into light emission.

[0010] To improve the luminescence efficiency of light-emitting elements using thermally activated delayed-emission (TEFE) materials, it is important not only to efficiently generate singlet excited states from triplet excited states in the TEFE material, but also to efficiently obtain luminescence from singlet excited states, i.e., high fluorescence quantum yield. However, it is difficult to design light-emitting materials that simultaneously satisfy both of these conditions.

[0011] Therefore, the following method has been proposed: in a light-emitting element comprising a thermally activated delayed fluorescent substance and a fluorescent material, the single excitation energy of the thermally activated delayed fluorescent substance is transferred to the fluorescent material, and light emission is obtained from the fluorescent material (see Patent Document 3).

[0012] [Patent Document 1] Japanese Patent Application Publication No. 2010-182699 [Patent Document 2] Japanese Patent Application Publication No. 2012-212879 [Patent Document 3] Japanese Patent Application Publication No. 2014-45179 Summary of the Invention

[0013] In order to improve luminous efficiency or reduce driving voltage in a light-emitting element containing thermally activated delayed phosphors and luminescent materials, it is preferable to efficiently recombine carriers in the thermally activated delayed phosphor.

[0014] Furthermore, in order to improve the luminous efficiency in a light-emitting element comprising a thermally activated delayed fluorescent material and a fluorescent material, it is preferable to efficiently generate a singlet excited state from a triplet excited state. Additionally, it is preferable that energy is efficiently transferred from the singlet excited state of the thermally activated delayed fluorescent material to the singlet excited state of the fluorescent material.

[0015] Therefore, one objective of one embodiment of the present invention is to provide a light-emitting element comprising fluorescent or phosphorescent materials and having high luminous efficiency. Another objective of one embodiment of the present invention is to provide a light-emitting element with reduced power consumption. Furthermore, one objective of one embodiment of the present invention is to provide a novel light-emitting element. Additionally, one objective of one embodiment of the present invention is to provide a novel light-emitting device. Finally, one objective of one embodiment of the present invention is to provide a novel display device.

[0016] Note that the description of the above objectives does not preclude the existence of other objectives. One embodiment of the present invention does not necessarily need to achieve all of the above objectives. Furthermore, objectives other than those described above can be derived from the description in the specification, etc.

[0017] One embodiment of the present invention is a light-emitting element comprising a light-emitting layer that efficiently forms an excited-state complex. Another embodiment of the present invention is a light-emitting element capable of converting triplet excitons into singlet excitons to cause a material having singlet excitons to emit light, or causing a fluorescent material to emit light due to energy transfer from singlet excitons.

[0018] One embodiment of the present invention is a light-emitting element, comprising: a host material; and a guest material, wherein the host material has a first organic compound and a second organic compound, the guest material has the function of exhibiting fluorescence, the difference between the singlet excitation energy level and the triplet excitation energy level of the first organic compound is greater than 0 eV and less than 0.2 eV, and one of the first organic compound and the second organic compound has a HOMO energy level greater than or equal to the HOMO energy level of the other of the first organic compound and the LUMO energy level of the other of the first organic compound and the second organic compound.

[0019] Another embodiment of the present invention is a light-emitting element, comprising: a host material; and a guest material, wherein the host material has a first organic compound and a second organic compound, the guest material has the function of exhibiting fluorescence, the difference between the singlet excitation energy level and the triplet excitation energy level of the first organic compound is greater than 0 eV and less than 0.2 eV, and one of the first organic compound and the second organic compound has an oxidation potential greater than or equal to the oxidation potential of the other of the first organic compound and the second organic compound, and has a reduction potential greater than or equal to the reduction potential of the other of the first organic compound and the second organic compound.

[0020] Another embodiment of the present invention is a light-emitting element, comprising: a host material; and a guest material, wherein the host material has a first organic compound and a second organic compound, the guest material has the function of converting triple excitation energy into light emission, the difference between the single excitation energy level and the triple excitation energy level of the first organic compound is greater than 0 eV and less than 0.2 eV, and one of the first organic compound and the second organic compound has a HOMO energy level higher than the HOMO energy level of the other of the first organic compound and a LUMO energy level higher than the LUMO energy level of the other of the first organic compound and the second organic compound.

[0021] Another embodiment of the present invention is a light-emitting element, comprising: a host material; and a guest material, wherein the host material has a first organic compound and a second organic compound, the guest material has the function of converting triple excitation energy into light emission, the difference between the single excitation energy level and the triple excitation energy level of the first organic compound is greater than 0 eV and less than 0.2 eV, and one of the first organic compound and the second organic compound has an oxidation potential greater than or equal to the oxidation potential of the other of the first organic compound and the other of the second organic compound, and has a reduction potential greater than or equal to the reduction potential of the other of the first organic compound and the other of the second organic compound.

[0022] Of the above structures, the preferred one is that the first organic compound and the second organic compound form an excited-state complex.

[0023] Another embodiment of the present invention is a light-emitting element, comprising: a host material; and a guest material, wherein the host material has a first organic compound and a second organic compound, the guest material has the function of exhibiting fluorescence, the difference between the singlet excitation energy level and the triplet excitation energy level of the first organic compound is greater than 0 eV and less than 0.2 eV, and the first organic compound and the second organic compound form an excited-state complex.

[0024] Another embodiment of the present invention is a light-emitting element, comprising: a host material; and a guest material, wherein the host material has a first organic compound and a second organic compound, the guest material has the function of converting triple excitation energy into light emission, the difference between the single excitation energy level and the triple excitation energy level of the first organic compound is greater than 0 eV and less than 0.2 eV, and the first organic compound and the second organic compound form an excited-state complex.

[0025] In the above structures, the excited-state complex preferably exhibits thermally activated delayed fluorescence at room temperature. Furthermore, the excited-state complex preferably has the function of supplying excitation energy to the guest material. Additionally, it is preferable that the emission spectrum exhibited by the excited-state complex has a region overlapping with the absorption band on the lowest energy side of the absorption spectrum of the guest material.

[0026] In the above structures, the first organic compound preferably has the function of exhibiting thermally activated delayed fluorescence at room temperature.

[0027] In the aforementioned structures, preferably, one of the first organic compound and the second organic compound has the function of transporting holes, and the other of the first organic compound and the second organic compound has the function of transporting electrons. Furthermore, preferably, one of the first organic compound and the second organic compound has at least one of a π-electron-rich heteroaromatic skeleton and an aromatic amine skeleton, and the other of the first organic compound and the second organic compound has a π-electron-deficient heteroaromatic skeleton. Furthermore, preferably, the first organic compound has at least one of a π-electron-rich heteroaromatic skeleton and an aromatic amine skeleton, and also has a π-electron-deficient heteroaromatic skeleton.

[0028] In the above structures, preferably, the π-electron-rich heteroaromatic skeleton has one or more selected from the acridine skeleton, phenoxazine skeleton, phenanthridine skeleton, furan skeleton, thiophene skeleton, and pyrrole skeleton, and the π-electron-deficient heteroaromatic skeleton has a diazine skeleton or a triazine skeleton. Furthermore, the pyrrole skeleton is preferably an indole skeleton, a carbazole skeleton, or a 3-(9-phenyl-9H-carbazole-3-yl)-9H-carbazole skeleton.

[0029] In addition, another embodiment of the present invention is a display device, including: light-emitting elements of the above-described structures; and at least one of a color filter and a transistor. In addition, another embodiment of the present invention is an electronic device, including: the display device; and at least one of a housing and a touch sensor. In addition, another embodiment of the present invention is a lighting device, including: light-emitting elements of the above-described structures; and at least one of a housing and a touch sensor. Furthermore, one embodiment of the present invention, within its scope, includes not only light-emitting devices having light-emitting elements, but also electronic devices having light-emitting devices. Therefore, the light-emitting device in this specification refers to an image display device or a light source (including lighting devices). In addition, the light-emitting device is sometimes also included in modules such as: a display module in which connectors such as FPC (Flexible Printed Circuit) or TCP (Tape Carrier Package) are mounted in the light-emitting device; a display module in which a printed circuit board is provided at the TCP end; or a display module in which an IC (integrated circuit) is directly mounted on the light-emitting element by means of COG (Chip On Glass).

[0030] According to one embodiment of the present invention, a light-emitting element comprising fluorescent or phosphorescent materials and exhibiting high luminous efficiency can be provided. Furthermore, according to one embodiment of the present invention, a light-emitting element with reduced power consumption can be provided. Additionally, according to one embodiment of the present invention, a novel light-emitting element can be provided. Furthermore, according to one embodiment of the present invention, a novel light-emitting device can be provided. Furthermore, according to one embodiment of the present invention, a novel display device can be provided.

[0031] Note that the description of these effects does not preclude the existence of other effects. One embodiment of the present invention does not necessarily require achieving all of the above-described effects. Furthermore, effects other than those described above can be derived from the description in the specification, drawings, claims, etc. Simple Explanation of the Diagram

[0032] In the diagram: Figures 1A to 1C are schematic cross-sectional views of a light-emitting element according to an embodiment of the present invention and diagrams illustrating the energy level relationship in the light-emitting layer; Figures 2A and 2B are band-related diagrams illustrating the light-emitting layer of a light-emitting element according to one embodiment of the present invention; Figures 3A to 3C are diagrams illustrating the energy level correlation in the light-emitting layer of a light-emitting element according to one embodiment of the present invention; Figures 4A to 4C are schematic cross-sectional views of a light-emitting element according to an embodiment of the present invention and diagrams illustrating the energy level relationship in the light-emitting layer; Figures 5A to 5C are schematic cross-sectional views of a light-emitting element according to an embodiment of the present invention and diagrams illustrating the energy level relationship in the light-emitting layer; Figures 6A and 6B are schematic cross-sectional views of a light-emitting element according to one embodiment of the present invention; Figures 7A and 7B are schematic cross-sectional views of a light-emitting element according to one embodiment of the present invention; Figures 8A and 8B are schematic cross-sectional views of a light-emitting element according to one embodiment of the present invention; Figures 9A to 9C are schematic cross-sectional views illustrating a method for manufacturing a light-emitting element according to one embodiment of the present invention; Figures 10A to 10C are schematic cross-sectional views illustrating a method for manufacturing a light-emitting element according to one embodiment of the present invention; Figures 11A and 11B are a top view and a cross-sectional schematic diagram illustrating a display device according to an embodiment of the present invention; Figures 12A and 12B are schematic cross-sectional views illustrating a display device according to one embodiment of the present invention; Figure 13 is a cross-sectional schematic diagram illustrating a display device according to one embodiment of the present invention; Figures 14A and 14B are schematic cross-sectional views illustrating a display device according to one embodiment of the present invention; Figures 15A and 15B are schematic cross-sectional views illustrating a display device according to one embodiment of the present invention; Figure 16 is a cross-sectional schematic diagram illustrating a display device according to one embodiment of the present invention; Figures 17A and 17B are schematic cross-sectional views illustrating a display device according to one embodiment of the present invention; Figure 18 is a cross-sectional schematic diagram illustrating a display device according to one embodiment of the present invention; Figures 19A and 19B are schematic cross-sectional views illustrating a display device according to one embodiment of the present invention; Figures 20A and 20B are block diagrams and circuit diagrams illustrating a display device according to one embodiment of the present invention; Figures 21A and 21B are circuit diagrams illustrating the pixel circuit of a display device according to one embodiment of the present invention; Figures 22A and 22B are circuit diagrams illustrating the pixel circuit of a display device according to one embodiment of the present invention; Figures 23A and 23B are perspective views illustrating an example of a touch panel according to one embodiment of the present invention; Figures 24A to 24C are cross-sectional views illustrating an example of a display device and a touch sensor according to one embodiment of the present invention; Figures 25A and 25B are cross-sectional views illustrating an example of a touch panel according to one embodiment of the present invention; Figures 26A and 26B are block diagrams and timing diagrams of a touch sensor according to one embodiment of the present invention; Figure 27 is a circuit diagram of a touch sensor according to one embodiment of the present invention; Figure 28 is a perspective view illustrating a display module according to one embodiment of the present invention; Figures 29A to 29G are diagrams illustrating an electronic device according to one embodiment of the present invention; Figures 30A to 30D are diagrams illustrating an electronic device according to one embodiment of the present invention; Figures 31A and 31B are perspective views illustrating a display device according to one embodiment of the present invention; Figures 32A to 32C are perspective views and cross-sectional views illustrating a light-emitting device according to one embodiment of the present invention; Figures 33A to 33D are cross-sectional views illustrating a light-emitting device according to one embodiment of the present invention; Figures 34A to 34C are illustrations of a lighting device and electronic apparatus according to one embodiment of the present invention; Figure 35 is a diagram illustrating a lighting device according to one embodiment of the present invention; Figures 36A and 36B are diagrams illustrating the luminance-current density characteristics of the light-emitting element according to an embodiment; Figures 37A and 37B are diagrams illustrating the brightness-voltage characteristics of the light-emitting element according to an embodiment; Figures 38A and 38B are graphs illustrating the current efficiency-luminance characteristics of the light-emitting element according to an embodiment; Figures 39A and 39B are graphs illustrating the power efficiency-luminance characteristics of the light-emitting element according to an embodiment; Figures 40A and 40B are diagrams illustrating the external quantum efficiency-luminance characteristics of the light-emitting element according to an embodiment; Figures 41A and 41B are diagrams illustrating the electroluminescence spectrum of the light-emitting element according to an embodiment; Figure 42 is a graph illustrating the emission spectrum of the thin film according to the embodiment; Figure 43 is a graph illustrating the emission spectrum of the thin film according to the embodiment; Figure 44 is a diagram illustrating the emission spectrum of the thin film according to the embodiment; Figure 45 is a graph illustrating the emission spectrum of the thin film according to the embodiment; Figure 46 is a graph illustrating the emission spectrum of the thin film according to the embodiment; Figure 47 is a graph illustrating the emission spectrum of the thin film according to the embodiment; Figure 48 is a graph illustrating the emission spectrum of the thin film according to the embodiment; Figures 49A and 49B illustrate the NMR spectra of the compounds according to the reference example; Figure 50 illustrates the NMR spectrum of the compound according to the reference example; Figure 51 illustrates the NMR spectrum of the compound according to the reference example. Implementation

[0033] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the following description, and its methods and details can be varied in various forms without departing from the spirit and scope of the invention. Therefore, the present invention should not be construed as being limited only to the contents described in the embodiments shown below.

[0034] Furthermore, for ease of understanding, the positions, sizes, and extents of various structures shown in drawings, etc., do not necessarily represent their actual positions, sizes, and extents. Therefore, the disclosed invention is not necessarily limited to the positions, sizes, and extents disclosed in the drawings, etc.

[0035] Furthermore, in this specification and other documents, ordinal numbers such as "first," "second," etc., are added for convenience, but they do not always indicate the process sequence or stacking order. Therefore, for example, "first" can be appropriately replaced with "second" or "third," etc., for description. In addition, the ordinal numbers described in this specification and other documents are sometimes inconsistent with the ordinal numbers used to specify an embodiment of the present invention.

[0036] Note that in this specification and the like, when the structure of the invention is described using drawings, symbols representing the same parts are sometimes used in common in different drawings.

[0037] Additionally, in this specification and other materials, the terms "film" and "layer" may be interchanged. For example, "conductive layer" may sometimes be replaced with "conductive film." Furthermore, "insulating film" may sometimes be replaced with "insulating layer."

[0038] Furthermore, in this specification, a singlet excited state (S*) refers to a singlet state having an excitation energy. The S1 energy level is the lowest energy level of the singlet excited state, that is, the excitation energy level of the lowest singlet excited state. Similarly, a triplet excited state (T*) refers to a triplet state having an excitation energy. The T1 energy level is the lowest energy level of the triplet excited state, that is, the excitation energy level of the lowest triplet excited state. Moreover, in this specification, even when simply expressed as "singlet excited state" or "singlet excited state energy level," it may sometimes refer to the lowest singlet excited state or the S1 energy level, respectively. Similarly, even when simply expressed as "triple excited state" or "triple excited energy level," it may sometimes refer to the lowest triplet excited state or the T1 energy level, respectively.

[0039] Furthermore, in this specification, fluorescent materials refer to materials that emit light in the visible light region when returning from a singlet excited state to the ground state. Phosphorescent materials refer to materials that emit light in the visible light region at room temperature when returning from a triplet excited state to the ground state. In other words, phosphorescent materials are one type of material capable of converting triplet excitation energy into visible light.

[0040] Furthermore, the emission energy of thermally activated delayed fluorescence (TEF) can be derived from the emission peak (including the shoulder peak) on the shortest wavelength side of TEF. Similarly, the phosphorescence emission energy or triple excitation energy can be derived from the emission peak (including the shoulder peak) on the shortest wavelength side of phosphorescence. Moreover, the aforementioned phosphorescence emission can be observed using time-resolved photoluminescence spectroscopy at low temperatures (e.g., 10 K).

[0041] In addition, in this specification, room temperature refers to any temperature between 0°C and 40°C.

[0042] Furthermore, in this specification, the blue wavelength region refers to the wavelength region of 400 nm or more and less than 490 nm, and blue emission is emission with at least one emission spectral peak in this wavelength region. Similarly, the green wavelength region refers to the wavelength region of 490 nm or more and less than 580 nm, and green emission is emission with at least one emission spectral peak in this wavelength region. Finally, the red wavelength region refers to the wavelength region of 580 nm or more and less than 680 nm, and red emission is emission with at least one emission spectral peak in this wavelength region.

[0043] Implementation Method 1 In this embodiment, a light-emitting element according to one embodiment of the present invention will be described with reference to FIGS. 1A to 3C.

[0044] <Example of a light-emitting element structure> First, the structure of a light-emitting element according to an embodiment of the present invention will be described below with reference to Figures 1A to 1C.

[0045] Figure 1A is a cross-sectional schematic diagram of a light-emitting element 150 according to an embodiment of the present invention.

[0046] The light-emitting element 150 includes a pair of electrodes (electrode 101 and electrode 102) and an EL layer 100 disposed between the pair of electrodes. The EL layer 100 includes at least a light-emitting layer 130.

[0047] In addition, the EL layer 100 shown in Figure 1A includes functional layers such as hole injection layer 111, hole transport layer 112, electron transport layer 118, and electron injection layer 119, in addition to the light-emitting layer 130.

[0048] Note that although this embodiment describes electrode 101 as the anode and electrode 102 as the cathode, the structure of the light-emitting element 150 is not limited to this. That is, electrode 101 can also be used as the cathode and electrode 102 as the anode, and the layers between the electrodes can be stacked in reverse order. In other words, the hole injection layer 111, hole transport layer 112, light-emitting layer 130, electron transport layer 118, and electron injection layer 119 can be stacked sequentially from the anode side.

[0049] Note that the structure of the EL layer 100 is not limited to the structure shown in FIG1A, as long as it includes at least one selected from the hole injection layer 111, hole transport layer 112, electron transport layer 118, and electron injection layer 119. Alternatively, the EL layer 100 may also include a functional layer that can reduce the injection barrier of holes or electrons; improve the transport of holes or electrons; hinder the transport of holes or electrons; or suppress quenching phenomena caused by electrodes, etc. The functional layer can be a single layer or a structure with multiple layers stacked.

[0050] Figure 1B is a schematic cross-sectional view showing an example of the light-emitting layer 130 shown in Figure 1A. The light-emitting layer 130 shown in Figure 1B includes a host material 131 and a guest material 132. Furthermore, the host material 131 includes organic compound 131_1 and organic compound 131_2.

[0051] As the guest material 132, a luminescent organic material may be used, and preferably, a material capable of emitting fluorescence (hereinafter also referred to as a fluorescent material) is used. The following description will explain the structure using a fluorescent material as the guest material 132. Note that the guest material 132 may also be referred to as a fluorescent material.

[0052] In a light-emitting element 150 according to one embodiment of the present invention, electrons and holes are injected from the cathode and anode into the EL layer 100, respectively, by applying a voltage between a pair of electrodes (electrode 101 and electrode 102), thereby causing current to flow. The injected electrons and holes recombine to form excitons. Among the excitons generated by the recombination of carriers (electrons and holes), the statistical probability of the ratio of singlet excitons to triplet excitons (hereinafter referred to as the exciton generation probability) is 1:3. Therefore, in a light-emitting element using a fluorescent light-emitting material, the ratio of singlet excitons that contribute to light emission is 25%, while the ratio of triplet excitons that do not contribute to light emission is 75%. Therefore, in order to improve the luminous efficiency of the light-emitting element, it is important to convert triplet excitons that do not contribute to light emission into singlet excitons that contribute to light emission.

[0053] <Light-emitting mechanism of light-emitting elements> Next, the light emission mechanism of the light-emitting layer 130 will be explained.

[0054] The organic compounds 131_1 and 131_2 included in the host material 131 in the light-emitting layer 130 form an exciplex.

[0055] The combination of organic compound 131_1 and organic compound 131_2 can be any combination capable of forming an excited-state complex. Preferably, one of them is a compound with the function of transporting holes (hole transport) and the other is a compound with the function of transporting electrons (electron transport). In this case, it is easier to form a donor-acceptor type excited-state complex, and the excited-state complex can be formed efficiently.

[0056] Furthermore, as a combination of organic compound 131_1 and organic compound 131_2, it is preferable that one of organic compound 131_1 and organic compound 131_2 has a HOMO energy level above the highest occupied molecular orbital (HOMO) energy level of the other and a LUMO energy level above the lowest unoccupied molecular orbital (LUMO) energy level of the other.

[0057] For example, when organic compound 131_1 exhibits hole transport and organic compound 131_2 exhibits electron transport, as shown in the band diagram of Figure 2A, preferably, the HOMO level of organic compound 131_1 is higher than the HOMO level of organic compound 131_2, and the LUMO level of organic compound 131_1 is higher than the LUMO level of organic compound 131_2. Alternatively, when organic compound 131_2 exhibits hole transport and organic compound 131_1 exhibits electron transport, as shown in the band diagram of Figure 2B, preferably, the HOMO level of organic compound 131_2 is higher than the HOMO level of organic compound 131_1, and the LUMO level of organic compound 131_2 is higher than the LUMO level of organic compound 131_1. In this case, the excited-state complex formed by organic compounds 131_1 and 131_2 becomes an excited-state complex with an excitation energy approximately equivalent to the energy difference between the HOMO level of one and the LUMO level of the other. Furthermore, the difference between the HOMO energy levels of organic compound 131_1 and organic compound 131_2, as well as the difference between the LUMO energy levels of organic compound 131_1 and organic compound 131_2, is preferably 0.2 eV or more, and more preferably 0.3 eV or more. In Figures 2A and 2B, Host(131_1) represents organic compound 131_1, and Host(131_2) represents organic compound 131_2.

[0058] Based on the above relationship between the HOMO and LUMO energy levels, as a combination of organic compound 131_1 and organic compound 131_2, it is preferable that one has an oxidation potential higher than that of the other and a reduction potential higher than that of the other.

[0059] For example, when organic compound 131_1 has hole transport properties and organic compound 131_2 has electron transport properties, it is preferable that the oxidation potential of organic compound 131_1 is lower than the oxidation potential of organic compound 131_2 and the reduction potential of organic compound 131_1 is lower than the reduction potential of organic compound 131_2. Alternatively, when organic compound 131_2 has hole transport properties and organic compound 131_1 has electron transport properties, it is preferable that the oxidation potential of organic compound 131_2 is lower than the oxidation potential of organic compound 131_1 and the reduction potential of organic compound 131_2 is lower than the reduction potential of organic compound 131_1. Furthermore, the oxidation potential and reduction potential can be measured by cyclic voltammetry (CV).

[0060] Furthermore, when the combination of organic compound 131_1 and organic compound 131_2 is a combination of a compound with hole transport capability and a compound with electron transport capability, the balance of the carriers can be easily controlled by adjusting their mixing ratio. Specifically, the ratio of the compound with hole transport capability to the compound with electron transport capability is preferably in the range of 1:9 to 9:1 (weight ratio). In addition, by having this structure, the balance of the carriers can be easily controlled, thereby making it easy to control the carrier recombination region.

[0061] Organic compound 131_1 is preferably a thermally activated delayed fluorescence (TARF) material. Alternatively, it is more preferably capable of exhibiting TRF at room temperature. In other words, organic compound 131_1 can also be a material that generates a singlet excited state from a triplet excited state solely through antisystem crossing. Therefore, the difference between the singlet and triplet excitation energy levels is preferably greater than 0 eV and less than 0.2 eV. Organic compound 131_1 only needs to have the function of converting triplet excitation energy into singlet excitation energy, and may not necessarily exhibit TRF.

[0062] Organic compound 131_1 preferably comprises a skeleton with hole transport capability and a skeleton with electron transport capability. Furthermore, organic compound 131_1 preferably comprises at least one of a π-electron-rich heteroaromatic skeleton and an aromatic amine skeleton, as well as a π-electron-deficient heteroaromatic skeleton. Moreover, by directly bonding the π-electron-rich heteroaromatic skeleton and the π-electron-deficient heteroaromatic skeleton, both the donor and acceptor properties of the π-electron-rich heteroaromatic skeleton are strong, and the difference between the singlet and triplet excitation energy levels is reduced, making it particularly preferred. Due to the strong donor and acceptor properties of organic compound 131_1, it is easy to form a donor-acceptor type excited-state complex with organic compound 131_2.

[0063] The overlap between the HOMO and LUMO molecular orbital distribution regions of organic compound 131_1 is preferably small. Note that "molecular orbital" indicates the spatial distribution of electrons in the molecule, and can show the probability of electrons. The electronic configuration of the molecule (spatial distribution and energy of electrons) can be described in detail by the molecular orbital regions.

[0064] The excited-state complex formed by organic compounds 131_1 and 131_2 exhibits minimal overlap between HOMO and LUMO molecular orbitals due to the presence of HOMO molecular orbitals in one organic compound and LUMO molecular orbitals in the other. This means that the difference between the singlet and triplet excitation energy levels is small in this excited-state complex. Therefore, the preferred difference between the triplet and singlet excitation energy levels in the excited-state complex formed by organic compounds 131_1 and 131_2 is greater than 0 eV and less than 0.2 eV.

[0065] Here, Figure 1C shows the energy level correlation between organic compound 131_1, organic compound 131_2, and guest material 132 in the luminescent layer 130. Note that the symbols and labels in Figure 1C represent the following: • Host(131_1): Main material (organic compound 131_1) •Host(131_2): Main material (organic compound 131_2) •Guest(132): Object material 132 (fluorescent material) • SH1: The S1 energy level of the host material (organic compound 131_1) • TH1: The T1 energy level of the host material (organic compound 131_1) • SH2: S1 energy level of the host material (organic compound 131_2) • TH2: T1 energy level of the host material (organic compound 131_2) •SG: S1 energy level of guest material 132 (fluorescent material) •TG: T1 energy level of guest material 132 (fluorescent material) • SE: S1 energy level of excited-state complexes • TE: T1 energy level of excited-state complexes

[0066] In a light-emitting element according to one embodiment of the present invention, organic compounds 131_1 and 131_2 contained in the light-emitting layer 130 form an excited-state complex. The S1 energy level (SE) of the excited-state complex and the T1 energy level (TE) of the excited-state complex are adjacent to each other (see path E3 in Figure 1C).

[0067] Excited-state complexes are excited states formed by two substances. In the case of photoexcitation, excited-state complexes are formed through the interaction of one substance in the excited state with another substance in the ground state. When returning to the ground state by emitting light, the two substances that formed the excited-state complex revert to their original states. In the case of electrical excitation, when one substance is in the excited state, it rapidly interacts with the other substance to form an excited-state complex. Alternatively, excited-state complexes can be rapidly formed by one substance receiving a hole and the other substance receiving an electron. In this case, excited-state complexes can be formed without either substance forming an excited state on its own, so most of the excited states formed in the light-emitting layer 130 can exist as excited-state complexes. The excitation energy levels (SE and TE) of the excited-state complexes are lower than the S1 energy levels (SH1 and SH2) of the organic compounds (organic compound 131_1 and organic compound 131_2) that form the excited-state complexes, so the excited state of the host material 131 can be formed with a lower excitation energy. As a result, the driving voltage of the light-emitting element 150 can be reduced.

[0068] Since the S1 level (SE) and T1 level (TE) of the excited-state mispolymer are adjacent energy levels, the excited-state mispolymer exhibits the function of thermally activated delayed fluorescence. That is, the excited-state mispolymer has the function of converting triplet excitation energy into singlet excitation energy through antisystem upconversion (see path E4 in Figure 1C). Therefore, a portion of the triplet excitation energy generated in the emitting layer 130 is converted into singlet excitation energy due to the excited-state mispolymer. For this reason, the energy difference between the S1 level (SE) and T1 level (TE) of the excited-state mispolymer is preferably greater than 0 eV and less than 0.2 eV.

[0069] Furthermore, the S1 energy level (SE) of the excited-state complex is preferably higher than the S1 energy level (SG) of the guest material 132. Thus, the singlet excitation energy of the generated excited-state complex can be transferred from the S1 energy level (SE) of the excited-state complex to the S1 energy level (SG) of the guest material 132. As a result, the guest material 132 becomes a singlet excited state and emits light (see path E5 in Figure 1C).

[0070] In order to efficiently obtain luminescence from the singlet excited state of the guest material 132, the fluorescence quantum yield of the guest material 132 is preferably high, specifically, preferably 50% or more, more preferably 70% or more, and even more preferably 90% or more.

[0071] Note that, in order to efficiently generate inter-system crossing, the T1 energy level (TE) of the excited-state complex is preferably lower than the T1 energy levels (TH1 and TH2) of the organic compounds (organic compound 131_1 and organic compound 131_2) that form the excited-state complex. This reduces the likelihood of quenching the triple excitation energy of the excited-state complex caused by the organic compounds, thus enabling efficient inter-system crossing.

[0072] For example, in at least one of the compounds forming an excited-state complex, when the difference between the S1 and T1 energy levels is large, it is necessary to make the T1 energy level (TE) of the excited-state complex lower than that of each compound. Furthermore, it is preferable that the difference between the S1 and T1 energy levels of the excited-state complex is small, and that the S1 energy level of the guest material is lower than that of the excited-state complex. Therefore, when the difference between the S1 and T1 energy levels of at least one compound is large, it is not advisable to use a material with a high singlet excitation energy level, i.e., a material exhibiting high luminescence energy such as blue light, as the guest material 132.

[0073] Conversely, in one embodiment of the present invention, the difference between the S1 energy level (SH1) and the T1 energy level (TH1) of the organic compound 131_1 is small. Therefore, both the S1 and T1 energy levels of the organic compound 131_1 can be increased simultaneously, thereby increasing the T1 energy level of the excited-state complex. Therefore, one embodiment of the present invention is not limited to the emission color of the guest material 132; for example, it can be suitably used for various light-emitting elements, i.e., light-emitting elements exhibiting emission from high emission energy such as blue to low emission energy such as red.

[0074] When organic compound 131_1 has a strong donor framework, holes injected into the light-emitting layer 130 are easily injected into organic compound 131_1 and transported. In this case, organic compound 131_2 preferably includes a donor framework with stronger acceptor properties than organic compound 131_1. Thus, organic compound 131_1 and organic compound 131_2 readily form an excited-state complex. Alternatively, when organic compound 131_1 has a strong acceptor framework, electrons injected into the light-emitting layer 130 are easily injected into organic compound 131_1 and transported. In this case, organic compound 131_2 preferably includes a donor framework with stronger donor properties than organic compound 131_1. Thus, organic compound 131_1 and organic compound 131_2 readily form an excited-state complex.

[0075] When organic compound 131_1 has the ability to convert triplet excitation energy into singlet excitation energy independently via antisystem crossing, and organic compounds 131_1 and 131_2 do not easily form excited-state complexes, for example, when the HOMO energy level of organic compound 131_1 is higher than that of organic compound 131_2, and the LUMO energy level of organic compound 131_2 is higher than that of organic compound 131_1, electrons and holes injected into the luminescent layer 130 as carriers are easily injected into organic compound 131_1 and transported. In this case, the carrier balance in the luminescent layer 130 needs to be controlled by the hole transport and electron transport properties of organic compound 131_1. Therefore, in addition to having the ability to convert triplet excitation energy into singlet excitation energy independently, organic compound 131_1 also needs to have a molecular structure with appropriate carrier balance, making molecular structure design difficult. On the other hand, in one embodiment of the present invention, since electrons are injected into one of the organic compounds 131_1 and 131_2 and transported to the other through a hole, the carrier balance can be easily controlled according to their mixing ratio, and a light-emitting element exhibiting high luminous efficiency can be provided.

[0076] For example, when the HOMO energy level of organic compound 131_2 is higher than that of organic compound 131_1, and the LUMO energy level of organic compound 131_1 is higher than that of organic compound 131_2, electrons and holes injected into the light-emitting layer 130 as carriers are easily injected into organic compound 131_2 and transported. Therefore, carrier recombination easily occurs in organic compound 131_2. When organic compound 131_2 does not have the function of converting triplet excitation energy to singlet excitation energy independently via antisystem crossing, it becomes difficult to convert the triplet excitation energy of excitons directly generated by carrier recombination into singlet excitation energy. Therefore, the energy other than the singlet excitation energy in the excitons directly generated by carrier recombination is not easily used for luminescence. On the other hand, in one embodiment of the present invention, organic compounds 131_1 and 131_2 can form an excited-state complex, converting the triplet excitation energy to singlet excitation energy via antisystem crossing. Therefore, a light-emitting element with high luminous efficiency and high reliability can be provided.

[0077] Figure 1C shows a case where the S1 energy level of organic compound 131_2 is higher than that of organic compound 131_1, and the T1 energy level of organic compound 131_1 is higher than that of organic compound 131_2. However, one embodiment of the present invention is not limited to this. For example, as shown in Figure 3A, the S1 energy level of organic compound 131_1 may also be higher than that of organic compound 131_2, and the T1 energy level of organic compound 131_1 may also be higher than that of organic compound 131_2. Alternatively, as shown in Figure 3B, the S1 energy level of organic compound 131_1 may be approximately the same as that of organic compound 131_2. Alternatively, as shown in Figure 3C, the S1 energy level of organic compound 131_2 may also be higher than that of organic compound 131_1, and the T1 energy level of organic compound 131_2 may also be higher than that of organic compound 131_1. Note that in any of the above cases, in order to efficiently generate anti-system crossing, the T1 energy level of the excited-state complex is preferably lower than that of the organic compounds (organic compound 131_1 and organic compound 131_2) that form the excited-state complex. Furthermore, in the process of forming the excited-state complex, the process of first generating anti-system crossing in organic compound 131_1, increasing the ratio of singlet excited states (with the SH1 energy level) of organic compound 131_1, and then generating a singlet excited-state complex (with the SE energy level) (and then transferring energy to the guest) is also effective for improving efficiency. In this case, since the T1 energy level (TH2) of organic compound 131_2 is preferably higher than that of organic compound 131_1 (TH1), the structure shown in Figure 3C is preferred.

[0078] Since the direct transition from the singlet ground state to the triplet excited state in guest material 132 is a forbidden transition, the energy transfer from the S1 level (SE) of the excited-state complex to the T1 level (TG) of guest material 132 is not likely to become the main energy transfer process.

[0079] Furthermore, when a triplet excitation energy transfer occurs from the T1 energy level (TE) of the excited-state complex to the T1 energy level (TG) of the guest material 132, the triplet excitation energy is deactivated (refer to path E6 in Figure 1C). Therefore, the energy transfer via path E6 is preferably minimal to reduce the generation efficiency of the triplet excited state of the guest material 132 and decrease thermal deactivation. For this purpose, it is preferable that the proportion of the guest material 132 in the weight ratio of the host material 131 to the guest material 132 is low; specifically, the weight ratio of the guest material 132 relative to the host material 131 is preferably 0.001 or more and 0.05 or less, more preferably 0.001 or more and 0.03 or less, and even more preferably 0.001 or more and 0.01 or less.

[0080] Note that when the direct recombination process of carriers in guest material 132 is dominant, multiple triplet excitons are generated in the luminescent layer 130, and thermal deactivation leads to a decrease in luminescence efficiency. Therefore, it is preferable that the proportion of energy transfer processes via the generation of excited-state complexes (paths E4 and E5 in FIG. 1C) is higher than the proportion of the direct recombination process of carriers in guest material 132, because this can reduce the generation efficiency of triplet excited states of guest material 132 and suppress thermal deactivation. For this purpose, the proportion of guest material 132 in the weight ratio of host material 131 to guest material 132 is relatively low. Specifically, the weight ratio of guest material 132 relative to host material 131 is preferably 0.001 or more and 0.05 or less, more preferably 0.001 or more and 0.03 or less, and even more preferably 0.001 or more and 0.01 or less.

[0081] As described above, when the energy transfer processes of paths E4 and E5 occur efficiently, both the singlet excitation energy and the triplet excitation energy of the host material 131 are efficiently converted into the energy of the singlet excited state of the guest material 132, so the light-emitting element 150 can emit light with high luminous efficiency.

[0082] In this specification and other materials, the processes described above, such as paths E3, E4, and E5, are sometimes referred to as ExSET (Exciplex-Singlelet Energy Transfer) or ExEF (Exciplex-Enhanced Fluorescence). In other words, in the luminescent layer 130, an excitation energy supply is generated from the excited-state complex to the guest material 132.

[0083] By giving the light-emitting layer 130 the above structure, the light emitted from the guest material 132 from the light-emitting layer 130 can be obtained efficiently.

[0084] <Energy Transfer Mechanism> The controlling factors of the intermolecular energy transfer process between host material 131 and guest material 132 are explained below. Two mechanisms are proposed as the mechanisms for intermolecular energy transfer: the Förster mechanism (dipole-dipole interaction) and the Dexter mechanism (electron exchange interaction). Note that although the intermolecular energy transfer process between host material 131 and guest material 132 is explained here, the same applies when host material 131 is an excited-state complex.

[0085] "The Foster Mechanism" In the Foster mechanism, direct intermolecular contact is not required for energy transfer; energy transfer occurs through the resonance phenomenon of dipole oscillations between the host material 131 and the guest material 132. Through this resonance phenomenon, the host material 131 supplies energy to the guest material 132, transforming the excited state of the host material 131 into the ground state, and the ground state of the guest material 132 into the excited state. Furthermore, Equation 1 shows the rate constant kh*→g in the Foster mechanism.

[0086]

[0087] In Equation 1, ν represents the oscillation number, f'h(ν) represents the normalized emission spectrum of the host material 131 (equivalent to fluorescence when considering energy transfer from a singlet excited state, and equivalent to phosphorescence when considering energy transfer from a triplet excited state), εg(ν) represents the molar absorptivity of the guest material 132, N represents the Avogadro number, n represents the refractive index of the medium, R represents the intermolecular distance between the host material 131 and the guest material 132, τ represents the lifetime of the measured excited state (fluorescence lifetime or phosphorescence lifetime), c represents the speed of light, Φ represents the luminescence quantum yield (equivalent to fluorescence quantum yield when considering energy transfer from a singlet excited state, and equivalent to phosphorescence quantum yield when considering energy transfer from a triplet excited state), and K2 represents the alignment coefficient (0 to 4) of the transition dipole moments of the host material 131 and the guest material 132. Furthermore, in random alignment, K2 = 2 / 3.

[0088] "The Dexter Mechanism" In the Dexter mechanism, the host material 131 and the guest material 132 are close to the effective contact distance of overlapping production orbitals, and energy transfer occurs by exchanging electrons in the excited state of the host material 131 and the ground state of the guest material 132. Furthermore, Equation 2 shows the velocity constant kh*→g of the Dexter mechanism.

[0089]

[0090] In Equation 2, h represents Planck's constant, K represents a constant with energy dimension, ν represents the oscillation number, f'h(ν) represents the normalized emission spectrum of the host material 131 (equivalent to fluorescence when considering energy transfer from a singlet excited state, and equivalent to phosphorescence when considering energy transfer from a triplet excited state), ε'g(ν) represents the normalized absorption spectrum of the guest material 132, L represents the effective molecular radius, and R represents the intermolecular distance between the host material 131 and the guest material 132.

[0091] Here, the energy transfer efficiency ΦET from host material 131 to guest material 132 is expressed by Equation 3. kr represents the rate constant of the luminescence process of host material 131 (equivalent to fluorescence when considering energy transfer from a singlet excited state, and equivalent to phosphorescence when considering energy transfer from a triplet excited state), kn represents the rate constant of the non-luminescence process (thermal deactivation or intersystem crossing) of host material 131, and τ represents the lifetime of the excited state of host material 131 as measured.

[0092]

[0093] As can be seen from Formula 3, in order to improve the energy transfer efficiency ΦET, the energy transfer velocity constant kh*→g should be increased, while the other competing velocity constants kr+kn (=1 / τ) should be relatively reduced.

[0094] <> First, consider energy transfer based on the Foster mechanism. By substituting Equation 1 into Equation 3, τ can be eliminated. Therefore, in the Foster mechanism, the energy transfer efficiency ΦET does not depend on the lifetime τ of the excited state of the host material 131. Furthermore, when the luminescence quantum yield Φ (since this is an explanation of energy transfer from a singlet excited state, it refers to the fluorescence quantum yield here) is high, the energy transfer efficiency ΦET can be said to be high. Generally, the luminescence quantum yield of triplet excited states from organic compounds is very low at room temperature. Therefore, when the host material 131 is in a triplet excited state, the energy transfer process based on the Foster mechanism can be ignored, and only the case where the host material 131 is in a singlet excited state needs to be considered.

[0095] Furthermore, the overlap between the emission spectrum of the host material 131 (which is the fluorescence spectrum when describing energy transfer from the singlet excited state) and the absorption spectrum of the guest material 132 (corresponding to absorption during the migration from the singlet ground state to the singlet excited state) is preferably large. Moreover, the moiré absorptivity of the guest material 132 is preferably high. This means that the emission spectrum of the host material 131 overlaps with the absorption band appearing on the longest wavelength side of the guest material 132. Note that since the direct transition from the singlet ground state to the triplet excited state in the guest material 132 is a forbidden transition, the moiré absorptivity in the triplet excited state in the guest material 132 is negligible. Therefore, the energy transfer process from the guest material 132 to the triplet excited state based on the Foster mechanism can be ignored; only the energy transfer process from the guest material 132 to the singlet excited state needs to be considered. In other words, in the Foster mechanism, only the energy transfer process from the singlet excited state of the host material 131 to the singlet excited state of the guest material 132 needs to be considered.

[0096] Next, consider energy transfer based on the Dexter mechanism. As shown in Equation 2, to increase the rate constant kh*→g, the overlap between the emission spectrum of the host material 131 (which is the fluorescence spectrum when describing energy transfer from the singlet excited state) and the absorption spectrum of the guest material 132 (corresponding to absorption during the migration from the singlet ground state to the singlet excited state) should ideally be large. Therefore, the optimization of energy transfer efficiency can be achieved by overlapping the emission spectrum of the host material 131 with the absorption band present on the longest wavelength side of the guest material 132.

[0097] Furthermore, when Equation 2 is substituted into Equation 3, it can be seen that the energy transfer efficiency ΦET in the Dexter mechanism depends on τ. Because the Dexter mechanism is an energy transfer process based on electron exchange, similar to the energy transfer from the singlet excited state of the host material 131 to the singlet excited state of the guest material 132, energy transfer also occurs from the triplet excited state of the host material 131 to the triplet excited state of the guest material 132.

[0098] In one embodiment of the light-emitting element of the present invention, the guest material 132 is a fluorescent material, so the energy transfer efficiency from the host material 131 to the guest material 132 triplet excited state is preferably low. That is, the energy transfer efficiency from the host material 131 to the guest material 132 based on the Dexter mechanism is preferably low, while the energy transfer efficiency from the host material 131 to the guest material 132 based on the Foster mechanism is preferably high.

[0099] As mentioned above, the energy transfer efficiency based on the Foster mechanism does not depend on the lifetime τ of the excited state of the host material 131. On the other hand, the energy transfer efficiency based on the Dexter mechanism depends on the lifetime τ of the excited state of the host material 131. Therefore, in order to reduce the energy transfer efficiency based on the Dexter mechanism, the lifetime τ of the excited state of the host material 131 is preferably short.

[0100] Similar to the energy transfer from host material 131 to guest material 132, energy transfer from excited-state complex to guest material 132 also occurs based on both the Foster mechanism and the Dexter mechanism.

[0101] Therefore, one embodiment of the present invention provides a light-emitting element comprising organic compounds 131_1 and 131_2, which form a combination of excited-state complexes capable of efficiently transferring energy to a guest material 132 and serving as an energy donor, as a host material 131. The excited-state complexes formed by organic compounds 131_1 and 131_2 have a singlet excitation energy level close to a triplet excitation energy level. Therefore, migration from triplet excitons to singlet excitons (antisystem crossing) is readily generated in the light-emitting layer 130. Thus, the generation efficiency of singlet excitons in the light-emitting layer 130 can be improved. Furthermore, to facilitate energy transfer from the singlet excited state of the excited-state complex to the singlet excited state of the guest material 132 serving as an energy acceptor, it is preferable that the emission spectrum of the excited-state complex overlaps with the absorption band of the guest material 132 exhibiting the longest wavelength side (low energy side). This improves the generation efficiency of the singlet excited state of the guest material 132.

[0102] In addition, in the luminescence exhibited by the excited-state complex, the fluorescence lifetime of the thermally activated delayed fluorescence component is preferably short, specifically, 10 ns or more and 50 μs or less, more preferably 10 ns or more and 30 μs or less.

[0103] Furthermore, in the luminescence exhibited by the excited-state complex, the proportion of thermally activated delayed fluorescence is preferably high. Specifically, in the luminescence exhibited by the excited-state complex, the proportion of thermally activated delayed fluorescence is preferably 5% or more, and more preferably 10% or more.

[0104] <Material> Next, the components of a light-emitting element according to an embodiment of the present invention will be described.

[0105] <<Emitting Layer>> The materials that can be used in the light-emitting layer 130 are described below.

[0106] In the material weight ratio of the luminescent layer 130, the host material 131 accounts for the largest proportion, and the guest material 132 (fluorescent material) is dispersed in the host material 131. Preferably, the S1 energy level of the host material 131 (organic compounds 131_1 and 131_2) of the luminescent layer 130 is higher than the S1 energy level of the guest material 132 (fluorescent material) of the luminescent layer 130. Furthermore, preferably, the T1 energy level of the host material 131 (organic compounds 131_1 and 131_2) of the luminescent layer 130 is higher than the T1 energy level of the guest material 132 (fluorescent material) of the luminescent layer 130.

[0107] Organic compound 131_1 preferably has the function of converting a triple excitation energy into a single excitation energy by means of an anti-system crossover, and also has the function of exhibiting thermally activated delayed fluorescence at room temperature. Thermally activated delayed fluorescence materials can be cited as materials that convert the triple excitation energy into a single excitation energy. When the thermally activated delayed fluorescence material is composed of a single material, for example, the following materials can be used.

[0108] First, examples include fullerenes or their derivatives, acridine derivatives such as proflavin, and eosin. Additionally, examples include metalloporphyrins containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd). 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)), protoporphyrin-tin fluoride complexes (SnF2(Etio I)), and octaethylporphyrin-platinum chloride complexes (PtCl2OEP).

[0109]

[0110] In addition, as a thermally activated delayed fluorescence material composed of a single material, heterocyclic compounds with π-electron-rich and π-electron-deficient heterocyclic aromatic skeletons can also be used. Specifically, examples include 2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazole-11-yl)-1,3,5-triazine (abbreviated: PIC-TRZ), 2-{4-[3-(N-phenyl-9H-carbazole-3-yl)-9H-carbazole-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviated: PCCzPTzn), 2-[4-(10H-phenoxazine-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviated: PXZ-TRZ), and 3-[4-(5-phenyl-5,10-dihydrophenoxazine-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine. Examples of heterocyclic compounds include 4,5-diphenyl-1,2,4-triazole (PPZ-3TPT), 3-(9,9-dimethyl-9H-acridin-10-yl)-9H-oxazanth-9-one (ACRXTN), bis[4-(9,9-dimethyl-9,10-dihydroacridin)phenyl]thiophene (DMAC-DPS), and 10-phenyl-10H,10'H-spiro[acridin-9,9'-anthracene]-10'-one (ACRSA). These heterocyclic compounds possess both π-electron-rich and π-electron-deficient heteroaromatic skeletons, resulting in high electron and hole transport properties, making them preferred. Among π-electron-deficient heteroaromatic skeletons, diazine skeletons (pyrimidine skeletons, pyrazine skeletons, pyrazine skeletons) or triazine skeletons are stable and reliable, thus being preferred. Furthermore, among π-electron-rich heteroaromatic skeletons, acridine, phenoxazine, phenanthrene, furan, thiophene, and pyrrole skeletons are stable and reliable, so having one or more selected from these skeletons is preferred. As the pyrrole skeleton, indole or carbazole skeletons are preferred, and 3-(9-phenyl-9H-carbazole-3-yl)-9H-carbazole skeleton is particularly preferred. Moreover, in substances where π-electron-rich and π-electron-deficient heteroaromatic skeletons are directly bonded, the donor nature of the π-electron-rich heteroaromatic skeleton and the acceptor nature of the π-electron-deficient heteroaromatic skeleton are both strong, and the difference between the singlet and triplet excitation energy levels is smaller, making it especially preferred.

[0111]

[0112] Organic compound 131_1 may or may not possess the ability to convert triple excitation energy to single excitation energy via antisystem crossing. In this case, in organic compound 131_1, it is preferable that at least one of a π-electron-rich heteroaromatic skeleton and an aromatic amine skeleton is bonded to a π-electron-deficient heteroaromatic skeleton via a structure having at least one of a m-epylphenyl and an or o-epylphenyl group. Alternatively, it is preferable that the epylphenyl group is bonded via an aryl group having at least one of a m-epylphenyl and an or o-epylphenyl group; more preferably, the aryl group is a biphenylene. By employing the above structure, the T1 energy level of organic compound 131_1 can be increased. Furthermore, in this case, the π-electron-deficient heteroaromatic skeleton is preferably a diazine skeleton (pyrimidine skeleton, pyrazine skeleton, pyrazine skeleton) or a triazine skeleton. The π-electron-rich heteroaromatic skeleton is preferably one or more of an acridine skeleton, a phenoxazine skeleton, a phenoxythiazine skeleton, a furan skeleton, a thiophene skeleton, and a pyrrole skeleton. Furthermore, the furan skeleton is preferably a dibenzofuran skeleton, and the thiophene skeleton is preferably a dibenzothiophene skeleton. Additionally, the pyrrole skeleton is preferably an indole skeleton, a carbazole skeleton, and particularly preferably a 3-(9-phenyl-9H-carbazole-3-yl)-9H-carbazole skeleton. Furthermore, the aromatic amine skeleton is preferably a so-called tertiary amine without NH bonds, and particularly preferably a triarylamine skeleton. The aryl group in the triarylamine skeleton is preferably a substituted or unsubstituted aryl group with 6 to 13 carbon atoms forming the ring, such as phenyl, naphthyl, and geniyl.

[0113] Examples of the aforementioned aromatic amine skeletons and π-electron-rich heteroaromatic skeletons include those represented by the general formulas (101) to (117) below. Note that X in general formulas (113) to (116) represents an oxygen atom or a sulfur atom.

[0114]

[0115] Examples of π-electron-deficient heteroaromatic skeletons can be exemplified by the skeletons represented by the following general formulas (201) to (218).

[0116]

[0117] In cases where a skeleton with hole transport capability (specifically, at least one of a π-electron-rich heteroaromatic skeleton and an aromatic amine skeleton) is bonded to a skeleton with electron transport capability (specifically, a π-electron-deficient heteroaromatic skeleton) by a bonding group having at least one of m-phenyl and o-phenyl groups, or by a bonding group including an aryl group having at least one of m-phenyl and o-phenyl groups, an example of such a bonding group is a skeleton represented by the following general formulas (301) to (314). Furthermore, examples of the aforementioned aryl group include benzene skeletons, biphenyl dimethyl skeletons, naphthyl dimethyl skeletons, fenandiyl skeletons, phenanthrene dimethyl skeletons, etc.

[0118]

[0119] The aforementioned aromatic amine skeletons (specifically, triarylamine skeletons), π-electron-rich heteroaromatic skeletons (specifically, rings having an acridine skeleton, phenoxazine skeleton, phenanthrethazine skeleton, furan skeleton, thiophene skeleton, and pyrrole skeleton), π-electron-deficient heteroaromatic skeletons (specifically, rings having, for example, a diazine skeleton or a triazine skeleton), the aforementioned general formulas (101) to (117), general formulas (201) to (218), or general formulas (301) to (314) may have substituents. As substituents, alkyl groups having 1 to 6 carbon atoms, cycloalkyl groups having 3 to 6 carbon atoms, or substituted or unsubstituted aryl groups having 6 to 12 carbon atoms may be selected. Examples of alkyl groups having 1 to 6 carbon atoms include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tributyl, and n-hexyl. Furthermore, examples of cycloalkyl groups with 3 to 6 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl. Examples of aryl groups with 6 to 12 carbon atoms include phenyl, naphthyl, and biphenyl. Moreover, the aforementioned substituents can bond with each other to form a ring. As an example, when two phenyl groups are present as substituents at the 9th carbon position of the spirochete skeleton, these phenyl groups bond with each other to form a spirochete skeleton. Furthermore, in the unsubstituted case, there are advantages in terms of ease of synthesis or cost of raw materials.

[0120] Furthermore, Ar represents an aryl group having 6 to 13 carbon atoms, which may have substituents that can bond together to form a ring. Examples of this include cases where two phenyl groups are substituents at the 9-position of the aryl group, and these phenyl groups bond together to form a spirochete skeleton. Examples of aryl groups having 6 to 13 carbon atoms include phenylene, naphthyl, biphenylene, and pyridyl. When the aryl group has substituents, the substituents can be alkyl groups having 1 to 6 carbon atoms, cycloalkyl groups having 3 to 6 carbon atoms, or aryl groups having 6 to 12 carbon atoms. Specifically, examples of alkyl groups having 1 to 6 carbon atoms include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tributyl, and n-hexyl. In addition, examples of cycloalkyl groups with 3 to 6 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl. Examples of aryl groups with 6 to 12 carbon atoms include phenyl, naphthyl, and biphenyl.

[0121] Furthermore, the aryl group represented by Ar can be, for example, a group represented by the following structural formulas (Ar-1) to (Ar-18). However, the groups that can be used as Ar are not limited to these.

[0122]

[0123] Furthermore, R1 and R2 independently represent hydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 13 carbon atoms, respectively. Specifically, examples of alkyl groups having 1 to 6 carbon atoms include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tributyl, and n-hexyl. Specifically, examples of cycloalkyl groups having 3 to 6 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl. Specifically, examples of aryl groups having 6 to 13 carbon atoms include phenyl, naphthyl, biphenyl, and geniyl. Furthermore, the aforementioned aryl and phenyl groups may have substituents that can bond together to form a ring. Specifically, the substituents may be alkyl groups having 1 to 6 carbon atoms, cycloalkyl groups having 3 to 6 carbon atoms, or aryl groups having 6 to 12 carbon atoms. Examples of alkyl groups having 1 to 6 carbon atoms include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tributyl, and n-hexyl. Examples of cycloalkyl groups having 3 to 6 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl. Examples of aryl groups having 6 to 12 carbon atoms include phenyl, naphthyl, and biphenyl.

[0124] Additionally, the alkyl or aryl groups represented by R1 and R2 can be, for example, groups represented by the following structural formulas (R-1) to (R-29). However, the groups that can be used as alkyl or aryl groups are not limited to these.

[0125]

[0126] Furthermore, as substituents that can be present in general formulas (101) to (117), general formulas (201) to (218), general formulas (301) to (314), Ar, R1, and R2, alkyl or aryl groups represented by the above structural formulas (R-1) to (R-24) can be used. In addition, the groups that can be used as alkyl or aryl groups are not limited to these.

[0127] In the light-emitting layer 130, there are no particular restrictions on the guest material 132, but it is preferred to use anthracene derivatives, condensed tetraphenyl derivatives, etc. (chrysene) derivatives, phenanthrene derivatives, pyrene derivatives, perylene derivatives, stilbene derivatives, acridinone derivatives, coumarin derivatives, phenoxazine derivatives, phenanthrene-thiazine derivatives, etc., such as the following materials can be used.

[0128] Specifically, examples of this material include 5,6-bis[4-(10-phenyl-9-anthrayl)phenyl]-2,2'-bipyridine (abbreviated as: PAP2BPy), 5,6-bis[4'-(10-phenyl-9-anthrayl)biphenyl-4-yl]-2,2'-bipyridine (abbreviated as: PAPP2BPy), N,N'-diphenyl-N,N'-bis[4-(9-phenyl-9H-enrofloxacin-9-yl)phenyl]pyrene-1,6-diamine (abbreviated as: 1,6FLPAPrn), N,N'-bis(3-methylphenyl)-N,N'-bis[3-(9-phenyl-9H-enrofloxacin-9-yl)phenyl]pyrene-1, 6-Diamine (abbreviated as: 1,6mMemFLPAPrn), N,N'-bis[4-(9-phenyl-9H-en-9-yl)phenyl]-N,N'-bis(4-tert-butylphenyl)pyrene-1,6-diamine (abbreviated as: 1,6tBu-FLPAPrn), N,N'-diphenyl-N,N'-bis[4-(9-phenyl-9H-en-9-yl)phenyl]-3,8-dicyclohexylpyrene-1,6-diamine (abbreviated as: ch-1,6FLPAPrn), N,N'-bis[4-(9H-carbazole-9-yl)phenyl]-N,N'-diphenylstilbene-4,4'-diamine (abbreviated as: YG) A2S), 4-(9H-carbazole-9-yl)-4'-(10-phenyl-9-anthrayl)triphenylamine (abbreviation: YGAPA), 4-(9H-carbazole-9-yl)-4'-(9,10-diphenyl-2-anthrayl)triphenylamine (abbreviation: 2YGAPPA), N,9-diphenyl-N-[4-(10-phenyl-9-anthrayl)phenyl]-9H-carbazole-3-amine (abbreviation: PCAPA), perylene, 2,5,8,11-tetra(tertiary butyl)perylene (abbreviation: TBP), 4-(10-phenyl-9-anthrayl)-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCB) APA), N,N”-(2-tert-butylanthracene-9,10-diyldi-4,1-epenylphenyl)bis[N,N',N'-triphenyl-1,4-phenylenediamine] (abbreviated as: DPABPA), N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthrayl)phenyl]-9H-carbazole-3-amine (abbreviated as: 2PCAPPA), N-[4-(9,10-diphenyl-2-anthrayl)phenyl]-N,N',N'-triphenyl-1,4-phenylenediamine (abbreviated as: 2DPAPPA), N,N,N',N',N”,N”,N''',N'''-octaphenyldibenzo[g,p] (chrysene)-2,7,10,15-tetramine (abbreviation: DBC1), coumarin 30, N-(9,10-diphenyl-2-anthrayl)-N,9-diphenyl-9H-carbazole-3-amine (abbreviation: 2PCAPA), N-[9,10-bis(1,1'-biphenyl-2-yl)-2-anthrayl]-N,9-diphenyl-9H-carbazole-3-amine (abbreviation: 2PCABPhA), N-(9,10-diphenyl-2-anthrayl)-N,N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPA), N-[ [9,10-bis(1,1'-biphenyl-2-yl)-2-anthrayl]-N,N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPABPhA), 9,10-bis(1,1'-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracene-2-amine (abbreviation: 2YGABPhA), N,N,9-triphenylanthracene-9-amine (abbreviation: DPhAPhA), coumarin 6, coumarin 545T, N,N'-diphenylquinacridone (abbreviation: DPQd), fluorene, 2,8-di-tributyl-5 11-Bis(4-tert-butylphenyl)-6,12-diphenyl condensed tetraphenyl (abbreviation: TBRb), Nile Red, 5,12-bis(1,1'-biphenyl-4-yl)-6,11-diphenyl condensed tetraphenyl (abbreviation: BPT), 2-(2-{2-[4-(dimethylamino)phenyl]vinyl}-6-methyl-4H-pyran-4-ylidene)propanedionitrile (abbreviation: DCM1), 2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinazin-9-yl)vinyl]-4H-pyran-4-ylidene}propanedionitrile Nitriles (abbreviated as: DCM2), N,N,N',N'-tetra(4-methylphenyl)tetraphenyl-5,11-diamine (abbreviated as: p-mPhTD), 7,14-diphenyl-N,N,N',N'-tetra(4-methylphenyl)acenaphthene[1,2-a]propadiene-3,10-diamine (abbreviated as: p-mPhAFD), 2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinazin-9-yl)vinyl]-4H-pyran-4-yl}propanedionitrile (abbreviated as: DCJTI), 2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinazin-9-yl)vinyl]-4H-pyran-4-ylidene}propanedionitrile (abbreviation: DCJTB), 2-(2,6-bis{2-[4-(dimethylamino)phenyl]vinyl}-4H-pyran-4-ylidene)propanedionitrile (abbreviation: BisDCM), 2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinazine-9-yl]vinyl]-4H-pyran-4-ylidene}propanedionitrile (abbreviated as: BisDCJTM), 5,10,15,20-tetraphenylbisbenzo[5,6]indo[1,2,3-cd:1',2',3'-lm]perylene, etc.

[0129] Note that, as described above, the energy transfer efficiency based on the Dexter mechanism from the host material 131 (or the excited-state complex) to the guest material 132 is preferably low. The rate constant of the Dexter mechanism is inversely proportional to the exponential function of the distance between the two molecules. Thus, the Dexter mechanism dominates when the distance between the two molecules is less than approximately 1 nm, and the Foster mechanism dominates when the distance between the two molecules is greater than approximately 1 nm. Therefore, in order to reduce the energy transfer efficiency based on the Dexter mechanism, it is preferable to increase the distance between the host material 131 and the guest material 132, specifically, the distance is preferably 0.7 nm or more, more preferably 0.9 nm or more, and even more preferably 1 nm or more. From the above viewpoint, the guest material 132 preferably has a substituent that hinders the approach of the host material 131, preferably an aliphatic hydrocarbon, more preferably an alkyl group, and even more preferably a branched alkyl group. Specifically, the guest material 132 preferably includes at least two alkyl groups having two or more carbon atoms. Alternatively, guest material 132 is preferably a branched alkyl group having 3 or more but less than 10 carbon atoms. Alternatively, guest material 132 is preferably a branched cycloalkyl group having 3 or more but less than 10 carbon atoms.

[0130] As for organic compound 131_2, a combination capable of forming an excited-state complex with organic compound 131_1 is employed. Specifically, in addition to zinc and aluminum metal complexes, other examples include... Diazole derivatives, triazole derivatives, benzimidazole derivatives, quinolone porphyrin derivatives, dibenzoquinone Phosphine derivatives, dibenzothiophene derivatives, dibenzofuran derivatives, pyrimidine derivatives, triazine derivatives, pyridine derivatives, bipyridine derivatives, and cynolinite derivatives are among the examples. Other examples include aromatic amines or carbazole derivatives. Preferably, organic compound 131_1, organic compound 131_2, and guest material 132 (fluorescent material) are selected such that the emission peak of the excited-state complex formed by organic compound 131_1 and organic compound 131_2 overlaps with the absorption band of the longest wavelength side (low energy side) of guest material 132 (fluorescent material). This allows for the realization of a light-emitting element with significantly improved luminous efficiency.

[0131] In addition, the following hole transport materials and electron transport materials can be used as organic compound 131_2.

[0132] As a hole-transporting material, materials with higher hole transport properties than electron transport properties can be used, preferably materials with a hole mobility of 1×10⁻⁶ cm² / Vs or higher. Specifically, aromatic amines, carbazole derivatives, aromatic hydrocarbons, stilbene derivatives, etc., can be used. The aforementioned hole-transporting materials can also be polymeric compounds.

[0133] Materials with high hole transport properties, for example, as aromatic amine compounds, include N,N'-bis(p-tolyl)-N,N'-diphenyl-p-phenylenediamine (DTDPPA), 4,4'-bis[N-(4-diphenylaminophenyl)-N-anilino]biphenyl (DPAB), N,N'-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (DNTPD), and 1,3,5-tris[N-(4-diphenylaminophenyl)-N-anilino]benzene (DPA3B), etc.

[0134] In addition, as carbazole derivatives, specifically examples include 3-[N-(4-diphenylaminophenyl)-N-anilino]-9-phenylcarbazole (abbreviated as: PCzDPA1), 3,6-bis[N-(4-diphenylaminophenyl)-N-anilino]-9-phenylcarbazole (abbreviated as: PCzDPA2), and 3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole (abbreviated as: P). CzTPN2), 3-[N-(9-phenylcarbazole-3-yl)-N-anilino]-9-phenylcarbazole (abbreviated as PCzPCA1), 3,6-bis[N-(9-phenylcarbazole-3-yl)-N-anilino]-9-phenylcarbazole (abbreviated as PCzPCA2), 3-[N-(1-naphthyl)-N-(9-phenylcarbazole-3-yl)amino]-9-phenylcarbazole (abbreviated as PCzPCN1), etc.

[0135] In addition, other examples of carbazole derivatives include 4,4'-bis(N-carbazolyl)biphenyl (abbreviated as CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviated as TCPB), 9-[4-(10-phenyl-9-anthrayl)phenyl]-9H-carbazole (abbreviated as CzPA), and 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene.

[0136] In addition, examples of aromatic hydrocarbons include 2-tertiary butyl-9,10-bis(2-naphthyl)anthracene (t-BuDNA), 2-tertiary butyl-9,10-bis(1-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene (DPPA), 2-tertiary butyl-9,10-bis(4-phenylphenyl)anthracene (t-BuDBA), 9,10-bis(2-naphthyl)anthracene (DNA), 9,10-diphenylanthracene (DPAnth), 2-tertiary butylanthracene (t-BuAnth), and 9,10-bis(4-methyl-1-naphthyl)anthracene (DMN). A) 2-Tributyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene, 9,10-bis[2-(1-naphthyl)phenyl]anthracene, 2,3,6,7-tetramethyl-9,10-bis(1-naphthyl)anthracene, 2,3,6,7-tetramethyl-9,10-bis(2-naphthyl)anthracene, 9,9'-bianthracene, 10,10'-diphenyl-9,9'-bianthracene, 10,10'-bis(2-phenylphenyl)-9,9'-bianthracene, 10,10'-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9'-bianthracene, anthracene, condensed tetraphenylene, red fluorene, perylene, 2,5,8,11-tetra(tributyl)perylene, etc. In addition, condensed pentaphenylene, guanidine, etc., can also be used. Therefore, it is preferable to use aromatic hydrocarbons with a hole mobility of 1×10-6 cm2 / Vs or higher and a carbon number of 14 to 42.

[0137] Note that aromatic hydrocarbons can also have a vinyl skeleton. Examples of aromatic hydrocarbons with vinyl skeletons include 4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviated as DPVBi) and 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviated as DPVPA).

[0138] Alternatively, high molecular weight compounds such as poly(N-vinylcarbazole) (PVK), poly(4-vinyltriphenylamine) (PVTPA), poly[N-(4-{N'-[4-(4-diphenylamino)phenyl]phenyl-N'-phenylamino}phenyl)methacrylamide] (PTPDMA), and poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (Poly-TPD) can also be used.

[0139] In addition, materials with high hole transport properties, for example, 4,4'-bis[N-(1-naphthyl)-N-anilino]biphenyl (abbreviated as: NPB or α-NPD), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviated as: TPD), 4,4',4”-tris(carbazole-9-yl)triphenylamine (abbreviated as: TCTA), 4,4',4”-tris[N-(1-naphthyl)-N-anilino]triphenylamine (abbreviated as: 1'-TNATA), 4,4',4”-tris(N,N-diphenylamino)triphenylamine (abbreviated as: TDATA), 4,4',4”-tris[N-(3-methylphenyl)-N-anilino]triphenylamine Amine (abbreviation: MTDATA), 4,4'-bis[N-(spiro-9,9'-bifuran-2-yl)-N-anilino]biphenyl (abbreviation: BSPB), 4-phenyl-4'-(9-phenylfuran-9-yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl-3'-(9-phenylfuran-9-yl)triphenylamine (abbreviation: mBPAFLP), N-(9,9-dimethyl-9H-furan-2-yl)-N-{9,9-dimethyl-2-[N'-phenyl-N'-(9,9-dimethyl-9H-furan-2-yl)amino]-9H-furan-7-yl}phenylamine (abbreviation: DFLADFL), N-(9,9-dimethyl-2-diphenylamino-9H-furan-7-yl)diphenyl Amine (abbreviation: DPNF), 2-[N-(4-diphenylaminophenyl)-N-anilino]spiro-9,9'-biphenyl (abbreviation: DPASF), 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: PCCNBB), 4-phenyldiphenyl-(9-phenyl-9H- Carbazole-3-yl)amine (abbreviated as PCA1BP), N,N'-bis(9-phenylcarbazole-3-yl)-N,N'-diphenylphenyl-1,3-diamine (abbreviated as PCA2B), N,N',N”-triphenyl-N,N',N”-tris(9-phenylcarbazole-3-yl)phenyl-1,3,5-triamine (abbreviated as PCA3B), N-(4-biphenyl)-N-(9,9-dimethyl-9H-furo-2-yl)-9-phenyl-9H-carbazole-3-amine (abbreviated as PCBiF), N-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]-9,9-dimethyl-9H-furo-2-amine (abbreviated as PCBBiF), 9,9-Dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-2-amine (abbreviated: PCBAF), N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9'-bifuran-2-amine (abbreviated: PCBASF), 2-[N-(9-phenylcarbazol-3-yl)-N-anilino]spiro-9,9'-bifuran (abbreviated: Aromatic amine compounds such as PCASF, 2,7-bis[N-(4-diphenylaminophenyl)-N-anilino]-spiro-9,9'-bifuran (abbreviated as: DPA2SF), N-[4-(9H-carbazole-9-yl)phenyl]-N-(4-phenyl)phenylaniline (abbreviated as: YGA1BP), and N,N'-bis[4-(carbazole-9-yl)phenyl]-N,N'-diphenyl-9,9-dimethylfuran-2,7-diamine (abbreviated as: YGA2F). Alternatively, 3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviated as PCPN), 3-[4-(9-phenanthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviated as PCPPn), 3,3'-bis(9-phenyl-9H-carbazole) (abbreviated as PCCP), 1,3-bis(N-carbazolyl)benzene (abbreviated as mCP), and 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviated as mCP) can be used. Abbreviations: CzTP, 3,6-bis(9H-carbazole-9-yl)-9-phenyl-9H-carbazole (abbreviation: PhCzGI), 2,8-bis(9H-carbazole-9-yl)-dibenzothiophene (abbreviation: Cz2DBT), 4-{3-[3-(9-phenyl-9H-en-9-yl)phenyl]phenyl}dibenzofuran (abbreviation: mmDBFFLBi-II), 4,4',4”-(phenyl-1,3,5-triyl) Tris(dibenzofuran) (abbreviated as DBF3P-II), 1,3,5-tris(dibenzothiophene-4-yl)-benzene (abbreviated as DBT3P-II), 2,8-diphenyl-4-[4-(9-phenyl-9H-en-9-yl)phenyl]dibenzothiophene (abbreviated as DBTFLP-III), 4-[4-(9-phenyl-9H-en-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviated as DBTFLP-IV), 4-[3-(triphenyl-2-yl)phenyl]dibenzothiophene (abbreviated as mDBTPTp-II) and other amine compounds, carbazole compounds, thiophene compounds, furan compounds, enantiophene compounds, triphenylbenzene compounds, phenanthrene compounds, etc. The substances described herein are primarily those with a hole mobility of 1 × 10⁻⁶ cm² / Vs or higher. However, any substance other than those mentioned above can be used as long as its hole transport capability is higher than its electron transport capability.

[0140] As electron transport materials, materials with higher electron transport than hole transport can be used, preferably materials with an electron mobility of 1×10⁻⁶ cm² / Vs or higher. As materials that readily accept electrons (materials with electron transport properties), π-electron-deficient heteroaromatic compounds such as nitrogen-containing heteroaromatic compounds or metal complexes can be used. Specifically, examples include quinoline ligands, benzoquinoline ligands, etc. Metal complexes of azole ligands or thiazole ligands, Diazole derivatives, triazole derivatives, phenobarbital derivatives, pyridine derivatives, bipyridine derivatives, pyrimidine derivatives, etc.

[0141] Metal complexes with a quinoline or benzo[h]quinoline skeleton include, for example, tris(8-hydroxyquinoline)aluminum(III) (abbreviated: Alq), tris(4-methyl-8-hydroxyquinoline)aluminum(III) (abbreviated: Almq3), bis(10-hydroxybenzo[h]quinoline)beryllium(II) (abbreviated: BeBq2), bis(2-methyl-8-hydroxyquinoline)(4-phenylphenol)aluminum(III) (abbreviated: BAlq), and bis(8-hydroxyquinoline)zinc(II) (abbreviated: Znq). In addition, bis[2-(2-benzo[h]quinoline]... Zinc(II)[2-(2-benzothiazolyl)phenol]zinc(II) (abbreviated as ZnPBO) and bis[2-(2-benzothiazolyl)phenol]zinc(II) (abbreviated as ZnBTZ) have the following properties: Metal complexes of azole and thiazole ligands, etc. Furthermore, in addition to metal complexes, 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4- diazole (abbreviated as PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4- [diazol-2-yl]benzene (abbreviation: OXD-7), 9-[4-(5-phenyl-1,3,4-] [diazol-2-yl)phenyl]-9H-carbazole (abbreviation: CO11), 3-(4-biphenyl)-4-phenyl-5-(4-tributylphenyl)-1,2,4-triazole (abbreviation: TAZ), 9-[4-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenyl]-9H-carbazole (abbreviation: CzTAZ1), 2,2',2”-(1,3,5-phenyltriyl)tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI), 2-[3-(dibenzothiophene-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: Heterocyclic compounds such as mDBTBIm-II, BPhen, BCP, and NBPhen; 2-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoline. 2mDBTPDBq-II, 2-[3'-(dibenzothiophene-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoline 2mDBTBPDBq-II, 2-[3'-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoline Phosphoroline (abbreviation: 2mCzBPDBq), 2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoline 2CzPDBq-III, 7-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoline Phosphoroline (abbreviation: 7mDBTPDBq-II), 6-[3-(dibenzothiophene-4-yl)phenyl]dibenzo[f,h]quinoline Phosphoroline (abbreviation: 6mDBTPDBq-II), 2-[3-[3-(3,9'-bi-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoline Heterocyclic compounds with a diazine skeleton, such as porphyrin (abbreviated as 2mCzCzPDBq), 4,6-bis[3-(phenanthrene-9-yl)phenyl]pyrimidine (abbreviated as 4,6mPnP2Pm), 4,6-bis[3-(4-dibenzothiophene)phenyl]pyrimidine (abbreviated as 4,6mDBTP2Pm-II), and 4,6-bis[3-(9H-carbazole-9-yl)phenyl]pyrimidine (abbreviated as 4,6mCzP2Pm); heterocyclic compounds with a triazine skeleton, such as PCCzPTzn; heterocyclic compounds with a pyridine skeleton, such as 3,5-bis[3-(9H-carbazole-9-yl)phenyl]pyridine (abbreviated as 35DCzPPy) and 1,3,5-tris[3-(3-pyridyl)phenyl]benzene (abbreviated as TmPyPB); and 4,4'-bis(5-methylbenzo[3-] Heterocyclic compounds such as azole-2-yl)stilbene (abbreviated as BzOs) are used. Among these heterocyclic compounds, those with a diazine (pyrimidine, pyrazine, pyrazine) or pyridine skeleton are stable and reliable, and are therefore preferred. In particular, heterocyclic compounds with the above skeletons have high electron transport properties, which also helps to reduce the driving voltage. In addition, polymeric compounds such as poly(2,5-pyridindiyl) (abbreviated as PPy), poly[(9,9-dihexylenyran-2,7-diyl)-co-(pyridin-3,5-diyl)] (abbreviated as PF-Py), and poly[(9,9-dioctylenyran-2,7-diyl)-co-(2,2'-bipyridin-6,6'-diyl)] (abbreviated as PF-BPy) can also be used. The substances described herein are mainly those with an electron mobility of 1×10-6 cm2 / Vs or higher. Note that any substance other than those mentioned above can be used as long as its electron transport property is higher than its hole transport property.

[0142] The light-emitting layer 130 can also be formed from two or more layers. For example, when the light-emitting layer 130 is formed by sequentially stacking a first light-emitting layer and a second light-emitting layer from the hole transport layer side, a material with hole transport properties can be used as the main material of the first light-emitting layer, and a material with electron transport properties can be used as the main material of the second light-emitting layer.

[0143] In addition, the light-emitting layer 130 may also include materials other than the host material 131 and the guest material 132.

[0144] <<Electric Hole Injection Layer>> The hole injection layer 111 has the function of promoting hole injection by lowering the hole injection energy barrier from one of the pair of electrodes (electrode 101 or electrode 102), and is formed, for example, using transition metal oxides, phthalocyanine derivatives, or aromatic amines. Examples of transition metal oxides include molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, and manganese oxide. Examples of phthalocyanine derivatives include phthalocyanine or metallic phthalocyanine. Examples of aromatic amines include benzidine derivatives or phenylenediamine derivatives. Alternatively, polymeric compounds such as polythiophene or polyaniline can also be used, typically poly(ethyldioxythiophene) / poly(styrenesulfonic acid) as self-doped polythiophene.

[0145] As the hole injection layer 111, a layer of composite material consisting of a hole-transporting material and a material having the property of receiving electrons from the hole-transporting material can be used. Alternatively, a stack of a layer containing a material having electron-receiving properties and a layer containing a hole-transporting material can be used. Charge transfer and acceptance can occur between these materials in a stationary state or in the presence of an electric field. Examples of materials having electron-receiving properties include organic acceptors such as quinone dimethane derivatives, tetrachlorobenzoquinone derivatives, and hexaazatribenzene derivatives. Specifically, examples include compounds with electron-withdrawing groups (halogen or cyano groups) such as 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinone dimethane (abbreviated: F4-TCNQ), chloroquinone, and 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatribenzene (abbreviated: HAT-CN). In addition, transition metal oxides, such as oxides of group 4 to group 8 metals, can also be used. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, rhenium oxide, etc., can be used. Molybdenum oxide is particularly preferred because it is stable in the atmosphere, has low hygroscopicity, and is easy to handle.

[0146] As a hole transport material, materials with higher hole transport properties than electron transport properties can be used, preferably materials with a hole mobility of 1×10⁻⁶ cm² / Vs or higher. Specifically, aromatic amines, carbazole derivatives, aromatic hydrocarbons, stilbene derivatives, etc., can be used as hole transport materials suitable for use in the luminescent layer 130. The aforementioned hole transport materials can also be polymer compounds.

[0147] <<Electric Hole Transport Layer>> The hole transport layer 112 is a layer containing a hole transport material, and the hole transport material exemplified as the material used in the hole injection layer 111 can be used. The hole transport layer 112 has the function of transporting holes injected into the hole injection layer 111 to the light emission layer 130, so it is preferably a HOMO level that is the same as or close to the HOMO level of the hole injection layer 111.

[0148] Furthermore, it is preferable to use a material with a hole mobility of 1×10⁻⁶ cm² / Vs or higher. However, any material other than the aforementioned materials may be used, as long as its hole mobility is higher than its electron mobility. In addition, the layer including the material with high hole mobility is not limited to a single layer, but may also be a layer composed of two or more layers of the aforementioned materials.

[0149] <<Electron Transport Layer>> The electron transport layer 118 has the function of transporting electrons injected from one of the two electrodes (electrode 101 or electrode 102) through the electron injection layer 119 to the light-emitting layer 130. As an electron transport material, a material with electron transport capability higher than hole transport capability can be used, preferably a material with an electron mobility of 1×10⁻⁶ cm² / Vs or higher. As a compound that readily accepts electrons (a material with electron transport capability), π-electron-deficient heteroaromatic compounds such as nitrogen-containing heteroaromatic compounds or metal complexes can be used. Specifically, examples of electron transport materials that can be used in the light-emitting layer 130 include quinoline ligands, benzoquinoline ligands, etc. Metal complexes of azole or thiazole ligands. In addition, examples can be given. Diazole derivatives, triazole derivatives, benzyline derivatives, pyridine derivatives, bipyridine derivatives, pyrimidine derivatives, etc. Furthermore, it is preferable to use a substance with an electron mobility of 1×10⁻⁶ cm² / Vs or higher. Any substance other than those mentioned above can be used as long as its electron transport capacity is higher than its hole transport capacity. Furthermore, the electron transport layer 118 is not limited to a single layer, but can also be a stack of two or more layers composed of the aforementioned substances.

[0150] Additionally, a layer for controlling the movement of electron carriers can be provided between the electron transport layer 118 and the light-emitting layer 130. This layer is made by adding a small amount of a substance with high electron trapping properties to the aforementioned material with high electron transport properties. By suppressing the movement of electron carriers, the carrier balance can be adjusted. This structure is very effective in suppressing problems caused by electrons passing through the light-emitting layer (such as a decrease in device lifetime).

[0151] <<Electron Injection Layer>> The electron injection layer 119 has the function of promoting electron injection by reducing the electron injection barrier from the electrode 102. For example, it can use group 1 metals, group 2 metals, or their oxides, halides, carbonates, etc. Alternatively, it can use composite materials of the aforementioned electron transport materials and materials having electron-donating properties. Examples of materials with electron-donating properties include group 1 metals, group 2 metals, or their oxides. Specifically, alkali metals, alkaline earth metals, or compounds of these metals, such as lithium fluoride (LiF), sodium fluoride (NaF), cesium fluoride (CsF), calcium fluoride (CaF2), and lithium oxide (LiOx), can be used. Additionally, rare earth metal compounds such as erbium fluoride (ErF3) can be used. Furthermore, electron salts can be used in the electron injection layer 119. Examples of such electron salts include substances that add electrons at a high concentration to a mixed oxide of calcium and aluminum. Additionally, substances suitable for electron transport layers 118 can be used in the electron injection layer 119.

[0152] Alternatively, a composite material formed by mixing an organic compound with an electron donor can be used for the electron injection layer 119. This composite material exhibits excellent electron injection and electron transport properties because electrons are generated in the organic compound by the electron donor. In this case, the organic compound is preferably a material with excellent performance in transporting the generated electrons; specifically, for example, the substances constituting the electron transport layer 118 as described above (metal complexes, heteroaromatic compounds, etc.) can be used. As the electron donor, any substance that provides electrons to the organic compound is acceptable. Specifically, alkali metals, alkaline earth metals, and rare earth metals are preferred, such as lithium, sodium, cesium, magnesium, calcium, erbium, and ytterbium. Additionally, alkali metal oxides or alkaline earth metal oxides are preferred, such as lithium oxides, calcium oxides, and barium oxides. Furthermore, Lewisite such as magnesium oxide can also be used. Additionally, organic compounds such as tetrathiofulvalene (TTF) can also be used.

[0153] Furthermore, the aforementioned light-emitting layer, hole injection layer, hole transport layer, electron transport layer, and electron injection layer can all be formed by methods such as vapor deposition (including vacuum vapor deposition), inkjet printing, coating, and gravure printing. In addition to the materials mentioned above, inorganic compounds such as quantum dots or polymeric compounds (oligomers, dendritic polymers, polymers, etc.) can also be used as the aforementioned light-emitting layer, hole injection layer, hole transport layer, electron transport layer, and electron injection layer.

[0154] As quantum dots, various types can be used, including colloidal quantum dots, alloy quantum dots, core-shell quantum dots, and nucleated quantum dots. Additionally, quantum dots containing elements from Groups 2 and 16, 13 and 15, 13 and 17, 11 and 17, or 14 and 15 can also be used. Alternatively, quantum dots containing elements such as cadmium (Cd), selenium (Se), zinc (Zn), sulfur (S), phosphorus (P), indium (In), tellurium (Te), lead (Pb), gallium (Ga), arsenic (As), and aluminum (Al) can be used.

[0155] <> Electrodes 101 and 102 are used as the anode or cathode of the light-emitting element. Electrodes 101 and 102 can be formed from metals, alloys, conductive compounds, mixtures thereof, or laminates thereof.

[0156] One of electrodes 101 and 102 is preferably formed using a conductive material that has the function of reflecting light. Examples of such conductive materials include aluminum (Al) or alloys containing Al. Examples of alloys containing Al include alloys containing Al and L (L represents one or more of titanium (Ti), neodymium (Nd), nickel (Ni), and lanthanum (La), such as alloys containing Al and Ti or alloys containing Al, Ni, and La. Aluminum has low resistivity and high light reflectivity. Furthermore, since aluminum is abundant in the Earth's crust and inexpensive, using aluminum can reduce the manufacturing cost of the light-emitting element. Alternatively, silver (Ag), alloys containing Ag, N (N represents one or more of yttrium (Y), Nd, magnesium (Mg), ytterbium (Yb), Al, Ti, gallium (Ga), zinc (Zn), indium (In), tungsten (W), manganese (Mn), tin (Sn), iron (Fe), Ni, copper (Cu), palladium (Pd), iridium (Ir), and gold (Au)) can also be used. Examples of silver-containing alloys include: alloys containing silver, palladium, and copper; alloys containing silver and copper; alloys containing silver and magnesium; alloys containing silver and nickel; alloys containing silver and gold; and alloys containing silver and ytterbium. In addition to the above materials, transition metals such as tungsten, chromium (Cr), molybdenum (Mo), copper, and titanium can be used.

[0157] Furthermore, light obtained from the light-emitting layer is extracted through one or both of electrodes 101 and 102. Therefore, at least one of electrodes 101 and 102 is preferably formed using a conductive material that allows light to pass through. Examples of such conductive material include those with a visible light transmittance of 40% or more and 100% or less, preferably 60% or more and 100% or less, and a resistivity of 1 × 10⁻² Ω·cm or less.

[0158] Furthermore, electrodes 101 and 102 are preferably formed using a conductive material that has the function of allowing light to pass through and reflecting light. Examples of such conductive materials include those with a visible light reflectance of 20% or more and 80% or less, preferably 40% or more and 70% or less, and a resistivity of 1×10⁻² Ω·cm or less. For example, one or more of conductive metals, alloys, and conductive compounds can be used. Specifically, indium tin oxide (ITO), indium tin oxide containing silicon or silicon oxide (ITSO), indium zinc oxide, indium tin oxide containing titanium, indium titanium oxide, indium oxide containing tungsten and zinc, and other metal oxides can be used. Additionally, a metal film with a thickness that allows light to pass through (preferably 1 nm or more and 30 nm or less) can be used. Examples of metals that can be used include alloys of Ag, Ag and Al, Ag and Mg, Ag and Au, and Ag and Yb.

[0159] Note that, in this specification, materials that are transparent to light can be any material that is both conductive and allows visible light to pass through. Examples include oxide conductors such as ITO, oxide semiconductors, or organic conductors containing organic matter. Examples of organic conductors containing organic matter include composite materials comprising a mixture of organic compounds and an electron donor, and composite materials comprising a mixture of organic compounds and an electron acceptor. Inorganic carbon materials such as graphene can also be used. Furthermore, the resistivity of this material is preferably 1 × 10⁵ Ω·cm or less, and more preferably 1 × 10⁴ Ω·cm or less.

[0160] Alternatively, one or both of the above materials can be formed by stacking multiple of them.

[0161] To improve light extraction efficiency, a material with a higher refractive index than an electrode that allows light to pass through can be formed in contact with that electrode. This material can be either conductive or non-conductive, as long as it allows visible light to pass through. Examples include oxide semiconductors and organic materials, in addition to the aforementioned oxide conductors. Examples of organic materials include those exemplified as light-emitting layers, hole injection layers, hole transport layers, electron transport layers, or electron injection layers. Alternatively, inorganic carbon materials or metal thin films with a thickness sufficient to allow light to pass through can also be used. Multiple layers using this high-refractive-index material with thicknesses ranging from a few nm to tens of nm can be stacked.

[0162] When electrode 101 or electrode 102 is used as a cathode, it is preferable to use a material with a low work function (below 3.8 eV). For example, elements belonging to Group 1 or Group 2 of the periodic table (e.g., alkali metals such as lithium, sodium, and cesium, alkaline earth metals such as calcium or strontium, magnesium, etc.), alloys containing the above elements (e.g., Ag and Mg or Al and Li), rare earth metals such as europium (Eu) or Yb, alloys containing the above rare earth metals, alloys containing aluminum, silver, etc.

[0163] When electrode 101 or electrode 102 is used as an anode, it is preferable to use a material with a large work function (above 4.0 eV).

[0164] Electrodes 101 and 102 can also be made of a laminate of conductive materials that reflect light and conductive materials that allow light to pass through. In this case, electrodes 101 and 102 have the function of adjusting the optical distance so that light with the desired wavelength from each light-emitting layer resonates and enhances its wavelength, which is preferable.

[0165] As for the film formation methods of electrodes 101 and 102, sputtering, vapor deposition, printing, coating, MBE (Molecular Beam Epitaxy), CVD, pulsed laser deposition, ALD (Atomic Layer Deposition), etc. can be appropriately used.

[0166] 〈〈Substrate〉〉 Furthermore, the light-emitting element of one embodiment of the present invention can be manufactured on a substrate made of glass, plastic, or the like. As for the order of stacking on the substrate, it can be stacked sequentially from either the electrode 101 side or the electrode 102 side.

[0167] Furthermore, as a substrate for forming the light-emitting element according to one embodiment of the present invention, materials such as glass, quartz, or plastic can be used. Alternatively, a flexible substrate can also be used. A flexible substrate is a substrate that can be bent, such as a plastic substrate made of polycarbonate or polyarylate. Additionally, thin films, inorganic thin films formed by vapor deposition, etc., can be used. Note that other materials can be used as long as they function as a support in the manufacturing process of the light-emitting element and optical element. Alternatively, any material that functions to protect the light-emitting element and optical element is acceptable.

[0168] For example, in this invention, various substrates can be used to form the light-emitting element. There are no particular limitations on the type of substrate. Examples of substrates include semiconductor substrates (e.g., single-crystal substrates or silicon substrates), SOI substrates, glass substrates, quartz substrates, plastic substrates, metal substrates, stainless steel substrates, substrates with stainless steel foil, tungsten substrates, substrates with tungsten foil, flexible substrates, laminated films, cellulose nanofibers (CNF) containing fibrous materials, or paper or substrate films. Examples of glass substrates include barium borosilicate glass, aluminoborosilicate glass, and soda-lime glass. Examples of flexible substrates, laminated films, and substrate films include, for example, plastics such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersiloxane (PES), and polytetrafluoroethylene (PTFE). Alternatively, examples include resins such as acrylic resins. Alternatively, examples include polypropylene, polyester, ethylene fluoride, or polyvinyl chloride. Alternatively, examples could include polyamide, polyimide, aromatic polyamide, epoxy resin, inorganic vapor-deposited films, and paper.

[0169] Alternatively, a flexible substrate can be used as the substrate, and the light-emitting element can be directly formed on the flexible substrate. Alternatively, a release layer can be provided between the substrate and the light-emitting element. A release layer can be used when part or all of the light-emitting element is fabricated on the release layer, and then it is separated from the substrate and transferred to another substrate. In this case, the light-emitting element can also be transferred to a substrate with low heat resistance or a flexible substrate. Furthermore, as the aforementioned release layer, for example, a laminated structure of inorganic films such as tungsten film and silicon oxide film, or a structure in which a resin film such as polyimide is formed on the substrate, can be used.

[0170] In other words, a light-emitting element can be formed on one substrate and then transferred to another substrate. Examples of substrates on which the light-emitting element is transferred, besides those mentioned above, include cellophane substrates, stone substrates, wood substrates, fabric substrates (including natural fibers (silk, cotton, linen), synthetic fibers (nylon, polyurethane, polyester), or recycled fibers (acetate fiber, cupro fiber, rayon, recycled polyester), leather substrates, and rubber substrates. By using these substrates, it is possible to manufacture light-emitting elements that are not easily damaged, have high heat resistance, are lightweight, or are thin.

[0171] Alternatively, a field-effect transistor (FET) can be formed on the aforementioned substrate, and a light-emitting element can be fabricated on an electrode electrically connected to the FET. This allows for the fabrication of an active-matrix display device that controls the driving of the light-emitting element via a FET.

[0172] In this embodiment, one embodiment of the present invention will be described. Furthermore, in other embodiments, one embodiment of the present invention will be described. However, one embodiment of the present invention is not limited thereto. That is, various inventive methods are described in the embodiments and other embodiments, thus one embodiment of the present invention is not limited to a specific method. For example, although an example of applying one embodiment of the present invention to a light-emitting element is shown, one embodiment of the present invention is not limited thereto. For example, depending on the situation or circumstances, one embodiment of the present invention may not be applied to a light-emitting element. Alternatively, an example is shown in one embodiment of the present invention where the EL layer includes a host material and a guest material having the function of exhibiting fluorescence or a guest material having the function of converting triple excitation energy into light emission, and the host material has a first organic compound whose difference between the single excitation energy level and the triple excitation energy level is greater than 0 eV and less than 0.2 eV, but one embodiment of the present invention is not limited thereto. In one embodiment of the present invention, depending on the situation or circumstances, for example, the host material may not have a first organic compound whose difference between the single excitation energy level and the triple excitation energy level is greater than 0 eV and less than 0.2 eV. Alternatively, the difference between the singlet excitation energy level and the triplet excitation energy level of the first organic compound does not need to be greater than 0 eV and is less than 0.2 eV. Alternatively, for example, in one embodiment of the invention, an example is shown where the first organic compound and the second organic compound form an excited-state complex, but one embodiment of the invention is not limited thereto. In one embodiment of the invention, depending on the circumstances, for example, the first organic compound and the second organic compound may not form an excited-state complex. Alternatively, in one embodiment of the invention, an example is shown where one of the first organic compound and the second organic compound has a HOMO energy level higher than the HOMO energy level of the other of the first organic compound and the other of the second organic compound, and also has a LUMO energy level higher than the LUMO energy level of the other of the first organic compound and the other of the second organic compound, but one embodiment of the invention is not limited thereto. In one embodiment of the invention, depending on the circumstances, for example, the following structure may not be used: one of the first organic compound and the second organic compound has a HOMO energy level higher than the HOMO energy level of the other of the first organic compound and the other of the second organic compound, and also has a LUMO energy level higher than the LUMO energy level of the other of the first organic compound and the other of the second organic compound.

[0173] The structure shown in this embodiment can be implemented by appropriately combining it with the structures shown in other embodiments.

[0174] Implementation Method 2 In this embodiment, a light-emitting element with a structure different from that shown in Embodiment 1 and its light-emitting mechanism will be described with reference to FIGS. 4A, 4B, and 4C. In FIG. 4A, the same shaded lines as in FIG. 1A are used to indicate parts that have the same function as those in FIG. 1A, without additional component symbols. Furthermore, parts that have the same function as those shown in FIG. 1A are represented by the same component symbols, and sometimes their detailed descriptions are omitted.

[0175] <Example of a light-emitting element structure> Figure 4A is a cross-sectional schematic diagram of a light-emitting element 152 according to an embodiment of the present invention.

[0176] The light-emitting element 152 includes a pair of electrodes (electrode 101 and electrode 102) and an EL layer 100 disposed between the pair of electrodes. The EL layer 100 includes at least a light-emitting layer 140.

[0177] Note that the following description assumes that electrode 101 is used as the anode and electrode 102 is used as the cathode in the light-emitting element 152, but the structure of the light-emitting element 152 can also be the opposite.

[0178] Figure 4B is a schematic cross-sectional view showing an example of the light-emitting layer 140 shown in Figure 4A. The light-emitting layer 140 shown in Figure 4B includes a host material 141 and a guest material 142. In addition, the host material 141 includes organic compound 141_1 and organic compound 141_2.

[0179] As the guest material 142, a luminescent organic material may be used, and preferably, a material capable of emitting phosphorescence (hereinafter also referred to as a phosphorescent material) is used. The following description will explain the structure of using a phosphorescent material as the guest material 142. Note that the guest material 142 may also be referred to as a phosphorescent material.

[0180] <Light-emitting mechanism of light-emitting elements> Next, the light emission mechanism of the light-emitting layer 140 will be explained.

[0181] The organic compounds 141_1 and 141_2 included in the host material 141 in the light-emitting layer 140 form an excited-state complex.

[0182] The combination of organic compound 141_1 and organic compound 141_2 can be any combination capable of forming an excited-state complex, preferably one of which is a hole-transporting compound and the other is an electron-transporting compound. In this case, donor-acceptor type excited-state complexes are more easily formed, and excited-state complexes can be formed efficiently.

[0183] Furthermore, as a combination of organic compound 141_1 and organic compound 141_2, it is preferable that one of organic compound 141_1 and organic compound 141_2 has a HOMO energy level higher than the other and a LUMO energy level higher than the other.

[0184] Similar to organic compounds 131_1 and 131_2 in the band diagrams of Figures 2A and 2B described in Embodiment 1, for example, when organic compound 141_1 has hole transport and organic compound 141_2 has electron transport, it is preferable that the HOMO level of organic compound 141_1 is higher than the HOMO level of organic compound 141_2, and the LUMO level of organic compound 141_1 is higher than the LUMO level of organic compound 141_2. Alternatively, when organic compound 141_2 has hole transport and organic compound 141_1 has electron transport, it is preferable that the HOMO level of organic compound 141_2 is higher than the HOMO level of organic compound 141_1, and the LUMO level of organic compound 141_2 is higher than the LUMO level of organic compound 141_1. At this point, the excited-state complex formed by organic compound 141_1 and organic compound 141_2 becomes an excited-state complex with an excitation energy approximately equivalent to the energy difference between the HOMO energy level of one and the LUMO energy level of the other. Furthermore, the difference between the HOMO energy levels of organic compound 141_1 and organic compound 141_2, as well as the difference between the LUMO energy levels of organic compound 141_1 and organic compound 141_2, is preferably 0.2 eV or more, and more preferably 0.3 eV or more.

[0185] Based on the above relationship between the HOMO and LUMO energy levels, as a combination of organic compound 141_1 and organic compound 141_2, it is preferable that one has an oxidation potential higher than that of the other and a reduction potential higher than that of the other.

[0186] In other words, when organic compound 141_1 has hole transport properties and organic compound 141_2 has electron transport properties, it is preferable that the oxidation potential of organic compound 141_1 is lower than the oxidation potential of organic compound 141_2 and the reduction potential of organic compound 141_1 is lower than the reduction potential of organic compound 141_2. Alternatively, when organic compound 141_2 has hole transport properties and organic compound 141_1 has electron transport properties, it is preferable that the oxidation potential of organic compound 141_2 is lower than the oxidation potential of organic compound 141_1 and the reduction potential of organic compound 141_2 is lower than the reduction potential of organic compound 141_1.

[0187] Furthermore, when the combination of organic compound 141_1 and organic compound 141_2 is a combination of a hole-transporting compound and an electron-transporting compound, the carrier balance can be more easily controlled by adjusting their mixing ratio. Specifically, the ratio of the hole-transporting compound to the electron-transporting compound is preferably in the range of 1:9 to 9:1 (weight ratio). Additionally, with this structure, the carrier balance can be easily controlled, thereby allowing for easy control of the carrier recombination region.

[0188] Organic compound 141_1 is preferably a thermally activated delayed-fluorescence (TEF) material. Alternatively, it may possess the function of exhibiting TEF at room temperature. In other words, organic compound 141_1 may also be a material that generates a singlet excited state from a triplet excited state solely through antisystem crossing. Therefore, the difference between the singlet and triplet excited energy levels is preferably greater than 0 eV and less than 0.2 eV. Organic compound 141_1 only needs to have the function of converting the triplet excited energy into a singlet excited energy, or it may not necessarily exhibit TEF.

[0189] Organic compound 141_1 preferably comprises a skeleton with hole transport capability and a skeleton with electron transport capability. Furthermore, organic compound 141_1 preferably comprises at least one of a π-electron-rich heteroaromatic skeleton and an aromatic amine skeleton, as well as a π-electron-deficient heteroaromatic skeleton. Moreover, by directly bonding the π-electron-rich heteroaromatic skeleton and the π-electron-deficient heteroaromatic skeleton, both the donor and acceptor properties of the π-electron-rich heteroaromatic skeleton are strong, and the difference between the singlet and triplet excitation energy levels is reduced, making it particularly preferred. Due to the strong donor and acceptor properties of organic compound 141_1, it is easy to form a donor-acceptor type excited-state complex with organic compound 141_2.

[0190] In addition, the overlap between the HOMO molecular orbital distribution region and the LUMO molecular orbital distribution region of organic compound 141_1 is preferably small.

[0191] The excited-state complex formed by organic compounds 141_1 and 141_2 exhibits minimal overlap between HOMO and LUMO molecular orbitals due to the presence of HOMO molecular orbitals in one organic compound and LUMO molecular orbitals in the other. This means that the difference between the singlet and triplet excitation energy levels is small in this excited-state complex. Therefore, the difference between the triplet and singlet excitation energy levels in the excited-state complex formed by organic compounds 141_1 and 141_2 is preferably greater than 0 eV and less than 0.2 eV.

[0192] Here, Figure 4C shows the energy level correlation between organic compound 141_1, organic compound 141_2, and guest material 142 in the luminescent layer 140. Note that the symbols and labels in Figure 4C represent the following: • Host(141_1): Main material (organic compound 141_1) •Host(141_2): Main material (organic compound 141_2) •Guest(142): Guest material 142 (phosphorescent material) • SPH1: The S1 energy level of the host material (organic compound 141_1) • TPH1: T1 energy level of the host material (organic compound 141_1) • SPH2: The S1 energy level of the host material (organic compound 141_2) • TPH2: T1 energy level of the host material (organic compound 141_2) • T1 energy level of TPG: Guest material 142 (phosphorescent material) • SPE: S1 energy level of excited-state complexes • TPE: T1 energy level of excited-state complexes

[0193] In one embodiment of the light-emitting element of the present invention, organic compounds 141_1 and 141_2 contained in the light-emitting layer 140 form an excited-state complex. The S1 energy level (SPE) of the excited-state complex and the T1 energy level (TPE) of the excited-state complex are adjacent to each other (see path E7 in Figure 4C).

[0194] Organic compounds 141_1 and 141_2 interact to rapidly form an excited-state complex by one receiving a hole and the other receiving an electron. Alternatively, when one becomes excited, it rapidly forms an excited-state complex by interacting with the other. Therefore, most of the excited states formed in the light-emitting layer 140 exist as excited-state complexes. The excitation energy levels (SPE and TPE) of the excited-state complexes are lower than the S1 energy levels (SPH1 and SPH2) of the organic compounds (organic compounds 141_1 and 141_2) that form the excited-state complexes, so the excited states of the host material 141 (excited-state complexes) can be formed at a lower excitation energy. As a result, the driving voltage of the light-emitting element 152 can be reduced.

[0195] Then, luminescence is obtained by transferring the energy of both (SPE) and (TPE) of the excited state complex to the lowest energy level of the triplet excited state of the guest material 142 (phosphorescent material) (see paths E8 and E9 in Figure 4C).

[0196] Furthermore, the T1 energy level (TPE) of the excited-state complex is preferably higher than the T1 energy level (TPG) of the guest material 142. As a result, the singlet excitation energy and triplet excitation energy of the generated excited-state complex can be transferred from the S1 energy level (SPE) and T1 energy level (TPE) of the excited-state complex to the T1 energy level (TPG) of the guest material 142.

[0197] By adopting the above structure as the light-emitting layer 140, the light emission of the guest material 142 (phosphorescent material) from the light-emitting layer 140 can be obtained efficiently.

[0198] Note that in this specification, processes along paths E7, E8, and E9 are sometimes referred to as ExTET (Exciplex-Triplet Energy Transfer). In other words, in the luminescent layer 140, the supply of excitation energy from the excited-state complex to the guest material 142 is generated. In this case, it is not necessarily required to have high efficiency of anti-intersystem crossing from TPE to SPE and high luminescence quantum yield from SPE, so a wider variety of materials can be selected.

[0199] The above reactions can be represented by the following general formulas (G1) to (G3).

[0200] D++A-→(D‧A)* (G1) (D‧A)*+G→D+A+G* (G2) G*→G+hν (G3)

[0201] In the reaction shown in general formula (G1), one of organic compounds 141_1 and 141_2 accepts a hole (D+) and the other accepts an electron (A-), thereby generating an excited-state complex ((D‧A)*). Furthermore, in the reaction shown in general formula (G2), an energy transfer occurs from the excited-state complex ((D‧A)*) to the guest material 142 (G), thereby generating an excited state (G*) of the guest material 142. Then, as shown in general formula (G3), light (hν) is emitted from the excited state of the guest material 142.

[0202] Note that, in order to efficiently transfer the excitation energy from the excited-state complex to the guest material 142, the T1 energy level (TPE) of the excited-state complex is preferably equal to or lower than the T1 energy levels (TPH1 and TPH2) of the organic compounds (organic compound 141_1 and organic compound 141_2) that form the excited-state complex. This prevents the quenching of the triple excitation energy of the excited-state complex caused by the organic compounds, thus enabling efficient energy transfer to the guest material 142.

[0203] For example, in at least one of the compounds forming an excited-state complex, when the difference between the S1 and T1 energy levels is large, it is necessary to make the T1 energy level (TPE) of the excited-state complex equal to or lower than the T1 energy level of each compound. Furthermore, it is preferable that the T1 energy level of the guest material is equal to or lower than the T1 energy level of the excited-state complex. Therefore, when the difference between the S1 and T1 energy levels of at least one compound is large, it is not advisable to use a material with a high triplet excitation energy level, i.e., a material exhibiting high luminescence energy such as blue light, as the guest material 142.

[0204] Conversely, in one embodiment of the invention, the difference between the S1 energy level (SPH1) and the T1 energy level (TPH1) of the organic compound 141_1 is small. Therefore, both the S1 and T1 energy levels of the organic compound 141_1 can be increased simultaneously, thereby increasing the T1 energy level of the excited-state complex. Therefore, one embodiment of the invention is not limited to the emission color of the guest material 142; for example, it can be suitably used for various light-emitting elements, i.e., light-emitting elements exhibiting emission from high emission energy such as blue to low emission energy such as red.

[0205] When organic compound 141_1 has a strong donor framework, holes injected into the light-emitting layer 140 are easily injected into organic compound 141_1 and transported. In this case, organic compound 141_2 preferably includes a donor framework with stronger acceptor properties than organic compound 141_1. Thus, organic compound 141_1 and organic compound 141_2 readily form an excited-state complex. Alternatively, when organic compound 141_1 has a strong acceptor framework, electrons injected into the light-emitting layer 140 are easily injected into organic compound 141_1 and transported. In this case, organic compound 141_2 preferably includes a donor framework with stronger donor properties than organic compound 141_1. Thus, organic compound 141_1 and organic compound 141_2 readily form an excited-state complex.

[0206] When organic compound 141_1 has the function of converting triple excitation energy into single excitation energy independently via antisystem crossing, and organic compounds 141_1 and 141_2 do not easily form excited-state complexes, for example, when the HOMO energy level of organic compound 141_1 is higher than that of organic compound 141_2, and the LUMO energy level of organic compound 141_2 is higher than that of organic compound 141_1, electrons and holes injected into the luminescent layer 140 as carriers are easily injected into organic compound 141_1 and transported. In this case, the carrier balance in the luminescent layer 140 needs to be controlled by the hole transport and electron transport properties of organic compound 141_1. Therefore, in addition to having the function of converting triple excitation energy into single excitation energy independently, organic compound 141_1 also needs to have a molecular structure with appropriate carrier balance, making the design of the molecular structure difficult. On the other hand, in one embodiment of the present invention, since electrons are injected into one of the organic compounds 141_1 and 141_2 and electrons are injected into the other, the carrier balance can be easily controlled according to their mixing ratio, and a light-emitting element exhibiting high luminous efficiency can be provided.

[0207] For example, when the HOMO level of organic compound 141_2 is higher than that of organic compound 141_1, and the LUMO level of organic compound 141_1 is higher than that of organic compound 141_2, electrons and holes injected into the light-emitting layer 140 as carriers are easily injected into organic compound 141_2 and transported. Therefore, carrier recombination easily occurs in organic compound 141_2. When organic compound 141_2 does not have the function of converting a triplet excitation energy level to a singlet excitation energy through antisystem crossing, the energy difference between the S1 and T1 levels of organic compound 141_2 becomes larger, and therefore the energy difference between the T1 level of guest material 142 and the S1 level of organic compound 141_2 also becomes larger. Consequently, the driving voltage of the light-emitting element increases by a portion corresponding to this energy difference. On the other hand, in one embodiment of the present invention, organic compounds 141_1 and 141_2 are capable of forming excited-state complexes with an excitation energy lower than the individual excitation energy levels of each organic compound (organic compound 141_1 and organic compound 141_2). Therefore, the driving voltage of the light-emitting element can be reduced, thereby providing a light-emitting element with low power consumption.

[0208] Figure 4C shows a case where the S1 energy level of organic compound 141_2 is higher than that of organic compound 141_1, and the T1 energy level of organic compound 141_1 is higher than that of organic compound 141_2. However, one embodiment of the present invention is not limited to this. The S1 energy level of organic compound 141_1 may also be higher than that of organic compound 141_2, and the T1 energy level of organic compound 141_1 may also be higher than that of organic compound 141_2. Alternatively, the S1 energy level of organic compound 141_1 may be approximately the same as that of organic compound 141_2. Alternatively, the S1 energy level of organic compound 141_2 may also be higher than that of organic compound 141_1, and the T1 energy level of organic compound 141_2 may also be higher than that of organic compound 141_1. Note that in any of the above cases, the T1 energy level of the excited-state complex is preferably equal to or lower than the T1 energy level of the organic compounds (organic compound 141_1 and organic compound 141_2) that form the excited-state complex.

[0209] The mechanism of energy transfer between the molecules of host material 141 and guest material 142 can be explained using two mechanisms, the Förster mechanism (dipole-dipole interaction) and the Dexter mechanism (electron exchange interaction), similar to that in Embodiment 1. For details on the Förster and Dexter mechanisms, please refer to Embodiment 1.

[0210] Concepts used to enhance energy transfer In energy transfer based on the Foster mechanism, the energy transfer efficiency ΦET and the luminescence quantum yield Φ (or fluorescence quantum yield when describing energy transfer from a singlet excited state) are preferably high. Furthermore, the overlap between the emission spectrum of the host material 141 (or fluorescence spectrum when describing energy transfer from a singlet excited state) and the absorption spectrum of the guest material 142 (corresponding to absorption during the migration from the singlet ground state to the triplet excited state) is preferably large. Moreover, the moiré absorptivity of the guest material 142 is preferably high. This means that the emission spectrum of the host material 141 overlaps with the absorption band present on the longest wavelength side of the guest material 142.

[0211] Furthermore, in energy transfer based on the Dexter mechanism, to increase the rate constant kh*→g, the overlap between the emission spectrum of the host material 141 (fluorescence spectrum when describing energy transfer from a singlet excited state) and the absorption spectrum of the guest material 142 (equivalent to absorption during the migration from the singlet ground state to the triplet excited state) is preferably large. Therefore, the optimization of energy transfer efficiency can be achieved by overlapping the emission spectrum of the host material 141 with the absorption band present on the longest wavelength side of the guest material 142.

[0212] Similar to the energy transfer from host material 141 to guest material 142, energy transfer from excited-state complex to guest material 142 also occurs based on both the Foster mechanism and the Dexter mechanism.

[0213] Therefore, one embodiment of the present invention provides a light-emitting element comprising, as a host material 141, organic compounds 141_1 and 141_2 forming an excited-state complex, which functions as an energy donor capable of efficiently transferring energy to a guest material 142. The excited-state complex formed by organic compounds 141_1 and 141_2 has a singlet excitation energy level close to a triplet excitation energy level. Therefore, the excited-state complex generated in the light-emitting layer 140 can be formed at a lower excitation energy than that of organic compounds 141_1 and 141_2. This reduces the driving voltage of the light-emitting element 152. Furthermore, to facilitate energy transfer from the singlet excited state of the excited-state complex to the triplet excited state of the guest material 142, which acts as an energy acceptor, it is preferable that the emission spectrum of the excited-state complex overlaps with the absorption band of the guest material 142, which is located on the longest wavelength side (low energy side). This improves the generation efficiency of the triplet excited state of the guest material 142.

[0214] <Examples of materials that can be used in light-emitting layers> Next, the materials that can be used in the light-emitting layer 140 will be described.

[0215] In the material weight ratio of the luminescent layer 140, the host material 141 accounts for the largest proportion, and the guest material 142 (phosphorescent material) is dispersed in the host material 141. The T1 energy level of the host material 141 (organic compound 141_1 and organic compound 141_2) of the luminescent layer 140 is preferably higher than the T1 energy level of the guest material (guest material 142) of the luminescent layer 140.

[0216] Organic compound 141_1 preferably exhibits thermally activated delayed fluorescence at room temperature. That is, the energy difference between the triplet excitation level and the singlet excitation level is preferably small; specifically, the energy difference between the triplet excitation level and the singlet excitation level is preferably greater than 0 eV and less than 0.2 eV, more preferably greater than 0 eV and less than 0.1 eV. Thermally activated delayed fluorescence materials can be cited as materials with this small energy difference between the triplet excitation level and the singlet excitation level. The material exemplified in Embodiment 1 can be used as a thermally activated delayed fluorescence material.

[0217] Furthermore, the energy difference between the triplet excitation energy level and the singlet excitation energy level of organic compound 141_1 only needs to be small, and it may not need to exhibit the function of thermally activated delayed fluorescence. In this case, in organic compound 141_1, it is preferable that at least one of a π-electron-rich heteroaromatic skeleton and an aromatic amine skeleton is bonded to a π-electron-deficient heteroaromatic skeleton by means of at least one of a m-epylphenyl and an or o-epylphenyl. Alternatively, it is preferable that it is bonded by means of an aryl group having at least one of a m-epylphenyl and an or o-epylphenyl, and more preferably, the aryl group is a biphenylene. By adopting the above structure, the T1 energy level of organic compound 141_1 can be increased. In addition, in this case, the π-electron-deficient heteroaromatic skeleton is preferably a diazine skeleton (pyrimidine skeleton, pyrazine skeleton, pyrazine skeleton) or a triazine skeleton. The π-electron-rich heteroaromatic skeleton is preferably any one or more of an acridine skeleton, a phenoxazine skeleton, a phenoxazine skeleton, a furan skeleton, a thiophene skeleton, and a pyrrole skeleton. Furthermore, as the pyrrole skeleton, the indole skeleton or the carbazole skeleton is preferred, and the 3-(9-phenyl-9H-carbazole-3-yl)-9H-carbazole skeleton is particularly preferred.

[0218] As for organic compound 141_2, it is preferable to use a material that can combine with organic compound 141_1 to form an excited-state complex. Specifically, zinc or aluminum-based metal complexes can be used. Diazole derivatives, triazole derivatives, benzimidazole derivatives, quinolone porphyrin derivatives, dibenzoquinone The electron transport and hole transport materials described in Embodiment 1 can be heteroaromatic compounds such as porphyrin derivatives, dibenzothiophene derivatives, dibenzofuran derivatives, pyrimidine derivatives, triazine derivatives, pyridine derivatives, bipyridine derivatives, and benzyline derivatives, or aromatic amines and carbazole derivatives. Preferably, organic compound 141_1, organic compound 141_2, and guest material 142 (phosphorescent material) are selected such that the emission peak of the excited-state complex formed by organic compound 141_1 and organic compound 141_2 overlaps with the absorption band of the triple MLCT (Metal to Ligand Charge Transfer) transition of guest material 142 (phosphorescent material) (specifically, the absorption band on the longest wavelength side). This allows for the realization of a light-emitting element with significantly improved luminous efficiency. Note that when using a thermally activated delayed fluorescence material instead of a phosphorescent material, the absorption band on the longest wavelength side is preferably a singlet absorption band.

[0219] As guest materials 142 (phosphorescent materials), examples include iridium, rhodium, and platinum-based organometallic complexes or metal complexes, with organoiridium complexes being preferred, such as iridium-based ortho-metal complexes. As ortho-metallized ligands, examples include 4H-triazole ligands, 1H-triazole ligands, imidazole ligands, pyridine ligands, pyrazine ligands, or isoquinoline ligands. As metal complexes, examples include platinum complexes with porphyrin ligands.

[0220] Examples of substances exhibiting emission peaks in blue or green regions include tri{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazolato-3-yl-κN2]phenyl-κC}iridium(III) (abbreviated as Ir(mpptz-dmp)3), tri(5-methyl-3,4-diphenyl-4H-1,2,4-triazole)iridium(III) (abbreviated as Ir(Mptz)3), and tri[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazole]iridium(III) (abbreviated as Ir(Mptz)3). Organometallic iridium complexes with a 4H-triazole skeleton, such as Ir(iPrptz-3b)3 and tris[3-(5-biphenyl)-5-isopropyl-4-phenyl-4H-1,2,4-triazole]iridium(III) (abbreviated as Ir(iPr5btz)3); tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazole]iridium(III) (abbreviated as Ir(Mptz1-mp)3) and tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazole)iridium(III) (abbreviated as Ir(Prptz1-Me)3) Organometallic iridium complexes with a 1H-triazole skeleton, such as fac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazolium]iridium(III) (abbreviated as: Ir(iPrpmi)3) and tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III) (abbreviated as: Ir(dmpimpt-Me)3), and bis[2-(4',6'-difluorophenyl)pyridinium-N,C2']iridium(III)tetra(1-pyridinium) Organometallic iridium complexes with electron-withdrawing phenylpyridine derivatives as ligands include azirazole borate (FIr6), bis[2-(4',6'-difluorophenyl)pyridinium-N,C2']iridium(III)pyridinecarboxylate (FIrpic), bis{2-[3',5'-bis(trifluoromethyl)phenyl]pyridinium-N,C2'}iridium(III)pyridinecarboxylate (Ir(CF3ppy)2(pic)), and bis[2-(4',6'-difluorophenyl)pyridinium-N,C2']iridium(III)acetoacetone (FIr(acac)). Among these metal complexes, organometallic iridium complexes with a 4H-triazole skeleton are particularly preferred due to their excellent reliability and luminescence efficiency.

[0221] Examples of substances exhibiting emission peaks in green or yellow regions include tris(4-methyl-6-phenylpyrimidine)iridium(III) (abbreviated as Ir(mppm)3), tris(4-tert-butyl-6-phenylpyrimidine)iridium(III) (abbreviated as Ir(tBuppm)3), (acetylacetone)bis(6-methyl-4-phenylpyrimidine)iridium(III) (abbreviated as Ir(mppm)2(acac)), and (acetylacetone)bis(6-tert-butyl-4-phenylpyrimidine)iridium(III) (abbreviated as Ir(tBupp)3). m)2(acac)), (acetylacetone)bis[4-(2-norkenyl)-6-phenylpyrimidine]iridium(III) (abbreviation: Ir(nbppm)2(acac)), (acetylacetone)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidine]iridium(III) (abbreviation: Ir(mpmppm)2(acac)), (acetylacetone)bis{4,6-dimethyl-2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-κN3]phenyl-κC}iridium(III) (abbreviation: Ir) Organometallic iridium complexes with a pyrimidine skeleton, such as (dmppm-dmp)2(acac) and (acetylacetone)bis(4,6-diphenylpyrimidine)iridium(III) (abbreviated as: Ir(dppm)2(acac)), as well as (acetylacetone)bis(3,5-dimethyl-2-phenylpyrazine)iridium(III) (abbreviated as: Ir(mppr-Me)2(acac)) and (acetylacetone)bis(5-isopropyl-3-methyl-2-phenylpyrazine)iridium(III) (abbreviated as: Ir(mppr-iPr)2( Organometallic iridium complexes with pyrazine skeletons, such as tris(2-phenylpyridin-N,C2')iridium(III) (abbreviated as: Ir(ppy)3), bis(2-phenylpyridin-N,C2')iridium(III)acetophenone (abbreviated as: Ir(ppy)2(acac)), bis(benzo[h]quinoline)iridium(III)acetophenone (abbreviated as: Ir(bzq)2(acac)), tris(benzo[h]quinoline)iridium(III) (abbreviated as: Ir(bzq)3), tris(2-phenylquinoline-N,C2')iridium(III) (abbreviated as: Ir(pq)3), bis(2-phenylquinoline-N,C2')iridium(III)acetophenone (abbreviated as: Ir(pq)2(acac)), etc., and bis(2,4-diphenyl-1,3- Organometallic iridium complexes such as iridium(III)acetophenone (Ir(dpo)2(acac)), bis{2-[4'-(perfluorophenyl)phenyl]pyridine-N,C2'}iridium(III)acetophenone (Ir(p-PF-ph)2(acac)), and bis(2-phenylbenzothiazole-N,C2')iridium(III)acetophenone (Ir(bt)2(acac)) and rare earth metal complexes such as tri(acetophenone anion)(monoporphyrin) terbium(III) (Tb(acac)3(Phen)) are included. Among these metal complexes, organometallic iridium complexes with a pyrimidine framework are particularly preferred due to their excellent reliability and luminescence efficiency.

[0222] In addition, examples of substances that have emission peaks in yellow or red regions include (diisobutylmethane)bis[4,6-bis(3-methylphenyl)pyrimidinium]iridium(III) (abbreviated as: Ir(5mdppm)2(dibm)), bis[4,6-bis(3-methylphenyl)pyrimidinium](dineopentylmethane)iridium(III) (abbreviated as: Ir(5mdppm)2(dpm)), and bis[4,6-bis(naphthyl-1-yl)pyrimidinium](dineopentylmethane) Organometallic iridium complexes with a pyrimidine skeleton, such as (acetylene)bis(2,3,5-triphenylpyrazine)iridium(III) (abbreviated as Ir(tppr)2(acac)), (2,3,5-triphenylpyrazine)(dinepentylmethane)iridium(III) (abbreviated as Ir(tppr)2(dpm)), and (acetylene)bis[2,3-bis(4-fluorophenyl)quinoline. Organometallic iridium complexes with a pyrazine skeleton, such as iridium(III) cycloiridium (Ir(Fdpq)2(acac)); organometallic iridium complexes with a pyridine skeleton, such as tris(1-phenylisoquinoline-N,C2')iridium(III) (Ir(piq)3) and bis(1-phenylisoquinoline-N,C2')iridium(III)acetophenone (Ir(piq)2(acac)); 2,3,7,8,12,13,17,18-octaethyl-21H Platinum complexes such as 23H-porphyrin platinum(II) (abbreviated as PtOEP); and rare earth metal complexes such as tris(1,3-diphenyl-1,3-propanedionato) (monoporphyrin) europium(III) (abbreviated as Eu(DBM)3(Phen)) and tris[1-(2-thiophenecarboxyl)-3,3,3-trifluoroacetone] (monoporphyrin) europium(III) (abbreviated as Eu(TTA)3(Phen)). Among the above metal complexes, organometallic iridium complexes with a pyrimidine framework are particularly preferred due to their excellent reliability and luminescence efficiency. Furthermore, organometallic iridium complexes with a pyrazine framework can provide red luminescence with good colorimetry.

[0223] As the luminescent material included in the luminescent layer 140, a material capable of converting triple excitation energy into luminescence can be used. In addition to phosphorescent materials, thermally activated delayed fluorescence materials can be cited as such materials. Therefore, "phosphorescent material" can be regarded as "thermally activated delayed fluorescence material".

[0224] When the thermally activated delayed fluorescent material is composed of a single material, specifically, the thermally activated delayed fluorescent material shown in Embodiment 1 can be used.

[0225] The light-emitting layer 140 can also be formed from two or more layers. For example, when the light-emitting layer 140 is formed by sequentially stacking a first light-emitting layer and a second light-emitting layer from the hole transport layer side, a material with hole transport properties can be used as the main material of the first light-emitting layer, and a material with electron transport properties can be used as the main material of the second light-emitting layer.

[0226] In addition, the light-emitting layer 140 may include materials other than the host material 141 and the guest material 142.

[0227] Alternatively, the light-emitting layer 140 can be formed using methods such as vapor deposition (including vacuum vapor deposition), inkjet printing, coating, and gravure printing. Furthermore, in addition to the materials mentioned above, inorganic compounds such as quantum dots or polymeric compounds (oligomers, dendritic polymers, polymers, etc.) can also be used.

[0228] The structure shown in this embodiment can be implemented by appropriately combining it with the structures shown in other embodiments.

[0229] Implementation Method 3 In this embodiment, a light-emitting element having a structure different from that shown in Embodiments 1 and 2, and the light-emitting mechanism of the light-emitting element, will be described with reference to FIGS. 5A to 6B. Note that in FIGS. 5A to 6B, the same shaded lines as in FIG. 1A are used to show parts that have the same function as in FIG. 1A, and sometimes the element symbols are omitted. Furthermore, parts that have the same function as in FIG. 1A are represented by the same element symbols, and sometimes their detailed descriptions are omitted.

[0230] <Example 1 of the structure of a light-emitting element> Figure 5A is a cross-sectional schematic diagram of the light-emitting element 250.

[0231] The light-emitting element 250 shown in FIG5A has multiple light-emitting units (light-emitting unit 106 and light-emitting unit 108 in FIG5A) between a pair of electrodes (electrode 101 and electrode 102). One of the multiple light-emitting units preferably has the same structure as the EL layer 100 shown in FIG1A. That is, the light-emitting element 150 shown in FIG1A preferably has one light-emitting unit, while the light-emitting element 250 preferably has multiple light-emitting units. Note that although the case where electrode 101 is the anode and electrode 102 is the cathode is described in the light-emitting element 250, the structure of the light-emitting element 250 can also be the opposite.

[0232] Furthermore, in the light-emitting element 250 shown in FIG. 5A, light-emitting units 106 and 108 are stacked, and a charge-generating layer 115 is provided between the light-emitting units 106 and 108. Additionally, the light-emitting units 106 and 108 may have the same structure or different structures. For example, it is preferable to use the EL layer 100 shown in FIG. 1A for the light-emitting unit 108.

[0233] In addition, the light-emitting element 250 includes a light-emitting layer 120 and a light-emitting layer 130. Furthermore, the light-emitting unit 106, in addition to the light-emitting layer 120, also includes a hole injection layer 111, a hole transport layer 112, an electron transport layer 113, and an electron injection layer 114. Moreover, the light-emitting unit 108, in addition to the light-emitting layer 130, also includes a hole injection layer 116, a hole transport layer 117, an electron transport layer 118, and an electron injection layer 119.

[0234] The charge-generating layer 115 can have either a structure in which an acceptor substance as an electron acceptor is added to the hole-transporting material, or a structure in which a donor substance as an electron donor is added to the electron-transporting material. Alternatively, both structures can be stacked.

[0235] When the charge generation layer 115 comprises a composite material consisting of an organic compound and an acceptor substance, the same composite material used in the hole injection layer 111 shown in Embodiment 1 can be used as the composite material. Various compounds such as aromatic amine compounds, carbazole compounds, aromatic hydrocarbons, and polymers (oligomers, dendritic polymers, polymers, etc.) can be used as the organic compound. Furthermore, it is preferable to use a substance with a hole mobility of 1×10⁻⁶ cm² / Vs or higher as the organic compound. However, any other substance can be used as long as its hole transport capability is higher than its electron transport capability. Because the composite material consisting of the organic compound and the acceptor substance has good carrier injection and carrier transport capabilities, low-voltage driving and low-current driving can be achieved. Note that, as with the light-emitting unit 108, when the surface of the light-emitting unit on the anode side contacts the charge generation layer 115, the charge generation layer 115 can also function as a hole injection layer or a hole transport layer of the light-emitting unit; therefore, a hole injection layer or a hole transport layer may not be provided in this light-emitting unit.

[0236] Note that the charge-generating layer 115 can also be a laminated structure combining a layer of a composite material containing an organic compound and an acceptor substance with a layer composed of other materials. For example, it can also be a structure combining a layer of a composite material containing an organic compound and an acceptor substance with a layer containing a compound selected from an electron-donating substance and a compound with high electron transport capacity. Alternatively, it can be a structure combining a layer of a composite material containing an organic compound and an acceptor substance with a layer containing a transparent conductive material.

[0237] The charge generation layer 115 sandwiched between the light-emitting unit 106 and the light-emitting unit 108 only needs to have a structure that injects electrons into one light-emitting unit and holes into the other light-emitting unit when a voltage is applied between the electrodes 101 and 102. For example, in FIG5A, when a voltage is applied such that the potential of electrode 101 is higher than the potential of electrode 102, the charge generation layer 115 injects electrons into the light-emitting unit 106 and holes into the light-emitting unit 108.

[0238] From the viewpoint of light extraction efficiency, the charge generation layer 115 preferably has visible light transmittance (specifically, the charge generation layer 115 has a visible light transmittance of 40% or more). Furthermore, the charge generation layer 115 functions even if its conductivity is lower than that of the pair of electrodes (electrodes 101 and 102). When the conductivity of the charge generation layer 115 is approximately as high as that of the pair of electrodes, luminescence sometimes occurs in areas where electrodes 101 and 102 do not overlap, because the carriers generated by the charge generation layer 115 flow towards the film surface. To suppress this undesirable phenomenon, the charge generation layer 115 is preferably formed of a material with a conductivity lower than that of the pair of electrodes.

[0239] By using the above-mentioned material to form the charge generation layer 115, the increase in driving voltage during the stacking of the light-emitting layer can be suppressed.

[0240] Although a light-emitting element with two light-emitting units is illustrated in Figure 5A, the same structure can be applied to light-emitting elements with three or more light-emitting units stacked together. As shown in light-emitting element 250, by arranging multiple light-emitting units between a pair of electrodes and separating them by a charge-generating layer, a light-emitting element that can achieve high brightness while maintaining low current density and has a longer lifespan can be realized. In addition, a light-emitting element with low power consumption can also be realized.

[0241] Furthermore, by applying the EL layer 100 shown in FIG1A to at least one of the multiple cells, a light-emitting element with high luminous efficiency can be provided.

[0242] Furthermore, the light-emitting layer 130 included in the light-emitting unit 108 preferably has the structure shown in Embodiment 1. Therefore, the light-emitting element 250, as a light-emitting material containing fluorescent material, becomes a light-emitting element with high luminous efficiency, which is preferable.

[0243] Additionally, for example, as shown in FIG5B, the light-emitting layer 120 included in the light-emitting unit 106 comprises a host material 121 and a guest material 122. Note that a fluorescent material will be used as the guest material 122 in the following description.

[0244] <<The Light Emission Mechanism of Emissive Layer 120>> The light-emitting mechanism of the light-emitting layer 120 will be explained below.

[0245] Electrons and holes injected from a pair of electrodes (electrode 101 and electrode 102) or the charge generation layer recombine in the light-emitting layer 120, thereby generating excitons. Since the amount of host material 121 is greater than that of guest material 122, the generation of excitons results in an excited state of host material 121.

[0246] An exciton is a pair of carriers (electrons and holes). Because excitons possess energy, the material that generates excitons is called an excited state.

[0247] When the excited state of the host material 121 is a singlet excited state, the singlet excitation energy is transferred from the S1 energy level of the host material 121 to the S1 energy level of the guest material 122, thereby forming the singlet excited state of the guest material 122.

[0248] Since the guest material 122 is a fluorescent material, it will emit light rapidly when a singlet excited state is formed within it. Therefore, to obtain high luminescence efficiency, the guest material 122 preferably has a high fluorescence quantum yield. Furthermore, this also applies when the excited state generated by carrier recombination within the guest material 122 is a singlet excited state.

[0249] Next, the case of the triplet excited state of the host material 121 formed by carrier recombination will be explained. Figure 5C shows the energy level relationship between the host material 121 and the guest material 122 at this time. The diagrams and element symbols in Figure 5C are shown below. Note that since the T1 energy level of the host material 121 is preferably lower than that of the guest material 122, this is shown in Figure 5C. However, the T1 energy level of the host material 121 can also be higher than that of the guest material 122.

[0250] .Host(121): Main material 121 .Guest(122): Guest material 122 (fluorescent material) .SFH: S1 energy level of host material 121 .TFH: T1 energy level of host material 121 .SFG: S1 energy level of guest material 122 (fluorescent material) .TFG: T1 energy level of guest material 122 (fluorescent material)

[0251] As shown in Figure 5C, due to the recombination of carriers, the triplet excitons generated approach each other, supplying excitation energy and exchanging spin angular momentum. This results in a reaction in which one of the excitons transforms into a singlet exciton with the energy of the S1 level (SFH) of the host material 121, i.e., triplet-triplet annihilation (TTA) (refer to TTA in Figure 5C). The singlet excitation energy of the host material 121 is transferred from SFH to the S1 level (SFG) of the guest material 122, which has a lower energy (refer to path E1 in Figure 5C), forming a singlet excited state of the guest material 122, thereby causing the guest material 122 to emit light.

[0252] Furthermore, when the density of triplet excitons in the luminescent layer 120 is sufficiently high (e.g., above 1×10⁻¹² cm⁻³), the inactivation of a single triplet exciton can be ignored, and the reaction of two close triplet excitons can be considered.

[0253] Furthermore, when carriers recombine in the guest material 122 to form a triplet excited state, the triplet excited state of the guest material 122 is thermally deactivated, making it difficult to use for luminescence. However, when the T1 energy level (TFH) of the host material 121 is lower than the T1 energy level (TFG) of the guest material 122, the triplet excitation energy of the guest material 122 can be transferred from the T1 energy level (TFG) of the guest material 122 to the T1 energy level (TFH) of the host material 121 (refer to path E2 in Figure 5C), and then used for TTA.

[0254] In other words, the host material 121 preferably has the function of converting triple excitation energy into single excitation energy using TTA. Thus, a portion of the triple excitation energy generated in the luminescent layer 120 is converted into single excitation energy using the TTA in the host material 121, and this single excitation energy is transferred to the guest material 122, thereby enabling fluorescence extraction. Therefore, the S1 energy level (SFH) of the host material 121 is preferably higher than the S1 energy level (SFG) of the guest material 122. Furthermore, the T1 energy level (TFH) of the host material 121 is preferably lower than the T1 energy level (TFG) of the guest material 122.

[0255] In particular, when the T1 energy level (TFG) of the guest material 122 is lower than the T1 energy level (TFH) of the host material 121, it is preferable that the proportion of the guest material 122 in the weight ratio of the host material 121 to the guest material 122 is lower. Specifically, the weight ratio of the host material 121 to the guest material 122 is preferably greater than 0 and less than 0.05. This reduces the probability of carrier recombination in the guest material 122. It also reduces the probability of energy transfer from the T1 energy level (TFH) of the host material 121 to the T1 energy level (TFG) of the guest material 122.

[0256] Note that the main material 121 can be composed of a single compound or multiple compounds.

[0257] Furthermore, in the above structures, the guest materials (fluorescent materials) used for the light-emitting units 106 and 108 can be the same or different. When the light-emitting units 106 and 108 contain the same guest material, the light-emitting element 250 becomes a light-emitting element that exhibits high luminous brightness with a small current value, which is preferable. Conversely, when the light-emitting units 106 and 108 contain different guest materials, the light-emitting element 250 becomes a light-emitting element that exhibits multi-color luminescence, which is also preferable. Particularly preferred is to select the guest material in a manner that achieves high color rendering index (CRI) white luminescence or at least luminescence with red, green, and blue colors.

[0258] When the light-emitting unit 106 and the light-emitting unit 108 have different guest materials, the light emitted from the light-emitting layer 120 preferably has an emission peak on the shorter wavelength side compared to the light emitted from the light-emitting layer 130. Light-emitting elements using materials with high triplet excited states tend to degrade in brightness quickly. Therefore, by using TTA as the light-emitting layer to emit light at short wavelengths, a light-emitting element with less brightness degradation can be provided.

[0259] <Example 2 of the structure of a light-emitting element> Figure 6A is a cross-sectional schematic diagram of the light-emitting element 252.

[0260] Similar to the light-emitting element 250 described above, the light-emitting element 252 shown in FIG. 6A includes multiple light-emitting units (light-emitting unit 106 and light-emitting unit 110 in FIG. 6A) between a pair of electrodes (electrode 101 and electrode 102). A light-emitting unit preferably has the same structure as the EL layer 100 shown in FIG. 4A. Furthermore, light-emitting unit 106 and light-emitting unit 110 can have the same structure or different structures.

[0261] Furthermore, in the light-emitting element 252 shown in FIG. 6A, light-emitting units 106 and 110 are stacked, and a charge-generating layer 115 is provided between the light-emitting units 106 and 110. For example, it is preferable to apply the EL layer 100 shown in FIG. 4A to the light-emitting unit 110.

[0262] In addition, the light-emitting element 252 includes a light-emitting layer 120 and a light-emitting layer 140. Furthermore, the light-emitting unit 106, in addition to the light-emitting layer 120, also includes a hole injection layer 111, a hole transport layer 112, an electron transport layer 113, and an electron injection layer 114. Furthermore, the light-emitting unit 110, in addition to the light-emitting layer 140, also includes a hole injection layer 116, a hole transport layer 117, an electron transport layer 118, and an electron injection layer 119.

[0263] Furthermore, the light-emitting layer of the light-emitting unit 110 preferably contains a phosphorescent material. That is, preferably, the light-emitting layer 120 included in the light-emitting unit 106 has the structure shown in Structural Example 1 of this embodiment, and the light-emitting layer 140 included in the light-emitting unit 110 has the structure shown in Embodiment 2.

[0264] Furthermore, it is preferable to adopt the following structure: compared to the emission from the light-emitting layer 120, the emission from the light-emitting layer 140 has an emission peak on the shorter wavelength side. Light-emitting elements using phosphorescent materials that exhibit short-wavelength emission tend to experience rapid brightness degradation. Therefore, by employing fluorescence emission as the short-wavelength emission, a light-emitting element with minimal brightness degradation can be provided.

[0265] Furthermore, by having the light-emitting layer 120 and the light-emitting layer 140 emit light of different wavelengths, a multicolor light-emitting element can be realized. In this case, since light with different emission peaks is synthesized, the emission spectrum becomes an emission spectrum with at least two emission peaks.

[0266] Furthermore, the above structure is suitable for obtaining white light emission. By making the light emitted by the light-emitting layer 120 and the light-emitting layer 140 complementary colors, white light emission can be obtained.

[0267] Furthermore, by using multiple luminescent materials with different emission wavelengths in any one or two of the luminescent layers 120 and 140, it is also possible to obtain white light with high color rendering composed of three primary colors or four or more emission colors. In this case, any one or two of the luminescent layers 120 and 140 can be further divided into layers, and each of the divided layers contains a different luminescent material.

[0268] <Example 3 of the structure of a light-emitting element> Figure 6B is a cross-sectional schematic diagram of the light-emitting element 254.

[0269] Similar to the light-emitting element 250 described above, the light-emitting element 254 shown in FIG. 6B includes a plurality of light-emitting units (light-emitting unit 109 and light-emitting unit 110 in FIG. 6B) between a pair of electrodes (electrode 101 and electrode 102). At least one of the plurality of light-emitting units preferably has the same structure as the EL layer 100 shown in FIG. 1A, and another preferably has the same structure as the EL layer 100 shown in FIG. 4A.

[0270] Furthermore, in the light-emitting element 254 shown in FIG. 6B, light-emitting units 109 and 110 are stacked, and a charge-generating layer 115 is provided between the light-emitting units 109 and 110. For example, preferably, the same structure as the EL layer 100 shown in FIG. 1A is used for the light-emitting unit 109, and the same structure as the EL layer 100 shown in FIG. 4A is used for the light-emitting unit 110.

[0271] In addition, the light-emitting element 254 includes a light-emitting layer 130 and a light-emitting layer 140. Furthermore, the light-emitting unit 109, in addition to the light-emitting layer 130, also includes a hole injection layer 111, a hole transport layer 112, an electron transport layer 113, and an electron injection layer 114. Furthermore, the light-emitting unit 110, in addition to the light-emitting layer 140, also includes a hole injection layer 116, a hole transport layer 117, an electron transport layer 118, and an electron injection layer 119.

[0272] In other words, preferably, the light-emitting layer 130 included in the light-emitting unit 109 has the structure shown in Embodiment 1, and the light-emitting layer 140 included in the light-emitting unit 110 has the structure shown in Embodiment 2.

[0273] Furthermore, it is preferable to adopt the following structure: compared to the emission from the light-emitting layer 140, the emission from the light-emitting layer 130 has an emission peak on the shorter wavelength side. Light-emitting elements using phosphorescent materials that exhibit short-wavelength emission tend to experience rapid brightness degradation. Therefore, by employing fluorescence emission as the short-wavelength emission, a light-emitting element with minimal brightness degradation can be provided.

[0274] Furthermore, by having the light-emitting layer 130 and the light-emitting layer 140 emit light of different wavelengths, a multicolor light-emitting element can be realized. In this case, since light with different emission peaks is synthesized, the emission spectrum becomes an emission spectrum with at least two emission peaks.

[0275] Furthermore, the above structure is suitable for obtaining white light emission. By making the light emitted by the light-emitting layer 130 and the light-emitting layer 140 complementary colors, white light emission can be obtained.

[0276] Furthermore, by using multiple luminescent materials with different emission wavelengths in any one or two of the luminescent layers 130 and 140, it is also possible to obtain white light with high color rendering composed of three primary colors or four or more emission colors. In this case, any one or two of the luminescent layers 130 and 140 can be further divided into layers, and each of the divided layers contains a different luminescent material.

[0277] <Examples of materials that can be used in light-emitting layers> The materials that can be used in light-emitting layer 120, light-emitting layer 130 and light-emitting layer 140 will be described below.

[0278] <<Materials that can be used in light-emitting layer 120>> In the material weight ratio of the luminescent layer 120, the host material 121 accounts for the largest proportion, and the guest material 122 (fluorescent material) is dispersed in the host material 121. Preferably, the S1 energy level of the host material 121 is higher than that of the guest material 122 (fluorescent material), and the T1 energy level of the host material 121 is lower than that of the guest material 122 (fluorescent material).

[0279] In the light-emitting layer 120, there are no particular restrictions on the object material 122. For example, the material exemplified as object material 132 in Embodiment 1 can be used.

[0280] While there are no particular limitations on the materials that can be used as the host material 121 in the light-emitting layer 120, examples include: tris(8-hydroxyquinoline)aluminum(III) (abbreviated: Alq), tris(4-methyl-8-hydroxyquinoline)aluminum(III) (abbreviated: Almq3), bis(10-hydroxybenzo[h]quinoline)beryllium(II) (abbreviated: BeBq2), bis(2-methyl-8-hydroxyquinoline)(4-phenylphenol)aluminum(III) (abbreviated: BAlq), bis(8-hydroxyquinoline)zinc(II) (abbreviated: Znq), bis[2-(2-benzo[h]quinoline ...[2-benzo[h]quinoline)aluminum(III) (abbreviated: BAlq), bis[2-benzo[h]quinoline(III)aluminum(II) (abbreviated: Znq), bis[2-benzo[h]quinoline(III)aluminum(II)aluminum(III)aluminum(II)aluminum(III)aluminum(II)aluminum(III)aluminum(II)aluminum(III)aluminum(II)aluminum(III)aluminum(II)aluminum(III)aluminum(II)aluminum(III)aluminum(II)aluminum(III)aluminum(II)aluminum( Metal complexes such as [2-(2-benzothiazolyl)phenol]zinc(II) (abbreviated as ZnPBO) and bis[2-(2-benzothiazolyl)phenol]zinc(II) (abbreviated as ZnBTZ); 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4- diazole (abbreviated as PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4- [Diazol-2-yl]benzene (abbreviation: OXD-7), 3-(4-biphenyl)-4-phenyl-5-(4-trimethylbutylphenyl)-1,2,4-triazole (abbreviation: TAZ), 2,2',2”-(1,3,5-phenyltriyl)tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI), BPhen (abbreviation: BPhen), BCP (abbreviation: BCP), 9-[4-(5-phenyl-1,3,4-] Heterocyclic compounds such as [diazol-2-yl]phenyl]-9H-carbazole (abbreviated as CO11); aromatic amine compounds such as 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviated as NPB or α-NPD), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviated as TPD), and 4,4'-bis[N-(spiro-9,9'-dien-2-yl)-N-phenylamino]biphenyl (abbreviated as BSPB). Additionally, anthracene derivatives, phenanthrene derivatives, and dinaphthyl derivatives can be cited. (chrysene) derivatives, dibenzo[g,p] (chrysene) derivatives and other condensed polycyclic aromatic compounds. Specifically, examples include 9,10-diphenylanthracene (DPAnth), N,N-diphenyl-9-[4-(10-phenyl-9-anthrayl)phenyl]-9H-carbazole-3-amine (CzA1PA), 4-(10-phenyl-9-anthrayl)triphenylamine (DPhPA), 4-(9H-carbazole-9-yl)-4'-(10-phenyl-9-anthrayl)triphenylamine (YGAPA), and N,9-diphenyl-N... -[4-(10-phenyl-9-anthrayl)phenyl]-9H-carbazole-3-amine (abbreviation: PCAPA), N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthrayl)phenyl]phenyl}-9H-carbazole-3-amine (abbreviation: PCAPBA), N,9-diphenyl-N-(9,10-diphenyl-2-anthrayl)-9H-carbazole-3-amine (abbreviation: 2PCAPA), 6,12-dimethoxy-5,11-diphenyl 、N,N,N',N',N”,N”,N''',N'''-octaphenyldibenzo[g,p] (chrysene)-2,7,10,15-tetramine (abbreviation: DBC1), 9-[4-(10-phenyl-9-anthrayl)phenyl]-9H-carbazole (abbreviation: CzPA), 3,6-diphenyl-9-[4-(10-phenyl-9-anthrayl)phenyl]-9H-carbazole (abbreviation: DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA), 9,10-bis(2- Naphthyl)anthracene (abbreviated as DNA), 2-tert-butyl-9,10-bis(2-naphthyl)anthracene (abbreviated as t-BuDNA), 9,9'-bianthracene (abbreviated as BANT), 9,9'-(stilbene-3,3'-diyl)phenanthrene (abbreviated as DPNS), 9,9'-(diphenylethylene-4,4'-diyl)phenanthrene (abbreviated as DPNS2), and 1,3,5-tris(1-pyrene)benzene (abbreviated as TPB3), etc. One or more substances with a band gap larger than that of the aforementioned guest material 122 can be selected from these substances and known substances.

[0281] Alternatively, the light-emitting layer 120 may be formed from two or more layers. For example, when the light-emitting layer 120 is formed by sequentially stacking a first light-emitting layer and a second light-emitting layer from the hole transport layer side, a material with hole transport properties can be used as the main material of the first light-emitting layer, and a material with electron transport properties can be used as the main material of the second light-emitting layer.

[0282] Furthermore, in the light-emitting layer 120, the host material 121 can be composed of one compound or multiple compounds. Alternatively, the light-emitting layer 120 may also include materials other than the host material 121 and the guest material 122.

[0283] <<Materials that can be used in the light-emitting layer 130>> The material that can be used for the light-emitting layer 130 can be any material as described in Embodiment 1 above. Therefore, a light-emitting element with high singlet excitation efficiency and high luminous efficiency can be manufactured.

[0284] <<Materials that can be used in the light-emitting layer 140>> The material that can be used for the light-emitting layer 140 can be any material as described in Embodiment 2 above. This allows for the manufacture of a light-emitting element with a low driving voltage.

[0285] Furthermore, there are no restrictions on the emission colors of the luminescent materials contained in luminescent layers 120, 130, and 140; they can be the same or different. The emission from each material is mixed and extracted to the outside of the element, so that, for example, when two emission colors are complementary, the luminescent element can emit white light. Considering the reliability of the luminescent element, the emission peak wavelength of the luminescent material contained in luminescent layer 120 is preferably shorter than that of the luminescent materials contained in luminescent layers 130 and 140.

[0286] Alternatively, light-emitting units 106, 108, 109, 110 and charge-generating layer 115 can be formed using methods such as vapor deposition (including vacuum vapor deposition), inkjet printing, coating, and gravure printing.

[0287] The structure shown in this embodiment can be implemented by appropriately combining it with the structures shown in other embodiments.

[0288] Implementation Method 4 In this embodiment, an example of a light-emitting element having a structure different from that shown in Embodiments 1 to 3 will be described with reference to FIGS. 7A to 10C.

[0289] <Example 1 of the structure of a light-emitting element> Figures 7A and 7B are cross-sectional views illustrating a light-emitting element according to one embodiment of the present invention. In Figures 7A and 7B, the same shading lines as in Figure 1A are used to indicate portions having the same function as in Figure 1A, while sometimes element symbols are omitted. Furthermore, portions having the same function as shown in Figure 1A are represented by the same element symbols, and sometimes their detailed descriptions are omitted.

[0290] The light-emitting elements 260a and 260b shown in Figures 7A and 7B can be either bottom-emitting (emitting from the substrate 200) type light-emitting elements that extract light from the substrate 200, or top-emitting (emitting from the substrate 200) type light-emitting elements that extract light in the opposite direction to the substrate 200. Note that one embodiment of the present invention is not limited to this; it can also be a dual-emission type light-emitting element that extracts light emitted by the light-emitting element both above and below the substrate 200.

[0291] When light-emitting elements 260a and 260b are bottom-emitting types, electrode 101 preferably has the function of transmitting light. Additionally, electrode 102 preferably has the function of reflecting light. Alternatively, when light-emitting elements 260a and 260b are top-emitting types, electrode 101 preferably has the function of reflecting light. Additionally, electrode 102 preferably has the function of transmitting light.

[0292] Light-emitting elements 260a and 260b include electrodes 101 and 102 on the substrate 200. Additionally, light-emitting layers 123B, 123G, and 123R are included between electrodes 101 and 102. Furthermore, a hole injection layer 111, a hole transport layer 112, an electron transport layer 118, and an electron injection layer 119 are also included.

[0293] Furthermore, as part of the structure of electrode 101, light-emitting element 260b includes conductive layer 101a, conductive layer 101b on conductive layer 101a, and conductive layer 101c below conductive layer 101a. That is, light-emitting element 260b has a structure in which conductive layer 101a is sandwiched between conductive layer 101b and conductive layer 101c.

[0294] In the light-emitting element 260b, the conductive layer 101b and the conductive layer 101c can be formed from different materials or from the same material. When the electrode 101 has a structure in which the conductive layer 101a is sandwiched by the same conductive material, it is easier to form a pattern by etching process, so it is preferred.

[0295] Alternatively, the light-emitting element 260b may include only either the conductive layer 101b or the conductive layer 101c.

[0296] In addition, the conductive layers 101a, 101b, and 101c included in electrode 101 can use the same structure and materials as electrode 101 or electrode 102 shown in Embodiment 1.

[0297] In Figures 7A and 7B, partition walls 145 are provided between regions 221B, 221G, and 221R, which are sandwiched between electrodes 101 and 102. The partition walls 145 are insulating. The partition walls 145 cover the ends of the electrodes 101 and have openings that overlap with the electrodes. By providing the partition walls 145, the electrodes 101 on the substrate 200 in each region can be divided into island shapes.

[0298] Furthermore, light-emitting layers 123B and 123G may have overlapping regions in the area overlapping with the partition wall 145. Additionally, light-emitting layers 123G and 123R may have overlapping regions in the area overlapping with the partition wall 145. Furthermore, light-emitting layers 123R and 123B may have overlapping regions in the area overlapping with the partition wall 145.

[0299] The partition wall 145 only needs to be insulating and can be formed using inorganic or organic materials. Examples of inorganic materials include silicon oxide, silicon oxynitride, silicon oxynitride, silicon nitride, aluminum oxide, and aluminum nitride. Examples of organic materials include photosensitive resins such as acrylic resin or polyimide resin.

[0300] Note that silicon oxynitride membranes refer to membranes in which the oxygen content is greater than the nitrogen content, preferably containing oxygen, nitrogen, silicon, and hydrogen in the concentration ranges of 55 atoms% to 65 atoms%, 1 atoms% to 20 atoms%, 25 atoms% to 35 atoms%, and 0.1 atoms% to 10 atoms%, respectively. Silicon oxynitride membranes refer to membranes in which the nitrogen content is greater than the oxygen content, preferably containing nitrogen, oxygen, silicon, and hydrogen in the concentration ranges of 55 atoms% to 65 atoms%, 1 atoms% to 20 atoms%, 25 atoms% to 35 atoms%, and 0.1 atoms% to 10 atoms%, respectively.

[0301] Furthermore, it is preferable that the light-emitting layers 123R, 123G, and 123B each contain light-emitting materials capable of emitting different colors. For example, when the light-emitting layer 123R contains a red light-emitting material, region 221R emits red light; when the light-emitting layer 123G contains a green light-emitting material, region 221G emits green light; and when the light-emitting layer 123B contains a blue light-emitting material, region 221B emits blue light. By using light-emitting elements 260a or 260b with this structure as pixels in a display device, a display device capable of full-color display can be manufactured. Additionally, the film thickness of each light-emitting layer can be either the same or different.

[0302] Furthermore, one or more of the light-emitting layers 123B, 123G, and 123R are preferably at least one of the light-emitting layers 130 shown in Embodiment 1 and 140 shown in Embodiment 2. This allows for the manufacture of a light-emitting element with good luminous efficiency.

[0303] In addition, any one or more of the light-emitting layers 123B, 123G, and 123R can be stacked in two or more layers.

[0304] As shown above, by including at least one light-emitting layer containing the light-emitting layer shown in Embodiment 1 or Embodiment 2, and using light-emitting elements 260a or 260b including the light-emitting layer as pixels of the display device, a display device with high luminous efficiency can be manufactured. That is, a display device including light-emitting elements 260a or 260b can reduce power consumption.

[0305] Furthermore, by arranging light-emitting elements (e.g., color filters, polarizing plates, anti-reflective films) in the direction of light extraction of the light-extracting electrodes, the color purity of light-emitting elements 260a and 260b can be improved. Therefore, the color purity of the display device including light-emitting elements 260a or 260b can be improved. Additionally, external light reflection from light-emitting elements 260a and 260b can be reduced. Therefore, the contrast ratio of the display device including light-emitting elements 260a or 260b can be improved.

[0306] Note that for other structures in light-emitting elements 260a and 260b, refer to the structures of the light-emitting elements in Embodiments 1 to 3.

[0307] <Example 2 of the structure of a light-emitting element> Below, we will describe a structural example of a light-emitting element that differs from the one shown in Figures 7A and 7B, with reference to Figures 8A and 8B.

[0308] Figures 8A and 8B are cross-sectional views illustrating a light-emitting element according to one embodiment of the present invention. In Figures 8A and 8B, the same shading lines as in Figures 7A and 7B are used to indicate portions having the same function as those in Figures 7A and 7B, while sometimes element symbols are omitted. Furthermore, portions having the same function as those shown in Figures 7A and 7B are represented by the same element symbols, and sometimes their detailed descriptions are omitted.

[0309] Figures 8A and 8B show structural examples of light-emitting elements having a light-emitting layer between a pair of electrodes. The light-emitting element 262a shown in Figure 8A is a top-emitting (top-emitting) type light-emitting element that extracts light in a direction opposite to the substrate 200, and the light-emitting element 262b shown in Figure 8B is a bottom-emitting (bottom-emitting) type light-emitting element that extracts light through the substrate 200. Note that one embodiment of the present invention is not limited to this; it could also be a double-emitting (dual-emitting) type light-emitting element that extracts light emitted by the light-emitting element both above and below the substrate 200 on which the light-emitting element is formed.

[0310] Light-emitting elements 262a and 262b include electrodes 101, 102, 103, and 104 on the substrate 200. Furthermore, at least a light-emitting layer 170 and a charge-generating layer 115 are included between electrodes 101 and 102, between electrodes 102 and 103, and between electrodes 102 and 104. Additionally, a hole injection layer 111, a hole transport layer 112, a light-emitting layer 180, an electron transport layer 113, an electron injection layer 114, a hole injection layer 116, a hole transport layer 117, an electron transport layer 118, and an electron injection layer 119 are also included.

[0311] Electrode 101 includes a conductive layer 101a and a conductive layer 101b on and in contact with the conductive layer 101a. Electrode 103 includes a conductive layer 103a and a conductive layer 103b on and in contact with the conductive layer 103a. Electrode 104 includes a conductive layer 104a and a conductive layer 104b on and in contact with the conductive layer 104a.

[0312] The light-emitting elements 262a shown in Figure 8A and 262b shown in Figure 8B both include a partition wall 145 between the region 222B held by electrodes 101 and 102, the region 222G held by electrodes 102 and 103, and the region 222R held by electrodes 102 and 104. The partition wall 145 is insulating. The partition wall 145 covers the ends of electrodes 101, 103, and 104 and includes an opening overlapping the electrodes. By providing the partition wall 145, the electrodes on the substrate 200 in each region can be divided into island shapes.

[0313] Light-emitting elements 262a and 262b have substrates 220 comprising optical elements 224B, 224G, and 224R respectively, in the direction in which light emitted from regions 222B, 222G, and 222R is extracted. Light emitted from each region passes through each optical element and exits to the outside of the light-emitting element. That is, light emitted from region 222B passes through optical element 224B, light emitted from region 222G passes through optical element 224G, and light emitted from region 222R passes through optical element 224R.

[0314] Optical elements 224B, 224G, and 224R have the function of selectively transmitting incident light of a specific color. For example, light emitted from region 222B becomes blue light when it passes through optical element 224B, light emitted from region 222G becomes green light when it passes through optical element 224G, and light emitted from region 222R becomes red light when it passes through optical element 224R.

[0315] Optical elements 224R, 224G, and 224B can be, for example, color layers (also called color filters), bandpass filters, multilayer filters, etc. Furthermore, color conversion elements can be applied to the optical elements. A color conversion element is an optical element that converts incident light into light with a wavelength longer than the incident light. Preferably, a quantum dot-based element is used as the color conversion element. By utilizing quantum dots, the color reproduction of the display device can be improved.

[0316] Alternatively, one or more other optical elements may be stacked on optical elements 224R, 224G, and 224B. Other optical elements may include, for example, a circular polarizer or an anti-reflective film. By placing the circular polarizer on the side where the light emitted by the light-emitting element in the display device is extracted, the phenomenon of light incident from outside the display device being reflected inside and emitted to the outside can be prevented. Furthermore, by providing an anti-reflective film, external light reflected from the surface of the display device can be reduced. Therefore, the light emitted by the display device can be clearly observed.

[0317] In Figures 8A and 8B, dashed arrows schematically illustrate the blue (B), green (G), and red (R) light emitted from each region through each optical element.

[0318] A light-shielding layer 223 is included between each optical element. The light-shielding layer 223 has the function of blocking light emitted from adjacent areas. Alternatively, a structure without the light-shielding layer 223 may also be used.

[0319] The light-shielding layer 223 has the function of suppressing the reflection of external light. Alternatively, the light-shielding layer 223 has the function of preventing the light emitted from adjacent light-emitting elements from being mixed with color. The light-shielding layer 223 can be made of metal, resin containing black pigment, carbon black, metal oxide, composite oxide of solid solution containing multiple metal oxides, etc.

[0320] Furthermore, optical elements 224B and 224G may also have overlapping areas in the region overlapping with the light-shielding layer 223. Additionally, optical elements 224G and 224R may also have overlapping areas in the region overlapping with the light-shielding layer 223. Furthermore, optical elements 224R and 224B may also have overlapping areas in the region overlapping with the light-shielding layer 223.

[0321] In addition, regarding the substrate 200 and the substrate 220 having optical elements, please refer to Embodiment 1.

[0322] Furthermore, light-emitting elements 262a and 262b have microcavity structures.

[0323] Microcavity Structure Light emitted from light-emitting layers 170 and 180 is resonant between a pair of electrodes (e.g., electrodes 101 and 102). Furthermore, light-emitting layers 170 and 180 are formed at positions where the desired wavelength of light in the emitted light is enhanced. For example, by adjusting the optical distance from the reflective region of electrode 101 to the light-emitting region of light-emitting layer 170 and the optical distance from the reflective region of electrode 102 to the light-emitting region of light-emitting layer 170, the desired wavelength of light emitted from light-emitting layer 170 can be enhanced. Similarly, by adjusting the optical distance from the reflective region of electrode 101 to the light-emitting region of light-emitting layer 180 and the optical distance from the reflective region of electrode 102 to the light-emitting region of light-emitting layer 180, the desired wavelength of light emitted from light-emitting layer 180 can be enhanced. In other words, when using a light-emitting element with multiple stacked light-emitting layers (here, light-emitting layer 170 and light-emitting layer 180), it is preferable to optimize the optical distances of light-emitting layers 170 and 180 separately.

[0324] Furthermore, in light-emitting elements 262a and 262b, by adjusting the thickness of the conductive layers (conductive layers 101b, 103b, and 104b) in each region, the desired wavelength of light emitted by light-emitting layers 170 and 180 can be enhanced. Additionally, by making at least one of the hole injection layer 111 and the hole transport layer 112 different in each region, the light emitted from light-emitting layers 170 and 180 can also be enhanced.

[0325] For example, in electrodes 101 to 104, when the refractive index of the conductive material capable of reflecting light is less than the refractive index of the light-emitting layer 170 or 180, the film thickness of the conductive layer 101b in electrode 101 is adjusted such that the optical distance between electrode 101 and electrode 102 is mBλB / 2 (where mB represents a natural number and λB represents the wavelength of the light enhanced in region 222B). Similarly, the film thickness of the conductive layer 103b in electrode 103 is adjusted such that the optical distance between electrode 103 and electrode 102 is mGλG / 2 (where mG represents a natural number and λG represents the wavelength of the light enhanced in region 222G). Furthermore, the film thickness of the conductive layer 104b in electrode 104 is adjusted such that the optical distance between electrode 104 and electrode 102 is mRλR / 2 (where mR represents a natural number and λR represents the wavelength of the light enhanced in region 222R).

[0326] For example, when it is difficult to precisely determine the reflection areas of electrodes 101 to 104, by assuming that the reflection areas of electrodes 101 to 104 are defined as reflection areas, the optical distance for enhancing the light emitted from the light-emitting layer 170 or the light-emitting layer 180 can be derived. Furthermore, when it is difficult to precisely determine the light-emitting areas of the light-emitting layers 170 and 180, by assuming that either area of ​​the light-emitting layer 170 or the light-emitting layer 180 is defined as a light-emitting area, the optical distance for enhancing the light emitted from the light-emitting layer 170 and the light-emitting layer 180 can be derived.

[0327] As described above, by adjusting the optical distance between a pair of electrodes in each region using a microcavity structure, light scattering and absorption near the electrodes can be suppressed, thereby achieving high light extraction efficiency. Furthermore, in the above structure, conductive layers 101b, 103b, and 104b preferably have light-transmitting capabilities. Additionally, the materials constituting conductive layers 101b, 103b, and 104b can be the same or different. Using the same material to form conductive layers 101b, 103b, and 104b facilitates the formation of patterns through the etching process, which is preferable. Furthermore, conductive layers 101b, 103b, and 104b can each be two or more stacked layers.

[0328] Since the light-emitting element 262a shown in Figure 8A is a top-emitting type light-emitting element, the conductive layers 101a, 103a, and 104a preferably have the function of reflecting light. In addition, the electrode 102 preferably has the function of transmitting light and reflecting light.

[0329] Furthermore, since the light-emitting element 262b shown in Figure 8B is a bottom-emitting type light-emitting element, the conductive layers 101a, 103a, and 104a preferably have the functions of transmitting light and reflecting light. Additionally, the electrode 102 preferably has the function of reflecting light.

[0330] In light-emitting elements 262a and 262b, conductive layers 101a, 103a, or 104a can be made of the same material or different materials. When conductive layers 101a, 103a, and 104a are made of the same material, the manufacturing cost of light-emitting elements 262a and 262b can be reduced. Alternatively, conductive layers 101a, 103a, and 104a can each be two or more layers stacked together.

[0331] Furthermore, at least one of the light-emitting layers 170 and 180 in light-emitting elements 262a and 262b preferably has the structure shown in Embodiment 1 or Embodiment 2. Thus, light-emitting elements with high luminous efficiency can be manufactured.

[0332] For example, light-emitting layers 170 and 180 can have a structure in which two layers are stacked in one or both, as in light-emitting layers 180a and 180b. By using a first light-emitting material and a second light-emitting material, which are two light-emitting materials that have the function of emitting different colors, respectively, light emission containing multiple colors can be obtained. In particular, it is preferable to select the light-emitting materials for each light-emitting layer so that white light emission can be obtained by combining the light emitted by light-emitting layers 170 and 180.

[0333] One or both of the light-emitting layers 170 and 180 may have a structure with three or more layers stacked, and may also include layers that do not have light-emitting materials.

[0334] As shown above, by using light-emitting elements 262a or 262b, which have at least one of the light-emitting layers shown in Embodiment 1 and Embodiment 2, as pixels of a display device, a display device with high luminous efficiency can be manufactured. In other words, a display device including light-emitting elements 262a or 262b can reduce power consumption.

[0335] Note that for other structures in light-emitting elements 262a and 262b, refer to the structures of light-emitting elements 260a or 260b or the light-emitting elements shown in Embodiments 1 to 3.

[0336] <Manufacturing Method of Light Emitting Elements> Next, a method for manufacturing a light-emitting element according to one embodiment of the present invention will be described with reference to FIGS. 9A to 10C. Here, the method for manufacturing the light-emitting element 262a shown in FIG. 8A will be described.

[0337] Figures 9A to 10C are cross-sectional views illustrating a method for manufacturing a light-emitting element according to one embodiment of the present invention.

[0338] The manufacturing method of the light-emitting element 262a, which will be described below, includes seven steps, from the first step to the seventh step.

[0339] <<First Step>> The first step is the following process: forming the electrodes of the light-emitting element (specifically, the conductive layer 101a constituting electrode 101, the conductive layer 103a constituting electrode 103, and the conductive layer 104a constituting electrode 104) on the substrate 200 (see Figure 9A).

[0340] In this embodiment, a conductive layer with light-reflecting function is formed on the substrate 200, and the conductive layer is processed into a desired shape, thereby forming conductive layers 101a, 103a, and 104a. As the aforementioned conductive layer with light-reflecting function, an alloy film of silver, palladium, and copper (also known as an Ag-Pd-Cu film or APC) is used. Thus, by forming conductive layers 101a, 103a, and 104a through a process that processes the same conductive layer, manufacturing costs can be reduced, which is preferable.

[0341] Alternatively, multiple transistors may be formed on the substrate 200 prior to the first step. Furthermore, these multiple transistors may be electrically connected to conductive layers 101a, 103a, and 104a, respectively.

[0342] <<Second Step>> The second step is as follows: a conductive layer 101b with light transmission function is formed on the conductive layer 101a constituting electrode 101; a conductive layer 103b with light transmission function is formed on the conductive layer 103a constituting electrode 103; and a conductive layer 104b with light transmission function is formed on the conductive layer 104a constituting electrode 104 (see Figure 9B).

[0343] In this embodiment, conductive layers 101b, 103b, and 104b that transmit light are formed on conductive layers 101a, 103a, and 104a that have the function of reflecting light, thereby forming electrodes 101, 103, and 104. An ITSO film is used as the conductive layers 101b, 103b, and 104b.

[0344] Furthermore, the conductive layers 101b, 103b, and 104b, which have the function of transmitting light, can also be formed in multiple stages. By forming them in multiple stages, the conductive layers 101b, 103b, and 104b can be formed with a film thickness that achieves an appropriate microcavity structure in each region.

[0345] <<The Third Step>> The third step is the process of forming the partition wall 145 at the ends of each electrode covering the light-emitting element (see Figure 9C).

[0346] The separator 145 includes an opening that overlaps with the electrode. The conductive film exposed by this opening is used as the anode of the light-emitting element. In this embodiment, polyimide resin is used as the separator 145.

[0347] Furthermore, there is no possibility of damaging the EL layer (the layer containing organic compounds) in the first to third steps, thus allowing the use of a variety of film formation methods and microfabrication techniques. In this embodiment, a reflective conductive layer is formed by sputtering, a pattern is formed on the conductive layer by photolithography, and then the conductive layer is processed into islands by dry etching or wet etching to form the conductive layer 101a constituting electrode 101, the conductive layer 103a constituting electrode 103, and the conductive layer 104a constituting electrode 104. Then, a transparent conductive film is formed by sputtering, a pattern is formed on the transparent conductive film by photolithography, and then the transparent conductive film is processed into islands by wet etching to form electrodes 101, 103, and 104.

[0348] <<Fourth Step>> The fourth step is the process of forming the hole injection layer 111, the hole transport layer 112, the light emission layer 180, the electron transport layer 113, the electron injection layer 114 and the charge generation layer 115 (see Figure 10A).

[0349] A hole injection layer 111 can be formed by co-depositing a hole-transporting material and a material containing an acceptor substance. Note that co-depositing refers to a vapor deposition method in which multiple different substances are simultaneously evaporated from different evaporation sources. A hole transport layer 112 can be formed by vapor-depositing a hole-transporting material.

[0350] A light-emitting layer 180 can be formed by vapor deposition of a guest material that emits light selected from at least one of violet, blue, blue-green, green, yellow-green, yellow, orange, and red. As the guest material, a luminescent organic compound that emits fluorescence or phosphorescence can be used. Furthermore, the structure of the light-emitting layer shown in Embodiments 1 to 3 is preferred. Alternatively, the light-emitting layer 180 can also be a double-layer structure. In this case, the two light-emitting layers are preferably composed of luminescent materials that emit different colors from each other.

[0351] An electron transport layer 113 can be formed by vapor deposition of a material with high electron transport properties. In addition, an electron injection layer 114 can be formed by vapor deposition of a material with high electron injection properties.

[0352] By vapor deposition, a charge generation layer 115 can be formed by adding an electron acceptor to a hole transport material or adding an electron donor to an electron transport material.

[0353] <<Fifth Step>> The fifth step is the fabrication process of forming the hole injection layer 116, the hole transport layer 117, the light-emitting layer 170, the electron transport layer 118, the electron injection layer 119, and the electrode 102 (see Figure 10B).

[0354] A hole injection layer 116 can be formed using the same materials and methods as the hole injection layer 111 shown above. Similarly, a hole transport layer 117 can be formed using the same materials and methods as the hole transport layer 112 shown above.

[0355] A light-emitting layer 170 can be formed by vapor deposition of a guest material that emits light selected from at least one of violet, blue, blue-green, green, yellow-green, yellow, orange, and red. The guest material can be a fluorescent organic compound. Furthermore, the fluorescent organic compound can be vapor-deposited alone or mixed with other materials. Alternatively, a fluorescent organic compound can be used as the guest material, and the guest material can be dispersed in a host material whose excitation energy is greater than that of the guest material, thereby performing vapor deposition.

[0356] As the electron transport layer 118, it can be formed using the same material and the same method as the electron transport layer 113 described above. Similarly, as the electron injection layer 119, it can be formed using the same material and the same method as the electron injection layer 114 described above.

[0357] Electrode 102 can be formed by stacking a reflective conductive film and a transparent conductive film. Electrode 102 can adopt a single-layer structure or a stacked structure.

[0358] By means of the above process, a light-emitting element is formed on the substrate 200. The light-emitting element includes region 222B, region 222G and region 222R on electrodes 101, 103 and 104 respectively.

[0359] <<Sixth Step>> The sixth step is the process of forming a light-shielding layer 223, optical element 224B, optical element 224G and optical element 224R on the substrate 220 (see Figure 10C).

[0360] A resin film containing black pigment is formed in a desired area to form a light-shielding layer 223. Then, optical elements 224B, 224G, and 224R are formed on the substrate 220 and the light-shielding layer 223. An optical element 224B is formed in a desired area using a resin film containing blue pigment. An optical element 224G is formed in a desired area using a resin film containing green pigment. An optical element 224R is formed in a desired area using a resin film containing red pigment.

[0361] <<Seventh Step>> The seventh step is as follows: the light-emitting element formed on the substrate 200, the light-shielding layer 223 formed on the substrate 220, the optical element 224B, the optical element 224G and the optical element 224R are bonded together and sealed with a sealant (not shown).

[0362] The light-emitting element 262a shown in Figure 8A can be formed by the above process.

[0363] The structure shown in this embodiment can be implemented by appropriately combining it with the structures shown in other embodiments.

[0364] Implementation Method 5 In this embodiment, a display device according to an embodiment of the present invention will be described with reference to FIGS. 11A to 19B.

[0365] <Example 1 of the structure of a display device> Figure 11A is a top view showing the display device 600, and Figure 11B is a cross-sectional view along the dashed lines AB and CD in Figure 11A. The display device 600 includes a driving circuit section (signal line driving circuit section 601 and scan line driving circuit section 603) and a pixel section 602. The signal line driving circuit section 601, the scan line driving circuit section 603, and the pixel section 602 have the function of controlling the light emission of the light-emitting element.

[0366] The display device 600 includes a component substrate 610, a sealing substrate 604, a sealant 605, a region 607 surrounded by the sealant 605, lead wiring 608, and an FPC 609.

[0367] Note that lead wiring 608 is used to transmit signals input to the signal line drive circuit section 601 and the scan line drive circuit section 603, and receives video signals, clock signals, start signals, reset signals, etc. from the FPC 609, which serves as an external input terminal. Note that although only the FPC 609 is shown here, a printed wiring board (PWB) can also be mounted on the FPC 609.

[0368] The signal line driving circuit section 601 forms a CMOS circuit combining an N-channel transistor 623 and a P-channel transistor 624. Alternatively, the signal line driving circuit section 601 or the scan line driving circuit section 603 can utilize various CMOS circuits, PMOS circuits, or NMOS circuits. Furthermore, although this embodiment shows a display device with a driver and pixels having the driving circuit section formed on the same surface of the substrate, this structure is not mandatory; the driving circuit section can also be formed externally instead of on the substrate.

[0369] Additionally, the pixel unit 602 includes a switching transistor 611, a current control transistor 612, and a lower electrode 613 electrically connected to the drain of the current control transistor 612. Note that a partition wall 614 is formed to cover the end of the lower electrode 613. A positive photosensitive acrylic resin film can be used as the partition wall 614.

[0370] Furthermore, the upper or lower end of the separator 614 is formed as a curved surface to obtain good coverage. For example, when using positive photosensitive acrylic as the material of the separator 614, it is preferable that only the upper end of the separator 614 includes a curved surface with a radius of curvature (more than 0.2 μm and less than 3 μm). Negative photosensitive resin or positive photosensitive resin can be used as the separator 614.

[0371] There are no particular restrictions on the structure of the transistors (transistors 611, 612, 623, 624). For example, interleaved transistors can also be used. Furthermore, there are no particular restrictions on the polarity of the transistors; structures including both N-channel and P-channel transistors, or only one of N-channel and P-channel transistors, can be used. There are also no particular restrictions on the crystallinity of the semiconductor film used for the transistors. For example, amorphous or crystalline semiconductor films can be used. As semiconductor materials, Group 14 semiconductors (such as silicon), compound semiconductors (including oxide semiconductors), organic semiconductors, etc., can be used. As transistors, oxide semiconductors with a bandgap of 2 eV or more, preferably 2.5 eV or more, and more preferably 3 eV or more, are preferred because they can reduce the off-state current of the transistor. Examples of oxide semiconductors include In-Ga oxides and In-M-Zn oxides (where M represents aluminum (Al), gallium (Ga), yttrium (Y), zirconium (Zr), lanthanum (La), cerium (Ce), tin (Sn), hafnium (Hf), or neodymium (Nd)).

[0372] An EL layer 616 and an upper electrode 617 are formed on the lower electrode 613. The lower electrode 613 is used as the anode, and the upper electrode 617 is used as the cathode.

[0373] Furthermore, the EL layer 616 is formed by various methods such as vapor deposition using a vapor deposition mask, inkjet printing, and spin coating. Additionally, low-molecular-weight compounds or high-molecular-weight compounds (including oligomers and dendritic polymers) can be used as other materials constituting the EL layer 616.

[0374] A light-emitting element 618 is formed by a lower electrode 613, an EL layer 616, and an upper electrode 617. Preferably, the light-emitting element 618 is a light-emitting element having the structure constituting Embodiments 1 to 3. Note that when a pixel portion includes multiple light-emitting elements, it may also include the light-emitting elements described in Embodiments 1 to 3, as well as light-emitting elements having other structures.

[0375] Furthermore, by using sealant 605 to bond the sealing substrate 604 to the element substrate 610, a structure is formed in which the light-emitting element 618 is mounted in the region 607 surrounded by the element substrate 610, the sealing substrate 604, and the sealant 605. Note that the region 607 is filled with filler. Besides inert gases (nitrogen or argon, etc.), it may also be filled with UV-curable or thermosetting resins suitable for the sealant 605. Examples include PVC (polyvinyl chloride) resins, acrylic resins, polyimide resins, epoxy resins, silicone resins, PVB (polyvinyl butyral) resins, or EVA (ethylene vinyl acetate) resins. Forming a recess in the sealing substrate and placing a desiccant therein can suppress deterioration caused by moisture, which is preferable.

[0376] Furthermore, an optical element 621 is disposed below the sealing substrate 604, overlapping with the light-emitting element 618. Additionally, a light-shielding layer 622 is disposed below the sealing substrate 604. Both the optical element 621 and the light-shielding layer 622 can employ the same structure as the optical element and light-shielding layer shown in Embodiment 3.

[0377] Furthermore, epoxy resin or glass powder is preferably used as the sealant 605. Additionally, these materials are preferably those that are as impermeable as possible to water or oxygen. Moreover, as a material for the sealing substrate 604, in addition to glass substrates or quartz substrates, plastic substrates made of FRP (fiber reinforced plastics), PVF (polyvinyl fluoride), polyester, acrylic, etc., can also be used.

[0378] By using the above steps, a display device including the light-emitting element and optical element described in Embodiments 1 to 3 can be obtained.

[0379] <Example 2 of the structure of a display device> Hereinafter, other examples of the display device will be described with reference to FIGS. 12A, 12B, and 13. FIG. 12A, 12B, and 13 are cross-sectional views of a display device according to one embodiment of the present invention.

[0380] Figure 12A shows a substrate 1001, a base insulating film 1002, a gate insulating film 1003, gate electrodes 1006, 1007, and 1008, a first interlayer insulating film 1020, a second interlayer insulating film 1021, a peripheral portion 1042, a pixel portion 1040, a driving circuit portion 1041, lower electrodes 1024R, 1024G, and 1024B of the light-emitting element, a partition wall 1025, an EL layer 1028, an upper electrode 1026 of the light-emitting element, a sealing layer 1029, a sealing substrate 1031, and a sealant 1032.

[0381] In Figure 12A, as an example of an optical element, color layers (red color layer 1034R, green color layer 1034G, and blue color layer 1034B) are disposed on a transparent substrate 1033. Additionally, a light-shielding layer 1035 may be provided. The transparent substrate 1033, on which the color layers and light-shielding layers are disposed, is aligned and fixed to the substrate 1001. Furthermore, the color layers and light-shielding layers are covered by a capping layer 1036. In Figure 12A, the light passing through the color layers becomes red light, green light, and blue light, thus enabling the display of an image using pixels of three colors.

[0382] Figure 12B shows an example of an optical element in which a color layer (red color layer 1034R, green color layer 1034G, and blue color layer 1034B) is formed between the gate insulating film 1003 and the first interlayer insulating film 1020. As described above, the color layer may also be disposed between the substrate 1001 and the sealing substrate 1031.

[0383] In Figure 13, as an example of an optical element, a color layer (red color layer 1034R, green color layer 1034G, and blue color layer 1034B) is shown formed between a first interlayer insulating film 1020 and a second interlayer insulating film 1021. Thus, the color layer can also be disposed between the substrate 1001 and the sealing substrate 1031.

[0384] In addition, although the above describes a display device with a structure that extracts light through a substrate 1001 on which a transistor is formed (bottom-emitting type), a display device with a structure that extracts light through a sealed substrate 1031 (top-emitting type) can also be used.

[0385] <Example 3 of the structure of a display device> Figures 14A and 14B show an example of a cross-sectional view of a top-emitting display device. Figures 14A and 14B are cross-sectional views illustrating a display device according to one embodiment of the present invention, omitting the driving circuit section 1041, peripheral section 1042, etc. shown in Figures 12A, 12B, and 13.

[0386] In this case, substrate 1001 can be a substrate that does not allow light to pass through. The process up to manufacturing the connecting electrode that connects the transistor and the anode of the light-emitting element is performed in the same way as in a bottom-emitting display device. Then, a third interlayer insulating film 1037 is formed in a manner that covers electrode 1022. This insulating film may also have a planarization function. The third interlayer insulating film 1037 can be formed using the same material as the second interlayer insulating film or various other materials.

[0387] Although the lower electrodes 1024R, 1024G, and 1024B of this light-emitting element are all anodes, they can also be cathodes. Furthermore, in the case of a top-emitting display device as shown in Figures 14A and 14B, the lower electrodes 1024R, 1024G, and 1024B preferably have the function of reflecting light. Additionally, an upper electrode 1026 is provided on the EL layer 1028. Preferably, by utilizing the function of the upper electrode 1026 to reflect light and allow light to pass through, a microcavity structure is employed between the lower electrodes 1024R, 1024G, 1024B and the upper electrode 1026 to enhance the intensity of light at a specific wavelength.

[0388] When using the top-emitting structure shown in FIG14A, sealing can be achieved using a sealing substrate 1031 provided with color layers (red color layer 1034R, green color layer 1034G, and blue color layer 1034B). The sealing substrate 1031 may also be provided with a light-shielding layer 1035 located between pixels. Furthermore, it is preferable to use a light-transmitting substrate as the sealing substrate 1031.

[0389] Figure 14A illustrates a structure with multiple light-emitting elements and a color layer on each of these elements, but it is not limited to this. For example, as shown in Figure 14B, a full-color display using red, green, and blue colors can be achieved by providing a red color layer 1034R and a blue color layer 1034B without providing a green color layer. As shown in Figure 14A, providing a color layer on each light-emitting element helps to suppress external light reflection. On the other hand, as shown in Figure 14B, when a red and blue color layer are provided without a green color layer, the energy loss of the light emitted by the green light-emitting element is less, thus reducing power consumption.

[0390] <Example 4 of the structure of a display device> Although the above-described display device includes sub-pixels of three colors (red, green, and blue), it may also include sub-pixels of four colors (red, green, blue, and yellow, or red, green, blue, and white). Figures 15A to 17B show the structure of a display device including lower electrodes 1024R, 1024G, 1024B, and 1024Y. Figures 15A, 15B, and 16 show a display device with a structure in which light is extracted through a substrate 1001 on which transistors are formed (bottom-emitting type), and Figures 17A and 17B show a display device with a structure in which light is extracted through a sealed substrate 1031 (top-emitting type).

[0391] Figure 15A shows an example of a display device in which optical elements (color layers 1034R, 1034G, 1034B, and 1034Y) are disposed on a transparent substrate 1033. Figure 15B shows an example of a display device in which optical elements (color layers 1034R, 1034G, 1034B, and 1034Y) are formed between a first interlayer insulating film 1020 and a gate insulating film 1003. Figure 16 shows an example of a display device in which optical elements (color layers 1034R, 1034G, 1034B, and 1034Y) are formed between a first interlayer insulating film 1020 and a second interlayer insulating film 1021.

[0392] Color layer 1034R transmits red light, color layer 1034G transmits green light, and color layer 1034B transmits blue light. Additionally, color layer 1034Y transmits yellow light or multiple light sources selected from blue, green, yellow, and red. When color layer 1034Y transmits multiple light sources selected from blue, green, yellow, and red, the light transmitted through color layer 1034Y can also be white. Light-emitting elements that emit yellow or white light have high luminous efficiency; therefore, display devices including color layer 1034Y can reduce power consumption.

[0393] Furthermore, in the top-emitting display devices shown in Figures 17A and 17B, similarly to the display device in Figure 14A, a microcavity structure is preferably provided between the lower electrodes 1024R, 1024G, 1024B, 1024Y and the upper electrode 1026 in the light-emitting element including the lower electrode 1024Y. Additionally, in the display device of Figure 17A, sealing can be achieved using a sealing substrate 1031 provided with color layers (red color layer 1034R, green color layer 1034G, blue color layer 1034B, and yellow color layer 1034Y).

[0394] The light emitted through the microcavity and the yellow color layer 1034Y has an emission spectrum in the yellow region. Because yellow has a high visual sensitivity (luminosity factor), the luminous efficiency of the light-emitting element emitting yellow light is high. In other words, the display device with the structure shown in Figure 17A can reduce power consumption.

[0395] Figure 17A illustrates a structure with multiple light-emitting elements and a color layer on each of these elements, but it is not limited to this. For example, as shown in Figure 17B, a full-color display can be achieved using four colors: red, green, blue, and yellow, or four colors: red, green, blue, and white, by using a red color layer 1034R, a green color layer 1034G, and a blue color layer 1034B without a yellow color layer. As shown in Figure 17A, when light-emitting elements are provided and a color layer is provided on each of these elements, the effect of suppressing external light reflection is achieved. On the other hand, as shown in Figure 17B, when light-emitting elements and red, green, and blue color layers are provided without a yellow color layer, the energy loss of the light emitted by the yellow or white light-emitting elements is less, thus reducing power consumption.

[0396] <Example 5 of the structure of a display device> Next, FIG18 shows a display device according to another embodiment of the present invention. FIG18 is a cross-sectional view taken along the dashed lines AB and CD of FIG11A. In addition, in FIG18, parts having the same function as those shown in FIG11B are represented by the same element symbols, and their detailed descriptions are sometimes omitted.

[0397] The display device 600 shown in Figure 18 includes sealing layers 607a, 607b, and 607c in a region 607 surrounded by an element substrate 610, a sealing substrate 604, and a sealant 605. One or more of sealing layers 607a, 607b, and 607c can be made of resins such as PVC (polyvinyl chloride), acrylic resins, polyimide resins, epoxy resins, silicone resins, PVB (polyvinyl butyral) resins, or EVA (ethylene vinyl acetate) resins. Alternatively, inorganic materials such as silicon oxide, silicon oxynitride, silicon oxynitride, silicon nitride, aluminum oxide, and aluminum nitride can be used. Forming sealing layers 607a, 607b, and 607c can suppress the deterioration of the light-emitting element 618 caused by impurities such as water, which is preferable. In addition, when sealing layers 607a, 607b and 607c are formed, sealant 605 may not be provided.

[0398] Furthermore, one or two of the sealing layers 607a, 607b, and 607c can be formed, or more than four sealing layers can be formed. By having multiple sealing layers, it is preferable to effectively prevent impurities such as water from entering the light-emitting element 618 inside the display device 600 from the outside of the display device 600. Moreover, when the sealing layer is multi-layered, it contains laminated resin and inorganic materials, which is also preferable.

[0399] <Example 6 of the structure of a display device> The display devices shown in structural examples 1 to 4 of this embodiment include optical elements, but an embodiment of the present invention may also exclude optical elements.

[0400] The display devices shown in Figures 19A and 19B are top-emitting display devices with a structure that extracts light through a sealed substrate 1031. Figure 19A is an example of a display device including light-emitting layers 1028R, 1028G, and 1028B. Figure 19B is an example of a display device including light-emitting layers 1028R, 1028G, 1028B, and 1028Y.

[0401] Emitting layer 1028R emits red light, emitting layer 1028G emits green light, and emitting layer 1028B emits blue light. Emitting layer 1028Y has the function of emitting yellow light or emitting multiple lights selected from blue, green, and red. The light emitted by emitting layer 1028Y can also be white light. The luminous efficiency of light-emitting elements that emit yellow or white light is high, therefore display devices including emitting layer 1028Y can reduce power consumption.

[0402] The display devices shown in Figures 19A and 19B include EL layers that emit light of different colors in the sub-pixels, thereby eliminating the need for a color layer used as an optical element.

[0403] The sealing layer 1029 can be made of resins such as PVC (polyvinyl chloride), acrylic resins, polyimide resins, epoxy resins, silicone resins, PVB (polyvinyl butyral) resins, or EVA (ethylene vinyl acetate) resins. Alternatively, inorganic materials such as silicon oxide, silicon oxynitride, silicon oxynitride, silicon nitride, aluminum oxide, and aluminum nitride can be used. By forming the sealing layer 1029, the degradation of the light-emitting element caused by impurities such as water can be suppressed, making it a preferable option.

[0404] Furthermore, the sealing layer 1029 can be formed as a single layer or in multiple layers, or even four or more sealing layers 1029 can be formed. Having multiple layers of sealing layer effectively prevents impurities such as water from entering the display device from the outside, which is preferable. Moreover, when the sealing layer is multi-layered, it is preferable that resin and inorganic materials are layered within it.

[0405] The sealing substrate 1031 only needs to have the function of protecting the light-emitting element. Therefore, the sealing substrate 1031 can be a flexible substrate or thin film.

[0406] The structure shown in this embodiment can be appropriately combined with other embodiments or other structures in this embodiment.

[0407] Implementation Method 6 In this embodiment, a display device including a light-emitting element according to one embodiment of the present invention will be described with reference to FIGS. 20A to 22B.

[0408] Note that FIG20A is a block diagram illustrating a display device according to an embodiment of the present invention, and FIG20B is a circuit diagram illustrating the pixel circuit included in the display device according to an embodiment of the present invention.

[0409] <Explanation of the display device> The display device shown in Figure 20A includes: a region having pixels with display elements (hereinafter referred to as pixel section 802); a circuit section (hereinafter referred to as driving circuit section 804) disposed outside the pixel section 802 and having circuitry for driving the pixels; a circuitry having the function of a protection element (hereinafter referred to as protection circuitry 806); and a terminal section 807. Alternatively, the protection circuitry 806 may be omitted.

[0410] Preferably, part or all of the drive circuit section 804 is formed on the same substrate as the pixel section 802. This reduces the number of components or terminals. When part or all of the drive circuit section 804 is not formed on the same substrate as the pixel section 802, part or all of the drive circuit section 804 can be mounted by COG or TAB (Tape Automated Bonding).

[0411] The pixel unit 802 includes a circuit (hereinafter referred to as pixel circuit 801) for driving a plurality of display elements arranged in X rows (X is a natural number of 2 or more) and Y columns (Y is a natural number of 2 or more). The driving circuit unit 804 includes a circuit (hereinafter referred to as scan line driving circuit 804a) for outputting a signal (scan signal) for selecting pixels and a circuit (hereinafter referred to as signal line driving circuit 804b) for supplying signals (data signals) for driving the display elements for driving pixels.

[0412] The scan line drive circuit 804a includes a shift register, etc. The scan line drive circuit 804a receives a signal to drive the shift register via terminal 807 and outputs a signal. For example, the scan line drive circuit 804a receives a start pulse signal, a clock signal, etc., and outputs a pulse signal. The scan line drive circuit 804a has the function of controlling the potential of the wiring (hereinafter referred to as scan lines GL_1 to GL_X) to which the scan signal is supplied. Alternatively, multiple scan line drive circuits 804a can be provided, and each scan line GL_1 to GL_X can be controlled by a separate scan line drive circuit 804a. Alternatively, the scan line drive circuit 804a can supply an initialization signal. However, it is not limited to this; the scan line drive circuit 804a can also supply other signals.

[0413] The signal line drive circuit 804b includes a shift register, etc. The signal line drive circuit 804b receives signals used to drive the shift register and signals from which data signals (image signals) are derived via a terminal portion 807. The signal line drive circuit 804b has the function of generating data signals to be written to the pixel circuit 801 based on the image signals. Furthermore, the signal line drive circuit 804b has the function of controlling the output of the data signals in response to pulse signals generated by inputs such as start pulse signals and clock signals. Additionally, the signal line drive circuit 804b has the function of controlling the potential of the wiring to which data signals are supplied (hereinafter referred to as data lines DL_1 to DL_Y). Alternatively, the signal line drive circuit 804b can supply initialization signals. However, it is not limited to this; the signal line drive circuit 804b can supply other signals.

[0414] The signal line drive circuit 804b can be constructed using, for example, multiple analog switches. By sequentially turning on multiple analog switches, the signal line drive circuit 804b can output a signal obtained by time-dividing the image signal as a data signal. Alternatively, a shift register or similar device can be used to construct the signal line drive circuit 804b.

[0415] Pulse signals and data signals are input to each of the plurality of pixel circuits 801 via one of the plurality of scan lines GL supplied with scan signals and one of the plurality of data lines DL supplied with data signals, respectively. Furthermore, each of the plurality of pixel circuits 801 is controlled by a scan line driving circuit 804a to write and retain data signals. For example, a pulse signal is input to the pixel circuit 801 in the m-th row and n-th column via the scan line GL_m (m is a natural number less than X) from the scan line driving circuit 804a, and a data signal is input to the pixel circuit 801 in the m-th row and n-th column via the data line DL_n (n is a natural number less than Y) according to the potential of the scan line GL_m.

[0416] The protection circuit 806 shown in Figure 20A is connected, for example, to the scan line GL, which is the wiring between the scan line drive circuit 804a and the pixel circuit 801. Alternatively, the protection circuit 806 is connected to the data line DL, which is the wiring between the signal line drive circuit 804b and the pixel circuit 801. Alternatively, the protection circuit 806 may be connected to the wiring between the scan line drive circuit 804a and the terminal portion 807. Alternatively, the protection circuit 806 may be connected to the wiring between the signal line drive circuit 804b and the terminal portion 807. Furthermore, the terminal portion 807 refers to the portion provided with terminals for inputting power, control signals, and image signals to the display device from external circuitry.

[0417] The protection circuit 806 is a circuit that enables conduction between the connected wiring and other wiring when a potential outside a certain range is supplied to the wiring connected to it.

[0418] As shown in Figure 20A, by providing protection circuits 806 to both the pixel section 802 and the driving circuit section 804, the display device's tolerance to overcurrent caused by ESD (Electro Static Discharge) and other factors can be improved. However, the structure of the protection circuit 806 is not limited to this. For example, a structure in which the scan line driving circuit 804a is connected to the protection circuit 806 or a structure in which the signal line driving circuit 804b is connected to the protection circuit 806 can also be used. Alternatively, a structure in which the terminal section 807 is connected to the protection circuit 806 can also be used.

[0419] Furthermore, although Figure 20A shows an example of a drive circuit section 804 formed by a scan line drive circuit 804a and a signal line drive circuit 804b, it is not limited to this. For example, only the scan line drive circuit 804a may be formed and a substrate with a separately prepared signal line drive circuit (e.g., a drive circuit substrate formed of a single crystal semiconductor film or a polycrystalline semiconductor film) may be mounted.

[0420] <Example of pixel circuit structure> The multiple pixel circuits 801 shown in Figure 20A can, for example, adopt the structure shown in Figure 20B.

[0421] The pixel circuit 801 shown in Figure 20B includes transistors 852 and 854, capacitor 862, and light-emitting element 872.

[0422] One of the source and drain electrodes of transistor 852 is electrically connected to the wiring (data line DL_n) of the supplied data signal. Furthermore, the gate electrode of transistor 852 is electrically connected to the wiring (scan line GL_m) of the supplied gate signal.

[0423] The transistor 852 has the function of controlling the writing of data signals.

[0424] One of the electrodes of capacitor 862 is electrically connected to the wiring supplied with the potential (hereinafter referred to as the potential supply line VL_a), and the other is electrically connected to the other of the source electrode and drain electrode of transistor 852.

[0425] Capacitor 862 functions as a storage capacitor for storing written data.

[0426] One of the source electrode and drain electrode of transistor 854 is electrically connected to the potential supply line VL_a. Furthermore, the gate electrode of transistor 854 is electrically connected to the other of the source electrode and drain electrode of transistor 852.

[0427] One of the anode and cathode of the light-emitting element 872 is electrically connected to the potential supply line VL_b, and the other is electrically connected to the other of the source electrode and drain electrode of the transistor 854.

[0428] As the light-emitting element 872, the light-emitting elements shown in Embodiments 1 to 3 can be used.

[0429] In addition, one of the potential supply lines VL_a and VL_b is given a high power supply potential VDD, and the other is given a low power supply potential VSS.

[0430] For example, in a display device having the pixel circuit 801 of FIG20B, the scan line drive circuit 804a shown in FIG20A sequentially selects the pixel circuits 801 of each row and turns on the transistor 852 to write data signal data.

[0431] When transistor 852 is turned off, the pixel circuit 801, on which data is written, remains in a held state. Furthermore, the amount of current flowing between the source and drain electrodes of transistor 854 is controlled according to the potential of the written data signal, and the light-emitting element 872 emits light with a brightness corresponding to the amount of current flowing through it. By performing the above steps line by line, an image can be displayed.

[0432] Furthermore, the pixel circuit can be equipped with the function of correcting for the effects of variations in the transistor's threshold voltage, etc. Figures 21A and 21B, and 22A and 22B show an example of a pixel circuit.

[0433] The pixel circuit shown in Figure 21A includes six transistors (transistors 303_1 to 303_6), a capacitor 304, and a light-emitting element 305. Furthermore, wirings 301_1 to 301_5, wiring 302_1, and wiring 302_2 are electrically connected to the pixel circuit shown in Figure 21A. Note that, for example, p-channel type transistors can be used as transistors 303_1 to 303_6.

[0434] The pixel circuit shown in Figure 21B is a structure that includes transistor 303_7 in addition to the pixel circuit shown in Figure 21A. Furthermore, wiring 301_6 and wiring 301_7 are electrically connected to the pixel circuit shown in Figure 21B. Here, wiring 301_5 and wiring 301_6 can be electrically connected to each other. Note that, for example, a p-channel type transistor can be used as transistor 303_7.

[0435] The pixel circuit shown in Figure 22A includes six transistors (transistors 308_1 to 308_6), a capacitor 304, and a light-emitting element 305. Furthermore, wirings 306_1 to 306_3 and wirings 307_1 to 307_3 are electrically connected to the pixel circuit shown in Figure 22A. Here, wirings 306_1 and 306_3 can be electrically connected to each other. Note that, for example, p-channel type transistors can be used as transistors 308_1 to 308_6.

[0436] The pixel circuit shown in Figure 22B includes two transistors (transistor 309_1 and transistor 309_2), two capacitors (capacitor 304_1 and capacitor 304_2), and a light-emitting element 305. Wiring 311_1 to 311_3, wiring 312_1, and wiring 312_2 are electrically connected to the pixel circuit shown in Figure 22B. Furthermore, by adopting the structure of the pixel circuit shown in Figure 22B, the pixel circuit can be driven, for example, using a voltage input-current drive method (also known as a CVCC method). Note that transistors 309_1 and 309_2 can, for example, be p-channel transistors.

[0437] Furthermore, the light-emitting element of one embodiment of the present invention can be applied to an active matrix method that includes active elements in the pixels of a display device or a passive matrix method that does not include active elements in the pixels of a display device.

[0438] In active matrix configurations, various active (nonlinear) elements can be used besides transistors. For example, MIM (Metal Insulator Metal) or TFD (Thin Film Diode) devices can be used. Because these elements require fewer fabrication processes, manufacturing costs can be reduced or yields improved. Furthermore, their small size allows for increased aperture ratios, enabling lower power consumption or higher brightness.

[0439] In addition to the active matrix method, a passive matrix type can also be used, which does not use active elements (non-linear elements). Because it does not use active elements (non-linear elements), fewer processes are required, thereby reducing manufacturing costs or improving yield. Furthermore, since it does not use active elements (non-linear elements), the aperture ratio can be increased, enabling lower power consumption or higher brightness.

[0440] The structure shown in this embodiment can be implemented by appropriately combining it with the structures shown in other embodiments.

[0441] Implementation Method 7 In this embodiment, a display device including a light-emitting element according to an embodiment of the present invention and an electronic device on which an input device is mounted will be described with reference to FIGS. 23A to 27.

[0442] <Instructions on the Touch Panel 1> Note that in this embodiment, a touch panel 2000 combining a display device and an input device will be described as an example of an electronic device. Additionally, a case using a touch sensor will be described as an example of an input device.

[0443] Figures 23A and 23B are perspective views of the touch panel 2000. Additionally, for clarity, typical components of the touch panel 2000 are shown in Figures 23A and 23B.

[0444] The touch panel 2000 includes a display device 2501 and a touch sensor 2595 (see Figure 23B). Furthermore, the touch panel 2000 includes a substrate 2510, a substrate 2570, and a substrate 2590. Additionally, substrates 2510, 2570, and 2590 are all flexible. Note that any one or all of substrates 2510, 2570, and 2590 may not be flexible.

[0445] The display device 2501 includes a plurality of pixels on a substrate 2510 and a plurality of wirings 2511 capable of supplying signals to the pixels. The plurality of wirings 2511 are guided on the outer periphery of the substrate 2510, and a portion thereof constitutes a terminal 2519. The terminal 2519 is electrically connected to an FPC 2509 (1). In addition, the plurality of wirings 2511 can supply signals from a signal line driving circuit 2503s (1) to the plurality of pixels.

[0446] The substrate 2590 includes a touch sensor 2595 and a plurality of wirings 2598 electrically connected to the touch sensor 2595. The plurality of wirings 2598 are guided on the outer periphery of the substrate 2590, and a portion thereof constitutes a terminal. Furthermore, the terminal is electrically connected to the FPC 2509 (2). In addition, for clarity, the electrodes and wiring of the touch sensor 2595 disposed on the back side of the substrate 2590 (the side opposite to the substrate 2510) are shown in solid lines in FIG23B.

[0447] As a touch sensor 2595, a capacitive touch sensor can be used, for example. Examples of capacitive touch sensors include surface capacitive and projected capacitive types.

[0448] As a projection-type capacitive sensor, it is mainly divided into self-capacitance type and mutual capacitance type, depending on the driving method. When using the mutual capacitance type, multiple points can be detected simultaneously, so it is the better option.

[0449] Note that the touch sensor 2595 shown in Figure 23B adopts the structure of a projected capacitive touch sensor.

[0450] In addition, the touch sensor 2595 can be used with various sensors that can detect the proximity or contact of objects such as fingers.

[0451] The projection-type capacitive touch sensor 2595 includes electrodes 2591 and 2592. Electrode 2591 is electrically connected to any one of a plurality of wirings 2598, while electrode 2592 is electrically connected to any other one of the plurality of wirings 2598.

[0452] As shown in Figures 23A and 23B, electrode 2592 has a shape in which multiple quadrilaterals arranged in one direction are connected to each other at the corners.

[0453] Electrode 2591 is quadrilateral and is repeatedly arranged in a direction that intersects the direction of extension of electrode 2592.

[0454] Wiring 2594 is electrically connected to two electrodes 2591 that sandwich electrode 2592. Ideally, the area of ​​the intersection between electrode 2592 and wiring 2594 should be as small as possible. This reduces the area of ​​regions without electrodes, thereby reducing transmittance deviation. Consequently, brightness deviation of light transmitted through touch sensor 2595 can be reduced.

[0455] Note that the shapes of electrodes 2591 and 2592 are not limited to this and can have various shapes. For example, a structure can also be adopted in which multiple electrodes 2591 are arranged with as few gaps as possible between them, and multiple electrodes 2592 are spaced apart by an insulating layer to form areas that do not overlap with the electrodes 2591. In this case, by setting virtual electrodes that are electrically insulated from these electrodes between two adjacent electrodes 2592, the area of ​​regions with different transmittance can be reduced, which is preferable.

[0456] <Explanation of the display device> Next, the details of the display device 2501 will be described with reference to FIG24A. FIG24A is a cross-sectional view along the portion shown by the dashed line X1-X2 in FIG23B.

[0457] The display device 2501 includes a plurality of pixels configured in a matrix. Each pixel includes a display element and pixel circuitry for driving the display element.

[0458] The following description illustrates an example of a display element that emits white light, but the display element is not limited to this. For example, it may also include light-emitting elements that emit different colors, so that adjacent pixels emit different colors.

[0459] For example, flexible materials with a water vapor permeability of 1×10⁻⁵ g·m⁻²·day⁻¹ or less, preferably 1×10⁻⁶ g·m⁻²·day⁻¹ or less, can be used as substrates 2510 and 2570. Alternatively, materials with substantially the same coefficient of thermal expansion can be used for substrates 2510 and 2570. For example, the coefficient of linear expansion is preferably 1×10⁻³ / K or less, more preferably 5×10⁻⁵ / K or less, and even more preferably 1×10⁻⁵ / K or less.

[0460] Note that substrate 2510 is a laminate, including an insulating layer 2510a to prevent impurities from diffusing into the light-emitting element, a flexible substrate 2510b, and an adhesive layer 2510c for bonding the insulating layer 2510a and the flexible substrate 2510b. Additionally, substrate 2570 is a laminate, including an insulating layer 2570a to prevent impurities from diffusing into the light-emitting element, a flexible substrate 2570b, and an adhesive layer 2570c for bonding the insulating layer 2570a and the flexible substrate 2570b.

[0461] Adhesive layers 2510c and 2570c can be made of, for example, polyester, polyolefin, polyamide (nylon, aramid, etc.), polyimide, polycarbonate, or acrylic, urethane, epoxy. Materials including resins with siloxane bonds can also be used.

[0462] Furthermore, a sealing layer 2560 is included between substrate 2510 and substrate 2570. The sealing layer 2560 preferably has a refractive index greater than that of air. Additionally, as shown in FIG24A, when light is extracted through the sealing layer 2560, the sealing layer 2560 can also serve as an optical bonding layer.

[0463] Additionally, a sealant can be formed on the outer periphery of the sealing layer 2560. Using this sealant, a light-emitting element 2550R can be disposed in the area surrounded by the substrate 2510, substrate 2570, sealing layer 2560, and sealant. Note that the sealing layer 2560 can be filled with an inert gas (nitrogen or argon, etc.). Furthermore, a desiccant can be placed within the inert gas to absorb moisture, etc. Alternatively, a resin such as an acrylic resin or an epoxy resin can be used as the filler. As the sealant, an epoxy resin or glass powder is preferred, for example. Furthermore, as the material used for the sealant, a material that does not allow moisture or oxygen to permeate is preferred.

[0464] Additionally, the display device 2501 includes a pixel 2502R. Furthermore, the pixel 2502R includes a light-emitting module 2580R.

[0465] Pixel 2502R includes a light-emitting element 2550R and a transistor 2502t that can supply power to the light-emitting element 2550R. Note that the transistor 2502t is used as part of the pixel circuit. In addition, the light-emitting module 2580R includes the light-emitting element 2550R and a color layer 2567R.

[0466] The light-emitting element 2550R includes a lower electrode, an upper electrode, and an EL layer between the lower electrode and the upper electrode. For example, the light-emitting elements shown in Embodiments 1 to 3 can be used as the light-emitting element 2550R.

[0467] Alternatively, a microcavity structure can be used between the lower and upper electrodes to enhance the intensity of light at a specific wavelength.

[0468] In addition, when the sealing layer 2560 is disposed on the light extraction side, the sealing layer 2560 contacts the light-emitting element 2550R and the color layer 2567R.

[0469] The color layer 2567R is located at the position overlapping with the light-emitting element 2550R. As a result, a portion of the light emitted by the light-emitting element 2550R passes through the color layer 2567R and is emitted to the outside of the light-emitting module 2580R in the direction indicated by the arrow in Figure 24A.

[0470] Furthermore, in the display device 2501, a light-shielding layer 2567BM is provided in the direction of light emission. The light-shielding layer 2567BM is provided in a manner that surrounds the color layer 2567R.

[0471] The color layer 2567R only needs to have the function of allowing light in a specific wavelength region to pass through. For example, a color filter that allows light in the red wavelength region to pass through, a color filter that allows light in the green wavelength region to pass through, a color filter that allows light in the blue wavelength region to pass through, and a color filter that allows light in the yellow wavelength region to pass through can be used. Each color filter can be formed by printing, inkjet printing, etching using photolithography, etc., and using various materials.

[0472] Furthermore, an insulating layer 2521 is provided in the display device 2501. The insulating layer 2521 covers the transistor 2502t. In addition, the insulating layer 2521 has the function of flattening the unevenness caused by the pixel circuit. Furthermore, the insulating layer 2521 can have the function of suppressing impurity diffusion. As a result, the reliability reduction of the transistor 2502t and the like due to impurity diffusion can be suppressed.

[0473] Furthermore, a light-emitting element 2550R is formed above the insulating layer 2521. Additionally, a partition wall 2528 is provided such that it overlaps with the end of the lower electrode included in the light-emitting element 2550R. Furthermore, spacers controlling the spacing between the substrate 2510 and the substrate 2570 can be formed on the partition wall 2528.

[0474] The scan line driving circuit 2503g(1) includes a transistor 2503t and a capacitor 2503c. Note that the driving circuit and the pixel circuit can be formed on the same substrate using the same process.

[0475] Additionally, a signal supply wiring 2511 is provided on the substrate 2510. Furthermore, a terminal 2519 is provided on the wiring 2511. The FPC 2509(1) is electrically connected to the terminal 2519. Furthermore, the FPC 2509(1) has the function of supplying video signals, clock signals, start signals, reset signals, etc. Additionally, a printed circuit board (PWB) can also be mounted on the FPC 2509(1).

[0476] Furthermore, transistors of various structures can be used in the display device 2501. Although a bottom-gate transistor is shown in FIG24A, it is not limited thereto; for example, a top-gate transistor as shown in FIG24B can be used in the display device 2501.

[0477] Furthermore, there are no particular restrictions on the polarity of transistors 2502t and 2503t. For example, an n-channel transistor and a p-channel transistor, or either an n-channel transistor or a p-channel transistor, can be used. Additionally, there are no particular restrictions on the crystallinity of the semiconductor film used for transistors 2502t and 2503t. For example, amorphous semiconductor films and crystalline semiconductor films can be used. Furthermore, as semiconductor materials, Group 14 semiconductors (e.g., silicon-containing semiconductors), compound semiconductors (including oxide semiconductors), organic semiconductors, etc., can be used. Using an oxide semiconductor with a bandgap of 2 eV or more, preferably 2.5 eV or more, and more preferably 3 eV or more, for any one or both of transistors 2502t and 2503t is preferable as it reduces the off-state current of the transistor. Examples of such oxide semiconductors include In-Ga oxide and In-M-Zn oxide (where M represents Al, Ga, Y, Zr, La, Ce, Sn, Hf, or Nd).

[0478] <Explanation of Touch Sensors> Next, the details of the touch sensor 2595 will be described with reference to FIG24C. FIG24C is a cross-sectional view along the portion shown by the dashed line X3-X4 in FIG23B.

[0479] The touch sensor 2595 includes: electrodes 2591 and 2592 arranged in an interleaved shape on a substrate 2590; an insulating layer 2593 covering the electrodes 2591 and 2592; and wiring 2594 that electrically connects adjacent electrodes 2591.

[0480] Electrodes 2591 and 2592 are formed using a transparent conductive material. As a transparent conductive material, conductive oxides such as indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, and zinc oxide with added gallium can be used. Alternatively, a graphene-containing film can be used. A graphene-containing film can be formed, for example, by reducing a film containing graphene oxide. Examples of reduction methods include heating.

[0481] For example, after a transparent conductive material is formed on a substrate 2590 by sputtering, the unwanted parts can be removed by various patterning techniques such as photolithography to form electrodes 2591 and 2592.

[0482] In addition, as materials used for the insulating layer 2593, in addition to resins such as acrylic resin, epoxy resin, and resins with siloxane bonds, inorganic insulating materials such as silicon oxide, silicon oxynitride, and aluminum oxide can also be used.

[0483] Furthermore, the opening reaching electrode 2591 is provided in insulating layer 2593, and wiring 2594 is electrically connected to adjacent electrode 2591. Since a light-transmitting conductive material can increase the aperture ratio of the touch panel, it can be used for wiring 2594. In addition, since a material with higher conductivity than electrode 2591 and electrode 2592 can reduce resistance, it can also be used for wiring 2594.

[0484] Electrodes 2592 extend in one direction, and multiple electrodes 2592 are arranged in a stripe pattern. In addition, wiring 2594 is arranged in a manner that intersects with the electrodes 2592.

[0485] A pair of electrodes 2591 are provided, clamped between an electrode 2592. Additionally, wiring 2594 electrically connects the pair of electrodes 2591.

[0486] In addition, the multiple electrodes 2591 do not necessarily have to be arranged in a direction orthogonal to one electrode 2592, and can also be arranged to form an angle greater than 0° and less than 90°.

[0487] Furthermore, a wiring 2598 is electrically connected to an electrode 2591 or an electrode 2592. Additionally, a portion of the wiring 2598 is used as a terminal. The wiring 2598 can be made of, for example, metallic materials such as aluminum, gold, platinum, silver, nickel, titanium, tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium, or alloys containing such metallic materials.

[0488] In addition, by providing an insulating layer covering the insulating layer 2593 and the wiring 2594, the touch sensor 2595 can be protected.

[0489] In addition, the connection layer 2599 is electrically connected to the wiring 2598 and the FPC 2509 (2).

[0490] As the connecting layer 2599, anisotropic conductive film (ACF) or anisotropic conductive paste (ACP) can be used.

[0491] <Instructions on the Touch Panel 2> Next, the details of the touch panel 2000 will be described with reference to FIG25A. FIG25A is a cross-sectional view along the portion shown by the dotted lines X5-X6 in FIG23A.

[0492] The touch panel 2000 shown in Figure 25A is a structure in which the display device 2501 illustrated in Figure 24A and the touch sensor 2595 illustrated in Figure 24C are bonded together.

[0493] In addition, the touch panel 2000 shown in Figure 25A includes an adhesive layer 2597 and an anti-reflective layer 2567p, in addition to the structures illustrated in Figures 24A and 24C.

[0494] The adhesive layer 2597 is provided in contact with the wiring 2594. Note that the adhesive layer 2597 attaches the substrate 2590 to the substrate 2570 such that the touch sensor 2595 overlaps the display device 2501. Furthermore, the adhesive layer 2597 is preferably transparent. Additionally, thermosetting resins or UV-curing resins can be used as the adhesive layer 2597. For example, acrylic resins, urethane resins, epoxy resins, or silicone resins can be used.

[0495] The anti-reflective layer 2567p is positioned overlapping the pixels. For example, a circular polarizing plate can be used as the anti-reflective layer 2567p.

[0496] Next, a touch panel with a structure different from that shown in FIG25A will be described with reference to FIG25B.

[0497] Figure 25B is a cross-sectional view of the touch panel 2001. The difference between the touch panel 2001 shown in Figure 25B and the touch panel 2000 shown in Figure 25A is the position of the touch sensor 2595 relative to the display device 2501. The different structures will be described in detail here, while the description of the touch panel 2000 will be used for parts that can use the same structure.

[0498] The color layer 2567R is located overlapping with the light-emitting element 2550R. Furthermore, the light-emitting element 2550R, as shown in FIG25B, emits light onto the side where the transistor 2502t is disposed. Thus, a portion of the light emitted by the light-emitting element 2550R passes through the color layer 2567R and is emitted to the outside of the light-emitting module 2580R in the direction indicated by the arrow in FIG25B.

[0499] In addition, a touch sensor 2595 is disposed on one side of the substrate 2510 of the display device 2501.

[0500] The adhesive layer 2597 is located between the substrate 2510 and the substrate 2590, and attaches the display device 2501 and the touch sensor 2595 together.

[0501] As shown in Figures 25A and 25B, light emitted from the light-emitting element can pass through one or both of substrates 2510 and 2570 before exiting.

[0502] <Explanation of the driving method for the touch panel> Next, an example of a driving method for a touch panel will be described with reference to Figures 26A and 26B.

[0503] Figure 26A is a block diagram showing the structure of a mutual capacitance touch sensor. In Figure 26A, a pulse voltage output circuit 2601 and a current detection circuit 2602 are shown. Additionally, in Figure 26A, six wirings from X1 to X6 represent electrodes 2621 to which a pulse voltage is applied, and six wirings from Y1 to Y6 represent electrodes 2622 to detect changes in current. Furthermore, Figure 26A shows a capacitor 2603 formed by overlapping electrodes 2621 and 2622. Note that the functions of electrodes 2621 and 2622 can be interchanged.

[0504] The pulse voltage output circuit 2601 is used to sequentially apply pulse voltages to the wiring from X1 to X6. By applying pulse voltages to the wiring from X1 to X6, an electric field is generated between electrodes 2621 and 2622 that form capacitor 2603. By utilizing the change in mutual capacitance of capacitor 2603 caused by shielding or other factors due to the electric field generated between the electrodes, the proximity or contact of the detected object can be detected.

[0505] The current detection circuit 2602 is used to detect the current change in the wiring from Y1 to Y6 caused by the change in mutual capacitance of capacitor 2603. In the wiring from Y1 to Y6, if there is no object approaching or contacting the circuit, the detected current value remains unchanged. However, when the mutual capacitance decreases due to the approach or contact of an object, a decrease in the current value is detected. Furthermore, the current can be detected using an integrating circuit or similar means.

[0506] Next, Figure 26B shows a timing diagram of the input / output waveforms in the mutual capacitance touch sensor shown in Figure 26A. In Figure 26B, the detection of the object in each row and column is performed during one frame. Additionally, Figure 26B shows two cases: no object detected (not touched) and object detected (touched). Furthermore, Figure 26B shows the waveforms of the voltage values ​​corresponding to the current values ​​detected by the wiring from Y1 to Y6.

[0507] A pulse voltage is sequentially applied to the wiring from X1 to X6, and the waveforms of the wiring from Y1 to Y6 change according to this pulse voltage. When no object is near or in contact with the device, the waveforms of Y1 to Y6 change according to the voltage changes of the wiring from X1 to X6. On the other hand, when an object is near or in contact with the device, the current value decreases, and therefore the waveform of the corresponding voltage value also changes.

[0508] Thus, by detecting changes in mutual capacitance, the proximity or contact of the object being tested can be detected.

[0509] <Explanation of the sensor circuit> Furthermore, although Figure 26A shows a passive matrix touch sensor structure with only capacitor 2603 provided at the intersection of the wiring, an active matrix touch sensor including transistors and capacitors can also be used as a touch sensor. Figure 27 shows an example of the sensor circuitry included in an active matrix touch sensor.

[0510] The sensor circuit shown in Figure 27 includes capacitor 2603, transistor 2611, transistor 2612 and transistor 2613.

[0511] A signal G2 is applied to the gate of transistor 2613, a voltage VRES is applied to one of its source and drain terminals, and the other is electrically connected to one electrode of capacitor 2603 and the gate of transistor 2611. One of the source and drain terminals of transistor 2611 is electrically connected to one of the source and drain terminals of transistor 2612, and a voltage VSS is applied to the other. A signal G1 is applied to the gate of transistor 2612, and the other of its source and drain terminals is electrically connected to wiring ML. A voltage VSS is applied to the other electrode of capacitor 2603.

[0512] Next, the operation of the sensor circuit shown in FIG27 will be explained. First, by applying a potential that turns on transistor 2613 as signal G2, a potential corresponding to voltage VRES is applied to node n connected to the gate of transistor 2611. Then, by applying a potential that turns off transistor 2613 as signal G2, the potential of node n is maintained.

[0513] Next, as the detected object, such as a finger, approaches or touches it, the mutual capacitance of capacitor 2603 changes, and the potential of node n changes with it due to VRES.

[0514] During readout, a potential is applied as signal G1 to turn on transistor 2612. The current flowing through transistor 2611, that is, the current flowing through wiring ML, changes according to the potential of node n. By detecting this current, the proximity or contact of the object being detected can be detected.

[0515] In transistors 2611, 2612, and 2613, it is preferable to use an oxide semiconductor layer as the semiconductor layer in which the channel region is formed. In particular, by using such a transistor in transistor 2613, the potential of node n can be maintained for a long period of time, thereby reducing the frequency of resupplying VRES to node n (renewal operation).

[0516] The structure shown in this embodiment can be implemented by appropriately combining it with the structures shown in other embodiments.

[0517] Implementation Method 8 In this embodiment, a display module and electronic device including a light-emitting element according to an embodiment of the present invention will be described with reference to FIGS. 28 to 31B.

[0518] <Explanation of the display module> The display module 8000 shown in Figure 28 includes a touch sensor 8004 connected to FPC 8003, a display device 8006 connected to FPC 8005, a frame 8009, a printed circuit board 8010, and a battery 8011 between the upper cover 8001 and the lower cover 8002.

[0519] For example, the light-emitting element of one embodiment of the present invention can be used in a display device 8006.

[0520] The upper cover 8001 and the lower cover 8002 can be appropriately changed in shape or size according to the size of the touch sensor 8004 and the display device 8006.

[0521] The touch sensor 8004 can be a resistive film touch sensor or a capacitive touch sensor, and can be formed to overlap with the display device 8006. Alternatively, the opposing substrate (sealed substrate) of the display device 8006 can also function as a touch sensor. Furthermore, an optical touch sensor can be formed by providing a light sensor within each pixel of the display device 8006.

[0522] In addition to protecting the display device 8006, the frame 8009 also serves as electromagnetic shielding to block electromagnetic waves generated by the operation of the printed circuit board 8010. Furthermore, the frame 8009 can also function as a heat sink.

[0523] The printed circuit board 8010 includes a power supply circuit and a signal processing circuit for outputting video signals and clock signals. The power supply to the power supply circuit can be either an external commercial power supply or a separately provided battery 8011. When using a commercial power supply, the battery 8011 can be omitted.

[0524] In addition, components such as polarizing plates, phase difference plates, and prisms can also be installed in the display module 8000.

[0525] <Explanation of Electronic Devices> Figures 29A to 29G illustrate electronic devices. These electronic devices may include a housing 9000, a display unit 9001, a speaker 9003, operation keys 9005 (including a power switch or operation switch), connection terminals 9006, a sensor 9007 (which has the function of measuring factors such as force, displacement, position, velocity, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, tilt, vibration, odor, or infrared radiation), a microphone 9008, etc. Furthermore, the sensor 9007 may have the function of measuring biometric information, such as a pulse sensor or a fingerprint sensor.

[0526] The electronic devices shown in Figures 29A to 29G can have various functions. For example, they can have the following functions: displaying various information (still images, moving images, text images, etc.) on a display unit; a touch sensor function; displaying a calendar, date, or time; control processing via various software programs; wireless communication; connecting to various computer networks via wireless communication; sending or receiving various data via wireless communication; reading programs or data stored in a storage medium and displaying them on the display unit; etc. Note that the electronic devices shown in Figures 29A to 29G are not limited to the functions mentioned above, but can have various functions. Furthermore, although not shown in Figures 29A to 29G, the electronic device may include multiple display units. In addition, a camera or similar device can be installed in the electronic device to give it the following functions: capturing still images; capturing moving images; storing the captured images in a storage medium (external storage medium or storage medium built into the camera); displaying the captured images on the display unit; etc.

[0527] The electronic devices shown in Figures 29A to 29G will now be described in detail.

[0528] Figure 29A is a perspective view showing a portable information terminal 9100. The display unit 9001 included in the portable information terminal 9100 is flexible. Therefore, the display unit 9001 can be assembled along the curved surface of the curved housing 9000. In addition, the display unit 9001 is equipped with a touch sensor, and can be operated by touching the screen with a finger or stylus. For example, by touching an icon displayed on the display unit 9001, an application can be launched.

[0529] Figure 29B is a perspective view showing a portable information terminal 9101. The portable information terminal 9101 has one or more functions, such as a telephone, an electronic notebook, and an information reading device. Specifically, it can be used as a smartphone. Note that the speaker 9003, connection terminal 9006, sensor 9007, etc., are not shown in the portable information terminal 9101, but can be located in the same positions as the portable information terminal 9100 shown in Figure 29A. Furthermore, the portable information terminal 9101 can display text or image information on multiple surfaces. For example, three operation buttons 9050 (also called operation icons or simply icons) can be displayed on one surface of the display unit 9001. Additionally, information 9051, represented by a dashed rectangle, can be displayed on another surface of the display unit 9001. Furthermore, as an example of information 9051, it could display notifications of received messages from emails, SNS (Social Networking Services), or phone calls; the subject of the email or SNS message; the sender's name; the date; the time; battery level; and the antenna reception strength. Alternatively, an operation button 9050 could be displayed instead of information 9051 in the same location.

[0530] Figure 29C is a perspective view showing a portable information terminal 9102. The portable information terminal 9102 has the function of displaying information on three or more surfaces of the display unit 9001. Here, examples are shown where information 9052, information 9053, and information 9054 are displayed on different surfaces. For example, the user of the portable information terminal 9102 can check its display (in this case, information 9053) while the portable information terminal 9102 is placed in an upper pocket. Specifically, the phone number or name of the caller is displayed in a position that allows this information to be viewed from above the portable information terminal 9102. The user can check this display without taking the portable information terminal 9102 out of their pocket, thereby determining whether to answer the call.

[0531] Figure 29D is a perspective view showing a watch-type portable information terminal 9200. The portable information terminal 9200 can run various applications such as mobile phone calls, email, article reading and editing, music playback, internet communication, and computer games. Furthermore, the display surface of the display unit 9001 is curved, allowing display on the curved surface. Additionally, the portable information terminal 9200 can perform short-range wireless communication according to communication standards. For example, hands-free calling can be performed by communicating with a headset capable of wireless communication. Furthermore, the portable information terminal 9200 includes a connection terminal 9006, which allows direct data exchange with other information terminals via a connector. Charging can also be performed via the connection terminal 9006. Moreover, charging can also be performed wirelessly without using the connection terminal 9006.

[0532] Figures 29E to 29G are perspective views showing the foldable portable information terminal 9201. Figure 29E is a perspective view of the portable information terminal 9201 in its unfolded state, Figure 29F is a perspective view of the portable information terminal 9201 in a state transitioning between the unfolded and folded states, and Figure 29G is a perspective view of the portable information terminal 9201 in its folded state. The portable information terminal 9201 offers good portability in its folded state and excellent visibility in its unfolded state due to its large, seamlessly integrated display area. The display unit 9001 included in the portable information terminal 9201 is supported by three housings 9000 connected by hinges 9055. By bending two housings 9000 together using the hinges 9055, the portable information terminal 9201 can reversibly change from its unfolded state to its folded state. For example, the portable information terminal 9201 can be bent with a radius of curvature of more than 1 mm and less than 150 mm.

[0533] Examples of electronic devices include: television sets (also known as televisions or television receivers); monitors for computers, etc.; digital cameras; digital video cameras; digital photo frames; mobile phones (also known as mobile phones or mobile phone devices); goggle-type display devices (wearable display devices); portable game consoles; portable information terminals; audio playback devices; pinball machines and other large game machines, etc.

[0534] Figure 30A shows an example of a television set. In the television set 9300, the display unit 9001 is assembled in the housing 9000. The structure in which the housing 9000 is supported by the bracket 9301 is shown here.

[0535] The television 9300 shown in FIG30A can be operated using the operation switch provided in the casing 9000 and the separately provided remote control 9311. Alternatively, a touch sensor can be provided in the display unit 9001, allowing operation of the display unit 9001 by touching it with a finger or similar object. The remote control 9311 can also have a display unit that displays data output from the remote control 9311. Channel and volume can be adjusted using the operation keys or touch panel provided in the remote control 9311, and the images displayed on the display unit 9001 can also be manipulated.

[0536] Furthermore, the 9300 television set employs a structure that includes a receiver and a modem. It can receive general television broadcasts using the receiver. Moreover, the modem connects the television set to a wired or wireless communication network, enabling one-way (from sender to receiver) or two-way (between sender and receiver, or between receivers, etc.) data communication.

[0537] Furthermore, since the electronic device or lighting equipment of one embodiment of the present invention is flexible, it can also be assembled along the curved surfaces of the inner or outer walls of houses and high-rise buildings, or the interior or exterior decoration of automobiles.

[0538] Figure 30B shows the exterior of a car 9700. Figure 30C shows the driver's seat of the car 9700. The car 9700 includes a body 9701, wheels 9702, an instrument panel 9703, lights 9704, etc. A display device or light-emitting device according to one embodiment of the present invention can be used in the display section of the car 9700. For example, a display device or light-emitting device according to one embodiment of the present invention can be provided in display sections 9710 to 9715 shown in Figure 30C.

[0539] Display units 9710 and 9711 are display devices installed on the windshield of an automobile. By using a conductive material with light transmittance to manufacture the electrodes in the display device or light-emitting device, the display device or light-emitting device of one embodiment of the present invention can become a so-called transparent display device or input / output device that allows the view to be seen from the other side. The display units 9710 and 9711 of the transparent display device will not obstruct the view even when driving the automobile 9700. Therefore, the display device or light-emitting device of one embodiment of the present invention can be installed on the windshield of the automobile 9700. In addition, when a transistor or the like is provided in the display device or light-emitting device to drive the display device or input / output device, it is preferable to use a transparent transistor such as an organic transistor using an organic semiconductor material or an oxide semiconductor transistor.

[0540] Display unit 9712 is a display device installed on the pillar section. For example, by displaying images from an imaging unit installed on the vehicle body on display unit 9712, the field of vision obstructed by the pillar can be supplemented. Display unit 9713 is a display device installed on the dashboard section. For example, by displaying images from an imaging unit installed on the vehicle body on display unit 9713, the field of vision obstructed by the dashboard can be supplemented. In other words, by displaying images from imaging units installed on the exterior of the vehicle, blind spots can be filled, thereby improving safety. In addition, by displaying images that supplement areas that cannot be seen, safety can be confirmed more naturally and comfortably.

[0541] Figure 30D shows a car interior with a long bench serving as both the driver's and passenger's seats. Display unit 9721 is a display device installed in the door section. For example, by displaying images from an imaging unit installed in the vehicle body on display unit 9721, the view obstructed by the door can be supplemented. Display unit 9722 is a display device installed on the steering wheel. Display unit 9723 is a display device installed in the center of the long bench. Furthermore, by installing the display device on the seat surface or backrest, it can also be used as a seat heater with the display device as its heat source.

[0542] Display units 9714, 9715, or 9722 can provide navigation information, speedometer, tachometer, driving distance, fuel level, gear position, air conditioning settings, and various other information. Furthermore, the user can appropriately change the displayed content and layout. Display units 9710 to 9713, 9721, and 9723 can also display the aforementioned information. Display units 9710 to 9715, 9721 to 9723 can also be used as lighting equipment. Additionally, display units 9710 to 9715, 9721 to 9723 can also be used as heating devices.

[0543] An electronic device according to one embodiment of the present invention may include a secondary battery, preferably charged by contactless power transmission.

[0544] Examples of secondary batteries include lithium-ion secondary batteries (lithium-ion polymer batteries) that use gel electrolytes, lithium-ion batteries, nickel-metal hydride batteries, nickel-cadmium batteries, organic free radical batteries, lead-acid batteries, air secondary batteries, nickel-zinc batteries, and silver-zinc batteries.

[0545] An electronic device according to one embodiment of the present invention may also include an antenna. By receiving signals through the antenna, images or information can be displayed on the display unit. Furthermore, when the electronic device includes a secondary battery, the antenna can be used for contactless power transmission.

[0546] The display device 9500 shown in Figures 31A and 31B includes multiple display panels 9501, a shaft portion 9511, and a bearing portion 9512. Each of the multiple display panels 9501 includes a display area 9502 and a light-transmitting area 9503.

[0547] Multiple display panels 9501 are flexible. Adjacent display panels 9501 are arranged with a portion overlapping each other. For example, the light-transmitting areas 9503 of two adjacent display panels 9501 can overlap. By using multiple display panels 9501, a large-screen display device can be realized. Furthermore, the display panels 9501 can be rolled up depending on the application, thus enabling a highly versatile display device.

[0548] Figures 31A and 31B show the case where the display areas 9502 of adjacent display panels 9501 are separated from each other, but are not limited to this. For example, a continuous display area 9502 can also be achieved by overlapping the display areas 9502 of adjacent display panels 9501 without gaps.

[0549] The electronic device shown in this embodiment is characterized by including a display section for displaying certain information. Note that the light-emitting element of one embodiment of the present invention can also be applied to an electronic device that does not include a display section. Furthermore, although this embodiment shows a structure in which the display section of the electronic device is flexible and can display on a curved display surface, or a structure that allows the display section to be folded, it is not limited to this; a structure that is not flexible and displays on a flat surface can also be used.

[0550] The structure shown in this embodiment can be used in appropriate combinations with the structures shown in other embodiments.

[0551] Implementation Method 9 In this embodiment, a light-emitting device including a light-emitting element according to one embodiment of the present invention will be described with reference to FIGS. 32A to 32C and FIGS. 33A to 33D.

[0552] Figure 32A is a perspective view of the light-emitting device 3000 shown in this embodiment, and Figure 32B is a cross-sectional view taken along the dashed line EF shown in Figure 32A. Note that in Figure 32A, a portion of the component is indicated by a dashed line to avoid clutter.

[0553] The light-emitting device 3000 shown in Figures 32A and 32B includes a substrate 3001, a light-emitting element 3005 on the substrate 3001, a first sealing region 3007 disposed on the outer periphery of the light-emitting element 3005, and a second sealing region 3009 disposed on the outer periphery of the first sealing region 3007.

[0554] Furthermore, light emitted from the light-emitting element 3005 is emitted from either or both of the substrates 3001 and 3003. Figures 32A and 32B illustrate the structure in which light emitted from the light-emitting element 3005 is emitted to the lower side (the side of the substrate 3001).

[0555] Furthermore, as shown in Figures 32A and 32B, the light-emitting device 3000 has a double-sealed structure in which the light-emitting element 3005 is arranged in a manner surrounded by a first sealing region 3007 and a second sealing region 3009. By employing a double-sealed structure, impurities (e.g., water, oxygen, etc.) that may intrude into the light-emitting element 3005 from the outside can be appropriately suppressed. However, it is not necessarily required to provide both the first sealing region 3007 and the second sealing region 3009. For example, only the first sealing region 3007 may be provided.

[0556] Note that in Figure 32B, the first sealing region 3007 and the second sealing region 3009 are arranged in contact with the substrates 3001 and 3003. However, this is not a limitation; for example, one or both of the first sealing region 3007 and the second sealing region 3009 may be arranged in contact with an insulating film or conductive film formed on the upper surface of the substrate 3001. Alternatively, one or both of the first sealing region 3007 and the second sealing region 3009 may be arranged in contact with an insulating film or conductive film formed on the lower surface of the substrate 3003.

[0557] The substrates 3001 and 3003 can be constructed using the same structures as those of substrates 200 and 220 described in Embodiment 3. Similarly, the light-emitting element 3005 can be constructed using the same structure as those described in the embodiment.

[0558] The first sealing region 3007 can be formed using a glass-containing material (e.g., glass powder, glass tape, etc.). The second sealing region 3009 can be formed using a resin-containing material. Using a glass-containing material in the first sealing region 3007 improves productivity and sealing performance. Furthermore, using a resin-containing material in the second sealing region 3009 improves impact resistance and heat resistance. However, the materials used for the first sealing region 3007 and the second sealing region 3009 are not limited to these; the first sealing region 3007 can be formed using a resin-containing material, while the second sealing region 3009 can be formed using a glass-containing material.

[0559] In addition, examples of the aforementioned glass powder include magnesium oxide, calcium oxide, strontium oxide, barium oxide, cesium oxide, sodium oxide, potassium oxide, boron oxide, vanadium oxide, zinc oxide, tellurium oxide, aluminum oxide, silicon dioxide, lead oxide, tin oxide, phosphorus oxide, ruthenium oxide, rhodium oxide, iron oxide, copper oxide, manganese dioxide, molybdenum oxide, niobium oxide, titanium oxide, tungsten oxide, bismuth oxide, zirconium oxide, lithium oxide, antimony oxide, lead borate glass, tin phosphate glass, vanadate glass, or borosilicate glass. For the purpose of absorbing infrared light, the glass powder preferably contains one or more transition metals.

[0560] Furthermore, as the aforementioned glass powder, for example, a glass powder slurry is coated onto a substrate and then heated or irradiated with a laser. The glass powder slurry comprises the aforementioned glass powder and a resin (also called a binder) diluted with an organic solvent. Note that a glass powder slurry containing an absorber that absorbs the wavelength of the laser beam can also be used. Furthermore, as the laser, an Nd:YAG laser or a semiconductor laser is preferably used, for example. Additionally, the laser irradiation shape can be either circular or rectangular.

[0561] Furthermore, as the aforementioned resin-containing materials, for example, polyester, polyolefin, polyamide (nylon, aromatic polyamide, etc.), polyimide, polycarbonate, or acrylic, urethane, and epoxy resins can be used. Materials comprising resins having siloxane bonds can also be used.

[0562] Note that when either or both of the first sealing region 3007 and the second sealing region 3009 use a glass-containing material, the thermal expansion coefficient of the glass-containing material is preferably close to that of the substrate 3001. By adopting the above structure, cracks in the glass-containing material or the substrate 3001 due to thermal stress can be suppressed.

[0563] For example, when a glass-containing material is used in the first sealing region 3007 and a resin-containing material is used in the second sealing region 3009, the following excellent effects are achieved.

[0564] The second sealing region 3009 is positioned closer to the outer periphery of the light-emitting device 3000 than the first sealing region 3007. In the light-emitting device 3000, the closer to the outer periphery, the greater the strain caused by external forces, etc. Therefore, by using a resin-containing material to seal the outer periphery of the light-emitting device 3000, which generates greater strain—that is, the second sealing region 3009—and by using a glass-containing material to seal the first sealing region 3007 located inside the second sealing region 3009, the light-emitting device 3000 is less likely to be damaged even if strain caused by external forces, etc.

[0565] Additionally, as shown in FIG32B, a first region 3011 is formed in the region surrounded by substrate 3001, substrate 3003, first sealing region 3007 and second sealing region 3009. Furthermore, a second region 3013 is formed in the region surrounded by substrate 3001, substrate 3003, light-emitting element 3005 and first sealing region 3007.

[0566] The first region 3011 and the second region 3013 are preferably filled with an inert gas such as a rare gas or nitrogen. Alternatively, they can be filled with resins such as acrylic resins or epoxy resins. Note that the first region 3011 and the second region 3013 are preferably in a depressurized state compared to an atmospheric pressure state.

[0567] Additionally, Figure 32C shows a modified example of the structure shown in Figure 32B. Figure 32C is a cross-sectional view showing a modified example of the light-emitting device 3000.

[0568] In the structure shown in Figure 32C, a portion of the substrate 3003 is provided with a recess, and a desiccant 3018 is disposed in the recess. The other structures are the same as those shown in Figure 32B.

[0569] As a desiccant 3018, substances that adsorb moisture by chemical adsorption or by physical adsorption can be used. Examples of substances that can be used as desiccant 3018 include oxides of alkali metals, oxides of alkaline earth metals (such as calcium oxide or barium oxide), sulfates, metal halides, perchlorates, zeolites, or silica gel.

[0570] Next, a modified example of the light-emitting device 3000 shown in FIG32B will be described with reference to FIGS. 33A to 33D. Note that FIGS. 33A to 33D are cross-sectional views illustrating the modified example of the light-emitting device 3000 shown in FIG32B.

[0571] In the light-emitting devices shown in Figures 33A to 33D, the second sealing region 3009 is not provided, but only the first sealing region 3007 is provided. Furthermore, in the light-emitting devices shown in Figures 33A to 33D, region 3014 replaces the second region 3013 shown in Figure 32B.

[0572] For example, polyester, polyolefin, polyamide (nylon, aromatic polyamide, etc.), polyimide, polycarbonate, or acrylic, urethane, epoxy can be used in region 3014. Additionally, materials including resins with siloxane bonds can also be used.

[0573] By using the aforementioned material in region 3014, a so-called solid-sealed light-emitting device can be realized.

[0574] In addition, in the light-emitting device shown in FIG33B, a substrate 3015 is provided on one side of the substrate 3001 of the light-emitting device shown in FIG33A.

[0575] As shown in Figure 33B, the substrate 3015 has an uneven surface. By providing the uneven substrate 3015 on the light extraction side of the light-emitting element 3005, the light extraction efficiency from the light-emitting element 3005 can be improved. Note that a substrate used as a diffuser can be provided instead of the uneven structure shown in Figure 33B.

[0576] Furthermore, the light-emitting device shown in FIG33A has a structure that extracts light from the substrate 3001 side, while the light-emitting device shown in FIG33C has a structure that extracts light from the substrate 3003 side.

[0577] The light-emitting device shown in Figure 33C includes a substrate 3015 on one side of the substrate 3003. The other structures are the same as those of the light-emitting device shown in Figure 33B.

[0578] In addition, in the light-emitting device shown in FIG33D, the substrates 3003 and 3015 of the light-emitting device shown in FIG33C are not provided, but only the substrate 3016 is provided.

[0579] The substrate 3016 includes a first unevenness located on the side closer to the light-emitting element 3005 and a second unevenness located on the side farther from the light-emitting element 3005. By adopting the structure shown in FIG33D, the light extraction efficiency of light from the light-emitting element 3005 can be further improved.

[0580] Therefore, by using the structure shown in this embodiment, a light-emitting device can be realized that suppresses the deterioration of the light-emitting element due to impurities such as moisture or oxygen. Alternatively, by using the structure shown in this embodiment, a light-emitting device with h...

Claims

1. A host material for a light-emitting layer, comprising: A first organic compound and a second organic compound, wherein the first organic compound has the function of exhibiting thermally activated delayed fluorescence at room temperature; The first organic compound and the second organic compound are a combination that forms an excited-state complex; wherein the first organic compound has a π-electron-rich heteroaromatic skeleton and a π-electron-deficient heteroaromatic skeleton; The π-electron-rich heteroaromatic skeleton is directly bonded to the π-electron-deficient heteroaromatic skeleton; and the second organic compound has a carbazole skeleton.

2. A host material for a light-emitting layer, comprising: A first organic compound and a second organic compound, wherein the difference between the lowest singlet excitation energy level and the lowest triplet excitation energy level of the first organic compound is greater than 0 eV and less than 0.2 eV; wherein the first organic compound and the second organic compound are a combination that forms an excited-state complex; wherein the first organic compound has a π-electron-rich heteroaromatic skeleton and a π-electron-deficient heteroaromatic skeleton. The π-electron-rich heteroaromatic skeleton is directly bonded to the π-electron-deficient heteroaromatic skeleton; and the second organic compound has a carbazole skeleton.

3. A host material for a light-emitting layer, comprising: A first organic compound and a second organic compound, wherein the first organic compound is a material that can generate a minimum singlet excited state from a minimum triplet excited state by antisystem crossing; wherein the first organic compound and the second organic compound are a combination that forms an excited state complex; wherein the first organic compound has a π-electron-rich heteroaromatic skeleton and a π-electron-deficient heteroaromatic skeleton. The π-electron-rich heteroaromatic skeleton is directly bonded to the π-electron-deficient heteroaromatic skeleton; and the second organic compound has a carbazole skeleton.

4. The main material for the light-emitting layer according to any one of claims 1 to 3, wherein the main material for the light-emitting layer is used in a fluorescent light-emitting layer.

5. The main material for the light-emitting layer according to any one of claims 1 to 3, wherein the main material for the light-emitting layer is used in a phosphorescent light-emitting layer.

6. A light-emitting element comprising a light-emitting layer between a pair of electrodes, wherein the light-emitting layer has a phosphorescent material, a first organic compound, and a second organic compound; wherein the first organic compound has the function of exhibiting thermally activated delayed fluorescence at room temperature; wherein the first organic compound and the second organic compound are a combination forming an excited-state complex; wherein the first organic compound has a π-electron-rich heteroaromatic skeleton and a π-electron-deficient heteroaromatic skeleton; wherein the π-electron-rich heteroaromatic skeleton and the π-electron-deficient heteroaromatic skeleton are directly bonded; and wherein the second organic compound has a carbazole skeleton.

7. A light-emitting element comprising a light-emitting layer between a pair of electrodes, wherein the light-emitting layer has a phosphorescent material, a first organic compound, and a second organic compound; wherein the difference between the lowest singlet excitation energy level and the lowest triplet excitation energy level of the first organic compound is greater than 0 eV and less than 0.2 eV; wherein the first organic compound and the second organic compound are a combination forming an excited-state complex; wherein the first organic compound has a π-electron-rich heteroaromatic skeleton and a π-electron-deficient heteroaromatic skeleton; wherein the π-electron-rich heteroaromatic skeleton and the π-electron-deficient heteroaromatic skeleton are directly bonded; and wherein the second organic compound has a carbazole skeleton.

8. A light-emitting element comprising a light-emitting layer between a pair of electrodes, wherein the light-emitting layer has a phosphorescent material, a first organic compound, and a second organic compound; wherein the first organic compound is a material capable of generating a minimum singlet excited state from a minimum triplet excited state via antisystem crossing; wherein the first organic compound and the second organic compound are a combination forming an excited-state complex; wherein the first organic compound has a π-electron-rich heteroaromatic framework and a π-electron-deficient heteroaromatic framework; wherein the π-electron-rich heteroaromatic framework and the π-electron-deficient heteroaromatic framework are directly bonded; and wherein the second organic compound has a carbazole framework.

9. The light-emitting element according to any one of claims 6 to 8, wherein the phosphorescent material is a rhodium complex or a platinum complex.

10. A light-emitting device comprising a light-emitting element according to any one of claims 6 to 8.

11. A lighting device comprising a light-emitting element according to any one of claims 6 to 8.

12. An electronic device comprising a light-emitting element according to any one of claims 6 to 8.

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