Light-emitting element

Abstract

Light-emitting element comprising: a cathode, a plurality of light-emitting layers and an anode, in the order given; wherein the plurality of light-emitting layers comprises a first light-emitting layer on the cathode side, a second light-emitting layer remote from the first light-emitting layer, and a third light-emitting layer in contact with the second light-emitting layer in the order given; wherein the first light-emitting layer comprises a fluorescent substance and a host material; wherein one of the second or third light-emitting layers comprises: a first substance configured to convert triplet excitation energy into light emission, a first organic compound, and a second organic compound; wherein the first organic compound and the second organic compound are configured to form an exciplex; wherein the difference between the energy values ​​of a peak wavelength of the emission spectrum of the exciplex and a peak wavelength in the lowest energy absorption band of the first substance is 0.2 eV or less; wherein the other of the second or third light-emitting layers comprises a second substance configured to convert triplet excitation energy into light emission; wherein the emission spectrum of the first substance differs from the emission spectrum of the second substance; wherein a third organic compound and a fourth organic compound are contained between the first light-emitting layer and the second light-emitting layer; and wherein a triplet excitation level of the host material is lower than a triplet excitation level of the third organic compound and a triplet excitation level of the fourth organic compound.

Description

Technical area

[0001] The present invention relates to a light-emitting element containing an organic compound as a light-emitting substance. State of the art

[0002] In recent years, intensive research and development has been carried out on a light-emitting element (an organic EL element) that uses an organic compound and utilizes electroluminescence (EL). The basic structure of such a light-emitting element consists of an organic compound layer containing a light-emitting substance (an EL layer) sandwiched between a pair of electrodes. By applying a voltage to the element, light can be emitted from the light-emitting substance.

[0003] The light-emitting element is a self-luminous element and therefore has the advantages of higher pixel visibility than that of a liquid crystal display and the absence of a backlight. It is believed to be suitable for a flat panel display. Another major advantage is that a display incorporating the light-emitting element can be manufactured as a thin and lightweight display and has a very fast response time.

[0004] The light-emitting element can provide planar light emission. This feature is difficult to achieve with point light sources, such as incandescent lamps and LEDs, or linear light sources, such as fluorescent lamps. Therefore, the light-emitting element has great potential as a light source applicable to lighting devices and the like.

[0005] In such an organic EL element, electrons from a cathode and holes from an anode are injected into an EL layer. Through recombination of the injected electrons and holes, the organic compound with light-emitting properties is excited and provides light emission.

[0006] The excited state of an organic compound can be a singlet excited state or a triplet excited state. Light emission from the singlet excited state (S*) is called fluorescence, and light emission from the triplet excited state (T*) is called phosphorescence. It is assumed that the statistical generation ratio of the excited states in the light-emitting element is S*:T* = 1:3.

[0007] For a compound that emits light from the singlet excited state (hereinafter referred to as a fluorescent substance), phosphorescence is generally not observed at room temperature, while only fluorescence is observed. Therefore, the internal quantum yield (the ratio of generated photons to injected carriers) of a light-emitting element using a fluorescent substance is believed to have a theoretical limit of 25%, based on a 1:3 ratio of S* to T*.

[0008] In contrast, in a compound that emits light from the triplet excited state (hereinafter referred to as a phosphorescent compound), phosphorescence can be observed at normal temperature. Since intersystem crossing (a transfer of excitation energy from the singlet excited state to the triplet excited state) easily occurs in a phosphorescent compound, the internal quantum efficiency can theoretically be increased to 100%. This means that a light-emitting element using a phosphorescent substance can have higher emission efficiency than one using a fluorescent substance. As a result, light-emitting elements using phosphorescent compounds are currently being actively developed to obtain highly efficient light-emitting elements.

[0009] A white light-emitting element disclosed in Patent Document 1 includes a light-emitting region containing multiple types of light-emitting dopants that emit phosphorescence. An element disclosed in Patent Document 2 includes an intermediate layer (a charge generation layer) between a fluorescent layer and a phosphorescent layer (i.e., the element is a so-called tandem element). Further examples of light-emitting elements having multiple light-emitting dopants are disclosed in Patent Documents 2 to 4. [Reference] Patent Document 1: Japanese translation JP 2004 - 522 276 A of PCT international application WO 2002 / 091 814 A2 Patent Document 2: Japanese Patent Laid-Open Publication JP 2006-120689 A Patent document 3: WO 2012 / 111579 A9 Patent document 4: US 2013 / 0240851 A1 Disclosure of the invention

[0010] As a multicolor light-emitting element, such as a typical white light-emitting element, an element including a fluorescent layer (a layer that emits light with a short wavelength), a phosphorescent layer (a layer that emits light with a long wavelength), and an intermediate layer (a charge generation layer) between the fluorescent layer and the phosphorescent layer has been developed and partially put into practice, as shown in Patent Document 2. This element has a structure in which two light-emitting elements are connected in series with the intermediate layer between them.

[0011] In this structure, fluorescence is used as the short-wavelength light, which has a lifetime issue, and phosphorescence is used as the long-wavelength light. With this structure, a multicolor light-emitting element with stable properties can be achieved, although its emission efficiency is lower than that of an element using phosphorescence as the long-wavelength light and short-wavelength light.

[0012] The multi-color light-emitting element having the above-described structure has high reliability and is suitable for practical use; on the other hand, a larger number of films must be formed for the sake of a single light-emitting element, which prevents the light-emitting element from being put into practice.

[0013] There are several reasons for providing the intermediate layer between the phosphorescent layer and the fluorescent layer in a multicolor element. One of the reasons is to prevent the quenching of the phosphorescence caused by the fluorescent layer.

[0014] In the fluorescent layer, a substance with a condensed aromatic ring structure (especially a condensed aromatic hydrocarbon ring structure), such as anthracene, is often used as the host material. This is because when the substance with a condensed aromatic ring structure is used as the host material of the fluorescent layer, a light-emitting element with advantageous properties can always be obtained; on the other hand, a substance with a condensed aromatic ring structure generally has a disadvantage, namely a low triplet level. Accordingly, in the case where the fluorescent layer is formed in contact with a phosphorescent layer, the triplet excitation energy generated in the phosphorescent layer is transferred to the triplet level of the host material in the fluorescent layer and quenched.Because a triplet exciton has a long lifetime, the diffusion length of the exciton is long, and the excitation energy generated in the phosphorescent layer and the excitation energy generated at the interface between the fluorescent layer and the phosphorescent layer are quenched by the host material in the fluorescent layer. Therefore, a significant reduction in emission efficiency occurs.

[0015] The problems described above are solved by using a host material with high triplet excitation energy for the fluorescent layer. However, in this case, the singlet excitation energy of the host material is higher than the triplet excitation energy, so the energy difference between the singlet excitation energy of the host material and the singlet excitation energy of a fluorescent dopant becomes too large, and therefore energy is not sufficiently transferred from the host material to the fluorescent dopant. This results in insufficient emission efficiency in the fluorescent layer. As a result, non-radiative decay of the host material is accelerated, so that the properties (especially the lifetime) of the device deteriorate in some cases. When the singlet excitation energy of the host material is higher, the HOMO-LUMO gap of the host material is inevitably large, which leads to an increase in the operating voltage.

[0016] In view of the above, an object of one embodiment of the present invention is to provide a novel light-emitting element. Another object of one embodiment of the present invention is to provide a multicolor light-emitting element that utilizes fluorescence and phosphorescence and is suitable for practical use. Another object of one embodiment of the present invention is to provide a multicolor light-emitting element that utilizes fluorescence and phosphorescence, has a small number of manufacturing steps due to a relatively small number of layers to be formed, and is suitable for practical use.

[0017] Another object of an embodiment of the present invention is to provide a multicolor light-emitting element that utilizes fluorescence and phosphorescence and has high emission efficiency.

[0018] Another object of one embodiment of the present invention is to provide a multicolor light-emitting element that utilizes fluorescence and phosphorescence, has a relatively small number of layers to be formed, is practical, and has high emission efficiency. Another object of one embodiment of the present invention is to provide a novel light-emitting element.

[0019] Another object of an embodiment of the present invention is to provide a display module, a lighting module, a light-emitting device, a display device, an electronic device, and a lighting device that can be manufactured at low cost by using the light-emitting element.

[0020] Another object of an embodiment of the present invention is to provide a display module, a lighting module, a light-emitting device, a display device, an electronic device, and a lighting device having reduced power consumption by using the light-emitting element.

[0021] It is only necessary that the present invention achieves at least one of the objects described above.

[0022] The objects described above can be achieved by a light-emitting element having the features of the patent claims.

[0023] One embodiment of the present invention is a light-emitting element including a pair of electrodes and an EL layer disposed between the pair of electrodes. The EL layer comprises at least a first light-emitting layer, a second light-emitting layer, and a separation layer disposed between the first and second light-emitting layers. The emission spectrum of the first light-emitting layer is located in a shorter wavelength range than the emission spectrum of the second light-emitting layer. The first light-emitting layer contains at least one fluorescent substance and a host material. The second light-emitting layer contains at least one substance capable of converting triplet excitation energy into light emission, a first organic compound, and a second organic compound. The first organic compound and the second organic compound form an exciplex.

[0024] Another embodiment of the present invention is a light-emitting element having the above-described structure, in which the separation layer contains a substance having a hole transport property and a substance having an electron transport property.

[0025] Another embodiment of the present invention is a light-emitting element having the above-described structure in which the substance having a hole transport property and the substance having an electron transport property form a second exciplex.

[0026] Another embodiment of the present invention is a light-emitting element having the above-described structure, in which the thickness of the separation layer is greater than 0 nm and less than or equal to 20 nm.

[0027] Another embodiment of the present invention is a light-emitting element having the above-described structure, in which the thickness of the separation layer is greater than or equal to 1 nm and less than or equal to 10 nm.

[0028] Another embodiment of the present invention is a light-emitting element having the above-described structure, in which a combination of the substance having a hole transport property and the substance having an electron transport property is the same as a combination of the first organic compound and the second organic compound.

[0029] Another embodiment of the present invention is a light-emitting element having the above-described structure in which energy is transferred from the first exciplex to the substance capable of converting the triplet excitation energy into light emission.

[0030] Another embodiment of the present invention is a light-emitting element having the above-described structure in which the singlet excitation level of the host material is higher than the singlet excitation level of the fluorescent substance and the triplet excitation level of the host material is lower than the triplet excitation level of the fluorescent substance.

[0031] Another embodiment of the present invention is a light-emitting element having the above-described structure, in which the triplet excitation level of the host material is lower than the triplet excitation level of the substance having a hole transport property and the triplet excitation level of the substance having an electron transport property.

[0032] Another embodiment of the present invention is a light-emitting element having the structure described above, in which the host material is an organic compound having a condensed aromatic ring skeleton.

[0033] Another embodiment of the present invention is a light-emitting element having the structure described above, in which the host material is an organic compound having an anthracene skeleton.

[0034] Another embodiment of the present invention is a light-emitting element having the above-described structure, in which the host material is an organic compound having an anthracene skeleton and the fluorescent substance is an organic compound having a pyrene skeleton.

[0035] Another embodiment of the present invention is a light-emitting element having the above-described structure, in which the second light-emitting layer comprises n layers (n is an integer of 2 or more), and the n layers contain n kinds of substances having different emission spectra that can convert the triplet excitation energy into light emission.

[0036] Another embodiment of the present invention is a light-emitting element having the above-described structure, in which the second light-emitting layer contains a first phosphorescent substance and a second phosphorescent substance having different emission spectra as a substance capable of converting the triplet excitation energy into light emission.

[0037] Another embodiment of the present invention is a light-emitting element having the above-described structure in which the first phosphorescent substance emits light in a red region, the second phosphorescent substance emits light in a green region, and the fluorescent substance emits light in a blue region.

[0038] Another embodiment of the present invention is a light-emitting element having the above-described structure, in which the first phosphorescent substance has an emission spectrum peak of 580 nm to 680 nm, the second phosphorescent substance has an emission spectrum peak of 500 nm to 560 nm, and the fluorescent substance has an emission spectrum peak of 400 nm to 480 nm.

[0039] Another embodiment of the present invention is a light-emitting element having the above-described structure, wherein the second light-emitting layer comprises a first phosphorescent layer and a second phosphorescent layer, the first phosphorescent layer contains the first phosphorescent substance, and the second phosphorescent layer contains the second phosphorescent substance.

[0040] Another embodiment of the present invention is a light-emitting element having the above-described structure, in which the first phosphorescent substance has a charge trapping property in the first phosphorescent layer.

[0041] Another embodiment of the present invention is a light-emitting element having the above-described structure, in which the charge carrier trapping property is an electron trapping property.

[0042] Another embodiment of the present invention is a display module including one of the light-emitting elements described above.

[0043] Another embodiment of the present invention is a lighting module including one of the light-emitting elements described above.

[0044] Another embodiment of the present invention is a light-emitting device including one of the above-described light-emitting elements and a unit for controlling the light-emitting element.

[0045] Another embodiment of the present invention is a display device including one of the above-described light-emitting elements in a display section and a unit for controlling the light-emitting element.

[0046] Another embodiment of the present invention is a lighting device including one of the above-described light-emitting elements in a lighting section and a unit for controlling the light-emitting element.

[0047] Another embodiment of the present invention is an electronic device including one of the light-emitting elements described above.

[0048] Note that the light-emitting device in this specification includes, within its category, an image display device using a light-emitting element. The light-emitting device category in this specification includes a module in which a light-emitting element is provided with a connecting member such as an anisotropic conductive film or a tape carrier package (TCP); a module having a TCP with a printed circuit board provided at one end; and a module in which an integrated circuit (IC) is directly mounted on a light-emitting element by a chip-on-glass (COG) method. Furthermore, the category includes a light-emitting device used in lighting devices or the like.

[0049] In one embodiment of the present invention, a novel light-emitting element can be provided.

[0050] In one embodiment of the present invention, a multicolor light-emitting element utilizing fluorescence and phosphorescence, having a relatively small number of layers to be formed, and suitable for practical use can be provided.

[0051] In another embodiment of the present invention, a multicolor light-emitting element utilizing fluorescence and phosphorescence and having high emission efficiency can be provided.

[0052] In another embodiment of the present invention, there can be provided a multicolor light-emitting element which utilizes fluorescence and phosphorescence, has a relatively small number of layers to be formed, is practical, and has high emission efficiency.

[0053] In another embodiment of the present invention, there can be provided a display module, a lighting module, a light-emitting device, a display device, an electronic device, and a lighting device which can be manufactured at low cost by using any of the light-emitting elements described above.

[0054] In another embodiment of the present invention, a display module, a lighting module, a light-emitting device, a display device, an electronic device, and a lighting device having reduced power consumption can be provided by using any of the light-emitting elements described above. Note that the description of these effects does not preclude the existence of other effects. An embodiment of the present invention may not necessarily achieve all of the above-mentioned effects. Other effects are apparent from the explanation of the specification, drawings, claims, and the like, and can be derived therefrom. Short description of the drawings Fig. 1A and Fig. 1B are conceptual schemes of light-emitting elements. Fig. 2A and Fig. 2B are conceptual schematics of an active matrix light-emitting device. Fig. 3A and Fig. 3B are conceptual schematics of active matrix light-emitting devices. Fig. Figure 4 is a conceptual diagram of an active matrix light-emitting device. Fig. 5A and Fig. 5B are conceptual schematics of a passive matrix light-emitting device. Fig. 6A and Fig. 6B represent a lighting device. Fig. 7A to Fig. 7D represent electronic devices. Fig. 8 represents a light source device. Fig. 9 represents a lighting device. Fig. 10 represents a lighting device. Fig. 11 shows display devices and lighting devices in the vehicle. Fig. 12A to Fig. 12C represents an electronic device. Fig. Figure 13 shows the current density-luminance characteristics of light-emitting elements 1 to 4. Fig. Figure 14 shows the luminance-current efficiency characteristics of the light-emitting elements 1 to 4. Fig. Figure 15 shows the voltage-luminance characteristics of the light-emitting elements 1 to 4. Fig. Figure 16 shows the luminance-external quantum efficiency characteristics of the light-emitting elements 1 to 4. Fig. Figure 17 shows the emission spectra of the light-emitting elements 1 to 4. Fig. Figure 18 shows the current density-luminance characteristics of a light-emitting element 5. Fig. 19 shows the luminance-current efficiency characteristics of the light-emitting element 5. Fig. Figure 20 shows the voltage-luminance characteristics of the light-emitting element 5. Fig. Figure 21 shows the luminance-external quantum efficiency characteristics of the light-emitting element 5. Fig. 22 shows the emission spectrum of the light-emitting element 5. Fig. Figure 23 shows the luminance-CIE chromaticity characteristics of the light-emitting element 5. Fig. Figure 24 shows the current density-luminance characteristics of light-emitting elements 6 and 7. Fig. Figure 25 shows the luminance-current efficiency characteristics of the light-emitting elements 6 and 7. Fig. Figure 26 shows the voltage-luminance characteristics of the light-emitting elements 6 and 7. Fig. Figure 27 shows the luminance-external quantum efficiency characteristics of the light-emitting elements 6 and 7. Fig. Figure 28 shows the emission spectra of the light-emitting elements 6 and 7. Fig. Figure 29 shows the emission spectrum of a light-emitting element 8. Fig. 30 shows the current density-luminance characteristics of a light-emitting element 9. Fig. 31 shows the luminance-current efficiency characteristics of the light-emitting element 9. Fig. 32 shows the voltage-luminance characteristics of the light-emitting element 9. Fig. Figure 33 shows the luminance-external quantum efficiency characteristics of the light-emitting element 9. Fig. 34 shows the emission spectrum of the light-emitting element 9. Fig. 35 shows the luminance-power efficiency characteristics of a lighting device in Example 5. Best mode for carrying out the invention

[0055] Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, the invention should not be construed as being limited to the description in the following embodiments.

[0056] Fig. Figure 1A is a diagram illustrating a light-emitting element of one embodiment of the present invention. The light-emitting element includes at least a pair of electrodes (a first electrode 101 and a second electrode 102) and the EL layer 103, which includes a light-emitting layer 113. The light-emitting layer 113 has a multilayer structure in which the first light-emitting layer 113a, the separation layer 113b, and the second light-emitting layer 113c are arranged in this order and in contact with each other.

[0057] Fig. 1A also illustrates a hole injection layer 111, a hole transport layer 112, an electron transport layer 114, and an electron injection layer 115 in the EL layer 103. However, this multilayer structure is an example, and the structure of the EL layer 103 in the light-emitting element of one embodiment of the present invention is not limited thereto. It should be noted that in Fig. 1A the first electrode 101 serves as an anode and the second electrode 102 serves as a cathode.

[0058] The first light-emitting layer 113a contains a fluorescent substance and a host material. The second light-emitting layer 113c contains a first organic compound, a second organic compound, and a phosphorescent compound. In the light-emitting layer having this structure, a combination of the first organic compound and the second organic compound preferably forms a first exciplex.

[0059] This structure allows light originating from the fluorescent substance to be efficiently emitted from the first light-emitting layer 113a, and light originating from the phosphorescent substance to be efficiently emitted from the second light-emitting layer 113c. Note that even when the light-emitting element does not include a charge generation layer between the first light-emitting layer 113a and the second light-emitting layer 113c (that is, when the light-emitting element is not a tandem element), both fluorescence and phosphorescence can be efficiently obtained.

[0060] When a fluorescent layer and a phosphorescent layer are included in the same EL layer without being separated by a charge generation layer and emit light, the emission efficiency is generally significantly reduced. One reason for this is as follows: The triplet excitation energy of a host material of the fluorescent layer is low because a substance with a condensed aromatic ring structure (especially a condensed aromatic hydrocarbon ring structure), such as anthracene, is generally used as the host material. The triplet excitation energy generated in the phosphorescent layer is transferred to the fluorescent layer, resulting in non-radiative decay.Currently, it is difficult to achieve a desired emission wavelength, favorable element properties, or high reliability without using a substance having a condensed aromatic ring skeleton for the fluorescent layer; therefore, it is difficult to achieve favorable properties in a light-emitting element having the structure in which the fluorescent layer and the phosphorescent layer are included in the same EL layer.

[0061] Because a triplet excited state has a long relaxation time, the diffusion length of an exciton is long, and most of the excitons generated in the phosphorescent layer are transferred to the fluorescent layer as a result of diffusion, and non-radiative decay of the excitons occurs. This exacerbates the problem.

[0062] Currently, it is difficult to achieve a desired emission wavelength, favorable device properties, or high reliability by using a material without a condensed aromatic ring framework. Therefore, it is difficult to achieve favorable properties in a light-emitting element in which a fluorescent layer and a phosphorescent layer are formed adjacent to each other.

[0063] In a light-emitting element of this embodiment, the first organic compound and the second organic compound in the second light-emitting layer 113c form an exciplex, and the triplet excitation energy is transferred from the exciplex to the phosphorescent substance, so that light emission can be achieved. This structure can solve the problems described above.

[0064] An exciplex is an excited state formed by two types of substances (the first organic compound and the second organic compound in one embodiment of the present invention). After an exciplex releases energy, the two types of substances that formed the exciplex serve as original, distinct substances. In other words, an exciplex itself does not have a ground state, and therefore, in principle, energy transfer between exciplexes or energy transfer to an exciplex from another substance is unlikely to occur.

[0065] A process in which one of the first organic compound and the second organic compound are adjacent to each other as a cation, and the other of the first organic compound and the second organic compound are adjacent to each other as an anion, forming an exciplex (an electroplex process) is considered dominant for the generation of the exciplex in the light-emitting element. Even when one of the first organic compound and the second organic compound reaches an excited state, one quickly interacts with the other of the first organic compound and the second organic compound to form an exciplex; therefore, most of the excitons in the second light-emitting layer 113c are present as exciplexes. The exciplex has a smaller band gap than the first organic compound and the second organic compound.Furthermore, when the first organic compound and the second organic compound are selected such that the exciplex has a lower triplet excitation energy than at least one (preferably each) of the first organic compound and the second organic compound, energy transfer from the exciplex to the first organic compound and the second organic compound hardly occurs. Furthermore, as described above, energy transfer between exciplexes hardly occurs. Consequently, the excitation energy of the exciplex is transferred to the phosphorescent substance and converted into light emission. Therefore, diffusion of excitons hardly occurs at the second light-emitting layer 113c. Consequently, the problems described above can be solved.

[0066] Here, in the case where the first light-emitting layer 113a, which is a fluorescent layer, and the second light-emitting layer 113c, which is a phosphorescent layer, are in contact with each other, energy transfer from an exciplex or a phosphorescent dopant to the host material of the first light-emitting layer 113a (specifically, triplet-triplet energy transfer) slightly occurs at this interface. As described above, excitons of the exciplexes are unlikely to diffuse, and the excitons are easily transferred to the phosphorescent dopant; therefore, the influence of the excitons is relatively small. However, when the phosphorescence dopant exists in contact with the host material of the first light-emitting layer 113a at the interface, the host material largely quenches light emission from the phosphorescence dopant due to energy transfer by Dexter mechanism.Accordingly, the separation layer 113b is provided between the first light-emitting layer 113a and the second light-emitting layer 113c, whereby the energy transfer at the interface between the first light-emitting layer 113a and the second light-emitting layer 113c can be suppressed and both phosphorescence and fluorescence can be emitted with better characteristics.

[0067] In one embodiment of the present invention, when the first light-emitting layer 113a has a structure in which a singlet excitation state is easily generated by triplet-triplet annihilation (TT annihilation, TTA), the triplet excitation energy generated in the first light-emitting layer 113a can be converted into fluorescence in the first light-emitting layer 113a. This allows the energy loss of the light-emitting element of one embodiment of the present invention to be reduced.In order for the light-emitting layer 113a to have the structure in which the singlet excitation state is easily generated by TTA, a host material and a fluorescent substance in the first light-emitting layer 113a are preferably selected such that the singlet excitation level of the host material is higher than the singlet excitation level of the fluorescent substance, and the triplet excitation level of the host material is lower than the triplet excitation level of the fluorescent substance. As the combination of the host material and the fluorescent substance having such a relationship, a combination of a material having an anthracene skeleton as the host material and a material having a pyrene skeleton as the fluorescent substance, or the like, is preferable.

[0068] Note that if the first light-emitting layer 113a is too thick, the emission from the second light-emitting layer 113c is difficult to obtain. Furthermore, if the first light-emitting layer 113a is too thin, the emission from the first light-emitting layer 113c is difficult to obtain. For these reasons, the thickness of the first light-emitting layer 113a is preferably greater than or equal to 5 nm and less than or equal to 20 nm.

[0069] In the case where the first light-emitting layer 113a is formed on the anode side, the first light-emitting layer 113a preferably has a hole-transporting property. In this case, a bipolar material with a high hole-transporting property is preferably used. As such a material, a material having an anthracene skeleton is preferred. Moreover, when the fluorescent substance has a high hole-trapping property (e.g., a condensed aromatic amine compound described below is used), the concentration of the fluorescent substance is preferably less than or equal to 5%, more preferably higher than or equal to 1% and lower than or equal to 4%, even more preferably higher than or equal to 1% and lower than or equal to 3%, whereby phosphorescence and fluorescence can be obtained in a balanced manner and with high efficiency.It should be noted that the fluorescent substance exhibits a hole-trapping property when the HOMO level of the fluorescent substance is higher than the HOMO level of the host material.

[0070] Although there is no limitation on the combination of the first organic compound and the second organic compound in the second light-emitting layer 113c, as long as an exciplex can be formed, one organic compound is preferably a substance having a hole-transport property, and the other organic compound is preferably a substance having an electron-transport property. In this case, a donor-acceptor excited state is easily formed, allowing an exciplex to be formed efficiently. In the case where the combination of the first organic compound and the second organic compound is a combination of the substance having a hole-transport property and the substance having an electron-transport property, the carrier balance can be easily controlled by regulating the mixing ratio.In particular, the weight ratio of the substance having a hole-transporting property to the substance having an electron-transporting property is preferably 1:9 to 9:1. Since the carrier balance can be easily controlled in the light-emitting element having the above-described structure, a recombination range can also be easily regulated. The light-emitting element of one embodiment of the present invention also has a feature that an emission color can be regulated by controlling the carrier balance as described above.

[0071] The lowest-energy absorption band of the phosphorescent substance overlaps with the emission spectrum of the first exciplex in the second light-emitting layer 113c, thereby optimizing energy transfer from the first exciplex to the phosphorescent substance, and enabling the light-emitting element to exhibit favorable emission efficiency. The difference between the equivalent energy values ​​of a peak wavelength in the lowest-energy absorption band of the phosphorescent substance and a peak wavelength of the emission spectrum of the exciplex is preferably less than or equal to 0.2 eV, with a large overlap between the absorption band and the emission spectrum. Note that the lowest-energy absorption band of the phosphorescent substance is preferably a triplet absorption band.In the case where a thermally activated delayed fluorescence (TADF) material is used instead of the phosphorescent substance, the lowest energy absorption band is preferably a singlet absorption band.

[0072] In the light-emitting element of one embodiment of the present invention, a light-emitting substance in the second light-emitting layer 113c is preferably a substance that can convert triplet excitation energy into light emission. In this specification, the term "phosphorescent substance" may be replaced with the term "TADF material," and the term "phosphorescent layer" may be replaced with the term "TADF light-emitting layer." The TADF material is a substance that can upconvert a triplet excitation state to a singlet excitation state (i.e., reverse intersystem crossing is possible) using low thermal energy and efficiently emits light (fluorescence) from the singlet excitation state.The TADF is efficiently obtained under the condition where the difference between the energy of the triplet excitation level and the energy of the singlet excitation level is greater than or equal to 0 eV and less than or equal to 0.2 eV, preferably greater than or equal to 0 eV and less than or equal to 0.1 eV. Both the phosphorescent substance and the TADF material are substances that can convert the triplet excitation energy into light emission.

[0073] In the light-emitting element of this embodiment, a carrier recombination region is preferably formed not locally but dispersed to some extent. Therefore, each light-emitting layer preferably has an appropriate degree of carrier trapping property. In the structure where the first light-emitting layer 113a is formed on the anode side and the second light-emitting layer 113c is formed on the cathode side, the fluorescent substance in the first light-emitting layer 113a preferably has a hole-trapping property, and the phosphorescent substance in the second light-emitting layer 113c preferably has an electron-trapping property.In the structure where the first light-emitting layer 113a is formed on the cathode side and the second light-emitting layer 113c is formed on the anode side, the fluorescent substance in the first light-emitting layer 113a preferably has an electron-capturing property, and the phosphorescent substance in the second light-emitting layer 113c preferably has a hole-capturing property. Examples of a substance having a high electron-capturing property include transition metal complexes (e.g., an iridium complex and a platinum complex) whose ligands have a diazine skeleton, such as a pyrimidine skeleton or a pyrazine skeleton. Note that the phosphorescent substance has an electron-capturing property when the LUMO level of the phosphorescent substance is lower than the LUMO levels of both the first organic compound and the second organic compound.

[0074] Although the separation layer 113b can be formed from a single substance, the separation layer 113b preferably contains a substance with a hole-transport property and a substance with an electron-transport property. It is further preferred that these substances form an exciplex. By changing the mixing ratio of the substance with a hole-transport property to the substance with an electron-transport property, as in the second light-emitting layer 113c, the carrier balance can be easily controlled and the emission color can be regulated.

[0075] It is preferable that the singlet excitation energy and triplet excitation energy of a material forming the separation layer 113b be equal to or higher than those of the host material of the first light-emitting layer 113a. Note that in the case where a second exciplex is formed in the separation layer 113b, the singlet excitation energy and triplet excitation energy of the second exciplex may be lower than those of the host material because energy transfer to the exciplex hardly occurs, as described above.

[0076] The singlet excitation energy and triplet excitation energy of a material forming the separation layer 113b are not limited by the singlet excitation energy and triplet excitation energy of the first exciplex in the second light-emitting layer 113c. In other words, the singlet excitation energy and triplet excitation energy of the material forming the separation layer 113b may be higher or lower than those of the first exciplex in the second light-emitting layer 113c.In a general structure, light emission from the second light-emitting layer 113c is significantly reduced when the excitation energy of the separation layer is lower than the excitation energy of the second light-emitting layer 113c; however, in the structure of one embodiment of the present invention, most of the excitons in the second light-emitting layer 113c are present as exciplexes, so the excitons hardly diffuse and the energy loss is small.

[0077] In the case where the separation layer 113b contains the substance having a hole-transport property and a substance having an electron-transport property, the combination of these substances is preferably the same as the combination of the first organic compound and the second organic compound constituting the second light-emitting layer 113c, in which case, an increase in the operating voltage is suppressed. In other words, it is preferable that one of the first organic compound and the second organic compound is the substance having a hole-transport property in the separation layer 113b, and the other of the first organic compound and the second organic compound is the substance having an electron-transport property in the separation layer 113b.In other words, the second exciplex formed in the separation layer 113b is preferably the same as the first exciplex formed in the second light-emitting layer 113c.

[0078] Note that in the light-emitting element, the light emitted from the first light-emitting layer 113a preferably has a peak on the shorter wavelength side than the light emitted from the second light-emitting layer 113c. The luminance of a light-emitting element using the phosphorescent substance emitting light with a short wavelength tends to deteriorate rapidly. In view of the above, the fluorescent substance emitting light with a short wavelength is used, so that a light-emitting element with less deterioration in luminance can be provided. In this light-emitting element, only the separation layer 113b with a thickness of several nanometers is provided between the first light-emitting layer 113a, which is a fluorescent layer, and the second light-emitting layer 113c, which is a phosphorescent layer.Therefore, the number and thickness of layers constituting the EL layer in this light-emitting element are smaller than those in a tandem element; therefore, the light-emitting element of one embodiment of the present invention is cost-effective and suitable for mass production. Furthermore, as described above, the number of layers constituting the EL layer is small; accordingly, the thickness of the EL layer can be small, and the light-emitting element is optically advantageous (e.g., the outcoupling efficiency is high). Furthermore, the light-emitting element can have a low operating voltage and efficiently provide both fluorescence and phosphorescence at an operating voltage of 5 V or lower.

[0079] Furthermore, although the fluorescent layer and the phosphorescent layer are adjacent to each other, deactivation of the triplet excitation energy is less likely to occur due to the use of the above-described exciplex in the phosphorescent layer; therefore, both phosphorescence and fluorescence can be easily obtained.

[0080] In the light-emitting element of this embodiment, light with different emission wavelengths is obtained from the first light-emitting layer 113a and the second light-emitting layer 113c, so that the light-emitting element can be a multi-color light-emitting element. Therefore, the light-emitting element can provide different emission colors with a combination of light emitted from multiple light-emitting substances.

[0081] Such a light-emitting element is suitable for obtaining white light emission. When the first light-emitting layer 113a and the second light-emitting layer 113c emit light with complementary colors, white light emission can be obtained. Furthermore, white light emission with a high color rendering property formed by three primary colors or four or more colors can be obtained by using a plurality of light-emitting substances that emit light with different wavelengths for one or both of the light-emitting layers. In this case, each of the light-emitting layers can be divided into layers, and the divided layers can contain different light-emitting substances.Such a white light-emitting element utilizes phosphorescence, exhibits high emission efficiency, and can be manufactured at a lower cost because the white light-emitting element has a smaller number of layers and a smaller thickness than a tandem light-emitting element. Furthermore, the white light-emitting element improves light extraction efficiency due to its small thickness.

[0082] Next, an example of the structure of the light-emitting element described above is shown using Fig. 1A described in detail below.

[0083] A light-emitting element of this embodiment includes an EL layer comprising a plurality of layers between a pair of electrodes. In this embodiment, the light-emitting element includes the first electrode 101, the second electrode 102, and the EL layer 103 disposed between the first electrode 101 and the second electrode 102. Note that in this embodiment, the first electrode 101 serves as the anode, and the second electrode 102 serves as the cathode. Note that the order of the layers may be reversed. In other words, the first light-emitting layer 113a may be formed on the cathode side, and the second light-emitting layer 113c may be formed on the anode side.

[0084] Since the first electrode 101 serves as an anode, the first electrode 101 is preferably formed using one of metals, alloys, electrically conductive compounds with a high work function (particularly, a work function of 4.0 eV or more), mixtures thereof, and the like. Specific examples include indium oxide-tin oxide (ITO), indium oxide-tin oxide containing silicon or silicon oxide, indium oxide-zinc oxide, and indium oxide containing tungsten oxide and zinc oxide (IWZO). Films of these electrically conductive metal oxides are generally formed by a sputtering method, but may also be formed by applying a sol-gel method or the like. For example, indium oxide-zinc oxide is deposited by a sputtering method using a target obtained by adding 1 wt% to 20 wt% of zinc oxide to indium oxide.A film of indium oxide containing tungsten oxide and zinc oxide (IWZO) can be formed by a sputtering method using a target in which 0.5 wt% to 5 wt% of tungsten oxide and 0.1 wt% to 1 wt% of zinc oxide are added to indium oxide. In addition, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), nitrides of metal materials (e.g., titanium nitride), and the like can be specified. Graphene can also be used. Note that when a composite material below is used for a layer in contact with the first electrode 101 in the EL layer 103, an electrode material can be selected without considering its work function.

[0085] There is no particular limitation on the multilayer structure of the EL layer 103 as long as the light-emitting layer 113 has the structure described above. For example, the EL layer 103 can be formed by appropriately combining a hole injection layer, a hole transport layer, the light-emitting layer, an electron transport layer, an electron injection layer, a carrier blocking layer, an intermediate layer, and the like. In this embodiment, the EL layer 103 has a structure in which the hole injection layer 111, the hole transport layer 112, the light-emitting layer 113, the electron transport layer 114, and the electron injection layer 115 are arranged in this order above the first electrode 101. Specific examples of materials for each layer will be given below.

[0086] The hole-injection layer 111 is a layer containing a substance having a hole-injection property. Molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, manganese oxide, or the like can be used. Alternatively, the hole-injection layer 111 can be formed using a phthalocyanine-based compound such as phthalocyanine (abbreviation: H2Pc) or copper phthalocyanine (abbreviation: CuPc); an aromatic amine compound such as 4,4'-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB) or N,N'-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (abbreviation: DNTPD); a high-molecular compound such as ethylenediamine (EDI). B. poly(3,4-ethylenedioxythiophene) / poly(styrenesulfonic acid) (PEDOT / PSS); or the like.

[0087] Alternatively, a composite material in which a substance with a hole-transporting property contains a substance with an accepting property can be used for the hole-injection layer 111. Note that the use of such a substance with a hole-transporting property containing a substance with an accepting property allows a material for forming an electrode to be selected regardless of its work function. In other words, in addition to a material with a high work function, a material with a low work function can be used for the first electrode 101. Examples of accepting substances include 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ), chloranil, and the like. Furthermore, oxides of metals belonging to groups 4 to 8 of the periodic table can be used.In particular, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are preferred due to their high electron-accepting properties. Among these, molybdenum oxide is particularly preferred because of its stability in air, low hygroscopicity, and ease of handling.

[0088] As a substance with a hole-transporting property used for the composite material, one of various organic compounds, such as aromatic amine compounds, carbazole derivatives, aromatic hydrocarbons, and high-molecular compounds (such as oligomers, dendrimers, or polymers), can be used. It should be noted that the organic compound used for the composite material is preferably a substance with a hole-transporting property. In particular, a substance with a hole mobility of 10 -6 cm 2 / Vs or higher is used. Specific examples of the organic compound that can be used as a substance with a hole-transporting property in the composite material are given below.

[0089] Examples of aromatic amine compounds are N,N'-di(p-tolyl)-N,N'-diphenyl-p-phenylenediamine (abbreviation: DTDPPA), 4,4'-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB), N,N'-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (abbreviation: DNTPD) and 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene (abbreviation: DPA3B).

[0090] Specific examples of the carbazole derivatives that can be used for the composite material are 3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1), 3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2) and 3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1).

[0091] Other examples of the carbazole derivatives that can be used for the composite material are 4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA) and 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene.

[0092] Examples of the aromatic hydrocarbons that can be used for the composite material are 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA), 2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA), 9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene (abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene (abbreviation: DMNA), 2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene, 9,10-bis[2-(1-naphthyl)phenyl]anthracene, 2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene, 2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9'-bianthryl, 10,10'-diphenyl-9,9'-bianthryl, 10,10'-Bis(2-phenylphenyl)-9,9'-bianthryl, 10,10'-Bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9'-bianthryl, anthracene, tetracene, rubrene, perylene and 2,5,8,11-tetra(tert-butyl)perylene.Further examples are pentacene and coronene, the aromatic hydrocarbons with a hole mobility of 1 × 10. -6 cm 2 / Vs or higher and has 14 to 42 carbon atoms is particularly preferred.

[0093] It should be noted that the aromatic hydrocarbons that can be used for the composite material may have a vinyl backbone. Examples of the aromatic hydrocarbon with a vinyl group include 4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi) and 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA).

[0094] Further examples are high molecular weight compounds such as poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4-{N'-[4-(4-diphenylamino)phenyl]phenyl-N'-phenylamino}phenyl)methacrylamide] (abbreviation: PTPDMA) and poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (abbreviation: poly-TPD).

[0095] By providing a hole injection layer, a high hole injection property can be achieved, allowing a light-emitting element to be operated at a low voltage.

[0096] The hole-transport layer 112 is a layer containing a substance with a hole-transport property. Examples of the substance with a hole-transport property are aromatic amine compounds, such as ethylenediamine dimethylamine (EDI). B. 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4',4"-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA), 4,4',4"-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbreviation: MTDATA), 4,4'-bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB) and 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP). The substances listed here have high hole transport properties and are mainly those that have a hole mobility of 10 -6 cm 2 / Vs or higher. An organic compound exemplified as the substance having a hole-transporting property in the composite material described above can also be used for the hole-transporting layer 112. A high-molecular compound such as poly(N-vinylcarbazole) (abbreviation: PVK) and poly(4-vinyltriphenylamine) (abbreviation: PVTPA) can also be used. Note that the layer containing a substance having a hole-transporting property is not limited to a single layer and may be a stacked arrangement of two or more layers containing each of the above substances.

[0097] In the case where the first light-emitting layer 113a is arranged on the anode side in the light-emitting element of one embodiment of the present invention, it is preferable that the HOMO level of a substance used for the hole-transport layer 112 and the HOMO level of a host material in the first light-emitting layer 113a are close to each other (an energy difference of 0.2 eV or less). This can prevent too many holes from being trapped by trapping states and allow holes to flow into the separation layer 113b and the second light-emitting layer 113c. Therefore, fluorescence and phosphorescence can be easily obtained in a balanced manner with high efficiency.

[0098] The light-emitting layer 113 has the structure described above. In other words, the first light-emitting layer 113a, the separation layer 113b, and the second light-emitting layer 113c are arranged above the first electrode in this order. A host material and a fluorescent substance are contained in the first light-emitting layer 113a. A first organic compound, a second organic compound, and a substance capable of converting triplet excitation energy into luminescence (a phosphorescent compound or a TADF material) are contained in the second light-emitting layer 113c.

[0099] Examples of a material that can be used as a fluorescent substance in the first light-emitting layer 113a are given below. Fluorescent materials other than those given below may also be used.

[0100] Examples of the fluorescent substance are 5,6-bis[4-(10-phenyl-9-anthryl)phenyl]-2,2'-bipyridine (abbreviation: PAP2BPy), 5,6-bis[4'-(10-phenyl-9-anthryl)biphenyl-4-yl]-2,2'-bipyridine (abbreviation: PAPP2BPy), N,N'-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N'-diphenyl-pyrene-1,6-diamine (abbreviation: 1,6FLPAPrn), N,N'-bis(3-methylphenyl)-N,N'-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPrn), N,N'-Bis[4-(9H-carbazol-9-yl)phenyl]-N,N'-diphenylstilbene-4,4'-diamine (abbreviation: YGA2S), 4-(9H-carbazol-9-yl)-4'-(10-phenyl-9-anthryl)triphenylamine (abbreviation: YGAPA), 4-(9H-carbazol-9-yl)-4'-(9,10-diphenyl-2-anthryl)triphenylamine (abbreviation: 2YGAPPA), N,9-Diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: PCAPA), Perylene, 2,5,8,11-Tetra-tert-butylperylene (abbreviation: TBP), 4-(10-phenyl-9-anthryl)-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBAPA), N,N''-(2-tert-butylanthracene-9,1 0-diyldi-4, 1-phenylene)bis[N,N',N'-triphenyl-1,4-phenylenediamine] (abbreviation: DPABPA), N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: 2PCAPPA), N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPPA), N,N,N',N',N'',N'',N''',N'''-Octaphenyldibenzo[g,p]chrysen-2,7,10,15-tetraamine (abbreviation: DBC1), Coumarin 30, N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine (abbreviation: 2PCAPA), N-[9,10-Bis(1,1'-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine (abbreviation: 2PCABPhA), N-(9,10-Diphenyl-2-anthryl)-N,N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPA), N-[9,10-Bis(1,1'-biphenyl-2-yl)-2-anthryl]-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-phenylanthracen-2-amine (abbreviation: 2YGABPhA), N,N,9-Triphenylanthracene-9-amine (abbreviation: DPhAPhA), Coumarin 545T, N,N'-Diphenylquinacridone (abbreviation: DPQd), Rubrene, 5,12-Bis(1,1'-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT),2-(2-{2-[4-(Dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile (abbreviation: DCM1), 2-{2-Methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCM2), N,N,N',N'-Tetrakis(4-methylphenyl)tetracen-5,11-diamine (abbreviation: p-mPhTD), 7,14-Diphenyl-N,N,N',N'-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine (abbreviation: p-mPhAFD), 2-{2-Isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTI), 2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTB), 2-(2,6-Bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile (abbreviation: BisDCM) and 2-{2,6-Bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene,Propanedinitrile (abbreviation: BisDCJTM). Condensed aromatic diamine compounds, typically pyrenediamine compounds such as 1,6FLPAPrn and 1,6mMemFLPAPrn, are particularly preferred due to their high hole-trapping properties, high emission efficiency, and high reliability.

[0101] Examples of a substance that can be used as a host material in the first light-emitting layer 113a are given below.

[0102] The examples include anthracene compounds such as 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: PCzPA), 3-[4-(1-naphthyl)phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPN), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA), 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole (abbreviation: cgDBCzPA), 6-[3-(9,10-diphenyl-2-anthryl)phenyl]-benzo[b]naphtho[1,2-d]furan (abbreviation: 2mBnfPPA) and 9-Phenyl-10-{4-(9-phenyl-9H-fluoren-9-yl)biphenyl-4'-yl}anthracene (abbreviation: FLPPA). The use of a substance with an anthracene skeleton as a host material makes it possible to provide a light-emitting layer with high emission efficiency and durability. In particular, CzPA, cgDBCzPA, 2mBnfPPA, and PCzPA are particularly preferred due to their excellent properties.

[0103] A phosphorescent substance and a TADF material can be used in the second light-emitting layer 113c as a substance that can convert triplet excitation energy into luminescence. Examples of the phosphorescent substance and the TADF material are given below.

[0104] Examples of the phosphorescent substance are an organometallic iridium complex with a 4H-triazole skeleton, such as tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III) (abbreviation: Ir(mpptz-dmp)3), tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III) (abbreviation: Ir(Mptz)3) or tris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III) (abbreviation: Ir(iPrptz-3b)3); an organometallic iridium complex with a 1H-triazole skeleton, such as B. Tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III) (abbreviation: Ir(Mptz1-mp)3) or tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III) (abbreviation: Ir(Prptz1-Me)3); an organometallic iridium complex with an imidazole framework, such asfac-Tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III) (abbreviation: Ir(iPrpmi)3) or tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III) (abbreviation: Ir(dmpimpt-Me)3); and an organometallic iridium complex in which a phenylpyridine derivative with an electron-withdrawing group is a ligand, such as bis[2-(4',6'-difluorophenyl)pyridinato-N,C. 2 ']iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6), bis[2-(4',6'-difluorophenyl)pyridinato-N, C 2 ']iridium(III)picolinate (abbreviation: Flrpic), bis{2-[3',5'-bis(trifluoromethyl)phenyl]pyridinato-N,C 2 '}iridium(III)picolinate (abbreviation: Ir(CF3ppy)2(pic)) or bis[2-(4',6'-difluorophenyl)pyridinato-N,C 2 ']Iridium(III) acetylacetonate (abbreviation: Flr(acac)). These are compounds that emit blue phosphorescence and exhibit an emission peak between 440 nm and 520 nm.

[0105] Further examples are organometallic iridium complexes with pyrimidine frameworks, such as tris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation: Ir(mppm)3), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III) (abbreviation: Ir(tBuppm)3), (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: Ir(mppm)2(acac)), bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ 2O,O')iridium(III) (abbreviation: Ir(tBuppm)2(acac)), (acetylacetonato)bis[4-(2-norbornyl)-6-phenylpyrimidinato]iridium(III) (endo / exo mixture) (abbreviation: Ir(nbppm)2(acac)), (acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: Ir(mpmppm)2(acac)) and (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: Ir(dppm)2(acac)); organometallic iridium complexes with pyrazine frameworks, such as B. (Acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III) (abbreviation: Ir(mppr-Me)2(acac)) and (Acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III) (abbreviation: Ir(mppriPr)2(acac)); organometallic iridium complexes with pyridine frameworks, such as tris(2-phenylpyridinato-N,C 2' )iridium(III) (abbreviation: Ir(ppy)3), bis(2-phenylpyridinato-N,C 2')iridium(III)acetylacetonate (abbreviation: Ir(ppy)2(acac)), bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq)2(acac)), tris(benzo[h]quinolinato)iridium(III) (abbreviation: Ir(bzq)3), tris(2-phenylquinolinato-N,C 2' )iridium(III) (abbreviation: Ir(pq)3) and bis(2-phenylquinolinato-N,C 2' )iridium(III) acetylacetonate (abbreviation: Ir(pq)2(acac)); and a rare earth metal complex such as tris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation: Tb(acac)3(Phen)). These are mainly compounds that emit green phosphorescence and exhibit an emission peak at 500 nm to 600 nm. It should be noted that an organometallic iridium complex with a pyrimidine framework exhibits very high reliability and emission efficiency and is therefore particularly preferred.

[0106] Further examples are (diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III) (abbreviation: Ir(5mdppm)2(dibm)), bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: Ir(5mdppm)2(dpm)) and bis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: Ir(d1npm)2(dpm)); organometallic iridium complexes with pyrazine frameworks, such as. B. (Acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: Ir(tppr)2(acac)), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)2(dpm)) or (Acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: Ir(Fdpq)2(acac)); organometallic iridium complexes with pyridine frameworks, such as tris(1-phenylisoquinolinato-N,C 2' )iridium(III) (abbreviation: Ir(piq)3) and bis(1-phenylisoquinolinato-N,C 2')iridium(III) acetylacetonate (abbreviation: Ir(piq)2(acac)); a platinum complex such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (abbreviation: PtOEP); and rare earth metal complexes such as tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviation: Eu(DBM)3(Phen)) and tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: Eu(TTA)3(Phen)). These are compounds that emit red phosphorescence and exhibit an emission peak at 600 nm to 700 nm. The organometallic iridium complex with a pyrazine framework can provide red light emission with favorable chromaticity.

[0107] Other phosphorescent materials than those listed above may also be used.

[0108] Materials listed below can be used as TADF material.

[0109] A fullerene, a derivative thereof, an acridine derivative such as proflavin, eosin, or the like can be used. A metal-containing porphyrin, such as porphyrin containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd), can be used. Examples of the metal-containing porphyrin are a protoporphyrin-tin fluoride complex (abbreviation: SnF2(Proto IX)), a mesoporphyrin-tin fluoride complex (abbreviation: SnF2(Meso IX)), a hematoporphyrin-tin fluoride complex (abbreviation: SnF2(Hemato IX)), a coproporphyrin tetramethyl ester-tin fluoride complex (abbreviation: SnF2(Copro III-4Me)), an octaethylporphyrin-tin fluoride complex (abbreviation: SnF2(OEP)), an etioporphyrin-tin fluoride complex (abbreviation: SnF2(Etio I)) and an octaethylporphyrin-platinum chloride complex (abbreviation: PtCl2(OEP)), which are represented by the following structural formulas.

[0110] Alternatively, a heterocyclic compound containing a π-electron-rich heteroaromatic ring and a π-electron-poor heteroaromatic ring can be used, such as 2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine (abbreviation: PIC-TRZ), which is represented by the structural formula below. The heterocyclic compound is preferably used because of the π-electron-rich heteroaromatic ring and the π-electron-poor heteroaromatic ring; therefore, the electron-transport property and the hole-transport property are high.It should be noted that a substance in which the π-electron-rich heteroaromatic ring is directly bonded to the π-electron-poor heteroaromatic ring is particularly preferably used because the donor property of the π-electron-rich heteroaromatic ring and the acceptor property of the π-electron-poor heteroaromatic ring are both increased and the energy difference between the S1 level and the T1 level becomes small.

[0111] There are no particular restrictions on the materials that can be used as the first organic compound and the second organic compound, as long as the combination of the materials meets the conditions described above. Various charge carrier transport materials can be selected.

[0112] Examples of the substance with an electron transport property are a heterocyclic compound with a polyazole skeleton, such as bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq2), bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq), bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO) or bis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); a heterocyclic compound with a polyazole skeleton, such as2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 3-(4-Biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), 1,3-Bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 9-[4-(5-Phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation: CO11), 2,2',2''-(1,3,5-Benzenetriyl)tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI) or 2-[3-(Dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: mDBTBIm-II); a heterocyclic compound with a diazine skeleton, such as2-[3-(Dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3'-(Dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 2-[3'-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mCzBPDBq), 4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation: 4,6mPnP2Pm) or 4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation: 4,6mDBTP2Pm-II); and a heterocyclic compound having a pyridine skeleton, such as 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoline (abbreviation: 2mDBTBPDBQu-II), 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy), or 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB). Among the above materials, a heterocyclic compound having a diazine skeleton and a heterocyclic compound having a pyridine skeleton have high reliability and are thus preferred.In particular, a heterocyclic compound having a diazine skeleton (pyrimidine skeleton or pyrazine skeleton) exhibits a high electron transport property, which contributes to a reduction in operating voltage.

[0113] Examples of the substance with a hole transport property are a compound with an aromatic amine skeleton, such as4,4'-Bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), N,N'-Bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (abbreviation: TPD), 4,4'-Bis[N-(spiro-9,9'-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB), 4-Phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), 4-Phenyl-3'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-Phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4'-Diphenyl-4''-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBANB), 4,4'-Di(1-naphthyl)-4''-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 9,9-Dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine (abbreviation: PCBAF) or N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9'-bifluoren-2-amine (abbreviation: PCBASF); a compound with a carbazole skeleton, such as1,3-bis(N-carbazolyl)benzene (abbreviation: mCP), 4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP), 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP) or 3,3'-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP); a compound with a thiophene skeleton, such as B. 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), 2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviation: DBTFLP-III) or 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviation: DBTFLP-IV); and a compound with a furan skeleton, such as 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II) or 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviation: mmDBFFLBi-II).Among the above materials, a compound having an aromatic amine skeleton and a compound having a carbazole skeleton are preferred because these compounds are highly reliable and have high hole transport properties, which contributes to a reduction in operating voltage.

[0114] Charge-transport materials can be selected from various substances as well as from the charge-transport materials listed above. It should be noted that, as the first organic compound and the second organic compound, it is preferable to select substances whose triplet level (a difference in energy between a ground state and a triplet excited state) is higher than the triplet level of the phosphorescent compound. Furthermore, the combination of the first organic compound and the second organic compound is preferably selected to form an exciplex that emits light whose wavelength overlaps with a wavelength of a lowest-energy absorption band of the phosphorescent substance.

[0115] Furthermore, the combination of a substance with electron transport properties as one of the first organic compound and the second organic compound, and a substance with hole transport properties as the other organic compound, is advantageous for forming an exciplex. The transport properties of the light-emitting layer can be easily controlled, and a recombination region can be easily controlled by changing the amount of each compound contained. The ratio of the contained amount of the substance with hole transport properties to the contained amount of the substance with electron transport properties can be 1:9 to 9:1.

[0116] As materials constituting the separation layer 113b, the above-described materials that can be used as the first organic compound and the second organic compound can be used.

[0117] The second light-emitting layer 113c may be divided into two or more layers, and the divided layers preferably contain different light-emitting substances. In particular, a structure is preferably employed in which the second light-emitting layer 113c is divided into a first phosphorescent layer that emits red light (i.e., light having an emission spectrum peak at 580 nm to 680 nm) and a second phosphorescent layer that emits green light (i.e., light having an emission spectrum peak at 500 nm to 560 nm), and the first light-emitting layer 113a emits blue light (i.e., light having an emission spectrum peak at 400 nm to 480 nm), whereby white light emission with favorable color rendering properties can be obtained.Note that in this case, the first light-emitting layer 113a, the first phosphorescent layer, and the second phosphorescent layer for high durability are preferably stacked in this order. Furthermore, the first light-emitting layer 113a is preferably formed on the anode side, thereby achieving advantageous properties.

[0118] The electron-transport layer 114 is a layer containing a substance having an electron-transport property. For example, the electron-transport layer 114 is formed using a metal complex having a quinoline skeleton or a benzoquinoline skeleton, such as tris(8-quinolinolato)aluminum (abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq3), bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq2), or bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation: BAlq), or the like. A metal complex having an oxazole-based or thiazole-based ligand, such as tris(8-quinolinolato)aluminum (abbreviation: Alq2), or bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation: BAlq), is also suitable. B. Bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX)2) or Bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)2), or the like can also be used.In addition to metal complexes, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), and the like can also be used. The substances listed here exhibit high electron transport properties and are mainly those with an electron mobility of 10. -6 cm 2 / Vs or higher. Note that any of the substances described above having electron-transport properties can be used for the electron-transport layer 114.

[0119] The electron transport layer 114 is not limited to a single layer and may be a layered arrangement of two or more different layers, each containing any of the substances described above.

[0120] A layer that controls the movement of electron carriers can be provided between the electron-transport layer and the light-emitting layer. This layer is formed by adding a small amount of a substance with high electron-capturing properties to the above-described materials with high electron-transporting properties. This layer is capable of regulating the carrier balance by suppressing the movement of electron carriers. Such a structure is very effective in preventing problems (such as a shortened lifetime of the element) caused by electrons passing through the light-emitting layer.

[0121] An electron injection layer 115 may be provided in contact with the second electrode 102 between the electron transport layer 114 and the second electrode 102. For the electron injection layer 115, an alkali metal, an alkaline earth metal, or a compound thereof, such as lithium fluoride (LiF), cesium fluoride (CsF), or calcium fluoride (CaF2), may be used. For example, a layer formed using a substance having an electron transport property and containing an alkali metal, an alkaline earth metal, or a compound thereof may be used. Note that a layer formed using a substance having an electron transport property and containing an alkali metal or an alkaline earth metal is preferably used as the electron injection layer 115, in which case electron injection from the second electrode 102 occurs efficiently.

[0122] For the second electrode 102, any of metals, alloys, electrically conductive compounds, and mixtures thereof having a low work function (particularly, a work function of 3.8 eV or less), or the like can be used. Specific examples of such a cathode material are elements belonging to groups 1 and 2 of the periodic table, such as alkali metals (e.g., lithium (Li) and cesium (Cs)), magnesium (Mg), calcium (Ca), and strontium (Sr), alloys thereof (e.g., MgAg and AlLi), rare earth metals such as europium (Eu) and ytterbium (Yb), and alloys thereof. However, when the electron injection layer is provided between the second electrode 102 and the electron transport layer, any of various conductive materials, such as silicon dioxide (SiO), may be used for the second electrode 102. B. Al, Ag, ITO or indium oxide-tin oxide containing silicon or silicon oxide can be used without taking the work function into account.These conductive materials can be deposited by a sputtering process, an inkjet process, a spin coating process, or the like.

[0123] Any of various methods can be used to form the EL layer 103, whether a dry process or a wet process. For example, a vacuum evaporation method, an inkjet method, or a spin-coating method can be used. A different manufacturing method can be used for each electrode or layer.

[0124] The electrode can be formed by a wet process using a sol-gel method or a wet process using a paste of a metal material. Alternatively, the electrode can be formed by a dry process such as a sputtering method or a vacuum evaporation method.

[0125] Light emission is extracted to the outside through the first electrode 101 and / or the second electrode 102. Therefore, the first electrode 101 and / or the second electrode 102 is / are a light-transmitting electrode. In the case where only the first electrode 101 is a light-transmitting electrode, light emission is extracted through the first electrode 101. In the case where only the second electrode 102 is a light-transmitting electrode, light emission is extracted through the second electrode 102. In the case where both the first electrode 101 and the second electrode 102 are light-transmitting electrodes, light emission is extracted through the first electrode 101 and the second electrode 102.

[0126] Note that the structure of the layer disposed between the first electrode 101 and the second electrode 102 is not limited to the structure described above. Preferably, a light-emitting region where holes and electrons recombine is located away from the first electrode 101 and the second electrode 102, so that quenching due to the proximity between the light-emitting region and a metal used for electrodes and charge injection layers can be prevented.

[0127] In order to suppress energy transfer from an exciton generated in the light-emitting layer, it is preferable to form the hole transport layer and the electron transport layer in contact with the light-emitting layer 113, particularly a carrier transport layer in contact with a side closer to the light-emitting region in the light-emitting layer 113, using a substance having a larger band gap than the light-emitting substance of the light-emitting layer or the emission center substance contained in the light-emitting layer.

[0128] The light-emitting element of this embodiment can be formed over a glass substrate, a quartz substrate, a semiconductor substrate, a plastic substrate (polyester, polyolefin, polyamide (e.g., nylon or aramid), polyimide, polycarbonate, or an acrylic resin). Alternatively, the light-emitting element can be formed over a glass substrate, a quartz substrate, or a half-liter substrate and then transferred to a plastic substrate.

[0129] Although a single light-emitting element may be formed over a substrate in a light-emitting device, a plurality of light-emitting elements may be formed over a substrate. By using a plurality of light-emitting elements described above formed over a substrate, an element-separated lighting device or a passive matrix light-emitting device can be manufactured. A light-emitting element may be formed over an electrode electrically connected to, for example, a field-effect transistor (FET) formed over a substrate made of glass, plastic, or the like, so that an active matrix light-emitting device in which the FET controls the operation of the light-emitting element can be manufactured. Note that the structure of the FET is not particularly limited.In addition, the crystallinity of a semiconductor used for the FET is not particularly limited; an amorphous semiconductor or a crystalline semiconductor can be used. Furthermore, a driver circuit can be formed in an FET substrate with an n-type FET and a p-type FET, or with either an n-type FET or a p-type FET.

[0130] It should be noted that this embodiment may be appropriately combined with any of the other embodiments.

[0131] Next, a type of light-emitting element having a structure in which a plurality of light-emitting units are arranged (hereinafter also referred to as a multi-layer element) is described by Fig. 1B. In this light-emitting element, a plurality of light-emitting units are provided between a first electrode and a second electrode. Each light-emitting unit has a structure similar to that of the EL layer 103 in Fig. 1A. In other words, the light-emitting element in Fig. 1A, a single light-emitting unit; the light-emitting element in this embodiment includes a plurality of light-emitting units.

[0132] In Fig. 1B, a first light-emitting unit 511 and a second light-emitting unit 512 are arranged between a first electrode 501 and a second electrode 502, and a charge generation layer 513 is provided between the first light-emitting unit 511 and the second light-emitting unit 512. The first electrode 501 and the second electrode 502 correspond to the first electrode 101 and the second electrode 102, respectively, in Fig. 1A, and the description for Fig. 1A can be used. Furthermore, the first light-emitting unit 511 and the second light-emitting unit 512 may have the same structure or different structures.

[0133] The charge generation layer 513 contains a composite material of an organic compound and a metal oxide. As the composite material of the organic compound and the metal oxide, the composite material used for the hole injection layer 111 in Fig. 1A. Note that when a surface of a light-emitting unit on the anode side is in contact with a charge generation layer, the charge generation layer can also serve as a hole-transport layer of the light-emitting unit; therefore, a hole-transport layer may not necessarily be formed in the light-emitting unit.

[0134] The charge generation layer 513 may have a multilayer structure consisting of a layer containing the composite material of an organic compound and a metal oxide and a layer containing another material. For example, a layer containing a composite material of the organic compound and the metal oxide may be combined with a layer containing a compound of a substance selected from among substances having an electron-donating property and a substance having an electron-transporting property. Furthermore, a layer containing a composite material of the organic compound and the metal oxide may be combined with a transparent conductive film.

[0135] The light-emitting element, which comprises two light-emitting units, is identified by Fig. 1B; however, the present invention can be equally applied to a light-emitting element in which three or more light-emitting units are arranged. When a plurality of light-emitting units divided by the charge generation layer are arranged between a pair of electrodes, as in the light-emitting element of this embodiment, it is possible to provide a light-emitting element capable of emitting light with high luminance while keeping the current density low. As a result, it is possible to obtain a light-emitting device that can be operated at a low voltage and has low power consumption.

[0136] When the above-described structure of the light-emitting layer 113 is applied to at least one of the plurality of units, the number of manufacturing steps of the unit can be reduced; thus, a multi-color light-emitting element suitable for practical use can be provided.

[0137] The structure described above may be combined with any of the structures in this embodiment and the other embodiments. (light-emitting device)

[0138] Next, a light-emitting device of an embodiment of the present invention will be described.

[0139] The light-emitting device of one embodiment of the present invention is manufactured using the light-emitting element described above. It should be noted that Fig. 2A is a plan view of the light emitting device and Fig. 2B a cross-sectional view along lines AB and CD in Fig. 2A. This light-emitting device includes a driving circuit section (source line driving circuit) 601, a pixel section 602, and a driving circuit section (gate line driving circuit) 603, which control the light emission of the light-emitting element and are indicated by dotted lines. Reference numeral 604 denotes a sealing substrate; 605, a sealing material; and 607, a space surrounded by the sealing material 605. The space 607 may be filled with a dry inert gas or a solid-sealing resin. The sealing material 605 may be the same as or different from the solid-sealing resin.

[0140] Note that a lead line 608 is a line for transmitting signals input to the source line driver circuit 601 and the gate line driver circuit 603, and for receiving a video signal, a clock signal, a start signal, a reset signal, and the like from an FPC (flexible printed circuit) 609 serving as an external input terminal. Although only the FPC is illustrated here, a printed wiring board (PWB) may be attached to the FPC. The light-emitting device in this specification includes within its category not only the light-emitting device itself but also the light-emitting device provided with the FPC or the PWB.

[0141] Next, a cross-sectional structure is created based on Fig. 2B. The driver circuit section and the pixel section are formed over an element substrate 610. The source line driver circuit 601, which is a driver circuit section, and one of the pixels in the pixel section 602 are shown here.

[0142] In the source line driver circuit 601, a CMOS circuit is formed in which an n-channel FET 623 and a p-channel FET 624 are combined. Furthermore, the driver circuit can be formed using any of various circuits, such as a CMOS circuit, a PMOS circuit, and an NMOS circuit. Although a driver-integrated type in which a driver circuit is formed over a substrate is described in this embodiment, an embodiment of the present invention is not limited to this type, and the driver circuit may be formed outside the substrate.

[0143] The pixel section 602 includes a plurality of pixels, each including a switching FET 611, a current-controlling FET 612, and a first electrode 613 electrically connected to a drain of the current-controlling FET 612. An insulator 614 is formed to cover end portions of the first electrode 613. In this embodiment, the insulator 614 is formed using a positive photosensitive acrylic resin film.

[0144] To improve coverage, the insulator 614 preferably has a curved surface with the curvature at its upper end portion or lower end portion. For example, in the case where a positive photosensitive acrylic resin is used for a material of the insulator 614, only the upper end portion of the insulator 614 preferably has a surface with a radius of curvature (0.2 μm to 3 μm). Either a negative photosensitive resin or a positive photosensitive resin can be used as the insulator 614.

[0145] An EL layer 616 and a second electrode 617 are formed over the first electrode 613. As the material for the first electrode 613, which serves as an anode, a material with a high work function is preferably used. For example, a single-layer film of an ITO film, an indium tin oxide film containing silicon, an indium oxide film containing 2 wt% to 20 wt% zinc oxide, a titanium nitride film, a chromium film, a tungsten film, a Zn film, a Pt film, or the like, a stacked film including a titanium nitride film and a film containing aluminum as a main component, a stacked film including three layers of a titanium nitride film, a film containing aluminum as a main component, and a titanium nitride film, or the like can be used. The multilayer structure enables low wiring resistance, good ohmic contact, and function as an anode.

[0146] The EL layer 616 is formed by any of various methods, such as an evaporation method using an evaporation mask, an inkjet method, and a spin coating method. The EL layer 616 has a structure similar to that shown in Fig. 1A or Fig. 1B. As another material included in the EL layer 616, any of the low-molecular-weight compounds and the high-molecular-weight compounds (including oligomers and dendrimers) can be used.

[0147] As the material for the second electrode 617 formed over the EL layer 616 and serving as a cathode, a material with a low work function (e.g., Al, Mg, Li, Ca, or an alloy or compound thereof, such as MgAg, MgIn, or AlLi) is preferably used. In the case where light generated in the EL layer 616 passes through the second electrode 617, a stacked arrangement of a thin metal film and a transparent conductive film (e.g., ITO, indium oxide containing 2 wt% to 20 wt% zinc oxide, indium tin oxide containing silicon, or zinc oxide (ZnO)) is preferably used for the second electrode 617.

[0148] The sealing substrate 604 is attached to the element substrate 610 with the sealing material 605 such that the light-emitting element 618 is provided in the space 607 enclosed by the element substrate 610, the sealing substrate 604, and the sealing material 605. The space 607 may be filled with a filler, and may be filled with an inert gas (such as nitrogen or argon), a resin, or the sealing material 605. It is preferable that the sealing substrate be provided with a recessed portion and a desiccant be provided in the recessed portion, in which case deterioration due to the influence of moisture can be suppressed.

[0149] An epoxy-based resin or a glass frit is preferably used for the sealing material 605. It is preferred that such a material permits as little moisture or oxygen permeation as possible. A glass substrate, a quartz substrate, or a plastic substrate made of fiber-reinforced plastic (FRP), poly(vinyl fluoride) (PVF), polyester, acrylic, or the like can be used as the sealing substrate 604.

[0150] The light-emitting device of one embodiment of the present invention can have low power consumption. The lighting device can also be cost-effective.

[0151] Fig. 3A and Fig. 3B each illustrates an example of a light-emitting device in which a full-color display is achieved by forming a white light-emitting element and providing a color layer (a color filter) and the like. In Fig. 3A, 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, first electrodes 1024W, 1024R, 1024G, and 1024B of light-emitting elements, a partition wall 1025, an EL layer 1028, a second electrode 1029 of the light-emitting elements, a sealing substrate 1031, a sealing material 1032, and the like are shown.

[0152] In Fig. 3A, color layers (a red color layer 1034R, a green color layer 1034G, and a blue color layer 1034B) are provided on a transparent base material 1033. A black layer (a black matrix) 1035 may also be provided. The transparent base material 1033, provided with the color layers and the black layer, is positioned and attached to the substrate 1001. Note that the color layers and the black layer are covered with a covering layer 1036. In Fig. 3A, light emitted from one part of the light-emitting layer does not pass through the color layers, while light emitted from the other part of the light-emitting layer does pass through the color layers. Since the light that does not pass through the color layers is white, and the light that passes through one of the color layers is red, blue, or green, an image can be displayed using pixels for the four colors.

[0153] Fig. 3B illustrates an example in which the color layers (the red color layer 1034R, the green color layer 1034G, and the blue color layer 1034B) are provided between the gate insulating film 1003 and the first interlayer insulating film 1020. As shown in Fig. 3B, the color layers may be disposed between the substrate 1001 and the sealing substrate 1031.

[0154] The light-emitting device described above has a structure in which light is taken out from the side of the substrate 1001 on which the FETs are formed (a bottom-emission structure), but it may have a structure in which light is taken out from the side of the sealing substrate 1031 (a top-emission structure). Fig. 4 is a cross-sectional view of a light-emitting device with a top-emission structure. In this case, a substrate that does not transmit light can be used as the substrate 1001. The process up to the step of forming a connection electrode connecting the FET and the anode of the light-emitting element is performed similarly to that of the light-emitting device with a bottom-emission structure. A third interlayer insulating film 1037 is then formed to cover an electrode 1022. This insulating film may have a planarization function. The third interlayer insulating film 1037 may be formed using a material similar to that of the second interlayer insulating film, and may alternatively be formed using any of the other materials.

[0155] The first electrodes 1024W, 1024R, 1024G and 1024B of the light-emitting elements each serve as anode, but they can also serve as cathode. In the case of a Fig. In the light-emitting device with a top-emission structure shown in Figure 4, the first electrodes are preferably reflective electrodes. The EL layer 1028 is formed to have a structure similar to that shown in Fig. 1A, in which white light emission can be obtained.

[0156] In the case of a top issue structure as in Fig. 4, sealing can be performed with the sealing substrate 1031 on which the color layers (the red color layer 1034R, the green color layer 1034G, and the blue color layer 1034B) are provided. The sealing substrate 1031 can be provided with the black layer (the black matrix) 1035 sandwiched between pixels. The color layers (the red color layer 1034R, the green color layer 1034G, and the blue color layer 1034B) and the black layer (the black matrix) 1035 can be covered with a covering layer. Note that a light-transmitting substrate is used as the sealing substrate 1031.

[0157] Although an example in which a full-color display is performed using four colors, namely red, green, blue, and white, is shown here, there is no particular limitation, and a full-color display can be performed using three colors, namely red, green, and blue.

[0158] The light-emitting device in this embodiment is manufactured using the Fig. 1A or Fig. 1B and can therefore exhibit advantageous properties. Specifically: Since the light-emitting element shown in Fig. 1A or Fig. 1B has a high emission efficiency, the light-emitting device can have reduced power consumption. In addition, since the light-emitting element shown in Fig. 1A or Fig. 1B is relatively easy to produce in large quantities, the light-emitting device can be provided at low cost.

[0159] An active matrix light-emitting device has been described above, whereas a passive matrix light-emitting device will be described below. Fig. 5A and Fig. 5B illustrate a passive matrix light-emitting device fabricated using an embodiment of the present invention. Fig. 5A is a perspective view of the light-emitting device, and Fig. 5B is a cross-sectional view along the line XY in Fig. 5A. In Fig. 5A and Fig. 5B, an EL layer 955 is provided over a substrate 951 between an electrode 952 and an electrode 956. An end portion of the electrode 952 is covered with an insulating layer 953. A partition layer 954 is further provided over the insulating layer 953. The sidewalls of the partition layer 954 are tapered so that the distance between one sidewall and the other sidewall gradually decreases toward the surface of the substrate. In other words, a cross-section along the short side direction of the partition layer 954 is trapezoidal, and the lower side (a side located in the same direction as a planar direction of the insulating layer 953 and in contact with the insulating layer 953) is shorter than the upper side (a side located in the same direction as the planar direction of the insulating layer 953 and not in contact with the insulating layer 953).By providing the partition layer 954 in this way, failure of the light-emitting element due to static electricity or the like can be prevented. The passive matrix light-emitting device also includes the structure shown in FIG. Fig. 1A or Fig. 1B, which has high emission efficiency, can therefore consume less power. Furthermore, since the light-emitting element is easily mass-produced, the light-emitting device can be provided at low cost.

[0160] Since many microfine light-emitting elements in a matrix can be respectively controlled in the light-emitting device described above, the light-emitting device can be appropriately used as a display device for displaying images. (lighting device)

[0161] An example in which the Fig. 1A or Fig. 1B is used for a lighting device, is shown by Fig. 6A and Fig. 6B. Fig. 6B is a plan view of the lighting device, and Fig. 6A is a cross-sectional view taken along the line ef in Fig. 6B.

[0162] In the lighting device of this embodiment, a first electrode 401 is formed over a substrate 400, which is a support and has light transmittance. The first electrode 401 corresponds to the first electrode 101 in Fig. 1A. When light is taken out through the side of the first electrode 401, the first electrode 401 is formed using a material having light transmittance.

[0163] A contact pad 412 for applying a voltage to a second electrode 404 is provided above the substrate 400.

[0164] An EL layer 403 is formed over the first electrode 401. The structure of the EL layer 403 corresponds, for example, to the structure of the EL layer 103 in Fig. 1A or the structure in which the first light-emitting unit 511, the second light-emitting unit 512 and the charge generation layer 513 are arranged in Fig. 1B. Regarding these structures, reference can be made to the corresponding description.

[0165] The second electrode 404 is formed to cover the EL layer 403. The second electrode 404 corresponds to the second electrode 102 in Fig. 1A. The second electrode 404 is formed using a material with a high reflectance when light is extracted through the side of the first electrode 401. The second electrode 404 is connected to the pad 412, thereby applying a voltage thereto.

[0166] As described above, the lighting device of one embodiment of the present invention includes a light-emitting element including the first electrode 401, the EL layer 403, and the second electrode 404.

[0167] The light-emitting element with the above structure is attached to a sealing substrate 407 by means of sealing materials 405 and 406, and sealing is performed, thereby completing the lighting device. It is possible to use either the sealing material 405 or the sealing material 406 alone. Furthermore, the inner sealing material 406 (not shown) may be used. Fig. 6B) can be mixed with a desiccant, which allows the adsorption of moisture, resulting in increased reliability.

[0168] If parts of the contact pad 412 and the first electrode 401 extend outside the sealing materials 405 and 406, the extended parts can serve as external input terminals. An IC chip 420 on which a transducer or the like is mounted can be provided above the external input terminals.

[0169] Since the lighting device described in this embodiment, as described above, has the Fig. 1A or Fig. By incorporating the light-emitting element shown in Figure 1B as an EL element, the lighting device can have low power consumption. Furthermore, the light-emitting device can have a low operating voltage. Furthermore, the light-emitting device can be cost-effective. (electronic device)

[0170] Next, examples of electronic devices are described, each of which Fig. 1A or Fig. 1B. The light-emitting element shown in Fig. 1A or Fig. The light-emitting element shown in Figure 1B has high emission efficiency and reduced power consumption. As a result, the electronic devices described in this embodiment can each include a light-emitting portion with reduced power consumption. Fig. 1A or Fig. The light-emitting element shown in Figure 1B involves a smaller number of layers to be formed; therefore, the electronic devices can be inexpensive.

[0171] Examples of the electronic device to which the above light-emitting element is applied include televisions (also referred to as TVs or television receivers), monitors for computers and the like, cameras such as digital cameras and digital video cameras, digital photo frames, mobile phones (also referred to as cellular phones or portable telephones), portable game consoles, portable information terminals, audio playback devices, and large-scale gaming machines such as pinball machines. Specific examples of these electronic devices are given below.

[0172] Fig. Figure 7A shows an example of a television set. In the television set, a display section 7103 is installed in a housing 7101. In addition, the housing 7101 is supported by a stand 7105. Images can be displayed on the display section 7103 by Fig. 1A or Fig. 1B are arranged in a matrix.

[0173] The television can be operated using a control switch on the housing 7101 or a separate remote control 7110. Control buttons 7109 on the remote control 7110 can control the TV channels and volume, and images displayed on the display section 7103. Furthermore, the remote control 7110 can be provided with a display section 7107 for displaying data output from the remote control 7110.

[0174] It should be noted that the television is equipped with a receiver, a modem, and the like. The receiver can receive a general television broadcast. Furthermore, if the display device is connected to a communications network wirelessly or wired via the modem, unidirectional (from a transmitter to a receiver) or bidirectional (between a transmitter and a receiver, or between receivers) data communication can occur.

[0175] Fig. Fig. 7B1 illustrates a computer including a main body 7201, a housing 7202, a display section 7203, a keyboard 7204, an external connection terminal 7205, a pointing device 7206, and the like. It should be noted that this computer is manufactured by using light-emitting elements arranged in a matrix, which are similar to the Fig. 1A or Fig. 1B are used in the display section 7203. The computer in Fig. 7B1 can be a Fig. 7B2. A computer in Fig. 7B2 is provided with a second display section 7210 instead of the keyboard 7204 and the pointing device 7206. The second display section 7210 is a touchscreen, and input can be performed by controlling the input display on the second display section 7210 with a finger or an associated stylus. The second display section 7210 can also display images other than the input display. The display section 7203 can also be a touchscreen. Connecting the two screens by means of a hinge can prevent problems; for example, it can prevent the screens from being cracked or damaged while the computer is stored or being carried. It should be noted that this computer can be made by arranging the Fig. 1A or Fig. 1B is formed in a matrix in the display section 7203.

[0176] Fig. Figure 7C illustrates a portable game console including two housings, a housing 7301 and a housing 7302, which are connected via a hinge portion 7303 so that the portable game console can be opened or folded. The housing 7301 includes a display portion 7304 containing the light-emitting elements arranged in Fig. 1A or Fig. 1B and arranged in a matrix, and the housing 7302 includes a display section 7305. In addition, the portable game console in Fig. 7C, a speaker section 7306, a recording medium insertion section 7307, an LED lamp 7308, an input means (an operation button 7309, a connection terminal 7310, a sensor 7311 (a sensor with a function of measuring force, displacement, position, speed, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays) or a microphone 7312), and the like. Of course, the structure of the portable game console is not limited to the above structure, as long as the display section including the light-emitting elements, each in Fig. 1A or Fig. 1B and arranged in a matrix, is used as the display section 7304 and / or the display section 7305, and the structure may include other accessories as required. The portable game console in Fig. 7C has a function for reading a program or data stored in a storage medium to display it on the display section, and a function for sharing information with another portable game console via wireless communication. The portable game console in Fig. 7C may have various functions without limitation to the above functions.

[0177] Fig. 7D illustrates an example of a mobile phone. The mobile phone is equipped with a display section 7402 installed in a housing 7401, an operation button 7403, an external connection terminal 7404, a speaker 7405, a microphone 7406, and the like. It should be noted that the mobile phone includes the display section 7402, which includes the light-emitting elements, each of which Fig. 1A or Fig. 1B and are arranged in a matrix.

[0178] When the display section 7402 of the mobile phone is in Fig. 7D is touched with a finger or the like, data can be input into the mobile phone. In this case, operations such as making a call and sending an email can be performed by touching the display section 7402 with a finger or the like.

[0179] There are mainly three screen modes of the display section 7402. The first mode is a display mode, primarily used to display images. The second mode is an input mode, primarily used to input data such as text. The third mode is a display and input mode, which combines two modes: display mode and input mode.

[0180] For example, in the case of making a call or composing an email, a text input mode for primarily inputting text is selected for the display section 7402 so that the text displayed on a screen can be input. In this case, it is preferable that a keyboard or a numeric keypad be displayed on almost the entire screen of the display section 7402.

[0181] When a detection device having a sensor for detecting an inclination, such as a gyroscope or an acceleration sensor, is provided in the mobile phone, the direction of the mobile phone (whether the mobile phone is held horizontally or vertically, for landscape or portrait mode) is determined, so that the display on the screen of the display section 7402 can be automatically switched.

[0182] The screen modes are switched by touching the display section 7402 or by operating the operation knob 7403 of the case 7401. The screen modes can be switched depending on the type of images displayed on the display section 7402. For example, if a signal of an image displayed on the display section is a moving image data signal, the screen mode is switched to the display mode. If the signal is a text data signal, the screen mode is switched to the input mode.

[0183] Furthermore, in the input mode, when the input by touching the display section 7402 is not performed for a certain period of time while detecting a signal detected by an optical sensor in the display section 7402, the screen mode can be controlled to switch from the input mode to the display mode.

[0184] The display section 7402 can serve as an image sensor. For example, an image of a palm print, a fingerprint, or the like is captured by touching the display section 7402 with the palm or finger, thereby performing personal authentication. Furthermore, an image of a finger vein, a palm vein, or the like can be captured by providing a backlight or a scanning light source that emits light in the near-infrared range in the display section.

[0185] As described above, the application area of ​​the light-emitting device that Fig. 1A or Fig. 1B, so that the light-emitting device can be applied to electronic devices in various fields. Using the light-emitting element shown in Fig. 1A or Fig. 1B, an electronic device with reduced power consumption can be obtained.

[0186] Fig. Figure 8 shows an example of a liquid crystal display device in which the Fig. 1A or Fig. 1B is used for a backlight. The liquid crystal display device in Fig. 8 includes a housing 901, a liquid crystal layer 902, a backlight unit 903 and a housing 904. The liquid crystal layer 902 is connected to a driver IC 905. The Fig. 1A or Fig. The light-emitting element shown in Figure 1B is used for the backlight unit 903, which is supplied with power via a terminal 906.

[0187] The Fig. 1A or Fig. The light-emitting element shown in Figure 1B is used for the backlight of the liquid crystal display device. Therefore, the backlight can have reduced power consumption. The use of the light-emitting element shown in Fig. 1A or Fig. 1B additionally enables the manufacture of a planar emission illumination device and further enables the manufacture of a large-area planar emission illumination device; therefore, the backlight can be a large-area backlight, and the liquid crystal display device can also be a large-area device. In addition, the light-emitting device in which the Fig. 1A or Fig. 1B, the light-emitting element used may be thinner than a conventional light-emitting device. Accordingly, the display device may also be thinner.

[0188] Fig. 9 shows an example in which the Fig. 1A or Fig. 1B is used for a table lamp, which is a lighting device. The table lamp in Fig. 9 includes a housing 2001 and a light source 2002. The Fig. 1A or Fig. The lighting element shown in Figure 1B is used for the light source 2002.

[0189] Fig. 10 shows an example in which the Fig. 1A or Fig. 1B is used for an interior lighting device 3001. Since the light-emitting element shown in Fig. 1A or Fig. 1B can have a large area, the light-emitting element can be used for a large-area lighting device. Furthermore, since the light-emitting element shown in Fig. 1A or Fig. 1B is thin, the light-emitting element can be used for a lighting device with a reduced thickness.

[0190] The Fig. 1A or Fig. The light-emitting element shown in Figure 1B can also be used for a car windshield or a car dashboard. Fig. 11 shows an embodiment in which the Fig. 1A or Fig. 1B is used for a car windshield and a car dashboard. Display areas 5000 to 5005 each include the Fig. 1A or Fig. Light-emitting element shown in Figure 1B.

[0191] The display area 5000 and the display area 5001 are provided in the car windshield, in which the Fig. 1A or Fig. 1B are installed. The light-emitting elements shown in Fig. 1A or Fig. The light-emitting element shown in FIG. 1B can be manufactured as a so-called transparent display device through which the opposite side can be seen by including a first electrode and a second electrode formed using electrodes with light transmissivity. Such a transparent display device does not impair visibility and can therefore be provided in the car windshield. Note that in the case where a transistor is provided for driving or the like, it is preferable to use a transistor with light transmissivity, such as an organic transistor using an organic semiconductor material or a transistor using an oxide semiconductor.

[0192] In a column area, a display area 5002 is provided in which the Fig. 1A or Fig. 1B is installed. The display area 5002 can supplement the view obstructed by the pillar area by displaying an image captured by an imaging unit in the body. The display area 5003 in the instrument panel can similarly supplement the view obstructed by the body by displaying an image captured by an imaging unit outside the body, resulting in the elimination of blind spots and an increase in safety. Displaying a supplementary image for the area that a driver cannot see allows the driver to easily and conveniently determine safety.

[0193] Display areas 5004 and 5005 can display various types of information, such as navigation data, a speedometer, a tachometer, a mileage reading, a fuel gauge, a gearshift indicator, and air conditioning settings. The content or layout of the display can be appropriately changed by a user. Note that such information can also be displayed by display areas 5000 to 5003. Display areas 5000 to 5005 can also be used as lighting devices.

[0194] The Fig. 1A or Fig. The light-emitting element shown in Figure 1B can exhibit high emission efficiency and low power consumption. Therefore, the load on a battery is small even when many large screens, such as the display areas 5000 to 5005, are provided, resulting in convenient use. For this reason, the light-emitting device and the illumination device, each of which has the Fig. 1A or Fig. 1B, can be used as an in-vehicle light-emitting device and an in-vehicle lighting device as needed.

[0195] Fig. 12A and Fig. 12B illustrate an example of a foldable tablet computer. The tablet computer is in Fig. 12A and includes a housing 9630, a display section 9631a, a display section 9631b, a button 9034 for switching the display mode, a power switch 9035, a button 9036 for switching the power saving mode, a clasp 9033 and an operation button 9038. It should be noted that in the tablet computer, the display section 9631a and / or the display section 9631b is / are formed using a light-emitting device that displays the Fig. 1A or Fig. 1B shown light emitting element.

[0196] A part of the display section 9631a may be a touchscreen area 9632a, and data can be input when a displayed operation button 9637 is touched. Although a structure in which half of the display section 9631a has only a display function and the other half also has a touchscreen function is exemplified, the structure of the display section 9631a is not limited thereto. The entire area of ​​the display section 9631a may have a touchscreen function. For example, the entire area of ​​the display section 9631a may display a keyboard button and serve as a touchscreen, while the display section 9631b may be used as a display screen.

[0197] As with the display portion 9631a, a part of the display portion 9631b may be a touchscreen area 9632b. When a switch button 9639 for displaying / hiding a keyboard on the touchscreen is touched with a finger, a stylus, or the like, the keyboard may be displayed on the display portion 9631b.

[0198] A touch-sensitive input can be performed on the touchscreen areas 9632a and 9632b simultaneously.

[0199] For example, the display mode switching button 9034 allows switching between portrait and landscape modes, and between monochrome and color displays. The power saving mode switching button 9036 allows the tablet computer to optimize the display luminance according to the amount of external light detected by an optical sensor in the tablet computer. The tablet computer may include another detection device, such as an orientation sensor (e.g., a gyroscope or an accelerometer), in addition to the optical sensor.

[0200] Although the display section 9631a and the display section 9631b in Fig. 12A have the same display area, an embodiment of the present invention is not limited to this example. The display section 9631a and the display section 9631b may have different areas or different display qualities. For example, one of them may be a display panel that can display images with higher resolution than the other.

[0201] In Fig. 12B, the tablet computer is folded and includes the housing 9630, a solar cell 9633, a charge and discharge control circuit 9634, a battery 9635, and a DC-DC converter 9636. It should be noted that Fig. 12B illustrates an example in which the charge and discharge control circuit 9634 includes the battery 9635 and the DC-DC converter 9636.

[0202] Since the tablet computer is foldable, the casing 9630 can be closed when the tablet computer is not in use. Consequently, the display sections 9631a and 9631b can be protected, thereby providing a tablet computer with high durability and high reliability for long-term use.

[0203] The tablet computer in Fig. 12A and Fig. 12B may also have a function of displaying various types of data (e.g., a still image, a moving image, and a text image), a function of displaying a calendar, a date, a time, or the like on the display section, a touch input function of operating or editing data displayed on the display section by touch input, a function of controlling processing by various types of software (programs), and the like.

[0204] The solar cell 9633, which is attached to the surface of the tablet computer, supplies electric power to a touchscreen, a display section, an image signal processor, and the like. Note that the solar cell 9633 is preferably arranged on one or two surfaces of the housing 9630, allowing the battery 9635 to be charged efficiently.

[0205] The structure and operation of the charge and discharge control circuit 9634 in Fig. 12B are shown in a block diagram in Fig. 12C described. Fig. 12C illustrates the solar cell 9633, the battery 9635, the DC-DC converter 9636, a converter 9638, switches SW1 to SW3, and the display section 9631. The battery 9635, the DC-DC converter 9636, the converter 9638, and the switches SW1 to SW3 correspond to the charge and discharge control circuit 9634 in Fig. 12B.

[0206] First, an example of operation in the case where power is generated by the solar cell 9633 using external light will be described. The voltage of the power generated by the solar cell is increased or decreased by the DC-DC converter 9636 so that the power has a voltage for charging the battery 9635. Then, when power from the battery 9635 charged by the solar cell 9633 is used to operate the display section 9631, the switch SW1 is turned on, and the voltage of the power is increased or decreased by the converter 9638 to become a voltage necessary for the display section 9631. In addition, when the display on the display section 9631 is not performed, the switch SW1 is turned off, and a switch SW2 is turned on so that charging of the battery 9635 can be performed.

[0207] Although the solar cell 9633 is described as an example of a power generation means, there is no particular limitation on the power generation means, and the battery 9635 may be charged by another power generation means, such as a piezoelectric element or a thermoelectric conversion element (Peltier element). The battery 9635 may be charged by a non-contact power transmission module that can perform charging by wireless (contactless) transmission and reception of power, or another charging means used in combination, and the power generation means is not necessarily provided.

[0208] An embodiment of the present invention is not limited to the tablet computer with the Fig. 12A to Fig. 12C as long as the display section 9631 is included. [Example 1]

[0209] In this example, methods for manufacturing light-emitting elements 1 to 3, each of which is an embodiment of the present invention, and a light-emitting element 4, which is a comparative light-emitting element, and their properties are described. Structural formulas of organic compounds used for light-emitting elements 1 to 4 are shown below. (Method for manufacturing the light-emitting element 1)

[0210] A film of indium tin oxide containing silicon oxide (ITSO) was formed over a glass substrate by a sputtering method, forming the first electrode 101. The thickness was 110 nm and the electrode area was 2 mm × 2 mm. Here, the first electrode 101 serves as the anode of the light-emitting element.

[0211] Next, in the pretreatment for forming the light-emitting element over the substrate, a surface of the substrate was washed with water and baked at 200 °C for one hour, and then UV-ozone treatment was performed for 370 seconds.

[0212] The substrate was then transferred to a vacuum evaporation device where the pressure was increased to approximately 10 -4 Pa, and was heated for 30 minutes in vacuum at 170 °C in a heating chamber of the vacuum evaporation device, and then the substrate was cooled for about 30 minutes.

[0213] Then, the substrate provided with the first electrode 101 was attached to a substrate holder in the vacuum evaporation device so that the surface on which the first electrode 101 was formed was facing downward. The pressure in the vacuum evaporation device was set to about 10 -4Pa. Next, 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), represented by the structural formula (i), and molybdenum(VI) oxide were co-evaporated onto the first electrode 101 by a resistive heating evaporation method, thereby forming the hole-injection layer 111. The thickness was set to 40 nm, and the weight ratio of DBT3P-II to molybdenum oxide was set to 4:2 (=DBT3P-II:molybdenum oxide). Note that the co-evaporation method refers to an evaporation method in which evaporation is performed simultaneously from a plurality of evaporation sources in a treatment chamber.

[0214] Next, 3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPPn), which is represented by the structural formula (ii), was deposited on the hole injection layer 111 to a thickness of 20 nm, so that the hole transport layer 112 was formed.

[0215] On the hole transport layer 112, 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole (abbreviation: cgDBCzPA), which is represented by the structural formula (iii), and N,N-bis(3-methylphenyl)-N,N-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPrn), which is represented by the structural formula (iv), were co-evaporated to a thickness of 5 nm, so that the weight ratio of cgDBCzPA to 1,6mMemFLPAPrn was 1:0.03 (= cgDBCzPA: 1,6mMemFLPAPrn); In this way, the first light-emitting layer 113a, which was a fluorescent layer, was formed.Next, 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), represented by the structural formula (v), and N-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF), represented by the structural formula (vi), were co-deposited to a thickness of 2 nm by co-evaporation such that the weight ratio of 2mDBTBPDBq-II to PCBBiF was 0.6:0.4 (= 2mDBTBPDBq-II: PCBBiF); thus, the separation layer 113b was formed. Then, the first phosphorescent layer 113c-1 was formed such that 2mDBTBPDBq-II, PCBBiF and bis{4,6-dimethyl-2-[5-(2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-κN]phenyl-κC} (2,4-pentanedionato-κ. 2O,O')iridium(III) (abbreviation: [Ir(dmdppr-dmp)2(acac)]), which is represented by the structural formula (vii), was deposited by co-evaporation to a thickness of 5 nm, so that the weight ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(dmdppr-dmp)2(acac)] was 0.2:0.8:0.05 (= 2mDBTBPDBq-II: PCBBiF: [Ir(dmdppr-dmp)2(acac)]); the second phosphorescent layer 113c-2 was then formed such that 2mDBTBPDBq-II, PCBBiF and bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ 2O,O')iridium(III)) (abbreviation: [Ir(tBuppm)2(acac)]), represented by the structural formula (viii), was deposited by co-evaporation to a thickness of 20 nm, such that the weight ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(tBuppm)2(acac)] was 0.7:0.3:0.05 (= 2mDBTBPDBq-II: PCBBiF: [Ir(tBuppm)2(acac)]). Through the above steps, the second light-emitting layer 113c, which was a phosphorescent layer, was formed. In the light-emitting element 1, the light-emitting layer 113 includes the first light-emitting layer 113a and the second light-emitting layer 113c.

[0216] Note that 2mDBTBPDBq-II and PCBBiF form an exciplex in the phosphorescent layer (the second light-emitting layer 113c). This emission wavelength overlaps with absorption bands on the longest wavelength sides of [Ir(dmdppr-dmp)2(acac)] and [Ir(tBuppm)2(acac)], so the energy transfer efficiency is high.

[0217] The singlet excitation energy of cgDBCzPA, which is a host material in the fluorescent layer (the first light-emitting layer 113a), is higher than the singlet excitation energy of 1.6mMemFLPAPrn, which is a fluorescent substance. Furthermore, the triplet excitation energy of cgDBCzPA is lower than the triplet excitation energy of 1.6mMemFLPAPrn. Therefore, singlet exciton regeneration coupled with triplet-triplet annihilation and light emission are easily obtained in the fluorescent layer (the first light-emitting layer 113a).

[0218] Thereafter, on the phosphorescent layer (the second light-emitting layer 113c), 2mDBTBPDBq-II was deposited to a thickness of 10 nm, and bathophenanthroline (abbreviation: BPhen), which is represented by the structural formula (ix), was deposited to a thickness of 15 nm, so that the electron transport layer 114 was formed.

[0219] After forming the electron-transport layer 114, lithium fluoride (LiF) was deposited by evaporation to a thickness of 1 nm to form the electron-injection layer 115. Finally, aluminum was deposited by evaporation to a thickness of 200 nm to form the second electrode 102, which served as the cathode. Through the above steps, the light-emitting element 1 of this example was manufactured.

[0220] It should be noted that in all the above evaporation steps, evaporation was carried out by a resistance heating method. (Method for manufacturing the light-emitting elements 2 and 3)

[0221] The light-emitting element 2 and the light-emitting element 3 are elements in which the thickness of the separation layer 113b of the light-emitting element 1 is changed to 5 nm and 10 nm, respectively. (Method for manufacturing the light-emitting element 4)

[0222] The light-emitting element 4 has a structure in which the separation layer 113b of the structure of the light-emitting element 1 is not present.

[0223] In a glove box in a nitrogen atmosphere, light-emitting elements 1 to 4 were each sealed with a glass substrate to prevent exposure to air (specifically, a sealing material was applied to an outer edge of the element, and at the time of sealing, a UV treatment was performed, followed by a heat treatment at 80°C for one hour). The reliability of these light-emitting elements was then measured. Note that the measurement was conducted at room temperature (in an atmosphere maintained at 25°C).

[0224] Table 1 shows the element structures of the light-emitting elements 1 to 4. [Table 1] Lochinjektionsschicht Lochtransportschicht erste LichtemittierendeSchicht Trennschicht zweite LichtemittierendeSchicht Elektronentransportschicht Elektroneninjektionsschicht DBT3P-II: MoOx PCPPn cgDBCzPA: 1,6mMemFLPAPrn * ** *** 2mDBTBPDBq-II BPhen LiF 2:1 1:0,03 40 nm 20 nm 5 nm x 5 nm 20 nm 10 nm 15 nm 1 nm * 2mDBTBPDBq-II:PCBBiF = 0.6:0.4 X Light-emitting element 1: 2 nm, light-emitting element 2: 5 nm, light-emitting element 3: 10 nm, light-emitting element 40 nm ** 2mDBTBPDBq-II: PCBBiF: Ir(dmdppr-dmp)2(acac) = 0.2:0.8:0.05 *** 2mDBTBPDBq-II: PCBBiF: Ir(tBuppm)2(acac) = 0.7:0.3:0.05

[0225] Fig. Figure 13 shows current density-luminance characteristics of the light-emitting elements 1 to 4. Fig.Figure 14 shows luminance-current efficiency characteristics of the light-emitting elements 1 to 4. Fig. Figure 15 shows voltage-luminance characteristics of the light-emitting elements 1 to 4. Fig. Figure 16 shows luminance-external quantum efficiency characteristics of the light-emitting elements 1 to 4. Fig. Figure 17 shows the emission spectra of the light-emitting elements 1 to 4.

[0226] Although the light-emitting elements 1 to 4 did not include an intermediate layer, the light-emitting elements 1 to 4, as can be seen from the characteristics, had a current efficiency of 40 cd / A or higher at about 1000 cd / m 2 and an external quantum efficiency of 18% or higher. This indicates that light-emitting elements 1 to 4 exhibited high emission efficiency. The operating voltage was approximately 1000 cd / m 2is very low, i.e., it is in the 3 V range, which is much lower than the operating voltage of a tandem light-emitting element. Furthermore, light-emitting elements 1 to 3 each exhibited very favorable efficiency: an external quantum efficiency of 19% or higher at approximately 1000 cd / m 2 . Table 2 shows values ​​of main properties of the light-emitting elements 1 to 4 at about 1000 cd / m 2 . [Table 2] Voltage (V) Current density (mA / cm 2 ) Power efficiency (cd / A) Power efficiency (lm / W) external quantum yield (%) Energy efficiency (%) correlated color temperature (K) duv Light-emitting element 1 3,1 1,8 47 48 20 14 2570 0,011 Light-emitting element 2 32 20 43 42 19 13 2520 0.01 Light-emitting element 3 3,3 2,8 40 38 19 12 2180 0,006 Light-emitting element 4 3,2 2,5 45 44 18 12 2930 0,016

[0227] Furthermore, the emission spectrum in Fig.17, red light emission originating from [Ir(dmdppr-dmp)2(acac)], green light emission originating from [Ir(tBuppm)2(acac)], and blue light emission originating from 1.6mMemFLPAPrn were observed. This indicates that sufficient light emission was obtained from both the first light-emitting layer 113a, which was a fluorescent layer, and the second light-emitting layer 113c, which was a phosphorescent layer.

[0228] As described above, the light-emitting elements 1 to 4 exhibited highly well-balanced, advantageous properties and could be manufactured easily and inexpensively. The above-described results were attributed to the following: by using the exciplex as the energy donor of the phosphorescent layer, exciton diffusion was suppressed and non-radiative decay of the triplet excitation energy was reduced, and the emission efficiency was increased due to the appearance of delayed fluorescence due to triplet-triplet annihilation in the host material in the fluorescent layer. By using the separation layer 113b, energy transfer from the phosphorescent layer (the second light-emitting layer 113c) to the fluorescent layer (the first light-emitting layer 113a) at their interface is suppressed; therefore, the light-emitting elements 1 to 3 can exhibit even better properties. [Example 2]

[0229] In this example, a method for manufacturing a light-emitting element 5 according to one embodiment of the present invention and its properties are described. Structural formulas of organic compounds used for the light-emitting element 5 are shown below. (Method for manufacturing the light-emitting element 5)

[0230] A film of indium tin oxide containing silicon oxide (ITSO) was formed over a glass substrate by a sputtering method, forming the first electrode 101. The thickness was 110 nm and the electrode area was 2 mm × 2 mm. Here, the first electrode 101 serves as the anode of the light-emitting element.

[0231] Next, in the pretreatment for forming the light-emitting element over the substrate, a surface of the substrate was washed with water and baked at 200 °C for one hour, and then UV-ozone treatment was performed for 370 seconds.

[0232] The substrate was then transferred to a vacuum evaporation device where the pressure was increased to approximately 10 -4 Pa, and was heated for 30 minutes in vacuum at 170 °C in a heating chamber of the vacuum evaporation device, and then the substrate was cooled for about 30 minutes.

[0233] Then, the substrate provided with the first electrode 101 was attached to a substrate holder in the vacuum evaporation device so that the surface on which the first electrode 101 was formed was facing downward. The pressure in the vacuum evaporation device was set to about 10 -4Pa. Next, 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), represented by the structural formula (i), and molybdenum(VI) oxide were co-evaporated onto the first electrode 101 by a resistive heating evaporation method, thereby forming the hole-injection layer 111. The thickness was set to 40 nm, and the weight ratio of DBT3P-II to molybdenum oxide was set to 4:2 (=DBT3P-II:molybdenum oxide). Note that the co-evaporation method refers to an evaporation method in which evaporation is performed simultaneously from a plurality of evaporation sources in a treatment chamber.

[0234] Next, 3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPPn), which is represented by the structural formula (ii), was deposited on the hole injection layer 111 to a thickness of 10 nm, so that the hole transport layer 112 was formed.

[0235] On the hole transport layer 112, 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole (abbreviation: cgDBCzPA), which is represented by the structural formula (iii), and N,N-bis(3-methylphenyl)-N,N-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPrn), which is represented by the structural formula (iv), were co-evaporated to a thickness of 5 nm, so that the weight ratio of cgDBCzPA to 1,6mMemFLPAPrn was 1:0.04 (= cgDBCzPA: 1,6mMemFLPAPrn); In this way, the first light-emitting layer 113a, which was a fluorescent layer, was formed.Next, 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), represented by the structural formula (v), and N-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF), represented by the structural formula (vi), were co-deposited to a thickness of 2 nm by co-evaporation such that the weight ratio of 2mDBTBPDBq-II to PCBBiF was 0.6:0.4 (= 2mDBTBPDBq-II: PCBBiF); thus, the separation layer 113b was formed. Then, the first phosphorescent layer 113c-1 was formed such that 2mDBTBPDBq-II, PCBBiF and bis{4,6-dimethyl-2-[5-(2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-κN]phenyl-κC} (2,4-pentanedionato-κ. 2O,O')iridium(III) (abbreviation: [Ir(dmdppr-dmp)2(acac)]), which is represented by the structural formula (vii), was deposited by co-evaporation to a thickness of 5 nm, so that the weight ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(dmdppr-dmp)2(acac)] was 0.5:0.5:0.05 (= 2mDBTBPDBq-II: PCBBiF: [Ir(dmdppr-dmp)2(acac)]); the second phosphorescent layer 113c-2 was then formed such that 2mDBTBPDBq-II, PCBBiF and bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ 2 O,O')iridium(III)) (abbreviation: [Ir(tBuppm)2(acac)]), represented by the structural formula (viii), was deposited by co-evaporation to a thickness of 20 nm, such that the weight ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(tBuppm)2(acac)] was 0.7:0.3:0.05 (= 2mDBTBPDBq-II: PCBBiF: [Ir(tBuppm)2(acac)]). Through the above steps, the second light-emitting layer 113c, which was a phosphorescent layer, was formed.

[0236] Note that 2mDBTBPDBq-II and PCBBiF form an exciplex in the phosphorescent layer (the second light-emitting layer 113c). This emission wavelength overlaps with absorption bands on the longest wavelength sides of [Ir(dmdppr-dmp)2(acac)] and [Ir(tBuppm)2(acac)], so the energy transfer efficiency is high.

[0237] The singlet excitation energy of cgDBCzPA, which is a host material in the fluorescent layer (the first light-emitting layer 113a), is higher than the singlet excitation energy of 1.6mMemFLPAPrn, which is a fluorescent substance. Furthermore, the triplet excitation energy of cgDBCzPA is lower than the triplet excitation energy of 1.6mMemFLPAPrn. Therefore, singlet exciton regeneration coupled with triplet-triplet annihilation and light emission are easily obtained in the fluorescent layer (the first light-emitting layer 113a).

[0238] Thereafter, on the phosphorescent layer (the second light-emitting layer 113c), 2mDBTBPDBq-II was deposited to a thickness of 10 nm, and bathophenanthroline (abbreviation: BPhen), which is represented by the structural formula (ix), was deposited to a thickness of 15 nm, so that the electron transport layer 114 was formed.

[0239] After forming the electron-transport layer 114, lithium fluoride (LiF) was deposited by evaporation to a thickness of 1 nm to form the electron-injection layer 115. Finally, aluminum was deposited by evaporation to a thickness of 200 nm to form the second electrode 102, which served as the cathode. Through the above steps, the light-emitting element 5 of this example was manufactured.

[0240] It should be noted that in all the above evaporation steps, evaporation was carried out by a resistance heating method.

[0241] In a glove box in a nitrogen atmosphere, the light-emitting element 5 was sealed with a glass substrate to prevent exposure to air (specifically, a sealing material was applied to an outer edge of the element, and at the time of sealing, a UV treatment was performed, followed by a heat treatment at 80°C for one hour). The reliability of the light-emitting element was then measured. Note that the measurement was conducted at room temperature (in an atmosphere maintained at 25°C).

[0242] Table 3 shows the element structures of the light-emitting element 5. [Table 3] Hole injection layer Hole transport layer first light-emitting layer Separating layer second light-emitting layer Electron layer ansportnt Electron injection layer DBT3P-II: MoOx PCPPn cgDBCzPA: 1.6mMemFLPAPrn * ** *** 2mDBTBPDBq-II BPhen LiF 2:1 1:0,04 40 nm 10 nm 5 nm 2 nm 5 nm 20 nm 10 nm 15 nm 1 nm * 2mDBTBPDBq-II:PCBBiF = 0.6:0.4 ** 2mDBTBPDBq-II:PCBBiF:Ir(dmdppr-dmp)2(acac) = 0.5:0.5:0.05 *** 2mDBTBPDBq-II:PCBBiF:Ir(tBuppm)2(acac) = 0.7:0.3:0.05

[0243] Regarding the light-emitting element 5, Fig. 18 the current density-luminance properties, shows Fig. 19 the luminance-current efficiency characteristics, shows Fig. 20 the voltage-luminance properties, shows Fig. 21 the luminance-external quantum efficiency properties, shows Fig. 22 the emission spectrum, and shows Fig. 23 the luminance-CIE chromaticity properties.

[0244] Although the light-emitting element 5 did not include an intermediate layer, the light-emitting element 5, as can be seen from the characteristics, had a current efficiency of 40 cd / A or higher at about 1000 cd / m 2and an external quantum efficiency of 18% or higher. This indicates that the light-emitting element 5 exhibited high emission efficiency. The operating voltage is very low, i.e., in the 3 V range, which is much lower than the operating voltage of a tandem light-emitting element. Table 4 shows values ​​of the main characteristics of the light-emitting element 5 at approximately 1000 cd / m². 2 . [Table 4] Voltage (V) Current density (mA / cm 2 ) Power efficiency (cd / A) Power efficiency (Im / W) external quantum yield (%) Energy efficiency (%) correlated color temperature (K) duv Light-emitting element 5 3,2 2,5 46 46 18 12 3010 0,017

[0245] Furthermore, the emission spectrum in Fig.22, red light emission originating from [Ir(dmdppr-dmp)2(acac)], green light emission originating from [Ir(tBuppm)2(acac)], and blue light emission originating from 1.6mMemFLPAPrn were observed. This indicates that sufficient light emission was obtained from both the first light-emitting layer 113a, which was a fluorescent layer, and the second light-emitting layer 113c, which was a phosphorescent layer.

[0246] The luminance-CIE chromaticity properties in Fig. 23 indicate that the light-emitting element 5 exhibits a very small color change in the practical luminance range. It should be noted that the color change occurs at about 100 cd / m 2due to a difference between the emission start voltage for phosphorescence and that for fluorescence. Since the phosphorescence layer has a lower emission start voltage than the fluorescent layer, only phosphorescence is observed in a low luminance range, and fluorescence is also observed at about 100 cd / m 2 For this reason, the color change occurs at about 100 cd / m 2 In the practical luminance range, where both fluorescence and phosphorescence are stable, the color change is very small.

[0247] As described above, the light-emitting element 5 exhibited highly well-balanced, advantageous properties and could be manufactured easily and inexpensively. The above-described results were attributed to the following: by using the exciplex as the energy donor of the phosphorescent layer, exciton diffusion was suppressed and non-radiative decay of the triplet excitation energy was reduced, and the emission efficiency was increased due to the appearance of delayed fluorescence due to triplet-triplet annihilation in the host material in the fluorescent layer. By using the separation layer 113b, energy transfer from the phosphorescent layer (the second light-emitting layer 113c) to the fluorescent layer (the first light-emitting layer 113a) at their interface is suppressed; therefore, the light-emitting element 5 can exhibit even better properties. [Example 3]

[0248] In this example, methods for manufacturing light-emitting elements 6 and 7, each of which is an embodiment of the present invention, and their properties are described. Structural formulas of organic compounds used for light-emitting elements 6 and 7 are shown below. (Method for manufacturing the light-emitting element 6)

[0249] A film of indium tin oxide containing silicon oxide (ITSO) was formed over a glass substrate by a sputtering method, forming the first electrode 101. The thickness was 110 nm and the electrode area was 2 mm × 2 mm. Here, the first electrode 101 serves as the anode of the light-emitting element.

[0250] Next, in the pretreatment for forming the light-emitting element over the substrate, a surface of the substrate was washed with water and baked at 200 °C for one hour, and then UV-ozone treatment was performed for 370 seconds.

[0251] The substrate was then transferred to a vacuum evaporation device where the pressure was increased to approximately 10 -4 Pa, and was heated for 30 minutes in vacuum at 170 °C in a heating chamber of the vacuum evaporation device, and then the substrate was cooled for about 30 minutes.

[0252] Then, the substrate provided with the first electrode 101 was attached to a substrate holder in the vacuum evaporation device so that the surface on which the first electrode 101 was formed was facing downward. The pressure in the vacuum evaporation device was set to about 10 -4Pa. Next, 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), represented by the structural formula (i), and molybdenum(VI) oxide were co-evaporated onto the first electrode 101 by a resistive heating evaporation method, thereby forming the hole-injection layer 111. The thickness was set to 30 nm, and the weight ratio of DBT3P-II to molybdenum oxide was set to 2:1 (= DBT3P-II: molybdenum oxide).

[0253] Next, 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: PCzPA), which is represented by the structural formula (x), was deposited on the hole injection layer 111 to a thickness of 20 nm, so that the hole transport layer 112 was formed.

[0254] On the hole-transport layer 112, PCzPA and 1.6mMemFLPAPrn were co-evaporated to a thickness of 5 nm such that the weight ratio of PCzPA to 1.6mMemFLPAPrn was 1:0.05 (= PCzPA: 1.6mMemFLPAPrn); thus, the first light-emitting layer 113a, which was a fluorescent layer, was formed. Next, 4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine (abbreviation: 4,6mCzP2Pm), represented by the structural formula (xi), and 4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP), represented by the structural formula (xii), were co-deposited to a thickness of 2 nm by co-evaporation such that the weight ratio of 4,6mCzP2Pm to CBP was 0.4:0.6 (= 4,6mCzP2Pm: CBP); thus, the separation layer 113b was formed.Then, 2mDBTBPDBq-II, PCBBiF, and (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]), represented by the structural formula (xiii), were deposited by co-evaporation to a thickness of 20 nm such that the weight ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(dppm)2(acac)] was 0.8:0.2:0.05 (= 2mDBTBPDBq-II: PCBBiF: [Ir(dppm)2(acac)]); thus, the second light-emitting layer 113c, which was a phosphorescent layer, was formed.

[0255] Note that 2mDBTBPDBq-II and PCBBiF form an exciplex in the phosphorescent layer (the second light-emitting layer 113c). This emission wavelength overlaps with absorption bands on the longest wavelength side of [Ir(dppm)2(acac)], so the energy transfer efficiency is high.

[0256] The singlet excitation energy of PCzPA, which is a host material in the fluorescent layer (the first light-emitting layer 113a), is higher than the singlet excitation energy of 1.6mMemFLPAPrn, which is a fluorescent substance. Furthermore, the triplet excitation energy of PCzPA is lower than the triplet excitation energy of 1.6mMemFLPAPrn. Therefore, singlet exciton regeneration coupled with triplet-triplet annihilation and light emission are easily obtained in the fluorescent layer (the first light-emitting layer 113a).

[0257] Thereafter, 2mDBTBPDBq-II was deposited on the phosphorescent layer (the second light-emitting layer 113c) to a thickness of 10 nm, and BPhen was deposited to a thickness of 15 nm, so that the electron transport layer 114 was formed.

[0258] After forming the electron-transport layer 114, lithium fluoride (LiF) was deposited by evaporation to a thickness of 1 nm to form the electron-injection layer 115. Finally, aluminum was deposited by evaporation to a thickness of 200 nm to form the second electrode 102, which served as the cathode. Through the above steps, the light-emitting element 6 of this example was manufactured.

[0259] It should be noted that in all the above evaporation steps, evaporation was carried out by a resistance heating method. (Method for manufacturing the light-emitting element 7)

[0260] The light-emitting element 7 was manufactured in the same manner as the light-emitting element 6, except that the separation layer 113b was formed from only 4.6mCzP2Pm.

[0261] In a glove box in a nitrogen atmosphere, the light-emitting elements 6 and 7 were each sealed with a glass substrate to prevent exposure to air (specifically, a sealing material was applied to an outer edge of the element, and at the time of sealing, a UV treatment was performed, followed by a heat treatment at 80°C for one hour). The reliability of these light-emitting elements was then measured. Note that the measurement was conducted at room temperature (in an atmosphere maintained at 25°C).

[0262] Table 5 shows the element structures of the light-emitting elements 6 and 7. [Table 5] Hole injection layer Hole transport layer first light-emitting layer Separating layer second light-emitting layer Electron transport layer Electron injection layer DBT3P-II: MoOx PCzPA PCzPA: 1.6mMemFLPAPrn * 2mDBTBPDBq-II: PCBBiF 2mDBTBPDBq-II BPhen LiF 2:1 1:0,05 : Ir(dppm)2(acac)0.8:0.2:0.05 30 nm 20 nm 10 nm 2 nm 20 nm 10 nm 15 nm 1 nm * Light-emitting element 6: 4.6mCzP2Pm:CBP = 0.4:0.6 Light-emitting element 7:4.6mCzP2Pm

[0263] Fig. Figure 24 shows current density-luminance characteristics of the light-emitting elements 6 and 7. Fig.Figure 25 shows luminance-current efficiency characteristics of the light-emitting elements 6 and 7. Fig. Figure 26 shows voltage-luminance characteristics of the light-emitting elements 6 and 7. Fig. Figure 27 shows luminance-external quantum efficiency characteristics of the light-emitting elements 6 and 7. Fig. Figure 28 shows the emission spectra of the light-emitting elements 6 and 7.

[0264] The above results show that the light-emitting element 6 and the light-emitting element 7 each have a favorable emission efficiency, namely a current efficiency of 20 cd / A or higher at about 1000 cd / m 2 ,. In addition, the operating voltage is in the 3 V range, which is much lower than that of a tandem light-emitting element. Table 6 shows the values ​​of the main characteristics of light-emitting elements 6 and 7 at approximately 1000 cd / m 2 . [Table 6] Voltage (V) Current density (mA / cm 2 ) Power efficiency (cd / A) Power efficiency (Im / W) external quantum yield (%) Energy efficiency (%) correlated color temperature (K) duv Light-emitting element 6 3,1 1,7 31 32 12 9 2710 0,003 Light-emitting element 7 3.3 4,8 23 22 10 6 3540 0.009

[0265] Furthermore, the emission spectrum shows that orange light emission originating from [Ir(dppm)2(acac)] and blue light emission originating from 1.6mMemFLPAPrn were observed. This indicates that in light-emitting elements 6 and 7, sufficient light emission was obtained from both the first light-emitting layer 113a, which was a fluorescent layer, and the second light-emitting layer 113c, which was a phosphorescent layer.

[0266] As described above, the light-emitting elements 6 and 7 exhibit highly well-balanced, advantageous properties and can be manufactured easily and inexpensively. The above-described results were attributed to the following: by using the exciplex as the energy donor of the phosphorescent layer, exciton diffusion was suppressed and non-radiative decay of the triplet excitation energy was reduced, and the emission efficiency was increased due to the appearance of delayed fluorescence due to triplet-triplet annihilation in the host material in the fluorescent layer. Furthermore, by using the separation layer 113b, energy transfer from the phosphorescent layer (the second light-emitting layer 113c) to the fluorescent layer (the first light-emitting layer 113a) at their interface is suppressed, which is also a reason for the advantageous properties.The light-emitting element 6 has better properties than the light-emitting element 7; therefore, the separation layer 113b is preferably formed from a substance with a hole-transport property and a substance with an electron-transport property. Furthermore, it is further preferred that these substances form an exciplex. [Example 4]

[0267] In this example, a method for manufacturing a light-emitting element 8 of one embodiment of the present invention and its characteristics will be described. In the light-emitting element 8, the first light-emitting layer 113a was formed on the cathode side, and the second light-emitting layer 113c was formed on the anode side. Structural formulas of organic compounds used for the light-emitting element 8 are shown below. (Method for manufacturing the light-emitting element 8)

[0268] A film of indium tin oxide (ITO) was formed over a glass substrate with a high refractive index (n = 1.84) to a thickness of 110 nm by a sputtering method, forming the first electrode 101. The electrode area was 2 mm × 2 mm.

[0269] Next, in the pretreatment for forming the light-emitting element over the substrate, a surface of the substrate was washed with water, and then UV-ozone treatment was performed for 370 seconds.

[0270] The substrate was then transferred to a vacuum evaporation device where the pressure was increased to approximately 10 -4 Pa, and was heated for 60 minutes in vacuum at 190 °C in a heating chamber of the vacuum evaporation device, and then the substrate was cooled for about 30 minutes.

[0271] Then, the substrate provided with the first electrode 101 was attached to a substrate holder in the vacuum evaporation device so that the surface on which the first electrode 101 was formed was facing downward. The pressure in the vacuum evaporation device was set to about 10 -4 Pa. Next, 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), represented by the structural formula (i), and molybdenum(VI) oxide were co-evaporated onto the first electrode 101 by a resistive heating evaporation method, thereby forming the hole-injection layer 111. The thickness was set to 30 nm, and the weight ratio of DBT3P-II to molybdenum oxide was set to 1:0.5 (=DBT3P-II:molybdenum oxide).

[0272] Next, N-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF), represented by the structural formula (vi), was deposited on the hole-injection layer 111 to a thickness of 20 nm; thus, the hole-transport layer 112 was formed.

[0273] Then, the first phosphorescence layer 113c-1 was formed on the hole transport layer 112 such that 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), which is represented by the structural formula (v), N-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF), which is represented by the structural formula (vi), and bis{4,6-dimethyl-2-[5-(2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-κN]phenyl-κC} (2,4-pentanedionato-κ 2O,O')iridium(III) (abbreviation: [Ir(dmdppr-dmp)2(acac)]), which is represented by the structural formula (vii), was deposited by co-evaporation to a thickness of 15 nm, so that the weight ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(dmdppr-dmp)2(acac)] was 0.1:0.9:0.06 (= 2mDBTBPDBq-II:PCBBiF:[Ir(dmdppr-dmp)2(acac)]); the second phosphorescent layer 113c-2 was then formed such that 2mDBTBPDBq-II, PCBBiF and bis[2-(6-tert-butyl-4-pyrimidinyl-κN3)phenyl-κC](2,4-pentanedionato-κ 2O,O')iridium(III)) (abbreviation: [Ir(tBuppm)2(acac)]), represented by the structural formula (viii), was deposited by co-evaporation to a thickness of 5 nm, such that the weight ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(tBuppm)2(acac)] was 0.5:0.5:0.06 (= 2mDBTBPDBq-II: PCBBiF: [Ir(tBuppm)2(acac)]). Through the above steps, the second light-emitting layer 113c, which was a phosphorescent layer, was formed. Thereafter, 2mDBTBPDBq-II and PCBBiF were co-evaporated to a thickness of 2 nm such that the weight ratio of 2mDBTBPDBq-II to PCBBiF was 0.5:0.5 (= 2mDBTBPDBq-II:PCBBiF); thus, the separation layer 113b was formed.Next, 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole (abbreviation: cgDBCzPA), represented by the structural formula (iii), and N,N'-bis(3-methylphenyl)-N,N'-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPrn), represented by the structural formula (iv), were co-evaporated to a thickness of 20 nm such that the weight ratio of cgDBCzPA to 1,6mMemFLPAPrn was 1:0.025 (= cgDBCzPA: 1,6mMemFLPAPrn); thus, the first light-emitting layer 113a, which was a fluorescent layer, was formed. Through the steps described above, the light-emitting layer 113 was formed.

[0274] Note that 2mDBTBPDBq-II and PCBBiF form an exciplex in the phosphorescent layer (the second light-emitting layer 113c) and the separation layer 113b. This emission wavelength overlaps with absorption bands on the longest wavelength sides of [Ir(dmdppr-dmp)2(acac)] and [Ir(tBuppm)2(acac)], so the energy transfer efficiency is high.

[0275] The singlet excitation energy of cgDBCzPA, which is a host material in the fluorescent layer (the first light-emitting layer 113a), is higher than the singlet excitation energy of 1.6mMemFLPAPrn, which is a fluorescent substance. Furthermore, the triplet excitation energy of cgDBCzPA is lower than the triplet excitation energy of 1.6mMemFLPAPrn. Therefore, singlet exciton regeneration coupled with triplet-triplet annihilation and light emission are easily obtained in the fluorescent layer (the first light-emitting layer 113a).

[0276] Thereafter, on the phosphorescent layer (the first light-emitting layer 113a), cgDBCzPA was deposited to a thickness of 10 nm, and bathophenanthroline (abbreviation: BPhen), which is represented by the structural formula (ix), was deposited to a thickness of 15 nm, so that the electron transport layer 114 was formed.

[0277] After forming the electron-transport layer 114, lithium fluoride (LiF) was deposited by evaporation to a thickness of 1 nm to form the electron-injection layer 115. Finally, an alloy of silver and magnesium (1:0.5) was deposited to a thickness of 1 nm and silver to a thickness of 150 nm to form the second electrode 102 serving as a cathode. Through the above steps, the light-emitting element 8 of this example was manufactured. Note that in all the above evaporation steps, evaporation was performed by a resistance heating method.

[0278] Table 7 shows the element structure of the light-emitting element 8. [Table 7] Hole injection layer Hole transport layer two emitters th light layer Separating layer first light-emitting layer Electron transport layer Electron injection layer DBT3P-II: MoOx PCBBiF * ** *** cgDBCzPA: 1.6mMemFLPAPrn cgDBCzPA BPhen LiF 1:0,5 1:0,03 30 nm 20 nm 15 nm 5 nm 2 nm 5 nm 10 nm 15 nm 1 nm * 2mDBTBPDBq-II:PCBBiF:Ir(dmdppr-dmp)2(acac) = 0.1:0.9:0.06 ** 2mDBTBPDBq-II:PCBBiF:Ir(tBuppm)2(acac) = 0.5:0.5:0.06 *** 2mDBTBPDBq-II:PCBBiF = 0.5:0.5

[0279] In a glove box in a nitrogen atmosphere, the light-emitting element 8 was sealed with a glass substrate to prevent exposure to air (specifically, a sealing material was applied to an outer edge of the element, and at the time of sealing, a UV treatment was performed, followed by a heat treatment at 80°C for one hour). The characteristics of this light-emitting element were then measured. Note that the measurement was conducted using an integrating sphere at room temperature (in an atmosphere maintained at 25°C). Table 8 shows the characteristic values ​​at a current density of 3.75 mA / cm 2 . [Table 8] Voltage (V) correlated color temperature (K) duv general color rendering index Ra Power efficiency (Im / W) external quantum yield (%) Light-emitting element 8 2,8 2840 0,0149 87 57 21

[0280] Light-emitting element 8 exhibited favorable external quantum efficiency and power efficiency. Light-emitting element 8 exhibited a very low operating voltage of 2.8 V compared to a tandem light-emitting element.

[0281] Fig. Figure 29 shows the emission spectrum of the light-emitting element 8. As can be seen from the emission spectrum, red light emission originating from [Ir(dmdppr-dmp)2(acac)], green light emission originating from [Ir(tBuppm)2(acac)], and blue light emission originating from 1.6mMemFLPAPrn were observed. This indicates that sufficient light emission was obtained from both the first light-emitting layer 113a, which was a fluorescent layer, and the second light-emitting layer 113c, which was a phosphorescent layer.

[0282] The light-emitting element 8 had a general color rendering index (Ra) of 87, meaning that the light-emitting element 8 had favorable color rendering properties, and exhibited low duv (a deviation from the blackbody radiation curve); thus, the light-emitting element 8 is suitable for illumination. Furthermore, the light-emitting element 8 had a color temperature of 2840 K, corresponding to an incandescent color.

[0283] As described above, the light-emitting element 8 exhibited highly well-balanced, advantageous properties and could be easily and inexpensively manufactured. The above-described results were attributed to the following: exciton diffusion was suppressed and non-radiative decay of triplet excitation energy was reduced by using the exciplex as the energy donor of the phosphorescent layer, and the emission efficiency was increased due to the appearance of delayed fluorescence due to triplet-triplet annihilation in the host material in the fluorescent layer. [Example 5]

[0284] In this example, a method for manufacturing a light-emitting element 9 according to one embodiment of the present invention and its properties are described. Structural formulas of organic compounds used for the light-emitting element 9 are shown below. (Method for manufacturing the light-emitting element 9)

[0285] A film of indium tin oxide containing silicon oxide (ITSO) was formed over a glass substrate by a sputtering method, forming the first electrode 101. The thickness was 110 nm and the electrode area was 2 mm × 2 mm. Here, the first electrode 101 serves as the anode of the light-emitting element.

[0286] Next, in the pretreatment for forming the light-emitting element over the substrate, a surface of the substrate was washed with water and baked at 200 °C for one hour, and then UV-ozone treatment was performed for 370 seconds.

[0287] The substrate was then transferred to a vacuum evaporation device where the pressure was increased to approximately 10 -4Pa, and was heated for 30 minutes in vacuum at 170 °C in a heating chamber of the vacuum evaporation device, and then the substrate was cooled for about 30 minutes.

[0288] Then, the substrate provided with the first electrode 101 was attached to a substrate holder in the vacuum evaporation device so that the surface on which the first electrode 101 was formed was facing downward. The pressure in the vacuum evaporation device was set to about 10 -4Pa. Next, 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), represented by the structural formula (i), and molybdenum(VI) oxide were co-evaporated onto the first electrode 101 by a resistive heating evaporation method, thereby forming the hole-injection layer 111. The thickness was set to 15 nm, and the weight ratio of DBT3P-II to molybdenum oxide was set to 2:1 (= DBT3P-II: molybdenum oxide).

[0289] Next, 3-[4-(9-phenanthryl)phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPPn), represented by the structural formula (ii), was deposited on the hole-injection layer 111 to a thickness of 20 nm; thus, the hole-transport layer 112 was formed.

[0290] Then, on the hole-transporting layer 112, 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole (abbreviation: cgDBCzPA), which is represented by the structural formula (iii), and N,N-bis(3-methylphenyl)-N,N-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPrn), which is represented by the structural formula (iv), were co-evaporated to a thickness of 5 nm, so that the weight ratio of cgDBCzPA to 1,6mMemFLPAPrn was 2:0.1 (= cgDBCzPA: 1,6mMemFLPAPrn); In this way, the first light-emitting layer 113a, which was a fluorescent layer, was formed.Next, 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), represented by the structural formula (v), and N-(1,1'-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF), represented by the structural formula (vi), were co-deposited to a thickness of 2 nm by co-evaporation such that the weight ratio of 2mDBTBPDBq-II to PCBBiF was 0.4:1.6 (= 2mDBTBPDBq-II: PCBBiF); thus, the separation layer 113b was formed.Thereafter, the first phosphorescence layer 113c-1 was formed such that 2mDBTBPDBq-II, PCBBiF and (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]), which is represented by the structural formula (xiv), were deposited by co-evaporation to a thickness of 5 nm such that the weight ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(dppm)2(acac)] was 0.8:1.2:0.12 (= 2mDBTBPDBq-II: PCBBiF: [Ir(dppm)2(acac)]); The second phosphorescent layer 113c-2 was then formed such that 2mDBTBPDBq-II, PCBBiF and bis{2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-κN3]phenyl-κC}(2,4-pentanedionato-κO,O')iridium(III) (abbreviation: [Ir(ppm-dmp)2(acac)]), which is represented by the structural formula (xv), were deposited by co-evaporation to a thickness of 15 nm, so that the weight ratio of 2mDBTBPDBq-II to PCBBiF and [Ir(ppm-dmp)2(acac)] was 1.6:0.4:0.12 (= 2mDBTBPDBq-II: PCBBiF: [Ir(ppmdmp)2(acac)]).Through the above steps, the second light-emitting layer 113c, which was a phosphorescent layer, was formed. As described above, in the light-emitting element 9, the light-emitting layer 113 was formed from the first light-emitting layer 113a and the second light-emitting layer 113c.

[0291] Note that 2mDBTBPDBq-II and PCBBiF form an exciplex in the phosphorescent layer (the second light-emitting layer 113c). This emission wavelength overlaps with absorption bands on the longest wavelength sides of [Ir(dppm)2(acac)] and [Ir(ppm-dmp)2(acac)], so the energy transfer efficiency is high.

[0292] The singlet excitation energy of cgDBCzPA, which is a host material in the fluorescent layer (the first light-emitting layer 113a), is higher than the singlet excitation energy of 1.6mMemFLPAPrn, which is a fluorescent substance. Furthermore, the triplet excitation energy of cgDBCzPA is lower than the triplet excitation energy of 1.6mMemFLPAPrn. Therefore, singlet exciton regeneration coupled with triplet-triplet annihilation and light emission are easily obtained in the fluorescent layer (the first light-emitting layer 113a).

[0293] Thereafter, on the phosphorescent layer (the second light-emitting layer 113c), 2mDBTBPDBq-II was deposited to a thickness of 10 nm, and bathophenanthroline (abbreviation: BPhen), which is represented by the structural formula (ix), was deposited to a thickness of 15 nm, so that the electron transport layer 114 was formed.

[0294] After forming the electron-transport layer 114, lithium fluoride (LiF) was deposited by evaporation to a thickness of 1 nm; thus, the electron-injection layer 115 was formed. Finally, silver (Ag) and magnesium (Mg) were deposited by co-evaporation to a thickness of 1 nm so that the ratio of silver to magnesium was 1:0.5; thus, the second electrode 102, which served as the cathode, was formed. Then, silver was deposited to a thickness of 150 nm by a sputtering method. Through the above steps, the light-emitting element 9 of this example was manufactured.

[0295] It should be noted that in all the above evaporation steps, evaporation was carried out by a resistance heating method.

[0296] In a glove box in a nitrogen atmosphere, the light-emitting element 9 was sealed with a glass substrate to prevent exposure to air (specifically, a sealing material was applied to an outer edge of the element, and at the time of sealing, a UV treatment was performed, followed by a heat treatment at 80°C for one hour). The reliability of this light-emitting element was then measured. Note that the measurement was conducted at room temperature (in an atmosphere maintained at 25°C).

[0297] Table 9 shows the element structure of the light-emitting element 9. [Table 9] Hole injection layer Hole transport layer first light-emitting layer Separating layer second light-emitting layer Electron transport layer Electron injection layer DBT3P-II: MoOx PCPPn cgDBCzPA: 1.6mMemFLPAPrn * ** i *** 2mDBTBPDBq-II BPhen LiF 2:1 2:0,1 15 nm 20 nm 5 nm 2 nm 5 nm 15 nm 10 nm 15 nm 1 nm * 2mDBTBPDBq-II:PCBBiF = 0.4:1.6 ** 2mDBTBPDBq-II:PCBBiF:Ir(dppm)2(acac) = 0.8:1.2:0.12 *** 2mDBTBPDBq-II:PCBBiF:Ir(ppm-dmp)2(acac) = 1.6:0.4:0.12

[0298] Fig. 30 shows current density-luminance characteristics of the light-emitting element 9. Fig. 31 shows luminance-current efficiency characteristics of the light-emitting element 9. Fig.32 shows voltage-luminance characteristics of the light-emitting element 9. Fig. 33 shows luminance-external quantum efficiency characteristics of the light-emitting element 9. Fig. 34 shows the emission spectra of the light-emitting element 9.

[0299] Although the light-emitting element 9 did not include an intermediate layer, the light-emitting element 9, as can be seen from the characteristics, had a current efficiency of about 70 cd / A at about 1000 cd / m 2 and an external quantum efficiency of 22% or higher. This indicates that the light-emitting element 9 exhibited very high emission efficiency. The operating voltage is 2.9 V, which is much lower than the operating voltage of a tandem light-emitting element. [Table 10] Voltage (V) Current density (mA / cm 2 ) Power efficiency (cd / A) Power efficiency (Im / W) external quantum yield (%) correlated color temperature (K) Light-emitting element 9 2,9 1,3 69 75 22 2730

[0300] As can be seen from the emission spectrum, both phosphorescence originating from [Ir(dppm)2(acac)] and [Ir(ppm-dmp)2(acac)] and fluorescence originating from 1.6mMemFLPAPrn were observed. This indicates that sufficient light emission was obtained from both the first light-emitting layer 113a, which was the fluorescent layer, and the second light-emitting layer 113c, which was the phosphorescent layer.

[0301] As described above, the light-emitting element 9 emits white light with very high emission efficiency and could be manufactured easily and inexpensively. The results were attributed to the following: by using the exciplex as the energy donor of the phosphorescent layer, exciton diffusion was suppressed and non-radiative decay of the triplet excitation energy was reduced, and the emission efficiency was increased due to the appearance of delayed fluorescence due to triplet-triplet annihilation in the host material in the fluorescent layer. By using the separation layer 113b, energy transfer from the phosphorescent layer (the second light-emitting layer 113c) to the fluorescent layer (the first light-emitting layer 113a) at their interface is suppressed; therefore, the light-emitting element 9 can exhibit even better characteristics.

[0302] An organic EL lighting device was fabricated in the following manner: An element having a structure similar to the structure of the light-emitting element 9 and including a 70 nm thick first electrode was formed over a glass substrate having a refractive index of 1.84 such that an emission area became 90 mm × 90 mm; and a surface of the substrate from which light is emitted was frosted.

[0303] Fig. Figure 35 shows the luminance-power efficiency characteristics of the organic EL lighting device. The organic EL lighting device had a color temperature of 2700 K and duv = 0.019, which correspond to the standards of an incandescent color, and exhibited a very high power efficiency of 140 lm / W at a luminance of approximately 1500 cd / m². 2 on. Explanation of reference symbols

[0304] 101: first electrode, 102: second electrode, 103: EL layer, 111: hole injection layer, 112: hole transport layer, 113: light-emitting layer, 113a: first light-emitting layer, 113b: separation layer, 113c: second light-emitting layer, 113c-1: first phosphorescence layer, 113c-2: second phosphorescence layer, 114: electron transport layer, 115: electron injection layer, 400: substrate, 401: first electrode, 403: EL layer, 404: second electrode, 405: sealing material, 406: sealing material, 407: sealing substrate, 412: contact pad, 420: IC chip, 501: first electrode, 502: second electrode, 511: first light-emitting unit, 512: second light-emitting unit, 513: charge generation layer, 601: driver circuit section (source line driver circuit), 602: pixel section, 603: driver circuit section (gate line driver circuit), 604: sealing substrate, 605: sealing material, 607: space, 608: line, 609: FPC (flexible printed circuit board),610: Element substrate, 611: Switching FET, 612: Current controlling FET, 613: First electrode, 614: Insulator, 616: EL layer, 617: Second electrode, 618: Light-emitting element, 623: N-channel FET, 624: P-channel FET, 901, Package, 902: Liquid crystal layer, 903: Backlight unit, 904: Package, 905: Driver IC, 906: Terminal, 951: Substrate, 952: Electrode, 953: Insulating layer, 954: Partition layer, 955: EL layer, 956: Electrode, 1001: Substrate, 1002: Base insulating film, 1003: Gate insulating film, 1006: Gate electrode, 1007: Gate electrode, 1008: Gate electrode, 1020: First interlayer insulating film, 1021: Second interlayer insulating film, 1022: Electrode, 1024W: First electrode of the light-emitting element, 1024R: First electrode of the light-emitting element, 1024G: First electrode of the light-emitting element, 1024B: First electrode of the light-emitting element, 1025: Partition wall, 1028: EL layer, 1029: Second electrode of the light-emitting element,1031: Sealing substrate, 1032: Sealing material, 1033: Transparent base material, 1034R: Red ink layer, 1034G: Green ink layer, 1034B: Blue ink layer, 1035: Black layer (black matrix), 1036: Cover layer, 1037: Third interlayer insulating film, 1040: Pixel section, 1041: Driving circuit section, 1042: Peripheral section, 2001: Housing, 2002: Light source, 3001: Illumination device, 5000: Display section, 5001, Display section, 5002: Display section, 5003: Display section, 5004: Display section, 5005: Display section, 7101: Housing, 7103: Display section, 7105: Stand, 7107: Display section, 7109: Operation button, 7110: Remote control, 7201: Main body, 7202: Housing, 7203: Display section, 7204: Keyboard, 7205: External connection port, 7206: Pointing device, 7210: Second display section, 7301: Housing, 7302: Housing, 7303: Joint part, 7304: Display section, 7305: Display section, 7306: Speaker, 7307: Recording media insertion section,7308: LED lamp, 7309: Operation button, 7310: Connection terminal, 7311: Sensor, 7401: Housing, 7402: Display section, 7403: Operation knob, 7404: External connection terminal, 7405: Speaker, 7406: Microphone, 9033: Clasp, 9034: Switch, 9035: Power switch, 9036: Switch, 9038: Operation switch, 9630: Housing, 9631: Display section, 9631a: Display section, 9631b: Display section, 9632a: Touch screen area, 9632b: Touch screen area, 9633: Solar cell, 9634: Charge and discharge control circuit, 9635: Battery, 9636: DC-DC converter, 9637: Operating button, 9638: Converter, 9639: Switch button,

Claims

[1] Light-emitting element comprising: a cathode, a plurality of light-emitting layers and an anode, in the order given; wherein the plurality of light-emitting layers comprises a first light-emitting layer on the cathode side, a second light-emitting layer remote from the first light-emitting layer, and a third light-emitting layer in contact with the second light-emitting layer in the order given; wherein the first light-emitting layer comprises a fluorescent substance and a host material; wherein one of the second or third light-emitting layers comprises: a first substance configured to convert triplet excitation energy into light emission, a first organic compound, and a second organic compound; wherein the first organic compound and the second organic compound are configured to form an exciplex; wherein the difference between the energy values ​​of a peak wavelength of the emission spectrum of the exciplex and a peak wavelength in the lowest energy absorption band of the first substance is 0.2 eV or less; wherein the other of the second or third light-emitting layers comprises a second substance configured to convert triplet excitation energy into light emission; wherein the emission spectrum of the first substance differs from the emission spectrum of the second substance; wherein a third organic compound and a fourth organic compound are contained between the first light-emitting layer and the second light-emitting layer; and wherein a triplet excitation level of the host material is lower than a triplet excitation level of the third organic compound and a triplet excitation level of the fourth organic compound. [2] Light-emitting element comprising: a cathode, a plurality of light-emitting layers and an anode, in the order given; wherein the plurality of light-emitting layers comprises a first light-emitting layer on the cathode side, a second light-emitting layer remote from the first light-emitting layer, and a third light-emitting layer in contact with the second light-emitting layer in the order given; wherein the first light-emitting layer comprises a fluorescent substance and a host material; wherein one of the second or third light-emitting layers comprises: a first substance configured to convert triplet excitation energy into light emission, a first organic compound, and a second organic compound; wherein the first organic compound and the second organic compound are configured to form an exciplex; wherein the difference between the energy values ​​of a peak wavelength of the emission spectrum of the exciplex and a peak wavelength in the lowest energy absorption band of the first substance is 0.2 eV or less; wherein the other of the second or third light-emitting layers comprises a second substance configured to convert triplet excitation energy into light emission; wherein the fluorescent substance emits light in a blue range; wherein the first substance emits light in a green range; and wherein the second substance emits light in a red range. [3] Light-emitting element comprising: a cathode, a plurality of light-emitting layers and an anode, in the order given; wherein the plurality of light-emitting layers comprises a first light-emitting layer on the cathode side, a second light-emitting layer remote from the first light-emitting layer, and a third light-emitting layer in contact with the second light-emitting layer in the order given; wherein the first light-emitting layer comprises a fluorescent substance and a host material; wherein one of the second or third light-emitting layers comprises: a first substance configured to convert triplet excitation energy into light emission, a first organic compound, and a second organic compound; wherein the first organic compound and the second organic compound are configured to form an exciplex; wherein the difference between the energy values ​​of a peak wavelength of the emission spectrum of the exciplex and a peak wavelength in the lowest energy absorption band of the first substance is 0.2 eV or less; wherein the other of the second or third light-emitting layers comprises a second substance configured to convert triplet excitation energy into light emission; wherein the fluorescent substance has a peak wavelength of the emission spectrum of 400 nm to 480 nm; wherein the first substance has a peak wavelength of the emission spectrum of 500 nm to 560 nm; and wherein the second substance has a peak wavelength of the emission spectrum of 580 nm to 680 nm. [4] Light-emitting element according to claim 2 or 3, wherein a third organic compound and a fourth organic compound are contained between the first light-emitting layer and the second light-emitting layer, and wherein a triplet excitation level of the host material is lower than a triplet excitation level of the third organic compound and a triplet excitation level of the fourth organic compound. [5] A light-emitting element according to any one of claims 1, 2 and 3, further comprising: a layer between the cathode and the first light-emitting layer, the layer comprising a fifth organic compound, wherein the fifth organic compound has an anthracene skeleton. [6] The light-emitting element according to any one of claims 1, 2 and 3, wherein the host material is an organic compound having an anthracene skeleton. [7] The light-emitting element according to any one of claims 1, 2 and 3, wherein the fluorescent substance is a pyrenediamine compound. [8] Light-emitting element according to one of claims 1, 2 and 3, wherein a singlet excitation level of the host material is higher than a singlet excitation level of the fluorescent substance, and where a triplet excitation level of the host material is lower than a triplet excitation level of the fluorescent substance. [9] The light-emitting element according to any one of claims 1, 2 and 3, wherein a triplet excitation level of the exciplex is lower than a triplet excitation level of the first light-emitting layer and a triplet excitation level of the second light-emitting layer.

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