Light-emitting device

Abstract

To provide a long-life light-emitting device.SOLUTION: The present invention provides a light-emitting device having an EL layer between a pair of electrodes, which can improve efficiency and reliability by providing a functional lamination structure included in the EL layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to a light-emitting element, a light-emitting device, a display module, a lighting module, a display device, a light-emitting device, an electronic device, and a lighting device. Note that an embodiment of the present invention is not limited to the above technical field. A technical field of an embodiment of the present invention disclosed in the present specification and the like relates to an object, a method, or a manufacturing method. Alternatively, an embodiment of the present invention relates to a process, a machine, a manufacture, or a composition of matter. Therefore, more specifically, examples of the technical field of an embodiment of the present invention disclosed in the present specification include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a lighting device, a power storage device, a storage device, an imaging device, a driving method thereof, or a manufacturing method thereof. [Background technology]

[0002] Light-emitting devices (organic EL elements) that utilize electroluminescence (EL) using organic compounds are becoming more and more practical. The basic structure of these light-emitting devices is a pair of electrodes sandwiching an organic compound layer (EL layer) containing a light-emitting substance between them. By applying a voltage to this element, carriers are injected, and the recombination energy of the carriers is utilized to emit light from the light-emitting substance.

[0003] Since such light-emitting devices are self-emitting, when used as display pixels, they have advantages such as higher visibility than liquid crystals and no need for backlighting, making them suitable as flat panel display elements. Another major advantage of displays using such light-emitting devices is that they can be made thin and lightweight. Another characteristic is that they have an extremely fast response speed.

[0004] In addition, these light-emitting devices can have light-emitting layers formed continuously in two dimensions, making it possible to obtain surface-like light emission. This is a feature that is difficult to obtain with point light sources such as incandescent light bulbs and LEDs, or linear light sources such as fluorescent lamps, making them highly valuable as surface light sources for lighting and other applications.

[0005] Displays and lighting devices using such light-emitting devices are suitable for use in a variety of electronic devices, and research and development is ongoing to develop light-emitting devices with better efficiency and life span.

[0006] Patent Document 1 discloses a configuration in which a hole-transporting material having a HOMO level between the HOMO level of the first hole-injection layer and the HOMO level of the host material is provided between a first hole-transporting layer in contact with a hole-injection layer and a light-emitting layer.

[0007] Although the characteristics of light-emitting devices have improved remarkably, they are still insufficient to meet high demands for efficiency, durability, and all other characteristics. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2011 / 065136 Brochure Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the above, an object of one embodiment of the present invention is to provide a novel light-emitting device, to provide a light-emitting device with high emission efficiency, to provide a light-emitting device with a long lifetime, or to provide a light-emitting device with a low driving voltage.

[0010] Another object of another embodiment of the present invention is to provide a light-emitting device, an electronic device, and a display device with high reliability, or to provide a light-emitting device, an electronic device, and a display device with low power consumption.

[0011] It is sufficient for the present invention to solve any one of the above problems. [Means for solving the problem]

[0012] According to one embodiment of the present invention, in a light-emitting device having an EL layer between a pair of electrodes, the light-emitting layer of the EL layer has a functional stacked structure, whereby the reliability and light-emitting efficiency of the light-emitting device can be improved.

[0013] One embodiment of the present invention has an EL layer between an anode and a cathode. The EL layer has, in this order from the anode side, a hole-injection layer, a hole-transport layer, a light-emitting layer, and an electron-transport layer. The hole-injection layer is in contact with the anode. The light-emitting layer has a first light-emitting layer and a second light-emitting layer stacked from the anode side. The first light-emitting layer is in contact with the hole-transport layer. The second light-emitting layer is in contact with the electron-transport layer. The first light-emitting layer has a first substance and a second substance. The second light-emitting layer has a third substance and a fourth substance. The first substance and the third substance are the same or different light-emitting substances. The second substance and the fourth substance are the same or different substances. the injection layer includes a fifth substance and a sixth substance, the fifth substance being an acceptor material, and the sixth substance has a HOMO level of −5.7 eV or more and −5.4 eV or less; the hole-transporting layer includes a seventh substance, and the seventh substance has a HOMO level lower than that of the sixth substance and higher than that of the second substance; the electron-transporting layer includes an eighth substance and a ninth substance, and the eighth substance is an organometallic complex of an alkali metal or an alkaline earth metal, and the ninth substance has a HOMO level of −6.0 eV or more and an electron mobility of 1×10 at a square root of an electric field strength [V / cm] of 600. -7 cm 2 / Vs or more 5×10 -5 cm 2 / Vs or less.

[0014] Another embodiment of the present invention has an EL layer between an anode and a cathode. The EL layer has, from the anode side, a hole injection layer, a hole transport layer, a light-emitting layer, and an electron transport layer. The hole injection layer is in contact with the anode. The light-emitting layer has a first light-emitting layer and a second light-emitting layer stacked from the anode side. The first light-emitting layer is in contact with the hole transport layer. The second light-emitting layer is in contact with the electron transport layer. The first light-emitting layer has a first substance and a second substance. The second light-emitting layer has a third substance and a fourth substance. The first substance and the third substance are the same or different light-emitting substances. The second substance and the fourth substance are the same substance. the hole-transporting layer includes a seventh substance, the seventh substance having a HOMO level lower than that of the sixth substance and higher than that of the second substance; the electron-transporting layer includes an eighth substance and a ninth substance, the eighth substance being an organometallic complex of an alkali metal or an alkaline earth metal, the ninth substance having a HOMO level of −6.0 eV or higher and an electron mobility of 1×10 at a square root of an electric field strength [V / cm] of 600. -7 cm 2 / Vs or more 5×10 -5 cm 2 / Vs or less.

[0015] In the light-emitting device having the above configuration, it is preferable that both the first light-emitting layer and the second light-emitting layer emit blue light.

[0016] In the light-emitting device having each of the above configurations, the abundance ratio of the eighth substance to the ninth substance in the electron transport layer is preferably different between the cathode side and the second light-emitting layer side.

[0017] In the light-emitting device having the above-mentioned configuration, the abundance ratio of the eighth substance in the electron transport layer is preferably smaller on the cathode side than on the second light-emitting layer side.

[0018] In this specification, the term "light-emitting device" includes an image display device using a light-emitting device. Also, a module in which a connector, such as an anisotropic conductive film or TCP (Tape Carrier Package), is attached to a light-emitting device, a module in which a printed wiring board is provided at the end of a TCP, or a module in which an IC (integrated circuit) is directly mounted on a light-emitting device by a COG (Chip On Glass) method may be included in the light-emitting device. Furthermore, lighting fixtures and the like may have a light-emitting device. Effect of the Invention

[0019] According to one embodiment of the present invention, a novel light-emitting device can be provided. Alternatively, a light-emitting device having a long lifetime can be provided. Alternatively, a light-emitting device having high emission efficiency can be provided.

[0020] According to another embodiment of the present invention, a light-emitting device, an electronic device, and a display device with high reliability can be provided. According to another embodiment of the present invention, a light-emitting device, an electronic device, and a display device with low power consumption can be provided.

[0021] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract effects other than these from the description in the specification, drawings, claims, etc. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing the structure of a light-emitting device. [Diagram 2] 2A and 2B are diagrams illustrating the structure of a light-emitting device. [Diagram 3] 3A, 3B, and 3C are diagrams for explaining a light emitting device. [Figure 4]Fig. 4A is a top view illustrating the light emitting device, and Fig. 4B is a cross-sectional view illustrating the light emitting device. [Diagram 5] Fig. 5A is a diagram for explaining a mobile computer. Fig. 5B is a diagram for explaining a portable image playback device. Fig. 5C is a diagram for explaining a digital camera. Fig. 5D is a diagram for explaining a portable information terminal. Fig. 5E is a diagram for explaining a portable information terminal. Fig. 5F is a diagram for explaining a television device. Fig. 5G is a diagram for explaining a portable information terminal. [Figure 6] 6A, 6B, and 6C are diagrams for explaining electronic devices. [Figure 7] 7A and 7B are diagrams for explaining an automobile. [Figure 8] 8A and 8B are diagrams illustrating a lighting device. [Figure 9] FIG. 9 is a diagram showing the structure of an electron-only element. [Figure 10] FIG. 10 shows the current density-voltage characteristics of the electron-only element. [Figure 11] Figure 11 shows the frequency characteristics of the calculated capacitance C of ZADN:Liq (1:1) at a DC power supply of 7.0 V. [Figure 12] Figure 12 shows the frequency characteristics of -ΔB of ZADN:Liq(1:1) at a DC voltage of 7.0V. [Figure 13] FIG. 13 shows the electric field strength dependence of electron mobility in each organic compound. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that the form and details of the present invention can be modified in various ways without departing from the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0024] (Embodiment 1) In this embodiment, a structure of a light-emitting device which is one embodiment of the present invention will be described with reference to FIG.

[0025] 1 shows a light-emitting device having a structure in which an EL layer 103 is sandwiched between a first electrode 101 functioning as an anode and a second electrode 102 functioning as a cathode. Therefore, the EL layer 103 has a structure in which a hole injection layer 111, a hole transport layer 112, a light-emitting layer 113, an electron transport layer 114, and an electron injection layer 115 are sequentially laminated as functional layers.

[0026] In the light-emitting device according to one embodiment of the present invention, the light-emitting layer 113 included in the EL layer 103 has a stacked structure. Note that Fig. 1 illustrates a case where the light-emitting layer 113 has a two-layer structure in which a first light-emitting layer 113-1 and a second light-emitting layer 113-2 are stacked. However, the number of stacked layers of the light-emitting layer 113 is not particularly limited to two, and may be any structure that can provide the light-emitting layer 113 with a required function as one embodiment of the present invention.

[0027] The function required for the light emitting layer 113 is to increase the recombination probability of carriers (holes and electrons) in the light emitting layer 113 .

[0028] A light-emitting device according to one embodiment of the present invention is a light-emitting device that has a plurality of light-emitting layers with different carrier transport properties, and thereby can control the carrier balance, increase the probability of carrier recombination in the light-emitting layers, and prevent deterioration of the functional layers that constitute the EL layer. As a result, the reliability of the light-emitting device can be improved, and the light-emitting efficiency can be increased.

[0029] In one embodiment of the present invention, in the stacked light-emitting layers 113, the host material used in the first light-emitting layer 113-1 and the host material used in the second light-emitting layer 113-2 may be formed of different materials. The guest material used in the first light-emitting layer 113-1 and the guest material used in the second light-emitting layer 113-2 may be formed of different materials. Either the guest material or the host material used in the first light-emitting layer 113-1 and the second light-emitting layer 113-2 may be the same material. The host material used in the first light-emitting layer 113-1 and the second light-emitting layer 113-2 may be one type or multiple types. When multiple host materials are used in the first light-emitting layer 113-1 and the second light-emitting layer 113-2, the combination of these materials may form an exciplex. The carrier transport properties of the first light-emitting layer 113-1 and the second light-emitting layer 113-2 may be controlled by the host material, the guest material, or a combination of the host material and the guest material used in each layer.

[0030] As described above, by stacking light-emitting layers having different carrier transport properties, it is possible to control the light emission at the stacking interface of the different light-emitting layers. In addition, by stacking light-emitting layers having different guest materials, it is possible to enable energy transfer between these light-emitting layers, thereby increasing the light-emitting efficiency.

[0031] In one embodiment of the present invention, in the stacked light-emitting layers 113, each light-emitting layer may be formed so that the hole mobility of the second light-emitting layer 113-2 is smaller than that of the first light-emitting layer 113-1, and the recombination region may be controlled to be near the interface between the first light-emitting layer 113-1 and the second light-emitting layer 113-2. With such a configuration, the light-emitting efficiency of the light-emitting device can be improved. In addition, in the stacked light-emitting layers 113, each light-emitting layer may be formed so that the electron mobility of the second light-emitting layer is larger than that of the first light-emitting layer. In addition, both of these configurations may be combined. Note that carrier mobility such as hole mobility and electron mobility can be obtained by impedance spectroscopy.

[0032] Also, in the laminated light-emitting layer 113, the concentration of the guest material contained in the second light-emitting layer 113-2 may be formed to be lower than the concentration of the guest material contained in the first light-emitting layer 113-1 (for example, the concentration of the guest material contained in the second light-emitting layer 113-2 is 3 w% or less, more preferably 2 w% or less), and the carrier recombination region may be controlled to be near the interface between the first light-emitting layer and the second light-emitting layer. By adopting such a configuration, the light-emitting efficiency of the light-emitting device can be improved. This is because, in the case where the HOMO level of the guest material is shallower than that of the host material and is easily oxidized (the difference is 0.2 eV, more preferably 0.3 eV or more, in CV measurement), when the concentration of the guest material is low, the guest material traps holes, and when the concentration of the guest material is high, the guest material easily transports holes. Note that these differences can be confirmed as changes in resistance by impedance spectroscopy or the like.

[0033] Also, in the laminated light emitting layers 113, each light emitting layer may be formed so that the hole mobility of the second light emitting layer 113-2 is greater than that of the first light emitting layer 113-1, and a carrier recombination region at the beginning of operation may be located on the second light emitting layer 113-2 side rather than the laminated interface. By adopting such a configuration, the initial reliability (5% or 10% luminance deterioration) can be extended. Also, each light emitting layer may be formed so that the electron mobility of the second light emitting layer 113-2 is smaller than that of the first light emitting layer 113-1. Also, these configurations may be combined. These carrier mobilities can be obtained by impedance spectroscopy.

[0034] Furthermore, in the laminated light emitting layers 113, the light emitting layers may be formed so that the electrical resistance of the second light emitting layer 113-2 is lower than that of the first light emitting layer 113-1, and the recombination region of carriers in the initial stage of operation may be located closer to the second light emitting layer 113-2 than the laminated interface. With such a configuration, the reliability of the light emitting device in the initial stage of operation (5% or 10% luminance degradation) can be improved. The electrical resistance can be determined by impedance spectroscopy.

[0035] In addition, the stacked light emitting layers 113 may be formed so that the refractive index anisotropy with respect to the substrate surface is larger in the second light emitting layer 113-2 than in the first light emitting layer 113-1, and the recombination region of carriers at the initial stage of operation may be located on the second light emitting layer 113-2 side rather than the stacking interface. With such a configuration, the reliability at the initial stage of operation (5% or 10% luminance deterioration) can be improved. This is because the transition dipole moment becomes horizontal with respect to the substrate, making it easier to transport carriers. At this time, the concentration of the guest material in the second light emitting layer 113-2 is more preferably 2w% or more. The above carrier mobility can be obtained by impedance spectroscopy. The refractive index anisotropy with respect to the substrate surface can be obtained by spectroscopic ellipsometry.

[0036] (Embodiment 2) In this embodiment, a light-emitting device which is one embodiment of the present invention will be described.

[0037] <Example of light-emitting device configuration> 2A shows an example of a light-emitting device having an EL layer including a light-emitting layer between a pair of electrodes. Specifically, the EL layer 103 is sandwiched between a first electrode 101 and a second electrode 102. When the first electrode 101 is used as an anode, the EL layer 103 has a structure in which a hole injection layer 111, a hole transport layer 112, a light-emitting layer 113, an electron transport layer 114, and an electron injection layer 115 are sequentially stacked as functional layers.

[0038] Other light-emitting device structures include a light-emitting device having a structure (tandem structure) in which a charge generation layer is sandwiched between a pair of electrodes to enable low-voltage operation, and a light-emitting device having improved optical characteristics by forming a micro-optical resonator (microcavity) structure between a pair of electrodes, etc. The charge generation layer has a function of injecting electrons into one of the adjacent EL layers and injecting holes into the other EL layer when a voltage is applied between the first electrode 101 and the second electrode 102.

[0039] At least one of the first electrode 101 and the second electrode 102 of the light-emitting device is an electrode having translucency (transparent electrode, semi-transmissive / semi-reflective electrode, etc.). When the electrode having translucency is a transparent electrode, the visible light transmittance of the transparent electrode is 40% or more. When the electrode is a semi-transmissive / semi-reflective electrode, the visible light reflectance of the semi-transmissive / semi-reflective electrode is 20% or more and 80% or less, preferably 40% or more and 70% or less. Furthermore, these electrodes have a resistivity of 1×10 -2 It is preferable to set it to Ωcm or less.

[0040] In the above-described light-emitting device according to one embodiment of the present invention, when one of the first electrode 101 and the second electrode 102 is a reflective electrode (reflective electrode), the electrode has a visible light reflectance of 40% to 100%, preferably 70% to 100%. -2 It is preferable to set it to Ωcm or less.

[0041] <First Electrode and Second Electrode> As the material for forming the first electrode 101 and the second electrode 102, the following materials can be used in appropriate combination as long as the above-mentioned functions of both electrodes are satisfied. For example, metals, alloys, electrically conductive compounds, and mixtures thereof can be used appropriately. Specific examples include In-Sn oxide (also called ITO), In-Si-Sn oxide (also called ITSO), In-Zn oxide, and In-W-Zn oxide. In addition, metals such as aluminum (Al), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), gallium (Ga), zinc (Zn), indium (In), tin (Sn), molybdenum (Mo), tantalum (Ta), tungsten (W), palladium (Pd), gold (Au), platinum (Pt), silver (Ag), yttrium (Y), and neodymium (Nd), as well as alloys containing these in appropriate combinations, can also be used. Other examples that can be used include elements belonging to Group 1 or 2 of the periodic table (e.g., lithium (Li), cesium (Cs), calcium (Ca), and strontium (Sr)) that are not listed above, rare earth metals such as europium (Eu) and ytterbium (Yb), and alloys containing appropriate combinations of these, as well as graphene.

[0042] These electrodes can be fabricated by sputtering or vacuum deposition.

[0043] <Hole injection layer> The hole injection layer 111 is a layer including an organic acceptor material and a hole transport material having a deep HOMO. The organic acceptor material is a material that exhibits electron acceptance with respect to the hole transport material having a deep HOMO. The hole transport material having a deep HOMO is a material having a relatively deep HOMO level of -5.7 eV or more and -5.4 eV or less. When the hole transport material has such a relatively deep HOMO level, it becomes easy to inject holes into the hole transport layer 112.

[0044] The organic acceptor material can be an organic compound having an electron-withdrawing group (especially a halogen group such as a fluoro group or a cyano group), and from such substances, a substance that exhibits electron-accepting properties toward the second substance can be appropriately selected. Examples of such organic compounds include 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ), chloranil, 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation: HAT-CN), 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinodimethane (abbreviation: F6-TCNNQ), and 2-(7-dicyanomethylene-1,3,4,5,6,8,9,10-octafluoro-7H-pyren-2-ylidene)malononitrile. In particular, compounds in which an electron-withdrawing group is bonded to a condensed aromatic ring having multiple heteroatoms, such as HAT-CN, are thermally stable and preferred. Radialene derivatives having an electron-withdrawing group (especially a halogen group such as a fluoro group or a cyano group) [3] are preferred because they have a very high electron-accepting property, and specific examples thereof include α,α',α''-1,2,3-cyclopropane triylidene tris[4-cyano-2,3,5,6-tetrafluorobenzeneacetonitrile], α,α',α''-1,2,3-cyclopropane triylidene tris[2,6-dichloro-3,5-difluoro-4-(trifluoromethyl)benzeneacetonitrile], and α,α',α''-1,2,3-cyclopropane triylidene tris[2,3,4,5,6-pentafluorobenzeneacetonitrile].

[0045] The above-mentioned hole transport material with a deep HOMO is preferably a hole transport material having hole transport properties, and preferably has any one of a carbazole skeleton, a dibenzofuran skeleton, a dibenzothiophene skeleton, and an anthracene skeleton. In particular, it may be an aromatic amine having a substituent containing a dibenzofuran ring or a dibenzothiophene ring, an aromatic monoamine having a naphthalene ring, or an aromatic monoamine in which a 9-fluorenyl group is bonded to the nitrogen of the amine via an arylene group.

[0046] In addition, the above-mentioned deep HOMO hole transport material has an electron mobility of 1×10 at a square root of the electric field strength [V / cm] of 600. -6 cm 2 A material having a hole mobility of 100 / Vs or more is preferable. Any material other than these can be used as long as it has a higher hole transporting property than electron transporting property. It is preferable that these materials have an N,N-bis(4-biphenyl)amino group because a long-life light-emitting device can be manufactured.

[0047] Specific examples of such deep HOMO hole transport materials include N-(4-biphenyl)-6,N-diphenylbenzo[b]naphtho[1,2-d]furan-8-amine (abbreviation: BnfABP), N,N-bis(4-biphenyl)-6-phenylbenzo[b]naphtho[1,2-d]furan-8-amine (abbreviation: BBABnf), 4,4'-bis(6-phenylbenzo[b]naphtho[1,2-d]furan-8-yl-4''-phenyltriphenylamine (abbreviation: BnfBB1BP), N,N-bis(4-biphenyl)benzo[b]naphtho[1,2-d]furan-8-yl-4''-phenyltriphenylamine (abbreviation: BnfBB1BP), zo[b]naphtho[1,2-d]furan-6-amine (abbreviation: BBABnf(6)), N,N-bis(4-biphenyl)benzo[b]naphtho[1,2-d]furan-8-amine (abbreviation: BBABnf(8)), N,N-bis(4-biphenyl)benzo[b]naphtho[2,3-d]furan-4-amine (abbreviation: BBABnf(II)(4)), N,N-bis[4-(dibenzofuran-4-yl)phenyl]-4-amino-p-terphenyl (abbreviation: DBfBB1TP), N-[4-(dibenzothiophene-4-yl)phenyl] -N-phenyl-4-biphenylamine (abbreviation: ThBA1BP), 4-(2-naphthyl)-4',4''-diphenyltriphenylamine (abbreviation: BBAβNB), 4-[4-(2-naphthyl)phenyl]-4',4''-diphenyltriphenylamine (abbreviation: BBAβNBi), 4,4'-diphenyl-4''-(6;1'-binaphthyl-2-yl)triphenylamine (abbreviation: BBAαNβNB), 4,4'-diphenyl-4''-(7;1'-binaphthyl-2-yl)triphenylamine (abbreviation: BBAαNβN B-03), 4,4'-diphenyl-4''-(7-phenyl)naphthyl-2-yltriphenylamine (abbreviation: BBAPβNB-03), 4,4'-diphenyl-4''-(6;2'-binaphthyl-2-yl)triphenylamine (abbreviation: BBA(βN2)B), 4,4'-diphenyl-4''-(7;2'-binaphthyl-2-yl)triphenylamine (abbreviation: BBA(βN2)B-03), 4,4'-diphenyl-4''-(4;2'-binaphthyl-1-yl)triphenylamine (abbreviation: BBAβNαNB), 4,4'-Diphenyl-4''-(5;2'-binaphthyl-1-yl)triphenylamine (abbreviation: BBAβNαNB-02), 4-(4-biphenylyl)-4'-(2-naphthyl)-4''-phenyltriphenylamine (abbreviation: TPBiAβNB), 4-(3-biphenylyl)-4'-[4-(2-naphthyl)phenyl]-4''-phenyltriphenylamine (abbreviation: mTPBiAβNBi), 4-(4-biphenylyl)-4'-[4-(2-naphthyl)phenyl]-4''-phenyltriphenylamine (abbreviation: ''-Phenyltriphenylamine (abbreviation: TPBiAβNBi), 4-phenyl-4'-(1-naphthyl)triphenylamine (abbreviation: αNBA1BP), 4,4'-bis(1-naphthyl)triphenylamine (abbreviation: αNBB1BP), 4,4'-diphenyl-4''-[4'-(carbazol-9-yl)biphenyl-4-yl]triphenylamine (abbreviation: YGTBi1BP), 4'-[4-(3-phenyl-9H-carbazol-9-yl)phenyl]tris(1 ,1'-biphenyl-4-yl)amine (abbreviation: YGTBi1BP-02), 4-diphenyl-4'-(2-naphthyl)-4''-{9-(4-biphenylyl)carbazole)}triphenylamine (abbreviation: YGTBiβNB), N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-N-[4-(1-naphthyl)phenyl]-9,9'-spirobi(9H-fluorene)-2-amine (abbreviation: PCBNBSF), N,N-bis(4-biphenylyl)-9 ,9'-Spirobi[9H-fluorene]-2-amine (abbreviation: BBASF), N,N-bis(1,1'-biphenyl-4-yl)-9,9'-spirobi[9H-fluorene]-4-amine (abbreviation: BBASF(4)), N-(1,1'-biphenyl-2-yl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-9,9'-spirobi(9H-fluorene)-4-amine (abbreviation: oFBiSF), N-(4-biphenyl)-N-(dibenzofuran-4-yl)-9,9-Dimethyl-9H-fluoren-2-amine (abbreviation: FrBiF), N-[4-(1-naphthyl)phenyl]-N-[3-(6-phenyldibenzofuran-4-yl)phenyl]-1-naphthylamine (abbreviation: mPDBfBNBN), 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl-3'-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), 4-phenyl-4'-[4-(9-phenylfluoren-9-yl)phenyl]triphenylamine (abbreviation: BPAFLBi), 4-phenyl-4'-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4'-diphenyl-4''-(9- Examples of the 4-(1-naphthyl)-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), N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9'-bifluorene-2-amine (abbreviation: PCBASF), N-(1,1'-biphenyl-4-yl)-9,9-dimethyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9H-fluorene-2-amine (abbreviation: PCBBiF), etc. can be mentioned.

[0048] The hole injection layer 111 can be formed by using various known film formation methods, for example, by using a vacuum deposition method.

[0049] <Hole transport layer> The hole transport layer 112 is a layer that transports the holes injected from the first electrode 101 by the hole injection layer 111 to the light emitting layer 113 .

[0050] The hole transport layer 112 may be made of the above-mentioned hole transport material. The hole transport layer 112 may have a laminated structure. When the hole transport layer 112 has a laminated structure, the layer on the light emitting layer side may have a function as an electron blocking layer.

[0051] In addition, in comparison between the HOMO level of the hole-transporting material used in the hole-injection layer 111 and the HOMO level of the hole-transporting material used in the hole-transporting layer 112, it is preferable to select each material such that the HOMO level of the hole-transporting material used in the hole-transporting layer 112 is deeper than the HOMO level of the hole-transporting material used in the hole-injection layer 111, and the difference therebetween is 0.2 eV or less. Note that it is more preferable to use the same material for both, since this allows for smooth hole injection.

[0052] In addition, when the hole transport layer 112 has a laminated structure, it is preferable that the HOMO level of the hole transport material used in the hole transport layer formed on the electron injection layer 111 side is deeper than the HOMO level of the hole transport material used in the hole transport layer formed on the light emitting layer 113 side. Furthermore, it is preferable to select each material so that the difference is 0.2 eV or less. Note that, when the HOMO levels of the hole transport materials used in the hole injection layer 111 and the hole transport layer having a laminated structure have the above-mentioned relationship, hole injection into each layer is performed smoothly, and an increase in driving voltage and a state of insufficient holes in the light emitting layer 113 can be prevented.

[0053] It is preferable that the hole transporting materials used in the hole injection layer 111 and the hole transporting layer 112 having a stacked structure each have a hole transporting skeleton. As the hole transporting skeleton, a carbazole skeleton, a dibenzofuran skeleton, a dibenzothiophene skeleton, and an anthracene skeleton, which do not make the HOMO level of these hole transporting materials too shallow, are preferable. In addition, it is preferable that the hole transporting skeletons of the hole transporting materials used in the hole injection layer 111 and the hole transporting layer 112 having a stacked structure are common to adjacent layers, because this makes the injection of holes smooth. In particular, the dibenzofuran skeleton is preferable as these hole transporting skeletons.

[0054] In addition, it is preferable that the hole transporting materials used in the hole injection layer 111 and the hole transport layer 112 having a laminated structure are the same for adjacent layers, since this allows holes to be injected more smoothly into the layers adjacent in the cathode direction.

[0055] <Light-emitting layer> In the light-emitting device according to one embodiment of the present invention, the light-emitting layer 113 has a structure in which a plurality of light-emitting layers are stacked. Note that the functions of the plurality of light-emitting layers are as described in Embodiment 1, and the light-emitting layer can be formed using the following materials so that such functions can be satisfied.

[0056] The light-emitting layer 113 includes a light-emitting substance (guest material) and a host material in which the light-emitting substance is dispersed.

[0057] As the light-emitting material (guest material), a material that emits fluorescence (fluorescent material), a material that emits phosphorescence (phosphorescent material), a thermally activated delayed fluorescence (TADF) material that exhibits thermally activated delayed fluorescence, and other light-emitting materials can be used. As the host material, in addition to an electron transport material or a hole transport material, various carrier transport materials such as the above-mentioned TADF material can be used. As the host material, a hole transport material or an electron transport material can be used. As specific examples of the hole transport material or the electron transport material, the materials described in this specification or known materials can be used singly or in combination.

[0058] Examples of fluorescent substances that can be used as guest materials in the light-emitting layer 113 include the following: In addition, fluorescent substances other than these can also be used.

[0059] 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'-diphenyl-N,N'-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]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-9,10-diyldi-4,1-phenylene)bis[N,N',N'-triphenyl-1,4-phenylenediamine] (abbreviation: DPABPA), N,9 -Diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-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]chrysene-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: 2DPAB PhA), 9,10-bis(1,1'-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine (abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-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)tetracene-5,11-diamine (abbreviation: p-mPhTD), 7,14-diphenyl-N,N,N',N'-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine Amine (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), 2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: BisDCJTM), N,N'-diphenyl-N,N'-(1,6-pyrene-diyl)bis[(6-phenylbenzo[b ]naphtho[1,2-d]furan)-8-amine] (abbreviation: 1,6BnfAPrn-03), 3,10-bis[N-(9-phenyl-9H-carbazol-2-yl)-N-phenylamino]naphtho[2,3-b;6,7-b']bisbenzofuran (abbreviation: 3,10PCA2Nbf(IV)-02), 3,10-bis[N-(dibenzofuran-3-yl)-N-phenylamino]naphtho[2,3-b;6,7-b']bisbenzofuran (abbreviation: 3,10FrA2Nbf(IV)-02), etc. In particular, condensed aromatic diamine compounds such as pyrene diamine compounds such as 1,6FLPAPrn, 1,6mMemFLPAPrn, and 1,6BnfAPrn-03 are preferred because they have high hole trapping properties and excellent luminous efficiency and reliability.

[0060] Examples of phosphorescent materials that can be used as guest materials for the light-emitting layer 113 include the following.

[0061] Organometallic iridium complexes with 4H-triazole skeletons 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]), tris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III) (abbreviation: [Ir(iPrptz-3b)3]), and tris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III) (abbreviation: [Ir(iPrptz-3b)3]) are also available. Organometallic iridium complexes having a 1H-triazole skeleton, such as tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III) (abbreviation: [Ir(Prptz1-Me)3]), fac-tris[(1-2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III) (abbreviation: [Ir(iPrpmi)3]), tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III) (abbreviation: [Ir(dmpimpt-Me)3]), and 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: FIrpic), bis{2-[3',5'-bis(trifluoromethyl)phenyl]pyridinato-N,C 2’}Iridium(III) picolinate (abbreviation: [Ir(CF3ppy)2(pic)]), bis[2-(4',6'-difluorophenyl)pyridinato-N,C 2’] Organometallic iridium complexes with phenylpyridine derivatives having electron-withdrawing groups as ligands, such as iridium(III) acetylacetonate (abbreviated as FIracac), are examples of such compounds that exhibit blue phosphorescence and have emission peaks at 440 nm to 520 nm.

[0062] In addition, tris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)3]), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)3]), (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)2(acac)]), (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]), (acetylacetonato)bis[6-(2-norbornyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: [Ir(nbppm)2(acac)]), (acetylacetonato)bis[5-methyl-6-( Organometallic iridium complexes having a pyrimidine skeleton, such as (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(mppr-iPr)2(acac)]), and organometallic iridium complexes having a pyrazine skeleton, 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]), bis(2-phenylquinolinato-N,C 2’ In addition to organometallic iridium complexes having a pyridine skeleton such as iridium(III) acetylacetonate (abbreviation: [Ir(pq)2(acac)]), rare earth metal complexes such as tris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation: [Tb(acac)3(Phen)]) can be mentioned. These are compounds that mainly exhibit green phosphorescence, and have an emission peak at 500 nm to 600 nm. In addition, organometallic iridium complexes having a pyrimidine skeleton are particularly preferred because they are remarkably excellent in reliability and luminous efficiency.

[0063] In addition, organometallic iridium complexes having a pyrimidine skeleton, such as (diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III) (abbreviation: [Ir(5mdppm)2(dibm)]), bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: [Ir(5mdppm)2(dpm)]), and bis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: [Ir(d1npm)2(dpm)]), Organometallic iridium complexes with a pyrazine skeleton, such as (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: [Ir(tppr)2(acac)]), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(tppr)2(dpm)]), and (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: [Ir(Fdpq)2(acac)]), and tris(1-phenylisoquinolinato-N,C 2’ ) Iridium(III) (abbreviation: [Ir(piq)3]), bis(1-phenylisoquinolinato-N,C 2’ In addition to organometallic iridium complexes with a pyridine skeleton such as iridium(III) acetylacetonate (abbreviated as [Ir(piq)2(acac)]), platinum complexes such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (abbreviated as PtOEP), and rare earth metal complexes such as tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviated as [Eu(DBM)3(Phen)]) and tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviated as [Eu(TTA)3(Phen)]) are examples of such compounds that exhibit red phosphorescence and have a peak emission wavelength of 600 to 700 nm. Furthermore, an organometallic iridium complex having a pyrazine skeleton can emit red light with good chromaticity.

[0064] In addition to the above, known phosphorescent materials can also be used.

[0065] Examples of TADF materials that can be used as the guest material of the light-emitting layer 113 include the following.

[0066] Fullerene and its derivatives, acridine and its derivatives, eosin derivatives, etc. can be used. In addition, metal-containing porphyrins containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), palladium (Pd), etc. can be used. Examples of the metal-containing porphyrin include protoporphyrin-tin fluoride complex (SnF2(Proto IX)), mesoporphyrin-tin fluoride complex (SnF2(Meso IX)), hematoporphyrin-tin fluoride complex (SnF2(Hemato IX)), coproporphyrin tetramethyl ester-tin fluoride complex (SnF2(Copro III-4Me)), octaethylporphyrin-tin fluoride complex (SnF2(OEP)), etioporphyrin-tin fluoride complex (SnF2(Etio I)), and octaethylporphyrin-platinum chloride complex (PtCl2OEP), which are shown in the following structural formulas.

[0067] [ka]

[0068] In addition, as shown in the structural formula below, 2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine (abbreviation: PIC-TRZ), 2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn), 2- [4-(10H-phenoxazin-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviation: PXZ-TRZ), 3-[4-(5-phenyl-5,10-dihydrophenazin-10-yl)phenyl]-4,5-diphenyl-1,2,4-triazole (abbreviation: PPZ-3TPT), 3-(9,9-dimethyl-9H-acridin-10-yl)-9H-xanthen-9-one (abbreviation: ACRXT) N), bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (abbreviation: DMAC-DPS), 10-phenyl-10H,10'H-spiro[acridine-9,9'-anthracene]-10'-one (abbreviation: ACRSA), 4-(9'-phenyl-3,3'-bi-9H-carbazol-9-yl)benzofuro[3,2-d]pyrimidine (abbreviation: 4PCCzBfpm), 4-[4-(9'-fu Heterocyclic compounds having a π-electron rich heteroaromatic ring and a π-electron deficient heteroaromatic ring, such as 9-[3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-9'-phenyl-2,3'-bi-9H-carbazole (abbreviation: mPCCzPTzn-02), may also be used.

[0069] [ka]

[0070] The heterocyclic compound has a π-electron rich heteroaromatic ring and a π-electron deficient heteroaromatic ring, and therefore has high electron transport and hole transport properties, and is therefore preferred.Among the skeletons having a π-electron deficient heteroaromatic ring, pyridine skeleton, diazine skeleton (pyrimidine skeleton, pyrazine skeleton, pyridazine skeleton) and triazine skeleton are preferred because they are stable and have good reliability.In particular, benzofuropyrimidine skeleton, benzothienopyrimidine skeleton, benzofuropyrazine skeleton and benzothienopyrazine skeleton are preferred because they have high acceptor properties and good reliability.

[0071] Among the skeletons having a π-electron-rich heteroaromatic ring, it is preferable to have at least one of the acridine skeleton, the phenoxazine skeleton, the phenothiazine skeleton, the furan skeleton, the thiophene skeleton, and the pyrrole skeleton, since they are stable and reliable. As the furan skeleton, the dibenzofuran skeleton is preferable, and as the thiophene skeleton, the dibenzothiophene skeleton is preferable. As the pyrrole skeleton, the indole skeleton, the carbazole skeleton, the indolocarbazole skeleton, the bicarbazole skeleton, and the 3-(9-phenyl-9H-carbazol-3-yl)-9H-carbazole skeleton are particularly preferable.

[0072] In addition, a substance in which a π-electron rich heteroaromatic ring and a π-electron deficient heteroaromatic ring are directly bonded is particularly preferable because the electron donating property of the π-electron rich heteroaromatic ring and the electron accepting property of the π-electron deficient heteroaromatic ring are both strong, and the energy difference between the S1 level and the T1 level is small, so that thermally activated delayed fluorescence can be efficiently obtained. In addition, an aromatic ring to which an electron withdrawing group such as a cyano group is bonded may be used instead of the π-electron deficient heteroaromatic ring. In addition, an aromatic amine skeleton, a phenazine skeleton, etc. can be used as the π-electron rich skeleton. In addition, a xanthene skeleton, a thioxanthene dioxide skeleton, an oxadiazole skeleton, a triazole skeleton, an imidazole skeleton, an anthraquinone skeleton, a boron-containing skeleton such as phenylborane or boranthrene, an aromatic ring or a heteroaromatic ring having a nitrile group or a cyano group such as benzonitrile or cyanobenzene, a carbonyl skeleton such as benzophenone, a phosphine oxide skeleton, a sulfone skeleton, etc. can be used as the π-electron deficient skeleton.

[0073] In this way, a π-electron deficient skeleton and a π-electron rich skeleton can be used in place of at least one of a π-electron deficient heteroaromatic ring and a π-electron rich heteroaromatic ring.

[0074] TADF materials are materials that have a small difference between the S1 and T1 levels and have the function of converting triplet excitation energy to singlet excitation energy by reverse intersystem crossing. Therefore, triplet excitation energy can be upconverted to singlet excitation energy by a small amount of thermal energy (reverse intersystem crossing), and singlet excitation states can be generated efficiently. In addition, triplet excitation energy can be converted into light emission.

[0075] In addition, exciplexes (also called exciplexes), which form an excited state with two types of substances, have an extremely small difference between the S1 level and the T1 level and function as TADF materials that can convert triplet excitation energy into singlet excitation energy.

[0076] As an index of the T1 level, a phosphorescence spectrum observed at low temperatures (for example, 77 K to 10 K) may be used. For a TADF material, when a tangent is drawn at the base of the short wavelength side of the fluorescence spectrum, and the energy of the wavelength of the extrapolated line is taken as the S1 level, and a tangent is drawn at the base of the short wavelength side of the phosphorescence spectrum, and the energy of the wavelength of the extrapolated line is taken as the T1 level, the difference between S1 and T1 is preferably 0.3 eV or less, and more preferably 0.2 eV or less.

[0077] When a TADF material is used as the guest material of the light-emitting layer 113, the S1 level of the host material is preferably higher than the S1 level of the TADF material. The T1 level of the host material is preferably higher than the T1 level of the TADF material.

[0078] Next, as a hole transporting material that can be used as a host material for the light emitting layer 113, a material having an electron mobility of 1×10 -6 cm 2 A substance having a hole mobility of 1000 .mu.s or more is preferred, and examples thereof include the following.

[0079] 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'-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), N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9'-bifluoren-2-amine (abbreviation: PCBASF) and other aromatic amine skeletons. Compounds with a carbazole skeleton, such as 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP), 4,4'-di(N-carbazolyl)biphenyl (abbreviation: CBP), 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP), and 3,3'-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP), and compounds with a carbazole skeleton, such as 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), 2,Examples of the compound include compounds having a thiophene skeleton such as 8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviation: DBTFLP-III) and 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviation: DBTFLP-IV), and compounds having a furan skeleton such as 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II) and 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviation: mmDBFFLBi-II). Among the above, compounds having an aromatic amine skeleton and compounds having a carbazole skeleton are preferable because they have good reliability, high hole transportability, and contribute to reducing the driving voltage. In addition, the organic compounds listed as examples of the hole transport material above can also be used.

[0080] In addition, the electron transporting material that can be used as the host material of the light emitting layer 113 is a material having an electron mobility of 1×10 -6 cm 2 A substance having an electron mobility of 100 .mu.s or more is preferred, and examples thereof include the following: In addition, an electron transporting material that can be used for the electron transport layer 114 described later can also be used.

[0081] Metal complexes such as bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (BeBq2), bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (BAlq), bis(8-quinolinolato)zinc(II) (Znq), bis[2-(2-benzoxazolyl)phenolato]zinc(II) (ZnPBO), and bis[2-(2-benzothiazolyl)phenolato]zinc(II) (ZnBTZ), as well as 2-(4-biphenylyl)-5-(4-tert-butyl phenyl)-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( We have developed heterocyclic compounds with polyazole skeletons, such as 1-phenyl-1H-benzimidazole (abbreviation: TPBI) and 2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: mDBTBIm-II), 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-I), and We have developed heterocyclic compounds with diazine skeletons such as 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), and 4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation: 4,6mDBTP2Pm-II), as well as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy), 1,3,Examples of the heterocyclic compounds include heterocyclic compounds having a pyridine skeleton, such as 5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB). Among the above, heterocyclic compounds having a diazine skeleton and heterocyclic compounds having a pyridine skeleton are preferred because of their high reliability. In particular, heterocyclic compounds having a diazine (pyrimidine or pyrazine) skeleton have high electron transport properties and contribute to reducing the driving voltage.

[0082] In addition, when a TADF material is used as the host material of the light-emitting layer 113, the above-mentioned materials can be used in the same manner. When a TADF material is used as the host material, triplet excitation energy generated in the TADF material is converted to singlet excitation energy by reverse intersystem crossing, and the energy is further transferred to the light-emitting center material, thereby improving the light-emitting efficiency of the light-emitting element. At this time, the TADF material functions as an energy donor, and the light-emitting center material functions as an energy acceptor. Therefore, using a TADF material as a host material is very effective when a fluorescent light-emitting material is used as a guest material. In addition, in order to obtain high light-emitting efficiency, the S1 level of the TADF material is preferably higher than the S1 level of the fluorescent light-emitting material. In addition, the T1 level of the TADF material is preferably higher than the S1 level of the fluorescent light-emitting material. Therefore, the T1 level of the TADF material is preferably higher than the T1 level of the fluorescent light-emitting material.

[0083] It is also preferable to use a TADF material that emits light that overlaps with the wavelength of the lowest energy absorption band of the fluorescent material, because this allows for smooth transfer of excitation energy from the TADF material to the fluorescent material, resulting in efficient emission.

[0084] In addition, in order to efficiently generate singlet excitation energy from triplet excitation energy by reverse intersystem crossing, it is preferable that carrier recombination occurs in the TADF material. In addition, it is preferable that the triplet excitation energy generated in the TADF material does not transfer to the triplet excitation energy of the fluorescent material. For this purpose, it is preferable that the fluorescent material has a protective group around the luminophore (skeleton causing light emission) of the fluorescent material. As the protective group, a substituent having no π bond is preferable, and a saturated hydrocarbon is preferable, specifically, an alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, and a trialkylsilyl group having 3 to 10 carbon atoms are mentioned, and it is more preferable that there are a plurality of protective groups. Since a substituent having no π bond has poor function of transporting carriers, the distance between the TADF material and the luminophore of the fluorescent material can be increased without affecting carrier transport or carrier recombination. Here, the luminophore refers to an atomic group (skeleton) causing light emission in the fluorescent material. The luminophore preferably has a skeleton having a π bond, preferably contains an aromatic ring, and preferably has a condensed aromatic ring or a condensed heteroaromatic ring. Examples of the condensed aromatic ring or the condensed heteroaromatic ring include a phenanthrene skeleton, a stilbene skeleton, an acridone skeleton, a phenoxazine skeleton, and a phenothiazine skeleton. In particular, fluorescent substances having a naphthalene skeleton, an anthracene skeleton, a fluorene skeleton, a chrysene skeleton, a triphenylene skeleton, a tetracene skeleton, a pyrene skeleton, a perylene skeleton, a coumarin skeleton, a quinacridone skeleton, or a naphthobisbenzofuran skeleton are preferred because they have a high fluorescence quantum yield.

[0085] When a fluorescent substance is used as a guest material of the light-emitting layer 113, a material having an anthracene skeleton is suitable as a host material. By using a substance having an anthracene skeleton, it is possible to realize a light-emitting layer having good luminous efficiency and durability. As a substance having an anthracene skeleton, a substance having a diphenylanthracene skeleton, in particular a substance having a 9,10-diphenylanthracene skeleton, is preferable because it is chemically stable.

[0086] In addition, when the host material has a carbazole skeleton, it is preferable because the hole injection / transport property is enhanced, but when the host material contains a benzocarbazole skeleton in which a benzene ring is further condensed to carbazole, it is more preferable because the HOMO is shallower than that of carbazole by about 0.1 eV, and holes can easily enter. In particular, when the host material contains a dibenzocarbazole skeleton, it is preferable because the HOMO is shallower than that of carbazole by about 0.1 eV, and holes can easily enter, and the hole transport property is excellent and the heat resistance is also high.

[0087] Therefore, a substance having both an anthracene skeleton, ie, a 9,10-diphenylanthracene skeleton, and a carbazole skeleton (or a benzocarbazole skeleton or a dibenzocarbazole skeleton) is more preferable as a host material. From the viewpoint of improving the hole injection / transport property, a benzofluorene skeleton or a dibenzofluorene skeleton may be used instead of the carbazole skeleton. Examples of such a substance include 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-anthracenyl)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), 9-phenyl-10-{4-(9-phenyl-9H-fluoren-9-yl)biphenyl-4'-yl}anthracene (abbreviation: FLPPA), 9-(1-naphthyl)-10-[4-(2-naphthyl)phenyl]anthracene (abbreviation: BH513), etc. In particular, CzPA, cgDBCzPA, 2mBnfPPA, and PCzPA are preferred because they show very good properties.

[0088] The host material may be a mixture of a plurality of substances, and when a mixture of the host material is used, it is preferable to mix an electron transporting material and a hole transporting material. By mixing the electron transporting material and the hole transporting material, the transporting property of the light-emitting layer 113 can be easily adjusted, and the recombination region can be easily controlled. The weight ratio of the content of the hole transporting material to the electron transporting material may be 1:19 to 19:1.

[0089] In addition, when the host material is a mixture of a plurality of substances as described above, a phosphorescent substance can be used as a part of the host material. The phosphorescent substance can be used as an energy donor that provides excitation energy to a fluorescent substance when the fluorescent substance is used as the emission center material.

[0090] In addition, the materials mixed as described above may form an exciplex. In this case, by selecting a combination of materials that forms an exciplex that emits light that overlaps with the wavelength of the lowest energy absorption band of the light-emitting material, energy transfer becomes smooth and light emission can be obtained efficiently. In addition, using such a configuration is preferable because it can reduce the driving voltage.

[0091] At least one of the materials forming the exciplex may be a phosphorescent material, in which case triplet excitation energy can be efficiently converted into singlet excitation energy by reverse intersystem crossing.

[0092] As a combination of materials that form an exciplex, it is preferable that the HOMO level of the hole transporting material is equal to or higher than the HOMO level of the electron transporting material. It is also preferable that the LUMO level of the hole transporting material is equal to or higher than the LUMO level of the electron transporting material. The LUMO level and HOMO level of the material can be derived from the electrochemical properties (reduction potential and oxidation potential) of the material measured by cyclic voltammetry (CV) measurement.

[0093] The formation of an exciplex can be confirmed, for example, by comparing the emission spectrum of a hole transport material, the emission spectrum of an electron transport material, and the emission spectrum of a mixed film obtained by mixing these materials, and observing the phenomenon that the emission spectrum of the mixed film shifts to a longer wavelength than the emission spectrum of each material (or has a new peak on the longer wavelength side). Alternatively, the formation of an exciplex can be confirmed by comparing the transient photoluminescence (PL) of a hole transport material, the transient PL of an electron transport material, and the transient PL of a mixed film obtained by mixing these materials, and observing the difference in transient response, such as the transient PL lifetime of the mixed film having a longer lifetime component than the transient PL lifetime of each material, or the proportion of delayed components becoming larger. The above-mentioned transient PL may also be read as transient electroluminescence (EL). That is, the formation of an exciplex can also be confirmed by comparing the transient EL of a hole transport material, the transient EL of a material having electron transport properties, and the transient EL of a mixed film obtained by mixing these materials, and observing the difference in transient response.

[0094] <Electron transport layer> The electron transport layer 114 is a layer that transports electrons injected from the second electrode 102 to the light-emitting layer 113, and is provided in contact with the light-emitting layer 113. Note that the electron transport layer 114 contains an electron transport material having a HOMO level of -6.0 eV or more, and an organometallic complex of an alkali metal or an alkaline earth metal. Note that the electron transport material having a HOMO level of -6.0 eV or more is an organometallic complex of an alkali metal or an alkaline earth metal having an electron mobility of 1×10 -7 cm 2 / Vs or more 5×10 -5 cm 2 / Vs or less is preferable, but 1×10 -7 cm 2 / Vs or more 1×10 -5 cm 2 It is more preferable that the value is equal to or less than / Vs.

[0095] In addition, the electron transporting material having a HOMO level of -6.0 eV or more preferably has an anthracene skeleton, and more preferably has an anthracene skeleton and a heterocyclic skeleton. In addition, the heterocyclic skeleton is preferably a nitrogen-containing five-membered ring skeleton. As the nitrogen-containing five-membered ring skeleton, it is particularly preferable to have a nitrogen-containing five-membered ring skeleton containing two heteroatoms in the ring, such as a pyrazole ring, an imidazole ring, an oxazole ring, or a thiazole ring. In addition, some of the electron transporting materials that can be used as the host material, or the materials that can be used as the host material in combination with the fluorescent material can be used for the electron transporting layer 114.

[0096] As the organometallic complex of an alkali metal or an alkaline earth metal, an organic complex of lithium is preferable, and in particular, 8-hydroxyquinolinato-lithium (abbreviation: Liq) is preferable.

[0097] Moreover, the electron mobility (electron mobility at a square root of the electric field strength [V / cm] of 600) of the electron transporting material having a HOMO level of -6.0 eV or more used in the electron transporting layer 114 is preferably smaller than the electron mobility of the host material used in the light-emitting layer 113. By reducing the electron transportability in the electron transporting layer, the amount of electrons injected into the light-emitting layer can be controlled, and the light-emitting layer can be prevented from becoming in an electron excess state.

[0098] <Electron injection layer> The electron injection layer 115 is a layer for increasing the efficiency of electron injection from the cathode 102, and it is preferable to use a material having a small difference (0.5 eV or less) between the work function value of the cathode 102 material and the LUMO level value of the material used for the electron injection layer 115. Therefore, the electron injection layer 115 may be made of any of the following metals: lithium, cesium, lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF2), 8-(hydroxyquinolinato)lithium (abbreviation: Liq), 2-(2-pyridyl)phenolatolithium (abbreviation: LiPP), 2-(2-pyridyl)-3-pyridinolatolithium (abbreviation: LiPPy), 4-phenyl-2-(2-pyridyl)phenolatolithium (abbreviation: LiPPP), lithium oxide (LiO x ), alkaline metals such as cesium carbonate, alkaline earth metals, or compounds thereof can be used. Also, rare earth metal compounds such as erbium fluoride (ErF3) can be used.

[0099] Also, as in the light-emitting device shown in Fig. 2B, a charge generating layer 104 is provided between two EL layers (103a, 103b), so that a structure in which a plurality of EL layers are stacked between a pair of electrodes (also called a tandem structure) can be obtained. Note that the hole injection layer (111), hole transport layer (112), light-emitting layer (113), electron transport layer (114), and electron injection layer (115) described in Fig. 2A in this embodiment have the same functions and materials as the hole injection layer (111a, 111b), hole transport layer (112a, 112b), light-emitting layer (113a, 113b), electron transport layer (114a, 114b), and electron injection layer (115a, 115b) described in Fig. 2B.

[0100] <Charge generation layer> In addition, the charge generation layer 104 in the light-emitting device of FIG. 2B has a function of injecting electrons into the EL layer 103a on the first electrode 101 side, which is the anode, and injecting holes into the EL layer 103b on the second electrode 102 side, which is the cathode, when a voltage is applied between the first electrode (anode) 101 and the second electrode (cathode) 102. The charge generation layer 104 may be a structure in which an electron acceptor is added to a hole transporting material (P-type layer), or a structure in which an electron donor is added to an electron transporting material (N-type layer). In addition, both of these structures may be laminated. In addition, the above-mentioned P-type layer may be formed by combining either one or both of an electron relay layer and an electron injection buffer layer, which will be described later. In addition, by forming the charge generation layer 104 using the above-mentioned material, it is possible to suppress an increase in the driving voltage when EL layers are laminated.

[0101] In the case where the charge generation layer 104 has a structure in which an electron acceptor is added to a hole-transporting material (P-type layer), the material shown in this embodiment mode can be used as the hole-transporting material. Examples of the electron acceptor include 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ) and chloranil. Examples of the oxide of a metal belonging to Groups 4 to 8 of the periodic table can also be used. Specific examples of the oxide include vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide.

[0102] In the case where the charge generation layer 104 has a structure in which an electron donor is added to an electron transporting material (N-type layer), the material shown in this embodiment can be used as the electron transporting material. In addition, as the electron donor, an alkali metal, an alkaline earth metal, a rare earth metal, or a metal belonging to Groups 2 and 13 of the periodic table, and an oxide or carbonate thereof can be used. Specifically, it is preferable to use lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca), ytterbium (Yb), indium (In), lithium oxide, cesium carbonate, or the like. In addition, an organic compound such as tetrathianaphthacene may be used as the electron donor.

[0103] The electron relay layer, which is preferably combined with the P-type layer, is provided between the electron injection buffer layer and the P-type layer, and has the function of preventing the interaction between the electron injection buffer layer and the P-type layer and smoothly transferring electrons. The electron relay layer contains at least an electron transporting material, and the LUMO level of the electron transporting material contained in the electron relay layer is preferably between the LUMO level of the electron accepting material in the P-type layer and the LUMO level of the material contained in the electron injection buffer layer. The specific energy level of the LUMO level of the electron transporting material used in the electron relay layer is -5.0 eV or more, preferably -5.0 eV or more and -3.0 eV or less. The electron transporting material used in the electron relay layer is preferably a phthalocyanine-based material or a metal complex having a metal-oxygen bond and an aromatic ligand.

[0104] The electron injection buffer layer can be made of a material with high electron injection properties, such as alkali metals, alkaline earth metals, rare earth metals, and compounds thereof (alkali metal compounds (including oxides such as lithium oxide, halides, and carbonates such as lithium carbonate and cesium carbonate), alkaline earth metal compounds (including oxides, halides, and carbonates), or rare earth metal compounds (including oxides, halides, and carbonates)).

[0105] In addition, when the electron injection buffer layer is formed containing an electron transporting material and an electron donating substance, examples of the electron donating substance include alkali metals, alkaline earth metals, rare earth metals, and compounds thereof (alkali metal compounds (including oxides such as lithium oxide, halides, and carbonates such as lithium carbonate and cesium carbonate), alkaline earth metal compounds (including oxides, halides, and carbonates), and rare earth metal compounds (including oxides, halides, and carbonates)), as well as organic compounds such as tetrathianaphthacene (abbreviation: TTN), nickelocene, and decamethylnickelocene. Note that the electron transporting material can be formed using the same material as that constituting the electron transporting layer described above.

[0106] Although FIG. 2B shows a configuration in which the EL layer 103 has two laminated layers, a laminated structure of three or more EL layers may be used by providing a charge generating layer between different EL layers.

[0107] The charge generating layer can be used in place of the electron injection layer. In this case, it is preferable that the electron injection buffer layer, the electron relay layer, and the P-type layer are laminated in this order from the anode side.

[0108] <Substrate> The light-emitting device shown in this embodiment mode can be formed on various substrates. The type of substrate is not limited to a specific one. Examples of the substrate include a semiconductor substrate (e.g., a single crystal substrate or a silicon substrate), an SOI substrate, a glass substrate, a quartz substrate, a plastic substrate, a metal substrate, a stainless steel substrate, a substrate having stainless steel foil, a tungsten substrate, a substrate having tungsten foil, a flexible substrate, a laminated film, a paper containing a fibrous material, or a base film.

[0109] Examples of glass substrates include barium borosilicate glass, aluminoborosilicate glass, soda lime glass, etc. Examples of flexible substrates, laminated films, base films, etc. include plastics such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyethersulfone (PES), synthetic resins such as acrylic resins, polypropylene, polyester, polyvinyl fluoride, polyvinyl chloride, polyamide, polyimide, aramid resin, epoxy resin, inorganic deposition film, and paper.

[0110] In addition, the light-emitting device shown in this embodiment can be manufactured by a vacuum process such as a deposition method, or a solution process such as a spin coating method or an ink-jet method. When a deposition method is used, a physical deposition method (PVD method) such as a sputtering method, an ion plating method, an ion beam deposition method, a molecular beam deposition method, or a vacuum deposition method, a chemical deposition method (CVD method), or the like can be used. In particular, the functional layers (hole injection layer (111, 111a, 111b), hole transport layer (112, 112a, 112b), light-emitting layer (113, 113a, 113b, 113c), electron transport layer (114, 114a, 114b), electron injection layer (115, 115a, 115b)) and charge generation layer (104, 104a, 104b) included in the EL layer of the light-emitting device can be formed by a deposition method (vacuum deposition method, etc.), a coating method (dip coating method, die coating method, bar coating method, spin coating method, spray coating method, etc.), a printing method (inkjet method, screen (screen printing) method, offset (lithographic printing) method, flexo (relief printing) method, gravure method, microcontact method, nanoimprint method, etc.), etc.

[0111] In addition, the functional layers (hole injection layer (111, 111a, 111b), hole transport layer (112, 112a, 112b), light emitting layer (113, 113a, 113b, 113c), electron transport layer (114, 114a, 114b), electron injection layer (115, 115a, 115b)) constituting the EL layer (103, 103a, 103b) of the light emitting device shown in this embodiment and the charge generation layer (104, 104a, 104b) are not limited to the above-mentioned materials, and other materials can be used in combination as long as they can fulfill the functions of each layer. As an example, a polymer compound (oligomer, dendrimer, polymer, etc.), a medium molecular compound (a compound in the intermediate range between a low molecular weight and a polymer: molecular weight 400 to 4000), an inorganic compound (quantum dot material, etc.), etc. can be used. As the quantum dot material, colloidal quantum dot materials, alloy type quantum dot materials, core-shell type quantum dot materials, core type quantum dot materials, etc. can be used.

[0112] A light-emitting device having the above structure and used in a light-emitting device of one embodiment of the present invention can have a long lifetime.

[0113] The structure described in this embodiment mode can be used in appropriate combination with structures described in other embodiments.

[0114] (Embodiment 3) In this embodiment, a light-emitting device according to one embodiment of the present invention will be described. The light-emitting device shown in Fig. 3A is an active matrix type light-emitting device in which a transistor (FET) 202 and light-emitting devices (203R, 203G, 203B, 203W) on a first substrate 201 are electrically connected, and the light-emitting devices (203R, 203G, 203B, 203W) have a common EL layer 204 and a microcavity structure in which the optical distance between the electrodes of each light-emitting device is adjusted according to the light-emitting color of each light-emitting device. In addition, the light-emitting device is a top-emission type light-emitting device in which light emitted from the EL layer 204 is emitted through color filters (206R, 206G, 206B) formed on a second substrate 205.

[0115] In the light-emitting device shown in Fig. 3A, the first electrode 207 is formed to function as a reflective electrode. The second electrode 208 is formed to function as a semi-transmissive / semi-reflective electrode having both the functions of transparency and reflectivity to light (visible light or near-infrared light). Note that the electrode materials for forming the first electrode 207 and the second electrode 208 can be appropriately selected by referring to the descriptions of other embodiments.

[0116] 3A, for example, when light emitting device 203R is a red light emitting device, light emitting device 203G is a green light emitting device, light emitting device 203B is a blue light emitting device, and light emitting device 203W is a white light emitting device, as shown in FIG 3B, light emitting device 203R is adjusted so that the optical distance between first electrode 207 and second electrode 208 is 200R, light emitting device 203G is adjusted so that the optical distance between first electrode 207 and second electrode 208 is 200G, and light emitting device 203B is adjusted so that the optical distance between first electrode 207 and second electrode 208 is 200B. Note that, as shown in FIG 3B, optical adjustment can be performed by stacking conductive layer 210R on first electrode 207 in light emitting device 203R and stacking conductive layer 210G in light emitting device 203G.

[0117] Color filters (206R, 206G, 206B) are formed on the second substrate 205. The color filters are filters that pass a specific wavelength range of visible light and block a specific wavelength range. Therefore, as shown in FIG. 3A, by providing a color filter 206R that passes only a red wavelength range at a position overlapping the light emitting device 203R, red light can be emitted from the light emitting device 203R. By providing a color filter 206G that passes only a green wavelength range at a position overlapping the light emitting device 203G, green light can be emitted from the light emitting device 203G. By providing a color filter 206B that passes only a blue wavelength range at a position overlapping the light emitting device 203B, blue light can be emitted from the light emitting device 203B. However, the light emitting device 203W can emit white light without providing a color filter. A black layer (black matrix) 209 may be provided at the end of one type of color filter. Furthermore, the color filters (206R, 206G, 206B) and the black layer 209 may be covered with an overcoat layer made of a transparent material.

[0118] FIG. 3A shows a light-emitting device having a structure (top emission type) in which light is extracted on the second substrate 205 side, but as shown in FIG. 3C, a light-emitting device having a structure (bottom emission type) in which light is extracted on the first substrate 201 side on which the FET 202 is formed may be used. In the case of a bottom emission type light-emitting device, the first electrode 207 is formed to function as a semi-transmissive / semi-reflective electrode, and the second electrode 208 is formed to function as a reflective electrode. The first substrate 201 is at least a light-transmitting substrate. The color filters (206R', 206G', 206B') may be provided on the first substrate 201 side of the light-emitting devices (203R, 203G, 203B) as shown in FIG. 3C.

[0119] 3A shows the case where the light-emitting device is a red light-emitting device, a green light-emitting device, a blue light-emitting device, and a white light-emitting device, but the light-emitting device according to one embodiment of the present invention is not limited to these configurations and may be a configuration having a yellow light-emitting device or an orange light-emitting device. Note that the materials used in the EL layer (light-emitting layer, hole injection layer, hole transport layer, electron transport layer, electron injection layer, charge generation layer, etc.) for producing these light-emitting devices may be appropriately selected by referring to the descriptions of other embodiments. Note that in this case, it is necessary to appropriately select a color filter according to the emission color of the light-emitting device.

[0120] With the above-mentioned configuration, a light emitting device including light emitting devices that emit light of a plurality of colors can be obtained.

[0121] Note that the structure described in this embodiment mode can be used in appropriate combination with structures described in other embodiments.

[0122] (Embodiment 4) In this embodiment, a light-emitting device which is one embodiment of the present invention will be described.

[0123] By applying the device configuration of the light-emitting device which is one embodiment of the present invention, an active matrix light-emitting device or a passive matrix light-emitting device can be manufactured. Note that an active matrix light-emitting device has a configuration in which a light-emitting device and a transistor (FET) are combined. Therefore, both a passive matrix light-emitting device and an active matrix light-emitting device are included in one embodiment of the present invention. Note that the light-emitting device described in the other embodiments can be applied to the light-emitting device shown in this embodiment.

[0124] In this embodiment mode, an active matrix light emitting device will be described with reference to FIG.

[0125] 4A is a top view showing the light-emitting device, and FIG. 4B is a cross-sectional view taken along dashed line A-A' in FIG. 4A. The active matrix light-emitting device has a pixel portion 302, a driver circuit portion (source line driver circuit) 303, and a driver circuit portion (gate line driver circuit) (304a, 304b) provided on a first substrate 301. The pixel portion 302 and the driver circuit portion (303, 304a, 304b) are sealed between the first substrate 301 and a second substrate 306 by a sealant 305.

[0126] Moreover, on the first substrate 301, lead wiring 307 is provided. The lead wiring 307 is electrically connected to an FPC 308 which is an external input terminal. The FPC 308 transmits signals (e.g., video signals, clock signals, start signals, reset signals, etc.) and potentials from the outside to the drive circuit units (303, 304a, 304b). A printed wiring board (PWB) may be attached to the FPC 308. The state in which the FPC and PWB are attached is included in the light-emitting device.

[0127] Next, a cross-sectional structure is shown in FIG. 4B.

[0128] The pixel section 302 is formed by a plurality of pixels each having a FET (switching FET) 311, a FET (current control FET) 312, and a first electrode 313 electrically connected to the FET 312. The number of FETs each pixel has is not particularly limited, and may be appropriately provided as necessary.

[0129] The FETs 309, 310, 311, and 312 are not particularly limited, and may be, for example, staggered or inverted staggered transistors, or may have a top-gate or bottom-gate transistor structure.

[0130] Note that the crystallinity of a semiconductor that can be used for these FETs 309, 310, 311, and 312 is not particularly limited, and any of an amorphous semiconductor and a semiconductor having crystallinity (a microcrystalline semiconductor, a polycrystalline semiconductor, a single crystal semiconductor, or a semiconductor having a crystalline region in a part) may be used. Note that the use of a semiconductor having crystallinity is preferable because it can suppress deterioration of transistor characteristics.

[0131] Examples of the semiconductor that can be used include Group 14 elements, compound semiconductors, oxide semiconductors, and organic semiconductors. Typically, a semiconductor containing silicon, a semiconductor containing gallium arsenide, and an oxide semiconductor containing indium can be used.

[0132] The driver circuit unit 303 has an FET 309 and an FET 310. The driver circuit unit 303 may be formed of a circuit including transistors of the same polarity (either N-type or P-type), or may be formed of a CMOS circuit including N-type transistors and P-type transistors. Also, the driver circuit unit 303 may be configured to have an external driver circuit.

[0133] The end of the first electrode 313 is covered with an insulator 314. For the insulator 314, organic compounds such as negative photosensitive resin and positive photosensitive resin (acrylic resin) or inorganic compounds such as silicon oxide, silicon oxynitride, and silicon nitride can be used. The upper end or lower end of the insulator 314 preferably has a curved surface having a curvature. This can improve the coverage of the film formed on the upper layer of the insulator 314.

[0134] An EL layer 315 and a second electrode 316 are stacked over the first electrode 313. The EL layer 315 has a light-emitting layer, a hole injection layer, a hole transport layer, an electron transport layer, an electron injection layer, a charge generation layer, and the like.

[0135] Note that the structures and materials described in the other embodiments can be applied to the structure of the light-emitting device 317 shown in this embodiment. Although not shown here, the second electrode 316 is electrically connected to the FPC 308 which is an external input terminal.

[0136] In addition, although only one light-emitting device 317 is illustrated in the cross-sectional view shown in FIG. 4B, a plurality of light-emitting devices are arranged in a matrix in the pixel section 302. In the pixel section 302, light-emitting devices capable of obtaining three types of light emission (R, G, B) can be selectively formed, respectively, to form a light-emitting device capable of full-color display. In addition to the light-emitting devices capable of obtaining three types of light emission (R, G, B), light-emitting devices capable of obtaining light emission of, for example, white (W), yellow (Y), magenta (M), cyan (C), etc. may be formed. For example, by adding the light-emitting devices capable of obtaining the above-mentioned several types of light emission to the light-emitting device capable of obtaining three types of light emission (R, G, B), effects such as improved color purity and reduced power consumption can be obtained. In addition, a light-emitting device capable of full-color display may be formed by combining with a color filter. Note that the types of color filters that can be used are red (R), green (G), blue (B), cyan (C), magenta (M), yellow (Y), etc.

[0137] The FETs (309, 310, 311, 312) on the first substrate 301 and the light emitting device 317 have a structure in which they are provided in a space 318 surrounded by the first substrate 301, the second substrate 306, and the sealant 305, by bonding the second substrate 306 and the first substrate 301 with the sealant 305. The space 318 may be filled with an inert gas (nitrogen, argon, etc.) or an organic substance (including the sealant 305).

[0138] The sealing material 305 can be made of epoxy resin or glass frit. It is preferable to use a material that is as impermeable to moisture and oxygen as possible for the sealing material 305. The second substrate 306 can be made of the same material as the first substrate 301. Therefore, it is possible to use various substrates described in other embodiments as appropriate. As the substrate, in addition to a glass substrate or a quartz substrate, a plastic substrate made of FRP (Fiber-Reinforced Plastics), PVF (Polyvinyl Fluoride), polyester, acrylic resin, or the like can be used. When glass frit is used as the sealing material, it is preferable that the first substrate 301 and the second substrate 306 are glass substrates from the viewpoint of adhesion.

[0139] In this manner, an active matrix light emitting device can be obtained.

[0140] In addition, when forming an active matrix type light emitting device on a flexible substrate, the FET and the light emitting device may be formed directly on the flexible substrate, or the FET and the light emitting device may be formed on another substrate having a peeling layer, and then the FET and the light emitting device may be peeled off at the peeling layer by applying heat, force, laser irradiation, or the like, and then transferred to the flexible substrate to fabricate the device. As the peeling layer, for example, a laminate of inorganic films of a tungsten film and a silicon oxide film, or an organic resin film such as polyimide, etc. may be used. In addition to substrates on which transistors can be formed, examples of the flexible substrate include paper substrates, cellophane substrates, aramid film substrates, polyimide film substrates, cloth substrates (including natural fibers (silk, cotton, hemp), synthetic fibers (nylon, polyurethane, polyester) or regenerated fibers (acetate, cupra, rayon, regenerated polyester), etc.), leather substrates, and rubber substrates. By using these substrates, it is possible to achieve excellent durability and heat resistance, and to achieve lighter weight and thinner thickness.

[0141] In addition, the light-emitting device of the active matrix type light-emitting device may be driven in a pulsed manner (using a frequency of, for example, kHz or MHz) to be used for display. The light-emitting device formed using the above organic compound has excellent frequency characteristics, so that the time for driving the light-emitting device can be shortened and power consumption can be reduced. In addition, the shortened driving time suppresses heat generation, so that deterioration of the light-emitting device can be reduced.

[0142] Note that the structure described in this embodiment mode can be used in appropriate combination with structures described in other embodiment modes.

[0143] (Embodiment 5) In this embodiment, examples of various electronic devices and automobiles completed by applying a light-emitting device according to one embodiment of the present invention and a light-emitting device having a light-emitting device according to one embodiment of the present invention will be described. Note that the light-emitting device can be applied mainly to a display portion in the electronic devices described in this embodiment.

[0144] The electronic device shown in Figures 5A to 5E may have a housing 7000, a display unit 7001, a speaker 7003, an LED lamp 7004, operation keys 7005 (including a power switch or an operation switch), a connection terminal 7006, a sensor 7007 (including a function to measure force, displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays), a microphone 7008, etc.

[0145] FIG. 5A is a mobile computer, which may have, in addition to those mentioned above, a switch 7009, an infrared port 7010, etc.

[0146] FIG. 5B shows a portable image reproducing device (for example, a DVD reproducing device) equipped with a recording medium, which may further include a second display unit 7002, a recording medium reading unit 7011, and the like in addition to the above-mentioned components.

[0147] FIG. 5C shows a digital camera with a television receiving function, which may further include an antenna 7014, a shutter button 7015, an image receiving unit 7016, and the like in addition to the components described above.

[0148] 5D shows a portable information terminal. The portable information terminal has a function of displaying information on three or more sides of a display unit 7001. Here, an example is shown in which information 7052, information 7053, and information 7054 are displayed on different sides. For example, a user can check information 7053 displayed in a position that can be observed from above the portable information terminal while the portable information terminal is stored in a breast pocket of clothes. The user can check the display without taking the portable information terminal out of the pocket and decide, for example, whether or not to answer a call.

[0149] FIG. 5E shows a mobile information terminal (including a smartphone), and a housing 7000 may have a display unit 7001, operation keys 7005, and the like. The mobile information terminal may also have a speaker 7003, a connection terminal 7006, a sensor 7007, and the like. The mobile information terminal may also display text and image information on a plurality of surfaces. Here, an example is shown in which three icons 7050 are displayed. Information 7051, indicated by a dashed rectangle, may also be displayed on another surface of the display unit 7001. Examples of the information 7051 include notifications of incoming e-mail, SNS, and phone calls, titles of e-mail and SNS, sender name, date and time, time, remaining battery level, and antenna reception strength. Alternatively, an icon 7050 or the like may be displayed at the position where the information 7051 is displayed.

[0150] FIG. 5F shows a large television device (also called a television or a television receiver), which may have a housing 7000, a display unit 7001, and the like. Here, a configuration in which the housing 7000 is supported by a stand 7018 is shown. The television device can be operated by a separate remote control unit 7111, and the like. Note that the display unit 7001 may be provided with a touch sensor, and may be operated by touching the display unit 7001 with a finger or the like. The remote control unit 7111 may have a display unit that displays information output from the remote control unit 7111. The channel and volume can be operated by the operation keys or touch panel provided in the remote control unit 7111, and the image displayed on the display unit 7001 can be operated.

[0151] The electronic devices shown in Figs. 5A to 5F can have various functions. For example, they can have a function of displaying various information (still images, videos, text images, etc.) on the display unit, a touch panel function, a function of displaying a calendar, date or time, etc., a function of controlling processing by various software (programs), a wireless communication function, a function of connecting to various computer networks using the wireless communication function, a function of transmitting or receiving various data using the wireless communication function, a function of reading out a program or data recorded on a recording medium and displaying it on the display unit, etc. Furthermore, in an electronic device having multiple display units, they can have a function of displaying image information mainly on one display unit and text information mainly on another display unit, or a function of displaying a stereoscopic image by displaying an image taking into account parallax on multiple display units, etc. Furthermore, in an electronic device having an image receiving unit, they can have a function of taking still images, a function of taking videos, a function of automatically or manually correcting the taken images, a function of saving the taken images on a recording medium (external or built-in to the camera), a function of displaying the taken images on the display unit, etc. Note that the functions that the electronic devices shown in Figs. 5A to 5F can have are not limited to these, and they can have various functions.

[0152] FIG. 5G shows a wristwatch-type mobile information terminal, which can be used as, for example, a smart watch. This wristwatch-type mobile information terminal includes a housing 7000, a display unit 7001, operation buttons 7022 and 7023, a connection terminal 7024, a band 7025, a microphone 7026, a sensor 7029, a speaker 7030, and the like. The display unit 7001 has a curved display surface, and can display information along the curved display surface. This mobile information terminal can also perform hands-free conversation by mutual communication with, for example, a headset capable of wireless communication. Note that the connection terminal 7024 can also perform data transmission between the mobile information terminal and another information terminal, and can also perform charging. Charging can also be performed by wireless power supply.

[0153] A display unit 7001 mounted on a housing 7000 that also serves as a bezel has a non-rectangular display area. The display unit 7001 can display an icon indicating the time, other icons, etc. The display unit 7001 may be a touch panel (input / output device) equipped with a touch sensor (input device).

[0154] The smart watch shown in Fig. 5G can have various functions. For example, it can have a function of displaying various information (still images, videos, text images, etc.) on the display unit, a touch panel function, a function of displaying a calendar, date or time, etc., a function of controlling processing by various software (programs), a wireless communication function, a function of connecting to various computer networks using the wireless communication function, a function of transmitting or receiving various data using the wireless communication function, a function of reading out a program or data recorded on a recording medium and displaying it on the display unit, etc.

[0155] The housing 7000 may also have a speaker, sensors (including functions to measure force, displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays), microphone, etc. inside the housing 7000.

[0156] Note that the light-emitting device which is one embodiment of the present invention can be used in each display portion of the electronic devices described in this embodiment, and the electronic devices can have a long lifetime.

[0157] An example of an electronic device to which a light-emitting device is applied is a foldable portable information terminal as shown in Fig. 6A to Fig. 6C. Fig. 6A shows a portable information terminal 9310 in an unfolded state. Fig. 6B shows the portable information terminal 9310 in a state in the process of changing from one of an unfolded state and a folded state to the other. Fig. 6C shows the portable information terminal 9310 in a folded state. The portable information terminal 9310 has excellent portability in a folded state, and has excellent viewability of a display due to a seamless wide display area in an unfolded state.

[0158] The display portion 9311 is supported by three housings 9315 connected by hinges 9313. Note that the display portion 9311 may be a touch panel (input / output device) equipped with a touch sensor (input device). The display portion 9311 can be reversibly transformed from an unfolded state of the portable information terminal 9310 to a folded state by bending the two housings 9315 via the hinges 9313. Note that the light-emitting device of one embodiment of the present invention can be used for the display portion 9311. In addition, an electronic device with a long life can be realized. A display region 9312 in the display portion 9311 is a display region located on a side surface of the portable information terminal 9310 in the folded state. In the display region 9312, information icons, frequently used apps, shortcuts to programs, and the like can be displayed, and thus information can be checked and apps can be started smoothly.

[0159] 7A and 7B show automobiles to which the light emitting device is applied. That is, the light emitting device can be provided integrally with the automobile. Specifically, the light emitting device can be applied to the exterior lights 5101 (including the rear of the vehicle body), the wheels 5102 of the tires, a part or the whole of the doors 5103, and the like, of the automobile shown in FIG. 7A. The light emitting device can also be applied to the interior display unit 5104, steering wheel 5105, shift lever 5106, seat 5107, inner rear view mirror 5108, windshield 5109, and the like, shown in FIG. 7B. It may also be applied to parts of other glass windows.

[0160] In the above manner, an electronic device or an automobile to which the light-emitting device according to one embodiment of the present invention is applied can be obtained. In that case, an electronic device with a long life can be realized. The electronic devices and automobiles to which the light-emitting device according to one embodiment of the present invention can be applied are not limited to those described in this embodiment, and can be applied in any field.

[0161] Note that the structure described in this embodiment mode can be used in appropriate combination with structures described in other embodiment modes.

[0162] (Embodiment 6) In this embodiment, a structure of a lighting device manufactured using a light-emitting device which is one embodiment of the present invention or a light-emitting device which is a part of the light-emitting device will be described with reference to FIGS.

[0163] 8A and 8B are cross-sectional views of an example of a lighting device. Note that Fig. 8A shows a bottom emission type lighting device that extracts light on the substrate side, and Fig. 8B shows a top emission type lighting device that extracts light on the sealing substrate side.

[0164] 8A includes a light-emitting device 4002 on a substrate 4001. The substrate 4001 also includes a substrate 4003 having projections and recesses on the outer side thereof. The light-emitting device 4002 includes a first electrode 4004, an EL layer 4005, and a second electrode 4006.

[0165] The first electrode 4004 is electrically connected to an electrode 4007, and the second electrode 4006 is electrically connected to an electrode 4008. In addition, an auxiliary wiring 4009 electrically connected to the first electrode 4004 may be provided. Note that an insulating layer 4010 is formed over the auxiliary wiring 4009.

[0166] The substrate 4001 and the sealing substrate 4011 are bonded together with a sealant 4012. A desiccant 4013 is preferably provided between the sealing substrate 4011 and the light-emitting device 4002. Since the substrate 4003 has projections and recesses as shown in FIG. 8A, the efficiency of extracting light generated in the light-emitting device 4002 can be improved.

[0167] 8B includes a light emitting device 4202 on a substrate 4201. The light emitting device 4202 includes a first electrode 4204, an EL layer 4205, and a second electrode 4206.

[0168] The first electrode 4204 is electrically connected to the electrode 4207, and the second electrode 4206 is electrically connected to the electrode 4208. In addition, an auxiliary wiring 4209 electrically connected to the second electrode 4206 may be provided. In addition, an insulating layer 4210 may be provided under the auxiliary wiring 4209.

[0169] The substrate 4201 and a sealing substrate 4211 having projections and recesses are bonded with a sealant 4212. A barrier film 4213 and a planarization film 4214 may be provided between the sealing substrate 4211 and the light-emitting device 4202. Since the sealing substrate 4211 has projections and recesses as shown in FIG. 8B, the efficiency of extracting light generated in the light-emitting device 4202 can be improved.

[0170] An example of the application of these lighting devices is a ceiling light for indoor lighting. Ceiling lights include a direct ceiling type and a ceiling recessed type. Such lighting devices are constructed by combining a light-emitting device with a housing and a cover.

[0171] In addition, it can be applied to footlights that can irradiate light onto the floor surface and increase the safety of the feet. Footlights are effective for use in bedrooms, stairs, and corridors, for example. In such cases, the size and shape can be changed appropriately according to the size and structure of the room. It is also possible to make a stationary lighting device that is configured by combining a light-emitting device with a support base.

[0172] It can also be used as a sheet-type lighting device (sheet lighting). Sheet lighting is attached to a wall surface, so it does not take up much space and can be used for a wide range of purposes. It can also be easily made larger. It can also be used on curved walls and housings.

[0173] In addition to the above, the light-emitting device according to one embodiment of the present invention or a light-emitting device that is a part of the light-emitting device can be used as a lighting device having a function as the furniture in a room.

[0174] As described above, various lighting devices using the light-emitting device can be obtained. Note that these lighting devices are included in one embodiment of the present invention.

[0175] The structure described in this embodiment mode can be used in appropriate combination with structures described in other embodiment modes.

[0176] <Reference example> In this reference example, a method for calculating the HOMO level, LUMO level, and electron mobility of the organic compound used in each embodiment will be described.

[0177] The HOMO level and the LUMO level can be calculated based on cyclic voltammetry (CV) measurements.

[0178] The measurement device used was an electrochemical analyzer (manufactured by BAS Co., Ltd., model number: ALS model 600A or 600C). The solution used for CV measurement was prepared by dissolving the supporting electrolyte tetra-n-butylammonium perchlorate (n-Bu4NClO4) (manufactured by Tokyo Chemical Industry Co., Ltd., catalog number: T0836) in dehydrated dimethylformamide (DMF) (manufactured by Aldrich Co., Ltd., 99.8%, catalog number: 22705-6) to a concentration of 100 mmol / L, and further dissolving the measurement target to a concentration of 2 mmol / L. A platinum electrode (PTE platinum electrode, BAS Co., Ltd.) was used as the working electrode, a platinum electrode (Pt counter electrode (5 cm) for VC-3, BAS Co., Ltd.) was used as the auxiliary electrode, and an Ag / Ag+ electrode (RE7 non-aqueous solvent reference electrode, BAS Co., Ltd.) was used as the reference electrode. The measurements were performed at room temperature (20-25°C). The scan rate during CV measurements was standardized to 0.1 V / sec, and the oxidation potential Ea [V] and reduction potential Ec [V] relative to the reference electrode were measured. Ea was the midpoint potential of the oxidation-reduction wave, and Ec was the midpoint potential of the reduction-oxidation wave. Here, since the potential energy of the reference electrode used in this reference example with respect to the vacuum level is known to be -4.94 [eV], the HOMO level and LUMO level can be calculated from the formulas HOMO level [eV] = -4.94-Ea and LUMO level [eV] = -4.94-Ec, respectively.

[0179] The electron mobility can be measured by impedance spectroscopy (IS method).

[0180] Measurements of carrier mobility in EL materials have long been known using the time-of-flight (TOF) method and the space-charge-limited current (SCLC) method, which uses the I-V characteristics of the SCLC. The TOF method requires samples with a significantly thicker film thickness than actual organic EL elements. The SCLC method has the disadvantage of not being able to obtain the electric field strength dependence of carrier mobility. The IS method requires a thin organic film thickness of only a few hundred nm for measurement, making it possible to form a film with a relatively small amount of EL material. This method is characterized by its ability to measure mobility at a film thickness close to that of actual EL elements, and also to obtain the electric field strength dependence of carrier mobility.

[0181] In the IS method, a minute sine wave voltage signal (V=V0[exp(jωt)]) is applied to the EL element, and the impedance (Z=V / I) of the EL element is calculated from the phase difference between the input signal and the current amplitude of the response current signal (I=I0exp[j(ωt+φ)]). By applying a voltage varying from high frequency to low frequency to the element, it is possible to separate and measure the components with various relaxation times that contribute to the impedance.

[0182] Here, admittance Y (=1 / Z), which is the reciprocal of impedance, can be expressed by conductance G and susceptance B as shown in the following equation (1).

[0183]

number

[0184] Furthermore, the following equations (2) and (3) can be calculated using a single charge injection model. Here, g (equation (4)) is the differential conductance. In the equations, C is the capacitance, θ is ωt, which is the travel angle, and ω is the angular frequency. t is the travel time. The current equation, Poisson's equation, and current continuity equation are used in the analysis, and the existence of diffusion current and trap levels is ignored.

[0185]

number

[0186] The -ΔB method is a method for calculating mobility from the frequency characteristics of capacitance, and the ωΔG method is a method for calculating mobility from the frequency characteristics of conductance.

[0187] In practice, first, an electron-only element is made of the material for which the electron mobility is to be determined. An electron-only element is an element designed so that only electrons flow as carriers. In this specification, a method for calculating mobility from the frequency characteristics of capacitance (-ΔB method) is explained. A schematic diagram of the electron-only element used is shown in Figure 9.

[0188] The structure of the electron-only element prepared for measurement this time has a first layer 910, a second layer 911, and a third layer 912 between a first electrode 901 and a second electrode 902, as shown in Figure 9. The material for which the electron mobility is to be determined may be used as the material for the second layer 911. Here, an example is given in which the electron mobility of a co-evaporated film of 2-{4-[9,10-di(naphthalene-2-yl)-2-anthryl]phenyl}-1-phenyl-1H-benzimidazole (abbreviation: ZADN) and Liq was measured in a weight ratio of 1:1. Specific configuration examples are summarized in the table below.

[0189] [Table 1]

[0190] FIG. 10 shows the current density-voltage characteristics of an electron-only element fabricated using a co-evaporation film of ZADN and Liq as the second layer 911.

[0191] The impedance measurement was performed under the conditions of an AC voltage of 70 mV and a frequency of 1 Hz to 3 MHz while applying a DC voltage in the range of 5.0 V to 9.0 V. The capacitance was calculated from the admittance (the above-mentioned formula (1)), which is the reciprocal of the impedance obtained here. The frequency characteristic of the calculated capacitance C at an applied voltage of 7.0 V is shown in Figure 11.

[0192] The frequency characteristic of capacitance C is obtained because the space charge caused by the carriers injected by the minute voltage signal cannot completely follow the minute AC voltage, and a phase difference occurs in the current. Here, the transit time of the carriers in the film is defined as the time T for the injected carriers to reach the opposing electrode, and is expressed by the following formula (5).

[0193]

number

[0194] The negative susceptance change (-ΔB) corresponds to the capacitance change -ΔC multiplied by the angular frequency ω (-ωΔC). The lowest frequency peak frequency f' max (=ω max From equation (3), the relationship between the distance (km) from the center of gravity (P) to the travel time T can be derived as shown in equation (6).

[0195]

number

[0196] The frequency characteristic of -ΔB calculated from the above measurement (i.e., when the DC voltage is 7.0 V) is shown in Figure 12. The lowest frequency peak frequency f' obtained from Figure 12 max is indicated by an arrow in the figure.

[0197] f' obtained from the above measurements and analysis maxFrom this, the transit time T can be calculated (see formula (6) above), and from formula (5) above, the electron mobility at a voltage of 7.0 V in this case can be calculated. By performing similar measurements at DC voltages in the range of 5.0 V to 9.0 V, the electron mobility at each voltage (electric field strength) can be calculated, and the electric field strength dependence of the mobility can also be measured.

[0198] The electric field strength dependence of the electron mobility of each organic compound finally obtained by the above calculation method is shown in Figure 13. From the figure, it can be seen that the square root of the electric field strength [V / cm] is 600 [V / cm]. 1 / 2 The electron mobility values ​​at this time are shown in Table 2.

[0199] [Table 2]

[0200] It is possible to calculate the electron mobility in this way. For details on the measurement method, please refer to Takayuki Okachi et al., "Japanese Journal of Applied Physics," Vol. 47, No. 12, 2008, pp. 8965-8972. [Explanation of symbols]

[0201] 101: first electrode, 102: second electrode, 103: EL layer, 111: hole injection layer, 112: hole transport layer, 113: light emitting layer, 113-1: first light emitting layer, 113-2: second light emitting layer, 114: electron transport layer, 115: electron injection layer, 103a, 103b: EL layer, 104: charge generation layer, 111a, 111b: hole injection layer, 112a, 112b: hole transport layer, 113a, 113b: light emitting layer, 114a, 114b: electron transport layer, 115a, 115b: electron injection layer, 200R, 200G, 200B: optical path, 201: first substrate, 202: transistor (FE T), 203R, 203G, 203B, 203W: light emitting device, 204: EL layer, 205: second substrate, 206R, 206G, 206B: color filter, 206R', 206G', 206B': color filter, 207: first electrode, 208: second electrode, 209: black layer (black matrix), 210R, 210G: conductive layer, 301: first substrate, 302: pixel section, 303: driving circuit section (source line driving circuit), 304a, 304b: driving circuit section (gate line driving circuit), 305: sealing material, 306: second substrate, 307: lead wiring, 30 8: FPC, 309: FET, 310: FET, 311: FET, 312: FET, 313: first electrode, 314: insulator, 315: EL layer, 316: second electrode, 317: light-emitting device, 318: space, 901: first electrode, 902: second electrode, 910: first layer, 911: second layer, 912: third layer, 4000: lighting device, 4001: substrate, 4002: light-emitting device, 4003: substrate, 4004: first electrode, 4005: EL layer, 4006: second electrode, 4007: electrode, 4008: electrode, 4009: auxiliary wiring, 4010: insulating layer, 4011 : sealing substrate, 4012: sealing material, 4013: desiccant, 4200: lighting device, 4201: substrate, 4202: light emitting device, 4204: first electrode, 4205: EL layer, 4206: second electrode, 4207: electrode, 4208: electrode, 4209: auxiliary wiring, 4210: insulating layer, 4211: sealing substrate, 4212: sealing material, 4213: barrier film, 4214: flattening film, 5101: light, 5102: wheel, 5103: door, 5104: display unit, 5105: handle, 5106: shift lever, 5107: seat, 5108: inner rear view mirror,5109: front glass, 7000: housing, 7001: display unit, 7002: second display unit, 7003: speaker, 7004: LED lamp, 7005: operation keys, 7006: connection terminal, 7007: sensor, 7008: microphone, 7009: switch, 7010: infrared port, 7011: recording medium reading unit, 7014: antenna, 7015: shutter button , 7016: image receiving unit, 7018: stand, 7020: camera, 7022, 7023: operation buttons, 7024: connection terminal, 7025: band, 7026: microphone, 7029: sensor, 7030: speaker, 7052, 7053, 7054: information, 9310: mobile information terminal, 9311: display unit, 9312: display area, 9313: hinge, 9315: housing,

Claims

1. a hole injection layer, a hole transport layer, a first light emitting layer, a second light emitting layer, and an electron transport layer between an anode and a cathode; the hole injection layer is located between the anode and the hole transport layer; the hole transport layer is located between the hole injection layer and the first light-emitting layer; the first light-emitting layer is located between the hole transport layer and the second light-emitting layer; the second light-emitting layer is located between the first light-emitting layer and the electron transport layer; the electron transport layer is located between the second light-emitting layer and the cathode; the first light-emitting layer includes a first material and a second material; the second light-emitting layer includes a third material and a fourth material; the first material and the third material are the same or different luminescent materials; the hole mobility of the second light-emitting layer is smaller than the hole mobility of the first light-emitting layer; the hole injection layer comprises a fifth material and a sixth material; the fifth substance is an acceptor material; the HOMO level of the sixth substance is −5.7 eV or more and −5.4 eV or less; the hole transport layer comprises a seventh material; a HOMO level of the seventh substance is lower than a HOMO level of the sixth substance and higher than a HOMO level of the second substance; the electron transport layer comprises an eighth substance and a ninth substance; the eighth substance is an organometallic complex of an alkali metal or an alkaline earth metal; A light-emitting device, wherein the ninth substance is a heterocyclic compound having a polyazole skeleton, a heterocyclic compound having a diazine skeleton, or a heterocyclic compound having a pyridine skeleton.

2. In claim 1, A light-emitting device, wherein the abundance ratio of the eighth substance to the ninth substance in the electron transport layer differs between the cathode side and the second light-emitting layer side.

3. In claim 1 or 2, The light-emitting device, wherein the abundance ratio of the eighth substance in the electron transport layer is smaller on the cathode side than on the second light-emitting layer side.

Images