Light-emitting devices

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

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

[0003] Because these light-emitting devices are self-emissive, using them as pixels in a display offers advantages such as higher visibility compared to liquid crystal displays and the elimination of the need for a backlight, making them suitable as flat panel display elements. Furthermore, displays using such light-emitting devices can be manufactured to be thin and lightweight, which is a significant advantage. Another characteristic is their extremely fast response speed.

[0004] Furthermore, since these light-emitting devices can form a light-emitting layer continuously in two dimensions, they can produce light in a planar manner. This is a feature that is difficult to obtain with point light sources such as incandescent bulbs and LEDs, or line light sources such as fluorescent lamps, and therefore has high value as a planar light source that can be applied to lighting and other applications.

[0005] While displays and lighting devices using light-emitting devices are suitable for various electronic devices, research and development are underway to find light-emitting devices with better efficiency and lifespan.

[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-transport layer in contact with the hole-injection layer and a light-emitting layer.

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

[0008] [Patent Document 1] International Publication No. 2011 / 065136 Pamphlet [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Therefore, one aspect of the present invention aims to provide a novel light-emitting device, or to provide a light-emitting device with good luminous efficiency, or to provide a long-life light-emitting device, or to provide a light-emitting device with a low driving voltage.

[0010] Alternatively, in another aspect of the present invention, an object is to provide a highly reliable light-emitting device, electronic device, and display device, respectively. Alternatively, in another aspect of the present invention, an object is to provide a light-emitting device, electronic device, and display device, respectively, with low power consumption.

[0011] The present invention is intended to solve any one of the above problems.

Means for Solving the Problems

[0012] In one aspect of the present invention, in a light-emitting device having an EL layer between a pair of electrodes, by making the light-emitting layer included in the EL layer have a functional laminated structure, the reliability and light-emitting efficiency of the light-emitting device can be improved.

[0013] One aspect of the present invention is a light-emitting device having an EL layer between an anode and a cathode. The EL layer has a hole injection layer, a hole transport layer, a light-emitting layer, and an electron transport layer from the anode side. 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 laminated 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 hole injection layer has a fifth substance and a sixth substance. 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 has a seventh substance. The seventh substance is smaller than the HOMO level of the sixth substance and larger than the HOMO level of the second substance. The electron transport layer has an eighth substance and a ninth substance. The eighth substance is an organometallic complex of an alkali metal or an alkaline earth metal. The HOMO level of the ninth substance is -6.0 eV or more, and the electron mobility at a square root of an electric field strength [V / cm] of 600 is -7 -7 cm 2 / Vs or more and -5 -5 cm 2 / Vs or less.

[0014] Another aspect of the present invention has an EL layer between the electrodes of the anode and the cathode. The EL layer has a hole injection layer, a hole transport layer, a light-emitting layer, and an electron transport layer from the anode side. 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 laminated 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 injection layer has a fifth substance and a sixth substance. 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 has a seventh substance. The seventh substance is smaller than the HOMO level of the sixth substance and larger than the HOMO level of the second substance. The electron transport layer has an eighth substance and a ninth substance. The eighth substance is an organometallic complex of an alkali metal or an alkaline earth metal. The HOMO level of the ninth substance is -6.0 eV or more, and the electron mobility at the square root of the electric field strength [V / cm] of 600 is 1×10 -7 cm​​​​​​​​​​​​​​​​​​​​​In this specification, the term "light-emitting device" includes image display devices that use light-emitting devices. Furthermore, modules in which a connector, such as an anisotropic conductive film or TCP (Tape Carrier Package), is attached to a light-emitting device, modules in which a printed circuit board is provided at the end of the TCP, or modules in which an IC (integrated circuit) is directly mounted to a light-emitting device using the COG (Chip On Glass) method may also be included in the definition of a light-emitting device. Additionally, lighting fixtures and the like may have light-emitting devices. [Effects of the Invention]

[0019] In one aspect of the present invention, a novel light-emitting device can be provided. Alternatively, a long-life light-emitting device can be provided. Alternatively, a light-emitting device with good luminous efficiency can be provided.

[0020] Alternatively, in another aspect of the present invention, highly reliable light-emitting devices, electronic devices, and display devices can be provided, respectively. Alternatively, in another aspect of the present invention, light-emitting devices, electronic devices, and display devices with low power consumption can be provided, respectively.

[0021] Furthermore, the description of these effects does not preclude the existence of other effects. Moreover, one aspect of the present invention does not necessarily have to possess all of these effects. Other effects will naturally become apparent from the description in the specification, drawings, and claims, and it is possible to extract other effects from the description in the specification, drawings, and claims. [Brief explanation of the drawing]

[0022] [Figure 1] Figure 1 shows the structure of a light-emitting device. [Figure 2] Figures 2A and 2B illustrate the structure of the light-emitting device. [Figure 3] Figures 3A, 3B, and 3C illustrate the light-emitting device. [Figure 4]Figure 4A is a top view illustrating the light-emitting device. Figure 4B is a cross-sectional view illustrating the light-emitting device. [Figure 5] Figure 5A is a diagram illustrating a mobile computer. Figure 5B is a diagram illustrating a portable image playback device. Figure 5C is a diagram illustrating a digital camera. Figure 5D is a diagram illustrating a personal digital assistant (PAD). Figure 5E is a diagram illustrating a PAD. Figure 5F is a diagram illustrating a television system. Figure 5G is a diagram illustrating a PAD. [Figure 6] Figures 6A, 6B, and 6C illustrate electronic devices. [Figure 7] Figures 7A and 7B are diagrams illustrating automobiles. [Figure 8] Figures 8A and 8B illustrate the lighting device. [Figure 9] Figure 9 shows the structure of an electron-only device. [Figure 10] Figure 10 shows the current density-voltage characteristics of an electron-only device. [Figure 11] Figure 11 shows the frequency characteristics of the calculated capacitance C in ZADN:Liq(1:1) at a DC power supply of 7.0V. [Figure 12] Figure 12 shows the frequency response of -ΔB for ZADN:Liq(1:1) at a DC voltage of 7.0V. [Figure 13] Figure 13 shows the electric field strength dependence characteristics of electron mobility in each organic compound. [Modes for carrying out the invention]

[0023] The embodiments of the present invention will be described in detail below with reference to the drawings. However, it will be readily apparent to those skilled in the art that the present invention is not limited to the following description, and that its form and details can be modified in various ways without departing from the spirit and scope of the present invention. Accordingly, the present invention shall not be interpreted as being limited to the contents of the embodiments shown below.

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

[0025] Figure 1 shows a light-emitting device having a structure in which an EL layer 103 is sandwiched between a first electrode 101 that functions as an anode and a second electrode 102 that functions as a cathode. Accordingly, 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.

[0026] Furthermore, in one embodiment of the present invention, the light-emitting device has a laminated structure in the light-emitting layer 113 included in the EL layer 103. Figure 1 shows the case where the light-emitting layer 113 has a two-layer structure formed by laminating a first light-emitting layer 113-1 and a second light-emitting layer 113-2. However, the number of layers of the light-emitting layer 113 does not necessarily have to be two; in one embodiment of the present invention, any configuration that allows the light-emitting layer 113 to have the necessary functions is acceptable.

[0027] Furthermore, the necessary function of the light-emitting layer 113 is to increase the recombination probability of carriers (holes and electrons) in the light-emitting layer 113.

[0028] One aspect of the present invention is a light-emitting device that, by providing multiple light-emitting layers with different carrier transport properties, can control the carrier balance, increase the probability of carrier recombination in the light-emitting layers, and prevent deterioration of the functional layers constituting the EL layer, thereby improving reliability and increasing luminous efficiency.

[0029] In one aspect of the present invention, in the stacked light-emitting layers 113, the host material used for the first light-emitting layer 113-1 and the host material used for the second light-emitting layer 113-2 may be formed from different materials. Alternatively, the guest material used for the first light-emitting layer 113-1 and the guest material used for the second light-emitting layer 113-2 may be formed from different materials. Furthermore, either the guest material or the host material used for the first light-emitting layer 113-1 and the second light-emitting layer 113-2 may be the same material. In addition, the host material used for the first light-emitting layer 113-1 and the second light-emitting layer 113-2 may be one type or multiple types. Furthermore, when multiple host materials are used for the first light-emitting layer 113-1 and the second light-emitting layer 113-2, the combination of these materials may be a combination that forms an excited complex. Furthermore, 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 used in each layer, by the guest material, or by a combination of the host material and the guest material.

[0030] As described above, by stacking light-emitting layers with different carrier transport properties, it becomes possible to control the emission of light at the stacking interface of different light-emitting layers. Alternatively, by stacking light-emitting layers made of different guest materials, energy transfer between these light-emitting layers can be enabled, thereby increasing the luminescence efficiency.

[0031] In one aspect of the present invention, in the stacked light-emitting layers 113, each light-emitting layer is formed such that the hole mobility of the second light-emitting layer 113-2 is lower than that of the first light-emitting layer 113-1, and the recombination region is controlled to be near the interface between the first light-emitting layer 113-1 and the second light-emitting layer 113-2. By adopting such a configuration, the luminescence efficiency of the light-emitting device can be increased. Alternatively, in the stacked light-emitting layers 113, each light-emitting layer may be formed such that the electron mobility of the second light-emitting layer is higher than that of the first light-emitting layer. Furthermore, both of these configurations may be combined. Note that carrier mobilities such as hole mobility and electron mobility can be determined by impedance spectroscopy.

[0032] Furthermore, in the stacked light-emitting layers 113, the concentration of the guest material in the second light-emitting layer 113-2 may be lower than the concentration of the guest material in the first light-emitting layer 113-1 (for example, the concentration of the guest material in the second light-emitting layer 113-2 is 3w% or less, more preferably 2w% or less), thereby controlling the carrier recombination region to be near the interface between the first and second light-emitting layers. By adopting such a configuration, the luminescence efficiency of the light-emitting device can be increased. This is because, when the HOMO level of the guest material is shallower than the HOMO level of the host material and is more easily oxidized (the difference is 0.2eV, more preferably 0.3eV or more, as measured by CV), if the concentration of the guest material is low, the guest material traps holes, and if the concentration of the guest material is high, holes are more easily transported. These differences can be confirmed as changes in resistance by impedance spectroscopy or the like.

[0033] Furthermore, in the stacked light-emitting layers 113, each light-emitting layer may be formed such that the hole mobility of the second light-emitting layer 113-2 is greater than that of the first light-emitting layer 113-1, so that the carrier recombination region in the initial stages of operation is on the second light-emitting layer 113-2 side of the stacking interface. By using such a configuration, the reliability in the initial stages (5% or 10% brightness degradation) can be extended. Alternatively, each light-emitting layer may be formed such that the electron mobility of the second light-emitting layer 113-2 is lower than that of the first light-emitting layer 113-1. These configurations may also be combined. These carrier mobilities can be determined by impedance spectroscopy.

[0034] Furthermore, in the stacked light-emitting layers 113, the light-emitting layers may be formed such that the electrical resistance of the second light-emitting layer 113-2 is lower than that of the first light-emitting layer 113-1, so that the carrier recombination region in the initial stages of operation is located on the second light-emitting layer 113-2 side of the stacking interface. By adopting such a configuration, the reliability of the light-emitting device in the initial stages of operation (5% or 10% brightness degradation) can be improved. The above electrical resistance can be determined by impedance spectroscopy.

[0035] Furthermore, in the stacked light-emitting layers 113, the light-emitting layers may be formed such that the refractive index anisotropy with respect to the substrate surface is greater for the second light-emitting layer 113-2 than for the first light-emitting layer 113-1, so that the carrier recombination region in the initial stages of operation is on the second light-emitting layer 113-2 side rather than the stacking interface. This configuration can improve reliability in the initial stages of operation (5% or 10% brightness degradation). This is because the transition dipole moment becomes horizontal with respect to the substrate, making it easier to transport carriers. In this case, the concentration of the guest material in the second light-emitting layer 113-2 is more preferably 2w% or more. The carrier mobility can be determined by impedance spectroscopy. The refractive index anisotropy with respect to the substrate surface can be determined by spectroscopic ellipsography.

[0036] (Embodiment 2) This embodiment describes a light-emitting device that is one aspect of the present invention.

[0037] <Example of light-emitting device configuration> Figure 2A shows an example of a light-emitting device having an EL layer including a light-emitting layer between a pair of electrodes. Specifically, it has a structure in which an EL layer 103 is sandwiched between a first electrode 101 and a second electrode 102. The EL layer 103 has a structure in which, for example, when the first electrode 101 is the anode, 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] Furthermore, other structures of light-emitting devices include light-emitting devices that enable low-voltage driving by having a configuration (tandem structure) with multiple EL layers formed by sandwiching a charge generation layer between a pair of electrodes, and light-emitting devices that improve optical properties by forming a microcavity structure between a pair of electrodes. The charge generation layer has the function of injecting electrons into one adjacent EL layer and holes into the other EL layer when a voltage is applied to the first electrode 101 and the second electrode 102.

[0039] Note that at least one of the first electrode 101 and the second electrode 102 of the above light-emitting device is an electrode having translucency (such as a transparent electrode, a semi-transmissive / semi-reflective electrode, etc.). When the electrode having translucency is a transparent electrode, the transmittance of visible light of the transparent electrode shall be 40% or more. In the case of a semi-transmissive / semi-reflective electrode, the reflectance of visible light of the semi-transmissive / semi-reflective electrode shall be 20% or more and 80% or less, preferably 40% or more and 70% or less. Further, these electrodes preferably have a resistivity of 1×10 -2 Ω·cm or less.

[0040] Further, in the light-emitting device which is one aspect of the present invention described above, when one of the first electrode 101 and the second electrode 102 is an electrode having reflectivity (reflective electrode), the reflectance of visible light of the electrode having reflectivity shall be 40% or more and 100% or less, preferably 70% or more and 100% or less. Further, this electrode preferably has a resistivity of 1×10 -2 Ω·cm or less.

[0041] <The first electrode and the second electrode> As materials for forming the first electrode 101 and the second electrode 102, any combination of the following materials can be used as long as the functions of both electrodes described above are met. For example, metals, alloys, electrically conductive compounds, and mixtures thereof can be used as appropriate. Specifically, these 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), neodymium (Nd), and alloys containing these in appropriate combinations can also be used. In addition, elements belonging to Group 1 or Group 2 of the periodic table not exemplified above (for example, lithium (Li), cesium (Cs), calcium (Ca), strontium (Sr)), rare earth metals such as europium (Eu) and ytterbium (Yb), and alloys containing these in appropriate combinations, as well as graphene and other materials can be used.

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

[0043] <Hole injection layer> The hole injection layer 111 is a layer containing an organic acceptor material and a hole-transporting material with a deep HOMO. The organic acceptor material is a substance that exhibits electron-accepting properties for the hole-transporting material with a deep HOMO. The hole-transporting material with a deep HOMO is a substance that has a relatively deep HOMO level between -5.7 eV and -5.4 eV. Having a relatively deep HOMO level in this way facilitates the injection of holes into the hole transport layer 112.

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

[0045] The above-mentioned deep HOMO hole-transporting material is preferably a hole-transporting material having hole-transporting properties, and preferably has one of the following skeletons: carbazole skeleton, dibenzofuran skeleton, dibenzothiophene skeleton, or anthracene skeleton. In particular, it may be an aromatic amine having substituents including 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] Furthermore, for the deep HOMO hole-transporting material mentioned above, the electron mobility at which the square root of the electric field strength [V / cm] is 600 is 1 × 10⁻¹⁶. -6 cm 2 Materials having a hole mobility of / Vs or higher are preferred. However, other materials can be used as long as they have higher hole transport than electron transport. Furthermore, materials having an N,N-bis(4-biphenyl)amino group are preferred because they can be used to create long-life light-emitting devices.

[0047] Examples of deep HOMO hole-transporting materials as described above 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), and N,N-bis(4-biphenyl)ben 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-(dibenzothiophen-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: TPBiAβNBi), 4-phenyl-4'-(1-naphthyl)triphenylamine (abbreviation: αNBA1BP), 4,4'-bis(1-naphthyl)triphenylamine (abbreviation: αNBB1BP), 4,4'-diphenyl-4''-[4'-(carbazole-9-yl)biphenyl-4-yl]triphenylamine (abbreviation: YGTBi1BP), 4'-[4-(3-phenyl-9H-carbazole-9-yl)phenyl]tris(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-carbazole-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-Fluorene-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-carbazole-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4'-diphenyl-4''-(9- Examples include phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBANB), 4,4'-di(1-naphthyl)-4''-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBNBB), N-phenyl-N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]spiro-9,9'-bifluoren-2-amine (abbreviation: PCBASF), N-(1,1'-biphenyl-4-yl)-9,9-dimethyl-N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]-9H-fluoren-2-amine (abbreviation: PCBBiF), etc.

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

[0049] <Hole transport layer> The hole transport layer 112 is a layer that transports 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 can be made of the hole transport material described above. The hole transport layer 112 may also have a laminated structure. If it has a laminated structure, the layer on the light-emitting layer side may function as an electron blocking layer.

[0051] Furthermore, when comparing the HOMO levels of the hole transport material used in the hole injection layer 111 and the hole transport material used in the hole transport layer 112, it is preferable to select materials such that the HOMO level of the hole transport material used in the hole transport layer 112 is deeper than that of the hole transport material used in the hole injection layer 111, and the difference is 0.2 eV or less. It is even preferable that both materials be the same, as this will result in smoother hole injection.

[0052] Furthermore, when the hole transport layer 112 has a multilayer 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. Moreover, it is preferable to select materials such that the difference is 0.2 eV or less. When the HOMO levels of these hole transport materials used in the hole injection layer 111 and the multilayer structured hole transport layer have the above relationship, hole injection into each layer is performed smoothly, preventing an increase in the driving voltage and a state of insufficient holes in the light-emitting layer 113.

[0053] Furthermore, 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 each have a hole-transporting skeleton. Preferred hole-transporting skeletons include carbazole skeletons, dibenzofuran skeletons, dibenzothiophene skeletons, and anthracene skeletons, which do not cause the HOMO level of these hole-transporting materials to become too shallow. It is also preferable that the hole-transporting skeletons of the hole-transporting materials used in the hole injection layer 111 and the hole transport layer 112 having a laminated structure are common to adjacent layers, as this facilitates smooth hole injection. In particular, dibenzofuran skeletons are preferred as these hole-transporting skeletons.

[0054] Furthermore, it is preferable that the hole transport material used in the hole injection layer 111 and the hole transport layer 112 having a laminated structure is the same in adjacent layers, as this allows for smoother injection of holes into adjacent layers in the cathode direction.

[0055] <Luminous layer> In one embodiment of the present invention, in a light-emitting device, the light-emitting layer 113 has a structure in which multiple light-emitting layers are stacked. The functions of the multiple light-emitting layers are as described in Embodiment 1, and the light-emitting layers can be formed using the materials shown below to satisfy these functions.

[0056] The light-emitting layer 113 comprises a light-emitting substance (guest material) and a host material that disperses the light-emitting substance.

[0057] As the luminescent material (guest material), fluorescent materials (fluorescent materials), phosphorescent materials (phosphorescent materials), thermally activated delayed fluorescence (TADF) materials, and other luminescent materials can be used. As the host material, various carrier transport materials can be used, including electron transport materials, hole transport materials, and the above-mentioned TADF materials. Furthermore, as the host material, hole transport materials and electron transport materials can be used. Specifically, one or more of the materials described in this specification or known materials can be used as appropriate.

[0058] Examples of fluorescent materials that can be used as guest materials for the light-emitting layer 113 include the following. Other fluorescent materials can also be used.

[0059] 5,6-Bis[4-(10-phenyl-9-antryl)phenyl]-2,2'-bipyridine (abbreviation: PAP2BPy), 5,6-Bis[4'-(10-phenyl-9-antryl)biphenyl-4-yl]-2,2'-bipyridine (abbreviation: PAPP2BPy), N,N'-Diphenyl-N,N'-Bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]pyren-1,6-diamine (abbreviation: 1,6FLPAPrn), N,N'-Bis(3-methylphenyl)-N,N'-Bis[3-(9-phenyl-9H-fluoren-9-yl )phenyl]pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPrn), N,N'-bis[4-(9H-carbazole-9-yl)phenyl]-N,N'-diphenylstilbene-4,4'-diamine (abbreviation: YGA2S), 4-(9H-carbazole-9-yl)-4'-(10-phenyl-9-anthryl)triphenylamine (abbreviation: YGAPA), 4-(9H-carbazole-9-yl)-4'-(9,10-diphenyl-2-anthryl)triphenylamine (abbreviation: 2YGAPPA), N,9-diphenyl-N-[4-( 10-phenyl-9-anthryl)phenyl]-9H-carbazole-3-amine (abbreviation: PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene (abbreviation: TBP), 4-(10-phenyl-9-anthryl)-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBAPA), N,N''-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N',N'-triphenyl-1,4-phenylenediamine] (abbreviation: DPABPA), N,9 -Diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazole-3-amine (abbreviation: 2PCAPPA), N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPPA), N,N,N',N',N'',N'',N''',N'''-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine (abbreviation: DBC1), coumarin 30, N-(9,10-diphenyl-2-anthryl)-N,9-Diphenyl-9H-carbazole-3-amine (abbreviation: 2PCAPA), N-[9,10-bis(1,1'-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazole-3-amine (abbreviation: 2PCABPhA), N-(9,10-diphenyl-2-anthryl)-N,N',N'-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPA), N-[9,10-bis(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-carbazole-9-yl)phenyl]-N-phenylanthracene-2-amine (abbreviation: 2YGABPhA), N,N,9-triphenylanthracene-9-amine (abbreviation: DPhAPhA), coumarin 545T, N,N'-diphenylquinacridone (abbreviation: DPQd), rubren, 5,12-bis(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]quinoridine-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCM2), N,N,N',N'-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation: p-mPhTD), 7,14-diphenyl-N,N,N',N'-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluorantene-3,10-di Amine (abbreviation: p-mPhAFD), 2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinoridine-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTI), 2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinoridine-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTB), 2-(2,6-Bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile (abbreviation: BisDCM), 2-{2,6-Bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinoridine-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: BisDCJTM), N,N'-diphenyl-N,N'-(1,6-pyrene-diyl)bis[(6-phenylbenzo[b Examples include ]naphtho[1,2-d]furan)-8-amine] (abbreviation: 1,6BnfAPrn-03), 3,10-bis[N-(9-phenyl-9H-carbazole-2-yl)-N-phenylamino]naphtho[2,3-b;6,7-b']bisbenzofuran (abbreviation: 3,10PCA2Nbf(IV)-02), and 3,10-bis[N-(dibenzofuran-3-yl)-N-phenylamino]naphtho[2,3-b;6,7-b']bisbenzofuran (abbreviation: 3,10FrA2Nbf(IV)-02). In particular, condensed aromatic diamine compounds, such as pyrenediamine compounds like 1,6FLPAPrn, 1,6mMemFLPAPrn, and 1,6BnfAPrn-03, are preferred because they have high hole-trapping properties and excellent luminescence efficiency and reliability.

[0060] Furthermore, examples of phosphorescent materials that can be used as guest materials for the light-emitting layer 113 include the following:

[0061] Organometallic iridium complexes having a 4H-triazole skeleton, such as Tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III) (abbreviation: [Ir(mpptz-dmp)3]), 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) ( Organometallic iridium complexes having a 1H-triazole skeleton, such as tris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III) (abbreviated as [Ir(Prptz1-Me)3]), or organometallic iridium complexes having an imidazole skeleton, such as fac-tris[(1-2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III) (abbreviated as [Ir(iPrpmi)3]), tris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridine]iridium(III) (abbreviated as [Ir(dmpimpt-Me)3]), or bis[2-(4',6'-difluorophenyl)pyridinate-N,C 2’ Iridium(III) tetrakis(1-pyrazolyl) borate (abbreviation: FIr6), bis[2-(4',6'-difluorophenyl)pyridinate-N,C 2’ Iridium(III) picolinate (abbreviation: Firpic), bis{2-[3',5'-bis(trifluoromethyl)phenyl]pyridinate-N,C 2’ Iridium(III) picolinate (abbreviation: [Ir(CF3ppy)2(pic)]), bis[2-(4',6'-difluorophenyl)pyridinate-N,C 2’Examples include organometallic iridium complexes that use phenylpyridine derivatives having electron-withdrawing groups, such as iridium(III) acetylacetonate (FIracac), as ligands. These compounds exhibit blue phosphorescence and have emission peaks between 440 nm and 520 nm.

[0062] Also, tris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)3]), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)3]), (acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(mppm)2(acac)]), (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm)2(acac)]), (acetylacetonato)bis[6-(2-norbornyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: [Ir(nbppm)2(acac)]), (acetylacetonato)bis[5-methyl-6-( Organometallic iridium complexes having a pyrimidine skeleton, such as [2-methylphenyl)-4-phenylpyrimidinato]iridium(III) (abbreviation: [Ir(mpmppm)2(acac)]), (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm)2(acac)]), organometallic iridium complexes having a pyrazine skeleton, such as [acetylacetonato]bis(3,5-dimethyl-2-phenylpyradinato)iridium(III) (abbreviation: [Ir(mppr-Me)2(acac)]), (acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyradinato)iridium(III) (abbreviation: [Ir(mppr-iPr)2(acac)]), and tris(2-phenylpyridinato-N,C 2’ Iridium(III) (abbreviation: [Ir(ppy)3]), bis(2-phenylpyridinate-N,C) 2’Iridium(III) acetylacetonate (abbreviation: [Ir(ppy)2(acac)]), bis(benzo[h]quinolinate)iridium(III) acetylacetonate (abbreviation: [Ir(bzq)2(acac)]), tris(benzo[h]quinolinate)iridium(III) (abbreviation: [Ir(bzq)3]), tris(2-phenylquinolinate-N,C) 2’ Iridium(III) (abbreviation: [Ir(pq)3]), bis(2-phenylquinolinato-N,C) 2’ Examples include organometallic iridium complexes with a pyridine skeleton, such as iridium(III) acetylacetonate (abbreviated as [Ir(pq)2(acac)]), and rare earth metal complexes, such as tris(acetylacetonate)(monophenanthroline)terbium(III) (abbreviated as [Tb(acac)3(Phen)]). These compounds mainly exhibit green phosphorescence and have an emission peak in the 500nm-600nm range. Organometallic iridium complexes with a pyrimidine skeleton are particularly preferred due to their outstanding reliability and luminescence efficiency.

[0063] Furthermore, organometallic iridium complexes having a pyrimidine skeleton, such as (diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III) (abbreviation: [Ir(5mdppm)2(dibm)]), bis[4,6-bis(3-methylphenyl)pyrimidinato](dipvaloylmethanato)iridium(III) (abbreviation: [Ir(5mdppm)2(dpm)]), and bis[4,6-di(naphthalene-1-yl)pyrimidinato](dipvaloylmethanato)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)]), as well as tris(1-phenylisoquinolinato-N,C) 2’ Iridium(III) (abbreviation: [Ir(piq)3]), bis(1-phenylisoquinolinato-N,C) 2’ Examples include organometallic iridium complexes with a pyridine skeleton, such as iridium(III) acetylacetonate (abbreviated as [Ir(piq)2(acac)]), as well as platinum complexes such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (abbreviated as PtOEP), and rare earth metal complexes such as tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviated as [Eu(DBM)3(Phen)]) and tris[1-(2-tenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviated as [Eu(TTA)3(Phen)]). These compounds exhibit red phosphorescence and have an emission peak between 600 nm and 700 nm. Furthermore, organometallic iridium complexes with a pyrazine skeleton produce a red emission with good chromaticity.

[0064] In addition, other known phosphorescent materials can be used besides those mentioned above.

[0065] Furthermore, the following are examples of TADF materials that can be used as guest materials for the light-emitting layer 113.

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

[0067] [ka]

[0068] In addition, as shown in the structural formulas below, there are 2-(biphenyl-4-yl)-4,6-bis(12-phenylindoro[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-phenoxazine-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviation: PXZ-TRZ), 3-[4-(5-phenyl-5,10-dihydrophenazine-10-yl)phenyl]-4,5-diphenyl-1,2,4-triazole (abbreviation: PPZ-3TPT), 3-(9,9-dimethyl-9H-acridine-10-yl)-9H-xanthene-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-carbazole-9-yl)benzoflou[3,2-d]pyrimidine (abbreviation: 4PCCzBfpm), 4-[4-(9'-f Heterocyclic compounds having π-electron-rich heteroaromatic rings and π-electron-deficient heteroaromatic rings, such as phenyl-3,3'-bi-9H-carbazole-9-yl)phenyl]benzofl[3,2-d]pyrimidine (abbreviation: 4PCCzPBfpm) and 9-[3-(4,6-diphenyl-1,3,5-triazine-2-yl)phenyl]-9'-phenyl-2,3'-bi-9H-carbazole (abbreviation: mPCCzPTzn-02), may also be used.

[0069] [ka]

[0070] The heterocyclic compound is preferred because it has both a π-electron-excess heteroaromatic ring and a π-electron-deficient heteroaromatic ring, resulting in high electron transport and hole transport properties. Among the skeletons having a π-electron-deficient heteroaromatic ring, the pyridine skeleton, diazine skeleton (pyrimidine skeleton, pyrazine skeleton, pyridazine skeleton), and triazine skeleton are preferred because they are stable and reliable. In particular, the benzoflopyrimidine skeleton, benzothienopyrimidine skeleton, benzoflopyrazine skeleton, and benzothienopyrazine skeleton are preferred because they have high acceptability and are reliable.

[0071] Furthermore, among skeletons having a π-electron-excess heteroaromatic ring, the acridine skeleton, phenoxazine skeleton, phenothiazine skeleton, furan skeleton, thiophene skeleton, and pyrrole skeleton are stable and reliable, and therefore it is preferable to have at least one of these skeletons. Dibenzofuran is preferred as the furan skeleton, and dibenzothiophene is preferred as the thiophene skeleton. Indole, carbazole, indrocarbazole, bicarbazole, and 3-(9-phenyl-9H-carbazole-3-yl)-9H-carbazole are particularly preferred as the pyrrole skeleton.

[0072] Furthermore, substances in which a π-electron-rich heteroaromatic ring and a π-electron-deficient heteroaromatic ring are directly bonded are particularly preferred because both the electron-donating and electron-accepting properties of the π-electron-rich heteroaromatic ring are strengthened, reducing the energy difference between the S1 and T1 levels, thus efficiently obtaining thermally activated delayed fluorescence. Alternatively, an aromatic ring bonded to an electron-withdrawing group such as a cyano group may be used instead of the π-electron-deficient heteroaromatic ring. As the π-electron-rich skeleton, aromatic amine skeletons, phenazine skeletons, etc., can be used. As the π-electron-deficient skeleton, xanthene skeletons, thioxanthene dioxide skeletons, oxadiazole skeletons, triazole skeletons, imidazole skeletons, anthraquinone skeletons, boron-containing skeletons such as phenylborane and volanthrene, aromatic rings or heteroaromatic rings having nitrile or cyano groups such as benzonitrile or cyanobenzene, carbonyl skeletons such as benzophenone, phosphine oxide skeletons, sulfone skeletons, etc., can be used.

[0073] Thus, a π-electron-deficient skeleton and a π-electron-excess skeleton can be used instead of at least one of a π-electron-deficient heteroaromatic ring and a π-electron-excess heteroaromatic ring.

[0074] TADF materials are materials that have a small difference between the S1 and T1 energy levels and possess the ability to convert energy from triplet excitation energy to singlet excitation energy through reverse intersystem crossing. Therefore, triplet excitation energy can be upconverted to singlet excitation energy with only a small amount of thermal energy (reverse intersystem crossing), and singlet excited states can be efficiently generated. Furthermore, triplet excitation energy can be converted into luminescence.

[0075] Furthermore, an excited complex (also called an exciplex) that forms an excited state with two types of substances has an extremely small difference between the S1 and T1 levels and functions as a TADF material that can convert triplet excitation energy into singlet excitation energy.

[0076] Furthermore, the phosphorescence spectrum observed at low temperatures (e.g., 77K to 10K) can be used as an indicator of the T1 level. For TADF materials, when a tangent is drawn at the short-wavelength tail of the fluorescence spectrum and the energy at the wavelength of the extrapolation is taken as the S1 level, and when a tangent is drawn at the short-wavelength tail of the phosphorescence spectrum and the energy at the wavelength of the extrapolation is taken as the T1 level, it is preferable that the difference between S1 and T1 is 0.3 eV or less, and more preferably 0.2 eV or less.

[0077] Furthermore, when a TADF material is used as the guest material for the light-emitting layer 113, it is preferable that the S1 level of the host material is higher than the S1 level of the TADF material. Also, it is preferable that the T1 level of the host material is higher than the T1 level of the TADF material.

[0078] Next, as a hole-transporting material that can be used as the host material for the light-emitting layer 113, the electron mobility at which the square root of the electric field strength [V / cm] is 600 is 1 × 10⁻⁶. -6 cm 2 A material having a hole mobility of / Vs or higher is preferred, and examples 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-carbazole-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4'-diphenyl-4''-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4'-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBANB), 4 It has aromatic amine skeletons such as ,4'-di(1-naphthyl)-4''-(9-phenyl-9H-carbazole-3-yl)triphenylamine (abbreviation: PCBNBB), 9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]fluoren-2-amine (abbreviation: PCBAF), and N-phenyl-N-[4-(9-phenyl-9H-carbazole-3-yl)phenyl]spiro-9,9'-bifluoren-2-amine (abbreviation: PCBASF). Compounds such as 1,3-bis(N-carbazolyl)benzene (abbreviated as mCP), 4,4'-di(N-carbazolyl)biphenyl (abbreviated as CBP), 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviated as CzTP), 3,3'-bis(9-phenyl-9H-carbazole) (abbreviated as PCCP), and compounds having a carbazole skeleton, as well as 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviated as DBT3P-II), 2,Examples include compounds having a thiophene skeleton such as 8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviated as DBTFLP-III) and 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviated as DBTFLP-IV), and compounds having a furan skeleton such as 4,4',4''-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviated as DBF3P-II) and 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviated as mmDBFFLBi-II). Among the above, compounds having an aromatic amine skeleton and compounds having a carbazole skeleton are preferred because they have good reliability, high hole transportability, and contribute to reducing the driving voltage. Organic compounds listed above as examples of hole transportable materials can also be used.

[0080] Furthermore, as an electron-transporting material that can be used as the host material for the light-emitting layer 113, the electron mobility at which the square root of the electric field strength [V / cm] is 600 is 1 × 10⁻¹⁰. -6 cm 2 Materials having an electron mobility of / Vs or higher are preferred, and examples include the following. In addition, electron transport materials that can be used in the electron transport layer 114 described later can also be used.

[0081] Metal complexes such as bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq2), bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq), bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), and bis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: 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-oxadiazole-2-yl]benzene (abbreviation: OXD-7), 9-[4-(5-phenyl-1,3,4-oxadiazole-2-yl)phenyl]-9H-carbazole (abbreviation: CO11), 2,2',2''-(1,3,5-benzenetriyl)tris( Heterocyclic compounds with a polyazole skeleton, such as 1-phenyl-1H-benzimidazole (abbreviated as TPBI), 2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviated as mDBTBIm-II), and 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviated as 2mDBTPDBq-II) and 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviated as 2mDBTBPDBq-I). I) Heterocyclic compounds having a diazine skeleton such as 2-[3'-(9H-carbazole-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mCzBPDBq), 4,6-bis[3-(phenanthrene-9-yl)phenyl]pyrimidine (abbreviation: 4,6mPnP2Pm), 4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation: 4,6mDBTP2Pm-II), and 3,5-bis[3-(9H-carbazole-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy), 1,3,Examples include heterocyclic compounds having a pyridine skeleton, such as 5-tri[3-(3-pyridyl)phenyl]benzene (abbreviated as TmPyPB). Among those mentioned above, heterocyclic compounds having a diazine skeleton and heterocyclic compounds having a pyridine skeleton are preferred due to their good reliability. In particular, heterocyclic compounds having a diazine (pyrimidine or pyrazine) skeleton exhibit high electron transport properties and contribute to reducing the driving voltage.

[0082] Furthermore, the same methods described above can be used when a TADF material is used as the host material for the light-emitting layer 113. When a TADF material is used as the host material, the triplet excitation energy generated by the TADF material is converted into singlet excitation energy by reverse intersystem crossing, and then energy is transferred to the light-emitting center material, thereby increasing the luminescence efficiency of the light-emitting device. In this case, the TADF material functions as an energy donor, and the light-emitting center material functions as an energy acceptor. Therefore, using a TADF material as the host material is very effective when a fluorescent material is used as the guest material. In this case, in order to obtain high luminescence efficiency, it is preferable that the S1 level of the TADF material is higher than the S1 level of the fluorescent material. Also, it is preferable that the T1 level of the TADF material is higher than the S1 level of the fluorescent material. Therefore, it is preferable that the T1 level of the TADF material is higher than the T1 level of the fluorescent material.

[0083] Furthermore, it is preferable to use a TADF material that exhibits emission that overlaps with the wavelength of the lowest-energy absorption band of the fluorescent material. This is preferable because it allows for smooth transfer of excitation energy from the TADF material to the fluorescent material, resulting in efficient emission.

[0084] Furthermore, for singlet excitation energy to be efficiently generated from triplet excitation energy by reverse intersystem crossing, it is preferable that carrier recombination occurs in the TADF material. It is also preferable that the triplet excitation energy generated in the TADF material does not transfer to the triplet excitation energy of the fluorescent material. To achieve this, it is preferable that the fluorescent material has protecting groups around the luminescent phosphodiocyte (the skeleton that causes luminescence). Preferred protecting groups are substituents without π bonds, and saturated hydrocarbons are preferred. Specifically, examples include alkyl groups having 3 to 10 carbon atoms, substituted or unsubstituted cycloalkyl groups having 3 to 10 carbon atoms, and trialkylsilyl groups having 3 to 10 carbon atoms. It is even preferable to have multiple protecting groups. Substituents without π bonds have poor carrier transport function, and therefore can increase the distance between the TADF material and the luminescent phosphodiocyte of the fluorescent material with little effect on carrier transport or carrier recombination. Here, the luminescent phosphodiocyte refers to the atomic group (skeleton) that causes luminescence in the fluorescent material. The luminescent phosphodiosity preferably has a skeleton containing π bonds, preferably contains an aromatic ring, and preferably has a condensed aromatic ring or a condensed heteroaromatic ring. Examples of condensed aromatic rings or condensed heteroaromatic rings include phenanthrene skeletons, stilbene skeletons, acridone skeletons, phenoxazine skeletons, and phenothiazine skeletons. Fluorescent materials having naphthalene, anthracene, fluorene, chrysene, triphenylene, tetracene, pyrene, perylene, coumarin, quinacridone, or naphthobisbenzofuran skeletons are particularly preferred due to their high fluorescence quantum yield.

[0085] Furthermore, when a fluorescent material is used as the guest material for the light-emitting layer 113, a material having an anthracene skeleton is preferred as the host material. Using a material having an anthracene skeleton makes it possible to realize a light-emitting layer with good luminescence efficiency and durability. Among materials having an anthracene skeleton, a diphenylanthracene skeleton, and especially a material having a 9,10-diphenylanthracene skeleton, is preferred because it is chemically stable.

[0086] Furthermore, while it is preferable for the host material to have a carbazole skeleton because it enhances hole injection and transport, it is even more preferable if the host material contains a benzocarbazole skeleton in which a benzene ring is further condensed onto the carbazole, as this makes the HOMO about 0.1 eV shallower than that of carbazole, allowing holes to enter more easily. In particular, it is preferable if the host material contains a dibenzocarbazole skeleton, as this not only makes the HOMO about 0.1 eV shallower than that of carbazole, allowing holes to enter more easily, but also provides excellent hole transport and high heat resistance.

[0087] Therefore, substances having both an anthracene skeleton, specifically the 9,10-diphenylanthracene skeleton and a carbazole skeleton (or a benzocarbazole skeleton or dibenzocarbazole skeleton), are more preferred as host materials. Furthermore, from the viewpoint of improving the hole injection and transport properties, a benzofluorene skeleton or a dibenzofluorene skeleton may be used instead of the carbazole skeleton. Examples of such substances include 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviated as PCzPA), 3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviated as PCPN), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviated as CzPA), and 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g Examples include carbazole (abbreviated as cgDBCzPA), 6-[3-(9,10-diphenyl-2-anthryl)phenyl]-benzo[b]naphtho[1,2-d]furan (abbreviated as 2mBnfPPA), 9-phenyl-10-{4-(9-phenyl-9H-fluoren-9-yl)biphenyl-4'-yl}anthracene (abbreviated as FLPPA), and 9-(1-naphthyl)-10-[4-(2-naphthyl)phenyl]anthracene (abbreviated as BH513). In particular, CzPA, cgDBCzPA, 2mBnfPPA, and PCzPA are preferred because they exhibit very good properties.

[0088] The host material may be a mixture of multiple substances, and when using a mixed host material, it is preferable to mix an electron-transporting material with a hole-transporting material. By mixing an electron-transporting material with a hole-transporting material, the transport properties of the light-emitting layer 113 can be easily adjusted, and the recombination region can also be easily controlled. The weight ratio of the hole-transporting material to the electron-transporting material should be 1:19 to 19:1.

[0089] Furthermore, as described above, when the host material is a mixture of multiple substances, a phosphorescent substance can be used as part of it. The phosphorescent substance can be used as an energy donor to supply excitation energy to a fluorescent substance when a fluorescent substance is used as the light-emitting center material.

[0090] Furthermore, the mixed materials described above may form an excited complex. In this case, by selecting a combination of materials that forms an excited complex that exhibits emission overlapping with the wavelength of the lowest-energy absorption band of the luminescent material, energy transfer becomes smoother, and luminescence can be obtained efficiently. Moreover, using such a configuration is preferable because it can reduce the driving voltage.

[0091] Furthermore, at least one of the materials forming the excitation complex may be a phosphorescent material. In this case, the triplet excitation energy can be efficiently converted to the singlet excitation energy by reverse intersystem crossing.

[0092] Furthermore, when forming the excited complex, it is preferable that the HOMO level of the hole-transporting material is higher than or equal to the HOMO level of the electron-transporting material. It is also preferable that the LUMO level of the hole-transporting material is higher than or equal to the LUMO level of the electron-transporting material. The LUMO and HOMO levels of the materials can be derived from the electrochemical properties (reduction potential and oxidation potential) of the materials measured by cyclic voltammetry (CV).

[0093] The formation of excited complexes can be confirmed, for example, by comparing the emission spectra of a hole-transporting material, an electron-transporting material, and a mixed film made by mixing these materials, and observing that the emission spectrum of the mixed film shifts to a longer wavelength than the emission spectra of each individual material (or has a new peak on the longer wavelength side). Alternatively, it can be confirmed by comparing the transient photoluminescence (PL) of a hole-transporting material, an electron-transporting material, and a mixed film made by mixing these materials, and observing differences in the transient response, such as the transient PL lifetime of the mixed film having a longer lifetime component or a larger proportion of the delayed component than the transient PL lifetime of each individual material. Furthermore, the above-mentioned transient PL can be read as transient electroluminescence (EL). That is, the formation of excited complexes can also be confirmed by comparing the transient EL of a hole-transporting material, an electron-transporting material, and a mixed film made by mixing these materials, and observing the differences in the 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. The electron transport layer 114 has an electron-transporting material with a HOMO level of -6.0 eV or higher, and an organometallic complex of an alkali metal or alkaline earth metal. The electron-transporting material with a HOMO level of -6.0 eV or higher has an electron mobility of 1 × 10⁻¹⁰ at a square root of 600 electric field strength [V / cm]. -7 cm 2 / Vs or more 5×10 -5 cm 2 It is preferable that it is less than or equal to / Vs, but 1 × 10 -7 cm 2 / Vs or more 1×10 -5 cm 2 It is more preferable if / Vs is less than or equal to / Vs.

[0095] Furthermore, electron transport materials with a HOMO level of -6.0 eV or higher are preferably those having an anthracene skeleton, and more preferably those containing both an anthracene skeleton and a heterocyclic skeleton. Among the heterocyclic skeletons, a nitrogen-containing five-membered ring skeleton is preferred. Among the nitrogen-containing five-membered ring skeletons, those containing two heteroatoms in the ring, such as a pyrazole ring, imidazole ring, oxazole ring, or thiazole ring, are particularly preferred. In addition, some of the electron transport materials that can be used as the host material, or materials that can be used as a host material in combination with the fluorescent material, can be used in the electron transport layer 114.

[0096] Furthermore, as the organometallic complex of an alkali metal or alkaline earth metal, an organometallic complex of lithium is preferred, and in particular, 8-hydroxyquinolinatolithium (abbreviated as Liq) is preferred.

[0097] Furthermore, it is preferable that the electron mobility (electron mobility at a square root of the electric field strength [V / cm] of 600) of the electron-transporting material used in the electron transport layer 114, which has a HOMO level of -6.0 eV or higher, is smaller than that of the host material used in the light-emitting layer 113. By reducing the electron transportability in the electron transport layer, the amount of electrons injected into the light-emitting layer can be controlled, preventing the light-emitting layer from becoming electron-excessive.

[0098] <Electron injection layer> The electron injection layer 115 is a layer for increasing the efficiency of electron injection from the cathode 102. When comparing the work function value of the cathode 102 material with the LUMO level value of the material used for the electron injection layer 115, it is preferable to use a material in which the difference is small (0.5 eV or less). Therefore, the electron injection layer 115 can be made of lithium, cesium, lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF2), 8-(hydroxyquinolinato)lithium (abbreviated as Liq), 2-(2-pyridyl)phenolate (abbreviated as LiPP), 2-(2-pyridyl)-3-pyridinolatritium (abbreviated as LiPPy), or 4-phenyl-2-(2-pyridyl)phenolate (abbreviated as LiPPP) lithium oxide (LiO2). x Alkali metals such as cesium carbonate, alkaline earth metals, or compounds thereof can be used. Rare earth metal compounds such as erbium fluoride (ErF3) can also be used.

[0099] Furthermore, as shown in the light-emitting device in Figure 2B, by providing a charge generation layer 104 between two EL layers (103a, 103b), a structure in which multiple EL layers are stacked between a pair of electrodes (also called a tandem structure) can be created. In this embodiment, the hole injection layer (111), hole transport layer (112), light-emitting layer (113), electron transport layer (114), and electron injection layer (115) described in Figure 2A have the same function and materials as the hole injection layers (111a, 111b), hole transport layers (112a, 112b), light-emitting layers (113a, 113b), electron transport layers (114a, 114b), and electron injection layers (115a, 115b) described in Figure 2B.

[0100] <Charge generation layer> In the light-emitting device shown in Figure 2B, the charge generation layer 104 has the function of injecting electrons into the EL layer 103a on the anode side (first electrode 101) and holes into the EL layer 103b on the cathode side (second electrode 102) 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 P-type layer in which an electron acceptor is added to a hole-transporting material, or an N-type layer in which an electron donor is added to an electron-transporting material. Both of these configurations may also be stacked. Furthermore, the P-type layer may be formed in combination with one or both of the electron relay layer and the electron injection buffer layer described later. By forming the charge generation layer 104 using the materials described above, the increase in driving voltage when the EL layers are stacked can be suppressed.

[0101] In the charge generation layer 104, if an electron acceptor is added to a hole transport material (P-type layer), the material shown in this embodiment can be used as the hole transport material. Examples of electron acceptors include 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviated as F4-TCNQ), chloranil, etc. Other examples include oxides of metals belonging to groups 4 through 8 of the periodic table. Specifically, examples include vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide.

[0102] Furthermore, in the charge generation layer 104, if an electron donor is added to the electron transport material (N-type layer), the materials shown in this embodiment can be used as the electron transport material. As the electron donor, alkali metals, alkaline earth metals, rare earth metals, or metals belonging to groups 2 and 13 of the periodic table, as well as their oxides and carbonates, can be used. Specifically, lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca), ytterbium (Yb), indium (In), lithium oxide, cesium carbonate, etc., are preferred. Organic compounds such as tetrathianaphthalene may also be used as electron donors.

[0103] As mentioned above, the electron relay layer, which is preferably combined with the P-type layer, has the function of preventing interaction between the electron injection buffer layer and the P-type layer and smoothly transferring electrons by being placed between the electron injection buffer layer and the P-type layer. The electron relay layer contains at least an electron transport material, and it is preferable that the LUMO level of the electron transport material contained in the electron relay layer is 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 transport material used in the electron relay layer is preferably -5.0 eV or higher, preferably -5.0 eV or higher and -3.0 eV or lower. It is preferable to use a phthalocyanine-based material or a metal complex having a metal-oxygen bond and an aromatic ligand as the electron transport material used in the electron relay layer.

[0104] The electron injection buffer layer can use materials with high electron injection potential, such as alkali metals, alkaline earth metals, rare earth metals, and compounds thereof (alkali metal compounds (including oxides such as lithium oxide, halides, and carbonates such as lithium carbonate and cesium carbonate), alkaline earth metal compounds (including oxides, halides, and carbonates), or rare earth metal compounds (including oxides, halides, and carbonates)).

[0105] Furthermore, when the electron injection buffer layer is formed by including an electron transport material and an electron-donating substance, the electron-donating substance can include alkali metals, alkaline earth metals, rare earth metals, and compounds thereof (alkali metal compounds (including oxides such as lithium oxide, halides, and carbonates such as lithium carbonate and cesium carbonate), alkaline earth metal compounds (including oxides, halides, and carbonates), or rare earth metal compounds (including oxides, halides, and carbonates)), as well as organic compounds such as tetratianaphthalene (abbreviated as TTN), nickerosene, and decamethylnickerosene. The electron transport material can be formed using the same materials as those used to constitute the electron transport layer described earlier.

[0106] Although Figure 2B shows a configuration in which two EL layers 103 are stacked, a stacked structure of three or more EL layers may be used by providing a charge generation layer between different EL layers.

[0107] Furthermore, the charge generation layer described above can also be used in place of the electron injection layer described above. In this case, it is preferable that the electron injection buffer layer, electron relay layer, and P-type layer are stacked in that order from the anode side.

[0108] <Circuit board> The light-emitting device shown in this embodiment can be formed on various substrates. The type of substrate is not limited to any particular type. Examples of substrates include semiconductor substrates (e.g., single crystal substrates or silicon substrates), SOI substrates, glass substrates, quartz substrates, plastic substrates, metal substrates, stainless steel substrates, substrates with stainless steel foil, tungsten substrates, substrates with tungsten foil, flexible substrates, laminated films, paper containing fibrous materials, or base films.

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

[0110] In this embodiment, the light-emitting device can be fabricated using vacuum processes such as vapor deposition, or solution processes such as spin coating or inkjet printing. When using vapor deposition, physical vapor deposition methods (PVD) such as sputtering, ion plating, ion beam deposition, molecular beam deposition, and vacuum deposition, or chemical vapor deposition (CVD) can be used. In particular, the functional layers included in the EL layer of light-emitting devices (hole injection layers (111, 111a, 111b), hole transport layers (112, 112a, 112b), light-emitting layers (113, 113a, 113b, 113c), electron transport layers (114, 114a, 114b), electron injection layers (115, 115a, 115b)), and charge generation layers (104, 104a, 104b) can be formed by methods such as vapor deposition (vacuum deposition, etc.), coating (dip coating, die coating, bar coating, spin coating, spray coating, etc.), and printing (inkjet, screen printing, offset printing, flexographic printing, gravure, microcontact, nanoimprint, etc.).

[0111] In this embodiment, the functional layers (hole injection layers (111, 111a, 111b), hole transport layers (112, 112a, 112b), light-emitting layers (113, 113a, 113b, 113c), electron transport layers (114, 114a, 114b), electron injection layers (115, 115a, 115b)) and charge generation layers (104, 104a, 104b) that constitute the EL layer (103, 103a, 103b) of the light-emitting device shown are not limited to the materials described above, and other materials can be used in combination as long as they can satisfy the function of each layer. For example, polymer compounds (oligomers, dendrimers, polymers, etc.), medium-molecular-weight compounds (compounds in the intermediate region between low molecular weight and high molecular weight: molecular weight 400 to 4000), inorganic compounds (quantum dot materials, etc.) can be used. Furthermore, colloidal quantum dot materials, alloy-type quantum dot materials, core-shell type quantum dot materials, and core-type quantum dot materials can be used as quantum dot materials.

[0112] A light-emitting device used in a light-emitting device according to one embodiment of the present invention having the above configuration can be a long-life light-emitting device.

[0113] The configuration shown in this embodiment can be used in appropriate combination with the configurations shown in other embodiments.

[0114] (Embodiment 3) This embodiment describes a light-emitting device that is one aspect of the present invention. The light-emitting device shown in Figure 3A is an active matrix type light-emitting device in which a transistor (FET) 202 on a first substrate 201 and light-emitting devices (203R, 203G, 203B, 203W) are electrically connected. The multiple 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 emission color of each light-emitting device. Furthermore, it is a top-emission type light-emitting device in which the light emitted from the EL layer 204 is emitted through a color filter (206R, 206G, 206B) formed on a second substrate 205.

[0115] In the light-emitting device shown in Figure 3A, the first electrode 207 is formed to function as a reflective electrode. The second electrode 208 is formed to function as a semi-transmitting / semi-reflective electrode, having both transmittance and reflectivity to light (visible light or near-infrared light). The electrode materials forming the first electrode 207 and the second electrode 208 can be used as appropriate, referring to the descriptions in other embodiments.

[0116] Furthermore, in Figure 3A, for example, if 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, then as shown in Figure 3B, light-emitting device 203R is adjusted so that the optical distance between the first electrode 207 and the second electrode 208 is 200R, light-emitting device 203G is adjusted so that the optical distance between the first electrode 207 and the second electrode 208 is 200G, and light-emitting device 203B is adjusted so that the optical distance between the first electrode 207 and the second electrode 208 is 200B. Note that, as shown in Figure 3B, optical adjustment can be performed by laminating a conductive layer 210R on the first electrode 207 of light-emitting device 203R and laminating a conductive layer 210G of light-emitting device 203G.

[0117] Color filters (206R, 206G, 206B) are formed on the second substrate 205. A color filter is a filter that allows a specific wavelength range of visible light to pass through and blocks a specific wavelength range. Therefore, as shown in Figure 3A, by providing a color filter 206R that allows only the red wavelength range to pass through in a position overlapping with the light-emitting device 203R, red light can be obtained from the light-emitting device 203R. Similarly, by providing a color filter 206G that allows only the green wavelength range to pass through in a position overlapping with the light-emitting device 203G, green light can be obtained from the light-emitting device 203G. Furthermore, by providing a color filter 206B that allows only the blue wavelength range to pass through in a position overlapping with the light-emitting device 203B, blue light can be obtained from the light-emitting device 203B. However, the light-emitting device 203W can obtain 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] Figure 3A shows a light-emitting device with a structure that extracts light from the second substrate 205 side (top emission type), but as shown in Figure 3C, it may also be a light-emitting device with a structure that extracts light from the first substrate 201 side on which the FET 202 is formed (bottom emission type). In the case of a bottom emission type light-emitting device, the first electrode 207 is formed to function as a semi-transparent / semi-reflective electrode, and the second electrode 208 is formed to function as a reflective electrode. In addition, the first substrate 201 is at least a light-transmitting substrate. Furthermore, 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 Figure 3C.

[0119] Furthermore, while Figure 3A shows the cases 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, the light-emitting device in one embodiment of the present invention is not limited to these configurations, and may also have a yellow light-emitting device or an orange light-emitting device. The materials used for the EL layer (light-emitting layer, hole injection layer, hole transport layer, electron transport layer, electron injection layer, charge generation layer, etc.) to fabricate these light-emitting devices may be used as appropriate, referring to the descriptions in other embodiments. In that case, it is necessary to appropriately select a color filter according to the light-emitting color of the light-emitting device.

[0120] By using the above configuration, it is possible to obtain a light-emitting device equipped with light-emitting devices that emit multiple colors.

[0121] The configuration shown in this embodiment can be used in appropriate combination with the configurations shown in other embodiments.

[0122] (Embodiment 4) This embodiment describes a light-emitting device that is one aspect of the present invention.

[0123] By applying the device configuration of a light-emitting device according to one aspect of the present invention, active-matrix type light-emitting devices and passive-matrix type light-emitting devices can be manufactured. The active-matrix type light-emitting device has a configuration combining a light-emitting device and a transistor (FET). Therefore, both passive-matrix type and active-matrix type light-emitting devices are included as aspects of the present invention. Furthermore, the light-emitting device shown in this embodiment can be adapted to the light-emitting device described in other embodiments.

[0124] In this embodiment, an active matrix type light-emitting device will be described using Figure 4.

[0125] Figure 4A is a top view showing the light-emitting device, and Figure 4B is a cross-sectional view obtained by cutting Figure 4A along the dashed line A-A'. The active matrix type light-emitting device has a pixel section 302, a drive circuit section (source line drive circuit) 303, and drive circuit sections (gate line drive circuits) (304a, 304b) provided on a first substrate 301. The pixel section 302 and the drive circuit sections (303, 304a, 304b) are sealed between the first substrate 301 and the second substrate 306 by a sealing material 305.

[0126] Furthermore, routing wiring 307 is provided on the first substrate 301. Routing wiring 307 is electrically connected to an external input terminal, FPC 308. The FPC 308 transmits external signals (e.g., video signals, clock signals, start signals, reset signals, etc.) and potentials to the drive circuit section (303, 304a, 304b). A printed wiring board (PWB) may also be attached to the FPC 308. Note that the state in which these FPCs and PWBs are attached is included in the light-emitting device.

[0127] Next, Figure 4B shows the cross-sectional structure.

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

[0129] FETs 309, 310, 311, and 312 are not particularly limited, and for example, staggered or inverse staggered transistors can be used. Furthermore, transistor structures such as top-gate or bottom-gate types may also be used.

[0130] Furthermore, there are no particular limitations on the crystallinity of the semiconductors that can be used in these FETs 309, 310, 311, and 312. Any amorphous semiconductor or a crystalline semiconductor (microcrystalline semiconductor, polycrystalline semiconductor, single-crystal semiconductor, or semiconductor having a crystalline region in part) may be used. However, using a crystalline semiconductor is preferable because it can suppress the degradation of transistor characteristics.

[0131] Furthermore, these semiconductors can include, for example, elements of Group 14, compound semiconductors, oxide semiconductors, and organic semiconductors. Typically, silicon-containing semiconductors, gallium arsenide-containing semiconductors, and indium-containing oxide semiconductors can be applied.

[0132] The drive circuit section 303 includes FET 309 and FET 310. The drive circuit section 303 may be formed by a circuit including unipolar (either N-type or P-type) transistors, or by a CMOS circuit including both N-type and P-type transistors. Furthermore, it may have an external drive circuit.

[0133] The end of the first electrode 313 is covered with an insulator 314. The insulator 314 can be an organic compound such as a negative-type photosensitive resin or a positive-type photosensitive resin (acrylic resin), or an inorganic compound such as silicon oxide, silicon oxide-nitride, or silicon nitride. Preferably, the upper or lower end of the insulator 314 has a curved surface with curvature. This improves 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 laminated on the first electrode 313. The EL layer 315 includes an emissive 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] The configuration of the light-emitting device 317 shown in this embodiment can be adapted to the configurations and materials described in other embodiments. Although not shown here, the second electrode 316 is electrically connected to the FPC 308, which is an external input terminal.

[0136] Furthermore, although only one light-emitting device 317 is shown in the cross-sectional view of Figure 4B, multiple light-emitting devices are assumed to be arranged in a matrix in the pixel section 302. In the pixel section 302, light-emitting devices that produce three types of light (R, G, B) can be selectively formed to create a light-emitting device capable of full-color display. In addition to light-emitting devices that produce three types of light (R, G, B), light-emitting devices that produce, for example, white (W), yellow (Y), magenta (M), cyan (C), etc., may also be formed. For example, by adding light-emitting devices that produce several types of light as described above to light-emitting devices that produce three types of light (R, G, B), effects such as improved color purity and reduced power consumption can be obtained. Furthermore, by combining with a color filter, a light-emitting device capable of full-color display may be created. As for the type of color filter, red (R), green (G), blue (B), cyan (C), magenta (M), yellow (Y), etc., can be used.

[0137] The FETs (309, 310, 311, 312) and the light-emitting device 317 on the first substrate 301 are bonded together with the second substrate 306 and the first substrate 301 using a sealing material 305, and the FETs have a structure provided in a space 318 surrounded by the first substrate 301, the second substrate 306, and the sealing material 305. The space 318 may be filled with an inert gas (such as nitrogen or argon) or an organic substance (including the sealing material 305).

[0138] The sealing material 305 can be epoxy resin or glass frit. It is preferable to use a material that does not permeate moisture or oxygen as much as possible for the sealing material 305. The second substrate 306 can be the same as the first substrate 301. Therefore, various substrates described in other embodiments can be used as appropriate. In addition to glass substrates and quartz substrates, plastic substrates made of FRP (Fiber-Reinforced Plastics), PVF (Polyvinyl Fluoride), polyester, or acrylic resin can be used as substrates. When using glass frit 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] As described above, an active matrix type light-emitting device can be obtained.

[0140] Furthermore, when forming an active matrix type light-emitting device on a flexible substrate, the FET and light-emitting device may be formed directly on the flexible substrate, or the FET and light-emitting device may be formed on another substrate having a release layer, and then the FET and light-emitting device may be peeled off by the release layer by applying heat, force, laser irradiation, etc., and then transferred to the flexible substrate for fabrication. As the release layer, for example, an inorganic film lamination of a tungsten film and a silicon oxide film, or an organic resin film such as polyimide can be used. As for the flexible substrate, in addition to substrates on which transistors can be formed, examples 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 recycled fibers (acetate, cupro, rayon, recycled polyester), etc.), leather substrates, or rubber substrates. By using these substrates, excellent durability and heat resistance can be achieved, and the device can be made lighter and thinner.

[0141] Furthermore, the light-emitting device in an active-matrix type light-emitting device may be driven by causing the light-emitting device to emit light in a pulsed manner (for example, using frequencies such as kHz or MHz) for display purposes. Since the light-emitting device formed using the above-mentioned organic compound has excellent frequency characteristics, the driving time of the light-emitting device can be shortened, and power consumption can be reduced. In addition, since heat generation is suppressed due to the shortened driving time, it is also possible to reduce the degradation of the light-emitting device.

[0142] Furthermore, the configuration shown in this embodiment can be used in appropriate combination with the configurations shown in other embodiments.

[0143] (Embodiment 5) In this embodiment, we will describe various electronic devices and automobiles that have been completed by applying a light-emitting device according to one aspect of the present invention, and a light-emitting apparatus having a light-emitting device according to one aspect of the present invention. The light-emitting apparatus can be mainly applied to the display unit in the electronic devices described in this embodiment.

[0144] The electronic devices shown in Figures 5A to 5E may include a housing 7000, a display unit 7001, a speaker 7003, an LED lamp 7004, operation keys 7005 (including a power switch or operation switch), connection terminals 7006, sensors 7007 (including functions for measuring force, displacement, position, velocity, acceleration, angular velocity, rotational speed, distance, light, liquid, magnetism, temperature, chemical substances, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared radiation), a microphone 7008, etc.

[0145] Figure 5A shows a mobile computer, which may have, in addition to the above-mentioned components, a switch 7009, an infrared port 7010, and the like.

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

[0147] Figure 5C shows a digital camera with a television receiving function, which may have, in addition to the above-mentioned components, an antenna 7014, a shutter button 7015, a receiving unit 7016, etc.

[0148] Figure 5D shows a personal digital assistant (PDA). The PDA has the function of displaying information on three or more sides of the 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, which is displayed in a position that can be observed from above the PDA while it is stored in the breast pocket of their clothing. The user can check the display without taking the PDA out of their pocket and decide, for example, whether or not to answer a call.

[0149] Figure 5E shows a personal information terminal (including a smartphone), and the housing 7000 may have a display unit 7001, operation keys 7005, etc. The personal information terminal may also be equipped with a speaker 7003, connection terminals 7006, sensors 7007, etc. Furthermore, the personal information terminal can display text and image information on multiple surfaces. Here, an example is shown where three icons 7050 are displayed. Information 7051, indicated by a dashed rectangle, can also be displayed on other surfaces of the display unit 7001. Examples of information 7051 include notifications of incoming emails, SNS messages, and phone calls; the subject, sender name, date, time, battery level, and antenna signal strength of emails and SNS messages. Alternatively, icons 7050 or the like may be displayed where the information 7051 is displayed.

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

[0151] The electronic devices shown in Figures 5A to 5F can have a variety of functions. For example, they can have functions to display various information (still images, videos, text images, etc.) on the display unit, touch panel functions, functions to display calendars, dates or times, functions to control processing by various software (programs), wireless communication functions, functions to connect to various computer networks using wireless communication functions, functions to transmit or receive various data using wireless communication functions, functions to read programs or data recorded on a recording medium and display them on the display unit, etc. Furthermore, electronic devices with multiple display units can have functions to primarily display image information on one display unit and primarily display text information on another display unit, or functions to display three-dimensional images by displaying images that take parallax into account on multiple display units, etc. Furthermore, electronic devices with an image receiving unit can have functions to capture still images, capture videos, automatically or manually correct captured images, save captured images to a recording medium (external or built into the camera), display captured images on the display unit, etc. It should be noted that the functions that the electronic devices shown in Figures 5A to 5F can have are not limited to these, and they can have a variety of functions.

[0152] Figure 5G shows a wristwatch-type personal information terminal, which can be used, for example, as a smartwatch. This wristwatch-type personal 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, etc. The display unit 7001 has a curved display surface, allowing it to display information along the curved surface. This personal information terminal can also make hands-free calls by communicating with, for example, a wireless headset. In addition, the connection terminal 7024 can be used to transmit data to other information terminals and to charge the device. Charging can also be performed by wireless power supply.

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

[0154] The smartwatch shown in Figure 5G can have a variety of functions. For example, it can have functions to display various information (still images, videos, text images, etc.) on the display unit, a touch panel function, a function to display a calendar, date or time, a function to control processing by various software (programs), a wireless communication function, a function to connect to various computer networks using the wireless communication function, a function to transmit or receive various data using the wireless communication function, a function to read programs or data recorded on a recording medium and display them on the display unit, etc.

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

[0156] Furthermore, a light-emitting device according to one aspect of the present invention can be used in each display unit of the electronic device shown in this embodiment, enabling the realization of an electronic device with a long lifespan.

[0157] Furthermore, examples of electronic devices to which a light-emitting device is applied include foldable portable information terminals, as shown in Figures 6A to 6C. Figure 6A shows the portable information terminal 9310 in its unfolded state. Figure 6B shows the portable information terminal 9310 in an intermediate state, transitioning from either the unfolded or folded state to the other. Figure 6C shows the portable information terminal 9310 in its folded state. The portable information terminal 9310 offers excellent portability in its folded state and excellent readability of the display due to its seamless, wide display area in its unfolded state.

[0158] The display unit 9311 is supported by three housings 9315 connected by a hinge 9313. The display unit 9311 may also be a touch panel (input / output device) equipped with a touch sensor (input device). Furthermore, the display unit 9311 can be reversibly transformed from an unfolded state to a folded state of the portable information terminal 9310 by bending the two housings 9315 via the hinge 9313. A light-emitting device according to one aspect of the present invention can be used in the display unit 9311. This also enables the realization of a long-life electronic device. The display area 9312 in the display unit 9311 is a display area located on the side of the portable information terminal 9310 in its folded state. The display area 9312 can display information icons and shortcuts to frequently used apps and programs, allowing for smooth information confirmation and app launches.

[0159] Furthermore, Figures 7A and 7B show automobiles to which the light-emitting device is applied. That is, the light-emitting device can be installed as an integral part of the automobile. Specifically, it can be applied to the exterior lights 5101 (including the rear of the vehicle body), the wheel 5102, and part or all of the door 5103 of the automobile shown in Figure 7A. It can also be applied to the interior display unit 5104, steering wheel 5105, shift lever 5106, seat 5107, inner rearview mirror 5108, windshield 5109, etc. of the automobile shown in Figure 7B. It may also be applied to part of other glass windows.

[0160] As described above, electronic devices and automobiles to which a light-emitting device according to one aspect of the present invention is applied can be obtained. In this case, long-life electronic devices can be realized. Furthermore, the electronic devices and automobiles to which this invention can be applied are not limited to those shown in this embodiment, but can be applied in any field.

[0161] The configuration shown in this embodiment can be used in appropriate combination with the configurations shown in other embodiments.

[0162] (Embodiment 6) In this embodiment, the configuration of a lighting device manufactured by applying a light-emitting device, or a light-emitting device which is a part thereof, according to one aspect of the present invention, will be explained with reference to Figure 8.

[0163] Figures 8A and 8B show examples of cross-sectional views of lighting devices. Figure 8A is a bottom-emission type lighting device that extracts light to the substrate side, while Figure 8B is a top-emission type lighting device that extracts light to the sealed substrate side.

[0164] The lighting device 4000 shown in Figure 8A has a light-emitting device 4002 on a substrate 4001. It also has a substrate 4003 with irregularities on the outside of the substrate 4001. The light-emitting device 4002 has a first electrode 4004, an EL layer 4005, and a second electrode 4006.

[0165] The first electrode 4004 is electrically connected to electrode 4007, and the second electrode 4006 is electrically connected to electrode 4008. An auxiliary wiring 4009 electrically connected to the first electrode 4004 may also be provided. An insulating layer 4010 is formed on the auxiliary wiring 4009.

[0166] Furthermore, the substrate 4001 and the encapsulating substrate 4011 are bonded together with a sealing material 4012. It is also preferable that a desiccant 4013 is provided between the encapsulating substrate 4011 and the light-emitting device 4002. Since the substrate 4003 has an uneven surface as shown in Figure 8A, the efficiency of light extraction from the light-emitting device 4002 can be improved.

[0167] The lighting device 4200 in Figure 8B has a light-emitting device 4202 on a substrate 4201. The light-emitting device 4202 has a first electrode 4204, an EL layer 4205, and a second electrode 4206.

[0168] The first electrode 4204 is electrically connected to electrode 4207, and the second electrode 4206 is electrically connected to electrode 4208. An auxiliary wire 4209 electrically connected to the second electrode 4206 may also be provided. An insulating layer 4210 may be provided below the auxiliary wire 4209.

[0169] The substrate 4201 and the uneven sealing substrate 4211 are bonded together with a sealing material 4212. A barrier film 4213 and a planarization film 4214 may also be provided between the sealing substrate 4211 and the light-emitting device 4202. Since the sealing substrate 4211 has an uneven surface as shown in Figure 8B, the efficiency of light extraction from the light-emitting device 4202 can be improved.

[0170] Another example of the application of these lighting devices is ceiling lights used for indoor lighting. Ceiling lights come in various types, including surface-mounted and recessed types. Such lighting devices are constructed by combining a light-emitting device with a housing or cover.

[0171] Other applications include footlights that illuminate the floor surface to enhance safety underfoot. Footlights are particularly effective in bedrooms, stairwells, and hallways. In such cases, the size and shape can be adjusted as needed depending on the room's size and structure. It is also possible to create a freestanding lighting device by combining a light-emitting unit with a support base.

[0172] Furthermore, it can be applied as a sheet-type lighting device (sheet-type lighting). Because sheet-type lighting is attached to walls, it takes up minimal space and can be used in a wide range of applications. It is also easy to increase the area of ​​application. It can also be used on curved walls and enclosures.

[0173] In addition to the above, a light-emitting device, or a light-emitting device that is a part thereof, according to one aspect of the present invention can be applied to a part of the furniture installed in the room, thereby creating a lighting device that also functions as furniture.

[0174] As described above, various lighting devices can be obtained by applying a light-emitting device. These lighting devices are included in one aspect of the present invention.

[0175] Furthermore, the configuration shown in this embodiment can be used in appropriate combination with the configurations shown in other embodiments.

[0176] <Reference example> This reference example describes the methods for calculating the HOMO level, LUMO level, and electron mobility of the organic compounds used in each embodiment.

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

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

[0179] Electron mobility can be measured using impedance spectroscopy (IS method).

[0180] Methods for measuring the carrier mobility of EL materials have long been known, including the transient photocurrent (TOF) method and the method of determining it from the IV characteristics of space-charge-limited current (SCLC) (SCLC method). The TOF method requires a sample with a considerably thicker film thickness compared to actual organic EL devices. The SCLC method has drawbacks, such as not being able to obtain the electric field strength dependence of the carrier mobility. The IS method requires a thin organic film thickness of only a few hundred nanometers, making it possible to deposit a film even with a relatively small amount of EL material. It is characterized by its ability to measure mobility at a film thickness close to that of actual EL devices, and it can also obtain the electric field strength dependence of the carrier mobility.

[0181] In the IS method, a small sinusoidal voltage signal (V=V0[exp(jωt)]) is applied to an EL element, and the impedance of the EL element (Z=V / I) is determined from the phase difference between the current amplitude of the response current signal (I=I0exp[j(ωt+φ)]) and the input signal. By varying the voltage from high frequency to low frequency and applying it to the element, various components with different relaxation times that contribute to the impedance can be separated and measured.

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

[0183]

number

[0184] Furthermore, equations (2) and (3) below can be calculated using the single-charge injection model. Here, g (equation (4)) is the differential conductance. In the equations, C is capacitance, θ is ωt (the travel angle), and ω is the angular frequency. t is the travel time. The current equation, Poisson's equation, and the 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. The ωΔG method is another method for calculating mobility from the frequency characteristics of conductance.

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

[0188] The electron-only device fabricated for measurement in this study has a first layer 910, a second layer 911, and a third layer 912 between the first electrode 901 and the second electrode 902, as shown in Figure 9. The material whose electron mobility is to be determined can be used as the material for the second layer 911. In this study, we will explain using an example of measuring the electron mobility of a co-evaporated film of 2-{4-[9,10-di(naphthalene-2-yl)-2-anthryl]phenyl}-1-phenyl-1H-benzimidazole (abbreviated as ZADN) and Liq in a 1:1 (weight ratio). Specific configuration examples are summarized in the table below.

[0189] [Table 1]

[0190] Figure 10 shows the current density-voltage characteristics of an electron-only device fabricated with a co-evaporated film of ZADN and Liq as the second layer 911.

[0191] Impedance measurements were performed under the conditions of applying a DC voltage in the range of 5.0V to 9.0V while maintaining an AC voltage of 70mV and a frequency of 1Hz to 3MHz. Capacitance was calculated from the admittance (equation (1) above), which is the reciprocal of the impedance obtained. Figure 11 shows the frequency characteristics of the calculated capacitance C at an applied voltage of 7.0V.

[0192] The frequency characteristics of capacitance C are obtained because the space charge due to carriers injected by a small voltage signal cannot completely follow the small AC voltage, resulting in a phase difference in the current. Here, the travel time of carriers in the film is defined as the time T it takes for the injected carriers to reach the counter electrode, and is expressed by the following equation (5).

[0193]

number

[0194] The negative susceptance change (-ΔB) corresponds to the value obtained by multiplying the capacitance change (-ΔC) by the angular frequency ω (-ωΔC). Its lowest frequency peak frequency is f'. max (=ω max From equation (3), it can be derived that the following relationship (6) exists between (2π) and the travel time T.

[0195]

number

[0196] Figure 12 shows the frequency characteristics of -ΔB calculated from the above measurements (i.e., when the DC voltage is 7.0V). The lowest frequency peak frequency f' can be found from Figure 12. max This is indicated by the arrow in the diagram.

[0197] f' obtained from the above measurements and analysis maxFrom this, the travel time T can be determined (see equation (6) above), and from equation (5) above, in this case, the electron mobility at a voltage of 7.0V can be determined. By performing similar measurements in the range of DC voltage from 5.0V to 9.0V, 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] Figure 13 shows the electric field strength dependence of the electron mobility of each organic compound, which was finally obtained using the calculation method described above. The square root of the electric field strength [V / cm] read from the figure is 600 [V / cm]. 1 / 2 Table 2 shows the electron mobility values ​​at that time.

[0199] [Table 2]

[0200] As described above, it is possible to calculate electron mobility. For detailed measurement methods, 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 distance, 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: 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 : Encapsulation 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: Encapsulation substrate, 4212: Sealing material, 4213: Barrier film, 4214: Planarization film, 5101: Light, 5102: Wheel, 5103: Door, 5104: Display unit, 5105: Handle, 5106: Shift lever, 5107: Seat, 5108: Inner rearview 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 media reader, 7014: Antenna, 7015: Shutter button 7016: Image receiver, 7018: Stand, 7020: Camera, 7022, 7023: Operation buttons, 7024: Connection terminal, 7025: Band, 7026: Microphone, 7029: Sensor, 7030: Speaker, 7052, 7053, 7054: Information, 9310: Portable information terminal, 9311: Display unit, 9312: Display area, 9313: Hinge, 9315: Housing,

Claims

1. Between the anode and the cathode, there is a hole injection layer, a hole transport layer, a first light-emitting layer, a second light-emitting layer, and an electron transport layer. 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 comprises a first material and a second material, The second light-emitting layer comprises a third material and a fourth material, The first substance and the third substance are the same or different light-emitting substances. The Hall mobility of the second light-emitting layer is smaller than the Hall mobility of the first light-emitting layer. The hole injection layer comprises a fifth substance and a sixth substance, The fifth substance is an acceptable material, The HOMO level of the sixth substance is between -5.7 eV and -5.4 eV. The hole transport layer has a seventh substance, The HOMO level of the seventh substance is smaller than the HOMO level of the sixth substance and larger than the HOMO level of the second substance. The electron transport layer comprises an eighth material and a ninth material, The eighth substance is an organometallic complex of an alkali metal or alkaline earth metal, The ninth substance is a heterocyclic compound having a polyazole skeleton or a heterocyclic compound having a diazine skeleton, wherein the light-emitting device.

2. In claim 1, A light-emitting device in which the 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 claim 2, A light-emitting device in which the relative abundance of the eighth substance in the electron transport layer is smaller on the cathode side than on the second light-emitting layer side.

4. In any one of Claims 1 to 3, A light-emitting device wherein the concentration of the third substance in the second light-emitting layer is lower than the concentration of the first substance in the first light-emitting layer.

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