Light-emitting element and display device having the same

Abstract

To provide a light-emitting element having a structure which can effectively prevent crosstalk in a display device.SOLUTION: A light-emitting element comprises an anode, a first function layer on the anode, a light-emitting layer located on and in contact with the first function layer, an electron transport layer on the light-emitting layer, and a cathode on the electron transport layer. The first function layer includes a first hole transport material and a hole trap material. The light-emitting layer includes a host material, a light-emitting material, and a hole trap material. In the first function layer and the light-emitting layer, concentration of the hole trap material is lower than concentrations of the first hole transport material and the host material. The highest occupied molecular orbit level of the hole trap material is higher than the highest occupied molecular orbit levels of the first hole transport material and the host material.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] As an example of a display device, an organic EL (Electroluminescence) display device can be mentioned. The organic EL display device has a plurality of organic light-emitting elements (hereinafter, referred to as light-emitting elements) formed on a substrate, and each light-emitting element has a basic structure of an electroluminescent layer (hereinafter, referred to as an EL layer) containing an organic compound between a pair of electrodes (a cathode and an anode). By applying a potential difference between the pair of electrodes, holes and electrons are supplied to the EL layer from the anode and the cathode, respectively. The holes and electrons recombine in the EL layer to form an excited state of the organic compound. By utilizing the light emission when this excited state undergoes radiative deactivation to the ground state, the function as a light-emitting element is exhibited.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] One embodiment of the present invention has an object of providing a light-emitting element having a new structure. Alternatively, one embodiment of the present invention has an object of providing a light-emitting element having a structure capable of effectively preventing crosstalk in a display device, and a display device including this light-emitting element.

Means for Solving the Problems

[0005] One embodiment of the present invention is a light-emitting element. This light-emitting element includes an anode, a first functional layer on the anode, a light-emitting layer located on the first functional layer and in contact with the first functional layer, an electron transport layer on the light-emitting layer, and a cathode on the electron transport layer. The first functional layer includes a first hole transport material and a hole trap material. The light-emitting layer includes a host material, a light-emitting material, and the hole trap material. In the first functional layer and the light-emitting layer, the concentration of the hole trap material is lower than the concentration of the first hole transport material and the host material, respectively. The highest occupied molecular orbital level of the hole trap material is higher than the highest occupied molecular orbital levels of the first hole transport material and the host material.

[0006] One embodiment of the present invention is a display device. This display device includes a first pixel having a first light-emitting element and a second pixel having a second light-emitting element. The first light-emitting element has a first anode, a first functional layer located on the first anode, a first light-emitting layer located on the first functional layer and in contact with the first functional layer, an electron transport layer on the first light-emitting layer, and a cathode on the electron transport layer. The first functional layer includes a first hole transport material and a hole trap material. The first light-emitting layer includes a first host material, a first light-emitting material, and the hole trap material. The second light-emitting element has a second anode, a hole transport layer located on the second anode, a second light-emitting layer located on the hole transport layer, the electron transport layer on the second light-emitting layer, and the cathode on the electron transport layer. The hole transport layer includes the first hole transport material. The second light-emitting layer includes a second host material and a second light-emitting material. In the first functional layer and the first light-emitting layer, the concentration of the hole trap material is lower than the concentration of the first hole transport material and the first host material, respectively. The highest occupied molecular orbital level of the hole trap material is lower than the highest occupied molecular orbital levels of the first hole transport material and the first host material, a display device.

[0007] One embodiment of the present invention is a light-emitting element. This light-emitting element includes an anode, a hole transport layer on the anode, a light-emitting layer on the hole transport layer, a first functional layer located on the light-emitting layer and in contact with the light-emitting layer, and a cathode on the first functional layer. The first functional layer includes a first electron transport material and an electron trap material. The light-emitting layer includes a host material, a light-emitting material, and the above electron trap material. In the first functional layer and the light-emitting layer, the concentration of the electron trap material is lower than the concentration of the first electron transport material and the host material, respectively. The lowest unoccupied molecular orbital level of the electron trap material is lower than the highest occupied molecular orbital level of the first electron transport material and the highest occupied molecular orbital level of the host material.

[0008] One embodiment of the present invention is a display device. This display device includes a first pixel having a first light-emitting element and a second pixel having a second light-emitting element. The first light-emitting element has a first anode, a hole transport layer located on the first anode, a first light-emitting layer located on the hole transport layer, a first functional layer located on the first light-emitting layer and in contact with the first light-emitting layer, and a cathode on the first functional layer. The first functional layer includes a first electron transport material and an electron trap material. The first light-emitting layer includes a first host material, a first light-emitting material, and the above electron trap material. The second light-emitting element has a second anode, the above hole transport layer located on the second anode, a second light-emitting layer located on the hole transport layer, an electron transport layer on the second light-emitting layer, and the above cathode on the electron transport layer. The second light-emitting layer includes a second host material and a second light-emitting material. The electron transport layer includes the above first electron transport material. In the first functional layer and the first light-emitting layer, the concentration of the electron trap material is lower than the concentration of the first electron transport material and the first host material, respectively. The lowest unoccupied molecular orbital level of the electron trap material is lower than the lowest unoccupied molecular orbital level of the first electron transport material and the lowest unoccupied molecular orbital level of the first host material. Display device.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] Hereinafter, each embodiment of the present invention will be described with reference to the drawings and the like. However, the present invention can be implemented in various modes without departing from the gist thereof, and is not to be construed as being limited to the description of the embodiments exemplified below.

[0011] For the sake of clearer explanation, the drawings may schematically represent the width, thickness, shape, etc. of each part as compared with the actual aspect, but this is merely an example and does not limit the interpretation of the present invention. In this specification and each figure, elements having the same functions as those described with respect to the previously shown figures may be denoted by the same reference numerals, and redundant descriptions may be omitted.

[0012] In an embodiment of the present invention, when a plurality of films are formed simultaneously in the same process, these films have the same layer structure, the same material, and the same composition. Therefore, these plurality of films are defined as being present within the same layer.

[0013] In this specification and the claims, when expressing the manner of disposing one structure on another structure, if simply expressed as "on", unless otherwise specified, it shall include both the case where another structure is disposed directly on a certain structure in contact therewith and the case where another structure is disposed above a certain structure via yet another structure.

[0014] In this specification and the claims, the expression "a certain structure is exposed from another structure" means a mode in which a part of a certain structure is not covered by another structure, and the part not covered by this other structure also includes a mode in which it is covered by yet another structure.

[0015] (First Embodiment) In this embodiment, a light-emitting element 100, which is one of the embodiments of the present invention, will be described.

[0016] 1. Structure of the Light-Emitting Element FIG. 1(A) shows a schematic cross-sectional view of a light-emitting element 100 according to this embodiment. The light-emitting element 100 is provided on a substrate (not shown) and includes a light-emitting layer 116 and a pair of electrodes (anode 102, cathode 104) sandwiching the light-emitting layer 116. The light-emitting element 100 further has one or more functional layers between the light-emitting layer 116 and the anode 102, and between the light-emitting layer 116 and the cathode 104, respectively. Hereinafter, all the layers provided between the anode 102 and the cathode 104 are collectively referred to as the EL layer 106. In the light-emitting element 100, by applying a potential difference equal to or greater than the light-emitting threshold voltage between the anode 102 and the cathode 104, holes and electrons are injected into the EL layer 106 from the anode 102 and the cathode 104, respectively. When these carriers recombine in the light-emitting layer 116, the light-emitting material contained in the light-emitting layer 116 is excited, and the energy when this excited state returns to the ground state is utilized as light emission. As shown in FIG. 1(A), the light-emitting element 100 may have a stacked structure in the order of the anode 102, the EL layer 106, and the cathode 104 from the substrate, and although not shown, it may also have a stacked structure in the reverse order of this order.

[0017] As the functional layer provided between the light-emitting layer 116 and the anode 102, for example, there are a hole injection layer 110 located on the anode 102 and in contact with the anode 102, a hole transport layer 112 located on the hole injection layer 110 and in contact with the hole injection layer 110, an electron blocking layer 114 located on the hole transport layer 112 and in contact with both the hole transport layer 112 and the light-emitting layer 116, and the like. As the functional layer provided between the light-emitting layer 116 and the cathode 104, for example, there are a hole blocking layer 118 located on the light-emitting layer 116 and in contact with the light-emitting layer 116, an electron transport layer 120 located on the hole blocking layer 118 and in contact with the hole blocking layer 118, an electron injection layer 122 located on the electron transport layer 120 and in contact with both the electron transport layer 120 and the cathode 104, and the like.

[0018] The light-emitting element 100 does not necessarily include all the above-described functional layers. For example, as shown in FIG. 1(B), the light-emitting element 100 may be configured such that the electron blocking layer 114 is not provided and the hole transport layer 112 is in contact with the light-emitting layer 116. Alternatively, as shown in FIG. 1(C), the light-emitting element 100 may be configured such that the hole blocking layer 118 is not provided and the electron transport layer 120 is in contact with the light-emitting layer 116. Although not shown, both the electron blocking layer 114 and the hole blocking layer 118 may not be provided, and the hole injection layer 110 or the electron injection layer 122 may not be provided.

[0019] Both the light-emitting layer 116 and the functional layer may have a single-layer structure, or may have a laminated structure in which a plurality of layers made of different materials are laminated.

[0020] Hereinafter, each component will be described. Note that each functional layer and the light-emitting layer 116 can be formed by co-evaporating a plurality of types of materials. In this case, the material with a higher concentration (volume fraction) is the main component, and the material with a lower concentration (volume fraction) than the main component is also called an additional component. The additional component is uniformly dispersed in the main component.

[0021] 1-1. Anode The anode 102 is an electrode provided for injecting holes into the EL layer 106, and it is preferable that its surface has a relatively high work function. Specific materials include conductive oxides such as indium-tin oxide (ITO) and indium-zinc oxide (IZO), and these may further contain silicon. With this structure, the light emission obtained from the light-emitting layer 116 can be extracted through the anode 102. On the other hand, when extracting the light emission obtained from the light-emitting layer 116 through the cathode 104, the anode 102 may further include a film containing a metal with a high visible light reflectance such as silver or aluminum. For example, the anode 102 can have a structure in which a first conductive film containing a conductive oxide, a second conductive film containing a metal such as silver or aluminum, and a third conductive film containing a conductive oxide are laminated in this order.

[0022] 1-2. Hole injection layer For the hole injection layer 110, a compound (electron-donating compound) that allows holes to be easily injected from the anode 102, that is, a compound that is easily oxidized, can be used as the hole injection material. In other words, a compound with a high (shallow) highest occupied molecular orbital (HOMO) level and higher hole transportability than electron transportability (i.e., a hole transport material) can be used. For example, phthalocyanine derivatives such as phthalocyanine, copper phthalocyanine, and vanadyl phthalocyanine, benzidine derivatives such as 4,4'-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (DPAB) and 4,4'-bis(N-{4-[N'-(3-methylphenyl)-N'-phenylamino]phenyl}-N-phenylamino)biphenyl (DNTPD), aromatic amines such as 4,4',4''-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (MTDATA) and 4,4',4''-tris(N,N-diphenylamino)triphenylamine (TDATA), carbazole derivatives, thiophene derivatives, etc. can be used. Alternatively, polymer compounds such as poly(N-vinylcarbazole), poly(4-vinyltriphenylamine), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine], poly(3,4-ethylenedioxythiophene) / poly(styrenesulfonic acid), polyaniline / poly(styrenesulfonic acid), etc. may be used. Alternatively, oxides of transition metals such as molybdenum oxide, vanadium oxide, and zirconium oxide can also be used.

[0023] Alternatively, a composite material in which an organic compound is doped with an acceptor may be used. In this case, as the organic compound, in addition to the above-described materials with high hole transportability, compounds having a condensed aromatic ring such as anthracene derivatives can also be used. Examples of acceptors include nitrogen-containing heteroaromatic compounds, heteroaromatic compounds having a strong electron-withdrawing group such as a cyano group, and transition metal oxides such as vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, and molybdenum oxide.

[0024] The thickness of the hole injection layer 110 can be arbitrarily set, for example, it can be selected from the range of 10 nm or more and 200 nm or less, 20 nm or more and 100 nm, or 20 nm or more and 50 nm or less.

[0025] 1-3. Hole transport layer The hole transport layer 112 has a function of transporting the holes injected into the hole injection layer 110 to the light-emitting layer 116 side. A hole transport material with higher hole transport property than electron transport property can also be used for the hole transport layer 112. Similar to or similar materials as those usable in the hole injection layer 110 can be appropriately used. For example, materials with a deeper HOMO level compared to the hole injection layer 110 but with a difference of 0.5 eV or less, 0.3 eV or less, or 0.1 eV or less can be used. Specifically, NPB such as 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPB) and 4,4'-bis[N-(2-naphthyl)-N-phenylamino]biphenyl (β-NPB), benzidine derivatives such as 4,4'-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (TPD), and carbazole derivatives such as 4,4'-di(N-carbazolyl)biphenyl (CBP) and 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (TCPB) are exemplified.

[0026] The thickness of the hole transport layer 112 can also be arbitrarily set, for example, it can be selected from the range of 20 nm or more and 100 nm or less, 20 nm or more and 50 nm, or 30 nm or more and 50 nm or less.

[0027] 1-4. Electron blocking layer The electron blocking layer 114 has a function of transporting holes transported from the anode 102 to the light-emitting layer 116 side and preventing electrons that pass through the light-emitting layer 116 from the cathode 104 side without recombination from being transported to the hole transport layer 112 side. The electron blocking material used for the electron blocking layer 114 can also be selected from hole transport materials that can be used in the hole injection layer 110 and the hole transport layer 112. However, in order to exhibit the function of effectively blocking electrons, its lowest unoccupied molecular orbital (LUMO) level is higher (shallower) than the LUMO level of the host material (described later) used in the light-emitting layer 116, and the difference is preferably selected so that it is 0.2 eV or more and 0.5 eV or less, or 0.3 eV or more and 0.5 eV or less. Thereby, electrons can be confined in the electron blocking layer 114, and the recombination probability in the light-emitting layer 116 can be increased.

[0028] The thickness of the electron blocking layer 114 can also be arbitrarily set. For example, it can be selected from the range of 1 nm or more and 20 nm or less, 1 nm or more and 10 nm, or 1 nm or more and 5 nm or less. When it has a thickness of 1 nm or more and 5 nm or less, holes can be transported from the hole transport layer 112 to the light-emitting layer 116 without depending on the energy barrier between the hole transport layer 112 and the light-emitting layer 116 due to the tunnel effect.

[0029] Note that the materials used for the electron transport layer 120 and the electron blocking layer 114 are both hole transport materials. Whether to define these as electron blocking materials is determined by whether they sufficiently have the function of blocking electrons from the light-emitting layer 116. Specifically, if its LUMO level is higher than the LUMO level of the host material contained in the light-emitting layer 116 and the difference is 0.2 eV or more or 0.3 eV or more, it functions as an electron blocking material.

[0030] 1-5. Light-emitting layer The light-emitting layer 116 is a layer that provides a space where holes and electrons recombine, and light emission is obtained from the light-emitting material contained in this layer. The light-emitting layer 116 can have a so-called host-guest type configuration. That is, the light-emitting layer 116 can contain a host material as the main component and a guest material contained at a low concentration compared to the host material as the light-emitting material. As will be described later, the light-emitting layer 116 further contains additional components.

[0031] As the host material, for example, condensed aromatic compounds such as stilbene derivatives and anthracene derivatives, carbazole derivatives, metal complexes containing quinolinol ligands, aromatic amines, nitrogen-containing heteroaromatic compounds such as phenanthroline derivatives, etc. can be used. Specifically, metal complexes having 8-quinolinol-based ligands such as tris(8-quinolinolato)aluminum(III) (Alq), tris(4-methyl-8-quinolinolato)aluminum(III) (Almq3), bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (BAlq), oxadiazole derivatives such as 2-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) and 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (OXD-7), triazole derivatives such as 3-(biphenyl-4-yl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ) and 3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole (p-EtTAZ), imidazole derivatives such as 2,2’,2’’-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole) (TPB), 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), phenanthroline derivatives such as bathophenanthroline (BPhen) and bathocuproine (BCP), anthracene derivatives such as 9,10-bis(3,5-diphenylphenyl)anthracene (DPPA), 9,10-di(2-naphthyl)anthracene (DNA), 2-tert-butyl-9,10-di(2-naphthyl)anthracene (t-BuDNA), 9,9’-bianthryl (BANT), etc., and in addition, condensed aromatic compounds such as 9,9’-(stilbene-3,3’-diyl)diphenanthrene (DPNS), 9,9’-(stilbene-4,4’-diyl)diphenanthrene (DPNS2), 3,3’,3’’-(benzene-1,3,5-triyl)tripyrene (TPB) can be used.

[0032] As the light-emitting material, fluorescent materials such as coumarin derivatives, pyran derivatives, quinocridone derivatives, tetracene derivatives, pyrene derivatives, anthracene derivatives, or phosphorescent materials such as iridium-based ortho-metal complexes can be used as the light-emitting material. When the light-emitting material is a phosphorescent material, the triplet level of the host material is higher than the triplet level of the light-emitting material, and the difference is preferably 0.2 eV or more and 0.7 eV or less, 0.3 eV or more and 0.6 eV or less, or 0.3 eV or more and 0.5 eV or less. More specifically, it is preferable to use metal complexes with relatively large band gaps (for example, 2.8 eV or more) such as phenanthroline derivatives, oxadiazole derivatives, triazole derivatives, and BALq as the host material.

[0033] There is no restriction on the emission wavelength of the light-emitting material. For example, a blue light-emitting material that gives an emission peak wavelength within the range of 400 nm or more and 500 nm or less, a green light-emitting material that gives an emission peak wavelength within the range of 500 nm or more and 600 nm or less, or a red light-emitting material that gives an emission peak wavelength within the range of 600 nm or more and 780 nm or less can be used.

[0034] The thickness of the light-emitting layer 116 can also be arbitrarily set, and for example, it can be selected from the range of 20 nm or more and 60 nm or less, 20 nm or more and 50 nm, or 30 nm or more and 50 nm or less.

[0035] 1-6. Hole Blocking Layer The hole blocking layer 118 confines holes in the light-emitting layer 116 by preventing holes injected from the anode 102 from passing through the light-emitting layer 116 and being injected into the electron transport layer 120 without contributing to recombination, and also has a function of preventing the excitation energy obtained in the light-emitting layer 116 from undergoing energy transfer to the molecules in the electron transport layer 120. Thereby, the recombination probability in the light-emitting layer 116 can be increased, and a decrease in luminous efficiency can be prevented.

[0036] In the hole-blocking layer 118, it is preferable to use, as the hole-blocking material, a material having higher electron-transporting property than hole-transporting property or comparable thereto, having a deeper HOMO level than the host material, and having a larger band gap than the host material and the light-emitting material. Specifically, examples of such materials include BAlq, OXD-7, TAZ, p-EtTAZ, BPhen, BCP, etc. described above. A material having a difference of 0.2 eV or more and 0.7 eV or less, 0.2 eV or more and 0.6 eV or less, or 0.2 eV or more and 0.5 eV or less from the HOMO level of the host material contained in the light-emitting layer 116 may be selected. Further, a material having a band gap of 0.2 eV or more and 0.7 eV or less, 0.2 eV or more and 0.6 eV or less, or 0.2 eV or more and 0.5 eV or less than the band gap of the light-emitting material is preferable. When the light-emitting material is a phosphorescent material, it is preferable to select a hole-blocking material such that the triplet level is higher than that of the light-emitting material.

[0037] The thickness of the hole-blocking layer 118 can also be arbitrarily set, and may be selected, for example, from the range of 1 nm or more and 20 nm or less, 1 nm or more and 10 nm, or 1 nm or more and 5 nm or less. When having a thickness of 1 nm or more and 5 nm or less, not only can holes be blocked, but electrons can be effectively transported to the light-emitting layer 116 without depending on the energy barrier between the electron-transporting layer 120 and the light-emitting layer 116 due to the tunnel effect.

[0038] 1-7. Electron-transporting layer The electron transport layer 120 has a function of transporting the electrons injected from the cathode 104 to the electron injection layer 122 toward the light-emitting layer 116. The electron transport layer 120 contains, as an electron transport material, a compound having higher electron transport property than hole transport property or having comparable electron transport property. Examples of such a compound include metal complexes such as aluminum complexes, lithium complexes, and beryllium, oxadiazole derivatives, triazole derivatives, silacyclopentadiene derivatives, anthracene derivatives, pyrene derivatives, condensed aromatic compounds such as perylene derivatives, nitrogen-containing condensed heteroaromatic compounds such as phenanthroline derivatives, and sulfur-containing condensed heteroaromatic compounds such as dibenzothiophene derivatives. Examples of the above metal complexes include metal complexes having an 8-quinolinol ligand such as lithium 8-quinolinolate (Liq), Alq, and BAlq. An example of the dibenzothiophene derivative includes 2,8-bis(diphenylphosphoryl)dibenzothiophene (PPT).

[0039] The thickness of the electron transport layer 120 can also be arbitrarily set, and for example, it may be selected from the range of 20 nm or more and 60 nm or less, 20 nm or more and 50 nm, or 30 nm or more and 50 nm or less.

[0040] Note that the materials used for the hole blocking layer 118 and the electron transport layer 120 are both electron transport materials, and whether to define them as hole blocking materials is determined by whether they sufficiently have a function of blocking holes from the light-emitting layer 116. Specifically, if its HOMO level is lower than the HOMO level of the host material contained in the light-emitting layer 116 and the difference is 0.2 eV or more or 0.3 eV or more, it functions as a hole blocking material.

[0041] 1-8. Electron Injection Layer The electron injection layer 122 has a function of promoting electron injection from the cathode 104. Examples of electron injection materials that can be used for the electron injection layer 122 include inorganic compounds such as lithium fluoride and calcium fluoride. Alternatively, a mixture of an electron transport material that can be used for the electron transport layer 120 and an electron-donating compound exemplified by a Group 1 metal such as lithium, a Group 2 metal such as magnesium or calcium, or a lanthanoid metal such as ytterbium can be used. Typically, a mixture of Alq and Li or a mixture of Liq and Li can be mentioned.

[0042] The thickness of the electron injection layer 122 can also be arbitrarily set, for example, it can be selected from the range of 1 nm or more and 100 nm or less, 1 nm or more and 50 nm, or 1 nm or more and 20 nm or less.

[0043] 1-9. Cathode The cathode 104 has a function of injecting electrons into the EL layer 106. At the same time, when extracting light emission from the light-emitting layer 116 from the anode 102, it functions as a reflective electrode, and when extracting light emission from the cathode 104, it functions as a light extraction electrode that reflects a part of the light emission and transmits a part of it. When using the cathode 104 as a reflective electrode, a film containing a metal such as aluminum, magnesium, silver or an alloy thereof and having a thickness that efficiently reflects visible light is used as the cathode 104. On the other hand, when using the cathode 104 as a light extraction electrode, the cathode 104 is configured to contain a light-transmissive conductive oxide such as ITO or IZO. Alternatively, a metal film containing the above-mentioned metal and having a thickness that allows visible light to pass through may be used. In this case, a laminate in which a light-transmissive conductive oxide is further laminated may also be used.

[0044] 2. Addition of additional components In the light-emitting element 100, at least one functional layer (at least one layer among the hole transport layer 112, the electron blocking layer 114, the hole blocking layer 118, and the electron transport layer 120) that is in direct contact with the light-emitting layer 116 is formed by co-evaporating two different materials. In the functional layer, in addition to the main component constituting the functional layer, a small amount of additional component is present in a state of being dispersed in the main component as compared with the main component. Similarly, in the light-emitting layer 116, in addition to the host material and the light-emitting material, a small amount of additional component is present in a state of being dispersed in the layer as compared with the host material which is the main component.

[0045] Furthermore, a layer (for example, the hole transport layer 112 in contact with the electron blocking layer 114, the electron transport layer 120 in contact with the hole blocking layer 118) that is located on the side opposite to the light-emitting layer 116 and is in direct contact with the functional layer in direct contact with the light-emitting layer 116 can also be configured such that, together with the main component constituting the layer, a small amount of additional component is present in a state of being dispersed in the main component as compared with the main component material. The additional components contained in the light-emitting layer 116 and the functional layer are the same as each other. Although details will be described later, by using such a configuration, in a display device composed of a plurality of light-emitting elements, crosstalk between adjacent light-emitting elements can be effectively prevented. This will be specifically described below.

[0046] 2-1. Case of the structure of the hole transport layer / electron blocking layer / light-emitting layer When the light-emitting element 100 includes a stacked structure of a hole transport layer 112, an electron blocking layer 114 in contact with the hole transport layer 112, and a light-emitting layer 116 in contact with the electron blocking layer 114 (for example, in the case of the structure shown in FIG. 1(A)), the hole transport layer 112 contains a hole transport material, the electron blocking layer 114 contains an electron blocking material, and the light-emitting layer 116 contains a host material and a light-emitting material. Furthermore, at least the electron blocking layer 114 and the light-emitting layer 116 can contain the same material as an additional component.

[0047] As this additional component, a material that can be used in the hole injection layer 110, the hole transport layer 112, or the electron blocking layer 114 can be selected. However, as shown in the band diagram of Fig. 2(A), the HOMO (HOMO2) level of the additional component represented by a straight line with arrows at both ends is the HOMO (HOMO EBL ) level of the electron blocking material and the HOMO (HOMO Host ) level of the host material, and the additional component is selected so that it is shallower. For example, the additional component and the electron blocking material are selected so that the difference between the HOMO2 level of the additional component and the HOMO EBL level of the electron blocking material is 0.2 eV or more. Further, in order to prevent quenching in the light-emitting layer 116, it is preferable that the additional component has a larger band gap than the light-emitting material. Note that the LUMO (LUMO2) level of the additional component can be arbitrarily determined, and the LUMO2 level may be lower or higher than the LUMO (LUMO EBL ) level of the electron blocking layer 114, the LUMO (LUMO HOST ) level of the host material, or the LUMO level of the light-emitting material.

[0048] In each of the electron blocking layer 114 and the light-emitting layer 116, the volume fraction of the additional component is lower than the volume fractions of the electron blocking material and the host material, which are the main components. For example, in each of the electron blocking layer 114 and the light-emitting layer 116, the volume fraction of the additional component can be 5 vol% or more and 30 vol% or less, 5 vol% or less and 20 vol% or less, or 5 vol% or more and 10 vol% or less. The volume fractions of the additional component in the electron blocking layer 114 and the light-emitting layer 116 may be the same as or different from each other. When they are different, it is preferable to configure the light-emitting element 100 so that the volume fraction of the additional component in the light-emitting layer 116 is lower than that in the electron blocking layer 114. This is because, usually, the LUMO HOST level of the host material is deeper than the HOMO EBL level of the electron blocking material, so that the hole traps described later occur more effectively in the light-emitting layer 116.

[0049] Specific combinations of the electron-blocking material, host material, and additional component include, for example, combinations where the electron-blocking material, host material, and additional component are MTDATA, CBP, and NPB respectively, combinations of MTDATA, CBP, and α-NDP, combinations of TPD, CBP, and NPB, and the like.

[0050] Note that the additional component may also be included in the hole transport layer 112. That is, the hole transport layer 112 may also contain the same additional component as that contained in the electron-blocking layer 114 and the light-emitting layer 116, and the additional component may be dispersed in the hole transport material that is the main component within the hole transport layer 112 (FIG. 2(B)). The HOMO2 level of the additional component may be deeper, the same, or shallower than the HOMO (HOMO HTL ) level of the hole transport material. Also, the volume fraction of the additional component in the hole transport layer 112 may be the same as or different from that in the electron-blocking layer 114 and the light-emitting layer 116. Similar to the electron-blocking layer 114 and the light-emitting layer 116, the volume fraction of the additional component in the hole transport layer 112 can be 5% by volume or more and 30% by volume or less, 5% by volume or less and 20% by volume or less, or 5% by volume or more and 10% by volume or less. Further, the light-emitting device 100 may be configured such that the volume fraction of the additional component decreases in the order of the hole transport layer 112, electron-blocking layer 114, and light-emitting layer 116.

[0051] When the additional component is also included in the hole transport layer 112, specific combinations of the hole transport material, electron-blocking material, host material, and additional component include, for example, combinations where the hole transport material, electron-blocking material, host material, and additional component are MTDATA, TPD, CBP, and α-NPD respectively, combinations of MTDATA, TPD, CBP, and β-NPB, and the like.

[0052] Alternatively, the hole transport layer 112 may be composed of additional components. That is, the hole transport layer 112 may consist of a single hole transport material, and the electron blocking layer 114 and the light emitting layer 116 may contain the hole transport material constituting the hole transport layer 112 as an additional component. Alternatively, the hole transport layer 112 may mainly contain the additional components contained in the electron blocking layer 114 and the light emitting layer 116.

[0053] When the hole transport layer 112 is composed of additional components, specific combinations of the electron blocking material, the host material, and the additional component include, for example, combinations of the electron blocking material, the host material, and the additional component such as TPD, CBP, and α-NPD, and combinations of TPD, CBP, and β-NPB.

[0054] Although not shown, the hole injection layer 110 may also contain the same additional components as those contained in the light emitting layer 116 and the like.

[0055] In such a configuration, first, holes (h + ) transported from the anode 102 side through the hole transport layer 112 are injected into the electron blocking layer 114 (FIG. 2(A)). At this time, the holes enter the HOMO EBL of the electron blocking material or the HOMO2 of the additional component, but the HOMO EBLThe holes that enter move quickly to the HOMO2 of the additional component with a shallower level. As described above, the volume fraction, i.e., the concentration, of the additional component in the electron blocking layer 114 is lower than that of the electron blocking material. Therefore, the probability that holes can hop (the dotted arrows in Fig. 2(A)) between the additional components dispersed in the electron blocking layer 114 is low. To transport the holes to the light-emitting layer 116 side, it is necessary to supply a voltage to overcome the energy barrier corresponding to the difference in HOMO levels between the additional component and the electron blocking material. In other words, in the electron blocking layer 114, the additional component functions as a hole trap material that provides hole trap sites. As a result, the hole transport layer of the entire electron blocking layer 114 decreases. Also in the light-emitting layer 116, since the HOMO2 level of the additional component is shallower than the HOMO HOST level of the host material, holes are similarly trapped. Also, usually, the HOMO HOST level of the host material is deeper than the HOMO EBL level of the electron blocking material, so holes are more strongly trapped within the light-emitting layer 116. The same applies when the hole transport layer 112 is composed of a hole transport material and an additional component with a shallower HOMO level, and holes are trapped in the hole transport layer 112. Therefore, the hole transport property in the light-emitting device 100 decreases.

[0056] Although the decrease in the hole transport property in the light-emitting device 100 leads to an increase in the emission threshold voltage, it does not cause a significant increase in the driving voltage. The reason is as follows. The voltage applied when the light-emitting device 100 emits light at a practical luminance is higher than the emission threshold voltage, and a sufficient amount of holes are injected from the anode 102 through the hole injection layer 110. At this time, although some holes are trapped by the additional component, in the hole transport layer 112, the electron blocking layer 114, and the light-emitting layer 116, the concentration of the additional component is lower than the concentration of the main component. Therefore, most of the holes are the HOMO of the electron blocking material EBL and the HOMO of the host material HOSTIt moves via. That is, at a high voltage for providing practical luminance, since the contribution of hole transport via HOMO2 of the additional component is relatively small, the influence on the drive voltage itself can be almost ignored.

[0057] This phenomenon can be explained by the schematic V-I curve shown in FIG. 3(A). By adding the second component, hole trap sites are formed in the hole transport layer 112 and / or the electron blocking layer 114 and the light emitting layer 116. For this reason, at a low voltage, hole transport is hindered, and as a result, the emission threshold voltage shifts from the emission threshold voltage V th0 to V th1 (V th1 >V th0 )(see the dashed line in FIG. 3(A)). However, in the practical luminance region, since a sufficiently high voltage is applied between the anode 102 and the cathode 104, the contribution of HOMO2 to hole transport is small, and holes are transported via HOMO HTL , HOMO EBL , HOMO EML . As a result, in the practical luminance region, it gives a V-I curve similar to that of the light emitting device without adding the additional component.

[0058] Thus, by using the additional component, the emission threshold voltage can be increased without causing a substantial increase in the drive voltage. Therefore, by applying the light emitting device 100 which is one embodiment of the present invention to a display device, it is possible to prevent deterioration of display quality due to crosstalk (emission of adjacent light emitting elements caused by lateral leakage of current). This effect will be explained with reference to FIG. 3(B).

[0059] As shown in FIG. 3(B), in the display device, for example, a plurality of anodes 102 are provided on a substrate 108 as pixel electrodes, and the ends of the anodes 102 are protected by an insulating film called a partition wall 178. An EL layer 106 and a cathode 104 are provided on the anode 102 and the partition wall 178. The region where the anode 102 is exposed from the partition wall 178 (light-emitting region) corresponds to each light-emitting element (light-emitting elements A and B in the figure). A constant voltage (Vss) is applied to the cathode 104. A voltage based on video data is applied to the anode 102 for a certain period of time, or a constant voltage (Vdd) higher than Vss is applied to the anode 102 for a time based on video data. Thereby, the gradation is controlled in each light-emitting element, and an image is expressed.

[0060] Here, when driving one light-emitting element (the right light-emitting element B in FIG. 3(B)), a current flows through the EL layer 106 due to the potential difference between the anode 102 and the cathode 104. The current flowing here is called a space-charge-limited current and flows from the anode 102 toward the cathode 104 in a direction perpendicular to the surface of the anode 102 (see the solid-line arrow). The magnitude of the space-charge-limited current is inversely proportional to the cube of the film thickness (here, the thickness of the EL layer 106). On the other hand, since the distance between adjacent light-emitting elements is larger than the thickness of the EL layer 106, no space-charge-limited current flows in the current flowing in the direction parallel to the surface of the anode 102 (dotted-line arrow), and Ohm's law is applied. The EL layer 106 itself has only conductivity to the extent that it can be regarded as an insulator. For this reason, usually, the Ohmic current can be ignored, and the space-charge-limited current becomes dominant in the EL layer 106. As a result, the injected holes and electrons are not transported to the adjacent light-emitting element A, and light emission is selectively obtained from the selected light-emitting element.

[0061] However, if the carrier transportability of all or some of the functional layers constituting the EL layer 106 is greatly increased, the ohmic current cannot be ignored. In particular, when the width of the partition wall 178 is decreased to increase the definition of the display device and the distance between adjacent light-emitting elements is reduced, the influence of the ohmic current becomes apparent. As a result, the leakage current indicated by the dotted arrow flows into the adjacent light-emitting element A. The current flowing through this path undergoes a significant voltage drop when flowing through the EL layer 106 on the partition wall 178. Therefore, the voltage in the light-emitting element A of the leakage current is relatively low. However, if the light-emitting threshold voltage of this light-emitting element A is low, light emission occurs in the light-emitting layer, and as a result, the light-emitting element A emits light unintentionally. This phenomenon is crosstalk. When crosstalk occurs, the light emission of the light-emitting element A is mixed during the driving of the light-emitting element B, and the display quality deteriorates. In particular, when the light-emitting element A is a red or green light-emitting element with a low light-emitting threshold voltage, crosstalk is likely to occur.

[0062] However, in the light-emitting element 100 which is one embodiment of the present invention, the same additional component is added to the light-emitting layer 116 and the functional layer in contact therewith (the electron blocking layer 114 in the above-described example), and the functional layer adjacent to the functional layer and located on the opposite side of the light-emitting layer 116 (the hole transport layer 112 in the above-described example). As a result, the light-emitting threshold voltage increases. As a result, by applying the structure of the light-emitting element 100 to the light-emitting element A, even if a leakage current is injected from the adjacent light-emitting element B into the light-emitting element A, the light-emitting element A does not emit light, and crosstalk is prevented. On the other hand, when driving the light-emitting element A, it can be driven with a voltage comparable to that of an element to which no additional component is added, so that the driving voltage does not increase. Therefore, by using the light-emitting element 100 which is one embodiment of the present invention in a display device, it is possible to prevent a decrease in display quality due to crosstalk without causing an increase in power consumption.

[0063] 2-2. In the case of the structure of the hole transport layer / light-emitting layer When the light-emitting element 100 does not include the electron blocking layer 114 and includes a stacked structure of the hole transport layer 112 and the light-emitting layer 116 in contact with the hole transport layer 112 (for example, in the case of the structure shown in FIG. 1(B)), the hole transport layer 112 contains an additional component together with the hole transport material. Further, in the light-emitting layer 116, in addition to the host material and the light-emitting material, the same additional component as the additional component contained in the hole transport layer 112 can be included as a hole trap material (FIG. 4).

[0064] As this additional component, a material that can be used in the hole injection layer 110, the hole transport layer 112, or the electron blocking layer 114 can be selected. However, as shown in FIG. 4, the HOMO2 level of the additional component is shallower than the HOMO HTL level of the hole transport material and the HOMO Host level of the host material. Further, in order to prevent quenching in the light-emitting layer 116, the additional component preferably has a larger band gap than the light-emitting material. Note that the LUMO2 level of the additional component can be arbitrarily determined, and the LUMO2 level may be lower or higher than the LUMO HTL level of the hole transport material, the LUMO HOST level of the host material, or the LUMO level of the light-emitting material.

[0065] In each of the hole transport layer 112 and the light-emitting layer 116, the volume fraction of the additional component is lower than the volume fraction of the hole transport material or the host material that is the main component. For example, in each of the hole transport layer 112 and the light-emitting layer 116, the volume fraction of the additional component can be 5 vol% or more and 30 vol% or less, 5 vol% or less and 20 vol% or less, or 5 vol% or more and 10 vol% or less. The volume fractions of the additional component in the hole transport layer 112 and the light-emitting layer 116 may be the same as or different from each other. When they are different, it is preferable to configure the light-emitting element 100 such that the volume fraction of the additional component in the hole transport layer 112 is larger than that in the light-emitting layer 116. This is because the HOMO HOST level of the host material is usually deeper than the HOMO HTL level of the hole transport layer 112, so that high hole trapping properties can be obtained even with a low concentration of the additional component.

[0066] In the case of this configuration, specific combinations of the hole transport material, host material, and additional component include, for example, combinations of the hole transport material, host material, and additional component being MTDATA, CBP, and α-NPD, combinations of MTDATA, CBP, and β-NPB, and the like.

[0067] Also in this configuration, although holes are trapped in the hole transport layer 112 or the light-emitting layer 116 and the light-emitting threshold voltage increases, in the practical luminance region, the influence on the driving voltage is negligibly small. Therefore, by using the light-emitting element 100, which is one of the embodiments of the present invention, in a display device, it is possible to prevent a decrease in display quality caused by crosstalk without causing an increase in power consumption.

[0068] 2-3. In the case of the configuration of the light-emitting layer / hole-blocking layer / electron transport layer When the light-emitting element 100 includes a stacked structure of a light-emitting layer 116, a hole-blocking layer 118 in contact with the light-emitting layer 116, and an electron transport layer 120 in contact with the hole-blocking layer 118 (for example, in the case of the structure shown in FIG. 1(A)), the electron transport layer 120 contains an electron transport material, the hole-blocking layer 118 contains a hole-blocking material, and the light-emitting layer 116 contains a host material and a light-emitting material. Further, the same material can be included as an additional component in the hole-blocking layer 118 and the light-emitting layer 116 (FIG. 5(A)).

[0069] As this additional component, a material that can be used in the electron transport layer 120 or the hole-blocking layer 118 can be selected, but the LUMO2 level of the additional component is deeper than the LUMO HBL level of the hole-blocking material and the LUMO Host level of the host material, and the additional component is selected. For example, the LUMO2 level of the additional component is the LUMO HBL level and LUMO HBLAn additional component is selected such that the difference from the level is 0.2 eV or more. Further, in order to prevent quenching in the light-emitting layer 116, the additional component preferably has a larger band gap than the light-emitting material. Note that the HOMO2 level of the additional component can be arbitrarily determined, and the HOMO2 level may be lower or higher than the HOMO (HOMO HBL ) level of the hole-blocking layer 118 or the HOMO HOST level of the host material, or the HOMO level of the light-emitting material.

[0070] In each of the hole-blocking layer 118 and the light-emitting layer 116, the volume fraction of the additional component is lower than the volume fraction of the hole-blocking material or the host material that is the main component. For example, in each of the hole-blocking layer 118 and the light-emitting layer 116, the volume fraction of the additional component can be 5% by volume or more and 30% by volume or less, 5% by volume or less and 20% by volume or less, or 5% by volume or more and 10% by volume or less. The volume fractions of the additional component in the hole-blocking layer 118 and the light-emitting layer 116 may be the same as or different from each other. When they are different, it is preferable to configure the light-emitting element 100 such that the volume fraction of the additional component in the hole-blocking layer 118 is larger than that in the light-emitting layer 116. This is because, usually, the LUMO HOST level of the host material is shallower than the LUMO (LUMO HBL ) level of the hole-blocking material, so that the electron traps described later are more effectively generated in the light-emitting layer 116.

[0071] Note that the additional component may also be included in the electron transport layer 120. That is, the electron transport layer 120 may also include the same additional component as that included in the hole-blocking layer 118 and the light-emitting layer 116 and may be dispersed in the electron transport material that is the main component in the electron transport layer 120 (FIG. 5(B)). The LUMO2 level of the additional component is the LUMO (LUMO ETL)It may be deeper, the same, or shallower than the level. Also, the volume fraction of the additional component in the electron transport layer 120 may be the same as or different from that of the hole blocking layer 118 or the light emitting layer 116. Similar to the hole blocking layer 118 and the light emitting layer 116, the volume fraction of the additional component in the electron transport layer 120 can be 5% by volume or more and 30% by volume or less, 5% by volume or less and 20% by volume or less, or 5% by volume or more and 10% by volume or less.

[0072] Alternatively, the electron transport layer 120 may be composed of an additional component. That is, the electron transport layer 120 may consist of a single electron transport material, and the hole blocking layer 118 and the light emitting layer 116 may contain the electron transport material constituting the electron transport layer 120 as an additional component. Alternatively, the electron transport layer 120 may mainly contain the additional components contained in the hole blocking layer 118 and the light emitting layer 116.

[0073] Although not shown, the electron injection layer 122 may also contain an additional component.

[0074] In such a configuration, first, electrons (e - ) transported from the cathode 104 side through the electron transport layer 120 are injected into the hole blocking layer 118 (FIG. 5(A)). At this time, the electrons enter the LUMO HBL of the hole blocking material or the LUMO2 of the additional component, but the LUMO HBLThe holes that enter move to the LUMO2 of the additional component with a deeper level. As described above, the volume fraction, i.e., the concentration, of the additional component is lower than that of the hole-blocking material. Therefore, the probability that electrons can hop (dotted arrows in Fig. 5(A)) between the additional components dispersed in the hole-blocking layer 118 is low. In order to transport electrons to the light-emitting layer 116 side, it is necessary to supply a voltage to overcome the energy barrier corresponding to the difference in the LUMO levels between the additional component and the hole-blocking material. In other words, in the hole-blocking layer 118, the additional component functions as an electron trap material that provides electron trap sites. As a result, the electron transport layer of the entire hole-blocking layer 118 decreases. Also in the light-emitting layer 116, since the LUMO2 level of the additional component is deeper than the LUMO Host level, electrons are similarly trapped. Also, usually, the LUMO HOST level is shallower than the LUMO of the hole-blocking material HBL level, so electrons are more strongly trapped within the light-emitting layer 116. The same applies when the electron transport layer 120 is composed of an electron transport material and an additional component with a deeper LUMO level, and electrons are trapped in the electron transport layer 120. Therefore, the electron transport property of the light-emitting element 100 decreases.

[0075] Such a decrease in electron transport property, similar to the decrease in hole transport property caused by the above-described additional component, leads to an increase in the emission threshold voltage, but does not cause a large increase in the driving voltage. The reason is as follows. The voltage applied when the light-emitting element 100 emits light at a practical luminance is higher than the emission threshold voltage, and a sufficient amount of electrons are injected from the cathode 104 through the electron injection layer 122. At this time, although some electrons are trapped by the additional component, in the hole-blocking layer 118 and the light-emitting layer 116, the concentration of the additional component is lower than the concentration of the hole-blocking material and the host material, which are the main components. Therefore, most electrons are in the LUMO of the hole-blocking material HBL and the LUMO of the host material HOSTIt moves via. That is, at a high voltage for providing practical luminance, since the contribution of electron transport via LUMO2 of the additional component is relatively small, the influence on the driving voltage itself can be almost ignored. Therefore, by using the light-emitting element 100 which is one embodiment of the present invention in a display device, it is possible to prevent a decrease in display quality due to crosstalk without causing an increase in power consumption.

[0076] 2-4. In the case of the structure of the light-emitting layer / electron transport layer When the light-emitting element 100 does not include the hole-blocking layer 118 and includes a stacked structure of the light-emitting layer 116 and the electron transport layer 120 in contact with the light-emitting layer 116 (for example, in the case of the structure shown in FIG. 1(C)), the electron transport layer 120 contains an additional component together with the electron transport material. Further, in the light-emitting layer 116, in addition to the host material and the light-emitting material, the same additional component as the additional component contained in the electron transport layer 120 can be contained as an electron trap material (FIG. 6).

[0077] As this additional component, a material that can be used in the electron transport layer 120 or the hole-blocking layer 118 can be selected. However, the LUMO2 level of the additional component is the LUMO of the electron transport material ETL level and the LUMO of the host material Host level, and the additional component is selected so as to be deeper. Also, in order to prevent quenching in the light-emitting layer 116, the additional component preferably has a larger band gap than the light-emitting material. Note that the level of HOMO2 of the additional component can be arbitrarily determined, and the HOMO2 level may be deeper or shallower than the HOMO EBL level of the electron transport material, the HOMO HOST level of the host material, or the HOMO level of the light-emitting material.

[0078] In each of the electron transport layer 120 and the light-emitting layer 116, the volume fraction of the additional component is lower than the volume fractions of the electron transport material and the host material which are the main components. For example, in each of the electron transport layer 120 and the light-emitting layer 116, the volume fraction of the additional component can be 5% by volume or more and 30% by volume or less, 5% by volume or less and 20% by volume or less, or 5% by volume or more and 10% by volume or less. The volume fractions of the additional components in the electron transport layer 120 and the light-emitting layer 116 may be the same as or different from each other. When they are different, it is preferable to configure the light-emitting element 100 such that the volume fraction of the additional component in the electron transport layer 120 is larger than that in the light-emitting layer 116. This is because the LUMO Host level of the host material is shallower than the LUMO ETL level of the electron transport layer 120, so that high electron trapping properties can be obtained even with a low concentration of the additional component.

[0079] In the case of this configuration, specific combinations of the electron transport material, the host material, and the additional component include, for example, combinations of the electron transport material, the host material, and the additional component being TPBi, CBP, and Alq respectively, combinations of PPT, CBP, and Alq, and the like.

[0080] Even in this configuration, although electrons are trapped in the electron transport layer 120 or the light-emitting layer 116 and the emission threshold voltage increases, the influence on the driving voltage in the practical luminance region is negligibly small. Therefore, by using the light-emitting element 100 which is one of the embodiments of the present invention in a display device, it is possible to prevent a decrease in display quality due to crosstalk without causing an increase in power consumption.

[0081] (Second Embodiment) In this embodiment, a display device 150 having a light-emitting element 100 which is one of the embodiments of the present invention will be described. Regarding configurations that are the same as or similar to those described in the first embodiment, the description may be omitted.

[0082] 1. Overall Structure FIG. 7 and FIG. 8 respectively show a schematic top view and a cross-sectional view of the display device 150. The display device 150 has an array substrate 152 and a counter substrate 168 facing the array substrate 152, and a plurality of pixels 154 are provided on the array substrate 152. A region where the plurality of pixels 154 are arranged is a display region 156, and further, outside the display region 156 (peripheral region), a scanning line driving circuit 158 for controlling the pixels 154 is provided on the array substrate 152. The counter substrate is arranged on these so as to protect the pixels 154 and the scanning line driving circuit 158. Wiring 162 extends from the display region 156 and the scanning line driving circuit 158 to one side of the array substrate 152 and is electrically connected to a flexible printed circuit board (FPC) 164 at the end of the array substrate 152. A driver IC 166 for controlling the pixels 154 can be mounted on the FPC 164. Note that the driver IC 166 may be mounted on the array substrate 152 instead of being provided on the FPC 116, and instead of or together with the driver IC 166, a signal line driving circuit 160 may be formed on the array substrate 152.

[0083] The plurality of pixels 154 are composed of pixels that provide red, green, and blue that constitute the three primary colors. That is, the plurality of pixels 154 are composed of a plurality of pixels that provide red, a plurality of pixels that provide green, and a plurality of pixels that provide blue, and each of the plurality of pixels 154 is provided with a light-emitting element and a pixel circuit for controlling the light-emitting element. There is no restriction on the configuration of the pixel circuit, and the pixel circuit may include various elements such as a plurality of transistors and one or more capacitive elements. The pixel circuit is controlled by signals supplied from an external circuit (not shown) via the scanning line driving circuit 158, the driver IC 166, and the signal line driving circuit 160. By controlling the light emission obtained from the light-emitting element, an image is displayed in the display region 156.

[0084] Here, among the plurality of pixels 154 that constitute the display area 156, at least one is provided with the light-emitting element 100 described in the first embodiment. For example, the light-emitting element 100 is provided in each of the plurality of pixels 154 that give red. Alternatively, the light-emitting element 100 is provided in each of the plurality of pixels 154 that give red and the plurality of pixels 154 that give green. Alternatively, the light-emitting element 100 may be provided in each of all the pixels 154.

[0085] 2. Cross-sectional structure FIG. 8 is a schematic cross-sectional view of three pixels 154 (the first pixel 154-1, the second pixel 154-2, and the third pixel 154-3) provided on the array substrate 152. Here, the cross-sectional structures of the light-emitting element 100 included in each pixel 154 and the elements constituting the pixel circuit, namely, the driving transistor 172, the holding capacitor element 174, and the additional capacitor element 180 are shown, and the detailed configuration of the EL layer 106 is omitted. Since each element constituting the pixel circuit such as the driving transistor 172, the holding capacitor element 174, and the additional capacitor element 180 can have a known structure, a detailed description thereof is omitted.

[0086] Each element included in the pixel circuit is provided on the array substrate 152 via an undercoat 170. A planarization film 176 is provided on the driving transistor 172 and the holding capacitor element 174. The planarization film 176 has an opening that exposes the holding capacitor element 174, and through this opening, the additional capacitor element 180 and the light-emitting element 100 are electrically connected to the holding capacitor element 174 and the driving transistor 172. In the display device 150 shown in FIG. 8, the additional capacitor element 180 is composed of a capacitive electrode 182 provided on the planarization film 176, a capacitive insulating film 184 on the capacitive electrode 182, and a pixel electrode 190 on the capacitive insulating film 184.

[0087] The end of the pixel electrode 190 is covered by the partition wall 178, and the EL layer 106 is provided on the pixel electrode 190 and the partition wall 178. A common electrode 192 overlapping with a plurality of pixels 154 is provided on the EL layer 106. Therefore, each pixel electrode 190 is provided for each pixel 154 and independently constitutes a part of the light-emitting element 100, while the common electrode 192 is shared by a plurality of pixels 154. The pair of the pixel electrode 190 and the common electrode 192 corresponds to the pair of the anode 102 and the cathode 104 of the light-emitting element 100. Hereinafter, the case where the pixel electrode 190 corresponds to the anode 102 will be described.

[0088] As an optional configuration, the display device 150 may further include a passivation film 194 for protecting the light-emitting element 100 between the light-emitting element 100 and the counter substrate 168. The passivation film 194 can also be configured by applying known structures and materials.

[0089] 3. Structure of the light-emitting element provided for the pixel FIGS. 9(A) to 10(B) show schematic cross-sectional views of three pixels (the first pixel 154-1, the second pixel 154-2, and the third pixel 154-3) that are continuously arranged in the display device 150 and give different emission colors to each other. Hereinafter, the modes in which the first pixel 154-1, the second pixel 154-2, and the third pixel 154-3 give red, green, and blue emissions, respectively, will be described. Note that in these figures, the configuration on the array substrate 152 side with respect to the planarization film 176 is not shown.

[0090] 3-1. Case where the light-emitting element 100 is arranged for all pixels As described above, the light-emitting elements disposed in the first pixel 154-1, the second pixel 154-2, and the third pixel 154-3 that give different emission colors may all be the light-emitting element 100 described in the embodiment. Since the emission color is determined by the light-emitting material, three light-emitting layers corresponding to each color (the first light-emitting layer 116-1, the second light-emitting layer 116-2, and the third light-emitting layer 116-3) are provided independently in the first pixel 154-1, the second pixel 154-2, and the third pixel 154-3, respectively. Therefore, in this case, except for the light-emitting layer 116, each functional layer has the same configuration among the pixels 154 and can exist within the same layer (FIG. 9(A)). Also, all the functional layers may be shared by all the pixels 154.

[0091] 3-2. When adding additional components to the light-emitting layer and the functional layers on the anode side from the light-emitting layer (1) When disposing the light-emitting element 100 in the pixel that gives red emission As shown in FIG. 9(B), the light-emitting element 100 may be provided in the first pixel 154-1 that shows the peak of red emission, that is, the emission peak with the longest wavelength, and light-emitting elements that do not contain additional components in the functional layers may be disposed in the other pixels 154 that show emission peaks with wavelengths shorter than that of the first pixel 154-1. In this case, the light-emitting layer 116 of the light-emitting element 100 in the first pixel 154-1 may contain a phosphorescent material, and the hole injection layer 110, the hole blocking layer 118, the electron transport layer 120, and the electron injection layer 122 can be continuously provided across all the pixels 154 so as to be shared by all the pixels 154. Therefore, these functional layers can exist within the same layer in all the pixels 154.

[0092] On one hand, for example, when the functional layer in contact with the light-emitting layer 116 is the electron blocking layer 114, the first pixel 154-1 is provided with a first electron blocking layer 114-1 containing an additional component, and the second pixel 154-2 and the third pixel 154-3 are provided with an electron blocking layer 114-2 that does not contain an additional component. The first electron blocking layer 114-1 and the electron blocking layer 114 may mainly contain the same electron blocking material. The electron blocking layer 114-2 is shared by the second pixel 154-2 and the third pixel 154-3 and can be present in the same layer in the second pixel 154-2 and the third pixel 154-3.

[0093] When the hole transport layer 112 of the light-emitting device 100 also contains an additional component, the first pixel 154-1 is provided with a first hole transport layer 112-1 containing an additional component, and the second pixel 154-2 and the third pixel 154-3 are provided with a hole transport layer 112-2 that does not contain an additional component. The first hole transport layer 112-1 and the hole transport layer 112-2 may mainly contain the same hole transport material. The hole transport layer 112-2 is shared by the second pixel 154-2 and the third pixel 154-3 and can be present in the same layer in the second pixel 154-2 and the third pixel 154-3. When no additional component is added to the hole transport layer 112 of the light-emitting device 100, the hole transport layer 112 having the same structure and present in the same layer can be formed for all the pixels 154.

[0094] (2) When arranging the light-emitting device 100 in the pixels that give red light and green light As shown in FIG. 9(C), a light-emitting element 100 may be provided for each of a first pixel 154-1 and a second pixel 154-2 that respectively give red and green light emissions, and a light-emitting element that does not contain an additional component in the functional layer may be arranged in a third pixel 154-3. When the functional layer in contact with the light-emitting layer 116 is the electron blocking layer 114, a first electron blocking layer 114-1 containing an additional component is provided for the first pixel 154-1 and the second pixel 154-2, and an electron blocking layer 114-2 that does not contain an additional component is provided for the third pixel 154-3. The first electron blocking layer 114-1 and the electron blocking layer 114-2 may contain the same electron blocking material as the main component. The first electron blocking layer 114-1 is shared by the first pixel 154-1 and the second pixel 154-2 and can exist in the same layer in the first pixel 154-1 and the second pixel 154-2.

[0095] When the hole transport layer 112 of the light-emitting element 100 also contains an additional component, a first hole transport layer 112-1 containing an additional component is provided for the first pixel 154-1 and the second pixel 154-2, and a hole transport layer 112-2 that does not contain an additional component is provided for the third pixel 154-3. The first hole transport layer 112-1 and the hole transport layer 112-2 may contain the same hole transport layer as the main component. The first hole transport layer 112-1 is shared by the first pixel 154-1 and the second pixel 154-2 and can exist in the same layer in the first pixel 154-1 and the second pixel 154-2. When the hole transport layer 112 of the light-emitting element 100 does not contain an additional component, a hole transport layer 112 having the same structure and existing in the same layer can be formed for all the pixels 154.

[0096] 3-3. When adding an additional component to the light-emitting layer and the functional layer on the cathode side from the light-emitting layer (1) When arranging the light-emitting element 100 in a pixel that gives red light emission As shown in FIG. 10(A), a light-emitting element 100 may be provided in a first pixel 154-1 that exhibits the emission peak with the longest wavelength, and light-emitting elements that do not contain additional components in the functional layer may be arranged in other pixels 154. In this case, the hole injection layer 110, the hole transport layer 112, and the electron blocking layer 114 can be continuously provided across all the pixels 154 so as to be shared by all the pixels 154. Therefore, each of these functional layers can exist within the same layer in all the pixels 154.

[0097] On the other hand, for example, when the functional layer in contact with the light-emitting layer 116 is the hole blocking layer 118, a first hole blocking layer 118-1 containing an additional component is provided in the first pixel 154-1, and hole blocking layers 118-2 that do not contain additional components are provided in the second pixel 154-2 and the third pixel 154-3. The first hole blocking layer 118-1 and the hole blocking layer 118-2 may contain the same hole blocking material as the main component. The hole blocking layer 118-2 is shared by the second pixel 154-2 and the third pixel 154-3 and can exist within the same layer in the second pixel 154-2 and the third pixel 154-3.

[0098] When the electron transport layer 120 of the light-emitting element 100 contains an additional component, a first electron transport layer 120-1 containing the additional component is provided in the first pixel 154-1, and electron transport layers 120-2 that do not contain additional components are provided in the second pixel 154-2 and the third pixel 154-3. The first electron transport layer 120-1 and the electron transport layer 120-2 may contain the same electron transport material as the main component. The electron transport layer 120-2 is shared by the second pixel 154-2 and the third pixel 154-3 and can exist within the same layer in the second pixel 154-2 and the third pixel 154-3. When the electron transport layer 120 does not contain an additional component, electron transport layers 120 having the same structure and existing within the same layer can be formed across all the pixels 154.

[0099] (2) When arranging the light-emitting element 100 in pixels that give red emission and green As shown in FIG. 10(B), a light-emitting element 100 may be provided for each of a first pixel 154-1 and a second pixel 154-2 that respectively provide red and green light emission, and a light-emitting element that does not contain an additional component in the functional layer may be arranged in a third pixel 154-3. When the functional layer in contact with the light-emitting layer 116 is a hole-blocking layer 118, a first hole-blocking layer 118-1 containing an additional component is provided for the first pixel 154-1 and the second pixel 154-2, and a hole-blocking layer 118-2 that does not contain an additional component is provided for the third pixel 154-3. The first hole-blocking layer 118-1 and the hole-blocking layer 118-2 may contain the same hole-blocking material as the main component. The first hole-blocking layer 118-1 is shared by the first pixel 154-1 and the second pixel 154-2 and can exist in the same layer in the first pixel 154-1 and the second pixel 154-2.

[0100] When the electron transport layer 120 of the light-emitting element 100 does not contain an additional component, a first electron transport layer 120-1 containing an additional component is provided for the first pixel 154-1 and the second pixel 154-2, and an electron transport layer 120-2 that does not contain an additional component is provided for the third pixel 154-3. The first electron transport layer 120-1 and the electron transport layer 120-2 may contain the same electron transporting material as the main component. The first electron transport layer 120-1 is shared by the first pixel 154-1 and the second pixel 154-2 and can exist in the same layer in the first pixel 154-1 and the second pixel 154-2. In addition, when the electron transport layer 120 of the light-emitting element 100 does not contain an additional component, the electron transport layer 120 having the same structure and existing in the same layer can be formed across all the pixels 154.

[0101] As described in the first embodiment, although the emission threshold voltage of the light-emitting element 100 increases due to the additional component, it does not cause an increase in the driving voltage in the practical luminance region. Therefore, current leakage, particularly current leakage from pixels that provide short-wavelength light emission, is prevented, and a decrease in display quality due to crosstalk caused by this does not occur. Therefore, by applying the light-emitting element 100 which is one of the embodiments of the present invention, a display device capable of providing high-quality display while preventing an increase in power consumption can be provided.

[0102] As embodiments of the present invention, the above-described embodiments can be implemented in appropriate combination as long as they do not contradict each other. Further, based on the display device of each embodiment, those in which those skilled in the art have appropriately added, deleted, or changed the design of components, or added, omitted, or changed conditions of processes, are also included in the scope of the present invention as long as they have the gist of the present invention.

[0103] Even if there are other operational effects different from those brought about by the aspects of the above-described embodiments, those that are obvious from the description of this specification or can be easily predicted by those skilled in the art are naturally understood to be brought about by the present invention.

Description of Reference Numerals

[0104] 100: Light-emitting element, 102: Anode, 104: Cathode, 106: Electroluminescent layer, 108: Substrate, 110: Hole injection layer, 112: Hole transport layer, 112-1: First hole transport layer, 112-2: Hole transport layer, 114: Electron blocking layer, 114-1: First electron blocking layer, 114-2: Electron blocking layer, 116: Light-emitting layer, 116-1: First light-emitting layer, 116-2: Second light-emitting layer, 116-3: Third light-emitting layer, 118: Hole blocking layer, 118-1: First hole blocking layer, 118-2: Hole blocking layer, 120: Electron transport layer, 120-1: First electron transport layer, 120-2: Electron transport layer, 122: Electron injection layer, 150: Display device, 152: Array substrate, 154: Pixel, 154-1: First pixel, 154-2: Second pixel, 154-3: Third pixel, 156: Display area, 158: Scan line drive circuit, 160: Signal line drive circuit, 162: Wiring, 164: Flexible printed circuit board (FPC), 166: Driver IC, 168: Counter substrate, 170: Undercoat, 172: Driving transistor, 174: Holding capacitor element, 176: Planarization film, 178: Partition wall, 180: Additional capacitor element, 182: Capacitor electrode, 184: Capacitor insulating film, 190: Pixel electrode, 192: Common electrode, 194: Passivation film

Claims

1. An anode, A first functional layer located on the anode and containing a first hole transport material and a hole trap material, A second functional layer located between the anode and the first functional layer, in contact with the first functional layer, and containing a second hole transport material and the hole trap material, A light-emitting layer located on the first functional layer, in contact with the first functional layer, and containing a host material, a light-emitting material, and the hole trap material, An electron transport layer on the light-emitting layer, and A cathode on the electron transport layer, In the first functional layer and the light-emitting layer, the concentration of the hole trap material is lower than the concentration of the first hole transport material and the host material, respectively, The highest occupied molecular orbital level of the hole trap material is higher than the highest occupied molecular orbital level of the first hole transport material and the highest occupied molecular orbital level of the host material, The difference between the highest occupied molecular orbital level of the hole trap material and the highest occupied molecular orbital level of the first hole transport material is 0.2 eV or more, In the second functional layer, the concentration of the hole trap material is lower than the second hole transport material, A light-emitting device in which the highest occupied molecular orbital level of the second hole transport material is higher than the highest occupied molecular orbital level of the hole trap material.

2. The light-emitting device according to claim 1, wherein the lowest unoccupied molecular orbital level of the first hole transport material is 0.2 eV or more higher than the lowest unoccupied molecular orbital level of the host material.

3. The light-emitting device according to claim 1, wherein in the first functional layer and the light-emitting layer, the concentration of the hole trap material is 5% by volume or more and 30% by volume or less, respectively.

4. The light-emitting device according to claim 1, wherein in the first functional layer and the light-emitting layer, the concentration of the hole trap material is the same as each other.

5. The light-emitting device according to claim 1, wherein the concentration of the hole trap material in the light-emitting layer is lower than the concentration of the hole trap material in the first functional layer.

6. The light-emitting device according to claim 1, wherein the thickness of the first functional layer is 1 nm or more and 5 nm or less.

7. A first pixel having a first light-emitting device, and A second pixel having a second light-emitting device, The first light-emitting device is A first anode, A first functional layer located on the first anode and containing a first hole transport material and a hole trap material, The first light-emitting element is located between the first anode and the first functional layer, in contact with the first functional layer, and includes a second functional layer containing a second hole transport material and the hole trap material. It is located on the first functional layer, in contact with the first functional layer, and includes a first light-emitting layer containing a first host material, a first light-emitting material, and the hole trap material. An electron transport layer on the first light-emitting layer, and It has a cathode on the electron transport layer. The second light-emitting element is A second anode, A hole transport layer located on the second anode and containing the first hole transport material. A second light-emitting layer located on the hole transport layer and containing a second host material and a second light-emitting material. The electron transport layer on the second light-emitting layer, and It has the cathode on the electron transport layer. In the first functional layer and the first light-emitting layer, the concentration of the hole trap material is lower than the concentration of the first hole transport material and the first host material, respectively. The highest occupied molecular orbital level of the hole trap material is higher than the highest occupied molecular orbital levels of the first hole transport material and the first host material. The difference between the highest occupied molecular orbital level of the hole trap material and the highest occupied molecular orbital level of the first hole transport material is 0.2 eV or more. In the second functional layer, the concentration of the hole trap material is lower than the second hole transport material. The highest occupied molecular orbital level of the second hole transport material is higher than the highest occupied molecular orbital level of the hole trap material, a display device.

8. The difference between the highest occupied molecular orbital level of the hole trap material and the highest occupied molecular orbital level of the first hole transport material is 0.2 eV or more, the display device according to claim 7.

9. The lowest unoccupied molecular orbital level of the first hole transport material is 0.2 eV or more higher than the lowest unoccupied molecular orbital level of the first host material, the display device according to claim 7.

10. In the first functional layer and the first light-emitting layer, the concentration of the hole trap material is 5% by volume or more and 30% by volume or less, respectively, the display device according to claim 7.

11. In the first functional layer and the first light-emitting layer, the concentration of the hole trap material is the same as each other, the display device according to claim 7.

12. The display device according to claim 7, wherein the concentration of the hole trap material in the first light-emitting layer is lower than the concentration of the hole trap material in the first functional layer.

13. The display device according to claim 7, wherein the thickness of the first functional layer is 1 nm or more and 5 nm or less.

14. The display device according to claim 7, wherein the emission peak wavelength of the first light-emitting material is longer than the emission peak wavelength of the second light-emitting material.

15. The display device according to claim 7, wherein the first light-emitting material is a phosphorescent material.

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