Light-emitting element and display device

Abstract

A light-emission layer (24) includes quantum dots (30) and first ligands (32) coordinated to the quantum dots (30). An electron transporting layer (26) is in contact with the light-emission layer (24), and includes second ligands (34). The first ligands (32) and the second ligands (34) have the same functional group, are each a halide ion, or are each a chalcogenide ion.

Description

[Technical Field]

[0001] The present invention relates to a light-emitting element, a display device, and a method for manufacturing a light-emitting element. [Background technology]

[0002] US Patent No. 6,299,949 discloses an electroluminescent device comprising, in order, an anode, a hole injection layer, a hole transport layer, a light-emitting layer containing quantum dots having ligands attached thereto, an electron transport layer, and a cathode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-77610 (published May 21, 2020) Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the light-emitting device of Patent Document 1, when a solution containing an electron transport material is applied onto the light-emitting layer, the ligand is likely to be eluted from the light-emitting layer into the solution.

[0005] When the emissive layer lacks ligands, the ligands are removed from the quantum dots, exposing defects on the quantum dot surface. Quantum dots with exposed defects are prone to non-radiative recombination of electrons and holes. Furthermore, quantum dots with exposed defects are prone to increase in size through Ostwald ripening or aggregation.

[0006] These problems result in a decrease in the light-emitting efficiency and reliability of the light-emitting element. [Means for solving the problem]

[0007] A light-emitting element according to one embodiment of the present disclosure comprises a first electrode, a light-emitting layer including quantum dots, a first contact layer in contact with the light-emitting layer, and a second electrode, wherein the light-emitting layer includes a first ligand coordinated to the quantum dots, and the first contact layer includes a second ligand, and the first ligand and the second ligand have the same functional group, or are each a halide ion, or are each a chalcogenide ion.

[0008] A display device according to one aspect of the present disclosure includes the above-described light-emitting element.

[0009] A light-emitting element according to one embodiment of the present disclosure includes the steps of forming a first electrode, forming a light-emitting layer including quantum dots, forming a first contact layer in contact with the light-emitting layer, and forming a second electrode, wherein in the step of forming the light-emitting layer, a first liquid including the quantum dots and a first ligand that coordinates to the quantum dots is applied onto the first electrode, and in the step of forming the first contact layer, a second liquid including a second ligand is applied directly onto the light-emitting layer, and the first ligand and the second ligand have the same functional group, or are each a halide ion, or are each a chalcogenide ion. [Effects of the Invention]

[0010] According to one aspect of the present disclosure, the light emitting efficiency and reliability of a light emitting element can be improved. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic plan view of a display device according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view of the display area shown in FIG. [Figure 3] 3 is a schematic diagram showing a schematic configuration of the boundary between the light-emitting layer and the electron transport layer shown in FIG. 2 and the vicinity thereof. FIG. [Figure 4] FIG. 1 is a schematic flow diagram illustrating an example of a method for manufacturing a display device according to an embodiment of the present disclosure. [Figure 5]FIG. 3 is a schematic diagram showing the process of preparing a solution that will be the material for the blue light-emitting layer shown in FIG. 2. [Figure 6] FIG. 3 is a schematic diagram showing the process of preparing a solution that will be the material for the electron transport layer shown in FIG. 2. [Figure 7] 3 is a schematic diagram showing a schematic configuration of the boundary between the light-emitting layer and the hole-transporting layer shown in FIG. 2 and the vicinity thereof. FIG. [Figure 8] 1 is a schematic cross-sectional view of a display area of ​​a display device according to an embodiment of the present disclosure. [Figure 9] 9 is a schematic diagram showing a schematic configuration of the boundary between the light-emitting layer and the hole-transporting layer shown in FIG. 8 and the vicinity thereof. DETAILED DESCRIPTION OF THE INVENTION

[0012] In this disclosure, "ligand" refers to an atom, molecule, or ion that can be coordinated to a nanoparticle or quantum dot, and includes atoms, molecules, or ions that can be coordinated to, but are not currently bound to, a nanoparticle or quantum dot.

[0013] In this disclosure, "capping agent" refers to a material that is added to a solution as a source of ligand.

[0014] For example, when oleic acid is added to a quantum dot dispersion solution and the oleic acid is coordinated to the quantum dots, the oleic acid is both a capping agent and a ligand.Also, when a metal halide compound is added to a quantum dot dispersion solution and metal ions and halide ions are generated from the metal halide compound and the halide ions are coordinated to the quantum dots, the halide compound is a capping agent and the halide ions are a ligand.

[0015] [Embodiment 1] Fig. 1 is a schematic plan view of a display device 2 according to this embodiment. As shown in Fig. 1, the display device 2 according to this embodiment includes a display area DA in which light emitted from the electroluminescent elements of each sub-pixel is extracted for display, and a frame area NA surrounding the display area DA. In the frame area NA, terminals T to which signals for driving each light-emitting element of the display device 2 are input are formed.

[0016] The display device 2 according to this embodiment includes a plurality of electroluminescent elements in a display area DA.

[0017] Fig. 2 is a schematic cross-sectional view of the display area DA shown in Fig. 1. Fig. 2 corresponds to a cross-sectional view taken along line AB in Fig. 1.

[0018] 2 shows red light emitting element 6R, green light emitting element 6G, and blue light emitting element 6B among the multiple electroluminescent elements included in display device 2. Unless otherwise specified in this disclosure, the term "light emitting element" refers to any of red light emitting element 6R, green light emitting element 6G, and blue light emitting element 6B.

[0019] As shown in FIG. 2, the display device 2 includes a substrate 4, a light emitting element layer 6 on the substrate 4, and a sealing layer 8 that covers the light emitting element layer 6.

[0020] In the present disclosure, the direction from the light emitting element layer 6 to the substrate 4 is described as the "downward direction," and the direction from the light emitting element layer 6 to the sealing layer 8 is described as the "upward direction."

[0021] <Substrate> The substrate 4 includes a support substrate. The substrate 4 includes a thin film transistor layer (TFT layer) on which circuit elements such as thin film transistors (TFTs) are provided. The substrate 4 may further include additional components such as a barrier layer. The barrier layer reduces the penetration of moisture, oxygen, and the like into the light-emitting element layer 6 from outside the support substrate.

[0022] The support substrate may be a non-flexible substrate made of quartz or glass, or a flexible substrate made of a resin film or resin sheet. Quartz substrates and glass substrates are preferred because of their high light transmittance and gas barrier properties. Furthermore, in terms of light transmittance and gas barrier properties, the resin film material is preferably methacrylic resins such as polyethylene methacrylate (PMMA), polyester resins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene naphthalate (PBN), and polycarbonate resins.

[0023] <Light-emitting element layer> The light emitting element layer 6 is a layer in which light emitting elements are provided.

[0024] The light-emitting element layer 6 includes an anode 10 (first electrode) and a cathode 16 (second electrode) facing each other, an edge cover 12 covering the edge of the anode 10, and an active layer 14 provided between the anode 10 and the cathode 16. The active layer 14 includes, in order from the anode 10 side, a hole injection layer 20, a hole transport layer 22 (second contact layer), a light-emitting layer 24, and an electron transport layer 26 (first contact layer). The active layer 14 is also referred to as an electroluminescent layer (EL layer). However, the active layer 14 may include additional components such as an electron injection layer.

[0025] Fig. 3 is a schematic diagram showing the schematic configuration of the boundary between the light-emitting layer 24 and the electron transport layer 26 and its vicinity shown in Fig. 2. Fig. 3 corresponds to an enlarged view of the part indicated by box C in Fig. 2.

[0026] (electrode) As shown in FIG. 2, the anode 10 is formed individually for each light-emitting element. The anode 10 is provided in an island shape for each light-emitting element, i.e., for each subpixel, and is also referred to as a "pixel electrode." The anode 10 includes an anode 10R for the red light-emitting element 6R, an anode 10G for the green light-emitting element 6G, and an anode 10B for the blue light-emitting element 6B. On the other hand, the cathode 16 is formed in common for multiple light-emitting elements. The cathode 16 is also referred to as a "common electrode." Because the cathode 16 faces the pixel electrode, it is also referred to as a "counter electrode."

[0027] The sub-pixels may be simply referred to as "pixels."

[0028] The anode 10 and the cathode 16 contain a conductive material, and at least one of them is a transparent electrode. When the display device 2 is a single-sided display device, the electrode of the anode 10 and the cathode 16 closer to the display surface is a transparent electrode, and the electrode farther from the display surface is a reflective electrode. When the display device 2 is a double-sided display device, both the anode 10 and the cathode 16 are transparent electrodes. The transparent electrode can be made of a light-transmitting conductive material. The reflective electrode can be made of a light-reflective conductive material, or can be made of a laminate of a light-transmitting conductive material and a light-reflective conductive material.

[0029] Light-transmitting conductive materials include indium tin oxide (ITO), indium zinc oxide (IZO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), tin oxide (SnO2), fluorine-doped tin oxide (FTO), etc. These materials have high transmittance for visible light, which improves the luminous efficiency of light-emitting devices. Light-reflective conductive materials include aluminum (Al), silver (Ag), copper (Cu), gold (Au), etc. These materials have high reflectance for visible light, which improves the luminous efficiency of light-emitting devices.

[0030] The anode 10 supplies holes to the light-emitting layer 24, and the cathode 16 supplies electrons to the light-emitting layer 24. The anode 10 is disposed opposite the cathode 16.

[0031] (edge ​​cover) The edge cover 12 may be formed individually for each light-emitting element, or may be formed integrally for multiple light-emitting elements. The edge cover 12 may be a forward tapered type in which the top surface is smaller than the bottom surface, or a reverse tapered type in which the top surface is larger than the bottom surface. The edge cover 12 may be composed of a single layer or multiple layers.

[0032] The edge covers 12 are formed between adjacent light-emitting elements to electrically insulate the light-emitting elements. Therefore, the edge covers 12 divide the light-emitting element layer 6 into red light-emitting elements 6R, green light-emitting elements 6G, and blue light-emitting elements 6B. The edge covers 12 are also called "partition walls" or "banks." The edge covers 12 have multiple openings, and the top surfaces of the anodes 10 are exposed through each opening.

[0033] The edge cover 12 includes an insulating material such as polyimide resin, acrylic resin, novolac resin, or fluorene resin. The edge cover 12 is formed by patterning a photosensitive resin material using, for example, photolithography. The photosensitive resin may be negative or positive.

[0034] (Hole injection layer and hole transport layer) The hole injection layer 20 does not contact the light-emitting layer 24. On the other hand, the hole transport layer 22 directly contacts each of the red light-emitting layer 24R, the green light-emitting layer 24G, and the blue light-emitting layer 24B.

[0035] The hole injection layer 20 and the hole transport layer 22 may be formed individually for each light-emitting element, or may be formed in common for multiple light-emitting elements. When formed individually for each light-emitting element, the hole injection layer 20 and / or the hole transport layer 22 may differ in any one or more of the shape, thickness, and composition for each light-emitting element.

[0036] The hole injection layer 20 contains a material having hole transport properties and functions to inject holes from the anode 10 to the hole transport layer 22. The hole transport layer 22 contains a material having hole transport properties and functions to transport holes from the hole injection layer 20 to the light-emitting layer 24. It is preferable that at least one of the hole injection layer 20 and the hole transport layer 22 has a function to inhibit the transport of electrons from the light-emitting layer 24 to the anode 10.

[0037] The hole transport material may be an inorganic hole transport material or an organic hole transport material, and may be appropriately selected from materials commonly used in the art.

[0038] Examples of inorganic hole transport materials include metal oxides, metal nitrides, metal carbides, metal cyanides, metal thiocyanides, and metal selenocyanides containing one or more metal elements selected from the group consisting of Zn, Cr, Ni, Ti, Nb, Al, Si, Mg, Ta, Hf, Zr, Y, La, Sr, Mo, W, and Re. These materials may be in the form of nanoparticles.

[0039] Examples of organic hole transport materials include PEDOT:PSS (polyethylenedioxythiophene / polystyrene sulfonate), PVK (poly-N-vinylcarbazole), TFB (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl)diphenylamine)]), and poly-TPD (N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine).

[0040] (Emitting layer) The light-emitting layer 24 is formed so as to cover the upper surface of the corresponding anode 10 exposed from the opening in the edge cover 12. The light-emitting layer 24 is a layer that emits light when a light-emitting element is excited by recombination of holes from the anode 10 and electrons from the cathode 16, and the excited light-emitting element returns to the ground state.

[0041] The light-emitting layer 24 includes a red light-emitting layer 24R that emits red light, a green light-emitting layer 24G that emits green light, and a blue light-emitting layer 24B that emits blue light. The light-emitting layer 24 may be formed individually for each light-emitting element of the same color, or may be formed commonly for multiple light-emitting elements of the same color.

[0042] In the present disclosure, "blue light" refers to light having a central emission wavelength in the wavelength band of, for example, 400 nm or more and 500 nm or less. "Green light" refers to light having a central emission wavelength in the wavelength band of, for example, more than 500 nm and less than 600 nm. "Red light" refers to light having a central emission wavelength in the wavelength band of, for example, more than 600 nm and less than 780 nm.

[0043] However, the light-emitting layer 24 according to the present disclosure is not limited to this. For example, the light-emitting layer 24 may include a layer that emits light of a color other than red, green, and blue. Furthermore, for example, the light-emitting layer 24 may be capable of emitting light of two or fewer colors, or may be capable of emitting light of four or more colors.

[0044] As shown in FIG. 3, the blue light-emitting layer 24B includes blue quantum dots 30B that emit blue light as light emitters, and further includes first ligands 32B that are coordinated to the blue quantum dots 30B.

[0045] Similarly, although not shown, green light-emitting layer 24G includes green quantum dots that emit green light as light emitters and further includes first green ligands that coordinate to the green quantum dots. Red light-emitting layer 24R includes red quantum dots that emit red light as light emitters and further includes first red ligands that coordinate to the red quantum dots.

[0046] The compositions of the red quantum dots, green quantum dots, and blue quantum dots 30B may be the same or different. The first ligands of the red light-emitting layer 24R, the green light-emitting layer 24G, and the blue light-emitting layer 24B may be the same or different.

[0047] Unless otherwise specified in this disclosure, "quantum dot 30" refers to any of the red quantum dots, green quantum dots, and blue quantum dots 30B. Furthermore, "first ligand 32" refers to any of the first ligands in the red light-emitting layer 24R, the green light-emitting layer 24G, and the blue light-emitting layer 24B, 32B. The first ligands 32 will be described in more detail below.

[0048] The quantum dots 30 are semiconductor particles having a particle size of 100 nm or less, and may be selected from the group consisting of MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, and S The quantum dots may have a crystal of a II-VI group semiconductor compound such as rTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, CdZnSe, HgS, HgSe, HgTe, etc., and / or a crystal of a III-V group semiconductor compound such as GaAs, GaP, InN, InAs, InP, InSb, etc., and / or a crystal of a IV group semiconductor compound such as Si, Ge, Sn, Pb, etc. Furthermore, the quantum dots may have a core / shell structure in which the above-mentioned semiconductor crystal is used as a core and the core is overcoated with a shell material having a large band gap.

[0049] (electron transport layer) As shown in FIG. 2, the electron transport layer 26 according to this embodiment is in direct contact with each of the red light-emitting layer 24R, the green light-emitting layer 24G, and the blue light-emitting layer 24B.

[0050] The electron transport layer 26 may be formed individually for each light-emitting element, or may be formed commonly for multiple light-emitting elements. When the electron transport layer 26 is formed individually for each light-emitting element, any one or more of the shape, thickness, and composition of the electron transport layer 26 may be different for each light-emitting element.

[0051] 3, the electron transport layer 26 includes an electron transport material 40 having electron transport properties, and further includes a second ligand 34 that can be coordinated to the quantum dots 30. If the second ligand 34 has sufficient electron transport properties for the electron transport layer 26, the second ligand 34 may also serve as the electron transport material 40. The second ligand 34 will be described in detail later.

[0052] The electron transport layer 26 functions to transport electrons from the cathode 16 to the light-emitting layer 24. The electron transport layer 26 preferably functions to inhibit the transport of holes from the light-emitting layer 24 to the cathode 16.

[0053] The electron transport material may be an inorganic electron transport material or an organic electron transport material, and can be appropriately selected from materials commonly used in the relevant field.

[0054] Examples of inorganic electron transport materials include metal oxides containing one or more of the metal elements Zn, Ti, Mg, Zr, Sn, and Nb. These materials may be in the form of nanoparticles.

[0055] Examples of organic electron transport materials include compounds and complexes containing one or more nitrogen-containing heterocycles such as oxadiazole, triazole, triazine, quinoline, phenanthroline, pyrimidine, pyridine, imidazole, or carbazole rings. Specific examples include 1,10-phenanthroline derivatives such as bathocuproine and bathophenanthroline, benzimidazole derivatives such as 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI), metal complexes such as bis(10-benzoquinolinolato)beryllium complex, 8-hydroxyquinoline Al complex, and bis(2-methyl-8-quinolinato)-4-phenylphenolate aluminum, and 4,4'-biscarbazole biphenyl.

[0056] (light-emitting element) As described above, the red light-emitting element 6R according to this embodiment includes, in this order from the substrate 4 side, an anode 10R (first electrode), a red light-emitting layer 24R including red quantum dots, an electron transport layer 26 (first contact layer) in direct contact with the red light-emitting layer 24R, and a cathode 16 (second electrode). The red light-emitting layer 24R includes a first ligand that coordinates to the red quantum dots, and the electron transport layer 26 includes a second ligand 34 that can coordinate to the red quantum dots.

[0057] The green light-emitting element 6G according to this embodiment includes, in this order from the substrate 4 side, an anode 10G (first electrode), a green light-emitting layer 24G including green quantum dots, an electron transport layer 26 (first contact layer) in direct contact with the green light-emitting layer 24G, and a cathode 16 (second electrode). The green light-emitting layer 24G includes a first ligand that coordinates to the green quantum dots, and the electron transport layer 26 includes a second ligand 34 that can coordinate to the green quantum dots.

[0058] The blue light-emitting element 6B according to this embodiment includes, in this order from the substrate 4 side, an anode 10B (first electrode), a blue light-emitting layer 24B containing blue quantum dots, an electron transport layer 26 (first contact layer) in direct contact with the blue light-emitting layer 24B, and a cathode 16 (second electrode). The blue light-emitting layer 24B includes a first ligand that coordinates to the blue quantum dots, and the electron transport layer 26 includes a second ligand 34 that can coordinate to the blue quantum dots.

[0059] <Sealing layer> The sealing layer 8 covers the light-emitting element layer 6 and seals each light-emitting element included in the display device 2. The sealing layer 8 reduces the penetration of moisture, oxygen, etc. into the light-emitting element layer 6 and the like from the outside of the sealing layer 8 side of the display device 2. The sealing layer may have a laminated structure of, for example, an inorganic sealing film made of an inorganic material and an organic sealing film made of an organic material. The inorganic sealing film is formed, for example, by CVD, and is composed of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated film thereof. The organic sealing film is composed, for example, of a coatable resin material including polyimide or the like.

[0060] <Display Device Manufacturing Method> FIG. 4 is a schematic flow diagram showing an example of a method for manufacturing the display device 2 according to this embodiment.

[0061] In the manufacturing method of the display device 2 according to this embodiment, first, the substrate 4 is formed (step S2). The substrate 4 may be formed, for example, by forming a film substrate and TFTs on the film substrate on a rigid glass substrate, and then peeling the glass substrate from the film substrate. The above-mentioned peeling of the glass substrate may be performed after forming the light-emitting element layer 6 and the sealing layer 8, which will be described later. Alternatively, the substrate 4 may be formed, for example, by forming TFTs directly on the rigid glass substrate.

[0062] Next, the anode 10 is formed on the substrate 4 (step S4). The anode 10 may be formed, for example, by forming a thin film of a metal material by a sputtering method, a vacuum deposition method, or the like, and then patterning the thin film by dry etching or wet etching using a photoresist. This results in the formation of the anodes 10R, 10G, and 10B, each formed in an island shape for each subpixel, on the substrate 4.

[0063] Next, the edge cover 12 is formed (step S6). In step S6, the edge cover 12 is formed by photolithography. Specifically, for example, a positive photosensitive resin, which is the material for the edge cover 12, is applied to the upper surfaces of the substrate 4 and the anode 10. Next, a photomask having a light-transmitting portion is placed above the applied photosensitive resin at positions corresponding to each subpixel, and ultraviolet light or the like is irradiated through the photomask. Next, the photosensitive resin irradiated with ultraviolet light is washed with an appropriate developer. In this way, the edge cover 12 is formed between the positions corresponding to each subpixel on the substrate 4.

[0064] Next, the hole injection layer 20 is formed (step S8). The hole injection layer 20 may be formed by any method. In step S8, for example, a hole transport material is first dissolved or dispersed in a solvent to obtain a solution (hereinafter referred to as a "hole injection solution") that will be the material for the hole injection layer 20. The hole injection solution contains a hole transport material and a solvent. The hole injection solution is then applied onto the edge cover 12 and the anode 10 and solidified.

[0065] Here, when the hole injection layer 20 is formed in common for a plurality of light-emitting elements, the hole injection solution may be applied to the entire surface of the edge cover 12 and the anode 10 by bar coating, spin coating, or the like, and then solidified by heating or the like. When the hole injection layer 20 is formed individually for each light-emitting element, the hole injection solution may be applied to predetermined positions on the edge cover 12 and the anode 10 by using a printing technique such as an inkjet method, and then solidified by heating or the like. Alternatively, when the hole injection layer 20 is formed individually for each light-emitting element, the hole injection solution may be applied to the entire surface and solidified, and then the solidified hole injection solution may be patterned using a photolithography technique.

[0066] Next, the hole transport layer 22 is formed (step S10). The hole transport layer 22 may be formed by any method. For example, in step S10, a hole transport material is first dissolved or dispersed in a solvent to obtain a solution (hereinafter referred to as a "hole transport solution") that will be the material for the hole transport layer 22. The hole transport solution contains the hole transport material and a solvent. The hole transport solution is then applied and solidified on the hole injection layer 20 (and optionally the edge cover 12, etc.).

[0067] Next, the light-emitting layer 24 is formed (step S12). The red light-emitting layer 24R, the green light-emitting layer 24G, and the blue light-emitting layer 24B may be formed in any order. The light-emitting layer 24 may be formed by any method.

[0068] FIG. 5 is a schematic diagram showing the process of preparing a solution 66B (hereinafter referred to as "blue light-emitting solution 66B") that is the material for the blue light-emitting layer 24B shown in FIG.

[0069] 5, in forming the blue light-emitting layer 24B in step S12, for example, a first capping agent 64B is first added to a quantum dot dispersion solution 60B containing blue quantum dots 30B and a solvent 62B to obtain a blue light-emitting solution 66B (first liquid). Then, the blue light-emitting solution 66B is applied and solidified on the hole transport layer 22 (and optionally the edge cover 12, etc.). Here, the blue light-emitting solution 66B is applied onto the upper surface of the anode 10B exposed through the opening in the edge cover 12.

[0070] For example, in the solvent 62B, the first capping agent 64B generates the first ligand 32B and the by-product 33B, and the first ligand 32B may be coordinated to the surface of the blue quantum dot 30B. For example, when a metal halide compound (MX2) or a metal chalcogen compound (MY) is used as the first capping agent 64B and a polar solvent is used as the solvent 62B, the first capping agent 64B generates a halide ion (X - ) or chalcogenide ions (Y 2- ) and metal ions (M 2+ ) is generated. Then, a halide ion (X - ) or chalcogenide ions (Y 2- ) coordinates to the blue quantum dot 30B. 2+ ) is by-product 33B.

[0071] [ka] Here, M represents a metal element, X represents a halogen element, Y represents a chalcogen element, and Y 2- indicates a chalcogenide ion.

[0072] The halogen elements are group 17 elements in the new IUPAC system. The halogen elements include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0073] The chalcogen elements are group 16 elements in the new IUPAC system. The chalcogen elements include oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po).

[0074] Alternatively, for example, first capping agent 64B may be directly coordinated to the surface of blue quantum dot 30B. In this case, first ligand 32B is the same as first capping agent 64B, and by-product 33B is not generated. For example, when oleic acid is used as first capping agent 64B, oleic acid is coordinated to blue quantum dot 30B as first ligand 32B.

[0075] In either case, the blue light-emitting solution 66B includes blue quantum dots 30B and first ligands 32B coordinated to the blue quantum dots 30B.

[0076] The formation of green light-emitting layer 24G and red light-emitting layer 24R in step S12 is similar to the formation of blue light-emitting layer 24B in step S12, and therefore detailed description thereof will not be repeated.

[0077] Unless otherwise specified in this disclosure, the term "quantum dot dispersion solution 60" refers to any one of the quantum dot dispersion solution used in the formation process of the red light-emitting layer 24R, the quantum dot dispersion solution used in the formation process of the green light-emitting layer 24G, and the quantum dot dispersion solution 60B used in the formation process of the blue light-emitting layer 24B. The term "solvent 62" refers to any one of the solvent used in the formation process of the red light-emitting layer 24R, the solvent used in the formation process of the green light-emitting layer 24G, and the solvent 62B used in the formation process of the blue light-emitting layer 24B. The term "first capping agent 64" refers to any one of the first capping agent used in the formation process of the red light-emitting layer 24R, the first capping agent used in the formation process of the green light-emitting layer 24G, and the first capping agent 64B used in the formation process of the blue light-emitting layer 24B. Furthermore, "luminescent solution 66" refers to any one of the red luminescent solution used in the process of forming the red luminescent layer 24R, the green luminescent solution used in the process of forming the green luminescent layer 24G, and the blue luminescent solution 66B produced in the process of forming the blue luminescent layer 24B.

[0078] Unless otherwise specified in this disclosure, "by-product 33" refers to any of the by-products produced in the process of forming the red light-emitting layer 24R, the by-products produced in the process of forming the green light-emitting layer 24G, and the by-products 33B produced in the process of forming the blue light-emitting layer 24B.

[0079] Next, the electron transport layer 26 is formed (step S14). The electron transport layer 26 may be formed by any method including the step of applying a solution that will be the material for the electron transport layer 26.

[0080] FIG. 6 is a schematic diagram showing the process of preparing a solution 76 (hereinafter referred to as "electron transport solution 76") that is the material for the electron transport layer 26 shown in FIG.

[0081] 6, in step S14, for example, a second capping agent 74 is first added to a solution 70 containing an electron transport material 40 and a solvent 72 to obtain an electron transport solution 76 (second liquid), which is then applied directly onto the light-emitting layer 24 (and optionally the edge cover 12, etc.) and solidified.

[0082] For example, in the solvent 72, the second capping agent 74 may produce the second ligand 34 and the by-product 35, and the second ligand 34 may be capable of coordinating with the surface of the blue quantum dot 30B. Alternatively, for example, the second capping agent 74 may be capable of coordinating with the surface of the blue quantum dot 30B as is. In this case, the second ligand 34 is the same as the second capping agent 74, and the by-product 35 is not produced.

[0083] When the electron transport material 40 is a nanoparticle, the second ligands 34 may be coordinated to the surface of the electron transport material 40 .

[0084] In either case, for the blue light-emitting element 6B, the electron transport solution 76 includes an electron transport material 40 and a second ligand 34 capable of coordinating with the blue quantum dots 30B. The electron transport solution 76 is similar for the red light-emitting element 6R and the green light-emitting element 6G. That is, the second ligand 34 is capable of coordinating with any of the red quantum dots, the green quantum dots, and the blue quantum dots 30B.

[0085] In the prior art, applying a solution directly onto the light-emitting layer 24 deteriorates the light-emitting layer 24, resulting in a decrease in the luminous efficiency and reliability of the light-emitting device. This is because the first ligands 32 contained in the light-emitting layer 24 dissolve into the applied solution. A decrease in the amount of first ligands 32 in the light-emitting layer 24 can easily cause the first ligands 32 to detach from the quantum dots 30, exposing defects on the surface of the quantum dots 30. In quantum dots 30 with exposed defects, electrons and holes are more likely to recombine non-radiatively. Furthermore, quantum dots 30 with exposed defects are more likely to increase in size due to Ostwald ripening or aggregation. This results in a decrease in the luminous efficiency and reliability of the light-emitting device.

[0086] The inventors of the present disclosure have found that the above problem can be reduced or eliminated by selecting the first ligand 32 and the second ligand 34 so that the dissolution of the first ligand 32 and the second ligand 34 in the solvent competes with each other, and by adding the second ligand 34 to a solution that is applied directly onto the light-emitting layer 24. This is because the elution of the first ligand 32 into the applied solution is reduced due to competition with the second ligand 34.

[0087] As described above, the electron transport solution 76 according to this embodiment contains the second ligand 34, and the first ligand 32 competes with the second ligand 34. This makes it difficult for the first ligand 32 in the light-emitting layer 24 to dissolve into the electron transport solution 76. This improves the luminous efficiency and reliability of the light-emitting device.

[0088] In addition, when the first ligands 32 migrate from the light-emitting layer 24 toward the anode 10, the second ligands 34 are supplied from the electron transport layer 26 to the light-emitting layer 24. The second ligands 34 protect the surfaces of the quantum dots 30 together with or instead of the first ligands 32. Therefore, in a configuration in which the first ligands 32 migrate during operation of the light-emitting device, the light-emitting efficiency and reliability of the light-emitting device can be improved.

[0089] Next, the cathode 16 is formed (step S16). The cathode 16 may be formed by, for example, forming a thin film of a metal material by vacuum deposition or sputtering, etc., in common with a plurality of light-emitting element elements. This completes the formation of the light-emitting element layer 6.

[0090] Next, the sealing layer 8 is formed (step S18). When the sealing layer 8 includes an organic sealing film, the organic sealing film may be formed by applying an organic sealing material. When the sealing layer 8 includes an inorganic sealing film, the inorganic sealing film may be formed by a CVD method or the like. In this way, the sealing layer 8 that seals the light emitting element layer 6 is formed.

[0091] Then, as necessary, the glass substrate is peeled off and a functional film is attached to complete the manufacture of the display device 2. The functional film includes, for example, a polarizing film, a sensor film having a touch sensor panel function, a protective film, and an anti-reflection film.

[0092] <Ligand> The first ligand 32 and the second ligand 34 will be described in detail below.

[0093] As described above, the first ligand 32 coordinates to the quantum dot 30. The first ligand 32 and the second ligand 34 are selected so that the solubility of the first ligand 32 in the solvent 72 competes with the solubility of the second ligand 34 in the solvent 72. For example, the first ligand 32 and the second ligand 34 may have the same functional group, each may be a halide ion, or each may be a chalcogenide ion.

[0094] The properties of an organic compound or organic ion having a functional group, such as its ability to coordinate with quantum dots and its solubility in a solvent, depend on the functional group. Therefore, when the first ligand 32 and the second ligand 34 are organic compounds or organic ions having the same functional group, the solubility of the first ligand 32 in the solvent 72 competes with the solubility of the second ligand 34 in the solvent 72. The functional group that determines the solubility in the solvent is selected from the group including, for example, a hydroxyl group, an aldehyde group, a carboxyl group, a carbonyl group, an ether group, an amino group, a thiol group, and a phosphine group.

[0095] Organic substances with 19 or more carbon atoms tend to be poorly soluble in both polar and non-polar solvents. The poor solubility of the first ligand 32 and the second ligand 34 makes it difficult to form the light-emitting layer 24 and the electron transport layer 26. For this reason, when the first ligand 32 and the second ligand 34 are organic compounds or organic ions, it is preferable that the average number of carbon atoms in the first ligand 32 is 18 or less, and that the average number of carbon atoms in the second ligand 34 is 18 or less. The average number of carbon atoms is the arithmetic mean value of the number of carbon atoms.

[0096] Organic compounds or organic ions having 3 to 10 carbon atoms tend to form strong coordinate bonds with quantum dots, making them suitable as ligands for protecting quantum dots. Therefore, it is more preferable that the average number of carbon atoms in the first ligands 32 is 3 to 10, and that the average number of carbon atoms in the second ligands 34 is 3 to 10.

[0097] The smaller the carbon number of an organic compound or organic ion, the higher the charge transport efficiency, but on the other hand, the lower the hydrophobic protection ability. The higher the charge transport efficiency of the electron transport layer 26, the higher the luminous efficiency of the light-emitting device. The higher the protection ability of the electron transport layer 26, the longer the life of the light-emitting device. Therefore, it is more preferable that 30% to 95% of the first ligands 32 have 5 or less carbon atoms, and that 30% to 95% of the second ligands 34 have 5 or less carbon atoms.

[0098] The average number of carbon atoms in the first ligand 32 may be different from the average number of carbon atoms in the second ligand 34. Furthermore, the first ligand 32 may be the same organic compound or organic ion as the second ligand 34. When the first ligand 32 and the second ligand 34 are the same, the manufacturing cost of the light-emitting device can be reduced.

[0099] Halide ions compete with each other in terms of their coordination ability with quantum dots and their solubility in solvents. Therefore, when the first ligand 32 and the second ligand 34 are each a halide ion, the dissolution of the first ligand 32 in the solvent 72 competes with the dissolution of the second ligand 34 in the solvent 72. The halide ion includes a halogen element selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0100] The first ligand 32 and the second ligand 34 are preferably selected to minimize surface defects on the quantum dot 30. Specifically, halide ions that minimize surface defects on the quantum dot 30 are preferably used as the first ligand 32 and the second ligand 34. For this reason, it is particularly beneficial for the first ligand 32 and the second ligand 34 to be the same halide ion.

[0101] On the other hand, in some cases, the same ligand cannot be used as the first ligand 32 and the second ligand 34 due to considerations such as the solubility of the ligand in the solvent or the carrier transport properties of the ligand. In such cases, it is preferable to use ligands that are as similar as possible (i.e., competing) as the first ligand 32 and the second ligand 34. Therefore, it may be beneficial for the first ligand 32 and the second ligand 34 to be different halide ions.

[0102] Chalcogenide ions compete with each other in terms of coordination ability with quantum dots and solubility in a solvent. Therefore, when the first ligand 32 and the second ligand 34 are each a chalcogenide ion, the dissolution of the first ligand 32 in the solvent 72 competes with the dissolution of the second ligand 34 in the solvent 72. The chalcogenide ion contains a chalcogen element selected from the group consisting of oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po).

[0103] The first ligand 32 and the second ligand 34 are preferably selected to minimize surface defects on the quantum dot 30. Specifically, chalcogenide ions that minimize surface defects on the quantum dot 30 are preferably used as the first ligand 32 and the second ligand 34. For this reason, it is particularly beneficial for the first ligand 32 and the second ligand 34 to be the same chalcogenide ion.

[0104] On the other hand, in some cases, the same ligand cannot be used as the first ligand 32 and the second ligand 34 due to considerations such as the solubility of the ligand in a solvent or the carrier transport properties of the ligand. In such cases, it is preferable to use ligands that are as similar as possible (i.e., competing) as the first ligand 32 and the second ligand 34. Therefore, it may be beneficial for the first ligand 32 and the second ligand 34 to be different chalcogenide ions.

[0105] When halide ions or chalcogenides are used as ligands, metal halide compounds or metal chalcogen compounds are typically used as capping agents. The greater the ionization tendency of the metal element contained in the capping agent, the more easily the capping agent ionizes into metal ions and halide ions or chalcogenides in the material solution. Furthermore, the greater the ionization tendency of the metal element contained in the capping agent, the more easily the ionized halide ions or chalcogenides coordinate to the quantum dots 30. Among the metal elements typically used in quantum dots 30, lead has the lowest ionization tendency. Therefore, it is preferable that the first capping agent 64 used in the process of forming the light-emitting layer 24 contains a first metal element whose ionization tendency is equal to or greater than that of lead, and that the second capping agent 74 used in the process of forming the electron transport layer 26 contains a second metal element whose ionization tendency is equal to or greater than that of lead. The first and second metal elements remain in the light-emitting layer 24 and the electron transport layer 26, respectively. These metal elements may be the same or different.

[0106] Alkali metals and alkaline earth metals have a strong tendency to ionize, so it is preferable that the first metal element is selected from the group including alkali metals and alkaline earth metals, and the second metal element is selected from the group including alkali metals and alkaline earth metals.

[0107] To reduce dissolution of the quantum dots 30 in the luminescent solution 66, the metal element contained in the quantum dots 30 is preferably the same as the first metal element contained in the first capping agent 64 for the luminescent layer 24. The first metal element is selected from the group including, for example, zinc (Zn), tin (Sn), niobium (Nb), cadmium (Cd), indium (In), titanium (Ti), and zirconium (Zr). The first metal element may be different from or the same as the second metal element.

[0108] The amount of first ligand 32 contained in light-emitting layer 24 is preferably sufficient to protect quantum dots 30, while at the same time not inhibiting the movement of holes or electrons. Specifically, the preferred range of the concentration of first ligand 32 in light-emitting layer 24 is, in weight percentage (wt%), 0.001 wt% or more and 10 wt% or less. To achieve this, in step S12, the preferred range of the concentration of first ligand 32 in light-emitting solution 66 is 0.001 mol / L or more and 0.5 mol / L or less.

[0109] The amount of second ligand 34 contained in electron transport layer 26 is preferably sufficient to reduce elution of first ligand 32 from light-emitting layer 24, while at the same time not inhibiting the movement of holes or electrons. That is, the amount of second ligand 34 is preferably approximately the same as the amount of first ligand 32. Specifically, the preferred range of the concentration of second ligand 34 in electron transport layer 26 is, in weight percentage (wt%), 0.001 wt% or more and 10 wt% or less. To achieve this, in step S14, the preferred range of the concentration of second ligand 34 in electron transport solution 76 is 0.001 mol / L or more and 0.5 mol / L or less.

[0110] One method for forming the active layer 14 is to alternately repeat a process of applying and solidifying a solution of a material dissolved in a polar solvent and a process of applying and solidifying a solution of a material dissolved in a non-polar solvent.

[0111] In a preferred example, the solvent 62 contained in the luminescent solution 66 is a polar solvent, the solvent 72 contained in the electron transport solution 76 is a nonpolar solvent, and the first ligand 32 is soluble in a nonpolar solvent when it is free (i.e., isolated from the quantum dots 30) and is soluble in a polar solvent when it is protecting the quantum dots 30. In the luminescent layer 24, the first ligand 32 is in a state where it protects the quantum dots 30. Therefore, the first ligand 32 is less likely to be eluted from the luminescent layer 24. Note that, like the first ligand 32, the second ligand 34 is soluble in a nonpolar solvent when it is free, and is soluble in a polar solvent when it is protecting the quantum dots 30.

[0112] In another preferred example, the solvent 62 contained in the luminescent solution 66 is a nonpolar solvent, the solvent 72 contained in the electron transport solution 76 is a polar solvent, and the first ligand 32 is soluble in the polar solvent in its free state and in the nonpolar solvent in its state protecting the quantum dots 30. In the luminescent layer 24, the first ligand 32 is in a state protecting the quantum dots 30. Therefore, the first ligand 32 is less likely to elute from the luminescent layer 24. Note that, like the first ligand 32, the second ligand 34 is soluble in a polar solvent in its free state and in the nonpolar solvent in its state protecting the quantum dots 30.

[0113] (Variation) A modification of this embodiment will be described below.

[0114] Fig. 7 is a schematic diagram showing the schematic configuration of the boundary and its vicinity between the light-emitting layer 24 and the hole transport layer 22 shown in Fig. 2. Fig. 7 corresponds to an enlarged view of the part indicated by box D in Fig. 2.

[0115] 7, the hole transport layer 22 according to this modification includes a hole transport material 50 having hole transport properties, and further includes a third ligand 36 that can be coordinated to the quantum dots 30. When the third ligand 36 has sufficient hole transport properties for the hole transport layer 22, the third ligand 36 may also serve as the hole transport material 50.

[0116] In step S10, for example, a hole transport material 50 and a third capping agent are added to obtain a hole transport solution. In the solvent, a third ligand 36 and a by-product are generated from the third capping agent, and the third ligand 36 may be capable of coordinating to the surface of the quantum dots 30. Alternatively, for example, the third capping agent may be capable of coordinating to the surface of the quantum dots 30 as is. In this case, the third ligand 36 is the same as the third capping agent, and no by-product is generated.

[0117] The relationship between the third ligand 36 and the first ligand 32 is preferably similar to the relationship between the second ligand 34 and the first ligand 32. That is, the first ligand 32 and the third ligand 36 preferably have the same functional group, or each is a halide ion, or each is a chalcogenide ion.

[0118] For the same reasons as for the second ligand 34, the third ligand 36 is preferably an organic compound or organic ion having the same functional group as the first ligand 32. Furthermore, the average number of carbon atoms in the third ligand 36 is preferably 18 or less, and more preferably 3 to 10. It is preferable that 30% to 95% of the third ligands 36 have 5 or less carbon atoms. The average number of carbon atoms in the third ligand 36 may be different from the average number of carbon atoms in the first ligand 32, and the third ligand 36 may be the same organic compound or organic ion as the first ligand 32.

[0119] For the same reasons as for the second ligand 34, the third ligand 36 is preferably a halide ion when the first ligand 32 is a halide ion, and is preferably a chalcogenide ion when the first ligand 32 is a chalcogenide ion. Furthermore, the third capping agent preferably contains a third metal element having an ionization tendency equal to or greater than that of lead, and the third metal element is preferably selected from the group including alkali metals and alkaline earth metals. The first metal element may be different from or the same as the third metal element. The concentration of the third ligand 36 contained in the hole transport layer 22 is preferably 0.001 wt% or more and 10 wt% or less.

[0120] According to the configuration of this modification, when the first ligands 32 move from the light-emitting layer 24 toward the cathode 16, the third ligands 36 are supplied from the hole transport layer 22 to the light-emitting layer 24. The third ligands 36 protect the surfaces of the quantum dots 30 together with or instead of the first ligands 32. Therefore, in a configuration in which the first ligands 32 move while the light-emitting device is in operation, the light-emitting efficiency and reliability of the light-emitting device can be improved.

[0121] [Embodiment 2] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0122] FIG. 8 is a schematic cross-sectional view of a display area DA of the display device 2 according to this embodiment.

[0123] Fig. 9 is a schematic diagram showing the schematic configuration of the boundary and its vicinity between the light-emitting layer 24 and the hole transport layer 122 shown in Fig. 8. Fig. 9 corresponds to an enlarged view of the part indicated by box E in Fig. 8.

[0124] 8, the light-emitting element layer 6 according to this embodiment includes an anode 110 (second electrode) and a cathode 116 (first electrode) facing each other, an edge cover 112 covering the edge of the cathode 116, and an active layer 114 provided between the anode 110 and the cathode 116. The active layer 14 includes, in order from the anode 110 side, a hole injection layer 20, a hole transport layer 122 (first contact layer), a light-emitting layer 24, and an electron transport layer 126 (second contact layer). The active layer 114 is also referred to as an electroluminescent layer (EL layer). The active layer 114 may include additional components such as an electron injection layer.

[0125] The hole transport layer 122 includes a hole transport material 150 having hole transport properties, and further includes second ligands 134 capable of coordinating with the quantum dots 30 .

[0126] The electron transport layer 126 includes an electron transport material having electron transport properties. Optionally, the electron transport layer 126 may include a third ligand that can coordinate to the quantum dots 30.

[0127] Therefore, the light emitting element layer 6 according to this embodiment has the same configuration as the light emitting element layer 6 according to the first embodiment or its modified example, except that the stacked structure is upside down. Therefore, this embodiment has the same effects as the above-mentioned embodiments.

[0128] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. [Explanation of symbols]

[0129] 10 Anode (first electrode) 16 Cathode (second electrode) 22 hole transport layer (second contact layer) 24 Light-emitting layer 24R Red light-emitting layer (light-emitting layer) 24G Green light-emitting layer (light-emitting layer) 24R Blue light-emitting layer (light-emitting layer) 26 Electron transport layer (first contact layer) 30 quantum dots 30B Blue Quantum Dots (Quantum Dots) 32B, 32 First Ligand 34, 134 Secondary Ligand 36 Third Ligand 66 Luminescent Solution (1st Solution) 66B Blue luminescent solution (1st solution) 76 Electron transport solution (2nd solution) 110 Anode (second electrode) 116 Cathode (first electrode) 122 Hole transport layer (first contact layer) 126 Electron transport layer (second contact layer)

Claims

1. a first electrode, a light-emitting layer including quantum dots, a first contact layer in contact with the light-emitting layer, and a second electrode; the light-emitting layer includes a first ligand that coordinates to the quantum dots; the first contact layer comprises a second ligand; the first ligand and the second ligand have the same functional group, are each a halide ion, or are each a chalcogenide ion; The light-emitting device is characterized in that the first ligand is soluble in a non-polar solvent in a free state, and is soluble in a polar solvent in a state in which the first ligand protects the quantum dots.

2. a first electrode, a light-emitting layer including quantum dots, a first contact layer in contact with the light-emitting layer, and a second electrode; the light-emitting layer includes a first ligand that coordinates to the quantum dots; the first contact layer comprises a second ligand; the first ligand and the second ligand have the same functional group, are each a halide ion, or are each a chalcogenide ion; The light-emitting device is characterized in that the first ligand is soluble in a polar solvent in a free state, and is soluble in a non-polar solvent in a state in which the first ligand protects the quantum dots.

3. a first electrode, a light-emitting layer including quantum dots, a first contact layer in contact with the light-emitting layer, and a second electrode; the light-emitting layer includes a first ligand that coordinates to the quantum dots; the first contact layer comprises a second ligand; The first ligand and the second ligand are each a chalcogenide ion and contain a chalcogen element selected from the group consisting of oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po).

4. a first electrode, a light-emitting layer including quantum dots, a first contact layer in contact with the light-emitting layer, and a second electrode; the light-emitting layer includes a first ligand that coordinates to the quantum dots; the first contact layer comprises a second ligand; the first ligand and the second ligand are each a halide ion and comprise a halogen element selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I); the light-emitting layer contains a first metal element having an ionization tendency equal to or greater than that of lead, the first contact layer includes a second metal element having an ionization tendency equal to or greater than that of lead; the first metal element is selected from the group consisting of alkali metals and alkaline earth metals; The light-emitting device is characterized in that the second metal element is selected from the group consisting of alkali metals and alkaline earth metals.

5. the first ligand is an organic compound or an organic ion having the functional group; 3. The light-emitting device according to claim 1, wherein the second ligand is an organic compound or an organic ion having the functional group.

6. The light-emitting device according to claim 5, wherein the functional group is selected from the group consisting of a hydroxyl group, an aldehyde group, a carboxyl group, a carbonyl group, an ether group, an amino group, a thiol group, and a phosphine group.

7. the first ligand has an average carbon number of 18 or less; 7. The light-emitting device according to claim 5, wherein the average number of carbon atoms in the second ligand is 18 or less.

8. the average number of carbon atoms in the first ligand is 3 or more and 10 or less; The light-emitting device according to claim 7 , wherein the average number of carbon atoms in the second ligand is 3 or more and 10 or less.

9. 30% to 95% of the first ligands have 5 or less carbon atoms; 9. The light-emitting device according to claim 5, wherein 30% to 95% of the second ligands have 5 or less carbon atoms.

10. 10. The light-emitting device according to claim 5, wherein the average number of carbon atoms in the first ligand is different from the average number of carbon atoms in the second ligand.

11. The first ligand and the second ligand are the halide ion, 3. The light-emitting device according to claim 1, further comprising a halogen element selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

12. The first ligand and the second ligand are the chalcogenide ions, 3. The light-emitting device according to claim 1, further comprising a chalcogen element selected from the group consisting of oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po).

13. the light-emitting layer contains a first metal element having an ionization tendency equal to or greater than that of lead, The light-emitting device according to claim 11 or 12, wherein the first contact layer contains a second metal element having an ionization tendency equal to or greater than that of lead.

14. the first metal element is selected from the group consisting of alkali metals and alkaline earth metals; The light emitting device of claim 13, wherein the second metal element is selected from the group consisting of alkali metals and alkaline earth metals.

15. The light-emitting device according to claim 13 or 14, wherein the quantum dots contain the first metal element.

16. The light-emitting element according to any one of claims 13 to 15, wherein the first metal element is selected from the group including zinc (Zn), tin (Sn), niobium (Nb), cadmium (Cd), indium (In), titanium (Ti), and zirconium (Zr).

17. 17. The light-emitting element according to claim 13, wherein the first metal element is different from the second metal element.

18. 17. The light-emitting element according to claim 13, wherein the first metal element is the same as the second metal element.

19. 19. The light-emitting device according to claim 1, wherein the first ligand is the same as the second ligand.

20. 20. The light-emitting device according to claim 1, wherein the concentration of the first ligand in the light-emitting layer is 0.001 wt % or more and 10 wt % or less.

21. 21. The light-emitting device according to claim 1, wherein the concentration of the second ligand in the first contact layer is 0.001 wt % or more and 10 wt % or less.

22. 5. The light-emitting device according to claim 3, wherein the first ligand is soluble in a non-polar solvent in a free state, and is soluble in a polar solvent in a state in which the first ligand protects the quantum dots.

23. 5. The light-emitting device according to claim 3, wherein the first ligand is soluble in a polar solvent in a free state, and is soluble in a non-polar solvent in a state in which the first ligand protects the quantum dots.

24. 24. The light-emitting device according to claim 1, wherein the first contact layer is a hole transport layer or an electron transport layer.

25. a second contact layer located between the light-emitting layer and the first electrode, the second contact layer including a third ligand, and the second contact layer contacting the light-emitting layer; The light-emitting element according to any one of claims 1 to 23, characterized in that the first ligand and the third ligand have the same functional group, are each a halide ion, or are each a chalcogenide ion.

26. the first contact layer is either a hole transport layer or an electron transport layer; 26. The light emitting device of claim 25, wherein the second contact layer is the other of a hole transport layer and an electron transport layer.

27. In a display device having a plurality of pixels, each pixel includes a light-emitting element having a first electrode, a light-emitting layer, and a second electrode, the first electrode being provided independently for each pixel, and the second electrode being provided in common for each pixel, A display device, wherein the light-emitting element included in at least one pixel is the light-emitting element according to any one of claims 1 to 26.

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