Light-emitting element, display device, and manufacturing method for light-emitting element

Abstract

This light-emitting element (2) comprises a light-emitting layer (24) positioned between an anode (21) and a cathode (26), and an electron transport layer (25) positioned between the cathode and the light-emitting layer. The electron transport layer includes a plurality of nanoparticles (30) containing a metal oxide, and a metal sulfide (31) filling the space between at least two nanoparticles.

Description

Light-emitting element, display device, and method for manufacturing the same

[0001] The present disclosure relates to a light-emitting element, a display device including the light-emitting element, and a method for manufacturing the light-emitting element.

[0002] In a stacked-type light-emitting element, nanoparticles are sometimes used as a material for an electron transport layer that has the function of transporting electrons from a cathode to a light-emitting layer. Patent Document 1 discloses a technology for reducing aggregation of nanoparticles by forming silica around such nanoparticles using silane coupling.

[0003] US Patent Application Publication No. 2022 / 0250933

[0004] When nanoparticles surrounded by an insulator such as silica as described in Patent Document 1 are used as a material for the electron transport layer of a light-emitting element, the electrical resistance of the electron transport layer increases, which in turn increases the driving voltage of the light-emitting element.

[0005] A light-emitting element according to one aspect of the present disclosure includes an anode, a cathode facing the anode, a light-emitting layer located between the anode and the cathode, and an electron transport layer located between the cathode and the light-emitting layer, wherein the electron transport layer includes a plurality of nanoparticles containing a metal oxide and a metal sulfide filling spaces between at least two of the nanoparticles.

[0006] A method for manufacturing a light-emitting element according to one aspect of the present disclosure is a method for manufacturing a light-emitting element including an anode, a cathode facing the anode, a light-emitting layer located between the anode and the cathode, and an electron transport layer located between the cathode and the light-emitting layer, the method including forming the electron transport layer including a plurality of nanoparticles including a metal oxide and a metal sulfide filling spaces between at least two of the nanoparticles.

[0007] The aggregation of nanoparticles in the electron transport layer is reduced, while the increase in the driving voltage of the light-emitting device is reduced.

[0008] 1 is a schematic cross-sectional side view of a display device according to embodiment 1. FIG. 2 is a schematic diagram of a display device according to embodiment 1. FIG. 3 is a schematic enlarged view of a light-emitting layer and an electron transport layer in a cross-sectional side view of a light-emitting element according to embodiment 1. FIG. 4 is a schematic diagram showing an inorganic matrix filling spaces between quantum dots according to embodiment 1. FIG. 5 is a schematic diagram showing metal sulfide filling spaces between nanoparticles according to embodiment 1. FIG. 6 is a flowchart of a method for forming a light-emitting layer according to embodiment 1. FIG. 7 is a flowchart of a method for forming an electron transport layer according to embodiment 1. FIG. 8 is a schematic cross-sectional side view of a display device according to embodiment 2. FIG. 9 is a schematic cross-sectional side view of a display device according to embodiment 3. FIG. 10 is a schematic cross-sectional side view of a display device according to embodiment 4.

[0009] [Embodiment 1] <Display Device> Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that in each drawing, similar configurations are assigned the same reference numerals, and their description will be omitted. Furthermore, in this disclosure, for simplicity of illustration, components assigned the same reference numerals may be shown at different scales and with different hatching depending on the drawing. However, the components shown in each drawing of the present disclosure are merely examples, and the scales are not limited to those shown in the drawings. Furthermore, in this disclosure, components with different hatching have the same configuration as described above. Furthermore, in each drawing of the present disclosure, when two components have substantially the same shape but different compositions, etc., they may be assigned different reference numerals and the same hatching.

[0010] 2 is a schematic diagram of a display device 1 according to this embodiment. The display device 1 is a device that can be used, for example, as a display for a television, a smartphone, or the like. The display device 1 includes a display unit DA including a plurality of sub-pixels X, and a driver circuit DR that drives the plurality of sub-pixels X. Each of the plurality of sub-pixels X includes a light-emitting element 2 and a pixel circuit PC that drives the light-emitting element 2. The display device 1 performs display on the display unit DA by controlling light emission from each of the plurality of light-emitting elements 2 formed in the display unit DA via the driver circuit DR and the pixel circuit PC.

[0011] The structure of the display unit DA of the display device 1, particularly the structure of the light-emitting element 2, will be described in more detail with reference to Fig. 1. Fig. 1 is a schematic side cross-sectional view of the display device 1 according to an embodiment of the present disclosure, particularly showing a cross section perpendicular to the display surface of the display device 1 and passing through the light-emitting element 2. In other words, the cross section shown in Fig. 1 is a cross section perpendicular to the in-plane direction of each layer of the light-emitting element 2. Note that each schematic cross-sectional view of the display device in the present disclosure shows a cross section corresponding to the cross section of the display device 1 shown in Fig. 1.

[0012] 1, the display device 1 according to this embodiment includes a display section DA that includes the above-described plurality of light-emitting elements 2 and a substrate 3, and in particular includes the plurality of light-emitting elements 2 on the substrate 3. The display device 1 has a structure in which the layers of the light-emitting elements 2 are stacked on the substrate 3 on which, for example, TFTs (Thin Film Transistors) (not shown) are formed as pixel circuits PC. In this specification, the direction from the light-emitting elements 2 of the display device 1 to the substrate 3 is referred to as the "downward direction," and the direction opposite to the downward direction is referred to as the "upward direction."

[0013] 1 , the light-emitting element 2 includes, in order from the substrate 3 side, an anode 21, a hole injection layer 22, a hole transport layer 23, a light-emitting layer 24, an electron transport layer 25, and a cathode 26. In other words, the light-emitting element 2 includes the anode 21, a cathode 26 facing the anode 21, the light-emitting layer 24 located between the anode 21 and the cathode 26, and the electron transport layer 25 located between the cathode 26 and the light-emitting layer 24. In the light-emitting element 2 according to this embodiment, the anode 21 is located closer to the substrate 3 than the light-emitting layer 24.

[0014] <Light-emitting element: anode and cathode> The anode 21 according to this embodiment is a transparent electrode that transmits visible light, including at least the light emitted by the light-emitting layer 24. The anode 21 may contain an oxide conductor that is both conductive and transparent. The anode 21 may contain, for example, ITO, or may contain InZnO, SnO ２ , or FTO, etc. The cathode 26 according to this embodiment is a reflective electrode that reflects visible light, including at least the light emitted by the light-emitting layer 24. The cathode 26 may include a metal material that has a high reflectivity for visible light. The cathode 26 may include, for example, Al. Alternatively, the cathode 26 may include Ag, Cu, or Au, or an alloy of the above-mentioned metals.

[0015] For example, the anode 21 may be formed in an island shape for each subpixel, and each anode 21 may be electrically connected to the pixel circuit PC of the corresponding subpixel. The cathode 26 may also be formed in common to a plurality of subpixels. This allows the display device 1 to apply a common voltage to the cathode 26 while controlling the voltage applied to each anode 21 individually for each subpixel. As described above, the display device 1 may perform display by individually controlling the light emission of the light-emitting element 2 for each subpixel.

[0016] With the above configuration, a portion of light from the light-emitting layer 24 of the light-emitting element 2 is reflected by the cathode 26. Therefore, the light-emitting element 2 extracts light from the light-emitting layer 24 to the outside through the anode 21. Therefore, the display device 1 is a bottom-emission display device in which light from each light-emitting element 2 is extracted from the substrate 3 side. Bottom-emission display devices generally have a simpler manufacturing method than top-emission display devices in which light from each light-emitting element 2 is extracted from the side opposite the substrate 3. In this case, if the cathode 26 contains a metal material with high visible light reflectivity, the light-emitting element 2 can more efficiently extract light from the light-emitting layer 24 to the outside. The display device 1 may extract light from each light-emitting element 2 between multiple pixel circuits PC formed on the substrate 3. Alternatively, at least a portion of the substrate 3 including the multiple pixel circuits PC may be made of a transparent material. However, from the viewpoint of improving the aperture ratio of each subpixel of the display device 1, the display device 1 may be a top-emission display device. In this case, the anode 21 of each light-emitting element 2 may be a reflective electrode, and the cathode 26 may be a transparent electrode.

[0017] <Light-Emitting Element: Hole Injection Layer and Hole Transport Layer> The hole injection layer 22 is a layer that injects holes from the anode 21 toward the light-emitting layer 24. The hole injection layer 22 can be made of organic or inorganic materials with hole transport properties that have been conventionally used in light-emitting elements, such as quantum dot-containing light-emitting elements. The hole injection layer 22 may contain nickel oxide (NiO) nanoparticles. The hole injection layer 22 may also contain a self-assembled monolayer of [2-(3,6-dimethoxy-9H-carbozol-9-yl)ethyl]phosphonic acid (MeO-2PACz). Other examples of materials for the hole injection layer 22 include a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (abbreviated as "PEDOT:PSS"), CuSCN (copper thiocyanate), and the like. Furthermore, the hole injection layer 22 may contain bulk NiO (nickel oxide) instead of nanoparticles as a material. Note that these materials may be used alone or in combination of two or more types.

[0018] The hole transport layer 23 is a layer that transports holes injected from the anode 21 into the hole injection layer 22 to the light-emitting layer 24. The hole transport layer 23 can be made of an organic or inorganic material having hole transport properties that has been conventionally used in light-emitting devices containing quantum dots. Examples of materials for the hole transport layer 23 include poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl))diphenylamine)] (abbreviated as "TFB"), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (abbreviated as "poly-TPD"), and polyvinylcarbazole (abbreviated as "PVK"). These materials may be used alone, or two or more may be appropriately mixed or stacked.

[0019] <Light-emitting element: electron transport layer: overview> The light-emitting layer 24 and the electron transport layer 25 will be described in more detail below with reference to Fig. 3 in addition to Fig. 1. Fig. 3 is a schematic enlarged view showing the light-emitting layer 24 and the electron transport layer 25 in a side cross section of the light-emitting element 2 according to this embodiment, and is a view showing an enlarged view of region A shown in Fig. 1 in particular.

[0020] The electron transport layer 25 is a layer that transports electrons injected from the cathode 26 to the light-emitting layer 24. The electron transport layer 25 according to this embodiment includes a plurality of nanoparticles 30 containing a metal oxide as an electron transport material, and a metal sulfide 31 filling the spaces between at least two nanoparticles 30.

[0021] <Light-emitting element: electron transport layer: metal sulfide filling spaces between nanoparticles> Here, the material filling the spaces between the plurality of nanoparticles 30 will be described in more detail with further reference to FIG. 4. Schematic diagrams 401 and 402 in FIG. 4 are schematic diagrams showing the material filling the spaces between the nanoparticles 30. In particular, schematic diagrams 401 and 402 are respectively diagrams showing two examples of a set P1 of two nanoparticles 30 and the region (space) K1 between them, as shown in FIG. 3. In particular, schematic diagrams 401 and 402 are respectively diagrams showing sets P1 and P2, which are examples of sets of nanoparticles 30A and nanoparticles 30B.

[0022] In this specification, the term "a member fills the spaces between a plurality of nanoparticles 30" means that the member fills at least the region K1 between nanoparticle 30A and nanoparticle 30B, as shown in the schematic diagram 401 of set P1 in Fig. 4. Region K1 is a region surrounded by two lines (common circumscribing lines) tangent to the peripheries of nanoparticle 30A and nanoparticle 30B and the opposing peripheries of nanoparticle 30A and nanoparticle 30B in the cross section of the electron transport layer 25. Therefore, as shown in the schematic diagram 402 of set P2 in Fig. 4, region K1 can exist even if nanoparticle 30A and nanoparticle 30B are close to each other, and the member fills region K1.

[0023] The phrase "a material fills the gaps between the nanoparticles 30" does not necessarily mean that the region K1 between the nanoparticles 30A and 30B is entirely made of the material. For example, the region K1 between the nanoparticles 30A and 30B may contain a material, such as a ligand, that is different from the material of the material. Specifically, for example, the electron transport layer 25 may contain an organic ligand that is added to improve the dispersibility of the nanoparticles 30 in the dispersion liquid used for coating formation and that coordinates to the outer surfaces of the nanoparticles 30 in the dispersion liquid. In this case, in the electron transport layer 25, from the viewpoint of improving the reliability of the electron transport layer 25, for example, the weight ratio of the organic ligand to the total weight including the region K1 may be less than 5%.

[0024] The metal sulfide 31 filling the gap between the two nanoparticles 30 may include a continuous film along a plane direction perpendicular to the thickness direction of the electron transport layer 25. In the present disclosure, the continuous film of the metal sulfide 31 may refer to an integrated film connected without interruption by chemical bonding of the materials constituting the metal sulfide 31. In particular, in the present disclosure, the continuous film refers to a film having a thickness of 1000 nm or more in a certain plane direction. ２ It may also refer to a single membrane having an area of ​​100 mm or more.

[0025] <Light-emitting element: electron transport layer: nanoparticles> For example, the metal oxide contained in the nanoparticles 30 includes at least one of ZnO, ZnMgO, ZnAlO, and ZnLiO. This improves the efficiency of transporting electrons from the cathode 26 to the light-emitting layer 24 by the electron transport layer 25 in the light-emitting element 2.

[0026] As will be described later, in a light-emitting element 2 having quantum dots in the light-emitting layer 24, an excess of electrons may occur, in which the number of electrons injected into the light-emitting layer 24 during operation exceeds the number of holes injected into the light-emitting layer 24. Reducing the excess of electrons in the light-emitting layer 24 reduces Auger recombination associated with the generation of negative trions and the like, which have low light-emitting efficiency, in the light-emitting layer 24, thereby contributing to improving the light-emitting efficiency of the light-emitting element 2 or reducing deterioration of each layer of the light-emitting element 2, including the light-emitting layer 24.

[0027] When the nanoparticles 30 of the electron transport layer 25 contain ZnMgO or ZnLiO, the number of electrons excessively injected into the light-emitting layer 24 of the light-emitting device 2 can be reduced compared to when the nanoparticles 30 are made of only ZnO. This improves the balance between the numbers of holes and electrons injected into the light-emitting layer 24 of the light-emitting device 2, thereby improving the luminous efficiency or extending the lifetime.

[0028] In addition, the nanoparticles 30 may be zinc oxide (ZnO) or titanium oxide (TiO ２ ), or zirconium oxide (ZrO ２ ) may be included. In the present disclosure, chemical formulas are representative examples. In the present disclosure, the composition ratio described in a chemical formula does not necessarily have to be stoichiometry, in which the actual composition of the compound is the same as that of the chemical formula. The material possessed by the plurality of nanoparticles 30 may be the same, or the material possessed by at least one nanoparticle 30 among the plurality of nanoparticles 30 may be different from the material possessed by another nanoparticle 30.

[0029] <Light-emitting element: electron transport layer: metal sulfide> The metal sulfide 31 fills the spaces between the nanoparticles 30, thereby reducing the aggregation of the nanoparticles 30. Reducing the aggregation of the nanoparticles 30 results in a more uniform thickness of the applied electron transport layer 25, reducing spatial bias of the electron transport material in the electron transport layer 25, improving the efficiency of electron injection into the light-emitting layer 24, and increasing the light-emitting efficiency. The metal sulfide 31 also protects the nanoparticles 30 from heat or foreign matter such as moisture, thereby reducing degradation of the nanoparticles 30. Therefore, the metal sulfide 31 improves the efficiency of electron transport from the cathode 26 to the light-emitting layer 24 by the electron transport layer 25, while also improving the reliability of the electron transport layer 25. In particular, the metal sulfide 31 including a continuous film fills the spaces between the nanoparticles 30 more densely, further improving the reliability of the electron transport layer 25.

[0030] For example, the metal sulfide 31 fills the electron transport layer 25 from the lower surface 25B on the anode 21 side to the upper surface 25T on the cathode 26 side. In this case, the electron transport layer 25 contacts each of the cathode 26 and the light-emitting layer 24 via the metal sulfide 31. Furthermore, in the above case, the electron transport layer 25 has the metal sulfide 31 between at least one nanoparticle 30 and the cathode 26, and between at least one nanoparticle 30 and at least one quantum dot 40, which will be described later.

[0031] The electron transport layer 25 is in contact with the cathode 26, and thus the light-emitting element 2 improves the efficiency of electron injection from the cathode 26 to the electron transport layer 25. Furthermore, the electron transport layer 25 contains the metal sulfide 31 between the nanoparticles 30 and the quantum dots 40, and thus the light-emitting element 2 improves the efficiency of electron transport from the electron transport layer 25 to the quantum dots 40.

[0032] Furthermore, since the metal sulfide 31 is located between the nanoparticles 30 and the cathode 26, the light-emitting element 2 reduces contact between the nanoparticles 30 and the cathode 26. Therefore, the light-emitting element 2 reduces oxidation of the electron transport layer 25 side of the cathode 26 due to oxygen atoms of the metal oxide contained in the nanoparticles 30, and thus reduces the formation of a highly insulating oxide film between the electron transport layer 25 and the cathode 26. When the cathode 26 contains a metal material that is relatively easily oxidized, the effect of the light-emitting element 2 in reducing the formation of an oxide film between the electron transport layer 25 and the cathode 26 becomes more pronounced.

[0033] Furthermore, by positioning the metal sulfide 31 between the nanoparticles 30 and the light-emitting layer 24, the light-emitting element 2 reduces contact between the nanoparticles 30 and the light-emitting material of the light-emitting layer 24, including quantum dots 40, which will be described later. Therefore, the light-emitting element 2 reduces the transfer of energy that contributes to the light emission of the light-emitting material of the light-emitting layer 24, such as the energy of excitons generated in the quantum dots, which will be described later, to the nanoparticles 30, thereby improving the luminous efficiency of the light-emitting layer 24. Note that the metal sulfide 31 positioned between the nanoparticles 30 and the quantum dots 40, which will be described later, is 1000 nm in thickness along a plane direction perpendicular to the thickness direction of the electron transport layer 25. ２ The film may include a continuous film having an area of ​​more than 100 mm.

[0034] The metal sulfide 31 includes, for example, at least one of ZnS, ZnMgS, and ZnGaS. The metal sulfide 31 containing zinc sulfide as a main component fills the spaces between the nanoparticles 30 more densely, thereby better protecting the nanoparticles 30.

[0035] <Light-emitting element: electron transport layer: halogen atom> Furthermore, the electron transport layer 25 according to this embodiment contains a halide 32 containing a halogen atom. For example, the electron transport layer 25 contains zinc fluoride (ZnF ２ ), zinc chloride (ZnCl ２ ), zinc bromide (ZnBr ２ ), zinc iodide (ZnI ２ ), indium fluoride (InF ３ ), indium chloride (InCl ３ ), indium bromide (InBr３ ), or indium iodide (InI ３ ) The electron transport layer 25 may also include, but is not limited to, other halides 32, particularly those containing fluorine, chlorine, bromine, or iodine.

[0036] In this disclosure, the term "atom" does not necessarily mean that an atom exists as a single atom. In this disclosure, the term "atom" also includes atoms that exist in the form of a molecule having two or more atoms, including the atom and another atom, atoms that exist in the form of a complex, atoms that exist in the form of a compound, or atoms that exist in the form of an ion. However, the term "atom" in this disclosure does not limit the form of existence of other atoms. In other words, a halogen atom includes atoms that exist in the form of a compound containing a halogen atom, such as a halide 32, and also includes atoms that exist in the form of a halogen ion. Regardless of the form of existence of a halogen atom, if its presence in a substance can be identified by analysis, the substance may be considered to contain a halogen atom.

[0037] The halogen atoms contained in the halide 32 contained in the electron transport layer 25 may modify the outermost surface of the nanoparticle 30, thereby compensating for defects on the outermost surface of the nanoparticle 30. In this case, the electron transport layer 25 containing the halide 32 reduces degradation of the nanoparticle 30. At least one halogen atom may be located within 1 nm from the outer surface of the nanoparticle 30. More specifically, the halogen atom may be located within region B shown by the dotted line in FIG. 3 . Region B is a region extending from the center of the nanoparticle 30 to a position a distance L1 from the outermost surface of the nanoparticle 30 in the direction from the center to the periphery, where distance L1 is 1 nm. In this case, the halogen atoms contained in the halide 32 more efficiently compensate for defects on the outermost surface of the nanoparticle 30, thereby better reducing degradation of the nanoparticle 30. In addition, if cross-sectional observation of the electron transport layer 25 confirms that the halide 32 is located within 1 nm from the outer surface of the nanoparticle 30, it may be considered that the halogen atom is located within 1 nm from the outer surface of the nanoparticle 30. The cross-sectional observation may be performed by EELS (Electron Energy Loss Spectroscopy) using a TEM (Transmission Electron Microscope).

[0038] <Light-emitting element: light-emitting layer: overview> The light-emitting layer 24 is a layer containing a light-emitting material that emits light when excited by excitons generated by the recombination of holes from the anode 21 and electrons from the cathode 26. In this embodiment, the light-emitting layer 24 includes a plurality of quantum dots 40 as the light-emitting material, and an inorganic matrix 41 that fills the spaces between at least two quantum dots.

[0039] <Light-emitting element: light-emitting layer: inorganic matrix filling spaces between quantum dots> Here, the material filling the spaces between the quantum dots 40 will be described in more detail with further reference to FIG. 5. Schematic diagrams 501 and 502 in FIG. 5 are schematic diagrams showing the material filling the spaces between the quantum dots 40. In particular, schematic diagrams 501 and 502 are respectively diagrams showing two examples of a set P3 of two quantum dots 40 and the region (space) K2 between them, as shown in FIG. 3. In particular, schematic diagrams 501 and 502 are respectively diagrams showing sets P3 and P4, which are examples of sets of quantum dot 40A and quantum dot 40B.

[0040] In this specification, "a member filling the spaces between multiple quantum dots 40" means that the member fills at least the region K2 between quantum dot 40A and quantum dot 40B, as shown in the schematic diagram 501 of set P3 in Fig. 5. Region K2 is a region surrounded by two lines (common circumscribing lines) tangent to the peripheries of quantum dot 40A and quantum dot 40B and the opposing peripheries of quantum dot 40A and quantum dot 40B in the cross section of the light-emitting layer 24. Therefore, as shown in the schematic diagram 502 of set P4 in Fig. 5, region K2 can exist even if quantum dot 40A and quantum dot 40B are close to each other, and the member fills region K2.

[0041] The expression "a material fills the gap between the quantum dots 40" does not necessarily mean that the region K2 between the quantum dots 40A and 40B is entirely made of the material. For example, the region K2 between the quantum dots 40A and 40B may contain a material, such as a ligand, different from the material of the material. Specifically, the light-emitting layer 24 may contain an organic ligand that is added to improve the dispersibility of the quantum dots 40 in the dispersion liquid used for coating and that coordinates to the outer surfaces of the quantum dots 40 in the dispersion liquid. In this case, in the light-emitting layer 24, from the viewpoint of improving the reliability of the light-emitting layer 24, the weight ratio of the organic ligand to the total weight including the region K2 may be less than 5%. Furthermore, the inorganic matrix 41 filling the gap between the two quantum dots 40 may be formed within a 1000 nm thickness along a plane direction perpendicular to the thickness direction of the light-emitting layer 24. ２ The film may include a continuous film having an area of ​​more than 100 mm.

[0042] <Light-Emitting Element: Light-Emitting Layer: Quantum Dots> The quantum dots 40 may each have a core / shell structure, including a core and a shell surrounding the core. In this embodiment, the quantum dots 40 are, for example, luminescent semiconductor nanoparticles that emit light due to excitons generated by the recombination of injected electrons and holes. For example, the recombination of electrons and holes in the quantum dots 40 occurs primarily in the core. The core of the quantum dot 40 is a luminescent material that has a valence band level and a conduction band level and emits light due to the recombination of holes in the valence band level and electrons in the conduction band level. The light emitted from the quantum dots 40 has a narrow spectrum due to the quantum confinement effect, making it possible to obtain light with a relatively deep chromaticity. Furthermore, the shell functions to suppress the occurrence of defects or dangling bonds in the core and reduce the recombination of carriers undergoing a deactivation process.

[0043] The core and shell materials of the quantum dots 40 may each contain materials used for the core and shell materials of conventionally known core / shell quantum dots. The quantum dots 40 may have a core / shell structure such as InP / ZnS, InP / ZnSe / ZnS, CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, ZnSe / ZnS, ZnTeSe / ZnS, or CIGS / ZnS. The shell may be formed of multiple layers containing multiple different materials.

[0044] The quantum dots 40 have a particle size of about 1 to 100 nm. The wavelength of light emitted from the quantum dots 40 can be controlled by the particle size. In particular, since the quantum dots 40 have a core / shell structure, the wavelength of light emitted from the quantum dots 40 can be controlled by controlling the particle size of the core. Therefore, by controlling the particle size of the quantum dots 40, the wavelength of light emitted by the display device 1 can be controlled.

[0045] The light-emitting layer 24 according to this embodiment includes, but is not limited to, quantum dots 40 as a light-emitting material. For example, the light-emitting layer 24 may include a fluorescent material or phosphorescent material that emits light upon excitation by excitons generated by recombination of holes from the anode 21 and electrons from the cathode 26, and may further include an inorganic or organic material as the light-emitting material.

[0046] <Light-emitting element: light-emitting layer: inorganic matrix> The inorganic matrix 41 fills the spaces between the multiple quantum dots 40, thereby protecting the quantum dots 40 from heat or foreign substances such as moisture, and reducing deterioration of the quantum dots 40. Since the light-emitting layer 24 includes the inorganic matrix 41 that reduces deterioration of the quantum dots 40, the light-emitting element 2 has improved luminous efficiency and lifetime.

[0047] For example, the inorganic matrix 41 fills the light-emitting layer 24 from the lower surface 24B on the anode 21 side to the upper surface 24T on the cathode 26 side. In this case, the light-emitting layer 24 is in contact with each of the hole transport layer 23 and the electron transport layer 25 via the inorganic matrix 41. Furthermore, in the above case, the light-emitting layer 24 has the inorganic matrix 41 between the at least one quantum dot 40 and the hole transport layer 23, and between the at least one quantum dot 40 and the electron transport layer 25. In particular, the metal sulfide 31 and the inorganic matrix 41 may fill the space between the at least one nanoparticle 30 in the electron transport layer 25 and the at least one quantum dot 40 in the light-emitting layer 24.

[0048] By having the light-emitting layer 24 in contact with each of the hole transport layer 23 and the electron transport layer 25, the light-emitting element 2 improves the transport efficiency of both holes and electrons to the light-emitting layer 24, thereby improving the carrier concentration in the light-emitting layer 24.

[0049] Furthermore, since the metal sulfide 31 or the inorganic matrix 41 is located between the quantum dots 40 and the electron transport layer 25, the light-emitting device 2 reduces contact between the quantum dots 40 and the nanoparticles 30. Therefore, the light-emitting device 2 reduces the transfer of energy of excitons generated in the quantum dots 40 to the nanoparticles 30, thereby improving the luminous efficiency of the light-emitting layer 24.

[0050] The inorganic matrix 41 may be a semiconductor such as a metal sulfide, and may contain, for example, ZnS. The inorganic matrix 41 may also contain the same material as the metal sulfide 31 contained in the electron transport layer 25. When the inorganic matrix 41 contains a semiconductor such as a metal sulfide, the light-emitting element 2 has an improved injection efficiency of holes and electrons into the quantum dots 40, and an improved luminous efficiency, compared to when the inorganic matrix 41 contains an insulator such as silica.

[0051] However, in this embodiment, the material of the inorganic matrix 41 is not limited to ZnS. For example, the inorganic matrix 41 may be tin sulfide (SnS ２ ), indium sulfide (In ２ S ３ ), aluminum sulfide (Al ２ S ３ ), beryllium sulfide (BeS), germanium sulfide (GeS ２ The inorganic matrix 41 may include metal sulfides such as beryllium selenide (BeSe), barium selenide (BaSe), calcium selenide (CaSe), magnesium selenide (MgSe), metal tellurides such as calcium tellurium (CaTe) and magnesium telluride (MgTe), and metal oxides such as zinc oxide (ZnO).

[0052] <Summary of the Display Device> The electron transport layer 25 according to this embodiment includes nanoparticles 30 containing a metal oxide and metal sulfide 31 filling the spaces between at least two nanoparticles 30. The nanoparticles 30 containing a metal oxide transport electrons more efficiently than the metal sulfide 31. On the other hand, the metal sulfide 31 reduces the aggregation of the nanoparticles 30 and transports electrons from the cathode 26 to the nanoparticles 30 more efficiently than an insulator such as silica.

[0053] Therefore, the light-emitting element 2 according to this embodiment improves the efficiency of electron injection from the cathode 26 while reducing the aggregation of the nanoparticles 30 in the electron transport layer 25, thereby reducing an increase in the overall driving voltage of the light-emitting element 2. The display device 1 including the light-emitting element 2 achieves power saving and a long life.

[0054] <Manufacturing Method of Display Device: Up to Formation of Hole Transport Layer> The following describes a manufacturing method of the display device 1. The display device 1 may be manufactured, for example, by preparing a substrate 3 on which pixel circuits PC and the like are formed, and sequentially forming each layer of the light-emitting element 2 on the substrate 3.

[0055] For example, in a method for manufacturing the display device 1, the anode 21, the hole injection layer 22, and the hole transport layer 23 are formed in this order on the substrate 3. The anode 21 may be formed, for example, by forming a thin film of the above-mentioned light-transmitting conductive material by a vacuum deposition method, a sputtering method, or the like, and then patterning the thin film for each subpixel by a dry etching method, or the like. The hole injection layer 22 and the hole transport layer 23 may be formed, for example, by using the above-mentioned materials by a vacuum deposition method, a sputtering method, or a coating formation method using a colloidal solution, or the like.

[0056] <Display Device Manufacturing Method: Formation of Light-Emitting Layer: Preparation of Quantum Dot Dispersion> Next, the light-emitting layer 24 is formed on the hole transport layer 23. The method for forming the light-emitting layer 24 according to this embodiment will be described in detail with reference to Fig. 6 and Fig. 7. Fig. 6 is a flowchart of the method for forming the light-emitting layer 24 according to this embodiment. Fig. 7 is a schematic process diagram for explaining the method for forming the light-emitting layer 24 according to this embodiment.

[0057] In the method for forming the light-emitting layer 24, quantum dots 40 are first synthesized (step S1). The quantum dots 40 may be synthesized by various methods, including conventionally known methods such as a heating method, a hot injection method, a microwave-assisted method, and a continuous flow method. The quantum dots 40 may be synthesized in a solvent such as ethanol in which an organic ligand is dispersed. In this case, the organic ligand may be coordinated to the outermost surface of the quantum dots 40. Alternatively, the quantum dots 40 may be isolated by adding ethyl acetate to a dispersion liquid in which the quantum dots 40 are dispersed to precipitate the quantum dots 40, recovering the precipitate by centrifugation, and washing the precipitate.

[0058] Next, the quantum dots 40 and the precursor of the inorganic matrix 41 are dispersed in a solvent (step S2). As a result, in step S2, a quantum dot dispersion 50 is prepared, which is a dispersion in which the quantum dots 40 and the inorganic matrix 41 are dispersed, as shown in a schematic diagram 701 of Fig. 7. The quantum dot dispersion 50 is prepared, for example, by dispersing the quantum dots 40 and the precursor 41P of the inorganic matrix 41 in a solvent 51.

[0059] The solvent 51 may be a non-polar solvent such as octane, or a polar solvent such as N,N-dimethylformamide (DMF). In order to improve the dispersibility of the quantum dots 40 in the quantum dot dispersion 50, an organic ligand capable of coordinating to the outermost peripheral surface of the quantum dots 40 may be added to the quantum dot dispersion 50. The polarity of the solvent 51 may be determined by the polarity of the organic ligand coordinated to the quantum dots 40, and in particular, the polarity of the solvent 51 may have a polarity that improves the dispersibility of the organic ligand coordinated to the quantum dots 40.

[0060] The precursor 41P contains a material that will be converted into the inorganic matrix 41 by a process described later. The precursor 41P may contain, for example, an alkyl xanthogenate and zinc chloride. In this case, the zinc chloride may also function as a catalyst in the conversion of the precursor 41P into the inorganic matrix 41, which will be described later. By adjusting the concentration ratio of the quantum dots 40 to the precursor 41P in the quantum dot dispersion 50, the volume ratio of the quantum dots 40 to the inorganic matrix 41 in the light-emitting layer 24 after formation can be adjusted.

[0061] The alkyl xanthogenate may be represented by, for example, the following chemical formula: In the following chemical formula, R represents an alkyl group and M represents a metal atom. When the solvent 51 is a non-polar solvent, the alkyl group of the alkyl xanthogenate may have 8 or more carbon atoms in order to improve the dispersibility of the alkyl xanthogenate in the solvent 51.

[0062] For example, when the inorganic matrix 41 includes ZnS, the precursor 41P may include a zinc alkylxanthate and zinc chloride. The zinc alkylxanthate may be synthesized by substituting the metal element of a xanthate, such as magnesium xanthate or gallium xanthate, and adding an alkyl group.

[0063] At least a portion of the precursor 41P may be capable of coordinating with the outermost peripheral surface of the quantum dots 40. For example, when the precursor 41P contains an alkyl xanthogenate, the terminus of the alkyl group of the alkyl xanthogenate may be substituted with a coordinating functional group. In this case, in step S2, the quantum dot dispersion liquid 50 may be stirred to substitute the organic ligands that coordinate with the outermost peripheral surface of the quantum dots 40 with the precursor 41P.

[0064] <Display Device Manufacturing Method: Formation of Light-Emitting Layer: Coating and Deposition of Light-Emitting Layer> Next, the quantum dot dispersion liquid 50 is applied (step S3). In particular, in this embodiment, as shown in the schematic side cross-sectional view 702 of Figure 7, the quantum dot dispersion liquid 50 is applied onto the previously formed hole transport layer 23. The application of the quantum dot dispersion liquid 50 may be performed by a coating method including a conventionally known method such as spin coating.

[0065] Next, the applied quantum dot dispersion liquid 50 is heated (step S4). The applied quantum dot dispersion liquid 50 may be heated, for example, by heating each layer on the substrate 3 that contains the quantum dot dispersion liquid 50. This converts the precursors 41P contained in the applied quantum dot dispersion liquid 50 into the inorganic matrix 41.

[0066] From the viewpoint of preventing the precursor 41P from being converted into the inorganic matrix 41 at room temperature, the thermal decomposition temperature of the precursor 41P may be 60° C. or higher, and more preferably 110° C. or higher. In other words, the heating temperature in step S4 may be 60° C. or higher, and more preferably 110° C. or higher. Furthermore, from the viewpoint of reducing deterioration of each layer on the substrate 3 by heating the layer, the heating temperature in step S4 may be 300° C. or lower, and more preferably 200° C. or lower.

[0067] Although an example in which the quantum dot dispersion liquid 50 is heated in the conversion of the precursor 41P into the inorganic matrix 41 has been described, the present invention is not limited to this. For example, the conversion of the precursor 41P into the inorganic matrix 41 may be performed by irradiating the applied quantum dot dispersion liquid 50 with light. In this case, the light irradiated onto the quantum dot dispersion liquid 50 may have a wavelength of 200 nm or more and 450 nm or less, and may have an intensity of 10 mJ / cm. ２ More than 1000mJ / cm ２ The quantum dot dispersion 50 may be irradiated with light for one minute or more and for 24 hours or less. By irradiating the quantum dot dispersion 50 with light, the precursor 41P is converted into the inorganic matrix 41, which reduces thermal degradation of each layer on the substrate 3 in step S4.

[0068] In step S4, the solvent 51 contained in the applied quantum dot dispersion 50 volatilizes, and the precursor 41P is converted into the inorganic matrix 41, thereby filling the spaces between the quantum dots 40 with the inorganic matrix 41. As a result, the light-emitting layer 24 is formed on the hole-transport layer 23, as shown in the schematic cross-sectional side view 703 of FIG.

[0069] <Display Device Manufacturing Method: Formation of Electron Transport Layer: Preparation of Nanoparticle Dispersion> Next, the electron transport layer 25 is formed on the light-emitting layer 24. The method for forming the electron transport layer 25 according to this embodiment will be described in detail with reference to Figs. 8 and 9. Fig. 8 is a flowchart of the method for forming the electron transport layer 25 according to this embodiment. Fig. 9 is a schematic process chart for explaining the method for forming the electron transport layer 25 according to this embodiment.

[0070] In the method for forming the electron transport layer 25, the nanoparticles 30 are first synthesized (step S5). The nanoparticles 30 may be synthesized, for example, by mixing an alkaline aqueous solution with a metal salt to obtain a precipitate, followed by centrifuging, drying, and baking the precipitate. The nanoparticles 30 may then be washed by dispersing the nanoparticles 30 in ethanol, adding ethyl acetate to the ethanol to form a precipitate, and centrifuging the precipitate.

[0071] Next, the nanoparticles 30, the precursor of the metal sulfide 31, and the halide 32 are dispersed in a solvent (step S6). As a result, in step S6, a nanoparticle dispersion 52 is prepared, which is a dispersion in which the nanoparticles 30, the precursor 31P, and the halide 32 are dispersed, as shown in the schematic diagram 901 of FIG. 9. The nanoparticle dispersion 52 is prepared, for example, by dispersing the nanoparticles 30, the precursor 31P of the metal sulfide 31, and the halide 32 in a solvent 53. The solvent 53 may be a nonpolar solvent such as octane, or a polar solvent such as N,N-dimethylformamide (DMF).

[0072] The precursor 31P contains a material that is converted into the metal sulfide 31 by a process described later. By adjusting the concentration ratio of the nanoparticles 30 to the precursor 31P in the nanoparticle dispersion 52, it is possible to adjust the volume ratio of the nanoparticles 30 to the metal sulfide 31 in the formed electron transport layer 25. Therefore, by adjusting the concentration ratio of the nanoparticles 30 to the precursor 31P in the nanoparticle dispersion 52, it is possible to adjust the concentration ratio of the metal oxide to the metal sulfide 31 in the formed electron transport layer 25.

[0073] Precursor 31P may include, for example, an alkyl xanthogenate. Halide 32 may be zinc chloride, and halide 32 may also function as a catalyst in the conversion of precursor 31P to metal sulfide 31, which will be described later. The alkyl xanthogenate contained in precursor 31P may be represented by the chemical formula described above, for example, or may be the same as the alkyl xanthogenate contained in precursor 41P.

[0074] In this embodiment, an example has been described in which the halide 32 is added to the solvent 53 in step S6, in other words, in the preparation of the nanoparticle dispersion 52, but this is not limiting. For example, in this embodiment, in step S5, in other words, in the synthesis process of the nanoparticles 30, the halide 32 may be added to the alkaline aqueous solution before obtaining a precipitate containing the nanoparticles 30. This makes it possible to more efficiently modify the outermost surfaces of the nanoparticles 30 with the halide 32.

[0075] When the metal sulfide 31 includes ZnS, examples of the sulfur source for the precursor 31P include thiourea, dimethylthiourea, thioacetamide, tertiary alkyl thiol, and zinc alkyl xanthogenate. In particular, the precursor 31P may include zinc alkyl xanthogenate. In this case, the precursor 31P is stable at room temperature and can be easily converted to the metal sulfide 31 by the method described below. Therefore, the precursor 31P containing zinc alkyl xanthogenate allows for more efficient or simpler conversion of the precursor 31P, as described below. Furthermore, by adjusting the number of carbon atoms in the alkyl group of the zinc alkyl xanthogenate, the polarity of the solvent 53 in which the precursor 31P can be dispersed can be changed. In particular, when the solvent 53 is a nonpolar solvent, the alkyl group of the zinc alkyl xanthogenate contained in the precursor 31P may have 8 or more carbon atoms to improve the dispersibility of the precursor 31P in the solvent 53.

[0076] In step S6, the nanoparticle dispersion 52 may be stirred to coordinate the precursor 31P to the outermost peripheral surface of the nanoparticles 30. In this case, the nanoparticles 30 in the nanoparticle dispersion 52 may be modified with an alkyl xanthogenate. This improves the dispersibility of the nanoparticles 30 in the nanoparticle dispersion 52 in step S6. Alternatively, the nanoparticles 30 in the nanoparticle dispersion 52 may be modified with an alkyl xanthogenate and a halide 32. This improves the dispersibility of the nanoparticles 30 in the nanoparticle dispersion 52 and also compensates for defects in the outermost peripheral surface of the nanoparticles 30 with the halogen atoms of the halide 32 in step S6.

[0077] If it is confirmed that the metal sulfide 31 is located within 1 nm from the outer peripheral surface of the nanoparticle 30 in the formed electron transport layer 25, it may be considered that the alkyl xanthogenate modified the nanoparticle 30 in the nanoparticle dispersion 52 in step S6. If it is confirmed that the halide 32 is located within 1 nm from the outer peripheral surface of the nanoparticle 30 in the formed electron transport layer 25, it may be considered that the halide 32 modified the nanoparticle 30 in the nanoparticle dispersion 52 in step S6.

[0078] <Display Device Manufacturing Method: Formation of Electron Transport Layer: Coating and Deposition of Electron Transport Layer> Next, the nanoparticle dispersion 52 is applied (step S7). In particular, in this embodiment, as shown in the schematic cross-sectional side view 902 of FIG. 9 , the nanoparticle dispersion 52 is applied onto the previously formed light-emitting layer 24. In other words, in step S7, each layer from the substrate 3 to the light-emitting layer 24 is regarded as a substrate, and the nanoparticle dispersion 52 is applied to the substrate. The application of the nanoparticle dispersion 52 may be performed by a coating method including a conventionally known method such as spin coating.

[0079] Next, the applied nanoparticle dispersion liquid 52 is heated (step S8). The applied nanoparticle dispersion liquid 52 may be heated by the same method as in step S4. In other words, for the same reasons as described above, the heating temperature in step S8 may be 60°C or higher and 300°C or lower, and more preferably 110°C or higher and 200°C or lower. This converts the precursor 31P contained in the applied nanoparticle dispersion liquid 52 into metal sulfide 31.

[0080] Alternatively, the conversion of the precursor 31P to the metal sulfide 31 may be performed by irradiating the applied nanoparticle dispersion 52 with light. The irradiation of the nanoparticle dispersion 52 with light may be performed in the same manner as the irradiation of the quantum dot dispersion 50 described above. By irradiating the nanoparticle dispersion 52 with light to convert the precursor 31P to the metal sulfide 31, it is possible to reduce thermal degradation of each layer on the substrate 3 in step S8.

[0081] In step S8, the solvent 53 contained in the applied nanoparticle dispersion liquid 52 volatilizes, and the precursor 31P is converted into the metal sulfide 31, thereby filling the spaces between the nanoparticles 30 with the metal sulfide 31. As a result, an electron transport layer 25 is formed on the light-emitting layer 24, as shown in the schematic cross-sectional side view 903 of FIG.

[0082] <Display Device Manufacturing Method: After Cathode Formation> Next, the cathode 26 is formed on the electron transport layer 25. The cathode 26 may be formed by, for example, forming a thin film of the above-mentioned metal material by vacuum deposition, sputtering, or the like, so as to be common to a plurality of sub-pixels. In this way, the light-emitting element 2 is formed on the substrate 3, and the manufacturing method of the display device 1 is completed.

[0083] According to the above-described method, it is possible to form a light-emitting element 2 on the substrate 3, which reduces an increase in driving voltage while reducing aggregation of the nanoparticles 30 in the electron transport layer 25. In particular, according to this embodiment, the electron transport layer 25 is formed by converting the precursor 31P in the nanoparticle dispersion 52 applied to the light-emitting layer 24 into the metal sulfide 31. Therefore, according to the above-described method, it is possible to form the electron transport layer 25 containing the metal sulfide 31 that fills the spaces between the plurality of nanoparticles 30 by a simpler method, thereby realizing a reduction in cost or a shortened takt time in forming the light-emitting element 2.

[0084] [Embodiment 2] <Light-emitting element with reversed configuration> Figure 10 is a schematic side cross-sectional view of a display device 1 according to this embodiment. The display device 1 according to this embodiment has the same configuration as the display device 1 according to the previous embodiment, except for the stacking order of the layers of the light-emitting element 2 included therein. The light-emitting element 2 according to this embodiment includes, in order from the substrate 3 side, a cathode 26, an electron transport layer 25, a light-emitting layer 24, a hole transport layer 23, a hole injection layer 22, and an anode 21. In other words, in the light-emitting element 2 according to this embodiment, the cathode 26 is located closer to the substrate 3 than the light-emitting layer 24. The layers of the light-emitting element 2 according to this embodiment have the same configuration as the layers of the light-emitting element 2 according to the previous embodiment. However, in this embodiment, the cathode 26 may be formed in an island shape for each sub-pixel, and the anode 21 may be formed in common to multiple sub-pixels.

[0085] Therefore, in the display device 1 of this embodiment, a portion of the light from the light-emitting layer 24 of each light-emitting element 2 is reflected by the cathode 26 located on the substrate 3 side of the light-emitting layer 24, and the light from the light-emitting layer 24 is extracted from the anode 21 side, which is on the opposite side of the substrate 3 from the light-emitting layer 24.

[0086] The electron transport layer 25 according to this embodiment has the same configuration as the electron transport layer 25 according to the previous embodiment, in other words, it contains nanoparticles 30 containing a metal oxide and metal sulfide 31 filling the spaces between at least two nanoparticles 30. Therefore, for the same reasons as those described in the previous embodiment, the light-emitting element 2 according to this embodiment reduces the aggregation of the nanoparticles 30 in the electron transport layer 25 while reducing an increase in the overall driving voltage of the light-emitting element 2.

[0087] Furthermore, in the display device 1 according to this embodiment, light from each light-emitting element 2 is extracted from the side opposite to the substrate 3. Therefore, the display device 1 according to this embodiment can efficiently extract light from each light-emitting element 2 to the outside without needing to extract light from each light-emitting element 2 between the pixel circuits PC or to construct the pixel circuits PC from a light-transmitting material.

[0088] Therefore, the display device 1 according to this embodiment improves the light extraction efficiency from each sub-pixel while simplifying the configuration of the substrate 3, etc. Alternatively, the display device 1 according to this embodiment increases the light-emitting area of ​​each light-emitting element 2 in a planar view. As a result, the display device 1 according to this embodiment can reduce the voltage that needs to be applied to each light-emitting element 2 to obtain a desired brightness, thereby achieving power saving or a longer lifespan.

[0089] The display device 1 according to this embodiment can be manufactured by the same method as the method for manufacturing the display device 1 according to the previous embodiment, except that the order of forming the layers of the light-emitting elements 2 is reversed. Therefore, in the method for manufacturing the display device 1 according to this embodiment, the light-emitting layer 24 is not formed on the substrate 3 when the electron transport layer 25 is formed. Therefore, in the method for manufacturing the display device 1 according to this embodiment, the light-emitting layer 24 is not heated in the heating step for forming the electron transport layer 25. Therefore, the display device 1 according to this embodiment reduces deterioration of the light-emitting layer 24 during the manufacturing process, thereby achieving improved luminous efficiency or longer life of each light-emitting element 2.

[0090] 11 is a schematic side cross-sectional view of a display device 1 according to this embodiment. The display device 1 according to this embodiment has the same configuration as the display device 1 according to embodiment 1, except for the materials used for the anode 21 and the cathode 26 of the light-emitting element 2 included therein.

[0091] The anode 21 according to this embodiment may contain a metal material with high reflectivity for visible light. The anode 21 may contain, for example, Al, Ag, Cu, or Au, or may contain an alloy of the above metals. The cathode 26 according to this embodiment may contain an oxide conductor that is both conductive and translucent. The cathode 26 may contain, for example, ITO, or InZnO, SnO ２ , or FTO, etc. Therefore, the anode 21 according to this embodiment is a reflective electrode that reflects visible light including at least the light emitted by the light-emitting layer 24, and the cathode 26 according to this embodiment is a transparent electrode that transmits visible light including at least the light emitted by the light-emitting layer 24.

[0092] The electron transport layer 25 according to this embodiment also has the same configuration as the electron transport layer 25 according to each of the above-described embodiments, in other words, it contains nanoparticles 30 containing a metal oxide and metal sulfide 31 filling the spaces between at least two nanoparticles 30. Therefore, for the same reasons as those described above, the light-emitting element 2 according to this embodiment reduces the aggregation of the nanoparticles 30 in the electron transport layer 25 while reducing an increase in the overall driving voltage of the light-emitting element 2.

[0093] Furthermore, in the display device 1 according to this embodiment, light from each light-emitting element 2 is extracted from the side opposite to the substrate 3. Therefore, for the same reasons as those described in the previous embodiment, the display device 1 according to this embodiment can reduce the voltage that needs to be applied to each light-emitting element 2 to obtain a predetermined brightness, thereby achieving power saving or a longer lifespan. The display device 1 according to this embodiment can be manufactured by the same method as the display device 1 according to embodiment 1, except that the constituent materials of the anode 21 and the cathode 26 are changed.

[0094] [Embodiment 4] <Bottom-emission type light-emitting element having an inverted light-emitting element> Figure 12 is a schematic side cross-sectional view of a display device 1 according to this embodiment. The display device 1 according to this embodiment has the same configuration as the display device 1 according to the previous embodiment, except for the stacking order of the layers of the light-emitting element 2 included therein. The light-emitting element 2 according to this embodiment includes, in order from the substrate 3 side, a cathode 26, an electron transport layer 25, a light-emitting layer 24, a hole transport layer 23, a hole injection layer 22, and an anode 21. In other words, in the light-emitting element 2 according to this embodiment, the cathode 26 is located closer to the substrate 3 than the light-emitting layer 24. Each layer of the light-emitting element 2 according to this embodiment has the same configuration as each layer of the light-emitting element 2 according to the previous embodiment. Therefore, the display device 1 according to this embodiment extracts light from each light-emitting element 2 from the substrate 3 side.

[0095] The electron transport layer 25 according to this embodiment also has the same configuration as the electron transport layer 25 according to each of the above-described embodiments, in other words, it contains nanoparticles 30 containing a metal oxide and metal sulfide 31 filling the spaces between at least two nanoparticles 30. Therefore, for the same reasons as those described above, the light-emitting element 2 according to this embodiment reduces the aggregation of the nanoparticles 30 in the electron transport layer 25 while reducing an increase in the overall driving voltage of the light-emitting element 2.

[0096] The display device 1 according to this embodiment can be manufactured by the same method as that of the display device 1 according to the previous embodiment, except that the order of forming the layers of the light-emitting elements 2 is reversed. Therefore, for the same reasons as those described above, the display device 1 according to this embodiment reduces deterioration of the light-emitting layer 24 during the manufacturing process, thereby achieving improved luminous efficiency or longer life of each light-emitting element 2.

[0097] The present disclosure 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 disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0098] REFERENCE SIGNS LIST 1 Display device 2 Light-emitting element 3 Substrate 21 Anode 24 Light-emitting layer 25 Electron transport layer 26 Cathode 30 Nanoparticles 31 Metal sulfide 32 Halide 40 Quantum dots 41 Inorganic matrix 50 Quantum dot dispersion 52 Nanoparticle dispersion

Claims

1. A light-emitting device comprising: an anode; a cathode facing the anode; a light-emitting layer located between the anode and the cathode; and an electron transport layer located between the cathode and the light-emitting layer, wherein the electron transport layer contains a plurality of nanoparticles containing a metal oxide and a metal sulfide filling the spaces between at least two of the nanoparticles.

2. The light-emitting device according to claim 1, wherein the metal sulfide comprises a continuous film extending along a plane direction perpendicular to the thickness direction of the electron transport layer.

3. The light-emitting element according to claim 1 or 2, wherein the light-emitting layer contains quantum dots, and the electron transport layer is in contact with the light-emitting layer and contains the metal sulfide between at least one of the nanoparticles and at least one of the quantum dots.

4. The light-emitting device according to any one of claims 1 to 3, wherein the electron transport layer is in contact with the cathode and contains the metal sulfide between the cathode and at least one of the nanoparticles.

5. The light-emitting device according to any one of claims 1 to 4, wherein the cathode contains a metal.

6. The light-emitting device according to any one of claims 1 to 4, wherein the cathode comprises an oxide conductor.

7. The light-emitting element according to any one of claims 1 to 6, wherein the metal oxide includes at least one of ZnO, ZnMgO, ZnAlO, and ZnLiO.

8. The light-emitting element according to any one of claims 1 to 7, wherein the metal sulfide includes at least one of ZnS, ZnMgS, and ZnGaS.

9. The light-emitting device according to any one of claims 1 to 8, wherein the electron transport layer contains a halogen atom.

10. The light-emitting device according to claim 9, wherein at least one halogen atom is located within 1 nm from the outer peripheral surface of the nanoparticle.

11. The light-emitting device according to claim 3, wherein the light-emitting layer contains a plurality of the quantum dots and an inorganic matrix filling the spaces between at least two of the quantum dots.

12. A display device comprising a substrate and a plurality of light-emitting elements according to any one of claims 1 to 11 on said substrate.

13. The display device according to claim 12, wherein in at least one of the light-emitting elements, the anode is located closer to the substrate than the light-emitting layer.

14. The display device according to claim 12 or 13, wherein in at least one of the light-emitting elements, the cathode is located closer to the substrate than the light-emitting layer.

15. A method for manufacturing a light-emitting device comprising an anode, a cathode facing the anode, a light-emitting layer located between the anode and the cathode, and an electron transport layer located between the cathode and the light-emitting layer, the method comprising forming the electron transport layer including a plurality of nanoparticles containing a metal oxide and a metal sulfide filling spaces between at least two of the nanoparticles.

16. The method for manufacturing a light-emitting element according to claim 15, wherein the formation of the electron transport layer includes: preparing a dispersion in which a precursor of the metal sulfide and the nanoparticles are dispersed in a solvent; applying the dispersion to a substrate; and converting the precursor in the applied dispersion to the metal sulfide.

17. The method for producing a light-emitting element according to claim 16, wherein the applied dispersion liquid is heated to a temperature of 60°C or higher and 300°C or lower in the converting step.

18. The method for producing a light-emitting device according to claim 16, wherein the conversion comprises irradiating the applied dispersion with light.

19. A method for producing a light-emitting device according to any one of claims 16 to 18, wherein the precursor comprises zinc alkylxanthogenate.

20. A method for producing a light-emitting element according to any one of claims 16 to 18, wherein the nanoparticles in the dispersion are modified with alkyl xanthogenate.

21. The method for producing a light-emitting element according to any one of claims 16 to 18, wherein the nanoparticles in the dispersion are modified with an alkyl xanthogenate and a halide.

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