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

Abstract

A light-emitting element (11) is provided with an anode (21) and a cathode (26) facing each other, and a light-emitting layer (24) positioned between the anode and the cathode. The light-emitting layer may be configured from a plurality of quantum dots (50) and an inorganic filler (51). The inorganic filling material is filled among the plurality of quantum dots, and comprises at least one of a metal sulfide or a metal oxide. In the inorganic filler, the concentration of at least one of sulfur atoms and oxygen atoms gradually decreases in the direction from the anode toward the cathode.

Description

Technical Field

[0001] The present disclosure relates to a light-emitting element and a display device including the light-emitting element. Background Art

[0002] In a light-emitting element having a light-emitting layer containing quantum dots as a light-emitting material, there is a case where carriers are not injected into the quantum dots and an ineffective current is generated through the light-emitting layer. The generation of this ineffective current not only causes a decrease in the luminous efficiency of the light-emitting element, but also causes deterioration of the quantum dots or the peripheral layer of the light-emitting layer, resulting in a problem of reduced reliability of the light-emitting element. Patent Document 1 discloses a light-emitting element in which the light-emitting layer includes a plurality of quantum dots having different shell film thicknesses, thereby improving the confinement of carriers to the quantum dots. Prior Art Documents Patent Documents

[0003] Patent Document 1: Japanese Patent No. 6233417 Gazette Summary of the Invention Technical Problem to be Solved by the Invention

[0004] The light-emitting element disclosed in Patent Document 1 can be said to be configured to suppress an ineffective current by reducing the external outflow of carriers injected into the quantum dots to the outside of the quantum dots. Therefore, in the light-emitting element disclosed in Patent Document 1, it is difficult to reduce the ineffective current flowing between the quantum dots. Technical Solution for Solving the Technical Problem

[0005] A light-emitting element according to an aspect of the present invention includes: an anode; a cathode; and a light-emitting layer located between the anode and the cathode, the light-emitting layer having a plurality of quantum dots and an inorganic filler material, the inorganic filler material filling between the plurality of quantum dots, including at least one of a metal sulfide or a metal oxide, and in the inorganic filler material, the concentration of at least one of sulfur atoms and oxygen atoms becomes lower in the direction from the anode to the cathode.

[0006] A light-emitting element according to another aspect of the present invention includes: an anode; a cathode; and a light-emitting layer located between the anode and the cathode, the light-emitting layer having a plurality of quantum dots and an inorganic filler material, the inorganic filler material filling between the plurality of quantum dots, including at least one of a metal sulfide or a metal oxide, and in the inorganic filler material, a portion on the cathode side has a concentration of at least one of sulfur atoms and oxygen atoms lower than that on the anode side.

[0007] Another aspect of the present invention relates to a light-emitting element including: an anode; a cathode; and a light-emitting layer disposed between the anode and the cathode, the light-emitting layer having a plurality of quantum dots and an inorganic filler material, the inorganic filler material filling between the plurality of quantum dots and including at least one of metal sulfide or metal oxide, and in the inorganic filler material, the atomic defect density of at least one of sulfur atoms and oxygen atoms becomes higher in the direction from the anode to the cathode.

[0008] Another aspect of the present invention relates to a light-emitting element including: an anode; a cathode; and a light-emitting layer disposed between the anode and the cathode, the light-emitting layer including a plurality of quantum dots and an inorganic filler material, the inorganic filler material including a chalcogenide and filling between the plurality of quantum dots, and in the inorganic filler material, the atomic concentration of the chalcogen element becomes lower in the direction from the anode to the cathode.

[0009] Another aspect of the present invention relates to a light-emitting element including: an anode; a cathode; and a light-emitting layer disposed between the anode and the cathode, the light-emitting layer having a plurality of quantum dots and an inorganic filler material, the inorganic filler material filling between the plurality of quantum dots and including a ternary compound semiconductor having a metal atom, the inorganic filler material having a concentration gradient of the metal atom in the direction from the anode toward the cathode, and the band gap of the inorganic filler material becoming smaller in the direction from the anode to the cathode.

[0010] Another aspect of the present invention relates to a method for manufacturing a light-emitting element, the light-emitting element including: an anode; a cathode; and a light-emitting layer disposed between the anode and the cathode, the light-emitting layer having a plurality of quantum dots and an inorganic filler material, the inorganic filler material filling between the plurality of quantum dots and including at least one of metal sulfide or metal oxide, the manufacturing method including: coating a first solution containing the plurality of quantum dots and a first inorganic precursor; forming a first part of the light-emitting layer by heating the first solution at a first temperature to modify the first inorganic precursor into the inorganic filler material; coating a second solution containing a second inorganic precursor on the first part; and forming a second part of the light-emitting layer on the first part by heating the second solution at a second temperature higher than the first temperature to modify the second inorganic precursor into the inorganic filler material.

[0011] Another aspect of the present invention relates to a method for manufacturing a light-emitting element, which includes: an anode; a cathode; a light-emitting layer located between the anode and the cathode, the light-emitting layer having a plurality of quantum dots and an inorganic filler material, the inorganic filler material filling between the plurality of quantum dots and including a ternary compound semiconductor having a metal atom, the inorganic filler material having a concentration gradient of the metal atom in a direction from the anode toward the cathode, and the manufacturing method includes: coating a first solution containing the plurality of quantum dots and a first inorganic precursor having a plurality of metal sources; forming a first part of the light-emitting layer by heating the first solution to modify the first inorganic precursor into the inorganic filler material; coating a second solution on the first part, the second solution containing a second inorganic precursor having a plurality of the metal sources, and the ratio of the metal sources in the second solution being different from that in the first solution; and forming a second part of the light-emitting layer on the first part by heating the second solution to modify the second inorganic precursor into the inorganic filler material, and the bandgap of the inorganic filler material of the second part being smaller than that of the inorganic filler material of the first part. Advantageous Effects

[0012] By suppressing the ineffective current flowing between the quantum dots in the light-emitting layer, the luminous efficiency and reliability of the light-emitting element are improved. Description of the Drawings

[0013] Figure 1 FIG. is a schematic side sectional view of a display device according to Embodiment 1, a schematic sectional view of quantum dots, and a schematic view for showing an inorganic filler material filling between the quantum dots, which are shown side by side. Figure 2 FIG. is a schematic plan view of the display device according to Embodiment 1. Figure 3 FIG. is a flowchart illustrating an example of a method for manufacturing a light-emitting element according to Embodiment 1. Figure 4 FIG. is a schematic side sectional view of the display device according to Embodiment 2. Figure 5 FIG. is a schematic side sectional view of the display device according to Embodiment 3. Figure 6 FIG. is a schematic energy band diagram in each layer of a light-emitting element according to a modified example of Embodiment 3. Figure 7 FIG. is a schematic side sectional view of the display device according to Embodiment 4. Detailed Embodiments

[0014] [Embodiment 1] [Display Device] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In addition, the same components in the respective drawings are denoted by the same reference numerals and their descriptions are omitted. Figure 2 It is a schematic top view of the display device according to the present embodiment.

[0015] The display device 1 is a device that can be used for a display of a television, a smartphone, or the like, for example. The display device 1 includes a display unit DA and a frame unit NA formed on the outer periphery of the display unit DA. The display device 1 performs display in the display unit DA by controlling the light emission of each of a plurality of light-emitting elements described later formed in the display unit DA. In the frame unit NA, a driver or the like for driving each of the plurality of light-emitting elements of the display unit DA may be formed.

[0016] The display unit DA of the display device 1 according to the present embodiment may include a plurality of sub-pixels, and the plurality of sub-pixels include a red sub-pixel, a green sub-pixel, and a blue sub-pixel. A light-emitting element described later is formed in each sub-pixel, and each light-emitting element emits light. Thus, the display device 1 is displayed by a driver or the like formed in the frame unit NA by separately controlling the light emission of the plurality of light-emitting elements of the display unit DA.

[0017] <Light-emitting element: Outline> Refer to Figure 1 The structure of the display unit DA of the display device 1 according to the present embodiment will be described in more detail. Figure 1 They are a schematic side cross-sectional view 101 of the display device 1 according to the present embodiment, a schematic side cross-sectional view 102 of a quantum dot 50 described later, a schematic view 103 for showing an inorganic filler 51 filled between the quantum dots 50, and a schematic view 104. In the present disclosure, the direction from the substrate 20 described later toward the cathode 26 of the display device 1 is referred to as "up", and the opposite direction is referred to as "down".

[0018] The schematic side cross-sectional view 101 is Figure 2 A cross-sectional view taken along the line I-I shown in the figure, and is a view showing a cross-section passing through the light-emitting element 11 when the substrate 20 of the display device 1 according to the present embodiment is viewed from above. In addition, all the schematic side cross-sectional views of the display device in the present invention show the cross-section of the display device corresponding to the cross-section shown in the schematic side cross-sectional view 101.

[0019] The schematic side cross-sectional view 102 is a view showing a cross-section of the quantum dot 50 passing through the approximate center of the quantum dot 50. The schematic views 103 and 104 respectively show two examples of a group P of two quantum dots 50 shown in the schematic side cross-sectional view 101 and the region (space) K therebetween. In particular, the schematic view 103 and the schematic view 104 are views showing a group P1 and a group P2 as examples of a group of the quantum dots 50A and the quantum dots 50B, respectively.

[0020] As shown in the schematic side cross-sectional view 101, the display device 1 includes a light-emitting element 11. In the present embodiment, the light-emitting element 11 includes a substrate 20. For example, in a top view of the display device 1, the substrate 20 is formed at a position overlapping the display portion DA and the frame portion NA. When the display device 1 is viewed from above, it can be regarded that the light-emitting element 11 has a portion overlapping the display portion DA of the substrate 20. In other words, when the display device 1 is viewed from above, the substrate 20 can also be formed across the display portion DA and the frame portion NA. The upper surface of the substrate 20 can also be substantially parallel to the display surface of the display device 1. In other words, the top view of the substrate 20 can also be substantially the same as the top view of the display device 1.

[0021] In addition, the light-emitting element 11 includes 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 this order from the substrate 20 side. In addition, the present embodiment is not limited thereto, and the light-emitting element 11 may also include a cathode, an electron transport layer, a light-emitting layer, a hole transport layer, a hole injection layer, and an anode in this order from the substrate 20 side. Furthermore, the light-emitting element 11 may also include an electron injection layer between the electron transport layer 25 and the cathode 26.

[0022] The light-emitting elements 11 may be respectively formed in the above-mentioned plurality of sub-pixels. In addition, the display device 1 may include a driver (not shown) and the like at a position overlapping the frame portion NA of the substrate 20 when viewed from above. The substrate 20 may also have a pixel circuit (not shown) corresponding to each sub-pixel. The pixel circuit may also be electrically connected to the anode 21 of the light-emitting element 11. The display device 1 may also control the voltage application to the anode 21 of each pixel circuit via the control of the driver and the like, thereby controlling the light emission from each light-emitting element 11.

[0023] <Light-emitting element: Anode and cathode> At least one of the anode 21 and the cathode 26 is a transparent electrode that transmits visible light. As the transparent electrode, for example, ITO, InZnO, SnO 2 , or FTO, etc. may be used. In addition, either the anode 21 or the cathode 26 may also be a reflective electrode. The reflective electrode may also include a metal material with a high reflectivity to visible light. The metal material may be, for example, a single component of Al, Ag, Cu, or Au or an alloy thereof.

[0024] <Light-emitting element: Charge transport layer> The hole injection layer 22 is a layer that injects holes from the anode 21 into the light-emitting layer 24 side. In a light-emitting element including quantum dots or the like, as the material of the hole injection layer 22, an organic or inorganic material having hole-transporting properties used in the past can be used. The hole injection layer 22 may also contain nanoparticles of nickel oxide (NiO). In addition, the hole injection layer 22 may also contain a self-assembled monolayer of [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz). Further, as the material of the hole injection layer 22, for example, a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (abbreviation: "PEDOT:PSS"), CuSCN (copper thiocyanate), etc. can be cited. Moreover, the hole injection layer 22 may also contain powdered NiO (nickel oxide) that is not nanoparticles as a material. In addition, these materials may be used alone, or two or more of them may be appropriately mixed and used.

[0025] The hole transport layer 23 is a layer that transports the holes injected from the anode 21 to the hole injection layer 22 to the light-emitting layer 24. In a light-emitting element including quantum dots or the like, as the material of the hole transport layer 23, an organic or inorganic material having hole-transporting properties used in the past can be used. As the material of the hole transport layer 23, for example, poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (abbreviation: "TFB"), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (abbreviation: "p-TPD"), polyvinylcarbazole (abbreviation: "PVK"), etc. can be cited. These materials may be used alone, or two or more of them may be appropriately mixed or laminated and used.

[0026] The electron transport layer 25 is a layer that transports the electrons injected from the cathode 26 to the light-emitting layer 24. The electron transport layer 25 of the present embodiment has nanoparticles 30 as an electron transport material. In addition, the electron transport layer 25 may also contain a ligand that can coordinate with the nanoparticles 30.

[0027] For example, the nanoparticles 30 may also be zinc oxide (ZnO), titanium oxide (TiO 2 ) or zirconium oxide (ZrO 2 ) nanoparticles doped with at least one of zinc oxide (ZnO), Li, Mg, Al, Ti, Ga, Zr. It should be noted that in the present disclosure, the chemical formulas are representative examples. In addition, in the present invention, the composition ratios described in the chemical formulas may not necessarily be the same as the stoichiometry of the actual compounds as shown in the chemical formulas.

[0028] Note that the electron transport material contained in the electron transport layer 25 is not limited to the nanoparticles 30. For example, as the electron transport material of the electron transport layer 25, in a light-emitting element including quantum dots, etc., an organic or inorganic material having electron transport properties that have been conventionally used can be used. The electron transport material may also contain, for example, 2,2',2''-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzoimidazole) (abbreviation "TPBi"), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (abbreviation "BCP"), 4,7-diphenyl-1,10-phenanthroline (abbreviation "Bphen"), etc. Alternatively, as the electron transport material, the electron transport layer 25 may also contain powdered zinc oxide (ZnO), zinc oxide (ZnO), titanium oxide (TiO 2 ) or zirconium oxide (ZrO 2 ). The powdered zinc oxide (ZnO) may be doped with at least one of Li, Mg, Al, Ti, Ga, and Zr. Regarding the above materials, the electron transport material may contain only one kind, or may appropriately contain two or more kinds.

[0029] <Light-emitting element: Light-emitting layer: Quantum dots> The light-emitting layer 24 sequentially has a first light-emitting layer 40 as a first part and a second light-emitting layer 41 as a second part from the anode 21 side. Both the first light-emitting layer 40 and the second light-emitting layer 41 have a plurality of quantum dots 50 as light-emitting materials. The quantum dots 50, for example, have a core / shell structure. As shown in the schematic cross-sectional view 102, the core / shell structure includes a core 50C and at least one shell 50S covering the periphery of the core 50C. The shell 50S may also have a plurality of layers from the center to the periphery of the core 50C. The first light-emitting layer 40 and the second light-emitting layer 41 may also contain ligands that can coordinate with the outermost shell 50S of the quantum dots 50.

[0030] The core 50C of the quantum dots 50 is injected with holes from the anode 21 and electrons from the cathode 26, and the holes and electrons recombine to emit light through the excitons generated by the recombination. The shell 50S of the quantum dots 50 may also have a function of protecting the core 50C, such as compensating for the defects of the core 50C. In addition, the quantum dots 50 may have various structures known in the art.

[0031] In addition, in the present disclosure, a quantum dot means a point having a maximum width of 100 nm or less. For example, the shape of the quantum dots 50 is not particularly limited as long as it satisfies the above maximum width range, and is not limited to a spherical three-dimensional shape (circular in cross-section). For example, the shape of the quantum dots 50 may be a polygonal cross-sectional shape, a rod-shaped three-dimensional shape, a branched three-dimensional shape, a three-dimensional shape having irregularities on the surface, or a combination of these shapes.

[0032] The quantum dots 50 are typically composed of semiconductors. The semiconductors can have a certain bandgap. The semiconductors can be any materials that can emit light, and in addition, at least the following materials are included. The semiconductors can emit blue, green, and red light respectively. The semiconductors are, for example, at least one selected from the group consisting of II-VI group compounds, III-V group compounds, chalcogenides, and perovskite compounds. In addition, the II-VI group compounds refer to compounds containing group II elements and group VI elements, and the III-V group compounds refer to compounds containing group III elements and group V elements. In addition, the group II elements include the second group elements and the 12th group elements, the group III elements include the 3rd group elements and the 13th group elements, the group V elements include the 5th group elements and the 15th group elements, and the group VI elements can include the 6th group elements and the 16th group elements.

[0033] The II-VI group compounds contain at least one selected from the group consisting of, for example, MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, and HgTe.

[0034] The III-V group compounds include, for example, at least one selected from the group consisting of GaAs, GaP, GaSb, InN, InAs, InP, and InSb.

[0035] The chalcogenides are compounds containing group VIA (16) elements, for example, CdS or CdSe. The chalcogenides can also include these mixed crystals.

[0036] The perovskite compounds have a composition represented by, for example, the general formula CsPbX 3 , CsSnX 3 , CH 3 NH 3 PbX 3 or CH 3 NH 3 SnX 3 The constituent element X includes, for example, at least one selected from the group consisting of C1, Br, and I.

[0037] Here, the numbering of the element groups using Roman numerals is marked based on the old IUPAC (International Union of Pure and Applied Chemistry) method or the old CAS (Chemical Abstracts Service) method, and the numbering of the element groups using Arabic numerals is marked based on the current IUPAC method.

[0038] In this embodiment, the concentration of the quantum dots 50 in the first light-emitting layer 40 is higher than the concentration of the quantum dots 50 in the second light-emitting layer 41. Therefore, in the light-emitting layer 24, in the direction from the anode 21 toward the cathode 26, there is a portion where the concentration of the quantum dots 50 becomes lower, or a portion where it gradually becomes lower, or the entire light-emitting layer 24 may become lower, or may gradually decrease as a whole. Hereinafter, as an example, the case where it gradually decreases through the entire light-emitting layer 24 will be described, but it is not necessarily limited to this structure.

[0039] In the present disclosure, the case where the concentration of the material of each part of the light-emitting layer 24 "gradually decreases" is exemplified, but it is not necessarily limited to this structure. In the present disclosure, as long as there is no contradiction, when the concentration of the material "gradually becomes lower", the case where there is a portion where it becomes lower, the case where there is a portion where it gradually becomes lower, the case where it becomes lower in the entire light-emitting layer 24, or the case where it gradually becomes lower in the entire light-emitting layer 24 is not excluded. In addition, at the boundary between the light-emitting layer 24 and the adjacent layer, the above-mentioned "gradual decrease" in concentration sometimes additionally represents a change in concentration that has nothing to do with the composition of the desired concentration. That is, at the above-mentioned boundary, the change in the concentration of sulfur atoms and oxygen atoms does not necessarily become abrupt, and thus, a region of 1.2 nm or less from the interface may be removed from the light-emitting layer 27.

[0040] In addition, in the present invention, the material concentration in each part of the light-emitting layer 24 is, for example, the area ratio of the material in the cross-section of the light-emitting layer 24. In addition, in the present invention, the fact that the material concentration in each part of the light-emitting layer 24 gradually decreases means that the concentration gradually or stepwise decreases, and it is not limited that the material concentration has a portion with substantially the same concentration. Here, the portion with substantially the same material concentration means that in the cross-sectional observation of the light-emitting layer 24, the difference in the area ratio of the material in a region of 200 nm 2 is within 5%.

[0041] In the cross-section of the first light-emitting layer 40, from the viewpoint of reducing the ineffective current that does not contribute to light emission because carriers are not injected into the quantum dots, the area ratio occupied by the quantum dots 50 may also be 60% or more. In addition, from the viewpoint of improving the protection effect of the inorganic filler 51 described later on the quantum dots 50, the area ratio may be 90% or less. Further, in the cross-section of the second light-emitting layer 41, the area ratio occupied by the quantum dots 50 may be 5% or more, and from the viewpoint of improving the effect of the inorganic filler 51 in protecting the quantum dots 50 from foreign substances on the cathode 26 side described later, it may also be 60% or less.

[0042] <Light-emitting element: Light-emitting layer: Inorganic filler> The light-emitting layer 24 includes an inorganic filler material 51 that fills between multiple quantum dots 50. In other words, the light-emitting layer 24 includes the inorganic filler material 51 as an inorganic matrix material filled between multiple quantum dots 50. The inorganic filler material 51 includes a first inorganic filler material 52 and a second inorganic filler material 53. In particular, the first light-emitting layer 40 contains the first inorganic filler material 52 in the inorganic filler material 51, and the second light-emitting layer 41 contains the second inorganic filler material 53 in the inorganic filler material 51. In other words, the first light-emitting layer 40 includes multiple quantum dots 50 and the first inorganic filler material 52 filled between the multiple quantum dots 50, and the second light-emitting layer 41 includes multiple quantum dots 50 and the second inorganic filler material 53 filled between the multiple quantum dots 50.

[0043] In addition, the fact that the inorganic filler material 51 fills between multiple quantum dots 50 means that, as shown in the schematic diagram 103 of the group P1 in Figure 1 Figure, it is sufficient to fill at least the region K between the quantum dot 50A and the quantum dot 50B. The region K is a region surrounded by two straight lines (common external tangents) tangent to the outer peripheries of the quantum dot 50A and the quantum dot 50B and the outer peripheries facing the quantum dot 50A and the quantum dot 50B in the cross-section of the light-emitting layer 24. Therefore, as shown in the schematic diagram 104 of the group P2 in Figure 1 Figure, even if the quantum dot 50A and the quantum dot 50B approach each other, the region K may exist, and the inorganic filler material 51 fills this region K.

[0044] The fact that the inorganic filler material 51 fills between multiple quantum dots 50 does not necessarily mean that the entire region K between the quantum dot 50A and the quantum dot 50B is composed only of the inorganic filler material 51. For example, in the region K between the quantum dot 50A and the quantum dot 50B, materials such as ligands different from the material of the inorganic filler material 51 may be contained. Specifically, for example, in order to improve the dispersion of the quantum dots 50 in the solution for coating formation, the light-emitting layer 24 may add an organic ligand that coordinates with the outer peripheral surface of the quantum dots 50 in the solution. In this case, in the light-emitting layer 24, from the viewpoint of improving the reliability of the light-emitting layer 24, for example, the weight ratio of the organic ligand to the total weight including the region K may be less than 5%.

[0045] The inorganic filler 51 can fill the regions other than the multiple quantum dots 50 in the light-emitting layer 24. For example, the outer edges (the upper surface and the lower surface) of the light-emitting layer 24 can be covered by the inorganic filler 51. Additionally, it can be configured such that the inorganic filler 51 exists at the outer edge of the light-emitting layer 24 while the quantum dots 50 are located at positions away from the outer edge. The outer edge of the light-emitting layer 24 does not have to be formed only by the inorganic filler 51, and a part of the quantum dots 50 can also protrude from the inorganic filler 51. The inorganic filler 51 can refer to the part in the light-emitting layer 24 excluding the multiple quantum dots 50.

[0046] The inorganic filler 51 can also contain multiple quantum dots 50. The inorganic filler 51 can also be formed to fill the spaces formed between the multiple quantum dots 50. The multiple quantum dots 50 can also be embedded in the inorganic filler 51 at intervals.

[0047] The inorganic filler 51 can also include a continuous film having an area of 1000 nm 2 or more in the plane direction orthogonal to the film thickness direction. The continuous film can be a film that cannot be separated by materials other than the material constituting the continuous film on a single plane. The continuous film can be an integral film-like structure that is continuously connected through chemical bonding of the inorganic filler 51 without interruption.

[0048] The concentration of the inorganic filler 51 in the light-emitting layer 24 is, for example, the area ratio of the inorganic filler 51 in the cross-section of the light-emitting layer 24. In cross-sectional observation, this concentration can be 10% or more and 90% or less, or can be 30% or more and 70% or less. This concentration can be measured, for example, based on the area ratio of the image obtained through cross-sectional observation. When the quantum dot 50 has a structure with a core 50C and a shell 50S, the concentration of the shell 50S can be 1% or more and 50% or less. The ratios of the core 50C, the shell 50S, and the inorganic filler 51 can be appropriately adjusted to a total of 100% or less.

[0049] In the light-emitting layer 24, the outermost shell 50S of the quantum dot 50 and the inorganic filler 51 can also contain the same material. In this case, the lattice mismatch at the interface between the shell 50S and the inorganic filler 51 is reduced, and defects such as dangling bonds at this interface are reduced. Therefore, with the above configuration, the injection efficiency of carriers into the quantum dot 50 is improved. Additionally, with the above configuration, a decrease in the protection effect of the quantum dot 50 due to defects at this interface is suppressed, and inactivation of excitons in the quantum dot 50 can be suppressed, thereby improving the reliability of the light-emitting layer 24 and the luminous efficiency of the light-emitting element 11.

[0050] In particular, the outermost shell 50S of the quantum dot 50 and the inorganic filler 51 may also be made of the same material. In this case, the outermost shell 50S of the quantum dot 50 and the inorganic filler 51 can be distinguished by confirming the difference in crystallinity. For example, in the cross-sectional observation of the light-emitting layer 24, in the case of parts having the same composition but different crystallinities, the part with higher crystallinity can be regarded as the shell 50S, and the other part can be regarded as the inorganic filler 51. In the case where the shell 50S and the inorganic filler 51 cannot be distinguished, the shell 50S can also be regarded as a part of the inorganic filler 51.

[0051] The light-emitting layer 24 may also be composed of a plurality of quantum dots 50 and inorganic fillers 51. When analyzing the light-emitting layer 24, the intensity of carbon element detected by the chain structure can be below the noise level. In addition, the proportion of carbon detected from the light-emitting layer 24 can be 5% or less, or 1% or less, or may not be detected. As is well known, when the quantum dot 50 coordinated with an organic ligand is used in the light-emitting layer 24, with long-term driving, sometimes the carbon chain of the organic ligand decomposes, and the organic ligand itself detaches from the quantum dot, etc. In this case, the quantum dot 50 deteriorates, and sometimes the brightness decreases. As in the present disclosure, by filling the quantum dot 50 into the inorganic filler 51, the quantum dot 50 can be protected without using an organic ligand. Therefore, the display device 1 according to the present embodiment can achieve high reliability, in other words, can achieve suppression of brightness reduction during long-term driving of the light-emitting element 11.

[0052] The inorganic filler 51 contains at least one of a metal sulfide or a metal oxide. The metal sulfide can be, for example, zinc sulfide (ZnS), zinc magnesium sulfide (Zn x Mg 1-x S(0 < x < 1)), gallium sulfide (GaS, Ga 2 S 3 ), zinc tellurium sulfide (Zn x Te 1-x S(0 < x < 1)), magnesium sulfide (MgS), zinc gallium tetrasulfide (ZnGa 2 S 4 ), magnesium gallium tetrasulfide (MgGa 2 S 4 ). The metal oxide can be zinc oxide (ZnO), titanium oxide (TiO 2 ), tin oxide (SnO 2 ), tungsten oxide (WO 3 ), zirconium oxide (ZrO 2 ). The constituent material of the inorganic filler 51 preferably has a wider bandgap than the constituent material of the quantum dot 50 (for example, the material of the core 50C or the shell 50S).

[0053] In addition, the inorganic filler 51 may include a chalcogenide containing a metal sulfide or a metal oxide. In other words, the inorganic filler 51 may include a compound containing a Group VIA (16) element.

[0054] The first inorganic filler 52 and the second inorganic filler 53 may also be made of inorganic materials having the same composition. Thereby, the lattice mismatch between the first inorganic filler 52 and the second inorganic filler 53 is reduced. Therefore, according to the above configuration, the light-emitting element 11 reduces defects such as dangling bonds at the boundary between the first light-emitting layer 40 and the second light-emitting layer 41, and further improves the reliability of the light-emitting layer 24 and the light-emitting efficiency of the light-emitting element 11. In addition, in the present invention, materials having the same composition do not mean being composed of exactly the same materials. For example, they may also have a substitution or defect of 5% or less of atoms.

[0055] Here, at each position when the substrate 20 is viewed from above, a first plane connecting each quantum dot 50 closest to the cathode 26 side of the first light-emitting layer 40 and a second plane connecting each quantum dot 50 closest to the anode 21 side of the second light-emitting layer 41 are defined. When the first inorganic filler 52 and the second inorganic filler 53 are made of inorganic materials having the same composition, the interface between the first light-emitting layer 40 and the second light-emitting layer 41 may also be located between the first plane and the second plane. In addition, the light-emitting element 11 may also include a layer containing the first inorganic filler 52 and the second inorganic filler 53 and not containing the quantum dots 50 between the first plane and the second plane.

[0056] In the present embodiment, the boundary between the light-emitting layer 24 and the electron transport layer 25 can also be confirmed by observing the cross-section passing through the light-emitting layer 24 and the electron transport layer 25 and confirming the concentration of sulfur atoms or oxygen atoms at each position of the cross-section. For example, in this cross-section, a portion where the concentration of sulfur atoms or oxygen atoms is 25% or more can be set as the light-emitting layer 24, and a portion less than 25% can be regarded as the electron transport layer 25, and the boundary between the light-emitting layer 24 and the electron transport layer 25 can be confirmed. Alternatively, a portion where the concentration of sulfur atoms or oxygen atoms in this cross-section is reduced by 25% or more can also be regarded as the boundary between the light-emitting layer 24 and the electron transport layer 25. In addition, not only sulfur atoms and oxygen atoms, when there are atoms with a high concentration only in one of the light-emitting layer 24 and the electron transport layer 25, a portion where the concentration of the atom changes by 25% or more can also be regarded as the boundary between the light-emitting layer 24 and the electron transport layer 25. Therefore, as long as the above conditions are satisfied, a portion where the quantum dots 50 are not confirmed nearby can also be regarded as a part of the light-emitting layer 24. In addition, at the interface between the light-emitting layer 24 and the electron transport layer 25, the change in the concentration of sulfur atoms and oxygen atoms does not necessarily become sharp. Therefore, from the above-defined interface to the anode 21 side, a region of 1.2 nm or less can be removed from the light-emitting layer 24, or can also be included in the electron transport layer 25.

[0057] <Consideration of the density of free electrons in inorganic filler materials> When the inorganic filler material 51 contains a metal sulfide, the concentration of sulfur atoms in the first inorganic filler material 52 is higher than the concentration of sulfur atoms in the second inorganic filler material 53. Further, when the inorganic filler material 51 contains a metal oxide, the concentration of oxygen atoms in the first inorganic filler material 52 is higher than the concentration of oxygen atoms in the second inorganic filler material 53. Therefore, in the inorganic filler material 51, the concentration of at least one of sulfur atoms and oxygen atoms gradually decreases in the direction from the anode 21 toward the cathode 26. Further, when the inorganic filler material 51 contains a chalcogenide, in the inorganic filler material 51, the concentration of atoms of the chalcogen element contained in the chalcogenide gradually or stepwise decreases in the direction from the anode 21 toward the cathode 26.

[0058] In particular, when the inorganic filler material 51 contains a metal sulfide, the density of atomic defects of sulfur atoms in the first inorganic filler material 52 is lower than the density of atomic defects of sulfur atoms in the second inorganic filler material 53. Further, when the inorganic filler material 51 contains a metal oxide, the density of atomic defects of oxygen atoms in the first inorganic filler material 52 is lower than the density of atomic defects of oxygen atoms in the second inorganic filler material 53. Therefore, in the inorganic filler material 51, the density of atomic defects of at least one of sulfur atoms and oxygen atoms gradually increases in the direction from the anode 21 toward the cathode 26. The concentration difference of sulfur atoms or oxygen atoms at each position in the direction from the anode 21 toward the cathode 26 of the inorganic filler material 51 may also correspond to the density difference of defects of sulfur atoms or oxygen atoms in the inorganic filler material 51 at each position.

[0059] Further, when the inorganic filler material 51 contains a chalcogenide, in the inorganic filler material 51, the concentration of atomic defects gradually or stepwise increases for the atoms of the chalcogen element contained in the chalcogenide in the direction from the anode 21 to the cathode 26. In other words, in the inorganic filler material (inorganic matrix material) 51, the atomic concentration of the chalcogen element gradually or stepwise decreases in the direction from the anode 21 toward the cathode 26. Hereinafter, in the present disclosure, when the inorganic filler material 51 contains a chalcogenide, the metal sulfide and metal oxide of the inorganic filler material 51 may be respectively replaced with a chalcogenide, and the sulfur atoms and oxygen atoms of the inorganic filler material 51 may be replaced with atoms of a chalcogen element.

[0060] The concentration of sulfur atoms or oxygen atoms in the inorganic filler 51, particularly the density of atomic defects of sulfur atoms or oxygen atoms, is related to the density of free electrons at each position of the inorganic filler 51. This is because the concentration of free electrons possessed by the inorganic filler 51 changes according to the concentration of sulfur atoms or oxygen atoms in the inorganic filler 51. In particular, when defects of sulfur atoms or oxygen atoms are generated in the inorganic filler 51 and the defects are activated, two free electrons are generated per defect near the defects.

[0061] Here, in order to consider the density of free electrons on the hole transport layer 23 side of the light-emitting layer 24, the hole density at the interface between the hole transport layer 23 and the light-emitting layer 24 is considered. For example, when the hole transport layer 23 uses an organic material as the hole transport material, the current flowing in the hole transport layer 23 becomes a space-charge-limited current. Therefore, the hole density p near the interface between the hole transport layer 23 and the light-emitting layer 24 is expressed by the following mathematical formula.

[0062] [Equation 1] In the above formula, e is the elementary charge quantity, ε 0 is the permittivity of vacuum, ε r is the relative permittivity of the hole transport layer 23, J is the current density of the hole transport layer 23, L is the film thickness of the hole transport layer 23, and μ is the hole mobility of the hole transport layer 23. In addition, in the present invention, the vicinity of the interface means a region within 1.2 nm in the film thickness direction from the interface.

[0063] For example, when driving the light-emitting element 11, the current density J flowing in the hole transport layer 23 is 10 m / cm 2 . In addition, the relative permittivity ε r of the hole transport layer 23 is set to 3.5, the film thickness L is set to 30 nm, and the hole mobility μ is set to 10 -4 cm 2 / Vs. In this case, according to the above formula, the hole density p near the interface between the hole transport layer 23 and the light-emitting layer 24 is 1.4×10 16 cm -3 .

[0064] When there are free electrons near the interface between the hole transport layer 23 and the light-emitting layer 24, even when holes are injected from the hole transport layer 23 into the light-emitting layer 24, there are cases where recombination occurs with free electrons outside the quantum dots 50 near the interface but does not reach the light-emitting process. On the other hand, when the hole density near the interface between the hole transport layer 23 and the light-emitting layer 24 exceeds the density of free electrons near this interface, even when electron-hole recombination occurs at the interface, remaining holes are generated and are easily injected into the quantum dots 50. Therefore, from the viewpoint of improving the efficiency of hole injection from the hole transport layer 23 into the light-emitting layer 24, it is required that the hole density near the interface between the hole transport layer 23 and the light-emitting layer 24 be higher than the density of free electrons near this interface.

[0065] Therefore, in order to improve the efficiency of hole injection from the hole transport layer 23 into the light-emitting layer 24, in the region within 1.2 nm in the film thickness direction from the end face on the anode 21 side of the light-emitting layer 24, the density of free electrons in the inorganic filler 51 can be 1×10 16 cm -3 or less. In other words, in the region within 1.2 nm in the film thickness direction of the first light-emitting layer 40 starting from the interface between the hole transport layer 23 and the first light-emitting layer 40, the density of free electrons in the first inorganic filler 52 in the first light-emitting layer 40 can be 1×10 16 cm -3 or less.

[0066] Here, when the inorganic filler 51 has a polycrystalline or amorphous structure, the activation rate of the inorganic filler 51 is not high and can be considered to be about 1%. Therefore, the activation rate of the inorganic filler 51 in the light-emitting layer 24 is set to 1%. In other words, one out of every 100 defects of sulfur atoms or oxygen atoms in the inorganic filler 51 is activated, generating two free electrons. At this time, in the region within 1.2 nm in the film thickness direction starting from the end face on the anode 21 side of the light-emitting layer 24, the defect density of sulfur atoms or oxygen atoms in the inorganic filler 51 can be 5×10 17 cm -3 or less. With the above configuration, the density of free electrons in the inorganic filler 51 in this region is 1×10 16 cm -3 or less, and the efficiency of hole injection from the hole transport layer 23 into the light-emitting layer 24 can be improved. In addition, since the density of free electrons in the inorganic filler 51 is small, the resistivity of the inorganic filler 51 becomes high. Therefore, as carriers flow through the inorganic filler 51 without being injected into the quantum dots 50, the ineffective current generated that does not contribute to light emission is reduced. Therefore, with the above configuration, the luminous efficiency of the light-emitting element 11 is improved.

[0067] The ratio of defects of sulfur atoms or oxygen atoms in the inorganic filler 51 in the above case is studied. If the inorganic filler 51 is composed of zinc sulfide (ZnS), the lattice constant of zinc sulfide is about, and each lattice contains 4 sulfur atoms. Therefore, in the above case, the ratio of defects of sulfur atoms to zinc atoms in the inorganic filler 51 is 2.5×10 -3 % or so.

[0068] Next, the density of free electrons on the electron transport layer 25 side of the light-emitting layer 24 is studied. When free electrons exist near the interface between the electron transport layer 25 and the light-emitting layer 24, when driving the light-emitting element 11, these free electrons move toward the anode 21 side in the light-emitting layer 24. Therefore, when the density of free electrons on the electron transport layer 25 side of the light-emitting layer 24 is high, the ratio of free electrons injected into the quantum dots 50 and flowing between the quantum dots 50 increases. In addition, when the density of atomic defects of the inorganic filler 51 in the light-emitting layer 24 is high, there is a case where the electron mobility in the light-emitting layer 24 decreases, and further the electron transport ability of the light-emitting layer 24 decreases.

[0069] On the other hand, when the density of free electrons near the interface between the electron transport layer 25 and the light-emitting layer 24 is low, the concentration of electrons injected from the electron transport layer 25 decreases, which may lead to an excess of holes in the light-emitting layer 24.

[0070] Therefore, from the viewpoint of suppressing the flow of electrons between the quantum dots 50 and improving the efficiency of injecting electrons from the electron transport layer 25 into the light-emitting layer 24, it is required that the density of free electrons near the interface between the electron transport layer 25 and the light-emitting layer 24 is within a specified range.

[0071] In order to improve the efficiency of electron injection from the electron transport layer 25 into the light-emitting layer 24, it is preferable that the density of free electrons near the interface between the light-emitting layer 24 and the electron transport layer 25 in the light-emitting layer 24 is above the density of free electrons in the electron transport layer 25. For example, when the nanoparticles 30 in the electron transport layer 25 are zinc oxide-based nanoparticles, the density of free electrons in the electron transport layer 25 is 1×10 18 cm -3 or so. Therefore, in order to improve the efficiency of electron injection from the electron transport layer 25 into the light-emitting layer 24, in the region within 1.2 nm in the film thickness direction from the end face on the cathode 26 side of the light-emitting layer 24, the density of free electrons of the inorganic filler 51 can be 1×10 18 cm -3Above. In other words, in the region within 1.2 nm in the film thickness direction of the second light-emitting layer 41 from the interface between the electron transport layer 25 and the second light-emitting layer 41, the density of free electrons of the second inorganic filler material 53 in the second light-emitting layer 41 can be 1×10 18 cm -3 or more.

[0072] Here, similar to the above, the activation rate of the inorganic filler material 51 in the light-emitting layer 24 is set to 1%. At this time, in the region within 1.2 nm in the film thickness direction from the end face on the cathode 26 side of the light-emitting layer 24, the defect density of sulfur atoms or oxygen atoms of the inorganic filler material 51 can be 5×10 19 cm -3 or more. With the above configuration, the density of free electrons of the inorganic filler material 51 in this region is 1×10 18 cm -3 or more, and the efficiency of electron injection from the electron transport layer 25 to the light-emitting layer 24 can be improved.

[0073] On the other hand, in order to reduce the reduction of the electron transport ability of the light-emitting layer 24, the atomic defects of the inorganic filler material 51 in the light-emitting layer 24 near the interface between the electron transport layer 25 and the light-emitting layer 24 may be about 10% or less. If the inorganic filler material 51 is composed of zinc sulfide (ZnS), in order to make the atomic defects of the inorganic filler material 51 10% or less, the value obtained by multiplying the density of atomic defects by may be 0.1 or less. The density of atomic defects satisfying the above conditions is or less, about 2×10 21 cm -3 or less.

[0074] As described above, in order to reduce the reduction of the electron transport ability of the light-emitting layer 24 and improve the efficiency of electron injection from the electron transport layer 25 to the light-emitting layer 24, in the region within 1.2 nm in the film thickness direction from the end face on the cathode 26 side of the light-emitting layer 24, the defect density of sulfur atoms or oxygen atoms of the inorganic filler material 51 can be 2×10 21 cm -3 or less. In other words, in the region within 1.2 nm in the film thickness direction of the second light-emitting layer 41 from the interface between the electron transport layer 25 and the second light-emitting layer 41, the defect density of sulfur atoms or oxygen atoms of the second inorganic filler material 53 in the second light-emitting layer 41 can be 2×10 21 cm -3 or less.

[0075] Similarly, the activation rate of the inorganic filler 51 in the light-emitting layer 24 is set to 1%. In this case, in the region within 1.2 nm in the film thickness direction from the end face on the cathode 26 side of the light-emitting layer 24, the density of free electrons of the inorganic filler 51 can be 4×10 19 cm -3 or less. With the above configuration, the defect density of sulfur atoms or oxygen atoms of the inorganic filler 51 in this region can be 2×10 21 cm -3 or less, and a decrease in the electron transport ability of the light-emitting layer 24 can be reduced.

[0076] In addition, regarding the inorganic filler 51, the density of free electrons in the region within 1.2 nm in the film thickness direction from the end face on the anode 21 side of the light-emitting layer 24 can be one-tenth or less of the density of free electrons in the region within 1.2 nm in the film thickness direction from the end face on the cathode 26 side of the light-emitting layer 24. In other words, the density of free electrons of the first inorganic filler 52 in the first light-emitting layer 40 can also be one-tenth or less of the density of free electrons of the second inorganic filler 53 in the second light-emitting layer 41. In this case, since the efficiency of hole injection and the efficiency of electron injection into the light-emitting layer 24 can be improved bidirectionally, the driving voltage of the light-emitting element 11 can be reduced, and the energy efficiency of the light-emitting layer 24 can be improved. Moreover, the carrier balance in the light-emitting layer 24 can also be adjusted, and the light-emitting efficiency of the light-emitting element 11 is improved.

[0077] <Light-emitting element: Manufacturing method> Refer to Figure 3 , and the manufacturing method of the light-emitting element 11 of the present embodiment will be described. Figure 3 is a flowchart showing the manufacturing method of the light-emitting element 11 of the present embodiment.

[0078] As Figure 3 shown, in the manufacturing method of the light-emitting element 11 of the present embodiment, first, a substrate 20 is prepared (step S1). The substrate 20 may also be a substrate on which a pixel circuit is formed for each sub-pixel on a glass substrate or a thin film substrate, etc. Wires between the driver in the frame portion NA and each pixel circuit may also be formed on the substrate 20.

[0079] Next, an anode 21 is formed on the substrate 20 (step S2). The anode 21 may also be formed by depositing a thin film of a metal material on the substrate 20 using a sputtering method or the like. The anode 21 may be formed to be electrically connected to the pixel circuit, or may be patterned for each sub-pixel. For example, the anode 21 may also be formed by depositing an ITO film with a film thickness of 30 nm on the substrate 20 by a sputtering method.

[0080] Next, a hole injection layer 22 is formed on the anode 21 (step S3). In step S32, for example, a solution in which nickel oxide nanoparticles are dispersed at 15 mg / mL in a solvent obtained by mixing water and 2-methoxyethanol in equal volumes may be coated on the anode 21 by spin coating and fired at 200 degrees. The process may be performed only once, or may be repeated about two to five times. Next, in a nitrogen atmosphere, a solution in which MeO-2PACz is dispersed in an ethanol solvent is coated on the nickel oxide nanoparticle layer by spin coating, and then the solvent may be volatilized by firing. Thus, a laminated structure of a nickel oxide nanoparticle layer and a self-assembled monolayer of MeO-2PACz can be formed to form the hole injection layer 22.

[0081] Next, a hole transport layer 23 is formed on the hole injection layer 22 (step S4). In step S4, in a nitrogen atmosphere, a solution in which poly-TPD is dispersed in a chlorobenzene solvent may be coated on the self-organized monolayer by spin coating, and then the solvent may be volatilized by firing. Thus, a Poly-TPD film with a film thickness of 30 nm can also be formed on the self-assembled monolayer to form the hole transport layer 23. In step S3, a TFB film or a PVK film may be formed instead of the poly-TPD film.

[0082] Next, a light-emitting layer 24 is formed on the hole transport layer 23. In the present embodiment, an example in which after the first light-emitting layer 40 is formed, the second light-emitting layer 41 is formed on the first light-emitting layer 40 to form the light-emitting layer 24 will be described.

[0083] In the formation process of the light-emitting layer 24 according to the present embodiment, first, a first solution synthesized in another process is coated on the hole transport layer 23 by spin coating or the like (step S5). The first solution is a mixed solution containing a plurality of quantum dots 50 and a first inorganic precursor that is a precursor of the first inorganic filler 52. The first inorganic precursor contains a metal source and a sulfur source or an oxygen source of the first inorganic filler 52.

[0084] Next, the first solution coated on the hole transport layer 23 is heated at a first temperature (step S6). For example, the first temperature may also be 150°C. Specifically, in step S6, the first solution coated on the hole transport layer 23 in a 150°C atmosphere may be heated for 30 minutes.

[0085] Thus, while the solvent of the first solution evaporates, the first inorganic precursor in the first solution denatures to form the first inorganic filler 52. Here, the first inorganic precursor in the first solution denatures by heating in step S6, and the first inorganic filler 52 is formed successively around the quantum dots 50 in the first solution. Therefore, through step S6, the first inorganic filler 52 is formed to fill between the plurality of quantum dots 50. Through the above, the first light-emitting layer 40 containing the plurality of quantum dots 50 and the first inorganic filler 52 filling between the quantum dots 50 is formed.

[0086] Next, a second solution synthesized in different processes in advance is coated on the first light-emitting layer 40 by a spin coating method or the like (step S7). The second solution is a mixed solution containing a plurality of quantum dots 50 and a second inorganic precursor as a precursor of the second inorganic filler 53. The second inorganic precursor contains a metal source and a sulfur source or an oxygen source of the second inorganic filler 53. In addition, in the present disclosure, the precursors, that is, the first inorganic precursor and the second inorganic precursor may also include, for example, a zinc source containing zinc carboxylate, a magnesium source containing magnesium carboxylate, a selenium source containing selenourea, or a sulfur source containing thiourea. In addition, the precursor may contain, for example, a metal acetate, a metal nitrate, or a metal halide as a metal source, and at least one of thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N'-dimethylthiourea, tetramethylthiourea, or thioacetamide as a sulfur source. Alternatively, the precursor 36 may also include a metal complex in which thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N'-dimethylthiourea, tetramethylthiourea, or thioacetamide is coordinated to a metal atom.

[0087] It should be noted that the concentration of the quantum dots 50 is lower relative to the concentration of the second inorganic precursor in the second solution than the concentration of the quantum dots 50 relative to the first inorganic precursor in the first solution. Thereby, the coating amount of the second solution in step S8 can be made substantially the same as the coating amount of the first solution in step S6, and the concentration of the quantum dots 50 in the second light-emitting layer 41 formed by the method described later can be made lower than the concentration of the quantum dots 50 in the first light-emitting layer 40.

[0088] Next, the second solution coated on the first light-emitting layer 40 is heated at a second temperature higher than the first temperature (step S8). For example, the second temperature may also be 200 °C. Specifically, in step S8, the second solution coated on the first light-emitting layer 40 may be heated in a 200 °C atmosphere for 30 minutes.

[0089] Thus, while the solvent of the second solution evaporates, the second inorganic precursor in the second solution denatures to form the second inorganic filler 53. Through the above, similarly to the first light-emitting layer 40, the second light-emitting layer 41 is formed, which contains a plurality of quantum dots 50 and the second inorganic filler 53 filling between the quantum dots 50.

[0090] In addition, in steps S6 and S8, a process of heating a solution containing a precursor is included, where the precursor includes a metal source having an inorganic filler 51 and a sulfur source or an oxygen source. Here, due to the heating of the solution, the sulfur source or oxygen source possessed by the precursor in the solution volatilizes together with the solvent. Additionally, the higher the heating temperature of the solution, the more the volatilization amount of the sulfur source or oxygen source tends to increase.

[0091] Here, the heating temperature of the second solution in step S8 is a second temperature, which is higher than the heating temperature of the first solution in step S6, i.e., the first temperature. Therefore, in step S8, the proportion of the sulfur source or oxygen source volatilized from the second solution is higher than the proportion of the sulfur source or oxygen source volatilized from the first solution in step S6.

[0092] Moreover, both the first solution and the second solution heated in steps S6 and S8 contain quantum dots 50. Therefore, in order to improve the dispersibility of the quantum dots 50 in the first solution and the second solution, xanthic acid can also be added to the two solutions as a ligand capable of coordinating with the quantum dots 50.

[0093] Here, as described above, the concentration of the quantum dots 50 in the second solution is lower than the concentration of the quantum dots 50 in the first solution. Therefore, when xanthic acid is added to the first solution and the second solution, the proportion of xanthic acid coordinated with the quantum dots 50 in the second solution is lower than the proportion of xanthic acid coordinated with the quantum dots 50 in the first solution.

[0094] The xanthic acid not coordinated with the quantum dots 50 does not form a coordination bond with the quantum dots 50, so the attraction between them is small. Therefore, compared with the sulfur atoms of the xanthic acid coordinated with the quantum dots 50, the proportion of the sulfur atoms of the xanthic acid not coordinated with the quantum dots 50 volatilizing together with the solvent through heating is higher.

[0095] Therefore, the concentration of sulfur atoms from xanthic acid remaining in the second light-emitting layer 41 is lower than the concentration of sulfur atoms from xanthic acid remaining in the first light-emitting layer 40. Thus, the density of atomic defects of sulfur atoms in the second inorganic filler 53 of the second light-emitting layer 41 is higher than that of the first inorganic filler 52 of the first light-emitting layer 40.

[0096] As described above, the density of atomic defects of sulfur atoms or oxygen atoms in the second inorganic filler 53 formed in step S8 is higher than that of sulfur atoms or oxygen atoms in the first inorganic filler 52 formed in step S6. Therefore, through the above process, a light-emitting layer 24 having the inorganic filler 51 is formed, and in the direction from the anode 21 toward the cathode 26, the density of atomic defects of at least one of sulfur atoms and oxygen atoms gradually increases. In other words, through the above process, a light-emitting layer 24 having the inorganic filler 51 in which the concentration of at least one of sulfur atoms and oxygen atoms gradually decreases in the direction from the anode 21 toward the cathode 26 is formed.

[0097] After the formation of the light-emitting layer 24, an electron transport layer 25 is formed on the light-emitting layer 24 (step S9). In step S9, a solution in which zinc oxide nanoparticles 30 are dispersed in an ethanol solvent may be coated on the light-emitting layer 24 by spin coating or the like in a nitrogen atmosphere, and the solution may be dried to form an electron transport layer 25 having a film thickness of 60 nm. At least one of Li, Mg, Al, Ti, Ga, and Zr may be doped in the zinc oxide nanoparticles 30. In addition, the nanoparticles 30 may be titanium oxide or zirconium oxide nanoparticles.

[0098] Next, a cathode 26 is formed on the electron transport layer 25 (step S10). In step S10, the cathode 26 may be formed by vacuum deposition of a silver thin film having a film thickness of 50 nm. The light-emitting element 11 is manufactured by the above method. After the manufacture of the above-described light-emitting element 11 is completed, the manufacture of the display device 1 may be completed, or after the manufacture of the light-emitting element 11, a sealing layer or the like for sealing or protecting the light-emitting element 11 may be formed.

[0099] <Technical effects of the light-emitting element> The light-emitting element 11 includes a light-emitting layer 24, and the light-emitting layer 24 has a plurality of quantum dots 50 and an inorganic filler 51 filling between the plurality of quantum dots 50. The inorganic filler 51 contains at least one of a metal sulfide and a metal oxide, and in the direction from the anode 21 toward the cathode 26, the concentration of at least one of sulfur atoms and oxygen atoms gradually decreases. In particular, in the inorganic filler 51, in the direction from the anode 21 toward the cathode 26, the defect density of at least one of sulfur atoms and oxygen atoms gradually increases.

[0100] Therefore, in the inorganic filler 51, the density of free electrons becomes higher in the direction from the anode 21 toward the cathode 26. Therefore, for the reasons described above, the light-emitting element 11 can improve the efficiency of hole injection and the efficiency of electron injection into the light-emitting layer 24 in both directions. Thus, the driving voltage of the light-emitting element 11 can be reduced, and the energy efficiency of the light-emitting layer 24 can be improved. Moreover, the carrier balance in the light-emitting layer 24 can also be adjusted, and the light-emitting efficiency of the light-emitting element 11 is improved.

[0101] The concentration of the quantum dots 50 in the second light-emitting layer 41 is lower than the concentration of the quantum dots 50 in the first light-emitting layer 40. Therefore, in the light-emitting layer 24, the concentration of the quantum dots 50 gradually decreases in the direction from the anode 21 toward the cathode 26.

[0102] Generally, the mobility of electrons in a semiconductor is higher than the mobility of holes. Therefore, in the light-emitting layer 24 containing the quantum dots 50, light emission mainly occurs from the quantum dots 50 located on the anode 21 side. Thus, according to the above configuration, in the light-emitting layer 24, since the density of free electrons in the first inorganic filler 52 on the anode 21 side is small, the resistance becomes large. As a result, the light-emitting layer 24 can reduce the ineffective current that does not contribute to light emission and flows in the first inorganic filler 52 because carriers do not enter the quantum dots 50. Therefore, with the above configuration, the light-emitting element 11 can obtain light emission from the quantum dots 50 more effectively. In addition, defects in the inorganic filler 52 are more likely to form on the surface than inside. Therefore, in the above configuration, the average distance between the defects and the quantum dots 50 can be separated. Thus, inactivation of excitons caused by the defects can be suppressed, and the light-emitting efficiency of the light-emitting element 1 can be improved.

[0103] In addition, compared with the first light-emitting layer 40, the second light-emitting layer 41 can effectively increase the thickness of the inorganic filler 51 between the filled quantum dots 50, and can improve the protective effect of the inorganic filler 51 on the quantum dots 50. Therefore, the light-emitting element 11 can more effectively protect the light-emitting layer 24 from the influence of foreign substances such as moisture and oxygen infiltrating from the cathode 26 side, or heat transmitted from the cathode 26 side.

[0104] Specifically, the light-emitting element 11 of the present embodiment includes an anode 21 on the side of the substrate 20. Generally, compared with the layers between the electrodes of the light-emitting element 11, it is difficult for the substrate 20 to be infiltrated by foreign substances such as moisture. Therefore, foreign substances are likely to infiltrate into the light-emitting element 11 from the cathode 26 side, which is the side opposite to the substrate 20 side. Moreover, since the electron transport layer 25 located on the cathode 26 side and closer to the cathode 26 than the light-emitting layer 24 includes nanoparticles 30, foreign substances infiltrating into the light-emitting element 11 from the cathode 26 side can easily reach the light-emitting layer 24 through the spaces between the nanoparticles 30. Therefore, with the above configuration, the light-emitting element 11 can more effectively improve the protective effect of the inorganic filler 51 in the light-emitting layer 24 on the quantum dots 50. Compared with a thin-film substrate, it is difficult for a glass substrate to be infiltrated by foreign substances such as moisture. Therefore, the substrate 20 is preferably a glass substrate.

[0105] The inorganic filler 51 may include a binary compound semiconductor. In this case, it is easy to achieve a density difference in atomic defects of sulfur atoms or oxygen atoms at various positions of the inorganic filler 51 through the difference in heating temperature in the above-described step S6 and step S8. In particular, from the viewpoint of improving the protective effect on the quantum dots 50 and at the same time improving the injection efficiency of carriers into the quantum dots 50, the inorganic filler 51 may contain zinc sulfide.

[0106] [Embodiment 2] [Inorganic filler layer] Refer to Figure 4 The display device 2 according to the present embodiment will be described. Figure 4 FIG. is a schematic side cross-sectional view of the display device 2 according to the present embodiment. The display device 2 according to the present embodiment has the same configuration as the display device 1 according to the previous embodiment, except that it includes a light-emitting element 12 instead of the light-emitting element 11. The light-emitting element 12 has the same configuration as the light-emitting element 11 according to the previous embodiment, except that it includes a light-emitting layer 27 instead of the light-emitting layer 24.

[0107] The light-emitting layer 27 has a first light-emitting layer 40 and a second light-emitting layer 42 in order from the anode 21 side. The first light-emitting layer 40 of the present embodiment has the same structure as the first light-emitting layer 40 of the first embodiment. The second light-emitting layer 42 of the present embodiment is different in configuration from the second light-emitting layer 41 of the above-described embodiment only in that it only has a second inorganic filler 53 and does not have quantum dots 50.

[0108] In other words, the light-emitting layer 27 has a first light-emitting layer 40 as a quantum dot layer, where the first light-emitting layer 40 contains quantum dots 50 and a first inorganic filler 52 as an inorganic filler material 51. In addition, the light-emitting layer 27 has a second light-emitting layer 42 as an inorganic filler layer, and the second light-emitting layer 42 contains a second inorganic filler 53 as the inorganic filler material 51. Here, the second light-emitting layer 42 only has the inorganic filler material 51 among the quantum dots 50 and the inorganic filler material 51. As long as this structure is satisfied, the second light-emitting layer 42 may also have a material different from the quantum dots 50 and the inorganic filler material 51.

[0109] Therefore, in the present embodiment, the light-emitting layer 27 has a plurality of quantum dots 50. In addition, as the inorganic filler material 51, a first inorganic filler 52 and a second inorganic filler 53 are sequentially provided from the anode 21 side. Therefore, in the present embodiment, the inorganic filler material 51 also contains at least one of metal sulfides or metal oxides, and in the direction from the anode 21 toward the cathode 26, the concentration of at least one of sulfur atoms or oxygen atoms gradually decreases. In particular, in the inorganic filler material 51, in the direction from the anode 21 toward the cathode 26, the defect density of at least one of sulfur atoms and oxygen atoms gradually increases.

[0110] With the above configuration, for the same reasons as those described for the light-emitting element 11, the light-emitting element 12 suppresses the movement of electrons injected from the electron transport layer 25 between the quantum dots 50 in the light-emitting layer 27. Therefore, the light-emitting element 12 reduces the reactive current in the light-emitting layer 24 and improves the light-emitting efficiency and reliability.

[0111] In particular, in the present embodiment, the light-emitting layer 27 of the light-emitting element 12 has a second light-emitting layer 42 that does not have quantum dots 50. Therefore, the second light-emitting layer 42 on the cathode 26 side of the light-emitting layer 27 does not have quantum dots 50 that are deteriorated due to foreign substances or the like from the cathode 26 side. In addition, the second light-emitting layer 42 increases the effective film thickness of the second inorganic filler 53 by an amount that does not include the quantum dots 50, thereby increasing the protection effect of the light-emitting layer 27. Moreover, the light-emitting layer 27 transports electrons having a higher mobility than holes from the second light-emitting layer 42 to the first light-emitting layer 40, and obtains light emission from the quantum dots 50 of the first light-emitting layer 40. Therefore, the light-emitting element 12 can more effectively improve the protection effect of the inorganic filler material 51 of the light-emitting layer 24 on the quantum dots 50 and improve the light-emitting efficiency. In addition, the film thickness of the second light-emitting layer 42 may be 1.2 nm or more, or may be 6 nm or more. Thus, since the second light-emitting layer 42 has a film thickness of about two times or more of the unit lattice of the second inorganic filler, the protection effect of the light-emitting layer 27 can be effectively improved.

[0112] When the film thickness of the second light-emitting layer 42 is relatively thick, the driving voltage of the light-emitting element 12 may increase. Therefore, in the present embodiment, in the region within 1.2 nm in the film thickness direction from the end face on the cathode 26 side of the light-emitting layer 27, the density of free electrons of the inorganic filler 51 can be 1×10 18 cm -3 or more. The above structure can sufficiently increase the density of free electrons in this region. Therefore, it is preferable that the light-emitting layer 27 can reduce the resistivity of the inorganic filler 51 in the above region, minimize the increase in the driving voltage of the light-emitting element 12, and increase the protection effect of the quantum dots 50.

[0113] In the present embodiment, the boundary between the light-emitting layer 27 and the electron transport layer 25 can also be confirmed by observing the material composition of each position of the cross-section through the cross-section of the light-emitting layer 27 and the electron transport layer 25. In the present embodiment, for example, the part where the concentration of at least one atom contained in the second inorganic filler 53 is 25% or less can be regarded as the boundary between the light-emitting layer 27 and the electron transport layer 25. Or, the part where the concentration of at least one atom contained in the second inorganic filler 53 is reduced by 25% or more can be regarded as the boundary between the light-emitting layer 27 and the electron transport layer 25. In addition, when a high-concentration atom exists only in one of the second inorganic filler 53 and the electron transport layer 25, the part where the concentration of the atom changes by 25% or more can be regarded as the boundary between the light-emitting layer 27 and the electron transport layer 25. The above confirmation criteria for the boundary are in order of priority as described, in other words, the earlier description takes precedence over the later description.

[0114] In other words, when the light-emitting layer 27 has a part that does not contain quantum dots 50 like the second light-emitting layer 42, it can be regarded that the part where the composition of the second inorganic filler 53 can be confirmed is included in the second light-emitting layer 42 and further included in the light-emitting layer 27.

[0115] The light-emitting element 12 of the present embodiment can also be manufactured by the same method as along the Figure 3 flow chart shown, the manufacturing method of the light-emitting element 11 of the above embodiment, except for the material of the second solution coated on the first light-emitting layer 40 in step S7. In the present embodiment, the second solution contains only the quantum dots 50 and the second inorganic precursor among the second inorganic precursors as the second inorganic filler 53. For example, the second solution may also contain other materials in addition to the quantum dots 50 and the second inorganic precursor. Thus, in step S8, the second light-emitting layer 42 having the second inorganic filler 53 is formed on the first light-emitting layer 40 without the quantum dots 50.

[0116] [Embodiment 3] <Multiple quantum dot layers> Reference Figure 5 The display device 3 of the present embodiment will be described. Figure 5 FIG. 3 is a schematic side cross-sectional view of the display device 3 according to the present embodiment. The display device 3 according to the present embodiment has the same configuration as the display device 2 according to the previous embodiment, except that a light-emitting element 13 is provided instead of the light-emitting element 12. The light-emitting element 13 has the same configuration as the light-emitting element 12 according to the previous embodiment, except that a light-emitting layer 28 is provided instead of the light-emitting layer 27.

[0117] The light-emitting layer 28 sequentially includes a first light-emitting layer 40, a second light-emitting layer 43, a third light-emitting layer 44, and a fourth light-emitting layer 45 from the anode 21 side. The first light-emitting layer 40 has the same structure as the first light-emitting layer 40 according to the above-described embodiments. The second light-emitting layer 43 includes a plurality of quantum dots 50 and a second inorganic filler 54 filling between the plurality of quantum dots 50. The third light-emitting layer 44 contains a plurality of quantum dots 50 and a third inorganic filler 55 filling between the plurality of quantum dots 50. The fourth light-emitting layer 45 has the same structure as the second light-emitting layer 42 according to the previous embodiment, except that a fourth inorganic filler 56 is included instead of the second inorganic filler 53.

[0118] The quantum dots 50 included in the second light-emitting layer 43 and the third light-emitting layer 44 have the same structure as the quantum dots 50 according to the above-described embodiments. In addition, the second inorganic filler 54, the third inorganic filler 55, and the fourth inorganic filler 56 have the same structure as the first inorganic filler 52 according to the above-described embodiments, except for the concentration of at least one of sulfur atoms and oxygen atoms.

[0119] Therefore, the light-emitting layer 28 includes the first inorganic filler 52, the second inorganic filler 54, the third inorganic filler 55, and the fourth inorganic filler 56 as the quantum dots 50 and the inorganic filler 51. In particular, the light-emitting layer 28 includes the first light-emitting layer 40, the second light-emitting layer 43, and the third light-emitting layer 44 as quantum dot layers including the quantum dots 50 and the inorganic filler 51. In addition, the light-emitting layer 28 includes the fourth light-emitting layer 45 having only the inorganic filler 51 of the quantum dots 50 and the inorganic filler 51.

[0120] In the present embodiment, the concentrations of at least one of sulfur atoms and oxygen atoms in the first inorganic filler 52, the second inorganic filler 54, the third inorganic filler 55, and the fourth inorganic filler 56 gradually decrease in this order. In other words, in the present embodiment, in the inorganic filler 51, the concentration of at least one of sulfur atoms and oxygen atoms also gradually decreases in the direction from the anode 21 toward the cathode 26.

[0121] In particular, the density of atomic defects of at least one of sulfur atoms and oxygen atoms gradually increases in the first inorganic filler 52, the second inorganic filler 54, the third inorganic filler 55, and the fourth inorganic filler 56 in this order. In other words, in the present embodiment, in the inorganic filler 51, the density of atomic defects of at least one of sulfur atoms and oxygen atoms also gradually increases in the direction from the anode 21 toward the cathode 26.

[0122] Through the above, for the same reasons as those described in the above embodiments, the light-emitting element 13 of the present embodiment suppresses the movement of electrons injected from the electron transport layer 25 between the quantum dots 50 in the light-emitting layer 24. Therefore, the light-emitting element 13 reduces the reactive current in the light-emitting layer 24 and improves the luminous efficiency and reliability.

[0123] In addition, the concentration of the quantum dots 50 in the light-emitting layer 28 decreases in the order of the first light-emitting layer 40, the second light-emitting layer 43, and the third light-emitting layer 44. Further, as described above, the fourth light-emitting layer 45 does not have the quantum dots 50. Therefore, for the same reasons as those described in the above embodiments, the light-emitting element 13 can more effectively improve the protection effect of the inorganic filler 51 in the light-emitting layer 24 on the quantum dots 50 and can improve the luminous efficiency.

[0124] In particular, regarding the light-emitting element 13 of the present embodiment, even when the injection efficiency of holes into the light-emitting layer 28 decreases due to the deterioration of each part, a decrease in the light-emitting efficiency can be suppressed. For example, at the time of shipment of the display device 3, the light-emitting element 13 causes recombination of electrons and holes in the light-emitting layer 28 in the quantum dots 50 near the second light-emitting layer 43, and mainly the quantum dots 50 of the second light-emitting layer 43 emit light. In this case, due to deterioration caused by driving of the display device 3 or deterioration over time, sometimes accompanied by deterioration of each part of the light-emitting element 13, the mobility and injection efficiency of holes from the hole injection layer 22 to the light-emitting layer 28 decrease. This is generally because the durability of the hole injection layer 22 or the hole transport layer 23 is worse than that of the electron transport layer 25. In particular, this is significant when the hole transport layer 23 uses an organic material and the electron transport layer 25 uses an inorganic material. As a result, recombination of electrons and holes in the light-emitting layer 28 sometimes occurs in the quantum dots 50 closer to the anode 21 side than the second light-emitting layer 43. In this case, recombination of electrons and holes in the light-emitting layer 28 also occurs in the quantum dots 50 near the first light-emitting layer 40, and mainly the quantum dots 50 of the first light-emitting layer 40 can emit light. Therefore, the light-emitting element 13 reduces the light-emitting efficiency. In other words, even when the injection of holes into the light-emitting layer 28 deteriorates due to the deterioration of each layer of the light-emitting element 13, it is possible to suppress a decrease in the light-emitting efficiency of the light-emitting element 13 caused only by the shift of the light-emitting position toward the anode 21 side and the deterioration of the carrier balance in the light-emitting layer 28. Therefore, the light-emitting layer 28 can improve the reliability of the light-emitting element 13.

[0125] The manufacturing method of the light-emitting element 13 of the present embodiment can be manufactured by the same method as the manufacturing method of the light-emitting element 12 of the above embodiment, except for the method of forming the light-emitting layer 28. In the present embodiment, the first light-emitting layer 40, the second light-emitting layer 43, and the third light-emitting layer 44 in the light-emitting layer 28 can also be formed by repeatedly performing the above step S5 and step S6.

[0126] However, in the present embodiment, the concentration of the quantum dots 50 in the solution coated in step S5 is gradually thinned, and the heating temperature of the solution in step S6 is gradually increased, and steps S5 and S6 are repeatedly performed. Thereby, the above-described first light-emitting layer 40, second light-emitting layer 43, and third light-emitting layer 44 can be formed. It should be noted that the concentration of the quantum dots 50 in the coated solution does not necessarily need to be changed, and it may be substantially the same concentration.

[0127] Furthermore, in the present embodiment, the fourth light-emitting layer 45 can also be formed by performing step S7 and step S8 involved in the present embodiment. However, in the present embodiment, the heating temperature of the solution in step S6 is increased, and the heating temperature of the solution in step S8 and step S8 are performed. Thereby, the above-mentioned fourth light-emitting layer 45 can be formed, and the light-emitting layer 28 can be formed.

[0128] [Modification Example] <ternary compound semiconductor> Hereinafter, a display device according to a modification example of the present embodiment will be described. The display device of this modification example has the same configuration as the display device 3 of the present embodiment, except for the material of the inorganic filler 51 of the light-emitting layer 28 included in the light-emitting element 13.

[0129] The inorganic filler 51 according to this modification example contains a ternary compound semiconductor having a metal atom. In particular, in this modification example, the first inorganic filler 52, the second inorganic filler 54, the third inorganic filler 55, and the fourth inorganic filler 56 gradually increase or gradually decrease in the concentration of the above-mentioned metal atoms in this order. In other words, the inorganic filler 51 according to this modification example has a concentration gradient of metal atoms in the direction from the anode 21 toward the cathode 26.

[0130] For example, the inorganic filler 51 according to this modification example may contain a magnesium atom, and may also contain a sulfide containing a zinc atom. In particular, the inorganic filler 51 may contain zinc magnesium sulfide (ZnMgS, ZnMgS 2 ) as a sulfide containing both a magnesium atom and a zinc atom.

[0131] For example, the first inorganic filler 52, the second inorganic filler 54, the third inorganic filler 55, and the fourth inorganic filler 56 may contain zinc magnesium sulfide represented by the composition as Zn X Mg 1-X S 1-Y . Here, X and Y are real numbers satisfying 0 ≤ X ≤ 1 and 0 ≤ Y ≤ 1, respectively, and the value of X increases in the order of the first inorganic filler 52, the second inorganic filler 54, the third inorganic filler 55, and the fourth inorganic filler 56. In this case, the inorganic filler 51 has a concentration gradient in which the concentration of zinc atoms gradually increases in the direction from the anode 21 toward the cathode 26, and on the other hand, has a concentration gradient in which the concentration of magnesium atoms gradually decreases. In addition, Y represents the ratio of sulfur atom defects in the inorganic filler 51, and can increase in the order of the first inorganic filler 52, the second inorganic filler 54, the third inorganic filler 55, and the fourth inorganic filler 56.

[0132] For example, in the first inorganic filler 52, X = 0.3; in the second inorganic filler 54, X = 0.6; in the third inorganic filler 55, X = 0.9; and in the fourth inorganic filler 56, X = 1. In this case, the fourth inorganic filler 56 contains a binary compound semiconductor, namely zinc sulfide. Thus, the inorganic filler 51 according to the present embodiment is not limited to a structure composed only of a ternary compound semiconductor, and may also contain a part of a binary compound semiconductor.

[0133] The manufacturing method of the light-emitting element 13 according to this modification can be manufactured by the same method as the manufacturing method of the light-emitting element 13 according to the present embodiment, except for the method of forming the light-emitting layer 28. In this modification, the first light-emitting layer 40, the second light-emitting layer 43, and the third light-emitting layer 44 in the light-emitting layer 28 can also be formed by repeatedly performing the above steps S5 and step S6. Further, in this modification, the fourth light-emitting layer 45 can also be formed by performing steps S7 and SS8 according to the present embodiment.

[0134] For example, in the formation process of the first light-emitting layer 40, as step S5, a first solution containing a plurality of quantum dots 50 and a first inorganic precursor having a plurality of metal sources is coated on the hole transport layer 23. Then, in step S6, the coated first solution is heated to modify the first inorganic precursor into the first inorganic filler 52, thereby forming the first light-emitting layer 40.

[0135] For example, in the formation process of the second light-emitting layer 43, as step S5, a second solution containing a plurality of quantum dots 50 and a second inorganic precursor having a plurality of metal sources is coated on the hole transport layer 23. Here, by making the ratio of the metal sources in the second inorganic precursor different from that of the first inorganic precursor, the ratio of the metal sources in the second solution is made different from that in the first solution. As a result, then, in step S6, the second light-emitting layer 43 having a second inorganic filler 54 with a different concentration of metal atoms from that of the first inorganic filler 52 is formed. In addition, in the above step S6, the heating temperature of the second solution can also be higher than that of the first solution. Similarly, by forming the third light-emitting layer 44 and the fourth light-emitting layer 45, the light-emitting layer 28 is formed.

[0136] <Energy band diagram of each part of the light-emitting element> Refer to Figure 6 The band gaps of each part of the light-emitting element 13 according to this modification are described. Figure 6 FIG. is a simplified energy band diagram showing an example of the band gaps of each part of the light-emitting element 13 according to this modification. In addition, Figure 6 The energy band diagram is an energy band diagram having a vacuum energy level on the upper side in the plane of the paper. In addition, Figure 6The left - right direction of the energy band diagram represents the direction of the thickness in the display direction of the display device 3, with the left side of the paper surface shown as the anode 21 side and the right side as the cathode 26 side.

[0137] In Figure 6 the energy band diagram, for the anode 21 and the cathode 26, their respective Fermi levels are shown. In addition, for the hole injection layer 22, the hole transport layer 23, and the electron transport layer 25, their respective band gaps are shown. In particular, in Figure 6 the energy band diagram, as the band gap of the electron transport layer 25, the band gap of the nanoparticles 30 is shown.

[0138] Furthermore, in Figure 6 the energy band diagram, as the band gap of the light - emitting layer 28, the band gaps of the first light - emitting layer 40, the second light - emitting layer 43, the third light - emitting layer 44, and the fourth light - emitting layer 45 are shown. In particular, in Figure 6 the energy band diagram, the band gaps of the core 50C and the shell 50S of the quantum dots 50, and the band gaps of the first inorganic filler 52, the second inorganic filler 54, the third inorganic filler 55, and the fourth inorganic filler 56 are shown.

[0139] Here, in the first light - emitting layer 40, the second light - emitting layer 43, and the third light - emitting layer 44, inorganic fillers 51 are filled between the quantum dots 50. Therefore, in Figure 6 the energy band diagram, the band gaps of the first light - emitting layer 40, the second light - emitting layer 43, and the third light - emitting layer 44 can be illustrated such that the band gap of the inorganic filler 51 is located at both ends of the band gap of the quantum dots 50. It should be noted that for the fourth light - emitting layer 45, only the band gap of the fourth inorganic filler 56 is illustrated.

[0140] As Figure 6 shown, the band gaps of the first inorganic filler 52, the second inorganic filler 54, the third inorganic filler 55, and the fourth inorganic filler 56 gradually decrease in sequence. In other words, in this modified example, the band gap of the inorganic filler 51 gradually becomes smaller in the direction from the anode 21 towards the cathode 26. The gradient of the band gap of the above - mentioned inorganic filler 51 is achieved by the concentration gradient of the metal atoms of the above - mentioned inorganic filler 51.

[0141] In particular, the electron affinity of the inorganic filler 51 gradually becomes larger in the direction from the anode 21 towards the cathode 26. In Figure 6 the energy band diagram, the electron affinity of each part is equivalent to the distance from the vacuum level to the upper end of the band gap. Therefore, in Figure 6 the energy band diagram, the lower the upper end of the band gap of a certain layer is located, the larger the electron affinity of that layer is. In other words, there is a tendency that the larger the band gap of a certain layer is, the smaller the electron affinity of that layer is.

[0142] The injection barrier of electrons from the first layer to the second layer is equivalent to subtracting the electron affinity of the second layer from the electron affinity of the first layer. Therefore, in this modified example, there is a barrier in the injection of electrons from the fourth inorganic filler 56 to the third inorganic filler 55. Similarly, in this modified example, there are barriers in the injection of electrons from the third inorganic filler 55 to the second inorganic filler 54 and from the second inorganic filler 54 to the first inorganic filler 52.

[0143] Therefore, the light-emitting element 13 according to this modified example inhibits the movement of electrons from the cathode 26 toward the anode 21 via the inorganic filler 51. Therefore, the light-emitting element 13 can increase the proportion of carriers injected into the quantum dots 50 relative to the carriers of the ineffective current flowing through the inorganic filler 51.

[0144] Through the above, the light-emitting element 13 according to this modified example inhibits the movement of electrons injected from the electron transport layer 25 in the light-emitting layer 24 between the quantum dots 50, thereby reducing the reactive current in the light-emitting layer 24 and improving the light-emitting efficiency and reliability.

[0145] By including magnesium atoms in the inorganic filler 51, it is possible to easily design the bandgap of the inorganic filler 51 by adjusting the concentration of magnesium atoms. In addition, by including a sulfide containing zinc atoms in the inorganic filler 51, the protection effect of the quantum dots 50 can be improved, and at the same time, the injection efficiency of carriers into the quantum dots 50 can be increased.

[0146] <Display device having a plurality of sub-pixels> Refer to Figure 7 The display device 4 of the present embodiment will be described. Figure 7 FIG. is a schematic side cross-sectional view of the display device 4 according to the present embodiment. The display device 4 according to the present embodiment includes a light-emitting element 14 instead of the light-emitting element 13 as compared with the display device 3 according to the present embodiment. In addition, the display device 4 of the present embodiment has a plurality of sub-pixels in a plan view, and particularly includes a red sub-pixel SPR, a green sub-pixel SPG, and a blue sub-pixel SPB.

[0147] The light-emitting element 14 according to the present embodiment includes a red light-emitting element 14R, a green light-emitting element 14G, and a blue light-emitting element 14B. In a plan view of the substrate 20, the red light-emitting element 14R is located on the red sub-pixel SPR, the green light-emitting element 14G is located on the green sub-pixel SPG, and the blue light-emitting element 14B is located on the blue sub-pixel SPB.

[0148] In addition, compared with the light-emitting element 13 of the foregoing embodiment, the light-emitting element 14 has a bank 60 on the substrate 20. The bank 60 is made of, for example, an insulating resin material, such as polyimide. The bank 60 is formed in each layer of the light-emitting element 14, midway through the fourth light-emitting layer 45 from the anode 21 to the light-emitting layer 28. Therefore, the layers of the third light-emitting layer 44 from the anode 21 to the light-emitting layer 28 of the light-emitting element 14 are divided by the bank 60.

[0149] In particular, the layers of the third light-emitting layer 44 from the anode 21 to the light-emitting layer 28 of the light-emitting element 14 are divided into a red sub-pixel SPR, a green sub-pixel SPG, and a blue sub-pixel SPB in a plan view of the substrate 20. In addition, the fourth light-emitting layer 45, the electron transport layer 25, and the cathode 26 of the light-emitting layer 28 can be formed in common for the above-mentioned plurality of sub-pixels.

[0150] In this embodiment, the light-emitting layer 28 is divided into a red light-emitting layer 28R, a green light-emitting layer 28G, and a blue light-emitting layer 28B by the bank 60. In a plan view of the substrate 20, the red light-emitting layer 28R is located on the red sub-pixel SPR, the green light-emitting layer 28G is located on the green sub-pixel SPG, and the blue light-emitting layer 28B is located on the blue sub-pixel SPB.

[0151] In particular, the first light-emitting layer 40 is divided into a red first light-emitting layer 40R, a green first light-emitting layer 40G, and a blue first light-emitting layer 40B. In addition, the second light-emitting layer 43 is divided into a red second light-emitting layer 43R, a green second light-emitting layer 43G, and a blue second light-emitting layer 43B. Further, the third light-emitting layer 44 is divided into a red third light-emitting layer 44R, a green third light-emitting layer 44G, and a blue third light-emitting layer 44B. However, the red light-emitting layer 28R, the green light-emitting layer 28G, and the blue light-emitting layer 28B may also have a common fourth light-emitting layer 45.

[0152] The red first light-emitting layer 40R, the red second light-emitting layer 43R, and the red third light-emitting layer 44R include red quantum dots 57 that emit red light. The green first light-emitting layer 40G, the green second light-emitting layer 43G, and the green third light-emitting layer 44G include green quantum dots 58 that emit green light. The blue first light-emitting layer 40B, the blue second light-emitting layer 43B, and the blue third light-emitting layer 44B include blue quantum dots 59 that emit blue light. The red quantum dots 57, the green quantum dots 58, and the blue quantum dots 59 may each have the same configuration as the quantum dots 50 except for the emission color.

[0153] In addition, red light is light having an emission center wavelength in a wavelength band exceeding 600 nm and below 780 nm. In addition, green light is light having an emission center wavelength in a wavelength band exceeding 500 nm and below 600 nm, for example. Moreover, blue light is light having an emission center wavelength in a wavelength band of 400 nm or more and 500 nm or less.

[0154] In addition to the above, the red light-emitting layer 28R, the green light-emitting layer 28G, and the blue light-emitting layer 28B have the same configuration as the light-emitting layer 28 of the above-described embodiment. In other words, in the present embodiment, the first light-emitting layer 40, the second light-emitting layer 43, the third light-emitting layer 44, and the fourth light-emitting layer 45 each have a first inorganic filler 52, a second inorganic filler 54, a third inorganic filler 55, and a fourth inorganic filler 56, respectively. Further in other words, the red light-emitting layer 28R, the green light-emitting layer 28G, and the blue light-emitting layer 28B each have the same inorganic filler 51 as the inorganic filler 51 related to the previous embodiment.

[0155] Therefore, the red light-emitting element 14R includes a substrate 20 formed in the red sub-pixel SPR, an anode 21, a hole injection layer 22, a hole transport layer 23, a red light-emitting layer 28R, an electron transport layer 25, and a cathode 26. The green light-emitting element 14G includes a substrate 20 formed in the green sub-pixel SPG, an anode 21, a hole injection layer 22, a hole transport layer 23, a green light-emitting layer 28G, an electron transport layer 25, and a cathode 26. The blue light-emitting element 14B includes a substrate 20 formed in the blue sub-pixel SPB, an anode 21, a hole injection layer 22, a hole transport layer 23, a blue light-emitting layer 28B, an electron transport layer 25, and a cathode 26.

[0156] In the present embodiment, the anode 21, the hole injection layer 22, and the hole transport layer 23 can have the same concept in any of the red sub-pixel SPR, the green sub-pixel SPG, and the blue sub-pixel SPB. However, each anode 21 is electrically connected to the drive circuit of each sub-pixel formed on the substrate 20.

[0157] The display device 4 applies a common potential to the cathode 26 and controls the voltage application to each node 21 via the pixel circuit of the substrate 20. Thereby, red light from the red light-emitting element 14R, green light from the green light-emitting element 14G, and blue light from the blue light-emitting element 14B are separately taken out from each sub-pixel for color display.

[0158] The light-emitting element 14 of the present embodiment can be manufactured by the same method as the light-emitting element 13 of the foregoing embodiment, except for the manufacturing process of the light-emitting layer 28. In the present embodiment, in the process of forming the light-emitting layer 28, for example, by photolithography using a photosensitive resin, the photosensitive resin is formed only in specific sub-pixels. Next, a solution containing quantum dots is coated and formed into a film in common for a plurality of sub-pixels. Next, the light-emitting layer 28 can be formed only in specific sub-pixels by peeling off the photosensitive resin together with the solution after coating and forming. Alternatively, the light-emitting layer 28 can also be formed by coating the light-emitting layer 28 on each sub-pixel by an inkjet method or the like.

[0159] The red light-emitting element 14R, the green light-emitting element 14G, and the blue light-emitting element 14B according to the present embodiment have the same configuration as the light-emitting element 13 of the foregoing embodiment, except for the emission color of the quantum dots included in the light-emitting layer 28. Therefore, for the same reasons as described above, the red light-emitting element 14R, the green light-emitting element 14G, and the blue light-emitting element 14B can respectively more effectively improve the protection effect of the inorganic filler 51 in the light-emitting layer 24 on the quantum dots 50, and can improve the luminous efficiency.

[0160] Generally, the band gap of the material of the core of quantum dots varies depending on the emission color of the core. For this reason, for a light-emitting element having a light-emitting layer, the light-emitting layer has quantum dots as a light-emitting material, and the band gap of the light-emitting element is different from that of a charge transport layer including a hole injection layer, a hole transport layer, and an electron transport layer suitable for the emission color of the light-emitting layer. Therefore, when the same charge transport layer is applied to light-emitting elements each having a light-emitting layer including quantum dots with different emission colors, there may be a case where the carrier balance of the light-emitting layer 28 is not optimized in any of the light-emitting elements.

[0161] In the present embodiment, the red light-emitting element 14R, the green light-emitting element 14G, and the blue light-emitting element 14B respectively have inorganic fillers 51 having different band gaps from each other in the stacking direction. Therefore, in each of the red light-emitting element 14R, the green light-emitting element 14G, and the blue light-emitting element 14B, the emission position of the quantum dots is different in the stacking direction due to the band gap of the quantum dots they have.

[0162] Therefore, in the light-emitting element 14, even when the charge transport layers of the light-emitting elements in the respective sub-pixels are not optimized, by making the emission positions of the quantum dots different, the carrier balance of each light-emitting layer 28 can be optimized. Therefore, the light-emitting element 14 of the present embodiment can share the charge transport layer in the respective sub-pixels, simplify the manufacturing process, and improve the carrier balance of each light-emitting layer 28, thereby improving the luminous efficiency.

[0163] In addition, in the present embodiment, a case where the red light-emitting element 14R, the green light-emitting element 14G, and the blue light-emitting element 14B each have the same stacked structure as the light-emitting element 13 according to the previous embodiment has been described, but it is not limited thereto. For example, the red light-emitting element 14R, the green light-emitting element 14G, and the blue light-emitting element 14B may each have the same stacked structure as any one of the above-described light-emitting elements 11 or 12.

[0164] Moreover, in the present embodiment, any one of the red light-emitting element 14R, the green light-emitting element 14G, and the blue light-emitting element 14B only needs to have the same stacked structure as the light-emitting element according to any one of the foregoing embodiments. In other words, in the present embodiment, a part of the red light-emitting element 14R, the green light-emitting element 14G, and the blue light-emitting element 14B may also have a structure different from that of the light-emitting elements according to the above-described respective embodiments.

[0165] The present disclosure is not limited to the above-described respective embodiments, and various modifications can be made within the scope shown in the claims. Embodiments obtained by appropriately combining the technical solutions separately disclosed for different embodiments are also included in the technical scope of the present disclosure. Moreover, new technical features can be formed by combining the technical methods separately disclosed for each embodiment. Description of Reference Numerals

[0166] 1, 2, 3, 4 Display device 11, 12, 13, 14 Light-emitting element 14R Red light-emitting element 14G Green light-emitting element 14B Blue light-emitting element 20 Substrate 21 Anode 24, 27, 28 Light-emitting layer 25 Electron transport layer 26 Cathode 30 Nanoparticle 50 Quantum dot 50C Core 50S Shell 51 Inorganic filler

Claims

1. A light-emitting element, characterized in that, comprising: an anode; a cathode; a light-emitting layer located between the anode and the cathode, the light-emitting layer having a plurality of quantum dots and an inorganic filler material, the inorganic filler material filling between the plurality of quantum dots and containing at least one of a metal sulfide or a metal oxide, in the inorganic filler material, in a direction from the anode toward the cathode, the concentration of at least one of sulfur atoms or oxygen atoms becomes lower.

2. A light-emitting element, characterized in that, comprising: an anode; a cathode; a light-emitting layer located between the anode and the cathode, the light-emitting layer having a plurality of quantum dots and an inorganic filler material, the inorganic filler material filling between the plurality of quantum dots and containing at least one of a metal sulfide or a metal oxide, in the inorganic filler material, the cathode side has a portion where the concentration of at least one of sulfur atoms or oxygen atoms is lower than that on the anode side.

3. The light-emitting element according to claim 1 or 2, characterized in that, in the light-emitting layer, in a direction from the anode toward the cathode, the concentration of the quantum dots decreases.

4. The light-emitting element according to any one of claims 1 to 3, characterized in that, the light-emitting layer sequentially has, starting from the anode side: a quantum dot layer containing the quantum dots and the inorganic filler material, and an inorganic filler material layer containing only the inorganic filler material among the quantum dots and the inorganic filler material.

5. The light-emitting element according to claim 4, characterized in that, the film thickness of the inorganic filler material layer is 1.2 nm or more.

6. The light-emitting element according to any one of claims 1 to 5, characterized in that, the light-emitting element includes a substrate, on the substrate, the anode, the light-emitting layer, and the cathode are sequentially provided starting from the substrate side.

7. The light-emitting element according to any one of claims 1 to 6, characterized in that, In a region within 1.2 nm in the film thickness direction from the end face on the anode side of the light-emitting layer, the density of free electrons of the inorganic filler is 1×10 16 cm -3 or less.

8. The light-emitting element according to any one of claims 1 to 7, characterized in that, In a region within 1.2 nm in the film thickness direction from the end face on the anode side of the light-emitting layer, the defect density of the sulfur atom or the oxygen atom of the inorganic filler is 5×10 17 cm -3 or less.

9. The light-emitting element according to any one of claims 1 to 8, characterized in that, the density of free electrons of the inorganic filler material in a region within 1.2 nm in the film thickness direction starting from the end face on the anode side of the light-emitting layer is 10 times or less the density of free electrons of the inorganic filler material in a region within 1.2 nm in the film thickness direction starting from the end face on the cathode side of the light-emitting layer.

10. The light-emitting element according to any one of claims 1 to 9, characterized in that, In the region within 1.2 nm in the film thickness direction from the end face on the cathode side of the light-emitting layer, the density of free electrons of the inorganic filler is 1×10 18 cm -3 or more and 4×10 19 cm -3 or less.

11. The light-emitting element according to any one of claims 1 to 10, characterized in that, In a region within 1.2 nm in the film thickness direction from the end face on the cathode side of the light-emitting layer, the defect density of the sulfur atoms or the oxygen atoms of the inorganic filler is 5×10 19 cm -3 or more and 2×10 21 cm -3 or less.

12. The light-emitting element according to any one of claims 1 to 11, characterized in that, the quantum dots have a core and at least one shell covering the core, the outermost shell of the quantum dots in the shell contains the same material as the inorganic filler material.

13. The light-emitting element according to any one of claims 1 to 12, characterized in that, the inorganic filler material contains a binary compound semiconductor.

14. The light-emitting element according to any one of claims 1 to 13, wherein, the inorganic filler contains zinc sulfide.

15. The light-emitting element according to any one of claims 1 to 14, wherein, it further includes an electron transport layer located between the light-emitting layer and the cathode and having a plurality of nanoparticles.

16. A light-emitting element, wherein, it includes: an anode; a cathode; a light-emitting layer located between the anode and the cathode, the light-emitting layer having a plurality of quantum dots and an inorganic filler, the inorganic filler filling between the plurality of quantum dots and containing at least one of a metal sulfide or a metal oxide, in the inorganic filler, in the direction from the anode to the cathode, the atomic defect density of at least one of sulfur atoms and oxygen atoms gradually becomes higher.

17. A light-emitting element, wherein, it includes: an anode; a cathode; a light-emitting layer located between the anode and the cathode, the light-emitting layer containing a plurality of quantum dots and an inorganic filler, the inorganic filler containing a chalcogenide and filling between the plurality of quantum dots, in the inorganic filler, the atomic concentration of the chalcogen element becomes lower in the direction from the anode to the cathode.

18. A light-emitting element, wherein, it includes: an anode; a cathode; a light-emitting layer located between the anode and the cathode, the light-emitting layer having a plurality of quantum dots and an inorganic filler, the inorganic filler filling between the plurality of quantum dots and containing a ternary compound semiconductor having a metal atom, and the inorganic filler having a concentration gradient of the metal atom in the direction from the anode toward the cathode, the band gap of the inorganic filler becomes smaller in the direction from the anode to the cathode.

19. The light-emitting element according to claim 18, wherein, the inorganic filler contains magnesium atoms.

20. The light-emitting element according to claim 18 or 19, wherein, the inorganic filler contains a sulfide containing zinc atoms.

21. A display device, wherein, it includes a red light-emitting element, a green light-emitting element, and a blue light-emitting element, and at least one of the red light-emitting element, the green light-emitting element, and the blue light-emitting element is the light-emitting element according to any one of claims 1 to 20.

22. A method for manufacturing a light-emitting element, the light-emitting element including: an anode; a cathode; a light-emitting layer located between the anode and the cathode, the light-emitting layer having a plurality of quantum dots and an inorganic filler, the inorganic filler filling between the plurality of quantum dots and containing at least one of a metal sulfide or a metal oxide, the manufacturing method including: coating a first solution containing the plurality of quantum dots and a first inorganic precursor; forming a first part of the light-emitting layer by heating the first solution at a first temperature to modify the first inorganic precursor into the inorganic filler; coating a second solution containing a second inorganic precursor on the first part; and Forming a second portion of the light-emitting layer on the first portion by heating the second solution at a second temperature higher than the first temperature to modify the second inorganic precursor into the inorganic filler material.

23. A method of manufacturing a light-emitting device, the light-emitting device comprising: an anode; a cathode; a light-emitting layer positioned between the anode and the cathode, the light-emitting layer having a plurality of quantum dots and an inorganic filler material, the inorganic filler material filling between the plurality of quantum dots and comprising a ternary compound semiconductor having a metal atom, the inorganic filler material having a concentration gradient of the metal atom in a direction from the anode toward the cathode, the manufacturing method comprising: coating a first solution containing the plurality of quantum dots and a first inorganic precursor having a plurality of metal sources; forming a first portion of the light-emitting layer by heating the first solution to modify the first inorganic precursor into the inorganic filler material; coating a second solution on the first portion, the second solution containing a second inorganic precursor having a plurality of the metal sources, the ratio of the metal sources in the second solution being different from that in the first solution; and forming a second portion of the light-emitting layer on the first portion by heating the second solution to modify the second inorganic precursor into the inorganic filler material, wherein a bandgap of the inorganic filler material of the second portion is smaller than a bandgap of the inorganic filler material of the first portion.

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