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

Abstract

A light-emitting element (11) is provided with an anode (21), a cathode (26), and a light-emitting layer (24) positioned between the anode and the cathode. The light-emitting layer has a plurality of quantum dots (50) and an inorganic filler (51). The inorganic filler fills spaces among the plurality of quantum dots, and includes at least one of a metal sulfide and a metal oxide. In the inorganic filler, the concentration of at least sulfur atoms or oxygen atoms gradually becomes lower in a direction from the anode to 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 technology]

[0002] In a light-emitting device having an emission layer containing quantum dots as a light-emitting material, reactive current may occur when carriers pass through the emission layer without being injected into the quantum dots. The generation of such reactive current not only reduces the light-emitting efficiency of the light-emitting device, but also causes deterioration of the quantum dots or surrounding layers of the emission layer, resulting in reduced reliability of the light-emitting device. Patent Document 1 discloses a light-emitting device in which the emission layer contains multiple quantum dots with shells of different thicknesses, thereby improving carrier confinement in the quantum dots. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent No. 6233417 Summary of the Invention [Problem to be solved by the invention]

[0004] The light-emitting device disclosed in Patent Document 1 can be said to be configured to suppress reactive current by reducing the outflow of carriers injected into the quantum dots to the outside of the quantum dots. Therefore, it is difficult to reduce the reactive current flowing between the quantum dots in the light-emitting device disclosed in Patent Document 1. [Means for solving the problem]

[0005] A light-emitting element according to one aspect of the present disclosure 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, the inorganic filler filling spaces between the plurality of quantum dots and including at least one of a metal sulfide and a metal oxide, and the inorganic filler having a concentration of at least one of sulfur atoms and oxygen atoms decreasing in a direction from the anode to the cathode.

[0006] A light-emitting element according to another aspect of the present disclosure 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, the inorganic filler filling spaces between the plurality of quantum dots and including at least one of a metal sulfide and a metal oxide, and the inorganic filler having a portion on the cathode side where the concentration of at least one of sulfur atoms and oxygen atoms is lower than the concentration of the at least one of sulfur atoms and oxygen atoms on the anode side.

[0007] A light-emitting element according to another aspect of the present disclosure 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, the inorganic filler filling the spaces between the plurality of quantum dots and including at least one of a metal sulfide and a metal oxide, and the inorganic filler having a density of atomic defects of at least one of sulfur atoms and oxygen atoms increasing in a direction from the anode to the cathode.

[0008] A light-emitting element according to another aspect of the present disclosure includes an anode, a cathode, and a light-emitting layer located between the anode and the cathode, wherein the light-emitting layer has a plurality of quantum dots and an inorganic filler material containing a chalcogenide and filling spaces between the plurality of quantum dots, and the concentration of chalcogen element atoms in the inorganic filler material decreases in a direction from the anode to the cathode.

[0009] A light-emitting element according to another aspect of the present disclosure 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, the inorganic filler filling spaces between the plurality of quantum dots and including a ternary compound semiconductor having metal atoms, the inorganic filler having a concentration gradient of the metal atoms in a direction from the anode to the cathode, and a band gap of the inorganic filler decreasing in a direction from the anode to the cathode.

[0010] A method for manufacturing a light-emitting element according to another embodiment of the present disclosure 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, the inorganic filler filling spaces between the plurality of quantum dots and including at least one of a metal sulfide and a metal oxide. The method includes applying a first solution containing the plurality of quantum dots and a first inorganic precursor, heating the first solution at a first temperature to transform the first inorganic precursor into the inorganic filler, thereby forming a first portion of the light-emitting layer, applying a second solution containing a second inorganic precursor onto the first portion, and heating the second solution at a second temperature higher than the first temperature to transform the second inorganic precursor into the inorganic filler, thereby forming a second portion of the light-emitting layer on the first portion.

[0011] A method for manufacturing a light-emitting element according to another aspect of the present disclosure includes an anode, a cathode, and a light-emitting layer located between the anode and the cathode, the light-emitting layer including a plurality of quantum dots and an inorganic filler, the inorganic filler filling spaces between the plurality of quantum dots and including a ternary compound semiconductor having metal atoms, and having a concentration gradient of the metal atoms in a direction from the anode to the cathode. The method includes: applying a first solution including the plurality of quantum dots and a first inorganic precursor having a plurality of metal sources; heating the first solution to transform the first inorganic precursor into the inorganic filler, thereby forming a first portion of the light-emitting layer; applying, onto the first portion, a second solution including a second inorganic precursor having the plurality of metal sources, the second solution having a different ratio of the metal sources from that in the first solution; and heating the second solution to transform the second inorganic precursor into the inorganic filler, thereby forming a second portion of the light-emitting layer on the first portion, wherein the band gap of the inorganic filler in the second portion is smaller than the band gap of the inorganic filler in the first portion. [Effects of the Invention]

[0012] By suppressing reactive current flowing between quantum dots in the light-emitting layer, the light-emitting efficiency and reliability of the light-emitting device are improved. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing a schematic cross-sectional side view of a display device according to a first embodiment, a schematic cross-sectional view of quantum dots, and a schematic view showing an inorganic filler that fills spaces between the quantum dots. FIG. [Figure 2] 1 is a schematic plan view of a display device according to a first embodiment. [Figure 3] 3 is a flowchart illustrating an example of a method for manufacturing the light-emitting element according to the first embodiment. [Figure 4] FIG. 10 is a schematic cross-sectional side view of a display device according to a second embodiment. [Figure 5] FIG. 10 is a schematic cross-sectional side view of a display device according to a third embodiment. [Figure 6]FIG. 10 is a schematic band diagram of each layer of a light-emitting device according to a modified example of Embodiment 3. [Figure 7] FIG. 10 is a schematic cross-sectional side view of a display device according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Embodiment 1] <Display device> Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals, and the description thereof will be omitted. Fig. 2 is a schematic plan view of a display device according to this embodiment.

[0015] The display device 1 is a device that can be used, for example, as a display for a television or a smartphone. The display device 1 includes a display unit DA and a frame unit NA formed around the periphery of the display unit DA. The display device 1 displays an image on the display unit DA by controlling light emission from each of a plurality of light-emitting elements (described later) formed in the display unit DA. Drivers and the like for driving each of the light-emitting elements of the display unit DA may be formed in the frame unit NA.

[0016] The display unit DA of the display device 1 according to this embodiment may include multiple subpixels, including red, green, and blue subpixels. A light-emitting element (described later) is formed in each subpixel, and each light-emitting element individually emits light. This allows the display device 1 to display images by individually controlling the light emitted from the multiple light-emitting elements of the display unit DA using, for example, a driver or the like formed in the frame portion NA.

[0017] <Light Emitting Device: Overview> The structure of the display unit DA of the display device 1 according to this embodiment will be described in more detail with reference to Fig. 1. Fig. 1 shows a schematic side cross-sectional view 101 of the display device 1 according to this embodiment, a schematic cross-sectional view 102 of quantum dots 50, which will be described later, and schematic views 103 and 104 showing inorganic filler 51 that fills the spaces between the quantum dots 50. In this disclosure, the direction from a substrate 20 to a cathode 26, which will be described later, of the display device 1 may be referred to as "upper," and the opposite direction may be referred to as "lower."

[0018] 2, and illustrates a cross section passing through the light emitting element 11 in a plan view of the substrate 20 of the display device 1 according to this embodiment. Note that all of the schematic cross-sectional side views of the display device in the present disclosure illustrate a cross section of the display device corresponding to the cross section illustrated in the schematic cross-sectional side view 101.

[0019] Schematic cross-sectional view 102 is a diagram showing a cross section of quantum dot 50 passing through approximately the center of quantum dot 50. Schematic views 103 and 104 are diagrams showing two examples of a set P of two quantum dots 50 and a region (space) K between them, as shown in schematic side cross-sectional view 101. In particular, schematic views 103 and 104 are diagrams showing sets P1 and P2, respectively, which are examples of sets of quantum dot 50A and quantum dot 50B.

[0020] As shown in schematic side cross-sectional view 101, the display device 1 includes a light-emitting element 11. In this embodiment, the light-emitting element 11 includes a substrate 20. For example, the substrate 20 is formed at a position overlapping the display section DA and the frame section NA in a plan view of the display device 1, and the light-emitting element 11 may be considered to include a portion of the substrate 20 that overlaps with the display section DA in a plan view of the display device 1. In other words, the substrate 20 may be formed across the display section DA and the frame section NA in a plan view of the display device 1. The top surface of the substrate 20 may be approximately parallel to the display surface of the display device 1; in other words, the plan view of the substrate 20 may be approximately the same as the plan view of the display device 1.

[0021] Furthermore, the light-emitting element 11 includes, in order from the substrate 20 side, an anode 21, a hole injection layer 22, a hole transport layer 23, a light-emitting layer 24, an electron transport layer 25, and a cathode 26. Note that this embodiment is not limited to this, and the light-emitting element 11 may include, in order from the substrate 20 side, a cathode, an electron transport layer, a light-emitting layer, a hole transport layer, a hole injection layer, and an anode. Furthermore, the light-emitting element 11 may include an electron injection layer between the electron transport layer 25 and the cathode 26.

[0022] The light-emitting element 11 may be formed individually for each of the plurality of sub-pixels described above. The display device 1 may also include a driver (not shown) or the like at a position overlapping with the frame portion NA of the substrate 20 in a plan view. The substrate 20 may also include a pixel circuit (not shown) corresponding to each sub-pixel. The pixel circuit may be electrically connected to the anode 21 of the light-emitting element 11. The display device 1 may control light emission from each light-emitting element 11 by controlling the application of a voltage to the anode 21 by each pixel circuit through the control of the driver or the like.

[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. Examples of the transparent electrode that can be used include ITO, InZnO, SnO2, and FTO. Alternatively, either the anode 21 or the cathode 26 may be a reflective electrode. The reflective electrode may contain a metal material that has a high reflectivity for visible light, and the metal material may be, for example, Al, Ag, Cu, or Au alone or an alloy of these.

[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. The hole injection layer 22 can be made of organic or inorganic materials with hole transport properties that have been conventionally used in quantum dot-containing light-emitting devices. The hole injection layer 22 may contain nickel oxide (NiO) nanoparticles. The hole injection layer 22 may also contain a self-assembled monolayer of [2-(3,6-dimethoxy-9H-carbozol-9-yl)ethyl]phosphonic acid (MeO-2PACz). Other examples of the hole injection layer 22 include a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (abbreviated as "PEDOT:PSS"), CuSCN (copper thiocyanate), and the like. The hole injection layer 22 may also contain bulk NiO (nickel oxide) rather than nanoparticles. These materials may be used alone or in combination of two or more.

[0025] The hole transport layer 23 transports holes injected from the anode 21 into the hole injection layer 22 to the light-emitting layer 24. The hole transport layer 23 may be made of organic or inorganic materials having hole transport properties that have been conventionally used in quantum dot-containing light-emitting devices. Examples of materials for the hole transport layer 23 include poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl))diphenylamine] (abbreviated as "TFB"), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (abbreviated as "poly-TPD"), and polyvinylcarbazole (abbreviated as "PVK"). These materials may be used alone, or two or more may be mixed or stacked as appropriate.

[0026] The electron transport layer 25 is a layer that transports electrons injected from the cathode 26 to the light-emitting layer 24. The electron transport layer 25 according to this embodiment includes nanoparticles 30 as an electron transport material. The electron transport layer 25 may also include a ligand that can coordinate to the nanoparticles 30.

[0027] For example, the nanoparticles 30 may be nanoparticles of zinc oxide (ZnO), zinc oxide (ZnO) doped with at least one of Li, Mg, Al, Ti, Ga, and Zr, titanium oxide (TiO2), or zirconium oxide (ZrO2). In this disclosure, the chemical formulas are representative examples. Furthermore, in this disclosure, the composition ratios described in the chemical formulas do not necessarily have to be stoichiometric, meaning that the actual composition of the compound is the same as the chemical formula.

[0028] The electron transport material contained in the electron transport layer 25 is not limited to the nanoparticles 30. For example, the electron transport layer 25 may use, as the electron transport material, an organic or inorganic material having electron transport properties that has been conventionally employed in light-emitting devices including quantum dots. The electron transport material may include, for example, 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (abbreviated as “TPBi”), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (abbreviated as “BCP”), 4,7-diphenyl-1,10-phenanthroline (abbreviated as “Bphen”), or the like. Alternatively, the electron transport layer 25 may include, as the electron transport material, bulk zinc oxide (ZnO) that is not nanoparticles, zinc oxide (ZnO), titanium oxide (TiO), or zirconium oxide (ZrO). Bulk zinc oxide (ZnO) may be doped with at least one of Li, Mg, Al, Ti, Ga, and Zr. The electron transport material may contain only one of the above-mentioned materials, or may contain two or more of them as appropriate.

[0029] <Light-emitting element: Light-emitting layer: Quantum dots> The light-emitting layer 24 includes, in order from the anode 21 side, a first light-emitting layer 40 as a first portion and a second light-emitting layer 41 as a second portion. Both the first light-emitting layer 40 and the second light-emitting layer 41 include a plurality of quantum dots 50 as light-emitting materials. As shown in a schematic cross-sectional view 102, for example, the quantum dots 50 have a core / shell structure including a core 50C and at least one shell 50S surrounding the core 50C. The shell 50S may include multiple layers extending from the center of the core 50C to the periphery. The first light-emitting layer 40 and the second light-emitting layer 41 may include a ligand capable of coordinating with the outermost shell 50S of the quantum dots 50.

[0030] Holes from the anode 21 and electrons from the cathode 26 are injected into the core 50C of the quantum dot 50, and the recombination of the holes and electrons generates excitons, which emit light. The shell 50S of the quantum dot 50 may have a function to protect the core 50C, such as by compensating for defects in the core 50C. The quantum dot 50 may also have various other structures that are known in the art.

[0031] In the present disclosure, the term "quantum dot" refers to a dot 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-mentioned maximum width, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). The shape of the quantum dots 50 may be, for example, a polygonal cross-sectional shape, a rod-like three-dimensional shape, a branch-like three-dimensional shape, a three-dimensional shape with an uneven surface, or a combination thereof.

[0032] The quantum dots 50 are typically made of semiconductors. The semiconductors preferably have a certain band gap. The semiconductors may be any material capable of emitting light and may include at least the materials described below. The semiconductors may be capable of emitting blue, green, and red light, respectively. The semiconductors may include, for example, at least one selected from the group consisting of II-VI compounds, III-V compounds, chalcogenides, and perovskite compounds. The II-VI compounds refer to compounds containing Group II and Group VI elements, while the III-V compounds refer to compounds containing Group III and Group V elements. Furthermore, the group II elements may include Group 2 and Group 12 elements, the group III elements may include Group 3 and Group 13 elements, the group V elements may include Group 5 and Group 15 elements, and the group VI elements may include Group 6 and Group 16 elements.

[0033] The II-VI compound includes, for example, at least one selected from the group consisting of 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 compound includes, for example, at least one selected from the group consisting of GaAs, GaP, GaSb, InN, InAs, InP, and InSb.

[0035] Chalcogenides are compounds containing a Group VI A(16) element, such as CdS or CdSe. Chalcogenides may also include mixed crystals thereof.

[0036] The perovskite compound has a composition represented by the general formula CsPbX3, CsSnX3, CH3NH3PbX3, or CH3NH3SnX3, for example. The constituent element X includes at least one element selected from the group consisting of Cl, Br, and I, for example.

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

[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, the concentration of the quantum dots 50 in the direction from the anode 21 to the cathode 26 may have a portion where it is lower, a portion where it is gradually lower, or it may be lower throughout the entire light-emitting layer 24, or it may be gradually lower throughout the entire light-emitting layer 24. Hereinafter, as an example, a case where the concentration is gradually lower throughout the entire light-emitting layer 24 will be described, but the present invention is not necessarily limited to this configuration.

[0039] In this disclosure, the case where the concentration of a material in each part of the light-emitting layer 24 "gradually decreases" is exemplified, but is not necessarily limited to this configuration. In this disclosure, unless contradictory, when the concentration of the material "gradually decreases," it does not exclude cases where there are parts where the concentration is lower, where there are parts where the concentration is gradually lower, where the concentration is lower throughout the entire light-emitting layer 24, or where the concentration is gradually lower throughout the entire layer. Furthermore, when the concentration "gradually decreases" at the boundary between the light-emitting layer 24 and an adjacent layer, it may indicate a change in concentration that is not related to a desired concentration configuration. In other words, the change in the concentration of sulfur atoms and oxygen atoms at the boundary is not necessarily steep, so the region 1.2 nm or less from the interface may be a region where the concentration is lower than the light-emitting layer 24. 24 may be excluded from

[0040] In the present disclosure, the concentration of a material in each part of the light-emitting layer 24 refers to, for example, the area ratio of the material in the cross section of the light-emitting layer 24. In addition, in the present disclosure, the gradual decrease in the concentration of a material in each part of the light-emitting layer 24 refers to the concentration decreasing gradually or stepwise, and does not limit the presence of parts where the concentration of the material is approximately the same. Here, the term "parts where the concentration of the material is approximately the same" refers to parts where the concentration of the material is approximately the same in a cross section of the light-emitting layer 24, observed at 200 nm. 2 This refers to the area where the difference in the area occupied by the material in question is within 5%.

[0041] In the cross section of the first light-emitting layer 40, the area ratio occupied by the quantum dots 50 may be 60% or more from the viewpoint of reducing reactive current in which carriers are not injected into the quantum dots and do not contribute to light emission. Furthermore, this area ratio may be 90% or less from the viewpoint of enhancing the protective effect of the inorganic filler 51 on the quantum dots 50, which will be described later. Furthermore, 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, or may be 60% or less from the viewpoint of enhancing the protective effect of the inorganic filler 51 on the quantum dots 50 against foreign matter entering from the cathode 26 side, which will be described later.

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

[0043] Note that, when inorganic filler 51 fills the spaces between multiple quantum dots 50, it is sufficient to understand that inorganic filler 51 fills at least region K between quantum dot 50A and quantum dot 50B, as shown in schematic diagram 103 of set P1 in Fig. 1. Region K is a region surrounded by two lines (common circumscribing lines) tangent to the peripheries of quantum dot 50A and quantum dot 50B and the opposing peripheries of quantum dot 50A and quantum dot 50B in the cross section of light-emitting layer 24. Therefore, as shown in schematic diagram 104 of set P2 in Fig. 1, region K can exist even if quantum dot 50A and quantum dot 50B are close to each other, and inorganic filler 51 fills region K.

[0044] The expression "the inorganic filler 51 fills the spaces between the quantum dots 50" does not necessarily mean that the region K between the quantum dots 50A and 50B is entirely made of the inorganic filler 51. For example, the region K between the quantum dots 50A and 50B may contain a material, such as a ligand, different from the material of the inorganic filler 51. Specifically, the light-emitting layer 24 may contain an organic ligand that is added to improve the dispersibility of the quantum dots 50 in a solution used for coating and that coordinates to the outer surfaces 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 may fill regions of the light-emitting layer 24 other than the multiple quantum dots 50. For example, the outer edges (upper and lower surfaces) of the light-emitting layer 24 may be covered with the inorganic filler 51. Alternatively, the light-emitting layer 24 may be configured such that a portion of the inorganic filler 51 extends from the outer edge thereof, and the quantum dots 50 are positioned away from the outer edge. The outer edge of the light-emitting layer 24 may not be formed solely by the inorganic filler 51, and some of the quantum dots 50 may be exposed from the inorganic filler 51. The inorganic filler 51 may refer to the portion of the light-emitting layer 24 excluding the multiple quantum dots 50.

[0046] The inorganic filler 51 may contain a plurality of quantum dots 50. The inorganic filler 51 may be formed so as to fill spaces formed between the plurality of quantum dots 50. The plurality of quantum dots 50 may be embedded in the inorganic filler 51 at intervals.

[0047] The inorganic filler 51 is formed in a thickness of 1000 nm along the surface direction perpendicular to the film thickness direction. 2 The inorganic filler 51 may include a continuous film having an area of ​​at least 1000 nm. The continuous film may be a film that is not separated by any material other than the material that constitutes the continuous film in one plane. The continuous film may be an integrated film that is seamlessly connected by chemical bonds of the inorganic filler 51.

[0048] The concentration of the inorganic filler 51 in the light-emitting layer 24 is, for example, the area ratio occupied by the inorganic filler 51 in the cross section of the light-emitting layer 24. This concentration may be 10% to 90% or 30% to 70% in cross-sectional observation. This concentration may be measured, for example, from the area ratio in an image obtained by cross-sectional observation. When the quantum dot 50 has a structure having a core 50C and a shell 50S, the concentration of the shell 50S may be 1% to 50%. The ratios of the core 50C, the shell 50S, and the inorganic filler 51 may be appropriately adjusted so that the total is 100% or less.

[0049] In the light-emitting layer 24, the shell 50S, which is the outermost layer of the quantum dots 50, and the inorganic filler 51 may 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 the interface are reduced. Therefore, the above configuration improves the efficiency of carrier injection into the quantum dots 50. Furthermore, the above configuration suppresses a decrease in the protective effect of the quantum dots 50, which is caused by defects at the interface, and also suppresses deactivation of excitons in the quantum dots 50, 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 be made of the same material. In this case, the outermost shell 50S of the quantum dot 50 and the inorganic filler 51 may be distinguished by confirming the difference in crystallinity. For example, in the cross-sectional observation of the light-emitting layer 24, if there are parts with the same composition but a difference in crystallinity, the part with higher crystallinity may be regarded as the shell 50S, and the other part may be regarded as the inorganic filler 51. When the shell 50S and the inorganic filler 51 cannot be distinguished, the shell 50S may be regarded as a part of the inorganic filler 51.

[0051] The light-emitting layer 24 may be composed of a plurality of quantum dots 50 and an inorganic filler 51. When analyzing the light-emitting layer 24, the intensity of carbon detected by the chain structure may be below the noise level. Also, the ratio of carbon detected from the light-emitting layer 24 may be 5% or less, may be 1% or less, or may not be detected. When, as in the known art, quantum dots 50 coordinated with an organic ligand are used in the light-emitting layer 24, the carbon chain of the organic ligand may decompose or the organic ligand itself may detach from the quantum dots during long-term driving. In this case, the quantum dots 50 may deteriorate and the luminance may decrease. As in the present disclosure, by filling the quantum dots 50 with the inorganic filler 51, the quantum dots 50 can be protected without using an organic ligand. Therefore, the display device 1 according to the present embodiment can achieve high reliability, or in other words, can suppress the luminance decrease 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 is, for example, zinc sulfide (ZnS), zinc magnesium sulfide (Zn x Mg 1-x S(0 < x < 1), ZnMgS2), gallium sulfide (GaS, Ga2S3), zinc tellurium sulfide (Zn x Te 1-xS (where 0 < x < 1), magnesium sulfide (MgS), zinc gallium sulfide (ZnGa₂S₄), magnesium gallium sulfide (MgGa₂S₄) may be used. The metal oxide may be zinc oxide (ZnO), titanium dioxide (TiO₂), tin oxide (SnO₂), tungsten oxide (WO₃), zirconium oxide (ZrO₂). It is desirable that the constituent material of the inorganic filler 51 has a wider band gap than the constituent material of the quantum dot 50 (for example, the material of the core 50C or the shell 50S).

[0053] Further, the inorganic filler 51 may contain a chalcogenide containing a metal sulfide or a metal oxide. In other words, the inorganic filler 51 may contain a compound containing a Group VI A (16) element.

[0054] The first inorganic filler 52 and the second inorganic filler 53 may 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, with 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 the present disclosure, the materials having the same composition do not refer to being made of exactly the same material, and may have, for example, atomic substitutions or defects of 5% or less.

[0055] Here, at each position in the plan view of the substrate 20, a first plane connecting each quantum dot 50 located on the most cathode 26 side of the first light-emitting layer 40 and a second plane connecting each quantum dot 50 located on the most 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 be located between the first plane and the second plane. Further, the light-emitting element 11 may include a layer that includes the first inorganic filler 52 and the second inorganic filler 53 and does not include the quantum dot 50 between the first plane and the second plane.

[0056] In this embodiment, the boundary between the light-emitting layer 24 and the electron transport layer 25 may be confirmed by observing a 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 on the cross section. For example, the boundary between the light-emitting layer 24 and the electron transport layer 25 may be confirmed by defining the portion of the cross section where the concentration of sulfur atoms or oxygen atoms is 25% or more as the light-emitting layer 24 and the portion where the concentration is less than 25% as the electron transport layer 25. Alternatively, the portion of the cross section where the concentration of sulfur atoms or oxygen atoms decreases by 25% or more may be considered to be the boundary between the light-emitting layer 24 and the electron transport layer 25. Note that, in addition to sulfur atoms and oxygen atoms, if there are atoms with higher concentrations in only one of the light-emitting layer 24 and the electron transport layer 25, the portion where the concentration of the atom changes by 25% or more may be considered to be the boundary between the light-emitting layer 24 and the electron transport layer 25. Therefore, as long as the above conditions are met, even a portion near which quantum dots 50 are not confirmed may be considered to be part of the light-emitting layer 24. The change in the concentrations of sulfur atoms and oxygen atoms is not necessarily steep at the interface between the light-emitting layer 24 and the electron transport layer 25. For this reason, a region of 1.2 nm or less on the anode 21 side from the interface determined above may be excluded from the light-emitting layer 24, or may be included in the electron transport layer 25.

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

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

[0059] When inorganic filler 51 contains a chalcogenide, the concentration of atomic defects in atoms of the chalcogen element contained in the chalcogenide increases gradually or in steps in inorganic filler 51 in a direction from anode 21 to cathode 26. In other words, the atomic concentration of the chalcogen element in inorganic filler (inorganic matrix material) 51 decreases gradually or in steps in a direction from anode 21 to cathode 26. Hereinafter, in this disclosure, when inorganic filler 51 contains a chalcogenide, metal sulfide and metal oxide in inorganic filler 51 may be read as chalcogenide, and sulfur atoms and oxygen atoms in inorganic filler 51 may be read as atoms of the 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, correlates with the density of free electrons at each position in the inorganic filler 51. This is because the concentration of free electrons possessed by the inorganic filler 51 changes depending on the concentration of sulfur atoms or oxygen atoms in the inorganic filler 51. In particular, when defects of sulfur atoms or oxygen atoms occur in the inorganic filler 51 and are activated, two free electrons are generated per defect near the defect.

[0061] Here, in order to consider the density of free electrons on the hole transport layer 23 side of the light-emitting layer 24, we will consider the hole density at the interface between the hole transport layer 23 and the light-emitting layer 24. For example, when the hole transport layer 23 contains an organic material as a hole transport material, the current flowing through the hole transport layer 23 is 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 formula.

[0062]

number

[0063] For example, when the light emitting element 11 is driven, the current density J flowing through the hole transport layer 23 is set to 10 mA / cm 2 In addition, the relative dielectric constant ε of the hole transport layer 23 is r is 3.5, the film thickness L is 30 nm, and the hole mobility μ is 10 -4 cm 2 In this case, from 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 This becomes:

[0064] When free electrons are present 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, recombination with free electrons outside the quantum dots 50 located near the interface may occur, preventing 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 the interface, even when recombination of electrons and holes occurs at the interface, excess holes are generated and are more likely to be injected into the quantum dots 50. Therefore, from the viewpoint of improving the efficiency of hole injection from the hole transport layer 23 to the light-emitting layer 24, the hole density near the interface between the hole transport layer 23 and the light-emitting layer 24 is required to be higher than the density of free electrons near the interface.

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

[0066] Here, when inorganic filler 51 has a polycrystalline or amorphous structure, the activation rate of inorganic filler 51 is not high, and is considered to be about 1%. For this reason, the activation rate of inorganic filler 51 in light-emitting layer 24 is set to 1%, in other words, one out of every 100 sulfur or oxygen atom defects in inorganic filler 51 is activated to generate two free electrons. In this case, in a region within 1.2 nm in the film thickness direction from the end face on the anode 21 side of light-emitting layer 24, the defect density of sulfur or oxygen atoms in inorganic filler 51 is 5×10 17 cm -3 With the above configuration, the density of free electrons in the inorganic filler 51 in this region may be 1×10 16 cm -3As a result, the efficiency of hole injection from the hole transport layer 23 to the light-emitting layer 24 can be improved. Furthermore, since the free electron density of the inorganic filler 51 is low, the resistivity of the inorganic filler 51 is high. Therefore, reactive current that does not contribute to light emission, which occurs when carriers flow through the inorganic filler 51 and are not injected into the quantum dots 50, is reduced. Therefore, the above configuration improves the light-emitting efficiency of the light-emitting element 11.

[0067] Let us consider the ratio of sulfur atom or oxygen atom defects in the inorganic filler 51 in the above case. If the inorganic filler 51 is made of zinc sulfide (ZnS), the lattice constant of sulfur sulfide is about 5.87 Å, and each lattice contains four sulfur atoms. Therefore, in the above case, the ratio of sulfur atom defects to zinc atoms in the inorganic filler 51 is 5×10 17 cm -3 ×(5.87Å) 3 / 4, which is 2.5 × 10 -3 It is about %.

[0068] Next, the density of free electrons on the electron transport layer 25 side of the light-emitting layer 24 will be considered. If free electrons are present near the interface between the electron transport layer 25 and the light-emitting layer 24, the free electrons will move in the light-emitting layer 24 toward the anode 21 when the light-emitting element 11 is driven. Therefore, if the density of free electrons on the electron transport layer 25 side of the light-emitting layer 24 is high, a larger proportion of free electrons will flow between the quantum dots 50 where they are injected into the quantum dots 50. Furthermore, if the density of atomic defects in the inorganic filler 51 in the light-emitting layer 24 is high, the electron mobility in the light-emitting layer 24 will decrease, which may ultimately result in a decrease in the electron transport ability of the light-emitting layer 24.

[0069] On the other hand, if 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 will decrease, which may lead to an excess of holes in the light-emitting layer 24.

[0070] Therefore, in order to improve the efficiency of electron injection from the electron transport layer 25 to the light-emitting layer 24 while suppressing the flow of electrons between the quantum dots 50, the density of free electrons near the interface between the electron transport layer 25 and the light-emitting layer 24 is required to be within a predetermined range.

[0071] In order to improve the efficiency of electron injection from the electron transport layer 25 to the light emitting layer 24, it is preferable that the density of free electrons in the light emitting layer 24 near the interface between the light emitting layer 24 and the electron transport layer 25 is equal to or higher than 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 nanoparticles, the density of free electrons in the electron transport layer 25 is 1×10 18 cm -3 Therefore, in order to improve the efficiency of electron injection from the electron transport layer 25 to the light emitting layer 24, the density of free electrons in the inorganic filler 51 is set to about 1×10 in a region within 1.2 nm in the film thickness direction from the end face of the light emitting layer 24 on the cathode 26 side. 18 cm -3 In other words, in a region within 1.2 nm from the interface between the electron transport layer 25 and the second light-emitting layer 41 in the film thickness direction of the second light-emitting layer 41, the density of free electrons in the second inorganic filler 53 in the second light-emitting layer 41 is 1×10 18 cm -3 It may be more than that.

[0072] Here, as in the above, the activation rate of the inorganic filler 51 in the light-emitting layer 24 is assumed to be 1%. In this case, in a region within 1.2 nm in the film thickness direction from the end face of the light-emitting layer 24 on the cathode 26 side, the defect density of sulfur atoms or oxygen atoms in the inorganic filler 51 is 5×10 19 cm -3 With the above configuration, the density of free electrons in the inorganic filler 51 in the region may be 1×10 18 cm -3 As a result, 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 decrease in the electron transport ability of the light-emitting layer 24, it is sufficient that the atomic defects of the inorganic filler 51 of the light-emitting layer 24 near the interface between the electron transport layer 25 and the light-emitting layer 24 are about 10% or less. If the inorganic filler 51 is made of zinc sulfide (ZnS), the density of atomic defects must be (5.87 Å) 3 The atomic defect density that satisfies the above is 0.1 × 4 / (5.87Å) 3 is less than or equal to approximately 2 x 10 21 cm -3 The following is the result.

[0074] From the above, in order to reduce the decrease in 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, the defect density of sulfur atoms or oxygen atoms of the inorganic filler 51 is set to 2×10 in a region within 1.2 nm in the film thickness direction from the end face of the light-emitting layer 24 on the cathode 26 side. 21 cm -3 In other words, in a region within 1.2 nm from the interface between the electron transport layer 25 and the second light-emitting layer 41 in the film thickness direction of the second light-emitting layer 41, the defect density of sulfur atoms or oxygen atoms of the second inorganic filler 53 in the second light-emitting layer 41 may be 2×10 21 cm -3 It may be the following:

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

[0076] The density of free electrons in the inorganic filler 51 in a region within 1.2 nm in the film thickness direction from the end face of the light-emitting layer 24 on the anode 21 side may be one-tenth or less of the density of free electrons in a region within 1.2 nm in the film thickness direction from the end face of the light-emitting layer 24 on the cathode 26 side. In other words, the density of free electrons in the first inorganic filler 52 of the first light-emitting layer 40 may be one-tenth or less of the density of free electrons in the second inorganic filler 53 of the second light-emitting layer 41. In this case, the efficiency of hole injection and the efficiency of electron injection into the light-emitting layer 24 can be improved in both directions, thereby reducing the drive voltage of the light-emitting element 11 and improving the energy efficiency of the light-emitting layer 24. Furthermore, the carrier balance in the light-emitting layer 24 can be improved, improving the luminous efficiency of the light-emitting element 11.

[0077] <Light-emitting element: manufacturing method> A method for manufacturing the light emitting device 11 according to this embodiment will be described with reference to Fig. 3. Fig. 3 is a flowchart showing the method for manufacturing the light emitting device 11 according to this embodiment.

[0078] 3, in the method for manufacturing the light-emitting element 11 according to this embodiment, first, a substrate 20 is prepared (step S1). The substrate 20 may be a glass substrate, a film substrate, or the like, on which a pixel circuit is formed for each sub-pixel. The substrate 20 may also be formed with a driver in the frame portion NA and wiring between the driver and each pixel circuit.

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

[0080] Next, the hole injection layer 22 is formed on the anode 21 (Step S3). S3In this case, for example, a solution in which nickel oxide nanoparticles are dispersed at 15 mg / mL in a solvent consisting of an equal volume mixture of water and 2-methoxyethanol may be applied to the anode 21 by spin coating and then baked at 200°C. This process may be performed once, or may be repeated two to five times. Next, a solution in which MeO-2PACz is dispersed in an ethanol solvent may be applied to the nickel oxide nanoparticle layer by spin coating under a nitrogen atmosphere, and the solvent may then be volatilized by baking. This may result in a layered structure of the nickel oxide nanoparticle layer and a self-assembled monolayer of MeO-2PACz, forming 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, a solution in which poly-TPD is dispersed in a chlorobenzene solvent may be applied to the self-assembled monolayer by spin coating in a nitrogen atmosphere, and the solvent may then be evaporated by baking. This may result in a poly-TPD film with a thickness of 30 nm being formed on the self-assembled monolayer, forming 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, the light-emitting layer 24 is formed on the hole transport layer 23. In this embodiment, an example will be described in which the light-emitting layer 24 is formed by forming a first light-emitting layer 40 and then forming a second light-emitting layer 41 on the first light-emitting layer 40.

[0083] In the process of forming the light-emitting layer 24 according to this embodiment, first, a first solution synthesized in advance in a separate process is applied onto the hole transport layer 23 by a spin coating method or the like (step S5). The first solution is a mixed solution containing a plurality of quantum dots 50 and a first inorganic precursor, which is a precursor of the first inorganic filler 52. The first inorganic precursor contains a metal source for the first inorganic filler 52 and a sulfur source or an oxygen source.

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

[0085] As a result, the solvent of the first solution volatilizes, and the first inorganic precursor in the first solution is modified, forming first inorganic filler 52. Here, the first inorganic precursor in the first solution is modified by heating in step S6, and first inorganic filler 52 is gradually formed around the quantum dots 50 in the first solution. Therefore, in step S6, first inorganic filler 52 is formed so as to fill the spaces between the multiple quantum dots 50. As a result, a first light-emitting layer 40 is formed that includes multiple quantum dots 50 and first inorganic filler 52 that fills the spaces between the quantum dots 50.

[0086] Next, a second solution synthesized in advance in a separate process is applied to the first light-emitting layer 40 by spin coating or the like (step S7). The second solution is a mixed solution containing a plurality of quantum dots 50 and a second inorganic precursor, which is a precursor of the second inorganic filler 53. The second inorganic precursor contains a metal source for the second inorganic filler 53 and a sulfur source or an oxygen source. In the present disclosure, the precursors, i.e., the first inorganic precursor and the second inorganic precursor, may contain, for example, a zinc source including zinc carboxylate or the like, a magnesium source including magnesium carboxylate or the like, a selenium source including selenourea or the like, or a sulfur source including thiourea or the like. Furthermore, the precursor may contain, for example, a metal acetate, a metal nitrate, or a metal halide salt 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, precursor 36 may include a metal complex in which thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N'-dimethylthiourea, tetramethylthiourea, or thioacetamide is coordinated to the metal atom.

[0087] The concentration of the quantum dots 50 relative to the concentration of the second inorganic precursor in the second solution is lower than the concentration of the quantum dots 50 relative to the concentration of the first inorganic precursor in the first solution. This makes it possible to make the concentration of the quantum dots 50 in the second light-emitting layer 41 formed by the method described below lower than the quantum dots 50 in the first light-emitting layer 40, while making the amount of the second solution applied in step S8 substantially the same as the amount of the first solution applied in step S6.

[0088] Next, the second solution applied onto 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 be 200°C. Specifically, in step S8, the second solution applied onto the first light-emitting layer 40 may be heated in an atmosphere of 200°C for 30 minutes.

[0089] As a result, the solvent of the second solution volatilizes and the second inorganic precursor in the second solution is modified to form second inorganic filler 53. As a result, similar to first light-emitting layer 40, second light-emitting layer 41 is formed, which includes a plurality of quantum dots 50 and second inorganic filler 53 filling the spaces between quantum dots 50.

[0090] Note that both steps S6 and S8 include a process of heating a solution containing a precursor having a metal source of inorganic filler 51 and a sulfur source or an oxygen source. Here, heating the solution may cause the sulfur source or oxygen source contained in the precursor in the solution to volatilize together with the solvent. Furthermore, the amount of volatilization of the sulfur source or oxygen source tends to increase as the heating temperature of the solution increases.

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

[0092] Furthermore, the first solution and the second solution heated in step S6 and step S8 both contain quantum dots 50. Therefore, in order to improve the dispersibility of the quantum dots 50 in the first solution and the second solution, xanthogenic acid may be added to both solutions as a ligand capable of coordinating with the quantum dots 50.

[0093] 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 xanthogenic acid is added to the first solution and the second solution, the proportion of xanthogenic acid coordinated to the quantum dots 50 in the second solution is lower than the proportion of xanthogenic acid coordinated to the quantum dots 50 in the first solution.

[0094] The xanthogenic acid that is not coordinated to the quantum dots 50 does not form a coordinate bond with the quantum dots 50, and therefore has a weak attractive force with the quantum dots 50. Therefore, the sulfur atoms of the xanthogenic acid that are not coordinated to the quantum dots 50 are more likely to volatilize together with the solvent when heated than the sulfur atoms of the xanthogenic acid that are coordinated to the quantum dots 50.

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

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

[0097] Following 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 applied to 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 with a film thickness of 60 nm. The zinc oxide nanoparticles 30 may be doped with at least one of Li, Mg, Al, Ti, Ga, and Zr. Alternatively, the nanoparticles 30 may be titanium oxide or zirconium oxide nanoparticles.

[0098] Next, the cathode 26 is formed on the electron transport layer 25 (step S10). In step S10, the cathode 26 may be formed by depositing a 50 nm-thick silver thin film by vacuum deposition. In this manner, the light-emitting element 11 is manufactured. Upon completion of the above-described manufacture of the light-emitting element 11, the manufacture of the display device 1 may be completed. Alternatively, following 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] <Effects of light-emitting elements> The light-emitting element 11 includes a light-emitting layer 24 having a plurality of quantum dots 50 and an inorganic filler 51 filling spaces between the plurality of quantum dots 50. The inorganic filler 51 contains at least one of a metal sulfide and a metal oxide, and the concentration of at least one of sulfur atoms and oxygen atoms gradually decreases in the direction from the anode 21 to the cathode 26. In particular, in the inorganic filler 51, the density of defects of at least one of sulfur atoms and oxygen atoms gradually increases in the direction from the anode 21 to the cathode 26.

[0100] Therefore, in the inorganic filler 51, the density of free electrons increases in the direction from the anode 21 to 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, thereby reducing the drive voltage of the light-emitting element 11 and improving the energy efficiency of the light-emitting layer 24. Furthermore, the carrier balance in the light-emitting layer 24 can be adjusted, improving the luminous efficiency of the light-emitting element 11.

[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 to the cathode 26.

[0102] Generally, electron mobility in semiconductors is higher than hole mobility, so in the light-emitting layer 24 containing quantum dots 50, light is mainly emitted from the quantum dots 50 located on the anode 21 side. Therefore, with the above-described configuration, the free electron density of the first inorganic filler 52 on the anode 21 side of the light-emitting layer 24 is low, resulting in high resistance. This allows the light-emitting layer 24 to reduce reactive current that does not contribute to light emission, which occurs when carriers flow through the first inorganic filler 52 without entering the quantum dots 50. Therefore, with the above-described configuration, the light-emitting element 11 can more efficiently emit light from the quantum dots 50. Furthermore, defects in the inorganic filler 52 are more likely to form on the surface than inside. Therefore, with the above-described configuration, the average distance between the defects and the quantum dots 50 can be increased, thereby suppressing exciton deactivation due to defects, resulting in a light-emitting element. 11 The luminous efficiency can be improved.

[0103] Furthermore, the second light-emitting layer 41 can effectively increase the thickness of the inorganic filler 51 that fills the spaces between the quantum dots 50 compared to the first light-emitting layer 40, thereby enhancing the protective effect of the inorganic filler 51 on the quantum dots 50. Therefore, the light-emitting element 11 can more efficiently protect the light-emitting layer 24 from foreign matter such as moisture and oxygen that infiltrate from the cathode 26 side, or heat that propagates from the cathode 26 side.

[0104] In particular, the light-emitting element 11 according to this embodiment includes an anode 21 on the substrate 20 side. Generally, the substrate 20 is less susceptible to infiltration of foreign matter such as moisture than the layers between the electrodes of the light-emitting element 11. Therefore, foreign matter is more likely to infiltrate the light-emitting element 11 from the cathode 26 side, which is the side opposite the substrate 20. Furthermore, since the electron transport layer 25, which is located closer to the cathode 26 than the light-emitting layer 24, includes nanoparticles 30, foreign matter that infiltrates the light-emitting element 11 from the cathode 26 side is more likely to pass between the nanoparticles 30 and reach the light-emitting layer 24. Therefore, with the above-described configuration, the light-emitting element 11 can more efficiently enhance the protective effect of the inorganic filler 51 in the light-emitting layer 24 on the quantum dots 50. Because glass substrates are less susceptible to infiltration of foreign matter such as moisture than film substrates, the substrate 20 is preferably a glass substrate.

[0105] The inorganic filler 51 may contain a binary compound semiconductor. In this case, the difference in density of atomic defects of sulfur atoms or oxygen atoms at each position in the inorganic filler 51 can be easily achieved by the difference in heating temperature in the above-described steps S6 and S8. In particular, the inorganic filler 51 may contain zinc sulfide from the viewpoint of enhancing the protection effect of the quantum dots 50 and increasing the efficiency of carrier injection into the quantum dots 50.

[0106] [Embodiment 2] <Inorganic filler layer> A display device 2 according to this embodiment will be described with reference to Fig. 4. Fig. 4 is a schematic side cross-sectional view of the display device 2 according to this embodiment. The display device 2 according to this 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, in this order from the anode 21 side, a first light-emitting layer 40 and a second light-emitting layer 42. The first light-emitting layer 40 according to this embodiment has the same configuration as the first light-emitting layer 40 according to the previous embodiment. The second light-emitting layer 42 according to this embodiment differs from the second light-emitting layer 41 according to the previous embodiment only in that it has only 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 including quantum dots 50 and a first inorganic filler 52 as an inorganic filler 51. The light-emitting layer 27 also has a second light-emitting layer 42 as an inorganic filler layer including a second inorganic filler 53 as an inorganic filler 51. Here, the second light-emitting layer 42 includes only the inorganic filler 51 out of the quantum dots 50 and the inorganic filler 51. As long as the above configuration is satisfied, the second light-emitting layer 42 may include a material different from the quantum dots 50 and the inorganic filler 51.

[0109] For this reason, also in this embodiment, the light-emitting layer 27 has a plurality of quantum dots 50, and further has, as the inorganic filler 51, a first inorganic filler 52 and a second inorganic filler 53, in that order from the anode 21 side. Therefore, also in this embodiment, the inorganic filler 51 contains at least one of a metal sulfide or a metal oxide, and the concentration of at least one of sulfur atoms or oxygen atoms gradually decreases in the direction from the anode 21 to the cathode 26. In particular, in the inorganic filler 51, the density of defects of at least one of sulfur atoms or oxygen atoms gradually increases in the direction from the anode 21 to the cathode 26.

[0110] With the above-described configuration, the light-emitting element 12 suppresses the electrons injected from the electron transport layer 25 in the light-emitting layer 27 from moving between the quantum dots 50 for the same reason as that explained for the light-emitting element 11. 7 This reduces the reactive current in the LED, improving the luminous efficiency and reliability.

[0111] In particular, in this 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 light-emitting layer 27 does not have quantum dots 50, which may be deteriorated by foreign matter from the cathode 26 side, in the second light-emitting layer 42 on the cathode 26 side. Furthermore, since the second light-emitting layer 42 does not contain quantum dots 50, the effective film thickness of the second inorganic filler 53 is increased, thereby enhancing the protective effect of the light-emitting layer 27. In addition, the light-emitting layer 27 efficiently transports electrons, which have a higher mobility than holes, from the second light-emitting layer 42 to the first light-emitting layer 40, and emits light from the quantum dots 50 in the first light-emitting layer 40. Therefore, the light-emitting element 12 has a light-emitting layer 2 7 This can improve the luminous efficiency while more efficiently enhancing the protective effect of the inorganic filler 51 on the quantum dots 50. The film thickness of the second light-emitting layer 42 may be 1.2 nm or more, or may be 6 nm or more. This allows the second light-emitting layer 42 to have a film thickness that is approximately twice or more the unit lattice of the second inorganic filler, thereby efficiently enhancing the protective effect of the light-emitting layer 27.

[0112] If the second light-emitting layer 42 is thick, there is a possibility that the driving voltage of the light-emitting element 12 will increase. For this reason, in this embodiment, in a region within 1.2 nm in the film thickness direction from the end face of the light-emitting layer 27 on the cathode 26 side, the density of free electrons in the inorganic filler 51 is set to 1×10 18 cm -3 The above configuration is preferable because it is possible to sufficiently increase the free electron density in the region, and therefore the light-emitting layer 27 can reduce the resistivity of the inorganic filler 51 in the region, thereby minimizing an increase in the driving voltage of the light-emitting element 12 and increasing the protection effect of the quantum dots 50.

[0113] In this embodiment, the boundary between the light-emitting layer 27 and the electron transport layer 25 may also be confirmed by observing a cross section passing through the light-emitting layer 27 and the electron transport layer 25 and confirming the composition of the material at each position on the cross section. In this embodiment, for example, a portion where the concentration of at least one atom contained in the second inorganic filler 53 is 25% or less may be considered to be the boundary between the light-emitting layer 27 and the electron transport layer 25. Alternatively, a portion where the concentration of at least one atom contained in the second inorganic filler 53 decreases by 25% or more may be considered to be the boundary between the light-emitting layer 27 and the electron transport layer 25. Note that if there is an atom with a high concentration in only one of the second inorganic filler 53 and the electron transport layer 25, the portion where the concentration of that atom changes by 25% or more may be considered to be the boundary between the light-emitting layer 27 and the electron transport layer 25. The criteria for confirming the boundary are given priority in the order of their description; in other words, an earlier description takes precedence over a later description.

[0114] In other words, even if the light-emitting layer 27 has a portion that does not contain quantum dots 50, such as the second light-emitting layer 42, the portion where the composition of the second inorganic filler 53 can be confirmed can be considered to be included in the second light-emitting layer 42, and therefore in the light-emitting layer 27.

[0115] The light-emitting element 12 according to this embodiment may be manufactured by the same method as the manufacturing method of the light-emitting element 11 according to the previous embodiment, following the flowchart shown in FIG. 3, except for the material of the second solution applied onto the first light-emitting layer 40 in step S7. In this embodiment, the second solution contains only the second inorganic precursor, which is a precursor of the quantum dots 50 and the second inorganic filler 53. For example, the second solution may contain other materials besides the quantum dots 50 and the second inorganic precursor. As a result, in step S8, a second light-emitting layer 42 having the second inorganic filler 53 but no quantum dots 50 is formed on the first light-emitting layer 40.

[0116] [Embodiment 3] <Multiple quantum dot layers> A display device 3 according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a schematic side cross-sectional view of the display device 3 according to this embodiment. The display device 3 according to this embodiment has the same configuration as the display device 2 according to the previous embodiment, except that it includes a light-emitting element 13 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 it includes a light-emitting layer 28 instead of the light-emitting layer 27.

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

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

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

[0120] In this embodiment, the concentration of at least one of sulfur atoms and oxygen atoms gradually decreases 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 other words, also in this embodiment, the concentration of at least one of sulfur atoms and oxygen atoms gradually decreases in the inorganic filler 51 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 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 other words, also in this embodiment, the density of atomic defects of at least one of sulfur atoms and oxygen atoms increases in the inorganic filler 51 in the direction from the anode 21 toward the cathode 26.

[0122] For the same reasons as those explained in the above-described embodiments, the light-emitting device 13 according to this embodiment has a light-emitting layer 2 8 In the light-emitting element 13, the electrons injected from the electron transport layer 25 are prevented from moving between the quantum dots 50. 8 This reduces the reactive current in the LED, improving the luminous efficiency and reliability.

[0123] The concentration of 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. Furthermore, as described above, the fourth light-emitting layer 45 does not have quantum dots 50. Therefore, for the same reasons as those described in the above embodiments, the light-emitting element 13 has the quantum dots 50 in the light-emitting layer 2. 8 This makes it possible to more efficiently enhance the protective effect of the inorganic filler 51 on the quantum dots 50 and improve the luminous efficiency.

[0124] In particular, the light-emitting element 13 according to this embodiment can reduce the decrease in luminous efficiency even when the efficiency of hole injection into the light-emitting layer 28 decreases due to deterioration of each component. For example, assume that, at the time of shipment of the display device 3, electron-hole recombination in the light-emitting layer 28 occurs in the quantum dots 50 near the second light-emitting layer 43, and the quantum dots 50 in the second light-emitting layer 43 are primarily emitting light. In this case, the mobility and injection efficiency of holes from the hole injection layer 22 to the light-emitting layer 28 may decrease due to deterioration of each component of the light-emitting element 13 caused by operation of the display device 3 or aging. This is generally due to the durability of the hole injection layer 22 or the hole transport layer 23 being inferior to the durability of the electron transport layer 25. This is particularly noticeable when the hole transport layer 23 is made of an organic material and the electron transport layer 25 is made of an inorganic material. As a result, the recombination of electrons and holes in the light-emitting layer 28 may occur in the quantum dots 50 closer to the anode 21 than the second light-emitting layer 43. Even in this case, recombination of electrons and holes in the light-emitting layer 28 can occur in the quantum dots 50 near the first light-emitting layer 40, causing the quantum dots 50 in the first light-emitting layer 40 to emit light, thereby reducing a decrease in the light-emitting efficiency of the light-emitting element 13. In other words, even if hole injection into the light-emitting layer 28 deteriorates due to deterioration of the layers of the light-emitting element 13, the light-emitting position simply shifts toward the anode 21, and a decrease in the light-emitting efficiency of the light-emitting element 13 due to a deterioration in the carrier balance in the light-emitting layer 28 can be suppressed. Therefore, the light-emitting layer 28 can improve the reliability of the light-emitting element 13.

[0125] The manufacturing method of the light emitting device 13 according to this embodiment can be the same as the manufacturing method of the light emitting device 12 according to the previous embodiment, except for the method of forming the light emitting layer 28. In this embodiment, the first light emitting layer 40, the second light emitting layer 43, and the third light emitting layer 44 of the light emitting layer 28 may be formed by repeatedly performing the above-described steps S5 and S6.

[0126] However, in this embodiment, the concentration of the quantum dots 50 in the solution to be applied in step S5 is gradually decreased, and the heating temperature of the solution in step S6 is gradually increased, and steps S5 and S6 are repeatedly performed. This allows the above-mentioned first light-emitting layer 40, second light-emitting layer 43, and third light-emitting layer 44 to be formed. Note that the concentration of the quantum dots 50 in the solution to be applied does not necessarily have to be changed, and may be approximately the same concentration.

[0127] Furthermore, in this embodiment, the fourth light-emitting layer 45 may be formed by performing steps S7 and S8 according to the previous embodiment. However, in this embodiment, the heating temperature of the solution in step S8 is higher than the heating temperature of the solution in step S6 described above, and steps S7 and S8 are performed. This allows the fourth light-emitting layer 45 described above to be formed, and the light-emitting layer 28 to be formed.

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

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

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

[0131] For example, the first inorganic filler 52, the second inorganic filler 54, the third inorganic filler 55, and the fourth inorganic filler 56 each have a composition of Zn X Mg 1-X S 1-Y where X and Y are real numbers satisfying 0≦X≦1 and 0≦Y<1, 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 to the cathode 26, while the concentration of magnesium atoms gradually decreases. Note that Y represents the proportion of sulfur atom defects in the inorganic filler 51, and may 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, X=0.3 in the first inorganic filler 52, X=0.6 in the second inorganic filler 54, X=0.9 in the third inorganic filler 55, and X=1 in the fourth inorganic filler 56. In this case, the fourth inorganic filler 56 contains zinc sulfide, which is a binary compound semiconductor. As such, the inorganic filler 51 according to this embodiment is not limited to a configuration consisting of only ternary compound semiconductors, and may also contain a portion of a binary compound semiconductor.

[0133] The manufacturing method of the light-emitting element 13 according to this modification can be the same as the manufacturing method of the light-emitting element 13 according to this 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 of the light-emitting layer 28 may be formed by repeatedly performing steps S5 and S6 described above. Furthermore, in this modification, the fourth light-emitting layer 45 may be formed by performing steps S7 and S8 according to this embodiment.

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

[0135] Next, in the process of forming the second light-emitting layer 43, in step S5, a second solution containing multiple quantum dots 50 and a second inorganic precursor having multiple metal sources is applied onto the hole transport layer 23. Here, the ratio of the metal sources in the second inorganic precursor is made different from that in the first inorganic precursor, thereby making the ratio of the metal sources in the second solution different from that in the first solution. As a result, in the next step S6, the second light-emitting layer 43 is formed, which has the first inorganic filler 52 and the second inorganic filler 54 having a different metal atom concentration. Note that in the above-mentioned step S6, the heating temperature of the second solution may be higher than the heating temperature of the first solution. Similarly, the third light-emitting layer 44 and the fourth light-emitting layer 45 are formed, thereby forming the light-emitting layer 28.

[0136] <Band diagram of each part of the light-emitting element> The band gaps of the respective parts of the light-emitting element 13 according to this modification will be described with reference to FIG. 6. FIG. 6 is a schematic band diagram showing an example of the band gaps of the respective parts of the light-emitting element 13 according to this modification. Note that the band diagram in FIG. 6 has a vacuum level at the upper side within the plane of the paper. The left and right directions of the band diagram in FIG. 6 represent the thickness direction in the display direction of the display device 3, with the left side of the plane of the paper being the anode 21 side and the right side being the cathode 26 side.

[0137] The band diagram in Figure 6 shows the Fermi levels of the anode 21 and the cathode 26. It also shows the band gaps of the hole injection layer 22, the hole transport layer 23, and the electron transport layer 25. In particular, the band gap of the nanoparticles 30 is shown as the band gap of the electron transport layer 25.

[0138] 6 shows the band gap of the light-emitting layer 28, including 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. In particular, the band diagram of FIG. 6 shows the band gaps of the core 50C and the shell 50S of the quantum dot 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.

[0139] Here, in the first light-emitting layer 40, the second light-emitting layer 43, and the third light-emitting layer 44, inorganic filler 51 fills the spaces between the quantum dots 50. Therefore, in the band diagram of Figure 6, 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 on both ends of the band gap of the quantum dots 50. Note that for the fourth light-emitting layer 45, only the band gap of the fourth inorganic filler 56 is illustrated.

[0140] 6, 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 become gradually smaller in this order. In other words, in this modification, the band gap of the inorganic filler 51 becomes gradually smaller in the direction from the anode 21 toward the cathode 26. The gradient of the band gap of the inorganic filler 51 described above is realized by the gradient of the concentration of metal atoms in the inorganic filler 51 described above.

[0141] In particular, the electron affinity of the inorganic filler 51 gradually increases in the direction from the anode 21 to the cathode 26. In the band diagram of FIG. 6, the electron affinity of each part corresponds to the distance from the vacuum level to the upper end of the band gap. Therefore, in the band diagram of FIG. 6, the lower the upper end of the band gap of a certain layer is located, the greater the electron affinity of that layer. In other words, the larger the band gap of a certain layer, the smaller the electron affinity of that layer tends to be.

[0142] The barrier to electron injection from the first layer to the second layer corresponds to the electron affinity of the first layer minus the electron affinity of the second layer. Therefore, in this modification, a barrier exists for electron injection from the fourth inorganic filler 56 to the third inorganic filler 55. Similarly, in this modification, a barrier exists for electron injection from the third inorganic filler 55 to the second inorganic filler 54, and for electron injection from the second inorganic filler 54 to the first inorganic filler 52.

[0143] Therefore, the light-emitting element 13 according to this modification suppresses the movement of electrons through the inorganic filler 51 in the direction from the cathode 26 to the anode 21. Therefore, the light-emitting element 13 can increase the ratio of carriers injected into the quantum dots 50 to carriers contributing to the reactive current flowing through the inorganic filler 51.

[0144] As described above, the light-emitting element 13 according to this modified example suppresses the movement of electrons injected from the electron transport layer 25 between the quantum dots 50 in the light-emitting layer 24, 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 inorganic filler 51, it is possible to easily design the band gap of inorganic filler 51 by adjusting the concentration of magnesium atoms. Furthermore, by including sulfide containing zinc atoms in inorganic filler 51, it is possible to improve the efficiency of carrier injection into quantum dots 50 while enhancing the protective effect of quantum dots 50.

[0146] <Display device having a plurality of sub-pixels> A display device 4 according to this embodiment will be described with reference to FIG. 7. FIG. 7 is a schematic side cross-sectional view of the display device 4 according to this embodiment. Compared to the display device 3 according to the previous embodiment, the display device 4 according to this embodiment includes a light-emitting element 14 instead of the light-emitting element 13. The display device 4 according to this embodiment also includes a plurality of subpixels in a plan view, and in particular includes a red subpixel SPR, a green subpixel SPG, and a blue subpixel SPB.

[0147] The light-emitting element 14 according to this 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 over the red sub-pixel SPR, the green light-emitting element 14G is located over the green sub-pixel SPG, and the blue light-emitting element 14B is located over the blue sub-pixel SPB.

[0148] Furthermore, compared to the light emitting element 13 according to the previous embodiment, the light emitting element 14 includes a bank 60 on the substrate 20. The bank 60 includes an insulating resin material such as polyimide, and is formed on each layer of the light emitting element 14, from the anode 21 to partway through the fourth light emitting layer 45 of the light emitting layer 28. Therefore, the bank 60 separates each layer of the light emitting element 14, from the anode 21 to the third light emitting layer 44 of the light emitting layer 28.

[0149] In particular, the layers from the anode 21 of the light-emitting element 14 to the third light-emitting layer 44 of the light-emitting layer 28 are partitioned into a red subpixel SPR, a green subpixel SPG, and a blue subpixel SPB in a plan view of the substrate 20. The fourth light-emitting layer 45, the electron transport layer 25, and the cathode 26 of the light-emitting layer 28 may be formed in common to the plurality of subpixels described above.

[0150] In this embodiment, the light-emitting layer 28 is partitioned into a red light-emitting layer 28R, a green light-emitting layer 28G, and a blue light-emitting layer 28B by the banks 60. In a plan view of the substrate 20, the red light-emitting layer 28R is located on the red subpixel SPR, the green light-emitting layer 28G is located on the green subpixel SPG, and the blue light-emitting layer 28B is located on the blue subpixel 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. 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. 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 have a common fourth light-emitting layer 45.

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

[0153] Red light is light having a central emission wavelength in a wavelength band of more than 600 nm and not more than 780 nm. Green light is, for example, light having a central emission wavelength in a wavelength band of more than 500 nm and not more than 600 nm. Blue light is, for example, light having a central emission wavelength in a wavelength band of 400 nm or more and not more than 500 nm.

[0154] Except for 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 according to the previous embodiment. In other words, also 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. 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 according to the previous embodiment.

[0155] Therefore, the red light-emitting element 14R includes a substrate 20, 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, which are formed in the red subpixel SPR. The green light-emitting element 14G includes a substrate 20, 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, which are formed in the green subpixel SPG. The blue light-emitting element 14B includes a substrate 20, 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, which are formed in the blue subpixel SPB.

[0156] In this embodiment, the anode 21, the hole injection layer 22, and the hole transport layer 23 may have the same design in any of the red subpixel SPR, the green subpixel SPG, and the blue subpixel SPB, except that each anode 21 is electrically connected to a driving circuit formed in each subpixel on the substrate 20.

[0157] The display device 4 applies a common potential to the cathode 26 and controls the voltage application to each anode 21 individually via the pixel circuit on the substrate 20. As a result, 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 extracted individually from each sub-pixel, thereby performing color display.

[0158] The light-emitting element 14 according to this embodiment may be manufactured by the same method as the light-emitting element 13 according to the previous embodiment, except for the manufacturing process of the light-emitting layer 28. In this embodiment, in the process of forming the light-emitting layer 28, for example, a photosensitive resin is formed only in specific subpixels by photolithography using a photosensitive resin. Next, a solution containing quantum dots is applied to form a film common to multiple subpixels. Next, the photosensitive resin may be peeled off together with the applied solution, thereby forming the light-emitting layer 28 only in specific subpixels. Alternatively, the light-emitting layer 28 may be formed by applying a different light-emitting layer 28 to each subpixel using an inkjet method or the like.

[0159] Each of the red light emitting element 14R, the green light emitting element 14G, and the blue light emitting element 14B according to this embodiment has the same configuration as the light emitting element 13 according to the previous embodiment, except for the emission color of the quantum dots included in the light emitting layer 28. Therefore, for the same reasons as those described above, each of the red light emitting element 14R, the green light emitting element 14G, and the blue light emitting element 14B has the same emission color as the light emitting layer 28. 8 This makes it possible to more efficiently enhance the protective effect of the inorganic filler 51 on the quantum dots 50 and improve the luminous efficiency.

[0160] Generally, the band gap of the material of the quantum dot core varies depending on the emission color of the core. Therefore, light-emitting devices having a light-emitting layer containing quantum dots as the light-emitting material have different band gaps in the charge transport layers, including the hole injection layer, hole transport layer, and electron transport layer, that are suited to the emission color of the light-emitting layer. Therefore, if the same charge transport layer is applied to light-emitting devices having light-emitting layers containing quantum dots with different emission colors, the carrier balance of the light-emitting layer 28 may not be optimized in any of the light-emitting devices.

[0161] In this embodiment, the red light emitting element 14R, the green light emitting element 14G, and the blue light emitting element 14B each have inorganic fillers 51 with different bandgaps in the stacking direction. Therefore, in the red light emitting element 14R, the green light emitting element 14G, and the blue light emitting element 14B, the light emitting positions of the quantum dots in each element differ in the stacking direction depending on the bandgaps of the quantum dots.

[0162] Therefore, in the light-emitting element 14, even if the charge transport layer is not optimized for the light-emitting element of each subpixel, by varying the light-emitting position of the quantum dots, it is possible to optimize the carrier balance of each light-emitting layer 28. Therefore, the light-emitting element 14 according to this embodiment can improve the carrier balance of each light-emitting layer 28 and increase the luminous efficiency while simplifying the manufacturing process by using a common charge transport layer for each subpixel.

[0163] In the present embodiment, the red light emitting element 14R, the green light emitting element 14G, and the blue light emitting element 14B each have the same layer structure as the light emitting element 13 according to the previous embodiment, but this is not limiting. For example, the red light emitting element 14R, the green light emitting element 14G, and the blue light emitting element 14B each may have the same layer structure as either the light emitting element 11 or the light emitting element 12 described above.

[0164] Furthermore, in this embodiment, any one of the red light emitting element 14R, the green light emitting element 14G, and the blue light emitting element 14B may have the same layered structure as the light emitting element according to any of the above-described embodiments. In other words, in this embodiment, some of the red light emitting element 14R, the green light emitting element 14G, and the blue light emitting element 14B may have a structure different from that of the light emitting element according to the above-described embodiments.

[0165] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. [Explanation of symbols]

[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 PCB 21 Anode 24, 27, 28 Light-emitting layer 25 Electron transport layer 26 cathode 30 nanoparticles 50 quantum dots 50C Core 50S Shell 51 Inorganic fillers

Claims

1. an anode; a cathode; a light-emitting layer located between the anode and the cathode; the light-emitting layer includes a plurality of quantum dots and an inorganic filler; the inorganic filler fills spaces between the quantum dots and includes at least one of a metal sulfide and a metal oxide; In the inorganic filler, the concentration of at least one of sulfur atoms and oxygen atoms decreases in a direction from the anode to the cathode.

2. an anode; a cathode; a light-emitting layer located between the anode and the cathode; the light-emitting layer includes a plurality of quantum dots and an inorganic filler; the inorganic filler fills spaces between the quantum dots and includes at least one of a metal sulfide and a metal oxide; The inorganic filler has a portion on the cathode side where the concentration of at least one of sulfur atoms and oxygen atoms is lower than the concentration of the at least one of sulfur atoms and oxygen atoms on the anode side.

3. The light-emitting device according to claim 1 , wherein the concentration of the quantum dots in the light-emitting layer decreases in a direction from the anode to the cathode.

4. 4. The light-emitting element according to claim 1, wherein the light-emitting layer includes, in order from the anode side, a quantum dot layer including the quantum dots and the inorganic filler, and an inorganic filler layer including only the inorganic filler among the quantum dots and the inorganic filler.

5. 5. The light-emitting device according to claim 4, wherein the inorganic filler layer has a thickness of 1.2 nm or more.

6. a substrate; The light-emitting element according to claim 1 , further comprising: the anode, the light-emitting layer, and the cathode, which are provided on the substrate in this order from the substrate side.

7. the density of free electrons in the inorganic filler is 1×10 in a region within 1.2 nm in a film thickness direction from the end face of the light-emitting layer on the anode side １６ cm －３ 4. The light-emitting device according to claim 1, wherein:

8. a defect density of the sulfur atoms or the oxygen atoms of the inorganic filler is 5×10 in a region within 1.2 nm in a film thickness direction from an end face of the light-emitting layer on the anode side; １７ cm －３ 4. The light-emitting device according to claim 1, wherein:

9. 4. The light-emitting element according to claim 1, wherein the density of free electrons in the inorganic filler in a region within 1.2 nm in the film thickness direction from the end face of the light-emitting layer on the anode side is equal to or less than one-tenth of the density of free electrons in the inorganic filler in a region within 1.2 nm in the film thickness direction from the end face of the light-emitting layer on the cathode side.

10. the density of free electrons in the inorganic filler is 1×10 in a region within 1.2 nm in a film thickness direction from the end face of the light-emitting layer on the cathode side １８ cm －３ That's it, 4 x 10 １９ cm －３ 4. The light-emitting device according to claim 1, wherein:

11. a defect density of the sulfur atoms or the oxygen atoms of the inorganic filler is 5×10 in a region within 1.2 nm in a film thickness direction from an end face of the light-emitting layer on the cathode side; １９ cm －３ That's it, 2 x 10 ２１ cm －３ 4. The light-emitting device according to claim 1, wherein:

12. The quantum dot has a core and at least one shell covering the core, The light-emitting element according to claim 1 , wherein the outermost shell of the quantum dots and the inorganic filler contain the same material.

13. The light-emitting device according to claim 1 , wherein the inorganic filler contains a binary compound semiconductor.

14. The light-emitting device according to claim 1 , wherein the inorganic filler contains zinc sulfide.

15. The light-emitting device according to claim 1 , further comprising an electron transport layer located between the light-emitting layer and the cathode, the electron transport layer having a plurality of nanoparticles.

16. an anode; a cathode; a light-emitting layer located between the anode and the cathode; the light-emitting layer includes a plurality of quantum dots and an inorganic filler; the inorganic filler fills spaces between the quantum dots and includes at least one of a metal sulfide and a metal oxide; In the inorganic filler, the density of atomic defects of at least one of sulfur atoms and oxygen atoms increases in the direction from the anode to the cathode.

17. an anode; a cathode; a light-emitting layer located between the anode and the cathode; The light-emitting layer is A plurality of quantum dots; an inorganic filler material containing a chalcogenide and filling spaces between the quantum dots; and In the inorganic filler, the concentration of chalcogen element atoms decreases in a direction from the anode to the cathode.

18. an anode; a cathode; a light-emitting layer located between the anode and the cathode; the light-emitting layer includes a plurality of quantum dots and an inorganic filler; the inorganic filler fills spaces between the quantum dots, includes a ternary compound semiconductor having metal atoms, and has a concentration gradient of the metal atoms in a direction from the anode to the cathode; The light-emitting device has a band gap of the inorganic filler that decreases in a direction from the anode to the cathode.

19. The light-emitting device 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 red light-emitting element, a green light-emitting element, and a blue light-emitting element; A display device, wherein 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 claim 1 .

22. an anode; a cathode; a light-emitting layer located between the anode and the cathode; the light-emitting layer includes a plurality of quantum dots and an inorganic filler; The inorganic filler fills spaces between the quantum dots and contains at least one of a metal sulfide and a metal oxide, applying a first solution comprising the plurality of quantum dots and a first inorganic precursor; forming a first portion of the light-emitting layer by heating the first solution at a first temperature to convert the first inorganic precursor into the inorganic filler; applying a second solution onto the first portion, the second solution including a second inorganic precursor; 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 convert the second inorganic precursor into the inorganic filler.

23. an anode; a cathode; a light-emitting layer located between the anode and the cathode; the light-emitting layer includes a plurality of quantum dots and an inorganic filler; the inorganic filler fills spaces between the quantum dots, includes a ternary compound semiconductor having metal atoms, and has a concentration gradient of the metal atoms in a direction from the anode to the cathode, applying a first solution comprising 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 convert the first inorganic precursor into the inorganic filler; applying onto the first portion a second solution comprising a second inorganic precursor having a plurality of said metal sources, the second solution having a different ratio of said metal sources than the first solution; forming a second portion of the light-emitting layer on the first portion by heating the second solution to convert the second inorganic precursor into the inorganic filler; A method for manufacturing a light-emitting device, wherein the band gap of the inorganic filler in the second portion is smaller than the band gap of the inorganic filler in the first portion.

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