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

Abstract

This light-emitting element (2) comprises a light-emitting layer (23) positioned between an anode (21) and a cathode (25). The light-emitting layer includes a plurality of quantum dots (30) and an inorganic matrix (31) that fills the spaces between the plurality of quantum dots and has a metal oxide. The inorganic matrix includes a first part (41) and a second part (42) each having a metal oxide. The ratio of oxygen atoms to metal atoms in the second part is higher than the ratio of oxygen atoms to metal atoms in the first part, and is equal to or less than the ratio of oxygen atoms to metal atoms in the metal oxides that are stoichiometric.

Description

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

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

[0002] Non-Patent Document 1 discloses a quantum dot structure having quantum dots (semiconductor nanoparticles) in a matrix containing silicon oxide (silica) as a light emitter used in a light-emitting device. The structure having quantum dots in a matrix protects the quantum dots with the matrix, improving the reliability of the quantum dots.

[0003] Cong Shen, Yanqing Zhu et al. Blue-Emitting InP / GaP / ZnS Quantum Dots with Enhanced Stability by Siloxane Capping: Implication for Electroluminescent Devices. ACS Appl. Nano Mater. 2022.5.2, pp. 2801-2811.

[0004] In a light-emitting device having a light-emitting layer including a structure such as that described in Non-Patent Document 1, the matrix may inhibit the injection of charges from each electrode into the quantum dots, resulting in an increase in the resistance of the light-emitting device or a decrease in the light-emitting efficiency of the light-emitting device. Furthermore, oxygen atoms in the matrix of the structure described in Non-Patent Document 1 may deteriorate the quantum dots, materials surrounding the quantum dots, or materials surrounding the structure.

[0005] A light-emitting element according to one aspect of the present disclosure includes an anode, a cathode facing the anode, and a light-emitting layer located between the anode and the cathode. The light-emitting layer includes a plurality of quantum dots and an inorganic matrix having a metal oxide and filling spaces between the quantum dots. The inorganic matrix includes a first portion having the metal oxide, and a second portion having the metal oxide, wherein the ratio of oxygen atoms to metal atoms is higher than the ratio of oxygen atoms to metal atoms in the first portion and is equal to or lower than the ratio of oxygen atoms to metal atoms in the metal oxide, which is stoichiometric.

[0006] A method for manufacturing a light-emitting element according to one aspect of the present disclosure is a method for manufacturing a light-emitting element including an anode, a cathode facing the anode, and a light-emitting layer located between the anode and the cathode, the method including forming the light-emitting layer, the light-emitting layer including a plurality of quantum dots and an inorganic matrix having a metal oxide and filling spaces between the plurality of quantum dots, the inorganic matrix including a first portion having the metal oxide, and a second portion having the metal oxide, the second portion having the metal oxide, the ratio of oxygen atoms to metal atoms being higher than the ratio of oxygen atoms to metal atoms in the first portion and equal to or lower than the ratio of oxygen atoms to metal atoms in the metal oxide, which is stoichiometric.

[0007] According to one aspect of the present disclosure, a configuration is provided in a light-emitting element that enables a design that can improve the efficiency of injection of charges from each electrode into quantum dots, or that reduces deterioration of the light-emitting layer or the area around the light-emitting layer.

[0008] 1 is a schematic side cross-sectional view of a display device according to embodiment 1. FIG. 2 is a schematic view of a display device according to embodiment 1. FIG. 3 is a schematic enlarged view of a cross section of a light-emitting layer according to embodiment 1. FIG. 4 is a schematic view showing an inorganic matrix filling spaces between quantum dots according to embodiment 1. FIG. 5 is a schematic view showing an example of the structure of the inorganic matrix according to embodiment 1. FIG. 6 is a schematic view showing another example of the structure of the inorganic matrix according to embodiment 1. FIG. 7 is a schematic view showing another example of the structure of the inorganic matrix according to embodiment 1. FIG. 8 is a flowchart showing a method for forming a light-emitting layer according to embodiment 1. FIG. 9 is a schematic view showing a first dispersion according to embodiment 1. FIG. 10 is a process cross-sectional view showing a part of the method for forming a light-emitting layer according to embodiment 1. FIG. 11 is a flowchart showing a method for forming a light-emitting layer according to embodiment 2. FIG. 12 is a schematic side cross-sectional view of a display device according to embodiment 3. FIG. 13 is a schematic enlarged view of a cross section of a light-emitting layer according to embodiment 3. FIG. 14 is a flowchart showing a method for forming a light-emitting layer according to embodiment 3. FIG. 15 is a process side view showing a mixing step in the method for forming a light-emitting layer according to embodiment 3. FIG. 16 is a schematic view showing a reaction process of precursors according to embodiment 3. FIG. 17 is a schematic view showing a third dispersion according to embodiment 3. FIG. 18 is a schematic view showing a fourth dispersion according to embodiment 3. Fig. 10 is a cross-sectional view showing a process of a part of a method for forming a light-emitting layer according to Embodiment 3. Fig. 11 is a flowchart showing a method for forming a light-emitting layer according to Embodiment 4. Fig. 12 is a schematic cross-sectional side view of a display device according to Embodiment 5.

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

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

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

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

[0013] The light-emitting element 2 includes an anode 21, a hole transport layer 22, a light-emitting layer 23, an electron transport layer 24, and a cathode 25, in this order from the substrate 3 side. The anode 21 is electrically connected to the TFT of the substrate 3.

[0014] <Outline of Light-Emitting Element> The structure of each layer of the light-emitting element 2 will be described in more detail below.

[0015] The anode 21 and the cathode 25 comprise conductive materials and are electrically connected to the hole transport layer 22 and the electron transport layer 24, respectively.

[0016] At least one of the anode 21 and the cathode 25 is a transparent electrode that transmits visible light. Examples of transparent electrodes that can be used include ITO (indium tin oxide), IZO (indium zinc oxide), ZnO, AZO (aluminum-doped zinc oxide, also known as ZAO), BZO (boron-doped zinc oxide), and FTO (fluorine-doped tin oxide). The transparent electrode may be formed by a sputtering method or the like. Alternatively, either the anode 21 or the cathode 25 may contain a metal material, preferably Al, Cu, Au, Ag, or Mg, or an alloy thereof, which have high reflectivity for visible light.

[0017] The hole transport layer 22 is a layer containing a hole transport material that transports holes from the anode 21 to the light-emitting layer 23. The material of the hole transport layer 22 can be an organic or inorganic material that has been conventionally used in light-emitting devices including quantum dots. For example, the hole transport layer 22 may contain at least one of polyvinylcarbazole (PVK) and [N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (TPD) as the hole transport material. As the organic material for the hole transport layer 22, conductive compounds such as 4,4'-bis(carbazol-9-yl)biphenyl (CBP), polyphenylene vinylene (PPV), a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT-PSS), and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl)diphenylamine)]) (TFB) can be used. As the inorganic material for the hole transport layer 22, molybdenum oxide, NiO, Cr ２ O ３ , MgO, MgZnO, LaNiO ３ , MoO ３ , or W.O. ３ In particular, as the material for the hole transport layer 22, a material having a large electron affinity and ionization potential is suitable.

[0018] The electron transport layer 24 is a layer containing an electron transport material that transports electrons from the cathode 25 to the light-emitting layer 23. The material of the electron transport layer 24 can be an organic or inorganic material that has been conventionally used in light-emitting devices containing quantum dots. For example, the electron transport layer 24 can be made of zinc oxide (ZnO), zinc magnesium oxide (ZnMgO), titanium oxide (TiO), and tungsten oxide (WO ３ ), or may contain an inorganic nanoparticle material that is a nanoparticle of these inorganic materials. Alternatively, the electron transport layer 24 may contain an organic material as the electron transport material, such as tris(8-quinolinol)aluminum complex (Alq3), bathocuproine (BCP), or (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) (t-Bu-PBD). Note that, as the inorganic material of the electron transport layer 24, metal oxides such as ZnO, ZAO, ITO, InGaZnO, or electride may be used. In particular, a material with a small electron affinity is suitable as the material of the electron transport layer 24.

[0019] In this embodiment, the hole transport layer 22 and the electron transport layer 24 can be formed by vacuum deposition, sputtering, or a coating method using a colloidal solution using the above-mentioned materials. The light-emitting element 2 may also include a hole injection layer between the anode 21 and the hole transport layer 22, or an electron injection layer between the cathode 25 and the electron transport layer 24. The light-emitting element 2 may also include an intermediate layer between the hole transport layer 22 and the light-emitting layer 23, or between the electron transport layer 24 and the light-emitting layer 23. The hole injection layer, electron injection layer, and intermediate layer may all be formed by the same method as the hole transport layer 22 or the electron transport layer 24.

[0020] <Light-emitting layer: quantum dots> The light-emitting layer 23 according to this embodiment will be described in more detail with reference to Fig. 3 in addition to Fig. 1. Fig. 3 is an enlarged schematic view of the light-emitting layer 23 in the cross section shown in Fig. 1, and in particular, an enlarged view of region E1 shown in Fig. 1.

[0021] The light-emitting layer 23 includes a plurality of quantum dots 30 and an inorganic matrix 31 .

[0022] The quantum dots 30 may each have a core / shell structure, including a core and a shell surrounding the core. In this embodiment, the quantum dots 30 are, for example, luminescent semiconductor nanoparticles that emit light due to excitons generated by the recombination of injected electrons and holes. For example, the recombination of electrons and holes in the quantum dots 30 occurs primarily in the core. The core of the quantum dot 30 is a luminescent material that has a valence band level and a conduction band level and emits light due to the recombination of holes in the valence band level and electrons in the conduction band level. The quantum dots 30 emit light with a narrow spectrum due to the quantum confinement effect, enabling the production of light with a relatively deep chromaticity. Furthermore, the shell functions to suppress the occurrence of defects or dangling bonds in the core and reduce the recombination of carriers undergoing a deactivation process.

[0023] The core and shell materials of the quantum dots 30 may each contain materials used for the core and shell materials of conventionally known core / shell quantum dots. The quantum dots 30 may have a core / shell structure such as InP / ZnS, CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, ZnSe / ZnS, or CIGS / ZnS. The shell may be formed of multiple layers containing multiple different materials.

[0024] The quantum dots 30 have a particle size of about 1 to 100 nm. The wavelength of light emitted from the quantum dots 30 can be controlled by the particle size. In particular, since the quantum dots 30 have a core / shell structure, the wavelength of light emitted from the quantum dots 30 can be controlled by controlling the particle size of the core. Therefore, by controlling the particle size of the quantum dots 30, the wavelength of light emitted by the display device 1 can be controlled.

[0025] <Light-Emitting Layer: Inorganic Matrix> In this embodiment, the inorganic matrix 31 fills the spaces between the quantum dots 30. The inorganic matrix 31 filling the spaces between the quantum dots 30 will be described in more detail with further reference to FIG. 4 . Schematic diagrams 401 and 402 in FIG. 4 are schematic diagrams showing the inorganic matrix 31 filling the spaces between the quantum dots 30. In particular, schematic diagrams 401 and 402 are respectively diagrams showing two examples of a set P of two quantum dots 30 and the region (space) K between them, as shown in FIG. 3 . In particular, schematic diagrams 401 and 402 are respectively diagrams showing set P1 and set P2, which are examples of sets of quantum dots 30A and quantum dots 30B.

[0026] In this specification, "the inorganic matrix 31 fills the spaces between the quantum dots 30" means that the inorganic matrix 31 fills at least the region K between the quantum dots 30A and 30B, as shown in the schematic diagram 401 of the set P1 in Fig. 4. The region K is a region surrounded by two lines (common circumscribing lines) tangent to the peripheries of the quantum dots 30A and 30B and the opposing peripheries of the quantum dots 30A and 30B in the cross section of the light-emitting layer 23. Therefore, as shown in the schematic diagram 402 of the set P2 in Fig. 4, the region K can exist even if the quantum dots 30A and 30B are close to each other, and the inorganic matrix 31 fills the region K.

[0027] The phrase "the inorganic matrix 31 fills the spaces between the quantum dots 30" does not necessarily mean that the region K between the quantum dots 30A and 30B is entirely composed of the inorganic matrix 31. For example, the region K between the quantum dots 30A and 30B may contain a material, such as a ligand, that is different from the material of the inorganic matrix 31. Specifically, for example, the light-emitting layer 23 may contain an organic ligand that is added to improve the dispersibility of the quantum dots 30 in a dispersion liquid used for coating and that coordinates to the outer surfaces of the quantum dots 30 in the dispersion liquid. In this case, in the light-emitting layer 23, from the viewpoint of improving the reliability of the light-emitting layer 23, for example, the weight ratio of the organic ligand to the total weight including the region K may be less than 5%.

[0028] 1 and 3 , the inorganic matrix 31 may fill the regions of the light-emitting layer 23 other than the regions where the quantum dots 30 are present. For example, the outer edges (upper and lower surfaces) of the light-emitting layer 23 may be covered with the inorganic matrix 31. Alternatively, the light-emitting layer 23 may be configured such that a portion of the inorganic matrix 31 extends from the outer edge thereof, with the quantum dots 30 positioned away from the outer edge. The outer edge of the light-emitting layer 23 may not be formed solely by the inorganic matrix 31, and some of the quantum dots 30 may be exposed from the inorganic matrix 31. The inorganic matrix 31 may refer to the portion of the light-emitting layer 23 other than the regions where the quantum dots 30 are present.

[0029] The inorganic matrix 31 is formed at a position in the thickness direction of the light-emitting layer 23 so as to have a thickness of 1000 nm in a plane perpendicular to the thickness direction. ２ In the light-emitting layer 23, the quantum dots 30 may be encapsulated in a continuous film of the inorganic matrix 31.

[0030] For example, when 60% or more of the surface of 80% or more of the quantum dots 30 constituting the light-emitting layer 23 is in contact with the continuous film of the inorganic matrix 31, the quantum dots 30 contained in the light-emitting layer 23 can be said to be encapsulated in the inorganic matrix 31. In this way, the light-emitting layer 23 containing the quantum dots 30 encapsulated in the inorganic matrix 31 has improved luminescence properties and a longer lifespan.

[0031] The light-emitting layer 23 has a thickness of 1000 nm or less in a plane direction perpendicular to the thickness direction at any position in the thickness direction. ２ The light-emitting layer 23 may contain one or more quantum dots 30 per layer. In this case, the light-emitting layer 23 generally contains quantum dots 30 at a concentration sufficient to function as a light-emitting layer of a light-emitting device.

[0032] The inorganic matrix 31 may be located, for example, around the entire periphery of the quantum dot 30. For example, as shown in Fig. 3, in any cross section passing through any quantum dot 30, the inorganic matrix 31 may be located around the entire periphery of the quantum dot 30. Here, "the inorganic matrix 31 is located around the entire periphery of the quantum dot 30" may mean that the inorganic matrix 31 is located around 90% or more of the periphery of the quantum dot 30. Furthermore, as shown in Fig. 3, the surface of the quantum dot 30 and the inorganic matrix 31 may be in contact with each other.

[0033] The band gap of the inorganic matrix 31 may be wider than the band gap of the constituent material of the quantum dots 30. When the quantum dots 30 have a core and a shell surrounding the core, the band gap of the inorganic matrix 31 may be wider than the band gap of the constituent material of the shell.

[0034] In this embodiment, the inorganic matrix 31 includes a metal oxide. Here, the metal oxide in this specification includes oxides having atoms that are sometimes generally called semimetal atoms, including silicon (Si), boron (B), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te) as metal atoms.

[0035] In this disclosure, the term "atom" does not only mean that an atom exists as a single atom. In this disclosure, the term "atom" also includes an atom that exists in the form of a molecule having two or more atoms, including the atom and another atom, an atom that exists in the form of a complex, an atom that exists in the form of a compound, or an atom that exists in the form of an ion. However, the term "atom" in this disclosure does not limit the form of existence of other atoms. In other words, a metal atom includes an atom that exists in the form of a compound having a metal atom, and an atom that exists in the form of a metal ion. Regardless of the form of existence of a metal atom, if its presence in a substance can be identified by analysis, the substance may be considered to contain the metal atom.

[0036] In particular, the inorganic matrix 31 is, for example, silicon oxide (SiO ２) as a metal oxide. Alternatively, the inorganic matrix 31 may contain, for example, titanium oxide (TiO ２ ), aluminum oxide (Al ２ O ３ ), boron oxide (B ２ O ３ ), phosphorus oxide (P ２ O ５ ), germanium oxide (GeO ２ ), hafnium oxide (HfO ２ ), zinc oxide (ZnO), zirconium oxide (ZrO ２ ), tellurium oxide (TeO ２ ), bismuth oxide (Bi ２ O ３ ), vanadium oxide (V ２ O ５ ), antimony oxide (Sb ２ O ５ The compound may include one or more selected from the group consisting of lead oxide (PbO), lead oxide (PbO), and copper oxide (CuO). The chemical formulas written in parentheses after the compound names are representative examples.

[0037] The chemical formulas of the metal oxides described above are based on the case where the metal oxides have a stoichiometric composition ratio. However, a portion of the inorganic matrix 31 according to this embodiment may contain a metal oxide having a composition ratio different from that of the stoichiometric metal oxide. In particular, the metal oxide contained in the inorganic matrix 31 according to this embodiment has a ratio of oxygen atoms to metal atoms that is equal to or less than the ratio of oxygen atoms to metal atoms in the stoichiometric metal oxide.

[0038] In this specification, the stoichiometric metal oxide may refer to a metal oxide having a composition ratio that can exist most stably among the composition ratios that can be obtained from the ratio of the valences of the metal atoms and oxygen atoms of the metal oxide. For example, silicon oxide as a metal oxide is SiO ２ and SiO as the chemical formula, but unless otherwise specified, in this specification, stoichiometric silicon oxide is SiO ２Similarly, stoichiometric titanium oxide refers to silicon oxide having the same composition ratio as TiO ２ , stoichiometric aluminum oxide is Al ２ O ３ , stoichiometric boron oxide is B ２ O ３ , stoichiometric phosphorus oxide is P ２ O ５ , stoichiometric germanium oxide is GeO ２ Hafnium oxide, which is stoichiometric, is HfO ２ , stoichiometric zinc oxide is ZnO, stoichiometric zirconium oxide is ZrO ２ , stoichiometric tellurium oxide is TeO ２ Bismuth oxide, which is stoichiometric, is Bi ２ O ３ , stoichiometric vanadium oxide is V ２ O ５ , stoichiometric antimony oxide is Sb ２ O ５ Stoichiometric lead oxide refers to PbO, and stoichiometric copper oxide refers to a metal oxide having the same composition ratio as CuO.

[0039] <Metal Oxide Structure> Specific examples of the structure of the metal oxide contained in the inorganic matrix 31 will be described with reference to Fig. 5 to Fig. 7. Fig. 5 to Fig. 7 are schematic diagrams showing examples of the structure of the metal oxide contained in the inorganic matrix 31 according to this embodiment. Fig. 5 to Fig. 7 show examples of the structure of the inorganic matrix 31 when the inorganic matrix 31 contains silicon oxide as the metal oxide 60.

[0040] 5, the metal oxide 60 contained in the inorganic matrix 31 has a two-dimensional network structure having Si—O—Si bonds. In addition, in FIG. 5, the metal oxide 60 has bonding portions BD in which some of the Si—O—Si bonds have been replaced with Si—Si bonds.

[0041] As shown in Fig. 6, the metal oxide 60 contained in the inorganic matrix 31 may be a metal oxide 64 containing SiO. For example, assume that the centers of silicon atoms and oxygen atoms of the metal oxide 64 shown in Fig. 6 are on the same plane. In this case, the metal oxide 64 may have Si-Si bonds extending in a direction approximately perpendicular to the extension direction of each Si-O-Si bond. As a result, the metal oxide 64 may have a two-dimensional network structure having approximately the same number of Si-O-Si bonds and Si-Si bonds.

[0042] 6 contains approximately the same number of silicon atoms and oxygen atoms as metal atoms. Therefore, the ratio of oxygen atoms to metal atoms in the metal oxide 64 is stoichiometric. ２ The ratio of oxygen atoms to metal atoms in the SiO2 film is 50%.

[0043] As shown in FIG. 7, the metal oxide 60 contained in the inorganic matrix 31 is SiO ２ In other words, it may contain stoichiometric silicon oxide. In this case, the metal oxide 65 may have a two-dimensional network structure having only Si—O—Si bonds.

[0044] 5 is equal to or less than the number of Si—O—Si bonds in the metal oxide 60. Therefore, the ratio of oxygen atoms to metal atoms in the metal oxide 60 is between the ratio of oxygen atoms to metal atoms in the metal oxide 64 and the ratio of oxygen atoms to metal atoms in the metal oxide 65. In other words, the ratio of oxygen atoms to metal atoms in the metal oxide 60 is 50% or more of the ratio of oxygen atoms to metal atoms in the metal oxide 65, which is stoichiometric.

[0045] 5, the average distance L between adjacent bonds BD in the metal oxide 60 increases as the number of bonds BD relative to the Si—O—Si bond decreases. The length of the average distance L will be considered below.

[0046] For example, the distance between the oxygen atom and the silicon atom of the Si—O—Si bond in the metal oxide 60 is defined as d. ２ In this case, the distance d is about 0.16 nm. In the metal oxide 60, the ratio of the bond portion BD to the total number of Si—O—Si bonds is r. In this case, when the metal oxide of the inorganic matrix 31 is SiO ｘ Then x=2(1−r).

[0047] Here, it is assumed that the silicon atoms and oxygen atoms in the metal oxide 60 are on a certain plane, and furthermore, a square SQ on the metal oxide 60 shown in Figure 5 is assumed on the plane. The square SQ has a side length of d, and one of the four vertices is located at the center of the silicon atom, and the other two are located at the centers of the oxygen atoms adjacent to the silicon atom. In this case, the area of ​​the square SQ is d ２ The number of oxygen atoms contained in the square SQ is 1 / 2. Therefore, the number of bonds BD contained in the square SQ is r / 2.

[0048] From this, the average value of the area including one bond BD in the metal oxide 60 is d ２ / (r / 2) = 2d ２ Therefore, since the square root of the area corresponds to the average distance L, L = d(2 / r) １／２ From this formula, it can be seen that the smaller the ratio r, in other words, the smaller the ratio of the bond portions BD to the Si—O—Si bonds, the longer the average distance L becomes.

[0049] 1 and 3, the inorganic matrix 31 includes a first portion 41 and a second portion 42 each having a metal oxide. In this embodiment, the ratio of oxygen atoms to metal atoms in the second portion 42 is higher than the ratio of oxygen atoms to metal atoms in the first portion 41. For example, when x and y are real numbers, the inorganic matrix 31 includes silicon oxide as a metal oxide, and the silicon oxide included in the first portion 41 is SiO ｘ The silicon oxide contained in the second portion 42 is SiO ｙ If x is greater than y, then y is higher than x.

[0050] The ratio of oxygen atoms to metal atoms in the metal oxide of the inorganic matrix 31 of the light-emitting layer 23 according to this embodiment may be confirmed by: Method 1: measuring the ratio of metal atoms to oxygen atoms in the thickness direction of the light-emitting layer 23 using SIMS (secondary ion mass spectroscopy). Alternatively, Method 2: measuring the ratio of metal atoms to oxygen atoms in the thickness direction of the light-emitting layer 23 by performing ion sputtering on the light-emitting layer 23 and XPS (X-ray photoelectron spectroscopy) to confirm the ratio. Alternatively, Method 3: performing AES (Auger electron spectroscopy) on a cross section of the light-emitting layer 23 to measure the ratio of metal atoms to oxygen atoms at a target location to confirm the ratio. Alternatively, Method 4: measuring the ratio of metal atoms to oxygen atoms at a target location on a cross section of the light-emitting layer 23 by EDX (energy dispersive X-ray spectroscopy) using an SEM (scanning electron microscope) or a TEM (transmission electron microscope) to confirm the ratio. When using TEM in Method 4, processing the cross section of the light-emitting layer 23 using FIB (focused ion beam) may be performed in combination. The methods for checking the ratio are prioritized in the order of Method 1 to Method 4 described above, and if the ratio can be checked by the first method, the check by the second method may be omitted.

[0051] In this embodiment, the first portion 41 is located closer to the anode 21 than the second portion 42. In particular, the light-emitting layer 23 may include a first light-emitting layer 23A including the first portion 41, and a second light-emitting layer 23B located closer to the cathode 25 than the first light-emitting layer 23A and including the second portion 42. In this case, some of the quantum dots 30 may be located at the boundary between the first light-emitting layer 23A and the second light-emitting layer 23B, in other words, they may be included in both the first light-emitting layer 23A and the second light-emitting layer 23B.

[0052] <Light-emitting layer: additional notes> The quantum dots 30 in the light-emitting layer 23 may be regularly arranged in the light-emitting layer 23, or may be included in the light-emitting layer 23 in a disordered manner. In the light-emitting layer 23 shown in FIG. 1 , an inorganic matrix 31 (described later) is formed between two quantum dots 30, and the quantum dots 30 are not in contact with each other. However, this is not limiting, and the light-emitting layer 23 may include two or more quantum dots 30 that are in contact with each other. The film thickness of the light-emitting layer 23 may be approximately 1 nm to 100 nm.

[0053] As will be described later, when the light-emitting layer 23 is formed from a quantum dot dispersion liquid containing the quantum dots 30, a step of heating the quantum dot dispersion liquid may be included. Therefore, in this embodiment, from the viewpoint of the heat resistance of the light-emitting element 2, all of the layers provided in the light-emitting element 2, from the anode 21 to the cathode 25, may be formed of inorganic layers.

[0054] <Injection of Charges into the Light-Emitting Layer> In this embodiment, the light-emitting layer 23 has a metal oxide in the inorganic matrix 31 that fills the spaces between the quantum dots 30. The inorganic matrix 31 also has a first portion 41 and a second portion 42 in which the ratio of oxygen atoms to metal atoms is higher than that of the first portion 41. Therefore, in the metal oxide contained in the inorganic matrix 31, the ratio of oxygen atoms to metal atoms varies depending on the position.

[0055] When the ratio of oxygen atoms to metal atoms in the metal oxide of inorganic matrix 31 is close to the ratio in a stoichiometric metal oxide, the number of bonds between metal atoms and oxygen atoms increases, and the structure formed by the metal oxide becomes denser. Therefore, second portion 42, in which the ratio of oxygen atoms to metal atoms is closer to the ratio in a stoichiometric metal oxide than first portion 41, better prevents foreign substances such as moisture from reaching quantum dots 30, improving the protective effect of quantum dots 30.

[0056] On the other hand, when the ratio of oxygen atoms to metal atoms in the metal oxide contained in the inorganic matrix 31 is low, the number of portions where metal atoms are bonded to each other increases, as in the above-mentioned bond portions BD. At the bond portions BD, the metal oxide has stronger metallic or semiconducting properties compared to portions having Si—O—Si bonds. Therefore, the inorganic matrix 31 having the bond portions BD is more likely to transport charges via the bond portions BD. In particular, metal oxides containing many bond portions BD transport charges more efficiently than metal oxides with fewer bond portions BD.

[0057] When the ratio of oxygen atoms to metal atoms in the metal oxide of the inorganic matrix 31 is low, the distance between two adjacent bonds BD becomes shorter. The shorter the distance between two adjacent bonds BD, the higher the probability of charge tunneling between the bonds BD. Therefore, when the ratio of oxygen atoms to metal atoms in the metal oxide of the inorganic matrix 31 is low, charge transfer becomes easier in the metal oxide.

[0058] As described above, the light-emitting layer 23 can improve the transfer of charges in the first portion 41 while protecting the quantum dots 30 in the second portion 42. Therefore, the light-emitting element 2 including the light-emitting layer 23 can be designed to improve the efficiency of injection of charges from each electrode into the quantum dots 30 while protecting the quantum dots 30, thereby achieving both a longer lifespan and higher luminous efficiency. A display device 1 including the light-emitting element 2 that achieves both a longer lifespan and higher luminous efficiency achieves a longer lifespan or lower power consumption.

[0059] In particular, the light-emitting layer 23 contains, in the inorganic matrix 31, a metal oxide having a lower ratio of oxygen atoms to metal atoms than a stoichiometric metal oxide. Therefore, the concentration of oxygen atoms in the light-emitting layer 23 is reduced compared to when the inorganic matrix 31 contains only a stoichiometric metal oxide. Therefore, the light-emitting layer 23 is less susceptible to deterioration caused by oxygen atoms contained in the inorganic matrix 31 oxidizing the quantum dots 30 or layers adjacent to the light-emitting layer 23. Therefore, the light-emitting element 2 according to this embodiment reduces deterioration of each layer between the anode 21 and the cathode 25, thereby extending the lifespan.

[0060] Furthermore, in the light-emitting layer 23 according to this embodiment, the first portion 41 is located closer to the anode 21 than the second portion 42. Therefore, the light-emitting element 2 including the light-emitting layer 23 can improve the injection efficiency of holes injected from the anode 21 side to the quantum dots 30 via the first portion 41, while protecting the quantum dots 30 located on the cathode 25 side of the light-emitting layer 23 with the second portion 42.

[0061] In general, due to the difference in mobility between holes and electrons, the light-emitting layer of a light-emitting device including quantum dots tends to have an excess of electrons, where the concentration of electrons is in excess of the concentration of injected holes. The excess of electrons in the light-emitting layer can reduce the efficiency of exciton generation in the light-emitting layer and can also increase the generation process of Auger electrons, which do not contribute to light emission and can cause deterioration of the light-emitting layer and surrounding layers.

[0062] The light-emitting element 2 according to this embodiment has the first portion 41 on the anode 21 side of the light-emitting layer 23, thereby increasing the efficiency of hole injection into the light-emitting layer 23 and reducing electron excess. Furthermore, the light-emitting element 2 has the second portion 42 on the cathode 25 side of the light-emitting layer 23, thereby protecting the quantum dots 30 on the cathode 25 side of the light-emitting layer 23. In particular, the second portion 42 efficiently reduces deterioration of the quantum dots 30 located on the cathode 25 side of the light-emitting layer 23, which is caused by Auger electrons resulting from electrons injected from the cathode 25. Therefore, the light-emitting element 2 according to this embodiment efficiently achieves both improved luminous efficiency of the light-emitting layer 23 and protection of the quantum dots 30.

[0063] Furthermore, in this embodiment, the light-emitting layer 23 includes a first portion 41 having a lower ratio of oxygen atoms to metal atoms than the second portion 42, and the first portion 41 is located closer to the anode 21 than the second portion 42. Therefore, the light-emitting layer 23 further reduces deterioration of the quantum dots 30 and hole transport layer 22 located on the anode 21 side of the light-emitting layer 23 due to oxygen atoms in the inorganic matrix 31. Therefore, the light-emitting element 2 according to this embodiment further suppresses a decrease in the efficiency of hole injection from the anode 21 to the quantum dots 30 in the light-emitting layer 23, and further reduces the excess of electrons in the light-emitting layer 23.

[0064] <Additional Note on the Ratio of Oxygen Atoms to Metal Atoms in the Inorganic Matrix> As described above, the ratio of oxygen atoms to metal atoms in the metal oxide of the inorganic matrix 31 may be 50% or more of the ratio of oxygen atoms to metal atoms in the stoichiometric metal oxide. With the above configuration, the light-emitting element 2 can improve the protective effect of the inorganic matrix 31 on the quantum dots 30.

[0065] In particular, the inorganic matrix 31 is made of SiO ｘ When the inorganic matrix 31 contains the metal oxide, x may be 1 or more and 2 or less. In this case, as described above, a two-dimensional network structure is formed in the metal oxide contained in the inorganic matrix 31, and therefore the effect of protecting the quantum dots 30 can be further improved.

[0066] As described above, taking into consideration that charge transfer is likely to occur via the bonding parts BD in the metal oxide of the inorganic matrix 31, the shorter the average distance L between the bonding parts BD, the more efficiently charge transfer occurs in the inorganic matrix 31. In particular, when the average distance L is 1 nm or less, charge tunnels between the bonding parts BD more efficiently.

[0067] Therefore, d = 0.16 nm, L = d(2 / r) １／２ , and L≦1 nm, r is found to be r≧0.051. ｘ In this case, x=2(1−r) holds as described above. Therefore, from the viewpoint of efficiently generating charge tunneling between the bonding portions BD and improving charge movement in the inorganic matrix 31, the value of x may be 1.9 or less.

[0068] <Method for Manufacturing Display Device> The display device 1 according to this embodiment may be manufactured by forming multiple light-emitting elements 2 on a substrate 3 on which a driver circuit DR, a pixel circuit PC, and the like are separately formed. In the method for manufacturing the light-emitting element 2 according to this embodiment, the layers other than the light-emitting layer 23 may be formed by any method, using common materials and common film-forming processes. For example, each layer can be formed by applying a solution containing the materials for each layer dispersed therein using a spin coating method, a slit coating method, or the like, and then drying the solution. For example, each layer can be formed by preparing a solution in which the materials for each layer are mixed with a solvent for viscosity control, and then printing the solution using an inkjet method, a screen printing method, or the like. Printing methods are suitable for producing light-emitting panels and display panels because they enable uniform deposition of each layer over a large area.

[0069] The method for manufacturing the light-emitting element 2 according to this embodiment includes a method for forming the light-emitting layer 23, which will be described later. The method for forming the light-emitting layer 23 according to this embodiment will be described with reference to Figs. 8 to 10. Fig. 8 is a flowchart showing the method for forming the light-emitting layer 23 according to this embodiment. Fig. 9 is a schematic diagram showing a first dispersion liquid, which will be described later, used in the method for forming the light-emitting layer 23 according to this embodiment. Fig. 10 is a cross-sectional view showing a process of a part of the method for forming the light-emitting layer 23 according to this embodiment.

[0070] In the method for forming the light-emitting layer 23 according to this embodiment, first, a first dispersion and a second dispersion are prepared (step S1). For example, the first dispersion and the second dispersion may be dispersions in which the quantum dots 30 and metal oxide fine particles of the inorganic matrix 31 are dispersed.

[0071] An example of the first dispersion liquid will be described with reference to FIG. 9 . FIG. 9 shows the first dispersion liquid L1 poured into the container C. The first dispersion liquid L1 is, for example, a dispersion liquid in which quantum dots 30 and nanoparticles 50 as first microparticles are dispersed in a solvent 51 containing, for example, toluene. The nanoparticles 50 are nanoparticles containing metal atoms and oxygen atoms, and may be, for example, silicon oxide nanoparticles. The ratio of oxygen atoms to metal atoms in the nanoparticles 50 may be approximately the same as the ratio of oxygen atoms to metal atoms in the first portion 41 described above. The particle diameter of the nanoparticles 50 may be, for example, 1 nm to 10 nm.

[0072] The second dispersion may have the same configuration as the first dispersion, except that instead of the first microparticles, i.e., nanoparticles 50, the second microparticles have a higher ratio of oxygen atoms to metal atoms than the nanoparticles 50.

[0073] The first and second dispersions may be prepared by adding separately synthesized quantum dots 30 and metal oxide nanoparticles to a solvent 51 such as toluene. For example, metal oxide nanoparticles may be synthesized by, for example, mixing an alkaline aqueous solution with a metal salt to obtain a precipitate, followed by centrifuging, drying, and calcining the precipitate. The ratio of oxygen atoms to metal atoms in the synthesized nanoparticles may be adjusted by adjusting the ratio of the alkaline aqueous solution and the metal salt to be mixed.

[0074] 8, after the preparation of the first dispersion and the second dispersion, the first dispersion L1 is applied to the substrate (step S2), which is a laminate including the substrate 3 and each layer formed on the substrate 3 up to the step of forming the light-emitting layer 23. Each step from step S2 onwards will be described in more detail with reference to FIG.

[0075] 10, at the start of execution of step S2, an anode 21 and a hole transport layer 22 are formed in this order on the substrate 3. In this case, in step S2, as shown in step S2-2 in FIG.

[0076] Next, each portion of the substrate 3 containing the applied first dispersion L1 is heated, for example, at 80° C. for 10 minutes to dry the first dispersion L1 (step S3). As a result, the solvent 51 of the applied first dispersion L1 volatilizes, and both the quantum dots 30 and the nanoparticles 50 accumulate on the substrate 3 side, and the nanoparticles 50 around the quantum dots 30 become first portions 41. As a result, a first light-emitting layer 23A is formed, which includes the quantum dots 30 and the first portions 41 filling the spaces between the quantum dots 30, as shown in step S3 of FIG. 10 .

[0077] Next, the second dispersion is applied to the substrate 3, which is a laminate including the first light-emitting layer 23A (step S4). The second dispersion is then dried by heating each portion of the substrate 3 containing the applied second dispersion (step S5). As described above, the nanoparticles contained in the second dispersion have a higher ratio of oxygen atoms to metal atoms than the nanoparticles 50 contained in the first dispersion L1. Therefore, in step S5, the second portion 42 is formed by the nanoparticles contained in the second dispersion. As a result, as shown in step S5 of FIG. 10 , the second light-emitting layer 23B is formed, which includes the quantum dots 30 and the second portion 42 filling the spaces between the quantum dots 30, completing the formation of the light-emitting layer 23.

[0078] The above-described method can produce the light-emitting element 2 including the light-emitting layer 23 according to this embodiment. In particular, the above-described method can appropriately design the ratio of oxygen atoms to metal atoms in each portion of the inorganic matrix 31 by adjusting the ratio of oxygen atoms to metal atoms in the fine particles added to each of the first dispersion liquid L1 and the second dispersion liquid.

[0079] [Embodiment 2] <Vapor Deposition of Inorganic Matrix> The display device 1 according to this embodiment has the same configuration as the display device 1 according to the previous embodiment, and differs only in the method for manufacturing the light-emitting element 2. The method for manufacturing the light-emitting element 2 according to this embodiment differs from the method for manufacturing the light-emitting element 2 according to the previous embodiment only in the method for forming the light-emitting layer 23. The method for forming the light-emitting layer 23 according to this embodiment will be described in detail with reference to FIGS. 11 and 12. FIG. 11 is a flowchart showing the method for forming the light-emitting layer 23 according to this embodiment. FIG. 12 is a cross-sectional view showing a process of a part of the method for forming the light-emitting layer 23 according to this embodiment.

[0080] In the method for forming the light-emitting layer 23 according to this embodiment, first, a first quantum dot layer including quantum dots 30 is formed on the upper surface of the hole transport layer 22 (step S6). Step S6 may be performed, for example, by applying a dispersion liquid in which a plurality of quantum dots 30 are dispersed in a solvent such as toluene to the upper surface of the hole transport layer 22, and then volatilizing the solvent by heating the applied dispersion liquid, etc. As a result, a first quantum dot layer 32 including quantum dots 30 is formed on the upper surface of the hole transport layer 22, as shown in step S6 in FIG.

[0081] Next, using a vapor deposition apparatus including a first metal oxide as a first vapor deposition source, such as the nanoparticles 50 described in the previous embodiment, metal oxide microparticles are vapor-deposited onto the formed first quantum dot layer 32 (step S7). As a result, as shown in step S7 of FIG. 12 , the first metal oxide in the first vapor deposition source, such as the nanoparticles 50, penetrates between the quantum dots 30 in the first quantum dot layer 32 and is deposited on the upper surface of the hole transport layer 22. Therefore, in step S7, the first metal oxide is formed in a position that surrounds the first quantum dot layer 32, and this first metal oxide becomes the first portion 41. Therefore, step S7 forms a first light-emitting layer 23A that includes the quantum dots 30 and the first portion 41 that fills the spaces between the quantum dots 30.

[0082] In step S6, the first quantum dot layer 32 is formed by, for example, applying a dispersion liquid in which the quantum dots 30 are dispersed, as described above. Therefore, the quantum dots 30 applied in step S6 may approach or come into contact with the upper surface of the hole transport layer 22 due to their own weight. Therefore, in the first light-emitting layer 23A according to this embodiment, the quantum dots 30 may be unevenly distributed on the hole transport layer 22 side, compared to the first light-emitting layer 23A according to the previous embodiment.

[0083] Next, a second quantum dot layer including quantum dots 30 is formed on the upper surface of the first light-emitting layer 23A (step S8). Step S8 may be performed by the same method as step S6, except that the layer to which the dispersion liquid is applied is the first light-emitting layer 23A. As a result, a second quantum dot layer including quantum dots 30 is formed on the upper surface of the first light-emitting layer 23A.

[0084] Next, metal oxide microparticles are vapor-deposited onto the formed second quantum dot layer (step S9). Step S9 may be performed in the same manner as step S7, except that the vapor deposition is performed using a second vapor deposition source containing a second metal oxide having a higher ratio of oxygen atoms to metal atoms than the first metal oxide in the first vapor deposition source. As a result, as shown in step S9 of FIG. 12 , a second light-emitting layer 23B is formed, including quantum dots 30 and second portions 42 filling the spaces between the quantum dots 30, thereby completing the formation of the light-emitting layer 23. For the same reasons as described above, in the second light-emitting layer 23B according to this embodiment, the quantum dots 30 may be unevenly distributed closer to the first light-emitting layer 23A than in the second light-emitting layer 23B according to the previous embodiment.

[0085] The above-described method can manufacture the light-emitting element 2 including the light-emitting layer 23 according to this embodiment. In particular, the above-described method uses vapor deposition to form the first portion 41 and the second portion 42, which shortens the time required to heat each portion on the substrate 3, including the quantum dots 30, or allows the heating to be performed at a low temperature. Therefore, the above-described method can further reduce deterioration of the quantum dots 30 in the light-emitting layer 23, the hole transport layer 22, etc.

[0086] Although the present embodiment describes a method of depositing fine particles of one type of metal oxide in steps S7 and S9, this is not limiting. For example, in steps S7 and S9, deposition may be performed using a first deposition source and a second deposition source containing a mixture of a first metal oxide and a second metal oxide. In this case, the second deposition source used in step S9 may have a higher ratio of the second metal oxide to the first metal oxide than the first deposition source used in step S7. According to the above method, the ratio of oxygen atoms to metal atoms in the first portion 41 and the second portion 42 formed in each step can be easily adjusted by adjusting the ratio of the first metal oxide to the second metal oxide in each of the first deposition source and the second deposition source.

[0087] In this embodiment, the first quantum dot layer 32 is first formed in step S6, and then metal oxide fine particles are vapor-deposited in step S7 to form the first light-emitting layer 23A. As a result, the quantum dots 30 in both the first light-emitting layer 23A and the second light-emitting layer 23B may be unevenly distributed on the hole transport layer 22 side. With this configuration, the quantum dots 30 in the light-emitting layer 23 are closer to the hole transport layer 22, thereby improving the efficiency of hole injection from the hole transport layer 22 to the quantum dots 30 in the light-emitting element 2 and further reducing the excess electrons in the light-emitting layer 23.

[0088] However, this embodiment is not limited to the above method. For example, prior to step S6, a step of forming a thin film containing metal oxide particles may be performed by the same method as step S7. In this case, direct contact of the quantum dots 30 contained in the first light-emitting layer 23A with the hole transport layer 22 may be reduced. This makes it possible to ensure a sufficient distance between the quantum dots 30 and the hole transport material of the hole transport layer 22. This configuration reduces the possibility of the energy of excitons generated in the quantum dots 30 being transferred to the hole transport material of the hole transport layer 22 that is in contact with or close to the quantum dots 30, thereby reducing the possibility of the quantum dots 30 being deactivated.

[0089] 13 is a schematic side cross-sectional view of a display device 4 according to this embodiment. Compared to the display device 1 according to the previous embodiment, the display device 4 according to this embodiment includes a light-emitting element 5 instead of the light-emitting element 2. Compared to the light-emitting element 2, the light-emitting element 5 includes a light-emitting layer 26 instead of the light-emitting layer 23.

[0090] The light-emitting layer 26 will be described in more detail with reference to Fig. 14. Fig. 14 is an enlarged schematic view of the light-emitting layer 26 in the cross section shown in Fig. 13, and in particular of a region E2 shown in Fig. 13.

[0091] The light-emitting layer 26 includes a plurality of quantum dots 30 and an inorganic matrix 31. The inorganic matrix 31 has a first portion 41 and a second portion 42. The light-emitting layer 26 differs from the light-emitting layer 23 only in the positional relationship between the first portion 41 and the second portion 42. Note that, for reasons described below, the positions of the quantum dots 30 in the light-emitting layer 26 may be unevenly distributed closer to the hole transport layer 22 than in the light-emitting layer 23.

[0092] 14 , in the light-emitting layer 26, the second portions 42 are located closer to the quantum dots 30 than the first portions 41. In particular, in the light-emitting layer 26, the second portions 42 are located around each quantum dot 30. More specifically, the second portions 42 may encapsulate each quantum dot 30. Furthermore, the first portions 41 are located around each second portion 42. More specifically, the first portions 41 may encapsulate each second portion 42. Therefore, the light-emitting layer 26 can also be considered to include a plurality of quantum dot structures, each having a quantum dot 30 and a second portion 42 located around the quantum dot 30, and a first portion 41 filling the spaces between the plurality of quantum dot structures.

[0093] Except for the above, the display device 4 according to this embodiment may have the same configuration as the display device 1 according to the previous embodiment.

[0094] In the light-emitting layer 26 according to this embodiment, the second portions 42 are located closer to each quantum dot 30 than the first portions 41. In particular, in the light-emitting layer 26, the second portions 42 are located around each quantum dot 30, and the first portions 41, which have a lower ratio of oxygen atoms to metal atoms than the second portions 42, are located around the second portions 42.

[0095] Therefore, the light-emitting layer 26 can protect each quantum dot 30 by the second portion 42, which is closer to each quantum dot 30 than the first portion 41. Furthermore, the light-emitting layer 26 more efficiently transports carriers from each charge transport layer by the first portion 41. Although the second portion 42 is located between each quantum dot 30 and the first portion 41 in the light-emitting layer 26, carriers transported from the first portion 41 toward each quantum dot 30 are injected into each quantum dot 30 by tunneling through the second portion 42. Therefore, the light-emitting device 5 including the light-emitting layer 26 according to this embodiment can more efficiently protect the quantum dots 30 and improve the efficiency of charge injection from each electrode into the quantum dots 30. Additionally, when the quantum dots 30 are unevenly distributed on the hole transport layer 22 side in the light-emitting layer 26 as described above, the light-emitting device 2 further reduces the excess electrons in the light-emitting layer 26 for the same reason as described above.

[0096] <Part 2 Located Inside Part 1: Manufacturing Method: Preparation of Dispersion> The manufacturing method for the light-emitting element 5 according to this embodiment differs from the manufacturing method for the light-emitting element 2 described above only in that the method for forming the light-emitting layer 23 is replaced with the method for forming the light-emitting layer 26 described below. The method for forming the light-emitting layer 26 according to this embodiment will be described in detail with reference to FIGS. 15 to 20 . FIG. 15 is a flowchart showing the method for forming the light-emitting layer 26 according to this embodiment. FIG. 16 is a side view showing a process of a mixing step described below in the method for forming the light-emitting layer 26 according to this embodiment. FIG. 17 is a schematic diagram showing a reaction process of precursors described below according to this embodiment. FIGS. 18 and 19 are schematic views showing third and fourth dispersions described below used in the method for forming the light-emitting layer 26 according to this embodiment. FIG. 20 is a cross-sectional view showing a process of a part of the method for forming the light-emitting layer 26 according to this embodiment.

[0097] In the method for forming the light-emitting layer 26 according to this embodiment, first, a third dispersion and a fourth dispersion are prepared (step S10). In particular, in this embodiment, the third dispersion is prepared by a method including a mixing step of mixing a dispersion containing quantum dots 30 with a dispersion containing a metal oxide precursor, as will be described later. This mixing step will be described with reference to FIG. 16 .

[0098] In the method for preparing the third dispersion according to this embodiment, prior to the mixing step, dispersions LA and LB are prepared as shown in step S10-1 of Fig. 16. In the method for preparing the third dispersion according to this embodiment, for example, commercially available blue quantum dots are used as the quantum dots 30, and zinc chloride (ZnCl) is used as the halogen source. ２ ) powder is prepared. The blue quantum dots have a core of ZnSeTe and a shell of ZnS, and may be coordinated with an organic ligand different from the precursor of the inorganic matrix 31 described below. Furthermore, as the precursor of the inorganic matrix 31, tetramethyl orthosilicate (TMOS) shown in the following formula (1) and 3-(mercaptopropyl)trimethoxysilane (MPS) shown in the following formula (2) are prepared. Furthermore, octane (C ８ H １８ ) and N,N-dimethylformamide (DMF) are prepared. However, this embodiment is not limited to this, and the precursor of the inorganic matrix 31 may be, for example, tetraethyl silicate (TEOS).

[0099] In this embodiment, ZnCl ２ , MPS, and TMOS to prepare 10 ml of Dispersion LA. Dispersion LA may contain ZnCl ２ The mixture may be 10 ml of a solution having a concentration of 0.6 mol / L, 0.2 mol / L of MPS, and 0.02 mol / L of TMOS.

[0100] In this embodiment, the quantum dots 30 coordinated with the organic ligands described above may be dispersed in octane to a concentration of 1 mg / ml to prepare 10 ml of dispersion LB. Since octane and DMF have different polarities, when dispersion LA and dispersion LB are allowed to stand in a container, the liquid in the container separates into a layer of dispersion LA and a layer of dispersion LB.

[0101] In the mixing step, the dispersion liquids LA and LB are thoroughly stirred and mixed. The stirring may be performed for 1 to 48 hours, preferably for approximately 10 to 20 hours. During the stirring process, some of the ligands coordinated to the quantum dots 30 are replaced by MPS from the organic ligands. This makes the quantum dots 30 more easily dispersible in DMF than in octane, and as shown in step S10-2 of FIG. 16 , the quantum dots 30 are transferred from the dispersion liquid LB to the dispersion liquid LA. In particular, MPS coordinates to the quantum dots 30 using thiol groups as coordinating functional groups. As described below, the MPS coordinated to the quantum dots 30 reacts with TMOS to form an inorganic matrix, which allows the MPS to coordinate to the quantum dots 30 more firmly than when an organic ligand is coordinated to the quantum dots 30. Therefore, the light-emitting layer 26 formed by the method according to this embodiment can more effectively protect the quantum dots 30. The organic ligands do not have to be completely replaced with MPS, and some of the organic ligands (e.g., less than 5% by weight) may remain in the ligands coordinated to the quantum dots 30. A moderate amount of remaining organic ligands prevents aggregation of the quantum dots 30 in the dispersion liquid or suppresses the occurrence of cracks in the light-emitting layer 26.

[0102] Furthermore, in the dispersion liquid LA, MPS and TMOS reacted in accordance with the reaction process described below, forming silicon oxide around the quantum dots 30. The reaction process of the precursor of the inorganic matrix 31, including MPS and TMOS, in the mixing process of step S10 will be described in detail with reference to FIG.

[0103] For example, two TMOS 61 shown in the schematic diagram 1701 of FIG. 17 are water (H ２ 17, the hydroxyl groups of the two derivatives 62 react with each other to form a condensate 63 having an Si—O—Si bond by dehydration condensation, as shown in schematic diagram 1703.

[0104] As the above reaction progresses, SiO ２ A metal oxide 65 having a two-dimensional network structure is formed. The above-mentioned reaction also occurs due to the reaction between the methoxy groups of the MPS and between the methoxy groups of the TMOS and the MPS.

[0105] Therefore, in the mixing step according to this embodiment, the trimethoxysilane group of the MPS coordinated to the quantum dots 30, located on the opposite side to the quantum dots 30, reacts with other MPS or TMOS. The silicon oxide formed in this reaction is less likely to have oxygen defects. Therefore, the composition of this silicon oxide is changed to SiO ｘ In this case, the value of x is approximately close to 2. Therefore, in the mixing step according to this embodiment, a second portion 42 containing a metal oxide having a relatively high ratio of oxygen atoms to metal atoms is formed around the quantum dots 30.

[0106] 16, the dispersion liquid LA and the dispersion liquid LB are mixed to form a quantum dot structure 52 including quantum dots 30 and a second portion 42 including a metal oxide encapsulating the quantum dots 30. In particular, in the mixing step according to this embodiment, the dispersion liquid including the plurality of quantum dots 30 and a precursor of a metal oxide is converted into the metal oxide of the precursor. Note that in step S10-2, the quantum dot structure 52 may migrate to the interface between the dispersion liquid LA and the dispersion liquid LB.

[0107] Subsequently, the quantum dot structures 52 are extracted from the dispersion liquid LA by, for example, centrifuging the dispersion liquid LA at 4000 rpm for 5 minutes. When centrifuging the dispersion liquid LA, a poor solvent such as ethyl acetate or acetone may be added to the dispersion liquid LA to precipitate the quantum dot structures 52. Next, the precipitated quantum dot structures 52 are extracted and dispersed in a solvent containing toluene to prepare a third dispersion liquid.

[0108] The third dispersion liquid prepared by the above mixing process will be described with reference to FIG. 18 . FIG. 18 illustrates a third dispersion liquid L3 poured into a container C. The third dispersion liquid L3 is, for example, a dispersion liquid in which a plurality of quantum dot structures 52 are dispersed in a solvent 51. As described above, the quantum dot structure 52 includes quantum dots 30 and a second portion 42 encapsulating the quantum dots 30. The quantum dot structure 52 may also include a thiol group and a carbon chain derived from the thiol group of MPS and the carbon chain bonded to the thiol group between the quantum dots 30 and the second portion 42. When the MPS coordinated to the quantum dots 30 reacts with TMOS to form the second portion 42, the MPS coordinates to the quantum dots 30 more strongly than when an organic ligand coordinates to the quantum dots 30. Therefore, the light-emitting layer 26 formed by the method according to this embodiment can more effectively protect the quantum dots 30. The organic ligands do not have to be completely replaced with MPS, and some of the organic ligands (e.g., less than 5% by weight) may remain in the ligands coordinated to the quantum dots 30. A moderate amount of remaining organic ligands prevents aggregation of the quantum dots 30 in the dispersion liquid or suppresses the occurrence of cracks in the light-emitting layer 26.

[0109] Next, the fourth dispersion liquid L4 will be described with reference to Fig. 19. As shown in Fig. 19, the fourth dispersion liquid L4 is a dispersion liquid in which, for example, a plurality of nanoparticles 50 described above as metal oxide microparticles are dispersed as third microparticles in a solvent 51. In other words, the fourth dispersion liquid L4 may have the same configuration as the first dispersion liquid L1 except that it does not contain quantum dots 30. In particular, the ratio of oxygen atoms to metal atoms in the nanoparticles 50 is lower than the ratio of oxygen atoms to metal atoms in the second portion 42 formed by the reaction of the metal oxide precursor described above.

[0110] 15 , after the preparation of the third dispersion and the fourth dispersion, a laminate including the substrate 3 and each layer formed on the substrate 3 up to the step of forming the light-emitting layer 26 is used as the substrate, and the third dispersion L3 is applied to the substrate (step S11). Each step from step S11 onwards will be described in more detail with reference to FIG.

[0111] For example, step S11 is performed in the same manner as step S2 described above, except that the third dispersion L3 is applied instead of the first dispersion L1. Therefore, as shown in step S11 in Fig. 20, the third dispersion L3 is applied to the upper surface of the hole transport layer 22.

[0112] Next, the third dispersion L3 is dried by, for example, heating each portion of the substrate 3 containing the applied third dispersion L3 (step S12). Step S12 may be performed in the same manner as step S3, except that the third dispersion L3 is dried instead of the first dispersion L1. As a result, as shown in step S12 of FIG. 20 , the solvent 51 of the applied third dispersion L3 volatilizes, and the quantum dot structures 52 accumulate on the substrate 3 side. As a result, a quantum dot structure layer 52A containing the quantum dot structures 52 is formed on the hole transport layer 22. In step S12, the quantum dot structures 52 accumulate on the hole transport layer 22 side due to their own weight. Therefore, in the light-emitting layer 26 formed by the method described below, the quantum dots 30 are closer to the hole transport layer 22.

[0113] Next, a laminate including the substrate 3 and the layers formed on the substrate 3 up to step S12 is used as a substrate, and a fourth dispersion L4 is applied to the substrate (step S13). In other words, in step S13, the fourth dispersion L4 is applied from above the quantum dot structure layer 52A. As a result, as shown in step S13 of FIG. 20 , the fourth dispersion L4 permeates between the quantum dot structures 52 of the quantum dot structure layer 52A, and the nanoparticles 50 thereby enter between the quantum dot structures 52.

[0114] Next, the fourth dispersion L4 is dried by, for example, heating each portion of the substrate 3, including the applied fourth dispersion L4 (step S14). Step S14 may be performed by the same method as step S3, except that the fourth dispersion L4 is dried instead of the first dispersion L1. As a result, the solvent 51 of the applied fourth dispersion L4 volatilizes, and the nanoparticles 50 around the quantum dot structures 52 become the first portions 41. As a result, as shown in step S14 of FIG. 20 , the light-emitting layer 26 is formed, including the quantum dot structures 52 and the first portions 41 filling the spaces between the quantum dot structures 52.

[0115] The above-described method can manufacture a light-emitting element 2 including the light-emitting layer 26 according to this embodiment. In particular, the above-described method forms the second portion 42 by the reaction of the precursors described above, and therefore can form the second portion 42 containing a dense metal oxide with few oxygen defects. Therefore, the above-described method can further improve the protection effect of the quantum dots 30 provided by the second portion 42. Furthermore, the above-described method can form a light-emitting layer 26 in which the quantum dots 30 are unevenly distributed on the hole transport layer 22 side.

[0116] [Embodiment 4] <Second Part Located Inside First Part: Combined Use of Vapor Deposition> A display device 4 according to this embodiment has the same configuration as the display device 4 according to the previous embodiment, and differs only in the method for manufacturing the light-emitting element 5. The method for manufacturing the light-emitting element 5 according to this embodiment differs from the method for manufacturing the light-emitting element 5 according to the previous embodiment only in the method for forming the light-emitting layer 26. The method for forming the light-emitting layer 26 according to this embodiment will be described in detail with reference to FIG. 21 . FIG. 21 is a flowchart showing the method for forming the light-emitting layer 26 according to this embodiment.

[0117] The method for forming the light-emitting layer 26 according to this embodiment can be performed by modifying some of the steps of the method for forming the light-emitting layer 26 according to the previous embodiment. For example, in the method for forming the light-emitting layer 26 according to this embodiment, first, a third dispersion is prepared (step S15). Step S15 may be performed by the same method as the preparation of the third dispersion L3 according to the previous embodiment. Therefore, the third dispersion L3 according to this embodiment may be the same as the third dispersion L3 according to the previous embodiment. In other words, step S15 may be performed by the same method as step S10 in the previous embodiment, except that the fourth dispersion L4 is not prepared.

[0118] Next, steps S11 and S12 in the previous embodiment are executed in this order, thereby forming the quantum dot structure layer 52A on the hole transport layer 22, as described in the previous embodiment.

[0119] Next, metal oxide microparticles are vapor-deposited onto the quantum dot structure layer 52A (step S16). In step S16, vapor deposition is performed using a third vapor deposition source containing a metal oxide having a lower ratio of oxygen atoms to metal atoms compared to the second portion 42. In particular, step S16 is performed by the same method as step S7 described above, except that the quantum dot structure layer 52A is the target of vapor deposition instead of the first quantum dot layer 32. Therefore, in step S16, metal oxide is vapor-deposited around the quantum dot structure 52. As a result, the light-emitting layer 26 is formed, including the quantum dot structure 52 and the first portion 41 filling the spaces between the quantum dot structures 52.

[0120] The above-described method makes it possible to manufacture the light-emitting element 2 including the light-emitting layer 26 according to this embodiment. In particular, the above-described method makes it possible to form the light-emitting layer 26 without performing a heating step or the like on the quantum dot structure layer 52A after forming the quantum dot structure layer 52A, which may cause deterioration of the quantum dots 30, etc. Therefore, the above-described method further reduces deterioration of the quantum dots 30 in the light-emitting layer 26.

[0121] 22 is a schematic side cross-sectional view of a display device 6 according to this embodiment. Compared to the display device 1 described above, the display device 6 according to this embodiment includes a light-emitting element 7 instead of the light-emitting element 2. Compared to the light-emitting element 2, the light-emitting element 7 includes a light-emitting layer 27 instead of the light-emitting layer 23.

[0122] The light-emitting layer 27 includes a plurality of quantum dots 30 and an inorganic matrix 31. The light-emitting layer 27 also includes a first light-emitting layer 27A, a second light-emitting layer 27B located closer to the cathode 25 than the first light-emitting layer 27A, and a third light-emitting layer 27C located between the first light-emitting layer 27A and the second light-emitting layer 27B, which are stacked one on top of the other.

[0123] The first light-emitting layer 27A and the second light-emitting layer 27B each have the same configuration as the first light-emitting layer 23A and the second light-emitting layer 23B described above. The third light-emitting layer 27C has the same configuration as the first light-emitting layer 23A, except that it has a third portion 43 instead of the first portion 41. The third portion 43 is a part of the inorganic matrix 31, and in other words, it has a metal oxide. The ratio of oxygen atoms to metal atoms in the third portion 43 is higher than the ratio of oxygen atoms to metal atoms in the first portion 41 and lower than the ratio of oxygen atoms to metal atoms in the second portion 42.

[0124] Except for the above, the display device 6 according to this embodiment has the same configuration as the display device 1 described above.

[0125] The light-emitting layer 27 according to this embodiment has, as part of the inorganic matrix 31, a third portion 43 in which the ratio of oxygen atoms to metal atoms is between the ratio in the first portion 41 and the ratio in the second portion 42. Therefore, the light-emitting element 7 including the light-emitting layer 27 can more efficiently achieve a configuration that achieves both a longer life and high luminous efficiency.

[0126] In particular, in this embodiment, the inorganic matrix 31 contained in the light-emitting layer 27 has, in order from the anode 21 side toward the cathode 25 side, a first portion 41, a third portion 43, and a second portion 42. Therefore, in the inorganic matrix 31 according to this embodiment, the ratio of oxygen atoms to metal atoms gradually increases from the anode 21 side toward the cathode 25 side. Therefore, the light-emitting element 7 including the light-emitting layer 27 more efficiently achieves both a longer lifespan and higher luminous efficiency.

[0127] The manufacturing method of the display device 6 according to this embodiment differs from the manufacturing method of the display device 1 described above only in the manufacturing method of the light-emitting element 7. The manufacturing method of the light-emitting element 7 according to this embodiment differs from the manufacturing method of the light-emitting element 2 described above only in that it includes a method of forming the light-emitting layer 27 instead of the method of forming the light-emitting layer 23. In particular, the method of forming the light-emitting layer 27 is performed by a method in which some of the steps of the method of forming the light-emitting layer 23 are modified.

[0128] Specifically, in the method for forming the light-emitting layer 27, a fifth dispersion liquid containing a quantum dot structure having quantum dots and a metal oxide encapsulating the quantum dots is prepared in step S1. The fifth dispersion liquid has the same composition as the first dispersion liquid except that the ratio of oxygen atoms to metal atoms in the metal oxide of the quantum dot structure to be dispersed is between the ratios in the first dispersion liquid and the second dispersion liquid.

[0129] The method for forming the light-emitting layer 27 also includes, between steps S3 and S4, a step of forming a third light-emitting layer 27C by applying a fifth dispersion and drying the fifth dispersion. The step of forming the third light-emitting layer 27C may be performed by the same method as steps S2 and S3, or steps S4 and S5, except that the third portion is formed from metal oxide fine particles in the fifth dispersion.

[0130] 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.

[0131] REFERENCE SIGNS LIST 1 Display device 2 Light-emitting element 3 Substrate 21 Anode 23 Light-emitting layer 25 Cathode 30 Quantum dots 31 Inorganic matrix 41 First part 42 Second part

Claims

1. A light-emitting element comprising: an anode; a cathode facing the anode; and a light-emitting layer located between the anode and the cathode, wherein the light-emitting layer includes a plurality of quantum dots and an inorganic matrix having a metal oxide filling spaces between the plurality of quantum dots, wherein the inorganic matrix includes a first portion having the metal oxide, and a second portion having the metal oxide, the second portion having the metal oxide, the ratio of oxygen atoms to metal atoms being higher than the ratio of oxygen atoms to metal atoms in the first portion and equal to or lower than the ratio of oxygen atoms to metal atoms in the metal oxide, which is stoichiometric.

2. The light-emitting element according to claim 1, wherein the ratio of oxygen atoms to metal atoms in each of the first and second portions is 50% or more of the ratio of oxygen atoms to metal atoms in the metal oxide which is stoichiometric.

3. A light-emitting device according to claim 1 or 2, wherein the first portion is located closer to the anode than the second portion.

4. A light-emitting device according to claim 1 or 2, wherein the second portion is located closer to the quantum dot than the first portion.

5. The light-emitting device according to claim 4, wherein the second portion is positioned around the quantum dot, and the first portion is positioned around the second portion.

6. The light-emitting element according to any one of claims 1 to 5, wherein the metal oxide includes silicon oxide.

7. The metal oxide is SiO ｘ The light-emitting element according to claim 6 , wherein x is 1 or more and 2 or less.

8. The light-emitting device according to claim 7, wherein x is 1.9 or less.

9. A light-emitting element described in any one of claims 1 to 8, wherein the inorganic matrix contains the metal oxide and includes a third portion in which the ratio of oxygen atoms to metal atoms is higher than the ratio of oxygen atoms to metal atoms in the first portion and lower than the ratio of oxygen atoms to metal atoms in the second portion.

10. The light-emitting element according to claim 9, wherein said third portion is located between said first portion and said second portion.

11. A display device comprising a plurality of light-emitting elements according to any one of claims 1 to 10.

12. A method for manufacturing a light-emitting element including an anode, a cathode facing the anode, and a light-emitting layer located between the anode and the cathode, the method including forming the light-emitting layer, the light-emitting layer including a plurality of quantum dots and an inorganic matrix having a metal oxide and filling spaces between the plurality of quantum dots, the inorganic matrix including a first portion having the metal oxide, and a second portion having the metal oxide, the second portion having the metal oxide, the ratio of oxygen atoms to metal atoms being higher than the ratio of oxygen atoms to metal atoms in the first portion and equal to or lower than the ratio of oxygen atoms to metal atoms in the metal oxide, which is stoichiometric.

13. A method for manufacturing a light-emitting element as described in claim 12, wherein the formation of the light-emitting layer includes: forming a first light-emitting layer including a plurality of the quantum dots and the first portion; and forming a second light-emitting layer including a plurality of the quantum dots and the second portion.

14. A method for manufacturing a light-emitting element as described in claim 13, wherein forming the first light-emitting layer includes applying to a substrate a first dispersion liquid containing a plurality of the quantum dots and first microparticles which are microparticles of the metal oxide, and forming the second light-emitting layer includes applying to a substrate a second dispersion liquid containing a plurality of the quantum dots and second microparticles which are microparticles of the metal oxide and have a higher ratio of oxygen atoms to metal atoms than the first microparticles.

15. A method for manufacturing a light-emitting element as described in claim 13, wherein forming the first light-emitting layer includes forming a first quantum dot layer containing a plurality of the quantum dots on a substrate, and depositing the metal oxide around the quantum dots of the first quantum dot layer using a first deposition source having the metal oxide, and forming the second light-emitting layer includes forming a second quantum dot layer containing a plurality of the quantum dots on a substrate, and depositing the metal oxide around the quantum dots of the second quantum dot layer using a second deposition source having the metal oxide and having a higher ratio of oxygen atoms to metal atoms than the first deposition source.

16. A method for manufacturing a light-emitting element as described in claim 15, wherein each of the first evaporation source and the second evaporation source has a first metal oxide and a second metal oxide having a higher ratio of oxygen atoms to metal atoms than the first metal oxide, and the ratio of the second metal oxide to the first metal oxide in the second evaporation source is higher than the ratio of the second metal oxide to the first metal oxide in the first evaporation source.

17. The method for manufacturing a light-emitting element described in claim 12, wherein the formation of the light-emitting layer includes: forming a plurality of quantum dot structures, each including the quantum dot and the second portion around the quantum dot; and forming the first portion around each of the quantum dot structures.

18. The method for producing a light-emitting element according to claim 17, wherein forming the quantum dot structure includes converting a precursor of the metal oxide into the metal oxide in a dispersion containing a plurality of the quantum dots and the precursor of the metal oxide.

19. A method for manufacturing a light-emitting element as described in claim 18, wherein the formation of the first portion includes applying a dispersion liquid containing third particles which are particles of the metal oxide and have a lower ratio of oxygen atoms to metal atoms than the metal oxide in the quantum dot structure onto a substrate including the quantum dot structure.

20. A method for manufacturing a light-emitting element as described in claim 18, wherein forming the first portion includes depositing the metal oxide around the quantum dot structure using a third deposition source having the metal oxide and a lower ratio of oxygen atoms to metal atoms than the metal oxide in the quantum dot structure.

Images