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

Abstract

A light-emitting element (1) comprises: a positive electrode (11); a negative electrode (15); and an EML (13) including QDs (21) and an MX (22). The MX has a first region including an inorganic compound (23) and a second region including an inorganic compound (24), the regions being in a linear direction (L1) that passes through a positive electrode-side outer edge (13a) and a negative electrode-side outer edge (13b) of the EML. The concentration of the inorganic compound (23) in the first region and the concentration of the inorganic compound (24) in the second region are different by a predetermined value or more.

Description

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

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

[0002] Patent Document 1 discloses a quantum dot device having a quantum dot layer containing luminescent quantum dots and non-luminescent quantum dots in order to improve light emission characteristics, and discloses that the shell of the luminescent quantum dot has a larger band gap than the core, thereby exerting a quantum confinement effect and emitting light.

[0003] US Patent Application Publication No. 2019 / 280232

[0004] However, in Patent Document 1, organic ligands such as oleic acid are coordinated to these quantum dots. Organic ligands made of organic substances have the problem of low stability and easy peeling, which leads to deterioration of luminescence properties and reliability.

[0005] Therefore, if the quantum dots are covered with an inorganic medium instead of an organic ligand, the quantum dots can be strongly protected. However, when the quantum dots are covered uniformly with an inorganic medium, if an inorganic compound with a large band gap is used as the inorganic medium to exert the quantum confinement effect, the efficiency of carrier injection of holes and electrons into the quantum dots decreases, causing a decrease in luminescence efficiency.

[0006] One aspect of the present disclosure has been made in consideration of the above-mentioned problems, and its object is to provide a light-emitting element and a display device that are highly stable, have high luminous efficiency, and are highly reliable, as well as a method for manufacturing the light-emitting element.

[0007] In order to solve the above problem, a light-emitting element according to one aspect of the present disclosure comprises a first electrode, a second electrode, and a light-emitting layer provided between the first electrode and the second electrode, wherein the light-emitting layer includes a plurality of quantum dots and a matrix material, wherein the matrix material includes a first inorganic compound and a second inorganic compound, and the matrix material has, in a linear direction passing through a first outer edge portion on the first electrode side of the light-emitting layer and a second outer edge portion on the second electrode side, a first region containing at least the first inorganic compound and a second region containing at least the second inorganic compound, wherein the second region is provided closer to the second outer edge than the first region, and the concentration of the first inorganic compound in the first region differs from the concentration of the first inorganic compound in the second region by a certain amount or more.

[0008] In order to solve the above problems, a display device according to an aspect of the present disclosure includes the light-emitting element according to an aspect of the present disclosure.

[0009] In order to solve the above-described problems, a method for manufacturing a light-emitting element according to one aspect of the present disclosure includes a first electrode, a second electrode, and a light-emitting layer provided between the first electrode and the second electrode, the light-emitting layer including a plurality of quantum dots and a matrix material, the matrix material including a first inorganic compound and a second inorganic compound, the matrix material including a first region including at least the first inorganic compound and a second region including at least the second inorganic compound in a linear direction passing through a first outer edge portion on the first electrode side and a second outer edge portion on the second electrode side in the light-emitting layer, a second region containing an inorganic compound, the second region being provided closer to the second outer edge portion than the first region, and a concentration of the first inorganic compound in the first region and a concentration of the first inorganic compound in the second region being different by a certain amount or more, the method comprising: (1) forming a light-emitting layer comprising the plurality of quantum dots, a precursor of the first inorganic compound, halide ions, and a first solvent, the precursor of the first inorganic compound being thermally decomposed to form the first inorganic compound; (2) a first film forming step of heating the quantum dot dispersion coating film at a temperature equal to or higher than the thermal decomposition temperature of a precursor of the first inorganic compound to thermally decompose at least a portion of the precursor of the first inorganic compound and remove the first solvent, thereby forming a first film including the plurality of quantum dots and a matrix material containing the first inorganic compound; (3) a second inorganic compound precursor solution supplying step of supplying onto the first film a second inorganic compound precursor solution containing a precursor of the second inorganic compound and a second solvent, the second inorganic compound precursor thermally decomposing to form the second inorganic compound; and (4) a second inorganic compound forming step of heating the second inorganic compound precursor solution supplied in the second inorganic compound precursor solution supplying step at a temperature equal to or higher than the thermal decomposition temperature of the precursor of the second inorganic compound to thermally decompose at least a portion of the precursor of the second inorganic compound and remove the second solvent, thereby forming a matrix material containing the second inorganic compound.

[0010] According to one aspect of the present disclosure, it is possible to provide a light-emitting element and a display device that have high stability, luminous efficiency, and reliability, and a method for manufacturing the light-emitting element.

[0011] 1 is a cross-sectional view showing an example of a schematic configuration of a light-emitting device according to embodiment 1. FIG. 2 is a cross-sectional view showing an example of a schematic configuration of a quantum dot and its vicinity in the light-emitting device shown in FIG. 1. FIG. 3 is a cross-sectional view showing a state in which adjacent quantum dots are approaching each other in the light-emitting device shown in FIG. 1. FIG. 4 is a cross-sectional view showing a schematic view of carrier injection in a comparative light-emitting device in which the periphery of a quantum dot is uniformly covered with a matrix material made of an inorganic compound. FIG. 5 is a diagram showing the energy band structure of each functional layer in the comparative light-emitting device shown in FIG. 4. FIG. 6 is a cross-sectional view showing a schematic view of carrier injection in a light-emitting device according to embodiment 1 in which the first inorganic compound is indium sulfide and the second inorganic compound is magnesium sulfide. FIG. 7 is a diagram showing the energy band structure of each functional layer in the light-emitting device shown in FIG. 6. FIG. 8 is a cross-sectional view showing an example of a measurement direction of the concentrations of the first inorganic compound and the second inorganic compound along an arbitrary straight line in the light-emitting layer of the light-emitting device according to embodiment 1. FIG. 9 is a graph showing the concentration distributions of indium sulfide and zinc sulfide in the light-emitting layer shown in FIG. 8, measured using X-ray photoelectron spectroscopy. FIG. 10 is a cross-sectional view showing another example of a measurement direction of the concentrations of the first inorganic compound and the second inorganic compound along an arbitrary straight line in the light-emitting layer of the light-emitting device according to embodiment 1. 11 is a graph showing the concentration distribution of indium sulfide and zinc sulfide in the light-emitting layer shown in FIG. 10, measured using XPS. FIG. 12 is an explanatory diagram showing a method for examining the concentration distribution in the film thickness direction of the first inorganic compound and the second inorganic compound contained in the light-emitting layer of the light-emitting element according to embodiment 1 using cross-sectional TEM / EDX. FIG. 13 is another explanatory diagram showing a method for examining the concentration distribution in the film thickness direction of the first inorganic compound and the second inorganic compound contained in the light-emitting layer of the light-emitting element according to embodiment 1 using cross-sectional TEM / EDX. FIG. 14 is a graph showing the concentration distribution of indium sulfide and zinc sulfide in the film thickness direction of the light-emitting layer shown in FIG. 12, measured using cross-sectional TEM / EDX. FIG. 15 is a cross-sectional view showing another example of the schematic configuration of the light-emitting element according to embodiment 1. FIG. 16 is a cross-sectional view showing yet another example of the schematic configuration of the light-emitting element according to embodiment 1. FIG. 17 is a cross-sectional view showing yet another example of the schematic configuration of the light-emitting element according to embodiment 1.23 is a cross-sectional view showing yet another example of the schematic configuration of the light-emitting device according to embodiment 1. FIG. 24 is a cross-sectional view showing yet another example of the schematic configuration of the light-emitting device according to embodiment 1. FIG. 25 is a flowchart showing an example of a manufacturing method for the light-emitting device according to embodiment 1. FIG. 26 is a cross-sectional view illustrating a ligand substitution step in the quantum dot dispersion manufacturing process shown in FIG. 22. FIG. 27 is a cross-sectional view illustrating a step subsequent to the ligand substitution step in the quantum dot dispersion manufacturing process. FIG. 28 is a cross-sectional view illustrating an example of a portion of the light-emitting layer forming process shown in FIG. 22. FIG. 29 is a graph illustrating a reaction scheme for manufacturing the first inorganic compound. FIG. 29 is a graph illustrating measurement results by TGA showing the thermal decomposition of zinc xanthogenate. FIG. 30 is a graph illustrating measurement results by a film thickness step meter during the formation of a first film of the light-emitting device according to the present embodiment. FIG. 31 is a cross-sectional view illustrating an example of a first layer formed in the first film forming process shown in FIG. 22. FIG. 32 is a cross-sectional view illustrating another example of a first layer formed in the first film forming process shown in FIG. 22. FIG. 33 is a cross-sectional view illustrating yet another example of a first layer formed in the first film forming process shown in FIG. 22. FIG. 23 is another process cross-sectional view showing an example of a part of the process of forming a light-emitting layer shown in FIG. 22 . FIG. 24 is a diagram showing a reaction scheme for forming a metal sulfide from a precursor of the metal sulfide when a matrix material contains the metal sulfide as an inorganic compound. FIG. 25 is a cross-sectional view showing an example of a schematic configuration of a light-emitting device according to a modified example of embodiment 1. FIG. 26 is a cross-sectional view showing an example of a schematic configuration of a light-emitting device according to embodiment 2. FIG. 27 is a flowchart showing an example of a method for manufacturing the light-emitting device according to embodiment 2. FIG. 28 is a plan view showing an example of the configuration of a display device according to embodiment 3.

[0012] [Embodiment 1] One embodiment of the present disclosure will be described in detail below. Note that, hereinafter, the expression "A to B" regarding two numbers A and B means "greater than or equal to A and less than or equal to B" unless otherwise specified. Furthermore, hereinafter, a layer formed in a process earlier than a layer to be compared will be referred to as a "lower layer," and a layer formed in a process later than a layer to be compared will be referred to as an "upper layer."

[0013] For the sake of convenience, the following description will be given with the same reference numerals as those previously described, and the description thereof will not be repeated. In the following embodiments, differences from the previously described embodiments will be described. It goes without saying that modifications similar to those of the previously described embodiments are possible, even if no special explanation is given.

[0014] (Schematic Configuration of Light-Emitting Device) The light-emitting device according to this embodiment includes a first electrode, a second electrode, and a light-emitting layer provided between the first electrode and the second electrode, the light-emitting layer including a plurality of quantum dots and a matrix material. Hereinafter, the light-emitting layer may be referred to as "EML," the quantum dots as "QD," and the matrix material as "MX."

[0015] One of the first electrode and the second electrode is an anode and the other is a cathode. In this disclosure, the layer between the first electrode and the second electrode is referred to as a functional layer. The functional layer includes at least an EML.

[0016] The light-emitting device according to this embodiment may be a single-layer type including only one EML as a functional layer, or may be a multi-layer type including multiple functional layers. A charge transport layer, for example, may be provided as a functional layer between at least one of the first electrode and the EML and the second electrode and the EML. The charge transport layer may be either a hole transport layer or a charge transport layer. Hereinafter, the charge transport layer may be referred to as a "CTL," the hole transport layer may be referred to as a "HTL," and the electron transport layer may be referred to as an "ETL." The light-emitting device may further include, optionally, layers such as a hole injection layer, an electron blocking layer, a hole blocking layer, and an electron injection layer. Hereinafter, the hole injection layer may be referred to as a "HIL."

[0017] The light-emitting element may have a conventional structure in which the anode is the lower electrode and the cathode is the upper electrode, or an inverted structure in which the cathode is the lower electrode and the anode is the upper electrode.

[0018] Fig. 1 is a cross-sectional view showing an example of a schematic configuration of a light-emitting element 1 according to this embodiment. Fig. 2 is a cross-sectional view showing an example of a schematic configuration of a QD 21 and its vicinity in the light-emitting element 1 shown in Fig. 1. Fig. 3 is a cross-sectional view showing a state in which adjacent QDs 21 are close to each other in the light-emitting element 1 shown in Fig. 1.

[0019] 1, the light-emitting element 1 includes an anode 11 and a cathode 15 facing each other, and an EML 13 provided between the anode 11 and the cathode 15. As shown in FIG. 1, an HTL 12 may be optionally provided between the anode 11 and the EML 13. Furthermore, an ETL 14 may be optionally provided between the cathode 15 and the EML 13.

[0020] The anode 11 is an electrode that supplies holes to the EML 13 when a voltage is applied thereto. The cathode 15 is an electrode that supplies electrons to the EML 13 when a voltage is applied thereto. The anode 11 and the cathode 15 each contain a conductive material and are connected to a power supply (e.g., a DC power supply) (not shown) so that a voltage is applied between them.

[0021] At least one of the anode 11 and the cathode 15 is a light-transmitting electrode. Either the anode 11 or the cathode 15 may be a light-reflective electrode. The light-emitting element 1 can extract light from the light-transmitting electrode side.

[0022] For example, if the light-emitting element 1 is a top-emission type light-emitting element that emits light from the upper electrode side, a translucent electrode is used for the upper electrode and a reflective electrode is used for the lower electrode. On the other hand, if the light-emitting element 1 is a bottom-emission type light-emitting element that emits light from the lower electrode side, a translucent electrode is used for the lower electrode and a reflective electrode is used for the upper electrode.

[0023] The translucent electrode is made of a conductive translucent material that transmits visible light, such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), or fluorine-doped tin oxide (FTO).

[0024] The reflective electrode is preferably made of a conductive light-reflective material with high visible light reflectance, such as a metal such as aluminum (Al), copper (Cu), gold (Au), or silver (Ag), or an alloy containing such a metal, such as a magnesium-silver alloy (MgAg).The reflective electrode may be made by laminating a layer made of the above-mentioned light-transmitting material and a layer made of the above-mentioned light-reflective material.

[0025] The HTL 12 is a charge transport layer that contains a hole transport material and has a hole transport function of transporting holes injected from the anode 11 to the EML 13. As the hole transport material, an organic or inorganic material that has conventionally been used for the HTL in a quantum dot light-emitting diode (QLED), which is a light-emitting element containing QDs, or an organic light-emitting diode (OLED), can be used.

[0026] Examples of organic materials used for the HTL 12 include conductive compounds such as poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl))diphenylamine)] (TFB), poly(4-butyltriphenylamine) (p-TPD), 4,4'-bis(carbazol-9-yl)biphenyl (CBP), polyphenylenevinylene (PPV), a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT:PSS), TFB (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl))diphenylamine)]), or polyvinylcarbazole (PVK).

[0027] The inorganic material used for the HTL 12 is, for example, molybdenum oxide (MoO ２ , MoO ３ ), nickel oxide (NiO), chromium oxide (Cr ２ O ３ ), magnesium oxide (MgO), magnesium zinc oxide (MgZnO), lanthanum nickelate (LaNiO ３ ), or tungsten oxide (WO ３In particular, materials with large electron affinity and ionization potential are suitable for the HTL 12.

[0028] The ETL 14 is a charge transport layer that contains an electron transport material and has an electron transport function of transporting electrons injected from the cathode 15 to the EML 13. As the electron transport material, for example, an organic or inorganic material that has conventionally been used for the ETL in a QLED, an OLED, or the like can be used.

[0029] Examples of organic materials used for the ETL 14 include conductive compounds 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).

[0030] Examples of inorganic materials that can be used for the ETL 14 include metal oxides such as zinc oxide (ZnO), aluminum zinc oxide (AlZnO), lithium zinc oxide (LiZnO), and magnesium zinc oxide (MgZnO). In particular, materials with low electron affinity are suitable for the ETL 14.

[0031] The EML 13 includes multiple QDs 21 and MX 22. In the EML 13, holes transported from the anode 11 and electrons transported from the cathode 15 recombine, and the resulting excitons emit light during the transition from the conduction band level to the valence band level of the QDs 21. The EML 13 includes nano-sized QDs 21 as a light-emitting material, which correspond to the emission color.

[0032] QD21s are dots with a maximum particle width of 100 nm or less. QD21s are generally sometimes referred to as semiconductor nanoparticles because their composition is derived from semiconductor materials. QD21s are generally sometimes referred to as inorganic nanoparticles because their composition is derived from inorganic materials. QD21s are also sometimes referred to as nanocrystals because their structure has, for example, a specific crystalline structure.

[0033] The shape of the QD21 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). For example, the shape may be 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.

[0034] The QDs 21 may contain at least one metal element, such as Cd, Zn, In, Sb, Al, Si, Ga, Pb, Ge, or Mg. Alternatively, the QDs 21 may be a semiconductor material that combines at least one metal element with a nonmetal element, such as S, Te, Se, N, P, or As.

[0035] QD21 may be formed of only a core, or may be a two-component, three-component, or four-component core. Alternatively, QD21 may have a core-shell structure including a core 21C and a shell 21S, as shown in FIG. 2, or may be a core-shell or core-multishell structure.

[0036] As shown in FIG. 2 , when a QD21 includes a shell 21S, a core 21C is located at the center, and the shell 21S is provided on the surface of the core 21C. While the shell 21S preferably covers the entire core 21C, it is not necessary for the shell 21S to completely cover the core 21C. The shell 21S may be formed on only a portion of the surface of the core 21C. A QD21 can be said to have a core-shell structure if, upon observing a cross-section of the QD21, it is clear that the shell 21S is formed on only a portion of the surface of the core 21C, or if it is clear that the shell 21S surrounds the core 21C. Therefore, it is sufficient to determine from a cross-section of the QD21 that the shell 21S covers the entire core 21C. The cross-sectional observation can be performed, for example, using a scanning transmission electron microscope (STEM) or a transmission electron microscope (TEM).

[0037] The QD 21 may also include doped nanoparticles or have a compositionally graded structure. The shell 21S may be formed as a solid solution on the surface of the core 21C. In FIG. 2, the boundary between the core 21C and the shell 21S is shown by a dotted line, indicating that the boundary between the core 21C and the shell 21S may or may not be identifiable by analysis. The shell 21S may be formed in multiple layers.

[0038] The core 21C and shell 21S of the QD 21 may contain materials used for the core and shell materials of conventionally known QDs. The core 21C may be made of, for example, Si, Ge, CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, ZnTe, CdSeTe, GaInP, ZnSeTe, etc. The shell 21S may be made of, for example, CdS, ZnS, CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, AIP, etc. For example, when the shell 21S contains ZnSSe, the ZnSSe contained in the shell 21S may be made of ZnS. ｘ Se １－ｘ (0≦x≦1) When the QD21 has a core-shell structure, examples of the material of the QD21 (combination of the materials of the core 21C and the shell 21S) include ZnSe / ZnS, InP / ZnS, CdSe / CdS, CdSe / ZnSe, and CIGS / ZnS.

[0039] It should be noted that the compositions shown in chemical formulas in this disclosure are representative examples. The composition ratios shown in the chemical formulas are preferably stoichiometric, so that the actual composition of the compounds conforms to the chemical formulas. However, this does not exclude non-stoichiometric ratios.

[0040] The emission wavelength of QD21 can be varied by adjusting the particle size, composition, etc. QD21 is a QD that emits visible light, and by appropriately adjusting the particle size and composition of QD21, the emission wavelength can be controlled from the blue wavelength region to the red wavelength region.

[0041] The core 21C of the QD 21 is a light-emitting material that has a valence band level and a conduction band level and emits light by recombination of holes in the valence band level and electrons in the conduction band level. The light emitted from the QD 21 has a narrow spectrum due to the quantum confinement effect, making it possible to obtain light with a relatively deep chromaticity.

[0042] It should be noted that the QDs21 in the EML13 do not need to be arranged regularly as shown in Fig. 1, and the QDs21 may be included in the EML13 in a disordered manner. In addition, in the EML13, the QDs21 may be in a state where MX22 is formed between adjacent QDs21 as shown in Fig. 1, and the QDs21 are not close to each other, or the EML13 may include two or more QDs21 that are close to each other as shown in Fig. 3. It should be noted that the layer thickness of the EML13 may be set in the same manner as in the conventional case, and is not particularly limited.

[0043] MX22 is an MX whose main material is an inorganic compound (inorganic medium), and contains two or more types of inorganic compounds, including at least inorganic compound 23 and inorganic compound 24. In the following description, inorganic compound 23 is referred to as the first inorganic compound and inorganic compound 24 as the second inorganic compound, but the present embodiment is not limited to this. MX22 may also be an inorganic MX (inorganic matrix material) composed of inorganic compounds.

[0044] In this disclosure, MX refers to a material that contains and holds other substances, and can be referred to as a base material, a substrate, or a filler. In other words, in this disclosure, MX22 refers to a material that contains and holds QD21. MX22 is an element that constitutes the membrane in which QD21 are dispersed, and as shown in Figure 1, it is one of the components of EML13, which contains multiple QD21. Note that MX22 may be solid at room temperature.

[0045] MX22 may be filled in the EML 13. Focusing on two of the multiple QDs 21 as shown in Fig. 1 , MX22 may fill the space between the two QDs 21 (i.e., the region Y (space) between the two QDs 21). If the two QDs 21 are a first QD 21a and a second QD 21b, the region Y is the region enclosed in a cross-sectional view by two lines (common circumtangents) tangent to the outer peripheries of the first QD 21a and the second QD 21b and the corresponding outer peripheries of the first QD 21a and the second QD 21b.

[0046] 1 illustrates an example in which the QDs 21 are embedded in the MX 22 at intervals. However, as described above, in the EML 13, adjacent QDs 21 may be close to each other or may be close to each other. As shown in FIG. 3, even if adjacent first QDs 21a and second QDs 21b are close to each other, a region Y (space) may exist between the first QDs 21a and second QDs 21b. Even if the first QDs 21a and second QDs 21b are close to each other, the MX 22 may fill the region Y (space) between the first QDs 21a and second QDs 21b.

[0047] Therefore, MX22 may fill regions (spaces) in the EML13 other than those occupied by the QDs21. Therefore, MX22 may fill regions (spaces) in the EML13 other than those occupied by the QDs21. The EML13 has a QD group (quantum dot group) including a plurality of QDs21, and MX22 may fill regions (spaces) in the EML13 other than those occupied by the QD group. Here, three or more QDs21 are collectively referred to as a QD group. MX22 may fill regions (spaces) in the EML13 other than those occupied by the plurality of QDs21. As shown in FIG. 1 , the outer edge 13a (first outer edge) on the anode 11 side and the outer edge 13b (second outer edge) on the cathode 15 side of the EML13 may be covered with MX22. Alternatively, a portion of MX22 may be present from the outer edge 13a or 13b of the EML 13, and QD21 may be located away from at least one of the outer edge 13a and 13b of the EML 13. However, the configuration of the light-emitting element 1 is not limited to the above configuration, and at least one of the outer edge 13a and 13b of the EML 13 may not be formed solely by MX22, with part of the QD21 exposed from MX22. ​​MX22 may refer to the portion of the EML 13 excluding QD21.

[0048] In this embodiment, the outer edge 13a of the EML 13 on the anode 11 side refers to the interface between the EML 13 and the HTL 12, which is a layer adjacent to the EML 13 in the direction of the anode 11. The outer edge 13b of the EML 13 on the cathode 15 side refers to the interface between the EML 13 and the ETL 14, which is a layer adjacent to the EML 13 in the direction of the cathode 15.

[0049] The MX22 may contain multiple QDs 21. The MX22 may be formed so as to fill the spaces between the multiple QDs 21 (i.e., the spaces formed between the multiple QDs 21). The MX22 may partially or completely fill the spaces between the multiple QDs 21.

[0050] MX22 is a 1000 nm layer along the surface direction perpendicular to the layer thickness direction. ２The MX22 may include a continuous film having an area of ​​at least 1000 nm. A continuous film means a film that is not separated in one plane by any material other than the material that constitutes the continuous film. The continuous film may be an integrated film that is seamlessly connected by chemical bonds of the materials that constitute the MX22.

[0051] The MX22 may be formed of a different material from the shells 21S contained in each of the multiple QDs 21, or may contain the same material as the shells 21S. In other words, the shells 21S may contain only a material different from the at least one inorganic compound contained in the MX22, or may contain the same material as the at least one inorganic compound contained in the MX22. ​​When the shells 21S contain the same material as the at least one inorganic compound contained in the MX22, the inorganic compound may be inorganic compound 23, inorganic compound 24, or an inorganic compound other than inorganic compound 23 and inorganic compound 24. When the shells 21S contain the same material as the at least one inorganic compound contained in the MX22, the carrier confinement effect is enhanced, which suppresses the diffusion of excitons from the QDs 21 to the MX22 and improves the luminous efficiency. Furthermore, since the shells 21S and the at least one inorganic compound contained in the MX22 are continuously connected, the quality of the MX22 can be improved.

[0052] In this way, when the MX22 contains the same material as the shell 21S, the average distance between adjacent cores 21C (core-to-core distance) may be 3 nm or more, or even 5 nm or more, to avoid contact between the QD21 and aggregation of the QD21. Alternatively, the average distance between adjacent cores 21C may be 0.5 times or more the average core diameter. The core-to-core distance is the average distance between 20 adjacent cores 21C in a space containing 20 cores. The core-to-core distance should be kept wider than the distance when the shells 21S are in contact with each other. The average core diameter is the average core diameter of 20 cores 21C in a cross-sectional observation of a space containing 20 cores. The core diameter can be the diameter of a circle having the same area as the core area in cross-sectional observation.

[0053] The concentration of MX22 in the EML13 is, for example, the area ratio occupied by MX22 in the cross section of the EML13. The MX22 concentration may be 10% or more and 90% or less, or 30% or more and 70% or less, when observing the cross section of the EML13. The MX22 concentration may be measured, for example, from the area ratio obtained by image processing during cross-sectional observation of the EML13. When the QD21 has a core-shell structure, the concentration of the shell 21S may be 1% or more and 50% or less. When the shell 21S and the MX22 are made of the same material (same composition) and are indistinguishable from each other, the concentration of the combined region of the shell 21S and the MX22 may be within the range obtained by adding the range of the concentration of the shell 21S to the range of the concentration of the MX22. ​​The ratio of the core 21C of the QD21 to the shell 21S and the MX22 may be appropriately adjusted so that the sum of these ratios is 100% or less. In this way, when the shell 21S and the MX 22 cannot be distinguished from each other, the shell 21S may be treated as a part of the MX 22.

[0054] EML 13 may be composed of a plurality of QDs 21 and MXs 22. When EML 13 is analyzed, the intensity of carbon detected due to the chain structure may be equal to or less than noise.

[0055] The material constituting MX22 preferably has a wider (larger) band gap (hereinafter referred to as "Eg") than the material constituting QD21. For example, as described above, when QD21 has a core 21C and a shell 21S, it is desirable that the Eg of at least one inorganic compound contained in MX22 be larger than the Eg of the core 21C or the shell 21S.

[0056] Recombination of carriers (electrons and holes) injected into QD21 occurs mainly in core 21C. Shell 21S has the function of suppressing the occurrence of defects or dangling bonds in core 21C and reducing the recombination of carriers undergoing a deactivation process. When Eg of MX22 is larger than Eg of core 21C or shell 21S, the exciton confinement effect in core 21C is high, and excitons generated by carrier recombination or light absorption in core 21C are less likely to diffuse into MX22, thereby improving the luminous efficiency of light-emitting element 1.

[0057] Note that the Eg of the at least one inorganic compound contained in MX22 may be equal to or smaller than the Eg of the shell 21S, as long as it is larger than the Eg of the core 21C. However, it is preferable that the Eg of the at least one inorganic compound contained in MX22 is larger than the Eg of the shell 21S. In this case, the exciton confinement effect in the core 21C is enhanced, which suppresses the diffusion of excitons from QD21 to MX22 and further improves the luminous efficiency.

[0058] The at least one inorganic compound (inorganic material) contained in MX22 may be a semiconductor material or an insulating material. A suitable example of the at least one inorganic compound contained in MX22 is a metal sulfide. Metal sulfide precursors thermally decompose at relatively low temperatures and have easy control of Eg. Therefore, it is preferable that MX22 contains a metal sulfide as the inorganic compound, and metal sulfides are preferred as inorganic compound 23 and inorganic compound 24.

[0059] Examples of the metal sulfide include tin sulfide (SnS ２ ), indium sulfide (In ２ S ３ ), zinc sulfide (ZnS), aluminum sulfide (Al ２ S ３ ), beryllium sulfide (BeS), germanium sulfide (GeS ２ ), barium sulfide (BaS), calcium sulfide (CaS), magnesium sulfide (MgS), etc.

[0060] However, the inorganic compound is not limited to these metal sulfides, and may be an inorganic compound other than metal sulfides. Examples of inorganic compounds other than metal sulfides include metal selenides, metal tellurides, metal oxides, and inorganic compounds containing Group IV elements (specifically, Group 16 elements in the notation based on the new IUPAC system).

[0061] Examples of the metal selenides include beryllium selenide (BeSe), barium selenide (BaSe), calcium selenide (CaSe), magnesium selenide (MgSe), etc. Examples of the metal tellurides include calcium tellurium (CaTe), magnesium telluride (MgTe), etc. Examples of the metal oxides include zinc oxide (ZnO), etc.

[0062] It should be noted that MX22 may contain two or more types of inorganic compounds, including at least inorganic compound 23 and inorganic compound 24, and this does not exclude the addition of materials other than these inorganic compounds as additives.

[0063] As described above, in the EML 13, MX 22 is filled around the QD 21. In this way, in the light-emitting element 1, the periphery of the QD 21 is covered with MX 22, and thus the periphery of the QD 21 is protected by MX 22.

[0064] MX, which contains an inorganic compound as an inorganic medium, is less likely to peel off from QD21 than organic ligands, and by covering the periphery of QD21 with MX22, the QDs can be strongly protected. Therefore, by including MX22 containing an inorganic compound in EML13, the stability of EML13 can be improved compared to when an organic ligand is used for EML13. Furthermore, deterioration of QD21 can be suppressed, thereby improving the light-emitting characteristics and reliability of the light-emitting element 1.

[0065] However, when the periphery of the QD21 is uniformly covered with an inorganic compound, using an inorganic compound with a large Eg as the inorganic compound reduces the carrier injection efficiency of holes and electrons into the QD21, causing a decrease in luminous efficiency. Therefore, in this embodiment, as described above, two or more types of inorganic compounds including inorganic compound 23 and inorganic compound 24 are used for MX22, and the composition of MX22 in the layer thickness direction of the EML13 is changed. This changes the energy level of MX22 between the HTL12 side and the ETL14 side.

[0066] MX22 has a first region containing at least inorganic compound 23 and a second region containing at least inorganic compound 24, arranged in the direction of a straight line L1 that passes through outer edge 13a and outer edge 13b of EML13. The second region is provided closer to outer edge 13b than the first region. The concentration of inorganic compound 23 in the first region differs from the concentration of inorganic compound 23 in the second region by a certain amount or more. For example, it is desirable that the concentration of inorganic compound 23 in the first region differs from the concentration of inorganic compound 23 in the second region by 20% or more.

[0067] That is, MX22 has, in the direction of straight line L1, (1) a first region containing at least inorganic compound 23, and (2) a second region containing at least inorganic compound 24, which is provided closer to outer edge portion 13b than the first region and has a concentration of inorganic compound 23 different from that of inorganic compound 23 in the first region by a certain amount or more. Note that, since the concentration of inorganic compound 23 in the second region is different from that of inorganic compound 23 in the first region by a certain amount or more, the concentration of inorganic compound 24 in the second region is also different from that of inorganic compound 24 in the first region by a certain amount or more.

[0068] Furthermore, the MX22 has a first region containing at least an inorganic compound 23 and a second region containing at least an inorganic compound 24 in the direction of a straight line L1 that passes through the outer edge portion 13a and the outer edge portion 13b of the EML13.

[0069] The concentration of the inorganic compound 23 in the first region is greater than the concentration of the inorganic compound 24 in the first region, and the concentration of the inorganic compound 24 in the second region is greater than the concentration of the inorganic compound 23 in the second region.

[0070] FIG. 1 illustrates an example in which MX22 includes, as the first region, a first layer 22a whose main component is an inorganic compound 23, and, as the second region, a second layer 22b whose main component is an inorganic compound 24.

[0071] In addition, unless otherwise specified or contradictory, the structure of MX22 is observed in a cross-sectional view of EML13 with a width of about 100 nm, and it is sufficient to determine that it has the desired structure; it is not necessary to observe the desired structure throughout the entire EML13.

[0072] 4 is a cross-sectional view showing a schematic diagram of carrier injection in a comparative light-emitting element 101 in which the periphery of a QD 21 is uniformly covered with MX 122 made of an inorganic compound 23. In FIG. ＋ ) and electrons (e － The number of layers is indicated by an arrow. In addition, layers other than the HTL 12, the EML 113, and the ETL 14 are omitted in Fig. 4. Fig. 5 is a diagram showing the energy band structure of each functional layer in the comparative light-emitting element 100 shown in Fig. 4.

[0073] The comparative light-emitting element 101 has the same configuration as the light-emitting element 1 shown in FIG. 1, except that the EML 13 is replaced with an EML 113 in which the periphery of a QD 21 is covered with MX 122 made of an inorganic compound 23.

[0074] 4 illustrates an example in which the anode 11 is made of ITO, the HTL 12 is made of p-TPD, the ETL 14 is made of ZnMgO, and the cathode 15 is made of Al. In such a light-emitting device 101, if zinc sulfide (ZnS) is used as the inorganic compound 23 and the QDs 21 are uniformly covered with ZnS, as shown in FIGS. 4 and 5, the balance of electrons and holes in the EML 13 is, for example, approximately 6:4. Therefore, in this case, there is an excess of electrons and a shortage of holes, resulting in a poor carrier balance and reduced luminous efficiency and reliability.

[0075] Therefore, in the case of such an electron excess and hole deficiency, in order to improve the carrier balance, it is desirable to reduce the amount of electron injection into EML 13 or increase the amount of hole injection. In this embodiment, in the case of such an electron excess and hole deficiency, it is desirable to use (I) an inorganic compound having an elemental composition ratio with an energy level or characteristics that more easily promotes hole injection than inorganic compound 24 as inorganic compound 23, or to use (II) an inorganic compound having an elemental composition ratio with an energy level or characteristics that more easily suppresses electron injection than inorganic compound 23 as inorganic compound 24. By satisfying at least one of the above conditions (I) and (II), it is possible to provide a light-emitting element 1 that has a good carrier balance, high stability, high luminous efficiency, and high reliability.

[0076] Therefore, in the case of an excess of electrons and a shortage of holes as described above, it is desirable to use, for example, an inorganic compound having a larger Eg than inorganic compound 23 as inorganic compound 24. In other words, it is desirable to use, for inorganic compound 23, an inorganic compound having a smaller Eg than inorganic compound 24. In this case, it is possible to suppress injection of electrons, adjust the carrier balance, and improve luminous efficiency and reliability.

[0077] Furthermore, in the case of an excess of electrons and a shortage of holes as described above, it is preferable to use, for example, an inorganic compound having a higher hole mobility as inorganic compound 23 than inorganic compound 24. In other words, it is preferable to use, for inorganic compound 24, an inorganic compound having a lower hole mobility than inorganic compound 23. In this case, it is possible to facilitate hole injection, adjust the carrier balance, and improve luminous efficiency and reliability.

[0078] The carrier mobility, such as hole mobility or electron mobility, is calculated by the following formula (A): μ=eτ / m ＊ In formula (A), e represents the charge, τ represents the mean free time (scattering time), and m ＊ denotes the effective mass.

[0079] Assuming the charge e and mean free time τ are constant, the smaller the effective mass, the higher the carrier mobility.

[0080] Therefore, if you want to improve hole injection properties, it is generally desirable to use an inorganic compound 23 that has a larger Eg and a smaller hole effective mass than ZnS, which is used as the material for the shell 21S of QD21.

[0081] Table 1 shows examples of metal sulfides having relatively high hole transport properties as inorganic compounds with relatively high hole transport properties, with their Eg and effective mass. Table 2 shows examples of metal sulfides having relatively low hole transport properties as inorganic compounds with relatively low hole transport properties.

[0082] Therefore, in the case of an excess of electrons and a deficiency of holes as described above, for example, (a) the inorganic compound 23 may be indium sulfide (InS) and the inorganic compound 24 may be magnesium sulfide (MgnS). Alternatively, (b) the inorganic compound 23 may be zinc sulfide (ZnS) and the inorganic compound 24 may be magnesium sulfide (MgS). Alternatively, (c) the inorganic compound 23 may be indium sulfide (InS) and the inorganic compound 24 may be zinc sulfide (ZnS). Note that examples of the indium sulfide (InS) include In ２ S ３ Examples include:

[0083] In this way, when there is an electron excess and a hole deficiency, hole injection can be promoted and the electron excess can be adjusted by, for example, changing MX22 (specifically, inorganic compound 23) on the HTL 12 side to MX22 mainly composed of an inorganic compound having a smaller Eg and higher hole mobility (smaller hole effective mass) than MX22 (specifically, inorganic compound 24) on the ETL 14 side. Also, for example, changing MX22 on the ETL 14 side to MX22 mainly composed of an inorganic compound having a larger Eg and lower carrier mobility (larger effective mass) than MX22 on the HTL 12 side can suppress electron injection and adjust the hole deficiency.

[0084] FIG. 6 shows an example in which (a) the inorganic compound 23 is indium sulfide (In ２ S ３ 6 is a cross-sectional view schematically illustrating carrier injection in the light-emitting element 1 when the inorganic compound 24 is magnesium sulfide (MgS). In FIG. 6, illustrations of layers other than the HTL 12, EML 13, and ETL 14 are omitted. Similarly to the light-emitting element 101, FIG. 6 also illustrates an example in which the anode 11 is made of ITO, the HTL 12 is made of p-TPD, the ETL 14 is made of ZnMgO, and the cathode 15 is made of Al. Similarly to FIG. 4, FIG. 6 also illustrates the injection of holes (h ＋ ) and electrons (e － The number of functional layers is indicated by an arrow. Fig. 7 is a diagram showing the energy band structure of each functional layer in the light-emitting element 1 shown in Fig. 6. For comparison, Fig. 7 also shows the energy band structure of zinc sulfide (ZnS).

[0085] As shown in FIGS. 6 and 7, In, which has a smaller Eg than ZnS, is present on the HTL 12 side. ２ S ３ By providing the first layer 22a mainly composed of MgS, hole injection into the QDs 21 can be promoted more than when the QDs 21 are covered only with ZnS. Furthermore, by providing the second layer 22b mainly composed of MgS, which has a higher Eg than ZnS, on the ETL 14 side, electron injection into the QDs 21 can be suppressed more than when the QDs 21 are covered only with ZnS. In this case, the balance between electrons and holes in the EML 13 can be improved to approximately 5:5, thereby achieving a balanced carrier ratio.

[0086] In FIG. 6, (a) the inorganic compound 23 is In ２ S ３ In the above description, the inorganic compound 23 is ZnS and the inorganic compound 24 is MgS. However, in the following cases, the inorganic compound 23 is ZnS and the inorganic compound 24 is MgS, and the inorganic compound 23 is InS. ２ S ３ Similarly, when the inorganic compound 24 is InS such as InS and ZnS, the balance between electrons and holes can be improved to approximately 5:5.

[0087] On the other hand, in the case of an electron deficiency and a hole excess, it is desirable to reduce the amount of hole injection or increase the amount of electron injection in order to improve the carrier balance. Therefore, in such a case of an electron deficiency and a hole excess, it is desirable to use (i) an inorganic compound 23 having an elemental composition ratio with an energy level or characteristics that makes it easier to suppress holes than inorganic compound 24, or (ii) an inorganic compound 24 having an elemental composition ratio with an energy level or characteristics that makes it easier to promote electron injection than inorganic compound 23. By satisfying at least one of the above conditions (i) and (ii), it is possible to provide a light-emitting element 1 that has a good carrier balance, high stability, high luminous efficiency, and high reliability.

[0088] Therefore, in the case of electron deficiency and hole excess as described above, it is desirable to use, for example, an inorganic compound having a larger Eg than inorganic compound 24 as inorganic compound 23. In other words, it is desirable to use, for inorganic compound 24, an inorganic compound having a smaller Eg than inorganic compound 23. In this case, it is possible to suppress hole injection and adjust the carrier balance, thereby improving luminous efficiency and reliability.

[0089] Furthermore, in the case of a deficiency of electrons and an excess of holes as described above, it is desirable to use, for example, an inorganic compound having a higher electron mobility than inorganic compound 23 as inorganic compound 24. In other words, it is desirable to use, for inorganic compound 23, an inorganic compound having a lower electron mobility than inorganic compound 24. In this case, it is possible to facilitate electron injection, adjust the carrier balance, and improve luminous efficiency and reliability.

[0090] Therefore, in the case of an electron deficiency and an excess of holes, electron injection can be promoted and the excess of holes can be adjusted by, for example, changing MX22 on the ETL 14 side to MX22 mainly composed of an inorganic compound that has a smaller Eg and higher electron mobility (smaller electron effective mass) than MX22 on the HTL 12 side. Also, electron injection can be promoted and the excess of holes can be adjusted by, for example, changing MX22 on the HTL 12 side to MX22 mainly composed of an inorganic compound that has a larger Eg and lower electron mobility (larger electron effective mass) than MX22 on the ETL 14 side.

[0091] Tables 1 and 2 show examples of Eg and effective mass when the inorganic compound constituting MX22 is a metal sulfide. However, as described above, the inorganic compound constituting MX22 may be an inorganic compound other than a metal sulfide, such as a metal selenide, a metal telluride, or a metal oxide.

[0092] Therefore, Table 3 shows examples of Eg and effective mass of inorganic compounds other than metal sulfides that have a relatively high hole transport property as inorganic compounds with a relatively high hole transport property. Table 4 shows examples of Eg and effective mass of inorganic compounds other than metal sulfides that have a relatively low hole transport property as inorganic compounds with a relatively low hole transport property.

[0093] For example, different inorganic compounds have different energy levels, as shown in Tables 1 to 4. Therefore, according to this embodiment, by changing the composition of MX22 between the first and second regions as described above, the hole and electron transport capabilities can be changed.

[0094] In this embodiment, the concentration of the inorganic compound 23 in the first region is greater than the concentration of the inorganic compound 24 in the first region, and the concentration of the inorganic compound 24 in the second region is greater than the concentration of the inorganic compound 23 in the second region.

[0095] As described above, according to the present embodiment, MX22 contains the inorganic compound 23 and the inorganic compound 24, and the carrier balance can be adjusted and the luminous efficiency can be improved by changing the concentrations of these inorganic compounds 23 and 24 in MX22 between the outer edge portion 13a and the outer edge portion 13b in the EML 13. Therefore, according to the present embodiment, it is possible to provide a light-emitting element 1 that is highly stable, has high luminous efficiency, and is highly reliable.

[0096] In this embodiment, the concentration of the inorganic compound is defined by the ratio of elements constituting the inorganic compound, and can be determined by analysis using XPS (X-ray photoelectron spectroscopy).

[0097] In destructive testing (e.g., XPS analysis), the amounts and ratios of constituent elements in an inorganic compound are basically detected separately. For example, if the inorganic compound contained in MX22 is ZnS, Zn and S are detected separately in destructive testing. In this case, the detected elements are Zn:S = 1:1. This indicates that the inorganic compound contained in the first region is ZnS.

[0098] On the other hand, for example, suppose that MX22 contains two kinds of inorganic compounds, both of which are sulfides. In this case, the inorganic compounds contained in MX22 are ZnS and In. ２ S ３ In this case, the elements detected by the above analysis are Zn, In, and S. In this case, the concentration of ZnS and In ２ S３ If the concentration of ZnS is equal to that of In ２ S ３ = 1:1), it is detected as Zn:In:S = 1:2:4.

[0099] However, when the mixing ratio of these inorganic compounds (for example, the mixing ratio of inorganic compound 23 to inorganic compound 24) becomes complicated, it becomes difficult to identify these inorganic compounds. Therefore, in this case, the actual detection method using XPS analysis is to compare only the elemental amounts and elemental ratios of Zn and In. Then, whether the inorganic compound containing the detected element is a sulfide such as ZnS or an oxide such as ZnO is indirectly inferred from other elements.

[0100] In this case, whether the inorganic compound is ZnS or ZnO may be confirmed, for example, from the energy of the chemical bond detected by the above-mentioned detection method (inspection method), or the above-mentioned detection method may be combined with another detection method. As described above, XPS analysis is the most preferred detection method. However, a cross-sectional TEM / EDX method using a cross-sectional TEM (transmission electron microscope) and EDX (energy dispersive X-ray spectroscopy) may be used as the next preferred analysis method after XPS. For example, analysis may be performed by combining XPS with an inspection method such as the cross-sectional TEM / EDX method. Furthermore, analysis of the crystal form using XRD (X-ray diffraction) may be used as the next preferred analysis method after the cross-sectional TEM / EDX method. For example, analysis may be performed by combining XPS with an inspection method such as XRD.

[0101] The concentration of the inorganic compound contained in MX22 is measured along an arbitrary straight line L1 that passes through the outer edge 13a (first outer edge) on the anode 11 side of the EML 13 and the outer edge 13b (second outer edge) on the cathode 15 side of the EML 13. The concentration of the inorganic compound contained in MX22 is detected (measured) as the concentration of the inorganic compound contained in a measurement plane in the EML 13 that is perpendicular to the straight line L1.

[0102] When XPS is used to measure the above concentration, measurements are taken at multiple depths in the depth direction of the EML 13. XPS involves sputter etching the sample with Ar (argon) ions accelerated to several hundred volts to several kV, while irradiating the exposed sample surface with X-rays to measure the kinetic energy of photoelectrons emitted from the sample surface. This allows the composition and chemical bonding state of the elements that make up the sample surface to be analyzed.

[0103] Therefore, when XPS is used to measure the above concentrations, each measurement surface becomes the X-ray irradiation surface, and the size and shape of the X-ray irradiation spot become the size and shape of the measurement surface. Therefore, each measurement surface has the same area and shape. The concentrations of inorganic compound 23 and inorganic compound 24 are each measured under the same conditions along an arbitrary straight line L1 passing through outer edge portion 13 a and outer edge portion 13 b.

[0104] Figure 8 is a cross-sectional view showing an example of the measurement direction of the concentrations of inorganic compound 23 and inorganic compound 24 along an arbitrary straight line L1 in EML13. Note that for convenience of illustration, QD21 is omitted from Figure 8. Also, Figure 8 illustrates an example in which MX22 includes a first layer 22a containing inorganic compound 23 as a primary component as a first region, and a second layer 22b containing inorganic compound 24 as a primary component as a second region, in which inorganic compound 23 is InS and inorganic compound 24 is ZnS. Also, in Figure 8, line L1 is indicated by an arrow to indicate the measurement direction.

[0105] 9 shows the InS (e.g., In) in the EML13 shown in FIG. 8 measured along the line L1 shown in FIG. 8 using XPS. ２ S ３ 9 is a graph showing the concentration distributions of inorganic compounds 23 and 24. For ease of explanation and illustration, FIG. 9 shows an example of measurement results when QD21 are not present on any line L1. However, when QD21 are present on line L1, the concentrations of inorganic compounds 23 and 24 may be determined by interpolation. Furthermore, in FIG. 9, the measurement time is proportional to the measurement depth (measurement distance) along line L1 shown in FIG. 8. Therefore, the measurement time in FIG. 9 can be replaced with the measurement depth (measurement distance) along line L1.

[0106] 9 , XPS analysis can quantify elements at any measurement depth (measurement distance) in the EML 13 (in other words, elements at any measurement plane). For example, the ZnS concentration can be determined as the Zn element concentration by the following formula: ZnS concentration (= Zn element concentration) = (Zn element amount) / {(Zn element amount) + (In element amount)}. Similarly, the InS concentration can be determined as the In element concentration by the following formula: InS concentration (= In element concentration) = (In element amount) / {(Zn element amount) + (In element amount)}.

[0107] In this way, the concentration distribution of each inorganic compound at any measurement depth (measurement distance) in the EML 13 can be investigated from the element concentration at any measurement depth (measurement distance) in the EML 13.

[0108] The measurement results shown in Figure 9 reveal that a boundary between inorganic compound 23 (InS) and inorganic compound 24 (ZnS) exists in EML 13. That is, it is revealed that there is a portion in EML 13 where the concentrations of inorganic compound 23 (InS) and inorganic compound 24 (ZnS) are equal. This reveals the existence of regions of different inorganic compounds in EML 13. Furthermore, while Figure 8 shows a case in which MX22 is completely separated into a first region and a second region, this is not limiting. For example, since the first region is a region mainly composed of inorganic compound 23 and the second region is a region mainly composed of inorganic compound 24, the first region and the second region do not necessarily need to be completely adjacent to each other and may exist with an interval between them.

[0109] Furthermore, if there is a portion in the first region where the concentration of the inorganic compound 23 differs by a certain amount (e.g., 20%) or more, i.e., if there is a portion where the concentration of the inorganic compound 23 is, for example, 100% and a portion where the concentration is 80%, then it can be assumed that the concentration of the inorganic compound 23 changes significantly in that portion. Therefore, it can be assumed that a boundary exists in that portion. Similarly, if there is a portion in the second region where the concentration of the inorganic compound 24 differs by a certain amount (e.g., 20%) or more, it can be assumed that a boundary exists in that portion. Furthermore, if there is a portion in the first region where the concentration of the inorganic compound 23 differs by a certain amount (e.g., 20%) or more, and further if there is a portion in the second region where the concentration of the inorganic compound 24 differs by a certain amount (e.g., 20%) or more, then it can be assumed that a boundary exists. These findings indicate that there are regions of different inorganic compounds in the EML 13.

[0110] Figure 10 is a cross-sectional view showing another example of the measurement direction of the concentrations of inorganic compound 23 and inorganic compound 24 along an arbitrary straight line L1 in EML13. Note that, for convenience of illustration, QD21 is also omitted from Figure 10. Also, Figure 10 illustrates an example in which MX22 includes, as the first region, a first layer 22a whose main component is inorganic compound 23, and as the second region, a second layer 22b whose main component is inorganic compound 24, in which inorganic compound 23 is InS and inorganic compound 24 is ZnS. Also, Figure 10 illustrates the line L1 with an arrow to indicate the measurement direction.

[0111] Fig. 11 is a graph showing the concentration distribution of InS and ZnS in the EML13 shown in Fig. 10, measured by XPS along the line L1 shown in Fig. 10. For convenience of explanation and illustration, Fig. 10 also shows the measurement results for the case where no QDs 21 are located on any line L1.

[0112] As can be seen from FIGS. 8 to 11 , even when the same measurement method is used, the direction of the line L1, i.e., the penetration paths of the Ar ions and X-rays, may be perpendicular to the layer surface of the EML13 as shown in FIG. 8 , or may be oblique to the layer surface of the EML13 as shown in FIG. 10 .

[0113] In this embodiment, the concentration distribution of the inorganic compound in the EML 13 can be measured using XPS by the above-described method. However, this embodiment is not limited to this, and the concentration distribution of the inorganic compound contained in the EML 13 may also be measured using cross-sectional TEM / EDX. Note that the measurement results using XPS take precedence over the measurement results using cross-sectional TEM / EDX. FIGS. 12 and 13 are explanatory diagrams showing a method for examining the concentration distribution of the inorganic compound 23 and the inorganic compound 24 contained in the EML 13 in the film thickness direction using cross-sectional TEM / EDX. Note that, for convenience of illustration, the QDs 21 are also omitted in FIGS. 12 and 13 . Also, FIGS. 12 and 13 illustrate an example in which the MX 22 includes, as a first region, a first layer 22 a mainly composed of the inorganic compound 23 and, as a second region, a second layer 22 b mainly composed of the inorganic compound 24, in which the inorganic compound 23 is InS and the inorganic compound 24 is ZnS. Also in FIG. 13, the line L1 is indicated by an arrow to indicate the measurement direction.

[0114] When examining the concentration distribution of inorganic compounds 23 and 24 contained in EML13 in the film thickness direction using cross-sectional TEM / EDX, first, as shown in FIG. 12 , the light-emitting element 1 is processed using FIB (Focused Ion Beam) processing or the like to form a cross section of EML13 along the layer thickness direction of EML13. Next, as shown in FIG. 13 , the cross section of EML13 is observed using cross-sectional TEM, and EDX is used to scan multiple sections along the dotted lines shown in FIG. 13 in a direction perpendicular to the layer thickness direction (direction perpendicular to line L1), and the number of elements contained in the MX22 portion in each scanned measurement line is counted. If the device has a function for counting the number of elements along the measurement line, this function may be used; otherwise, image analysis of the EDX scan image may be performed. This allows the amount (concentration) of each inorganic compound element distributed in the direction of line L1 in the cross section of EML13 to be quantified. In this case, the size and shape of each measurement line are determined by the area scanned by EDX (i.e., the area scanned by X-rays) on the cross section, so that in this case too, each measurement line has the same shape.

[0115] Even when cross-sectional TEM / EDX is used to measure the concentrations of the inorganic compounds contained in EML13, the concentrations of the inorganic compounds contained in MX22 at each measurement surface in the layer thickness direction (direction of straight line L1) in EML13 can be calculated based on the above-mentioned formula. For example, the ZnS concentration can be determined as the Zn element concentration using the following formula: ZnS concentration (= Zn element concentration) = (Zn element amount) / {(Zn element amount) + (In element amount)}. Similarly, the InS concentration can be determined as the In element concentration using the following formula: InS concentration (= In element concentration) = (In element amount) / {(Zn element amount) + (In element amount)}.

[0116] Fig. 14 is a graph showing the concentration distribution of InS and ZnS in the film thickness direction (direction of line L1) of EML13 shown in Fig. 12, measured by the cross-sectional TEM / EDX method. As described above, Fig. 14 shows the concentrations of InS and ZnS in MX22.

[0117] As described above, in the light-emitting element 1 according to this embodiment, as an example, MX22 includes, as a first region, a first layer 22a whose main component is inorganic compound 23, and, as a second region, a second layer 22b whose main component is inorganic compound 24.

[0118] The inorganic compounds 23 and 24 penetrate and mix with each other, for example, at the interface between the first layer 22a and the second layer 22b, resulting in a concentration distribution in the thickness direction of the EML 13, as shown in Figures 9, 11, and 14.

[0119] In this case, the concentration of the inorganic compound 23 may change continuously or stepwise in the direction of the straight line L1. Similarly, the concentration of the inorganic compound 24 may also change continuously or stepwise in the direction of the straight line L1.

[0120] When a medium with a large Eg is inserted into the interface between the EML 13 and a layer adjacent to the EML 13, all carriers must overcome the barrier of the medium. However, by continuously or stepwise changing the concentration of inorganic compound 23 or inorganic compound 24, the carrier injection barrier can be changed stepwise, making carrier injection easier than when a large injection barrier is overcome all at once. Therefore, having a concentration distribution of inorganic compound 23 and inorganic compound 24 in the EML 13 can also reduce the driving voltage.

[0121] However, as described above, the light-emitting element 1 may have two or more regions between the outer peripheral portion 13 a and the outer peripheral portion 13 b in the thickness direction of the EML 13, in which the concentration of the inorganic compound constituting MX22 differs by a certain amount or more. As described above, it is desirable that the inorganic compound has a concentration distribution in the thickness direction of the EML 13, but the present disclosure does not exclude a 100% difference in concentration of the inorganic compound between the first layer 22 a and the second layer 22 b. In other words, the first layer 22 a may contain only the inorganic compound 23, and the second layer 22 b may contain only the inorganic compound 24.

[0122] Furthermore, it is desirable that the EML 13 includes a region within at least 1 nm from the outer edge 13 a where the concentration of the inorganic compound 23 in the MX 22 is 80% or more. Since the MX 22 near the outer edge 13 a is formed of a relatively uniform composition in this way, carriers can be easily injected from the anode 11 side into the QDs 21 near the outer edge 13 a.

[0123] Similarly, it is desirable that the EML 13 includes a region within at least 1 nm from the outer edge 13 b where the concentration of the inorganic compound 24 in the MX 22 is 80% or more. Since the MX 22 near the outer edge 13 b is formed of a relatively uniform composition in this way, carriers can be easily injected from the cathode 15 side into the QDs 21 near the outer edge 13 b.

[0124] When the EML 13 includes a region in which the concentration of inorganic compound 23 in MX22 is 80% or more within a range of at least 1 nm from the outer edge 13a, it is preferable that the outer edge 13a be covered with MX22, as shown in Figure 1. Similarly, when the EML 13 includes a region in which the concentration of inorganic compound 24 in MX22 is 80% or more within a range of at least 1 nm from the outer edge 13b, it is preferable that the outer edge 13b be covered with MX22, as shown in Figure 1. That is, it is preferable that part of MX22 is present at the outer edges 13a and 13b of the EML 13, and that QD21 is located away from the outer edges 13a and 13b of the EML 13.

[0125] The concentrations of these inorganic compounds 23 and 24, as well as the thicknesses of the first layer 22a and the second layer 22b, can be changed as desired by utilizing the volume change that occurs when these inorganic compounds are formed from thermally decomposable or photodecomposable precursors.

[0126] Therefore, the interface between the first region and the second region may intersect with the plurality of QDs 21. For example, in the light-emitting device 1 shown in Fig. 1 , the EML 13 includes one QD row 21L (quantum dot row) in the thickness direction of the EML 13, in which the plurality of QDs 21 are aligned in a direction perpendicular to the thickness direction of the EML 13. In the light-emitting device 1 shown in Fig. 1 , the interface 22I between the first layer 22 a and the second layer 22 b intersects with the QD row 21L.

[0127] In the light-emitting device 1, the concentration of each inorganic compound contained in MX22 can be changed within the range of the thickness of one QD21 in the thickness direction of the EML 13. Therefore, even when only one QD21 (i.e., one layer) is stacked in the thickness direction of the EML 13, such as when only one row of QD21 is stacked in the thickness direction of the EML 13 as shown in Fig. 1, or when the QD21 are not stacked in an orderly manner, the carrier balance can be adjusted and the luminous efficiency can be improved.

[0128] Furthermore, by directly contacting each QD21 particle with an inorganic compound having an arbitrary Eg in an arbitrary ratio within the EML13, the inorganic compound can exert its influence more effectively.

[0129] As described above, Fig. 1 shows an example of the schematic configuration of the light-emitting element 1 according to this embodiment. The light-emitting element 1 according to this embodiment is not limited to the configuration shown in Fig. 1. Figs. 15 to 21 are cross-sectional views showing other examples of the schematic configuration of the light-emitting element 1 according to this embodiment. Note that in Figs. 15 to 21, components other than the HTL 12, EML 113, and ETL 14 are omitted from the illustration.

[0130] As shown in FIG. 15 , the QD rows 21L may be arranged in multiple rows (e.g., two rows) in the thickness direction of the EML 13. That is, multiple QDs 21 may be stacked in the thickness direction of the EML 13. In this case, the interface 22I between the first layer 22a and the second layer 22b may intersect with the QD row 21L on the HTL 12 side, in other words, the bottommost layer, as shown in FIG. 1 . Furthermore, the interface 22I between the first layer 22a and the second layer 22b may intersect with the QD row 21L located above the bottommost layer (the ETL 14 side), as shown in FIG. 15 . Specifically, for example, when two layers of QDs 21 are stacked as shown in FIG. 15 , the interface 22I between the first layer 22a and the second layer 22b may be located at about 1.5 layers of QDs 21.

[0131] 16, the first layer 22a and the second layer 22 may each contain QD21. Therefore, in the light-emitting element 1, as shown in FIG. 16, the EML13 may include an EML13A (first light-emitting layer) and an EML13B (second light-emitting layer), with the first layer 22a being used for the EML13A and the second layer 22b being used for the EML13B. Therefore, the EML13A may include the inorganic compound 23 and QD21, and the EML13B may include the inorganic compound 24 and QD21. In this case, the QD21 contained in the EML13A and the QD21 contained in the EML13B may be the same as or different from each other.

[0132] Also, as shown in Figure 17, the EML13 has multiple rows of QD rows 21L stacked in the layer thickness direction of the EML13, but the interface 22I between the first layer 22a and the second layer 22 may be configured in such a way that it is not clearly separated.

[0133] Furthermore, the QDs 21 do not necessarily need to be aligned as a QD row 21L in the EML 13. As shown in FIG. 18 , the QDs 21 may be stacked in a complex manner within the EML 13. In this case, too, the interface 22I between the first layer 22a and the second layer 22b may intersect with the QD row 21L located above the bottommost QD row 21L (on the ETL 14 side). For example, when two layers of QDs 21 are stacked, the interface 22I between the first layer 22a and the second layer 22b may be located approximately 1.5 layers from the QDs 21. Although not shown, the interface 22I may of course intersect with the HTL 12 side, in other words, the bottommost QD row 21L.

[0134] 19, the EML 13 may have a configuration in which only the first layer 22a contains QD21 and the second layer 22b does not contain QD21, or the second layer 22b may contain at least a portion of QD21 as shown in Fig. 20. Fig. 19 illustrates an example in which QD21 are stacked in a complex manner within the EML 13, the interface 22I between the first layer 22a and the second layer 22 is not clearly separated, and QD21 are contained only in the first layer 22a and not in the second layer 22b. Figure 20 also illustrates an example in which QDs 21 are stacked in a complex manner within the EML 13, the interface 22I between the first layer 22a and the second layer 22 is not clearly separated, and the interface 22I between the first layer 22a and the second layer 22 intersects with the QD row 21L of the lowest layer in some parts and with the QD row 21L above the QD row 21L of the lowest layer (towards the ETL 14) in other parts.

[0135] Furthermore, as shown in FIG. 21, the EML 13 may have a gradation in the concentration of a plurality of inorganic compounds, and the concentration of each inorganic compound may gradually change from the outer edge portion 13b to the outer edge portion 13b, thereby forming an element gradient.

[0136] In this way, the boundary surface between the first region and the second region may be provided at the center of the EML 13 in the thickness direction as shown in FIG. 1 , or may be provided closer to the HTL 12 side (i.e., the anode 11 side) or the ETL 14 side (i.e., the cathode 15 side) than the center of the EML 13 in the thickness direction.

[0137] Furthermore, as shown in FIGS. 18 to 20, the QDs 21 may be exposed from the MX 22 at least at one of the outer edge 13a and the outer edge 13b of the EML 13.

[0138] For example, as shown in Figures 18 to 20, a portion of MX22 may be located from at least one of outer edge 13a and outer edge 13b of EML13, and QD21 may be configured to be located away from at least one of outer edge 13a and outer edge 13b.

[0139] In any case, by using inorganic compounds with different energy levels on the HTL 12 side and the ETL 14 side of the EML 13, it is possible to form an EML 13 in which holes and electrons are easily transported to and injected into the QDs 21, respectively.

[0140] MX22 may further contain at least one halogen element in addition to the inorganic compound 23 and the inorganic compound 24. For example, as shown in FIG. 2, MX22 may contain fluoride ions (F － ), chloride ions (Cl － ), bromide ion (Br － ), iodide ion (I － ) may contain halide ions 31a having at least one of the following.

[0141] 2, the presence of halide ions 31a near the surface of QD 21 improves the dispersibility of QD 21. For this reason, it is desirable that MX 22 contains a halogen element. Note that the area near the surface of QD 21 may be within a range approximately the thickness of shell 21S.

[0142] Furthermore, halogen elements bond with the unpaired electrons of the inorganic compound that constitutes MX22 to stabilize it. Therefore, when MX22 contains halogen elements, defects in MX22 can be inactivated. Here, "inactivating defects in MX22" means that the unpaired electrons are used to bond with the halogen elements, and the defects no longer function as non-radiative centers or carrier traps.

[0143] MX22 may contain 1 atomic % or more of halogen elements. The concentration of halide ions 31 a near each QD21 is preferably higher than the concentration of halide ions 31 a in the surrounding area. For example, the vicinity of a given QD21 may be within 1 nm of the outermost surface of the QD21.

[0144] 2, the average total concentration of halogen atoms within a distance DA of 1 nm from the outer surface of the shell 21S, which is the outermost surface of the QD21, may be higher than the average total concentration of halogen atoms at other positions. In this case, the average total concentration of halogen atoms within the distance DA of 1 nm may be 10% or more higher, 50% or more higher, or 100% or more higher than the average total concentration of halogen atoms at other positions. Such a concentration distribution can be confirmed, for example, by elemental mapping using cross-sectional TEM-EDX (transmission electron microscope-energy dispersive X-ray spectroscopy).

[0145] Here, "other positions" can also be considered to be positions where no QD21 is present within 1 nm. Multiple QD21 are contained within the EML13. Therefore, the above value can be considered to be a value obtained by comparing the average total concentration of halogen atoms within a 1-nm range around each QD21 in the EML13 with the average total concentration of halogen atoms in portions of the EML13 that are more than 1 nm away from any QD21.

[0146] In other words, the average value of the total concentration of halogen elements in the region within 1 nm from the outermost surface of each of the multiple QD21 in MX22 is preferably higher than the average value of the total concentration of the halogen elements in the region in MX22 that is more than 1 nm away from the outermost surface of each of the multiple QD21, and may be, for example, 10% or more, 50% or more, or 100% or more higher.

[0147] This can further improve the dispersibility of the QDs 21, and can form an EML 13 with a more uniform thickness.

[0148] MX22 can contain halide ions by forming EML13 using a QD dispersion containing a halogen element and QD21.

[0149] (Method for Manufacturing the Light-Emitting Element 1) Next, a method for manufacturing the light-emitting element 1 according to this embodiment will be described below with reference to Fig. 22 to Fig. 34. Fig. 22 is a flowchart showing an example of the method for manufacturing the light-emitting element 1 according to this embodiment.

[0150] As shown in Figure 22, in the method for manufacturing the light-emitting element 1 according to this embodiment, first, an anode 11 is formed on a substrate serving as a support (step S1, anode formation step). Next, an HTL 12 is formed (step S2, hole transport layer (HTL) formation step). In parallel, a QD dispersion is produced (prepared) (step S11, quantum dot (QD) dispersion production step). Next, an EML 13 is formed using the QD dispersion (step S3, emissive layer (EML) formation step). Next, an ETL 14 is formed (step S4, electron transport layer (ETL) formation step). Next, a cathode 15 is formed (step S5, cathode formation step). This completes the manufacture of the light-emitting element 1.

[0151] The anode 11 is formed in step S1 and the cathode 15 is formed in step S5 by, for example, vapor deposition or sputtering.

[0152] The HTL 12 is formed in step S2 and the ETL 14 is formed in step S4 by, for example, vacuum deposition, sputtering, a coating method using a colloidal solution, a sol-gel method, or the like.

[0153] Before explaining step S3, step S11 will be explained.

[0154] (Step S11) The QD dispersion preparation process in step S11 includes a ligand substitution process (step S21) for substituting the ligands coordinated to the QDs 21, as shown in Fig. 23. Fig. 23 is a cross-sectional schematic diagram for explaining the ligand substitution process (step S21) in step S11.

[0155] Synthesized or commercially available QDs often have an organic ligand (hereinafter, for convenience of explanation, referred to as a "first organic ligand") coordinated as the ligand. Commercially available QDs are generally provided in the form of a QD dispersion containing a first organic ligand as the ligand. The first organic ligand is used as a dispersant to improve the dispersibility of QDs in the QD dispersion, as well as to improve the surface stability and storage stability of QDs. Furthermore, QDs are synthesized, for example, by a wet method, and the particle size of QDs is controlled by coordinating the first organic ligand to the surface of the QDs. For this reason, QD dispersions synthesized by a wet method contain, for example, the first organic ligand used in the synthesis of QDs. Such a first organic ligand may be used as is, or may be replaced with a desired first organic ligand depending on the type of solvent, etc. In any case, the EML obtained by applying and drying a QD dispersion containing a first organic ligand that is conventionally commonly used as an organic ligand contains the first organic ligand.

[0156] In this embodiment, to mineralize EML 13, a ligand substitution step is carried out in which the first organic ligand coordinated to QD 21 is substituted with a second organic ligand that is thermally decomposed by heating and halide ions 31a. An organic ligand that is a precursor of MX 22 is used as the second ligand.

[0157] A method for substituting the first organic ligand coordinated to the QD 21 with the second organic ligand and halide ions 31a will be described below with reference to FIG.

[0158] As shown in Figure 23, in the above-mentioned ligand substitution process, first, a ligand solution 30 in which halide ions 31a and an organic ligand 32 as a second organic ligand are dissolved, and a QD dispersion liquid 40 in which QDs 21 coordinated with an organic ligand 41 as a first organic ligand are dispersed are poured into a container 61 (step S21a).

[0159] The halide ions 31a are supplied as, for example, metal halide 31. The metal halide 31 exists as anionic halide ions 31a and cationic metal ions 31b. Of these halide ions 31a and metal ions 31b, the halide ions 31a are negatively charged and are therefore attracted to the positively charged surface of the QD21 as halogen ligands.

[0160] As described above, the halide ion 31a, which is an anion, is, for example, a fluoride ion (F － ), chloride ions (Cl － ), bromide ion (Br － ), iodide ion (I － ) etc.

[0161] The metal ion 31b, which is a cation, is, for example, Li ＋ , Na ＋ , K. ＋ , Rb ＋ , Cs ＋ , Be ２＋ , Mg ２＋ , Ca ２＋ , Sr ２＋ , Ba ２＋ , Zn ２＋ , Al ３＋ , Ga ３＋ , In ３＋ , Sn ２＋ , Pb ２＋ etc.

[0162] The organic ligand 32 is not particularly limited as long as it is a compound that decomposes thermally upon heating, contains at least one element contained in the inorganic compound 23, and serves as a precursor of MX22. ​​For example, xanthogenic acid is preferably used as the organic ligand 32. Other materials that can be used as the organic ligand 32 include thiourea, thioacetamide, dithiocarboxylic acid, dithiocarbamic acid, trithiocarbonate, dimethylthiourea, and tertiary thiol.

[0163] In the following, as an example, the inorganic compound 23 is ZnS, and the organic ligand 41 is a chloride ion (Cl) as the halide ion 31a. － ) and xanthogenic acid as the organic ligand 32. Xanthogenic acid is a part of the precursor of MX22 (ZnS precursor) and is used as a part of the S (sulfur) source of ZnS.

[0164] FIG. 23 shows an example in which the metal halide 31 is ZnCl ２ and the halide ion 31a is Cl － and the metal ion 31b is Zn ２＋ The organic ligand 32 is xanthogenic acid (denoted by "Xan" in FIG. 23) as an example.

[0165] The ligand solution 30 contains a solvent 33 in which the halide ions 31a and the organic ligand 32 are soluble, and the QD dispersion 40 contains a solvent 42 in which the organic ligand 41 is soluble. For example, the solvent 42 has a different polarity from the solvent 33 and a lower specific gravity than the solvent 33. Note that a separation liquid (not shown) having a specific gravity and polarity between the solvent 33 and the solvent 42 may be poured into the container 61 to more clearly distinguish the boundary between the ligand solution 30 and the QD dispersion 40.

[0166] The solvent 33 may contain at least one organic solvent selected from the group consisting of, for example, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N-methylformamide (NMF), tetrahydrofuran (THF), formamide, N,N'-dimethylpropylene urea, dimethylacetamide, N-methylpyrrolidone, gamma-butyrolactone, propylene carbonate, acetonitrile, 2-methoxyethanol, methyl acetate, ethyl acetate, ethyl formate, tetrahydrofuran, diethyl ether, tetrahydrothiophene, and diethyl sulfide. In this case, the solvent 33 effectively disperses both the QD21 coordinated with the halide ion 31a and the precursor of MX22. ​​The solvent 33 may also be a polar solvent with a higher polarity than the solvent 42. The solvent 33 may be prepared by dispersing, for example, zinc chloride, sodium chloride, hydrochloric acid, or the like in NMF, DMF, DMSO, or the like. The solvent 42 is preferably, for example, toluene, hexane, octane, octadecene, etc. The solvent 42 is preferably a non-polar solvent that is immiscible with the solvent 33.

[0167] As described above, the organic ligand 41 may be a carbon chain, which is commonly used as a ligand for QDs. The solvent 42 is a solvent in which the organic ligand 41 is soluble, so that the QDs 21 coordinated with the organic ligand 41 are easily dispersed in the QD dispersion liquid 40.

[0168] The ligand solution 30 contains dissolved halide ions 31a in an amount exceeding the amount of halide ions 31a capable of coordinating with the QDs 21, and dissolved organic ligands 32 in an amount exceeding the amount of organic ligands 32 capable of coordinating with the QDs 21. For example, the ligand solution 30 may contain dissolved halide ions 31a at a concentration of 0.1 mol / L or more and organic ligands 32 at a concentration of 0.1 mol / L or more. The molar ratio of the dissolved amounts of halide ions 31a and organic ligands 32 in the ligand solution 30 may be 3:1.

[0169] Next, the container 61 containing the ligand solution 30 and the QD dispersion 40 is vibrated at high speed by a stirrer to mix the ligand solution 30 and the QD dispersion 40 (step S21b). To improve the efficiency of the mixing, a stir bar may be placed in the container 61. In other words, the process of mixing the ligand solution 30 and the QD dispersion 40 is a process of treating the QDs 21 with the halide ions 31a and the organic ligands 32, and in particular, a process of producing QDs 21 coordinated with the halide ions 31a and the organic ligands 32.

[0170] As described above, the ligand solution 30 contains an excess of halide ions 31a and an excess of organic ligands 32. Generally, when two or more types of ligands are contained in a solution in which QDs are dispersed, the ligands coordinated to the QDs are in equilibrium with each other. Therefore, when the ligand solution 30 and the QD dispersion 40 are stirred, at least a portion of the ligands coordinated to the QDs 21 are replaced by the halide ions 31a and the organic ligands 32 from the organic ligands 41.

[0171] Therefore, by the above stirring, as shown in step S21b of Figure 23, a QD dispersion 51 in which QDs 21 coordinated with halide ions 31a and organic ligands 32 are dispersed in solvent 33, and a ligand solution 52 in which organic ligands 41 are dissolved in solvent 42 are obtained in container 61.

[0172] As a result, QDs 21 coordinated with halide ions 31a and organic ligands 32 are obtained in QD dispersion 51. The stirring may be completed by irradiating the liquid in container 61 with ultraviolet light or the like and confirming that the luminescent liquid layer has shifted from the top to the bottom of container 61.

[0173] Next, as shown in step S21c of Figure 23, only the QD dispersion liquid 51 is extracted from the container 61 to the container 62.

[0174] FIG. 24 is a schematic cross-sectional view showing the process after step S21 in step S11.

[0175] 24, when the inorganic compound 23 is ZnS, after step S21c, the QD dispersion 51 extracted in step S21c and zinc xanthate as a precursor 34 (ZnS precursor) of MX22 are mixed in a container 62 (step S22). ２ shows zinc xanthate, which is used as part of the S (sulfur) source for ZnS and as a Zn (zinc) source.

[0176] As a result, chloride ions (Cl) are formed as halide ions 31a. － MX22), and QDs 21 coordinated with xanthogenic acid as organic ligand 32 used as a precursor, and zinc xanthogenate as precursor 34 serving as part of the S source and the Zn source are dispersed in a first solvent, such as solvent 33. This produces (prepares) a QD dispersion 53 (see S31 in FIG. 25 ) containing QDs 21, xanthogenic acid and zinc xanthogenate as precursors (ZnS precursors) of inorganic compound 23 (MX22), halide ions 31 a, and solvent 33.

[0177] When halide ions 31a are used as the ligand, the quantum yield (QY) of the resulting light-emitting device 1 is slightly lower than when an organic ligand is used.

[0178] However, as described above, the use of halide ions 31a as ligands makes it possible to disperse QD21 in polar solvents. For example, as shown in Figure 2, when halide ions 31a are coordinated to the shell 21S of QD21, the QD21 is highly dispersible in polar solvents, making it less likely to precipitate. Furthermore, the coordination of halide ions 31a to the shell 21S of QD21 suppresses aggregation of QD21, which occurs when the MX22 precursor reacts with the surface of the QD21, and allows the QD21 to maintain its dispersibility for a long period of time.

[0179] On the other hand, the organic ligand xanthogenic acid has a lower dispersibility of QD21 in polar solvents than the halogen ligand, but the QY of the resulting light-emitting device 1 can be improved by using xanthogenic acid as the ligand.

[0180] Next, step S3 will be described.

[0181] 25 is a cross-sectional view showing an example of a part of the EML formation step (step S3). Note that the substrate as a support and the anode 11 are omitted from the illustration of FIG.

[0182] 25, in step S3, the QD dispersion 53 produced in step S11 is first applied to the HTL 12. As described above, the QD dispersion 53 contains a plurality of QDs 21, xanthogenic acid and zinc xanthate as precursors of the inorganic compound 23 (first inorganic compound), halide ions 31a, and a solvent 33 as a first solvent. In FIG. 25, Xan represents xanthogenic acid, and Zn(EtXan) represents Zn(EtXan). ２ indicates zinc xanthate, and Cl － indicates halide ions 31a. In this way, a coating film of the QD dispersion 53 is formed on the HTL 12 (step S31, quantum dot dispersion coating step).

[0183] The coating film may be formed by any method, such as bar coating, spin coating, or ink jet printing.

[0184] Next, the coating of the QD dispersion 53 is heated to a temperature (e.g., 150 to 200°C as shown in FIG. 26 ) equal to or higher than the thermal decomposition temperature of xanthogenic acid and zinc xanthate, which are precursors of the inorganic compound 23. This thermally decomposes at least a portion of the precursor of the inorganic compound 23 and removes the solvent 33. This results in the formation of a first film containing a plurality of QDs 21 and MX 22 containing the inorganic compound 23, which constitutes the first layer 22a (step S32, first film formation step).

[0185] FIG. 26 is a diagram schematically showing a reaction scheme for producing inorganic compound 23.

[0186] As shown in Figure 26, zinc xanthogenate has a structure in which Zn is bonded to xanthogenic acid. Xanthogenic acid and zinc xanthogenate are precursors of inorganic compound 23. Xanthogenic acid and zinc xanthogenate are thermally decomposed by heating, vaporizing the organic components, while Zn and S bond to form ZnS. In this way, the QD dispersion 53 forms bulk inorganic compound 23 through the thermal decomposition of the precursor of inorganic compound 23. Note that if nanoparticles of an inorganic compound are used as the inorganic compound, there will be many gaps, making it impossible to achieve the aforementioned objective.

[0187] Figure 27 shows the structure of zinc xanthate (Zn(EtXan) ２ 1 is a graph showing the results of TGA (differential thermal analysis) measurements showing the thermal decomposition of

[0188] As shown in Fig. 27, if the mass of zinc xanthogenate before heating is 100 wt%, zinc xanthogenate undergoes thermal decomposition by heating, and organic components are vaporized, resulting in a gradual decrease in mass. As shown in Fig. 27, zinc xanthogenate undergoes significant thermal decomposition between 125°C and 150°C, for example, and its mass decreases to 40 wt% or less of its mass before heating.

[0189] Figure 28 is a graph showing the results of measurements taken with a film thickness step meter during the formation of the first film. In Figure 28, the horizontal axis represents the scanned distance, and the vertical axis represents the film thickness (step). Figure 28 shows the change in film thickness of the first layer 22a of MX22 when a coating of QD dispersion 53 was heated at 100°C, 125°C, and 175°C, respectively, when p-TPD was used as HTL 12, THF was used as solvent 33, and ZnS was used as inorganic compound 23.

[0190] As shown in Figure 27, when the heating temperature exceeds 125°C, zinc xanthate undergoes significant thermal decomposition, resulting in a decrease in mass and a corresponding decrease in volume, which in turn reduces the film thickness of the first layer 22a of MX22, as shown in Figure 28. In particular, when the coating of the QD dispersion 53 is heated to 175°C, which completely exceeds the thermal decomposition point of zinc xanthate, the entire coating decomposes, resulting in a significant decrease in mass and film thickness.

[0191] In this embodiment, the bulk of ZnS (in other words, the thickness of the first layer 22a) can be adjusted by utilizing this mass reduction of the precursor.

[0192] 29 to 31 are cross-sectional views showing examples of the first layer 22a formed in step S32.

[0193] In step S32, the mass reduction (film thickness reduction) of the precursor of the inorganic compound 23 can be controlled by adjusting the concentration (medium mass) of the precursor of the inorganic compound 23 contained in the QD dispersion liquid 53.

[0194] Therefore, by adjusting the concentration of the precursor of the inorganic compound 23 contained in the QD dispersion liquid 53 so that one outer edge of the MX22 containing the inorganic compound 23, which becomes the boundary surface 22I between the first layer 22a and the second layer 22b shown in Figure 1, intersects with the QD row 21L, it is possible to form, for example, the first layer 22a shown in Figure 29.

[0195] 29 , according to this embodiment, it is possible to change the concentration of, for example, the inorganic compound 23 contained in the MX 22 within the range of the thickness of one QD 21 in the thickness direction of the EML 13. Therefore, even if only one layer of QD 21 is stacked in the thickness direction of the EML 13, it is possible to adjust the carrier balance and improve the luminous efficiency.

[0196] In step S32, for example, if the inorganic compound 23 has good adhesion to the QDs 21, the inorganic compound 23 is formed around the QDs 21, which reduces the overall bulk of the first layer 22a. In this case, by adjusting the concentration of the precursor of the inorganic compound 23 and controlling the mass reduction (film thickness reduction) of the precursor of the inorganic compound 23, the first layer 22a shown in FIG. 30 or 31 can be formed.

[0197] 32 and 33 are cross-sectional views illustrating an example of a part of the EML formation process (step S3). Note that, as an example, FIG. 32 and FIG. 33 illustrate a case where the second layer 22b is formed on the first layer 22a shown in FIG. 29.

[0198] Thus, when QD dispersion 53 containing QDs 21 and xanthogenic acid and zinc xanthogenate as precursors of inorganic compound 23 is applied to an underlayer, such as HTL 12, and heated, the xanthogenic acid and zinc xanthogenate around QDs 21 decompose. This results in the formation of ZnS as inorganic compound 23, which coats QDs 21 and forms part of MX 22. As described above, by adjusting the concentration of the precursor of inorganic compound 23, it is possible to coat only the periphery of QDs 21 with inorganic compound 23, or to coat the periphery of that with inorganic compound 23.

[0199] As shown in Figures 22 and 32, in step S3, after step S32, an inorganic compound precursor solution 54 is supplied onto the first film formed in step S32 as a second inorganic compound precursor solution containing a precursor of inorganic compound 24 (step S33, second inorganic compound precursor solution supplying process).

[0200] The inorganic compound precursor solution 54 contains a precursor of the inorganic compound 24 and a solvent 55 (second solvent) that dissolves the inorganic compound 24. The solvent 55 may be the same as the solvent exemplified as the first solvent. FIG. 32 illustrates an example in which the inorganic compound 24 is magnesium sulfide (MgS) and magnesium xanthate is used as the precursor of the inorganic compound 24. In FIG. 32, Mg(EtXan) ２ indicates zinc xanthogenate. In this way, a coating film of the inorganic compound precursor solution 54 is formed on the first film.

[0201] The supply of the inorganic compound precursor solution 54 onto the first film is not particularly limited. For example, the inorganic compound precursor solution 54 may be sprayed onto the first film, or the inorganic compound precursor solution 54 may be applied onto the first film by a bar coating method, a spin coating method, an inkjet method, or the like.

[0202] Next, the inorganic compound precursor solution 54 supplied in step S33 is heated to a temperature equal to or higher than the thermal decomposition temperature of the precursor of the inorganic compound 24, thereby thermally decomposing at least a portion of the precursor of the inorganic compound 24 and removing the solvent 55. Like zinc xanthate, magnesium xanthate used as the precursor of the inorganic compound 24 also undergoes thermal decomposition upon heating, evaporating the organic components, gradually reducing its mass. This corresponding reduction in volume reduces the film thickness of the second layer 22b of MX22. ​​As a result, as shown in FIG. 33 , MX22 containing the inorganic compound 24 as a main component is formed as the second layer 22b (step S34, second inorganic compound formation step). This results in the formation of an EML 13 containing QD21 and the first and second layers 22a and 22b of MX22.

[0203] Fig. 34 is a diagram showing a reaction scheme for forming a metal sulfide from a precursor of the metal sulfide when MX22 contains a metal sulfide as an inorganic compound as described above. In Fig. 34, M represents a metal source, and R represents an arbitrary organic residue. As described above, when inorganic compound 24 is MgS and magnesium xanthate is used as a precursor of inorganic compound 24, M represents Mg (magnesium). Magnesium xanthate is used as the S source and Mg source for MgS.

[0204] Magnesium xanthogenate is a precursor of the inorganic compound 24, and when heated, magnesium xanthogenate is thermally decomposed to vaporize the organic components, while Mg and S are bonded to form MgS. In this way, the inorganic compound precursor solution 54 forms the bulk inorganic compound 24 by thermally decomposing the precursor of the inorganic compound 24.

[0205] Thus, in this embodiment, by supplying an inorganic compound precursor solution 54 containing a precursor of inorganic compound 24 onto a first film containing a plurality of QDs 21 and inorganic compound 23 and heating it, a second layer 22b of MX22 is formed on the first film as MX22 containing inorganic compound 24 as a main component.

[0206] As shown in FIG. 26, when the inorganic compound is ZnS and ZnS is used as a precursor of the inorganic compound, M shown in FIG. 34 becomes Zn. ２ S ３ When indium xanthate is used as a precursor of the inorganic compound, M is In (indium). Indium xanthate is used as a source of S and In for InS.

[0207] 1 illustrates an example in which the anode 11 is a lower electrode, the cathode 15 is an upper electrode, and the EML 13 is provided on the HTL 12. However, the present disclosure is not limited to this.

[0208] FIG. 35 is a cross-sectional view showing an example of a schematic configuration of the light-emitting element 1 according to this modification.

[0209] The light-emitting element 1 may have a conventional structure as shown in FIG. 1, or an inverted structure as shown in FIG.

[0210] 35 has a configuration in which the cathode 15 is a lower electrode, the anode 11 is an upper electrode, and the HTL 12 is provided on the EML 13. As shown in Fig. 35, the light-emitting element 1 may have a configuration in which, for example, the cathode 15, the ETL 14, the EML 13, the HTL 12, and the anode 11 are provided in this order from the lower layer side (for example, the support side such as the substrate, not shown).

[0211] In this case, as shown in FIG. 35 , the stacking order of the light-emitting element 1 is reversed from that of the light-emitting element 1 shown in FIG. Therefore, when manufacturing such a light-emitting element 1, first, a cathode 15 is formed on a substrate serving as a support (step S5, cathode formation step). Next, an ETL 14 is formed (step S4, ETL formation step). In parallel, a QD dispersion is manufactured (prepared) (step S11, QD dispersion manufacturing step). Next, an EML 13 is formed using the QD dispersion (step S3, EML formation step). Next, a HTL 12 is formed (step S2, HTL formation step). Next, an anode 11 is formed (step S1, anode formation step). In this manner, the light-emitting element 1 is manufactured.

[0212] In this case, inorganic compound 24 is used as the first inorganic compound, and inorganic compound 23 is used as the second inorganic compound. Therefore, in step S11, a QD dispersion is produced that contains a precursor of inorganic compound 24 instead of a precursor of inorganic compound 23. Therefore, when inorganic compound 24 is MgS, for example, the first solvent contained in the QD dispersion is a QD dispersion that contains QDs 21, xanthogenic acid and magnesium xanthate as precursors (MgS precursors) of inorganic compound 24 (MX22), halide ions 31a, and a solvent (first solvent) that disperses or dissolves them.

[0213] Also, in step S33, an inorganic compound precursor solution containing a precursor of inorganic compound 23 is supplied as a second inorganic compound precursor solution onto the first film formed in step S32 using the above QD dispersion liquid.

[0214] Second Embodiment FIG. 36 is a cross-sectional view showing an example of a schematic configuration of a light-emitting element 1 according to this embodiment.

[0215] MX22 may contain an inorganic compound other than inorganic compound 23 and inorganic compound 24.

[0216] MX22 shown in FIG. 36 further contains inorganic compound 25 in addition to inorganic compound 23 and inorganic compound 24 as inorganic compounds.

[0217] 36, MX22 has a first region containing at least inorganic compound 23, a second region containing at least inorganic compound 24, and a third region containing at least inorganic compound 25, arranged in the direction of a straight line L1 passing through outer edge portion 13a and outer edge portion 13b in EML13. The second region is provided closer to outer edge portion 13b than the first region. The third region is provided closer to outer edge portion 13b than the second region.

[0218] In this case, the first region contains inorganic compound 23 as a main component. The first region may further contain inorganic compound 24, or may contain inorganic compound 23 and inorganic compound 25. The second region contains inorganic compound 24 as a main component. The second region may further contain inorganic compound 23 or inorganic compound 25, or may further contain inorganic compound 23 and inorganic compound 25. The third region contains inorganic compound 25 as a main component. The third region may further contain inorganic compound 24, or may further contain inorganic compound 24 and inorganic compound 23.

[0219] In this case, the concentration of the inorganic compound 23 in the first region differs by a certain amount from the concentrations of the inorganic compound 23 in the second and third regions. In this case, it is desirable that the concentration of the inorganic compound 23 in the first region differs by 20% or more from the concentrations of the inorganic compound 23 in the second and third regions.

[0220] The concentration of the inorganic compound 24 in the second region differs by a certain amount from the concentrations of the inorganic compound 24 in the first and third regions. In this case, it is desirable that the concentration of the inorganic compound 24 in the second region differs by 20% or more from the concentrations of the inorganic compound 24 in the first and third regions.

[0221] The concentration of the inorganic compound 25 in the third region differs from the concentrations of the inorganic compound 25 in the first and second regions by a certain amount or more. In this case, it is desirable that the concentration of the inorganic compound 25 in the third region differs from the concentrations of the inorganic compound 25 in the first and second regions by 20% or more.

[0222] In the first region, the second region is sandwiched between the first region and the third region, so that the degree of penetration of the inorganic compound 24 into the first region differs from the degree of penetration of the inorganic compound 25. Therefore, in the first region, the concentration of the inorganic compound 24 differs from the concentration of the inorganic compound 25, and the concentration of the inorganic compound 24 is greater than the concentration of the inorganic compound 25. Similarly, in the third region, the second region is sandwiched between the third region and the first region, so that the degree of penetration of the inorganic compound 24 into the third region differs from the degree of penetration of the inorganic compound 23. Therefore, in the third region, the concentration of the inorganic compound 24 differs from the concentration of the inorganic compound 23, and the concentration of the inorganic compound 24 is greater than the concentration of the inorganic compound 23. However, in the second region, it is possible that the inorganic compound 23 and the inorganic compound 25 have the same concentration.

[0223] The concentrations of inorganic compound 23, inorganic compound 24, and inorganic compound 25 can be measured by the same method as that described in embodiment 1 with reference to FIGS. 8, 10, 12, and 13.

[0224] 36 illustrates an example in which MX22 includes, as the first region, first layer 22a containing inorganic compound 23 as a main component, second layer 22b containing inorganic compound 24 as a main component, and third layer 22c containing inorganic compound 25 as a main component. Also illustrated in FIG. 36 is an example in which EML13 includes one QD row 21L in the thickness direction of EML13, in which a plurality of QDs 21 are aligned in a direction perpendicular to the thickness direction of EML13, and interface 22I between first layer 22a and second layer 22b and interface 22B between second layer 22b and third layer 22c each intersect with QD row 21L. However, this embodiment is not limited to this. In this embodiment, for example, as shown in Figures 15 to 21, multiple QDs 21 may be stacked in the thickness direction of the EML 13, and the interface between each layer may not be clearly separated.

[0225] In this embodiment, the EML 13 also preferably includes a region within a range of at least 1 nm from the outer edge 13 a where the concentration of the inorganic compound 23 in the MX 22 is 80% or more. As described above, since the MX 22 near the outer edge 13 a is formed of a relatively uniform composition, carriers can be easily injected from the anode 11 side into the QDs 21 near the outer edge 13 a.

[0226] In this embodiment, the EML 13 preferably includes a region within a range of at least 1 nm from the outer edge 13 b where the concentration of the inorganic compound 25 in the MX 22 is 80% or more. Since the MX 22 near the outer edge 13 b is formed of a relatively uniform composition, carriers can be easily injected from the cathode 15 side into the QDs 21 near the outer edge 13 b.

[0227] In this embodiment as well, for example, when there is an excess of electrons and a shortage of holes, it is desirable to reduce the amount of electrons injected into the EML 13 or increase the amount of holes injected in order to improve the carrier balance.

[0228] Therefore, in the case of an excess of electrons and a shortage of holes as described above, it is desirable to use, for example, an inorganic compound having a larger Eg than inorganic compound 23 as inorganic compound 24, and to use, for inorganic compound 25, an inorganic compound having a larger Eg than inorganic compound 24. In other words, it is desirable to use, for inorganic compound 23, an inorganic compound having a smaller Eg than inorganic compound 24, and to use, for inorganic compound 24, an inorganic compound having a smaller Eg than inorganic compound 25. In this case, it is possible to suppress electron injection, adjust the carrier balance, and improve luminous efficiency and reliability.

[0229] Furthermore, in the case of an excess of electrons and a shortage of holes as described above, it is desirable to use, for example, an inorganic compound having a higher hole mobility than inorganic compound 24 as inorganic compound 23, and an inorganic compound having a lower electron mobility than inorganic compound 24 as inorganic compound 25. In this case, it is possible to adjust the carrier balance by making it easier to inject holes while suppressing injection of electrons, thereby improving luminous efficiency and reliability.

[0230] Therefore, in the case of an excess of electrons and a deficiency of holes as described above, for example, the inorganic compound 23 may be indium sulfide (InS), the inorganic compound 24 may be zinc sulfide (ZnS), and the inorganic compound 25 may be magnesium sulfide (MgS). ２ S ３ Examples include:

[0231] In this way, when there is an electron excess and a hole deficiency, hole injection can be promoted and the electron excess can be adjusted by, for example, changing MX22 (specifically, inorganic compound 23) on the HTL 12 side to MX22 containing as its main component an inorganic compound having a smaller Eg and higher hole mobility (smaller hole effective mass) than MX22 (specifically, inorganic compound 25) on the ETL 14 side. Furthermore, for example, changing MX22 on the ETL 14 side to MX22 containing as its main component an inorganic compound having a larger Eg and lower electron mobility (larger electron effective mass) than MX22 on the HTL 12 side can suppress electron injection and adjust the hole deficiency.

[0232] On the other hand, in the case of a deficiency of electrons and an excess of holes, it is desirable to use, for example, an inorganic compound having a larger Eg than inorganic compound 24 as inorganic compound 23, and an inorganic compound having a larger Eg than inorganic compound 24 as inorganic compound 25. In other words, it is desirable to use, as inorganic compound 24, an inorganic compound having a smaller Eg than inorganic compound 23, and to use, as inorganic compound 25, an inorganic compound having a smaller Eg than inorganic compound 24. In this case, it is possible to suppress injection of holes, adjust the carrier balance, and improve luminous efficiency and reliability.

[0233] Furthermore, in the case of a deficiency of electrons and an excess of holes as described above, it is desirable to use, for example, an inorganic compound having a higher electron mobility than inorganic compound 23 as inorganic compound 24, and an inorganic compound having a higher electron mobility than inorganic compound 24 as inorganic compound 25. In this case, electrons can be easily injected, the carrier balance can be adjusted, and the luminous efficiency and reliability can be improved.

[0234] (Manufacturing Method of Light-Emitting Element 1) FIG. 37 is a flowchart showing an example of a manufacturing method of the light-emitting element 1 according to this embodiment.

[0235] The method for manufacturing the light-emitting element 1 according to this embodiment is the same as the method for manufacturing the light-emitting element 1 according to the first embodiment, except for the following points.

[0236] In the manufacturing method of the light-emitting element 1 according to this embodiment, as shown in FIG. 37, in step S3, a third inorganic compound precursor solution containing a precursor of inorganic compound 25 is supplied onto MX22 containing inorganic compound 24 as a main component, which is formed as the second layer 22b in step S34 (step S35, third inorganic compound precursor solution supplying step).

[0237] The third inorganic compound precursor solution contains a precursor of the inorganic compound 25 and a solvent (third solvent) that dissolves the inorganic compound 25. The third solvent may be the same solvent as the solvent exemplified as the first solvent. Step S35 (third inorganic compound precursor solution supplying step) can be performed in the same manner as step S33 (second inorganic compound precursor solution supplying step).

[0238] As described above, the inorganic compound 23 may be, for example, indium sulfide (e.g., In ２ S ３ ) can be used. For example, zinc sulfide (ZnS) can be used as the inorganic compound 24. For example, magnesium sulfide (MgS) can be used as the inorganic compound 25. In this case, xanthogenic acid and indium xanthogenate are used as the precursor of the inorganic compound 23. Furthermore, zinc xanthogenate is used as the precursor of the inorganic compound 24. Furthermore, magnesium xanthogenate is used as the precursor of the inorganic compound 25. The reaction scheme is as shown in FIG. 34.

[0239] Next, the third inorganic compound precursor solution supplied in step S35 is heated to a temperature equal to or higher than the thermal decomposition temperature of the precursor of inorganic compound 25 to thermally decompose at least a portion of the precursor of inorganic compound 25 and remove the third solvent. This forms MX22 containing inorganic compound 25 as a main component as third layer 22c (step S36, third inorganic compound formation step). This forms EML13 containing QD21 and MX22 as first layer 22a, second layer 22b, and third layer 22c.

[0240] As a result, according to this embodiment, it is possible to manufacture a light-emitting element 1 capable of adjusting the carrier balance more precisely and improving the luminous efficiency.

[0241] In this embodiment, the case where MX22 contains three types of inorganic compounds has been described as an example, but the present embodiment is not limited to this. MX22 may contain, for example, four or more types of inorganic compounds.

[0242] [Embodiment 3] The light-emitting element 1 can be suitably used as a light source for a light-emitting device such as a display device or a lighting device. The light-emitting device may include at least one light-emitting element 1. The following description will be given taking as an example a case where the light-emitting element 1 is used as a light source for a display device.

[0243] Fig. 38 is a plan view showing an example of the configuration of a display device according to this embodiment. As shown in Fig. 38, the display device 70 includes a display unit 71 including a plurality of sub-pixels X, and a driver circuit 72 that drives the display unit 71. For example, the sub-pixels X include the light-emitting element 1 and pixel circuit 2 described in the first or second embodiment. The display device 70 may also be a lighting device.

[0244] 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.

[0245] 1, 100 Light-emitting element 11 Anode 15 Cathode 13, 13A, 13B EML (light-emitting layer) 13a, 13b Outer edge portion 21 QD (quantum dot) 21L QD array (quantum dot array) 21C Core 21S Shell 22 MX (matrix material) 22I, 22B Interface 23, 24, 25 Inorganic compound 31a Halide ion 33 Solvent (first solvent) 34 Precursor 53 QD dispersion (quantum dot dispersion) 54 Inorganic compound precursor solution (second inorganic compound precursor solution) 55 Solvent (second solvent) 70 Display device L1 Straight line

Claims

1. A light-emitting device comprising a first electrode and a second electrode, and a light-emitting layer provided between the first electrode and the second electrode, wherein the light-emitting layer includes a plurality of quantum dots and a matrix material, the matrix material includes a first inorganic compound and a second inorganic compound, the matrix material has a first region containing at least the first inorganic compound and a second region containing at least the second inorganic compound in a linear direction passing through a first outer edge portion on the first electrode side and a second outer edge portion on the second electrode side in the light-emitting layer, the second region is provided closer to the second outer edge portion side than the first region, and a concentration of the first inorganic compound in the first region and a concentration of the first inorganic compound in the second region are different by a certain amount or more, the light-emitting device.

2. The light-emitting device according to claim 1, wherein in a range of at least 1 nm from the first outer edge portion in the light-emitting layer, a region having a concentration of the first inorganic compound in the matrix material of 80% or more is included.

3. The light-emitting device according to claim 1 or 2, wherein a concentration of at least one of the first inorganic compound and the second inorganic compound changes continuously or stepwise in the linear direction.

4. The light-emitting device according to claim 1 or 2, wherein an interface between the first region and the second region intersects the plurality of quantum dots.

5. The light-emitting layer includes at least one row of quantum dot rows in which the plurality of quantum dots are arranged in a direction perpendicular to the layer thickness direction of the light-emitting layer in the layer thickness direction of the light-emitting layer, the matrix material includes a first layer mainly composed of the first inorganic compound as the first region and a second layer mainly composed of the second inorganic compound as the second region, and an interface between the first layer and the second layer intersects the quantum dot row, the light-emitting device according to claim 1 or 2.

6. The light-emitting device according to claim 1 or 2, wherein a concentration of the first inorganic compound in the first region is greater than a concentration of the second inorganic compound in the first region, and a concentration of the second inorganic compound in the second region is greater than a concentration of the first inorganic compound in the second region.

7. The first electrode is an anode, the second electrode is a cathode, and the second inorganic compound has a larger band gap than the first inorganic compound, the light-emitting device according to claim 6.

8. The first electrode is an anode, the second electrode is a cathode, The light-emitting device according to claim 6, wherein the first inorganic compound has a larger band gap than the second inorganic compound.

9. The first electrode is an anode, The second electrode is a cathode, The light-emitting device according to claim 6, wherein the first inorganic compound has a higher hole mobility than the second inorganic compound.

10. The first electrode is an anode, The second electrode is a cathode, The light-emitting device according to claim 6, wherein the second inorganic compound has a higher electron mobility than the first inorganic compound.

11. The light-emitting device according to claim 1 or 2, wherein the first inorganic compound and the second inorganic compound are metal sulfides.

12. The first inorganic compound is indium sulfide, The light-emitting device according to claim 1 or 2, wherein the second inorganic compound is magnesium sulfide.

13. The first inorganic compound is zinc sulfide, The light-emitting device according to claim 1 or 2, wherein the second inorganic compound is magnesium sulfide.

14. The first inorganic compound is indium sulfide, The light-emitting device according to claim 1 or 2, wherein the second inorganic compound is zinc sulfide.

15. The light-emitting device according to claim 1 or 2, wherein in the light-emitting layer, in a range of at least 1 nm from the second outer edge portion, a region having a concentration of the second inorganic compound in the matrix material of 80% or more is included.

16. The matrix material further includes a third inorganic compound, The matrix material further has a third region including at least the third inorganic compound in the linear direction, The third region is provided closer to the second outer edge portion than the second region, The light-emitting device according to claim 1 or 2, wherein the concentration of the third inorganic compound in the third region is different by a certain amount or more from the concentration of the third inorganic compound in at least one of the first region and the second region.

17. The matrix material further includes a third inorganic compound having a larger band gap than the second inorganic compound, The matrix material further has a third region including at least the third inorganic compound in the linear direction, The third region is provided closer to the second outer edge portion than the second region, The light-emitting device according to claim 7, wherein the concentration of the third inorganic compound in the third region is higher than the concentration of the third inorganic compound in the first region and the second region.

18. The matrix material further includes a third inorganic compound having a smaller band gap than the second inorganic compound. The matrix material further has a third region including at least the third inorganic compound in the linear direction. The third region is provided closer to the second outer edge side than the second region. The light-emitting device according to claim 8, wherein the concentration of the third inorganic compound in the third region is higher than the concentrations of the third inorganic compound in the first region and the second region.

19. The matrix material further includes a third inorganic compound having a smaller electron mobility than the second inorganic compound. The matrix material further has a third region including at least the third inorganic compound in the linear direction. The third region is provided closer to the second outer edge side than the second region. The light-emitting device according to claim 9, wherein the concentration of the third inorganic compound in the third region is higher than the concentrations of the third inorganic compound in the first region and the second region.

20. The matrix material further includes a third inorganic compound having a larger electron mobility than the second inorganic compound. The matrix material further has a third region including at least the third inorganic compound in the linear direction. The third region is provided closer to the second outer edge side than the second region. The light-emitting device according to claim 10, wherein the concentration of the third inorganic compound in the third region is higher than the concentrations of the third inorganic compound in the first region and the second region.

21. The first inorganic compound is indium sulfide. The second inorganic compound is zinc sulfide. The light-emitting device according to claim 16, wherein the third inorganic compound is magnesium sulfide.

22. The light-emitting device according to claim 16, wherein in the light-emitting layer, in a range of at least 1 nm from the second outer edge, a region having a concentration of the third inorganic compound in the matrix material of 80% or more is included.

23. The quantum dot has a core and a shell. The light-emitting device according to claim 1 or 2, wherein the band gap of at least one inorganic compound contained in the matrix material is larger than the band gap of the core or the shell.

24. The light-emitting device according to claim 23, wherein the average distance between the cores of adjacent quantum dots is 3 nm or more.

25. The light-emitting device according to claim 1 or 2, wherein the matrix material is filled between the plurality of quantum dots in the light-emitting layer.

26. The matrix material has a continuous film having an area of 1000 nm or more in a plane direction orthogonal to the thickness direction of the light-emitting layer. ２ The light-emitting element according to claim 1 or 2, which has a continuous film having an area of 1000 nm or more in a plane direction orthogonal to the thickness direction of the light-emitting layer.

27. The light-emitting device according to claim 1 or 2, wherein the plurality of quantum dots are dispersed in the matrix material.

28. The light-emitting device according to claim 1 or 2, wherein the plurality of quantum dots are encapsulated in the matrix material.

29. The light-emitting device according to claim 1 or 2, wherein the matrix material further contains a halogen element.

30. The light-emitting device according to claim 29, wherein the matrix material contains 1 atomic% or more of the halogen element.

31. The light-emitting device according to claim 29, wherein the average value of the total concentration of the halogen element in a region within 1 nm from the outermost surface of each of the plurality of quantum dots in the matrix material is 10% or more higher than the average value of the total concentration of the halogen element in a region where the distance from the outermost surface of each of the plurality of quantum dots in the matrix material exceeds 1 nm.

32. A display device including the light-emitting device according to claim 1 or 2.

33. A method for manufacturing a light-emitting device, comprising a first electrode and a second electrode, and a light-emitting layer provided between the first electrode and the second electrode, the light-emitting layer including a plurality of quantum dots and a matrix material, the matrix material including a first inorganic compound and a second inorganic compound, the matrix material having a first region including at least the first inorganic compound and a second region including at least the second inorganic compound in a linear direction penetrating a first outer edge portion on the first electrode side and a second outer edge portion on the second electrode side in the light-emitting layer, the second region being provided closer to the second outer edge portion side than the first region, and the concentration of the first inorganic compound in the first region being different from the concentration of the first inorganic compound in the second region by a certain amount or more, including a light-emitting layer forming step of forming the light-emitting layer, the light-emitting layer forming step includes a quantum dot dispersion liquid coating step of applying a quantum dot dispersion liquid including the plurality of quantum dots, a precursor of the first inorganic compound, halide ions, and a first solvent, and forming a coating film of the quantum dot dispersion liquid by thermal decomposition of the precursor of the first inorganic compound to form the first inorganic compound. A first film forming step of forming a first film including the plurality of quantum dots and a matrix material containing the first inorganic compound by heating the coating film of the quantum dot dispersion liquid at a temperature equal to or higher than the thermal decomposition temperature of the precursor of the first inorganic compound to thermally decompose at least a part of the precursor of the first inorganic compound and remove the first solvent; A second inorganic compound precursor solution supply step of supplying, onto the first film, a second inorganic compound precursor solution containing a precursor of the second inorganic compound and a second solvent, wherein the precursor of the second inorganic compound thermally decomposes to form the second inorganic compound; A second inorganic compound forming step of heating the second inorganic compound precursor solution supplied in the second inorganic compound precursor solution supply step at a temperature equal to or higher than the thermal decomposition temperature of the precursor of the second inorganic compound to thermally decompose at least a part of the precursor of the second inorganic compound and remove the second solvent, thereby forming a matrix material containing the second inorganic compound. A method for manufacturing a light emitting device including these steps.

34. In the light emitting layer forming step, there is at least one row of quantum dot arrays in which the plurality of quantum dots are arranged in a direction perpendicular to the layer thickness direction of the light emitting layer in the layer thickness direction of the light emitting layer, and one outer edge portion of the matrix material containing the first inorganic compound in the first film intersects the quantum dot array. The method for manufacturing a light emitting device according to claim 33, wherein the concentration of the precursor of the first inorganic compound contained in the quantum dot dispersion liquid is adjusted.

35. The matrix material further contains a third inorganic compound. The light emitting layer forming step includes: A third inorganic compound precursor solution supply step of supplying, onto the matrix material containing the second inorganic compound, a third inorganic compound precursor solution containing a precursor of the third inorganic compound and a third solvent, wherein the precursor of the third inorganic compound thermally decomposes to form the third inorganic compound; The method for manufacturing a light emitting device according to claim 33 or 34, further comprising a third inorganic compound forming step of heating the third inorganic compound precursor solution supplied in the third inorganic compound precursor solution supply step at a temperature equal to or higher than the thermal decomposition temperature of the precursor of the third inorganic compound to thermally decompose at least a part of the precursor of the third inorganic compound and remove the third solvent, thereby forming a matrix material containing the third inorganic compound.

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