Light-emitting element, display device, and method for forming light-emitting layer

Abstract

A light-emitting element (1) is provided with an anode (22), a cathode (25), and a light-emitting layer (38) provided between the anode (22) and the cathode (25). The light-emitting layer (38) contains a plurality of quantum dots (17), continuous compounds (18a, 18b) provided around each of the plurality of quantum dots (17), and an electron-transporting material having electron-transporting properties.

Description

Technical Field

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

[0002] In recent years, a display device of QLED (Quantum dot Light Emitting Diode) including a light-emitting element containing quantum dots has attracted attention in terms of achieving low power consumption, thinning, and high image quality. For this reason, an active study has also been conducted on a method for forming a light-emitting layer containing quantum dots included in QLED.

[0003] For example, Patent Document 1 describes that QLED is made to have a low voltage by including a quantum dot light-emitting layer having an organic ligand distribution in which a first surface in contact with a hole transport layer and a second surface in contact with an electron transport layer are different from each other. Prior Art Documents Patent Documents

[0004] Patent Document 1: Japanese Patent Laid-Open Gazette "JP-A-2010-114079" Summary of the Invention Technical Problem to be Solved by the Invention

[0005] The ligands in the quantum dot light-emitting layer of the QLED described in Patent Document 1 are organic ligands. The bond between the organic ligand and the quantum dot is a coordination bond, which is a very weak chemical bond. Therefore, it is easily dissociated (detached) by contact with a solvent or other surrounding materials, heating, energization, etc. Therefore, the defect protection effect as the role of the ligand is reduced, and the light-emitting characteristics (external quantum efficiency (EQE)) and reliability of QLED are reduced. In addition, since the physical shielding on the surface of the quantum dot based on the ligand disappears, oxygen, moisture, etc. easily come into contact with the quantum dot itself, which may cause deterioration of the quantum dot itself. In addition, the above-mentioned organic ligand does not have carrier transportability, and therefore does not contribute to the improvement of the carrier balance of QLED.

[0006] One aspect of the present disclosure has been completed in view of the above problems, and an object thereof is to provide a light-emitting element, a display device, and a method for forming a light-emitting layer with improved carrier balance, external quantum efficiency (EQE), and reliability. Technical Solution for Solving the Technical Problem

[0007] In order to solve the above problems, the light-emitting element of the present disclosure includes: an anode, a cathode, and a light-emitting layer provided between the anode and the cathode, the light-emitting layer including a plurality of quantum dots, a continuous compound provided around each of the plurality of quantum dots, and a carrier transport material having carrier transportability.

[0008] In order to solve the above problems, the display device of the present disclosure includes: a first light-emitting element that emits a first color light; a second light-emitting element that emits a second color light having a shorter emission peak wavelength than the first color light; and a third light-emitting element that emits a third color light having a shorter emission peak wavelength than the second color light, and the third light-emitting element is the light-emitting element.

[0009] In order to solve the above problems, the method for forming a light-emitting layer of the present disclosure uses a first solution to form at least a part of the light-emitting layer, wherein the first solution includes a plurality of quantum dots, a precursor of the continuous compound that forms a continuous compound around each of the plurality of quantum dots, a carrier transport material having carrier transport properties, and a solvent. Advantageous Effects

[0010] According to one aspect of the present disclosure, it is possible to provide a light-emitting element, a display device, and a method for forming a light-emitting layer that have improved carrier balance, external quantum efficiency (EQE), and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a graph for explaining the tendency of the change rate of the emission intensity in the constant current drive test of the light-emitting element of Embodiment 1 and the tendency of the luminance recovery during the power-off period of the light-emitting element of Comparative Example 1. Figure 2 It is a schematic cross-sectional view showing the general configuration of the light-emitting element of Comparative Example 1. Figure 3 It is a graph for explaining the reason for the large change rate of the emission intensity in the constant current drive test and the reason for the slow luminance recovery during the power-off period in the light-emitting element of Comparative Example 1. Figure 4 It is a graph for explaining the reason for the large change rate of the emission intensity in the constant current drive test and the reason for the slow luminance recovery during the power-off period in the light-emitting element of Comparative Example 2. Figure 5 It is a graph for explaining the reason for the large change rate of the emission intensity in the constant current drive test and the reason for the slow luminance recovery during the power-off period in the light-emitting element of Comparative Example 3. Figure 6 It is a graph for explaining the reason for the large change rate of the emission intensity in the constant current drive test and the reason for the slow luminance recovery during the power-off period in the light-emitting element of Comparative Example 4. Figure 7 It is a schematic cross-sectional view showing the general configuration of the light-emitting element of Embodiment 1. Figure 8 It is for explaining in Figure 7A diagram of the region formed between two adjacent quantum dots among the multiple quantum dots included in the light-emitting layer of the light-emitting element of Embodiment 1 shown, when the two adjacent quantum dots are arranged closely. Figure 9 It is for explaining Figure 7 A diagram of the region formed between two adjacent quantum dots among the multiple quantum dots included in the light-emitting layer of the light-emitting element of Embodiment 1 shown, when the two adjacent quantum dots are arranged slightly farther apart. Figure 10 A diagram for explaining the reason why electrons are less likely to remain in the light-emitting layer or at the interface between the light-emitting layer and the electron transport layer in the light-emitting element of Embodiment 1 compared to the light-emitting element of Comparative Example 1. Figure 11 A diagram for explaining the reason why the brightness recovery during the power-off period is faster in the light-emitting element of Embodiment 1 compared to the light-emitting element of Comparative Example 1. Figure 12 A schematic cross-sectional view showing the schematic configuration of the light-emitting element of Embodiment 2. Figure 13 A diagram for explaining the reason why electrons are less likely to remain in the light-emitting layer or at the interface between the light-emitting layer and the electron transport layer in the light-emitting element of Embodiment 2 compared to the light-emitting element of Comparative Example 1. Figure 14 A schematic cross-sectional view showing the schematic configuration of the light-emitting element of Embodiment 3. Figure 15 A diagram for explaining the reason why electrons are less likely to remain in the light-emitting layer or at the interface between the light-emitting layer and the electron transport layer in the light-emitting element of Embodiment 3 compared to the light-emitting element of Comparative Example 1. Figure 16 A schematic cross-sectional view showing the schematic configuration of the light-emitting element of Embodiment 4. Figure 17 A diagram for explaining the reason why holes are less likely to remain in the light-emitting layer or at the interface between the light-emitting layer and the hole transport layer in the light-emitting element of Embodiment 4 compared to the light-emitting element of Comparative Example 2. Figure 18 A diagram for explaining the reason why the brightness recovery during the power-off period is faster in the light-emitting element of Embodiment 4 compared to the light-emitting element of Comparative Example 2. Figure 19 A schematic cross-sectional view showing the schematic configuration of the light-emitting element of Embodiment 5. Figure 20 A diagram for explaining the reason why holes are less likely to remain in the light-emitting layer or at the interface between the light-emitting layer and the hole transport layer in the light-emitting element of Embodiment 5 compared to the light-emitting element of Comparative Example 2. Figure 21 A schematic cross-sectional view showing the schematic configuration of the light-emitting element of Embodiment 6. Figure 22 This is a diagram for explaining the reason why holes are less likely to stay in the light-emitting layer or at the interface between the light-emitting layer and the hole transport layer in the light-emitting element of Embodiment 6 compared to the light-emitting element of Comparative Example 2. Figure 23 This is a schematic cross-sectional view showing the schematic configuration of the light-emitting element of Embodiment 7. Figure 24 This is a schematic cross-sectional view showing the schematic configuration of the light-emitting element of Embodiment 8. Figure 25 This is a schematic cross-sectional view showing the schematic configuration of the display device of Embodiment 9. Detailed Embodiments

[0012] Based on Figures 1 to 25 , the embodiments of the present disclosure will be described as follows. Hereinafter, for ease of explanation, components having the same function as those described in a specific embodiment may be denoted by the same reference numerals, and their description may be omitted.

[0013] [Embodiment 1] Figure 1 This is a diagram for explaining the tendency of the change rate of the light-emitting intensity in the constant current drive test of the light-emitting element of Embodiment 1 and the light-emitting element of Comparative Example 1, and the tendency of the brightness recovery during the power-off period.

[0014] Figure 2 This is a schematic cross-sectional view showing the general configuration of the light-emitting element 50 of Comparative Example 1.

[0015] Figure 3 This is a diagram for explaining the reason why the change rate of the light-emitting intensity is large in the constant current drive test of the light-emitting element 50 of Comparative Example 1 and the reason why the brightness recovery is slow during the power-off period.

[0016] Figure 4 This is a diagram for explaining the reason why the change rate of the light-emitting intensity is large in the constant current drive test of the light-emitting element 50a of Comparative Example 2 and the reason why the brightness recovery is slow during the power-off period.

[0017] Figure 5 This is a diagram for explaining the reason why the change rate of the light-emitting intensity is large in the constant current drive test of the light-emitting element of Comparative Example 3 and the reason why the brightness recovery is slow during the power-off period.

[0018] Figure 6 This is a diagram for explaining the reason why the change rate of the light-emitting intensity is large in the constant current drive test of the light-emitting element of Comparative Example 4 and the reason why the brightness recovery is slow during the power-off period.

[0019] Generally, QLEDs are prone to a state of poor carrier balance in which either holes or electrons, which are carriers, become excessive.

[0020] Figure 2 and Figure 3 the light-emitting element 50 of Comparative Example 1 shown in Figure 5 and the light-emitting element of Comparative Example 3 shown in are an example of a light-emitting element in an electron-excessive state.

[0021] As Figure 2 shown, the light-emitting element 50 includes an anode 22, a cathode 25, and a light-emitting layer 48 disposed between the anode 22 and the cathode 25. In addition, a hole transport layer 7 is provided between the anode 22 and the light-emitting layer 48, and an electron transport layer 9 is provided between the cathode 25 and the light-emitting layer 48.

[0022] The light-emitting layer 48 includes a plurality of quantum dots 17 and a continuous compound 18, such as a matrix, disposed around each of the plurality of quantum dots 17. When the light-emitting layer 48 contains an organic ligand, the reduction in external quantum efficiency (EQE) and the reduction in reliability caused by the organic ligand can be suppressed by the continuous compound 18, such as a matrix.

[0023] On the other hand, when the light-emitting layer 48 contains a continuous compound 18 that does not have electron transport properties, such as a matrix, as Figure 3 shown, the bottom of the conduction band (CBM) of the light-emitting layer 48 is shallow, and the bottom of the conduction band (CBM) of the electron transport layer 9 is deeper than the bottom of the conduction band (CBM) of the light-emitting layer 48. Therefore, the difference between the bottom of the conduction band (CBM) of the light-emitting layer 48 and the bottom of the conduction band (CBM) of the electron transport layer 9 is large, and electrons E, which are excessively present carriers, are likely to stay in the light-emitting layer 48 or at the interface between the light-emitting layer 48 and the electron transport layer 9. Figure 3 The quantum dots 17 included in the light-emitting layer 48 shown in are quantum dots corresponding to the wavelength region of blue light with a relatively wide difference between the bottom of the conduction band (CBM) and the top of the valence band (VBM). Figure 3 The continuous compound 18, such as a matrix, included in the light-emitting layer 48 shown in is formed of a material with high insulation and a relatively wide difference between the bottom of the conduction band (CBM) and the top of the valence band (VBM).

[0024] Similarly, as Figure 5As shown, the light-emitting layer 48a contains a continuous compound 18 that does not have electron-transporting properties. For example, in the case of containing a matrix, the lower end of the conduction band (CBM) of the light-emitting layer 48a is shallow, and the lower end of the conduction band (CBM) of the electron-transporting layer 9b is deeper than that of the light-emitting layer 48a. Therefore, the difference between the lower end of the conduction band (CBM) of the light-emitting layer 48a and the lower end of the conduction band (CBM) of the electron-transporting layer 9b is large, and electrons E as excessive carriers tend to stay in the light-emitting layer 48a and at the interface between the light-emitting layer 48a and the electron-transporting layer 9b. Figure 5 The quantum dots contained in the shown light-emitting layer 48a are quantum dots in which the difference between the lower end of the conduction band (CBM) and the upper end of the valence electron band (VBM) corresponds to the wavelength region of red light or green light. Figure 5 The continuous compound 18 contained in the shown light-emitting layer 48a, for example, the matrix, is formed of a highly insulating material with a relatively large difference between the lower end of the conduction band (CBM) and the upper end of the valence electron band (VBM).

[0025] As described above, in Figure 3 each of the light-emitting elements 50 of Comparative Example 1 shown and Figure 5 each of the light-emitting elements of Comparative Example 3 shown, electrons E as excessive carriers tend to stay in the light-emitting layers 48, 48a and at the interfaces between the light-emitting layers 48, 48a and the electron-transporting layers 9, 9b.

[0026] In Figure 2 each of the light-emitting elements 50 of Comparative Example 1 shown and Figure 5 each of the light-emitting elements of Comparative Example 3 shown during constant current driving, electrons E as excessive carriers stay in the light-emitting layers 48, 48a and at the interfaces between the light-emitting layers 48, 48a and the electron-transporting layers 9, 9b, thereby generating an electric field CUED in the direction opposite to the electric field DED during driving of the light-emitting element 50 of Comparative Example 1 and the light-emitting element of Comparative Example 3, resulting in a decrease in the brightness of the light-emitting element 50 of Comparative Example 1 and the light-emitting element of Comparative Example 3. In Figure 1 this, as an example, during constant current driving of the light-emitting element 50 of Comparative Example 1, the decrease in the brightness of the generated light-emitting element 50, that is, the change rate of the light emission intensity, is shown. Due to such a decrease in the brightness of the light-emitting element, there is a problem of a decrease in the external quantum efficiency (EQE), that is, the light emission efficiency, of the light-emitting element. In addition, in the case of the light-emitting element 50 of Comparative Example 1 and the light-emitting element of Comparative Example 3, there is also a problem that the carrier balance cannot be improved.

[0027] Figure 4 each of the light-emitting elements of Comparative Example 2 shown and Figure 6 each of the light-emitting elements of Comparative Example 4 shown is an example of a light-emitting element in a state of excessive holes.

[0028] As Figure 4 and Figure 6As shown, the light-emitting layers 48 and 48a include a plurality of quantum dots and a continuous compound 18, such as a matrix, disposed around each of the plurality of quantum dots. When the light-emitting layers 48 and 48a contain an organic ligand, the continuous compound 18, such as a matrix, can suppress a decrease in external quantum efficiency (EQE) and a decrease in reliability caused by the organic ligand.

[0029] On the other hand, when the light-emitting layers 48 and 48a include a continuous compound 18 that does not have hole-transporting properties, for example, when it contains a matrix, as Figure 4 and Figure 6 shown, the upper valence band (VBM) of the light-emitting layers 48 and 48a is deep, and the upper valence band (VBM) of the hole-transporting layers 7a and 7c is shallower than the upper valence band (VBM) of the light-emitting layers 48 and 48a. Therefore, the difference between the upper valence band (VBM) of the light-emitting layers 48 and 48a and the upper valence band (VBM) of the hole-transporting layers 7a and 7c is large, and holes H existing as excessive carriers are likely to stay in the light-emitting layers 48a and 48a and at the interfaces between the light-emitting layers 48a and 48a and the hole-transporting layers 7a and 7c.

[0030] As described above, in each of the light-emitting elements of Comparative Example 2 shown in Figure 4 and the light-emitting element of Comparative Example 4 shown in Figure 6 holes H as excessive carriers are likely to stay in the light-emitting layers 48 and 48a and at the interfaces between the light-emitting layers 48 and 48a and the hole-transporting layers 7a and 7c.

[0031] In Figure 4 the light-emitting element of Comparative Example 2 shown in Figure 6 and the light-emitting element of Comparative Example 4 shown in

[0032] During the constant-current driving of the light-emitting elements of Comparative Example 2 shown in Figures 7 to 11 and the light-emitting element of Comparative Example 4 shown in

[0033] Figure 7 holes H as excessive carriers stay in the light-emitting layers 48 and 48a and at the interfaces between the light-emitting layers 48 and 48a and the hole-transporting layers 7a and 7c, thereby generating an electric field CUED opposite to the driving electric field DED of the light-emitting elements of Comparative Example 2 and Comparative Example 4, resulting in a decrease in the brightness of the light-emitting elements of Comparative Example 2 and Comparative Example 4. Due to such a decrease in the brightness of the light-emitting elements, there is a problem of a decrease in the external quantum efficiency (EQE), that is, the luminous efficiency, of the light-emitting elements. In addition, in the case of the light-emitting elements of Comparative Example 2 and Comparative Example 4, there is also a problem that the carrier balance cannot be improved.

[0032] Therefore, according to Figures 7 to 11 an embodiment 1 of a light-emitting element 1 in which the light-emitting layer 38 includes an electron-transporting material 10 having electron-transporting properties as a carrier-transporting material having carrier-transporting properties will be described.

[0033] Figure 7It is a cross-sectional view schematically showing the configuration of the light-emitting element 1 of the embodiment.

[0034] Figure 8 It is for explaining Figure 7 A diagram of the region R formed between two adjacent quantum dots QD1 and QD2 among the plurality of quantum dots 17 included in the light-emitting layer 38 of the light-emitting element 1 of Embodiment 1 shown, when the two adjacent quantum dots are arranged close to each other.

[0035] Figure 9 For explaining Figure 7 A diagram of the region R formed between two adjacent quantum dots QD1 and QD2 among the plurality of quantum dots 17 included in the light-emitting layer 38 of the light-emitting element 1 of Embodiment 1 shown, when the two adjacent quantum dots are arranged slightly apart from each other.

[0036] As Figure 7 shown, the light-emitting element 1 includes an anode 22, a cathode 25, and a light-emitting layer 38 provided between the anode 22 and the cathode 25. The light-emitting layer 38 includes a plurality of quantum dots 17, a continuous first compound 18a and a continuous second compound 18b provided around each of the plurality of quantum dots 17, and an electron transport material 10 which is an electron transport material having carrier transport properties as a carrier transport material.

[0037] "The continuous compound provided around each of the plurality of quantum dots" of course also includes a continuous compound formed in one process, and as in this embodiment, it also includes a case where the continuous first compound 18a and the continuous second compound 18b formed in two different processes are provided in contact with each other.

[0038] "Compound continuous" means a state where the compounds of interest are continuously present without being separated by other compounds. The compounds of interest can be one kind or two or more kinds. The compounds of interest can be bonded by chemical bonds, can be arranged within the range of intermolecular forces, or can only be physically connected.

[0039] In this embodiment, a case where a continuous compound composed of the continuous first compound 18a and the continuous second compound 18b provided in contact with each other is provided around each of the plurality of quantum dots 17 is taken as an example for explanation, but it is not limited thereto. For example, either the continuous first compound 18a or the continuous second compound 18b can be provided around each of the plurality of quantum dots 17.

[0040] In this embodiment, as Figure 7As shown, an example is given where the light-emitting element 1 has a hole transport layer 7 as a hole functional layer between the anode 22 and the light-emitting layer 38, and an electron transport layer 9 as an electron functional layer between the cathode 25 and the light-emitting layer 38, but it is not limited thereto. The light-emitting element 1 may have at least one of a hole transport layer and a hole injection layer as the hole functional layer, and may have at least one of an electron transport layer and an electron injection layer as the electron functional layer. The light-emitting element 1 may not have at least one of the above-mentioned hole functional layer and the above-mentioned electron functional layer.

[0041] In the present embodiment, an example is given where a continuous compound composed of a continuous first compound 18a and a continuous second compound 18b provided in contact with each other is a matrix of an inorganic compound, and the matrix of the inorganic compound contains an electron transport material 10 having electron transport properties as a carrier transport material having carrier transport properties, but it is not limited thereto.

[0042] In the present embodiment, an example is given where the continuous first compound 18a and the continuous second compound 18b are the same inorganic compound, respectively, but it is not limited thereto, and they may be different inorganic compounds. Further, the continuous first compound 18a and the continuous second compound 18b may each be a matrix containing one or more selected from inorganic compounds, organic polymer compounds, and organic-inorganic hybrid compounds. For example, if the continuous first compound 18a is a matrix of an inorganic compound, the continuous second compound 18b may be a matrix of an organic polymer compound or an organic-inorganic hybrid compound.

[0043] A matrix refers to a component that contains and holds other substances, and may be called a base material, a base metal, or a filler. The matrix may also be a solid at normal temperature. The matrix may also be a component that contains and holds a plurality of quantum dots 17. In addition, a matrix containing one or more selected from inorganic compounds, organic polymer compounds, and organic-inorganic hybrid compounds or a matrix of an inorganic compound may be a component that contains quantum dots 17 and can hold them. In the present disclosure, it also includes cases where the quantum dots 17 are not evenly distributed in the matrix. Further, a region of the matrix that allows a certain matrix does not contain a region of the matrix of the quantum dots 17.

[0044] A matrix of an inorganic compound, which is an example of a matrix, may be filled between a plurality of quantum dots 17. "An inorganic compound matrix is filled between a plurality of quantum dots 17" only requires that an inorganic compound matrix be filled between at least two quantum dots 17. In addition, "an inorganic compound matrix is filled between two quantum dots 17" means that Figure 8 and Figure 9The region R shown is filled with a matrix of an inorganic compound or filled with an inorganic compound. The region R is a region surrounded by two lines (common external tangents) that are tangent to the outer perimeters of two adjacent quantum dots QD1 and QD2 and the opposing outer perimeters of the two adjacent quantum dots QD1 and QD2. As Figure 8 shown, even when two adjacent quantum dots QD1 and QD2 are arranged close to each other, as Figure 9 shown, even when two adjacent quantum dots QD1 and QD2 are arranged slightly apart from each other, there exists a region R, and the region R is filled with the matrix. In addition, in the present invention, two adjacent quantum dots QD1 and QD2 can be supported by the presence of the matrix of the inorganic compound in the region R. For example, at least a part of the region R is filled with the matrix.

[0045] In the present embodiment, an example is given of the case where the region R formed between two adjacent quantum dots QD1 and QD2 shown in Figure 8 and Figure 9 is filled with a matrix of an inorganic compound, that is, the space between multiple quantum dots 17, but it is not limited thereto.

[0046] In addition, holding the quantum dots QD1 and QD2 by the matrix present in the region R formed between the quantum dots QD1 and QD2 means that at least a part of the region R is filled with the matrix. Of course, it also includes the case where the matrix fills the entire region R and also means the case where the matrix fills a part of the region R.

[0047] The matrix of the inorganic compound as an example of the matrix can be formed so as to fill the region (space) other than the multiple quantum dots 17 of the light-emitting layer 38. In addition, it can also be configured such that the matrix of the inorganic compound forms the outer edge of the light-emitting layer 38, and the multiple quantum dots 17 are located at positions separated from the above outer edge. That is, the matrix of the inorganic compound can contain multiple quantum dots 17. Furthermore, at least a part of the outer edge of the light-emitting layer 38 can also be composed of the matrix and the quantum dots 17. In addition, the multiple quantum dots 17 can also be respectively embedded in the matrix of the inorganic compound at intervals. Here, the outer edge refers to the upper surface and the lower surface of the light-emitting layer 38.

[0048] The matrix of the inorganic compound as an example of the matrix can also include a continuous film having an area of 1000 nm 2 or more in the plane direction orthogonal to the layer thickness direction of the light-emitting layer 38. The continuous film refers to a film that is not separated by materials other than the materials constituting the continuous film on a plane. The continuous film can be an integral film-like structure that is continuously connected by chemical bonding of the matrix.

[0049] The matrix of the inorganic compound can also be the same material as the shell of the plurality of quantum dots 17. In this case, the average distance (inter-nuclear distance) between the nuclei of adjacent quantum dots 17 can be 3 nm or more, or can be 5 nm or more. Alternatively, the average distance between the nuclei of the adjacent quantum dots 17 can be 0.5 times or more of the average nuclear diameter of the quantum dots 17. In addition, the average distance (inter-nuclear distance) between the nuclei of the adjacent quantum dots 17 is obtained by averaging the distances between 20 adjacent nuclei in a space containing 20 nuclei. The average distance (inter-nuclear distance) between the nuclei can be maintained wider than the distance between the nuclei when the shells are in contact with each other. In addition, the average nuclear diameter of the quantum dots 17 is the nuclear diameter obtained by averaging the nuclear diameters of 20 quantum dots 17 in a cross-sectional view in a space containing 20 quantum dots QD. The nuclear diameter of the quantum dots 17 can be set as the diameter of a circle having the same area as the nuclear area of the quantum dots 17 in a cross-sectional view.

[0050] The constituent materials of the matrix of the inorganic compound, that is, the continuous first compound 18a and the continuous second compound 18b provided around each of the plurality of quantum dots 17 can be, for example, metal sulfides and / or metal oxides. The metal sulfide can be, for example, zinc sulfide (ZnS), zinc magnesium sulfide (ZnMgS, ZnMgS 2 ), gallium sulfide (GaS, Ga 2 S 3 ), zinc tellurium sulfide (ZnTeS), magnesium sulfide (MgS), zinc gallium sulfide (ZnGa 2 S 4 ), magnesium gallium sulfide (MgGa 2 S 4 ). The metal oxide can be zinc oxide (ZnO), titanium oxide (Ti0 2 ), tin oxide (Sn0 2 ), tungsten oxide (W0 3 ), zirconium oxide (Zr0 2 ). It should be noted that the chemical formulas described in parentheses after the compound names are representative examples. In addition, regarding the composition ratios described in the chemical formulas, as long as the composition of the actual compound is the stoichiometry as shown in the chemical formula, it is ideal, but it is not necessarily stoichiometry.

[0051] In the present disclosure, as long as the structure of the matrix or the like is not particularly mentioned or is not contradictory, in the cross-sectional view of the light-emitting layer 38, it can be understood that a width of about 100 nm is a desired configuration, and it is not necessary to observe the desired configuration in the entire light-emitting layer 38. The matrix can also contain a substance different from the main material (for example, an inorganic substance such as an inorganic semiconductor) as an additive, for example.

[0052] In addition, the constituent materials of the matrix, namely, the continuous first compound 18a and the continuous second compound 18b provided around each of the plurality of quantum dots 17, may be, for example, an organic polymer compound or an organic-inorganic hybrid compound. The organic polymer compound may be, for example, polymethyl methacrylate resin (MMA), biaxially stretched polystyrene sheet (OPS), polystyrene (PS), polycarbonate (PC), etc. The organic-inorganic hybrid compound may be, for example, polyacylsilsesquioxane as a siloxane-based polymer, MAPbI 3 and the like.

[0053] As Figure 7 shown, the light-emitting layer 38 included in the light-emitting element 1 includes a first part 8 and a second part 8'. The first part 8 is provided closer to the anode 22 than the second part 8', and the concentration of the electron-transporting electron-transporting material 10 included in the second part 8' is higher than the concentration of the electron-transporting electron-transporting material 10 included in the first part 8.

[0054] In the present embodiment, an example is given in which the first part 8 is composed of a plurality of quantum dots 17 and the continuous first compound 18a provided around each of the plurality of quantum dots 17, and the second part 8' is composed of a plurality of quantum dots 17, the continuous second compound 18b provided around each of the plurality of quantum dots 17, and the electron-transporting electron-transporting material 10, but it is not limited thereto. As long as the concentration of the electron-transporting electron-transporting material 10 included in the second part 8' is higher than the concentration of the electron-transporting electron-transporting material 10 included in the first part 8, the electron-transporting electron-transporting material 10 may also be contained in the first part 8. Moreover, the light-emitting layer 38 may also have a concentration gradient of the electron-transporting material 10 in which the concentration of the electron-transporting material 10 gradually increases as it approaches the electron-transporting layer 9 from the hole-transporting layer 7.

[0055] The electron-transporting electron-transporting material 10 having electron-transporting properties may be nanoparticles of a metal oxide containing at least one of Zn, Mg, Ti, Si, Sn, W, Ta, Ba, Zr, Al, Y, and Hf. For example, it may be nanoparticles of zinc oxide or zinc magnesium oxide.

[0056] The electron-transporting electron-transporting material 10 having electron-transporting properties may be an organic monomer having electron-transporting properties. The organic monomer having electron-transporting properties may be, for example, TPBi, B4PyMPy, BCP.

[0057] The electron transport material 10 having electron transport properties is preferably an organic semiconductor. When the electron transport material 10 having electron transport properties is an inorganic semiconductor, a small change in the Fermi level caused by the contact between semiconductors results in a large change, and there is a possibility of generating a large potential barrier. On the other hand, in the case of an organic semiconductor, the change in the Fermi level due to the contact between semiconductors is very gentle, and the dependence of the change in the Fermi level on the contact amount is low. Therefore, the control of the electron energy level is easy, it is difficult to generate an injection barrier for electrons E, and good injection characteristics of electrons E can be ensured.

[0058] The total weight of the electron transport material 10 having electron transport properties contained in the light-emitting layer 38 is preferably 10% or less, more preferably 1% or less, of the total weight of the plurality of quantum dots 17 contained in the light-emitting layer 38. In addition, the total weight of the electron transport material 10 contained in the second portion 8' is preferably about 70% or less of the total weight of the plurality of quantum dots 17 contained in the second portion 8'. By setting it within such a range, good injection characteristics of holes H into the quantum dots 17 can be ensured.

[0059] Figure 10 It is a diagram for explaining the reason why it is difficult to accumulate electrons E in the light-emitting layer 38 or at the interface between the light-emitting layer 38 and the electron transport layer 9 in the light-emitting element 1 of Embodiment 1 compared to the light-emitting element 50 of Comparative Example 1.

[0060] Figure 10 The light-emitting element 50 of Comparative Example 1 and the light-emitting element 1 of Embodiment 1 shown are an example of a light-emitting element in an electron-excessive state.

[0061] In Figure 10 In the case of the light-emitting element 50 of Comparative Example 1 shown, as time passes during constant current driving, electrons E as excessive carriers accumulate in the light-emitting layer 48 or at the interface between the light-emitting layer 48 and the electron transport layer 9, thereby generating an electric field opposite to the electric field during driving of the light-emitting element 50, as shown in Figure 1 shown, resulting in a decrease in the brightness of the light-emitting element 50. There is a problem that the luminous efficiency of the light-emitting element 50 decreases due to such a decrease in brightness. Although the above-mentioned reverse electric field can also be eliminated by increasing the driving voltage of the light-emitting element 50, in such a case, the materials of the respective layers constituting the light-emitting element 50 are subjected to large stress, and there is a problem that the reliability is significantly reduced.

[0062] On the other hand, in Figure 10In the case of the light-emitting element 1 of Embodiment 1 shown, since the electron-transporting material 10 having electron-transporting properties is dispersed in the light-emitting layer 38, electrons E, which are excessive carriers, slowly diffuse via the electron-transporting material 10 having electron-transporting properties existing three-dimensionally around to the hole-transporting layer 7, and are quenched and consumed by recombination with the hole-transporting layer 7. In addition, in order to suppress light emission when the electrons E recombine with the air-transporting layer 7, as the hole-transporting layer 7, a non-light-emitting material is preferably used. As the non-light-emitting material, for example, a material having a band gap (Eg) of 3.5 eV or more can be used. According to the configuration of the light-emitting element 1, even after the passage of the time during the constant-current driving period, the electrons E, which are excessive carriers, are difficult to accumulate, as shown in Figure 1 and the reduction in the brightness of the light-emitting element 1 can be suppressed. Therefore, according to the light-emitting element 1, the carrier balance, the external quantum efficiency (EQE), and the reliability can be improved.

[0063] In addition, during the power-off period, that is, during the period of maintaining the off-state, the electrons E existing as excessive carriers slowly diffuse via the electron-transporting material 10 having electron-transporting properties existing three-dimensionally around to the hole-transporting layer 7, and are quenched and consumed by recombination with the hole-transporting layer 7. Therefore, as shown in Figure 1 , in the light-emitting element 1 of Embodiment 1, the brightness recovery during the power-off period is fast.

[0064] Figure 11 is a diagram for explaining the reason why the brightness recovery during the power-off period is fast in the light-emitting element 1 of Embodiment 1 compared to the light-emitting element 50 of Comparative Example 1.

[0065] In Figure 11 the light-emitting element 50 of Comparative Example 1 and the light-emitting element 1 of Embodiment 1 shown, the electrons E accumulated in the light-emitting layers 38 and 48 or at the interface between the light-emitting layers 38 and 48 and the electron-transporting layer 9 gradually diffuse toward the cathode 25 side during the power-off period, that is, while maintaining the off-state, and finally return to the initial state at the start of driving. However, in the case of the light-emitting element 50 of Comparative Example 1, as shown in Figure 11 , the electrons E remaining at the interface between the light-emitting layer 48 and the electron-transporting layer 9 diffuse toward the cathode 25 side at an earlier stage during the power-off period, but the electrons E remaining in the light-emitting layer 48 do not diffuse toward the cathode 25 side and still remain even after a long power-off period. Therefore, as shown in Figure 1 , in the light-emitting element 50 of Comparative Example 1, the brightness is not restored when a short power-off measure is implemented, and the brightness can be restored when a long power-off measure is implemented. Therefore, the brightness recovery during the power-off period is slow.

[0066] On the other hand, in Figure 10In the case of the light-emitting element 1 of Embodiment 1 shown, since the electron-transporting material 10 having electron-transporting properties is dispersed in the light-emitting layer 38, electrons E remaining in the light-emitting layer 38 or at the interface between the light-emitting layer 38 and the electron-transporting layer 9 rapidly diffuse toward the cathode 25 side via the electron-transporting material 10 having electron-transporting properties present three-dimensionally around. Therefore, as Figure 1 shown, in the light-emitting element 1 of Embodiment 1, the luminance recovery during the power-off period is fast.

[0067] In the light-emitting element 1 of the present embodiment, in order to obtain both the effect that the excessively present carriers, i.e., electrons E, are difficult to accumulate, as shown Figure 10 and the effect that the excessively present carriers, i.e., electrons E, rapidly diffuse toward the cathode 25 side, as shown Figure 11 the concentration of the electron-transporting material 10 having electron-transporting properties contained in the second part 8' is higher than the concentration of the electron-transporting material 10 having electron-transporting properties contained in the first part 8. However, if only the effect that the most present carriers, i.e., electrons E, are difficult to accumulate, as shown Figure 10 is obtained, it is sufficient that only the electron-transporting material 10 having electron-transporting properties is contained in the light-emitting layer 38, and the electron-transporting material 10 having electron-transporting properties can be uniformly dispersed in the light-emitting layer 38. Further, in the case of a configuration in which only the electron-transporting material 10 having electron-transporting properties is contained in the light-emitting layer 38 or a configuration in which the electron-transporting material 10 having electron-transporting properties is uniformly dispersed in the light-emitting layer 38, it is preferable that the electron-transporting material 10 having electron-transporting properties does not contact the hole-transporting layer 7.

[0068] The light-emitting layer 38 included in the light-emitting element 1 of the present embodiment may include a plurality of ligands, and the plurality of ligands may be one or more selected from organic ligands, inorganic ligands, and halogen ligands.

[0069] The quantum dots 17 included in the light-emitting layer 38 of the light-emitting element 1 according to the present embodiment may also have, for example, a core structure, a core / shell structure, a core / shell / shell structure, or a shell structure in which the core / shell ratio continuously changes. In addition, although the shell may completely cover the core, it may also cover a part of the core. When the core part is a single-component system, it may be composed of, for example, Si, C, etc. When it is a binary system, it may be composed of, for example, CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, ZnTe, etc. When it is a ternary system, it may be composed of, for example, CdSeTe, GaInP, ZnSeTe, etc. When it is a quaternary system, it may be composed of, for example, AgInGaS (AIGS), etc. When the shell part is a binary system, it can be composed of, for example, CdS, CdTe, CdSe, ZnS, ZnSe, ZnTe, etc. When it is a ternary system, it can be composed of, for example, CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, AgInP (AIP), etc.

[0070] In addition, the quantum dots 17 refer to points with a maximum width of 100 nm or less. The shape of the quantum dots 17 is not particularly limited as long as it satisfies the above range of the maximum width, and is not limited to a spherical shape (circular cross-section). For example, it may be a polygonal cross-sectional shape, a rod-shaped three-dimensional shape, a branched three-dimensional shape, a three-dimensional shape with irregularities on the surface, or a combination of these shapes.

[0071] The quantum dots 17 are typically composed of a semiconductor. The semiconductor may have a certain bandgap. The semiconductor may be any material that can emit light, and in addition, it may at least contain the following materials. The semiconductor can emit red, green, and blue light respectively. The semiconductor is, for example, at least one selected from the group consisting of II-VI group compounds, III-V group compounds, chalcogenides, and perovskite compounds. In addition, II-VI group compounds refer to compounds containing a Group II element and a Group VI element, and III-V group compounds refer to compounds containing a Group III element and a Group V element. In addition, Group II elements include Group 2 elements and Group 12 elements, Group III elements include Group 3 elements and Group 13 elements, Group V elements include Group 5 elements and Group 15 elements, and Group VI elements may include Group 6 elements and Group 16 elements.

[0072] The II-VI group compounds contain at least one selected from, for example, MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, and HgTe.

[0073] III-V compounds include, for example, at least one selected from the group consisting of GaAs, GaP, InN, InAs, InP, and InSb.

[0074] Chalcogenides are compounds containing Group VIA (16) elements, such as CdS or CdSe. Chalcogenides may also include these mixed crystals.

[0075] Perovskite compounds have a composition represented by, for example, the general formula CsPbX 3 The constituent element X includes, for example, at least one selected from the group consisting of C1, Br, and I.

[0076] Here, the numbering of element groups using Roman numerals is marked based on the old IUPAC (International Union of Pure and Applied Chemistry) method or the old CAS (Chemical Abstracts Service) method, and the numbering of element groups using Arabic numerals is marked based on the current IUPAC method.

[0077] In the present embodiment, as Figure 7 shown, the light-emitting element 1 includes an anode 22 and a cathode 25 above the anode 22. Between the anode 22 and the cathode 25, for example, a light-emitting element having a normal stacked structure in which a hole transport layer 7, a light-emitting layer 38, and an electron transport layer 9 are sequentially stacked from the anode 22 side will be described as an example, but it is not limited thereto. For example, the light-emitting element 1 may also be a light-emitting element having an inverted stacked structure. In the case of the light-emitting element having an inverted stacked structure, although not shown, it includes a cathode 25 and an anode 22 provided above the cathode 25. Between the cathode 25 and the anode 22, for example, an electron transport layer 9, a light-emitting layer 38, and a hole transport layer 7 are sequentially stacked from the cathode 25 side.

[0078] In addition, the light-emitting element 1 can be a top-emission type or a bottom-emission type. When the light-emitting element 1 has a laminated film with a positive lamination structure, the cathode 6 is arranged above the anode 2. Therefore, in order to be a top-emission type, the anode 22 may be formed of an electrode material that reflects visible light, and the cathode 25 may be formed of an electrode material that transmits visible light. In order to form a bottom-emission type, the anode 22 may be formed of an electrode material that transmits visible light, and the cathode 25 may be formed of an electrode material that reflects visible light. On the other hand, in order to make the light-emitting element with an inverted lamination structure a top-emission type, the cathode 25 may be formed of an electrode material that reflects visible light, and the anode 22 provided above the cathode 25 may be formed of an electrode material that transmits visible light. In order to make the light-emitting element with an inverted lamination structure a bottom-emission type, the cathode 25 may be formed of an electrode material that transmits visible light, and the anode 22 provided above the cathode 25 may be formed of an electrode material that reflects visible light.

[0079] As the electrode material that reflects visible light, as long as it can reflect visible light and has conductivity, there is no particular limitation. For example, metal materials such as Al, Mg, Li, Ag, alloys of the above metal materials, laminates of the above metal materials and transparent metal oxides (such as indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), or laminates of the above alloys and the above transparent metal oxides can be cited.

[0080] As the electrode material that transmits visible light, as long as it can transmit visible light and has conductivity, there is no particular limitation. For example, transparent metal oxides (such as indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), thin films composed of metal materials such as Al and Ag, or nanowires composed of metal materials such as Al and Ag can be cited.

[0081] Figure 7 The method for forming the light-emitting layer 38 included in the shown light-emitting element 1 includes a step of forming at least a part of the light-emitting layer 38 using a first solution. The first solution includes a plurality of quantum dots 17, a precursor of a continuous compound 18b that forms a continuous compound 18b around each of the plurality of quantum dots 17, an electron transport material 10 having electron transport properties as a carrier transport material having carrier transport properties, and a solvent.

[0082] Although it is also possible to form the entire light-emitting layer 38 using the above-described first solution, a configuration in which the light-emitting layer 38 contains only the electron-transporting material 10 having electron-transporting properties, or a configuration in which the electron-transporting material 10 having electron-transporting properties is uniformly dispersed in the light-emitting layer 38, in the present embodiment, by forming a first portion 8 of the light-emitting layer 38 using a second solution described later and forming a second portion 8' of the light-emitting layer 38 using the above-described first solution, the concentration of the electron-transporting material 10 having electron-transporting properties contained in the second portion 8' becomes higher than the concentration of the electron-transporting material 10 having electron-transporting properties contained in the first portion 8. The second solution is prepared such that only the content of the electron-transporting material 10 having electron-transporting properties in the first solution is less than the content of the electron-transporting material 10 having electron-transporting properties in the second solution. In the present embodiment, the second solution does not contain the electron-transporting material 10 having electron-transporting properties.

[0083] In addition, in the above-described method for forming the light-emitting layer 38, when the first solution and the second solution can be separately prepared, the content of the precursor of the continuous compound can be reduced, and after forming a part of the light-emitting layer 38 using the first solution or the second solution, a solution containing the precursor of the continuous compound is further formed from above.

[0084] The first solution and the second solution may each contain a ligand.

[0085] The solvent contains, for example, at least one of dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N-methylformamide (NMF), formamide, N,N'-dimethylpropyleneurea, dimethylacetamide, N-methylpyrrolidone, γ-butyrolactone, propylene carbonate, acetonitrile, 2-methoxyethanol, methyl acetate, ethyl acetate, ethyl formate, methyl formate, tetrahydrofuran, diethyl ether, tetrahydrothiophene, diethyl sulfide, octane, hexane, toluene, chlorobenzene, and chloroform.

[0086] The precursor of Compound 18b is, for example, a precursor of a metal sulfide, and may contain, for example, a metal acetate, a metal nitrate, or a metal halide as a metal source, and at least one of thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N'-dimethylthiourea, tetramethylthiourea, or thioacetamide as a sulfur source. In addition, the precursor of the metal sulfide may also contain a metal complex in which thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N'-dimethylthiourea, tetramethylthiourea, or thioacetamide is coordinated to a metal atom. Additionally, the precursor of the metal sulfide may be, for example, xanthic acid.

[0087] 〔Embodiment 2〕 Next, based on Figure 12 and Figure 13Describe Embodiment 2 of the present invention. The light-emitting layer 38a included in the light-emitting element 1a of this embodiment is different from the light-emitting element 1 described in Embodiment 1 in that it includes a hole-transporting material 11 having hole-transporting properties as a carrier-transporting material having carrier-transporting properties. Except for this, as described in Embodiment 1. For ease of explanation, components having the same functions as those shown in the drawings of Embodiment 1 are denoted by the same reference numerals, and their descriptions are omitted.

[0088] Figure 12 It is a cross-sectional view showing a schematic configuration of the light-emitting element 1a of Embodiment 2.

[0089] As Figure 12 shown, the light-emitting layer 38a included in the light-emitting element 1a includes a first part 8” and a second part 8. The first part 8” is arranged closer to the anode 22 than the second part 8, and the concentration of the hole-transporting material 11 having hole-transporting properties included in the first part 8” is higher than the concentration of the hole-transporting material 11 having hole-transporting properties included in the second part 8.

[0090] In this embodiment, a case where the first part 8” is composed of a plurality of quantum dots 17, a continuous third compound 18c provided around each of the plurality of quantum dots 17, and a hole-transporting material 11 having hole-transporting properties, and the second part 8 is composed of a plurality of quantum dots 17 and a continuous first compound 18a provided around each of the plurality of quantum dots 17 is taken as an example for explanation, but it is not limited thereto. As long as the concentration of the hole-transporting material 11 having hole-transporting properties included in the first part 8” is higher than the concentration of the hole-transporting material 11 having hole-transporting properties included in the second part 8, the hole-transporting material 11 having hole-transporting properties may also be included in the second part 8. Moreover, the light-emitting layer 38a may also have a concentration gradient of the hole-transporting material 11 in which the concentration of the hole-transporting material 11 having hole-transporting properties gradually increases as approaching the hole-transporting layer 7 from the electron-transporting layer 9.

[0091] In this embodiment, a case where the continuous third compound 18c and the continuous first compound 18a are the same inorganic compound is taken as an example for explanation, but it is not limited thereto, and they may also be different compounds.

[0092] The hole-transporting material 11 having hole-transporting properties may also be nanoparticles of a metal oxide containing at least one of Ni, Mg, Mo, Cu, Co, Cr, and Ti. For example, it may be nanoparticles of nickel oxide.

[0093] The hole-transporting material 11 having hole-transporting properties may be an organic monomer having hole-transporting properties. The organic monomer having hole-transporting properties may be, for example, TAPC, TCTA, NPD, or TPD.

[0094] The hole transport material 11 having hole transport properties is preferably an organic semiconductor. In the case where the hole transport material 11 having hole transport properties is an inorganic semiconductor, a change in the Fermi level caused by the contact between semiconductors produces a large change in a very small amount, and there may be a large obstacle. On the other hand, in the case of an organic semiconductor, the change in the Fermi level due to the contact between semiconductors is very gentle, and the change in the Fermi level due to the contact amount has low dependence. Therefore, it is easy to control the hole energy level, and it is not easy to generate an injection barrier for holes H, and good injection characteristics of holes H can be ensured.

[0095] The total weight of the hole transport material 11 having hole transport properties contained in the light-emitting layer 38a is preferably 10% or less, more preferably 1% or less, of the total weight of the plurality of quantum dots 17 contained in the light-emitting layer 38a. In addition, the total weight of the hole transport material 11 having hole transport properties contained in the first portion 8" is preferably about 70% or less of the total weight of the plurality of quantum dots 17 contained in the first portion 8". By setting it within such a range, good injection characteristics of holes H into the quantum dots 17 can be ensured.

[0096] Figure 13 is compared with Figure 10 the light-emitting element 50 of Comparative Example 1 shown, and is a diagram for explaining the reason why electrons E are not likely to stay in the light-emitting layer 38a or at the interface between the light-emitting layer 38a and the electron transport layer 9 in the light-emitting element 1a of Embodiment 2.

[0097] Figure 10 the light-emitting element 50 of Comparative Example 1 shown and Figure 13 the light-emitting element 1a of Embodiment 2 shown are an example of a light-emitting element in an electron-excessive state.

[0098] Figure 13 In the case of the light-emitting element 1a of Embodiment 2 shown, the hole transport material 11 having hole transport properties is dispersed in the light-emitting layer 38a. Therefore, electrons E as excessive carriers are quenched and consumed by recombination with the hole transport material 11 having hole transport properties existing three-dimensionally in the light-emitting layer 38a. In addition, in order to suppress light emission when electrons E and the hole transport material 11 recombine, a non-light-emitting material is preferably used as the hole transport material 11. As the non-light-emitting material, for example, a material having a band gap (Eg) of 3.5 eV or more can be used. According to the configuration of the light-emitting element 1a, even after the time of constant current driving, electrons E as excessive carriers are difficult to accumulate, and a decrease in the brightness of the light-emitting element 1a can be suppressed. Therefore, according to the light-emitting element 1a, the carrier balance, the external quantum efficiency (EQE), and the reliability can be improved.

[0099] In addition, even during the period when power supply is stopped, that is, during the period when the light is kept off, electrons E, which are excessive carriers, are quenched and consumed by recombination with the hole transport material 11 having hole transport properties existing three-dimensionally in the light-emitting layer 38a. Therefore, in the light-emitting element 1a of Embodiment 2, the brightness recovery during the power-off period is fast.

[0100] In the light-emitting element 1a of the present embodiment, the case where the concentration of the hole transport material 11 having hole transport properties contained in the first part 8" is higher than the concentration of the hole transport material 11 having hole transport properties contained in the second part 8 has been described as an example, but it is not limited thereto. As long as only the hole transport material 11 having hole transport properties is contained in the light-emitting layer 38a, the hole transport material 11 having hole transport properties may be uniformly dispersed in the light-emitting layer 38a. Further, in the case of a configuration in which only the hole transport material 11 having hole transport properties is contained in the light-emitting layer 38a or a configuration in which the hole transport material 11 having hole transport properties is uniformly dispersed in the light-emitting layer 38a, it is preferable that the hole transport material 11 having hole transport properties does not contact the electron transport layer 9.

[0101] 〔Embodiment 3〕 Next, based on Figure 14 and Figure 15 Embodiment 3 of the present invention will be described. In the light-emitting layer 38b included in the light-emitting element 1b of the present embodiment, the concentration of the hole transport material 11 having hole transport properties contained in the second part 8" is higher than the concentration of the hole transport material 11 having hole transport properties contained in the first part 8, which is different from the light-emitting element 1a described in Embodiment 2. Except for this, as described in Embodiments 1 and 2. For ease of explanation, components having the same functions as those shown in the drawings of Embodiments 1 and 2 are denoted by the same reference numerals, and their descriptions are omitted.

[0102] Figure 14 FIG. is a cross-sectional view showing a schematic configuration of the light-emitting element 1b of Embodiment 3.

[0103] As Figure 14 shown, the light-emitting layer 38b included in the light-emitting element 1b includes a first part 8 and a second part 8". The first part 8 is provided closer to the anode 22 than the second part 8", and the concentration of the hole transport material 11 having hole transport properties contained in the second part 8" is higher than the concentration of the hole transport material 11 having hole transport properties contained in the first part 8.

[0104] Figure 15 is the same as Figure 10A diagram for explaining the reason why electrons E are less likely to accumulate at the interface between the light-emitting layer 38b and the electron transport layer 9 in the light-emitting element 1b of Embodiment 3, as compared with the light-emitting element 50 of Comparative Example 1 shown.

[0105] Figure 10 The light-emitting element 50 of Comparative Example 1 shown in Figure 15 The light-emitting element 1b of Embodiment 3 shown in is an example of a light-emitting element in an electron-excessive state.

[0106] Figure 15 In the case of the light-emitting element 1b of Embodiment 3 shown, a hole transport material 11 having hole transport properties is dispersed in the light-emitting layer 38b. Therefore, electrons E as excessive carriers are quenched and consumed by recombination with the hole transport material 11 having hole transport properties existing three-dimensionally in the light-emitting layer 38b. According to the configuration of the light-emitting element 1b, even after the passage of the time during the constant current driving period, electrons E as excessive carriers are difficult to accumulate, and a decrease in the brightness of the light-emitting element 1b can be suppressed. Therefore, according to the light-emitting element 1b, the carrier balance, the external quantum efficiency (EQE), and the reliability can be improved.

[0107] In addition, even during the power-off period, that is, during the period of maintaining the light-off state, electrons E as excessive carriers are quenched and consumed by recombination with the hole transport material 11 having hole transport properties existing three-dimensionally in the light-emitting layer 38b. Therefore, in the light-emitting element 1b of Embodiment 3, the brightness recovery during the power-off period is fast.

[0108] 〔Embodiment 4〕 Next, based on Figures 16 to 18 Embodiment 4 of the present disclosure will be described. The light-emitting element 1c of the present embodiment is different from the light-emitting element 1a described in Embodiment 2 in that it is a light-emitting element in a hole-excessive state. Except for this, as described in Embodiment 2. For ease of explanation, components having the same functions as those shown in the drawings of Embodiment 2 are denoted by the same reference numerals, and their descriptions are omitted.

[0109] Figure 16 is a schematic cross-sectional view showing a schematic configuration of the light-emitting element 1c of Embodiment 4.

[0110] As Figure 16 shown, the light-emitting layer 38a included in the light-emitting element 1c includes a first part 8” and a second part 8. The first part 8” is provided closer to the anode 22 than the second part 8, and the concentration of the hole transport material 11 having hole transport properties contained in the first part 8” is higher than the concentration of the hole transport material 11 having hole transport properties contained in the second part 8.

[0111] Figure 17 This is a diagram for explaining the reason why holes H are not likely to accumulate in the light-emitting layer 38a or at the interface between the light-emitting layer 38a and the hole transport layer 7a in the light-emitting element 1c of Embodiment 4 as compared with the light-emitting element 50a of Comparative Example 2.

[0112] Figure 17 The light-emitting element 50a of Comparative Example 2 and the light-emitting element 1c of Embodiment 4 shown are examples of light-emitting elements in a state with an excessive amount of holes.

[0113] In Figure 17 In the case of the light-emitting element 50a of Comparative Example 2 shown, as time passes during constant current driving, holes H as excessive carriers accumulate in the light-emitting layer 48 or at the interface between the light-emitting layer 48 and the hole transport layer 7a, thereby generating an electric field opposite to the driving electric field of the light-emitting element 50a, resulting in a decrease in the brightness of the light-emitting element 50a. There is a problem that the luminous efficiency of the light-emitting element 50a decreases due to such a decrease in brightness. Although the above-mentioned reverse electric field can also be eliminated by increasing the driving voltage of the light-emitting element 50a, in such a case, the materials of the respective layers constituting the light-emitting element 50a are subjected to large stress, and there is a problem that the reliability is significantly reduced.

[0114] On the other hand, Figure 17 In the case of the light-emitting element 1c of Embodiment 4 shown, a hole transport material 11 having hole transport properties is dispersed in the light-emitting layer 38a. Therefore, holes H as excessively present carriers slowly diffuse via the hole transport material 11 having hole transport properties existing three-dimensionally around to the electron transport layer 9a, and are quenched and consumed by recombination with the electron transport layer 9a. In addition, in order to suppress light emission when holes H recombine with the electron transport layer 9a, as the electron transport layer 9a, a non-light-emitting material is preferably used. As the non-light-emitting material, for example, a material having a band gap (Eg) of 3.5 eV or more can be used. According to the configuration of the light-emitting element 1c, even after the time of the constant current driving period has passed, holes H as excessive carriers are difficult to accumulate, and the occurrence of a decrease in the brightness of the light-emitting element 1c can be suppressed. Therefore, according to the light-emitting element 1c, the carrier balance, the external quantum efficiency (EQE), and the reliability can be improved.

[0115] In addition, even during the power-off period, that is, during the period of maintaining the light-off state, holes H as excessive carriers slowly diffuse via the hole transport material 11 having hole transport properties existing three-dimensionally around to the electron transport layer 9a, and are quenched and consumed by recombination with the electron transport layer 9a. Therefore, in the light-emitting element 1c of Embodiment 4, the brightness recovery during the power-off period is fast.

[0116] Figure 18This is a diagram for explaining the reason why the luminance recovery during the power-off period is faster in the light-emitting element 1c of Embodiment 4 than in the light-emitting element 50a of Comparative Example 2.

[0117] In Figure 18 In the light-emitting element 50a of Comparative Example 2 and the light-emitting element 1c of Embodiment 4 shown, holes H accumulated in the light-emitting layers 38a and 48 or at the interface between the light-emitting layers 38a and 48 and the hole transport layer 7a gradually diffuse toward the anode 22 side during the power-off period, that is, by maintaining the light-off state, and any one returns to the initial state at the start of driving. However, in the case of the light-emitting element 50a of Comparative Example 2, as Figure 18 shown, the holes H remaining at the interface between the light-emitting layer 48 and the hole transport layer 7a diffuse toward the anode 22 side at an earlier stage during the power-off period, but the holes H remaining in the light-emitting layer 48 do not diffuse toward the anode 22 side and still remain even after a relatively long power-off period. Therefore, in the light-emitting element 50a of Comparative Example 2, the luminance does not recover when a short-time power-off measure is implemented, and the luminance can recover when a long-time power-off measure is implemented. Thus, the luminance recovery during the power-off period is slow.

[0118] On the other hand, in Figure 18 the case of the light-emitting element 1c of Embodiment 4 shown, a hole transport material 11 having hole transport properties is dispersed in the light-emitting layer 38a. Therefore, the holes H remaining in the light-emitting layer 38a or at the interface between the light-emitting layer 38a and the hole transport layer 7a rapidly diffuse toward the anode 22 side via the hole transport material 11 having hole transport properties present three-dimensionally around. Therefore, in the light-emitting element 1c of Embodiment 4, the luminance recovery during the power-off period is fast.

[0119] 〔Embodiment 5〕 Next, based on Figure 19 and Figure 20 Embodiment 5 of the present invention will be described. The light-emitting element 1d of this embodiment is different from the light-emitting element 1 described in Embodiment 1 in that it is a light-emitting element in a state with excessive holes. Except for this, as described in Embodiment 1. For ease of explanation, components having the same functions as those shown in the drawings of Embodiment 1 are denoted by the same reference numerals, and their descriptions are omitted.

[0120] Figure 19 This is a cross-sectional view showing a schematic configuration of the light-emitting element 1d of Embodiment 5.

[0121] As Figure 19As shown, the light-emitting layer 38 included in the light-emitting element 1d includes a first portion 8 and a second portion 8'. The first portion 8 is disposed closer to the anode 22 than the second portion 8', and the concentration of the electron transport material 10 having electron transport properties included in the second portion 8' is higher than the concentration of the electron transport material 10 having electron transport properties included in the first portion 8.

[0122] Figure 20 is for explaining the comparison with Figure 17 This is a diagram for explaining the reason why holes H are not easily accumulated in the light-emitting layer 38 or at the interface between the light-emitting layer 38 and the hole transport layer 7a in the light-emitting element 1d of Embodiment 5 as compared with the light-emitting element 50a of Comparative Example 2 shown.

[0123] Figure 20 In the case of the light-emitting element 1d of Embodiment 5 shown, a hole transport material 10 having hole transport properties is dispersed in the light-emitting layer 38. Therefore, electrons E as excessive carriers are quenched and consumed by recombination with the hole transport material 10 having hole transport properties existing three-dimensionally in the light-emitting layer 38b. In addition, in order to suppress light emission when holes H and the electron transport layer 10 recombine, as the electron transport layer 10, a non-light-emitting material is preferably used. As the non-light-emitting material, for example, a material having a band gap (Eg) of 3.5 eV or more can be used. According to the configuration of the light-emitting element 1d, even after the passage of time during the constant current driving period, holes H as excessive carriers are difficult to accumulate, and the occurrence of a decrease in the brightness of the light-emitting element 1d can be suppressed. Therefore, according to the light-emitting element 1d, the carrier balance, the external quantum efficiency (EQE), and the reliability can be improved.

[0124] In addition, even during the power-off period, that is, during the period of maintaining the off state, holes H as excessive carriers are quenched and consumed by recombination with the hole transport material 10 having hole transport properties existing three-dimensionally in the light-emitting layer 38b. Therefore, in the light-emitting element 1d of Embodiment 5, the brightness recovery during the power-off period is fast.

[0125] 〔Embodiment 6〕 Next, based on Figure 21 and Figure 22 Embodiment 6 of the present invention will be described. The light-emitting element 1e of the present embodiment is a light-emitting element in a hole-excessive state, and the concentration of the electron transport material 10 having electron transport properties included in the first portion 8' of the light-emitting layer 38c is higher than the concentration of the electron transport material 10 having electron transport properties included in the second portion 8, which is different from the light-emitting elements described in Embodiments 1 to 5. Except for this, as described in Embodiments 1 to 5. For ease of explanation, components having the same functions as those shown in the drawings of Embodiments 1 to 5 are denoted by the same reference numerals, and their descriptions are omitted.

[0126] Figure 21 It is a schematic cross-sectional view showing the schematic configuration of the light-emitting element 1e of Embodiment 6.

[0127] As Figure 21 shown, the first portion 8' of the light-emitting layer 38c is disposed closer to the anode 22 than the second portion 8 of the light-emitting layer 38c. The concentration of the electron-transporting material 10 having electron-transporting properties contained in the first portion 8' is higher than the concentration of the electron-transporting material 10 having electron-transporting properties contained in the second portion 8.

[0128] Figure 22 It is for explaining the reason why holes H are not easily accumulated in the light-emitting layer 38a or at the interface between the light-emitting layer 38a and the hole-transporting layer 7a in the light-emitting element 1e of Embodiment 6 as compared with the light-emitting element 50a of Comparative Example 2 shown Figure 17 in the figure.

[0129] Figure 22 In the case of the light-emitting element 1e of Embodiment 6 shown, a hole-transporting material 10 having hole-transporting properties is dispersed in the light-emitting layer 38b. Therefore, electrons E as excessive carriers are quenched and consumed by recombination with the hole-transporting material 10 having hole-transporting properties existing three-dimensionally in the light-emitting layer 38b. According to the configuration of the light-emitting element 1e, even after the passage of time during the constant-current driving period, holes H as excessive carriers are hardly accumulated, and the occurrence of a decrease in the brightness of the light-emitting element 1e can be suppressed. Therefore, according to the light-emitting element 1e, the carrier balance, the external quantum efficiency (EQE), and the reliability can be improved.

[0130] In addition, even during the power-off period, that is, during the period of maintaining the light-off state, holes H as excessive carriers are quenched and consumed by recombination with the hole-transporting material 10 having hole-transporting properties existing three-dimensionally in the light-emitting layer 38b. Therefore, in the light-emitting element 1e of Embodiment 6, the brightness recovery during the power-off period is fast.

[0131] 〔Embodiment 7〕 Next, based on Figure 23 the present disclosure will be described for Embodiment 7. The light-emitting element 1f of the present embodiment is a light-emitting element in an electron-excessive state, and the light-emitting layer 38d is different from the light-emitting elements described in Embodiments 1 to 6 in that it contains both an electron-transporting material 10 having electron-transporting properties and a hole-transporting material 11 having hole-transporting properties. Except for this, as described in Embodiments 1 to 6. For ease of explanation, components having the same functions as those shown in the drawings of Embodiments 1 to 6 are denoted by the same reference numerals, and their descriptions are omitted.

[0132] Figure 23It is a cross-sectional view showing a schematic configuration of the light-emitting element 1f according to Embodiment 7.

[0133] As Figure 23 shown, the light-emitting layer 38d includes a first portion 8” and a second portion 8’. The first portion 8” is arranged closer to the anode 22 than the second portion 8’. The concentration of the hole-transporting material 11 having hole-transporting properties contained in the first portion 8” is higher than the concentration of the hole-transporting material 11 having hole-transporting properties contained in the second portion 8’. The concentration of the electron-transporting material 10 having electron-transporting properties contained in the second portion 8’ is higher than the concentration of the electron-transporting material 10 having electron-transporting properties contained in the first portion 8”.

[0134] According to the light-emitting element 1f of Embodiment 7, it is possible to achieve both the effect that the excessively present carriers, i.e., electrons E, are difficult to accumulate and the effect that the excessively present carriers, i.e., electrons E, rapidly diffuse toward the cathode 25 side.

[0135] 〔Embodiment 8〕 Next, based on Figure 24 this, Embodiment 8 of the present disclosure will be described. The light-emitting element 1g of this embodiment is different from the light-emitting element 1f described in Embodiment 7 in that it is a light-emitting element in a state where holes are excessive. Except for this, as described in Embodiment 7. For the sake of convenience of explanation, components having the same functions as those shown in the drawings of Embodiment 7 are denoted by the same reference numerals, and their descriptions are omitted.

[0136] Figure 24 It is a schematic cross-sectional view showing a schematic configuration of the light-emitting element 1g according to Embodiment 8.

[0137] As Figure 24 shown, the light-emitting layer 38d includes a first portion 8” and a second portion 8’. The first portion 8” is arranged closer to the anode 22 than the second portion 8’. The concentration of the hole-transporting material 11 having hole-transporting properties contained in the first portion 8” is higher than the concentration of the hole-transporting material 11 having hole-transporting properties contained in the second portion 8’. The concentration of the electron-transporting material 10 having electron-transporting properties contained in the second portion 8’ is higher than the concentration of the electron-transporting material 10 having electron-transporting properties contained in the first portion 8”.

[0138] According to the light-emitting element 1g of Embodiment 7, it is possible to achieve both the effect that the excessively present carriers, i.e., holes H, are difficult to accumulate and the effect that the excessively present carriers, i.e., holes H, rapidly diffuse toward the cathode 22 side.

[0139] 〔Embodiment 9〕 Next, based on Figure 25Describe Embodiment 9 of the present disclosure. The display device 30 of this embodiment is different from Embodiments 1 to 8 in that it is a display device including light-emitting elements 1 to 1g. Except for this, as described in Embodiments 1 to 8. For the sake of convenience of description, components having the same functions as those shown in the drawings of Embodiments 1 to 8 are denoted by the same reference numerals, and their descriptions are omitted.

[0140] Figure 25 It is a schematic cross-sectional view showing the schematic configuration of the display device 30 of Embodiment 9.

[0141] As Figure 25 shown, the display device 30 includes: a first light-emitting element 5R that emits light of a first color (for example, red); a second light-emitting element 5G that emits light of a second color (for example, green) whose emission peak wavelength is shorter than that of the light of the first color; and a third light-emitting element 5B that emits light of a third color (for example, blue) whose emission peak wavelength is shorter than that of the light of the second color. The third light-emitting element 5B is any one of the light-emitting elements 1 to 1g in the above Embodiments 1 to 8.

[0142] In this embodiment, the case where the third light-emitting element 5B is any one of the light-emitting elements 1 to 1g in the above Embodiments 1 to 8 is taken as an example for description, but it is not limited thereto. At least one of the first light-emitting element 5R, the second light-emitting element 5G, and the third light-emitting element 5B may also be any one of the light-emitting elements 1 to 1g in the above Embodiments 1 to 8.

[0143] As Figure 25 shown, the red sub-pixel RSP of the display device 30 includes a first light-emitting element 5R, which includes a functional layer 24R containing a red light-emitting layer. The green sub-pixel GSP of the display device 30 includes a second light-emitting element 5G, which includes a functional layer 24G containing a green light-emitting layer. The blue sub-pixel BSP of the display device 30 includes a third light-emitting element 5B, which includes a functional layer 24B containing a blue light-emitting layer.

[0144] As Figure 25 shown, in the display area DA of the display device 30, on the substrate 12, from the substrate 12 side, there are successively: a barrier layer 3, a thin-film transistor layer 4 including a transistor TR, a first light-emitting element 5R, a second light-emitting element 5G, a third light-emitting element 5B, and a bank 23, a sealing layer 6, and a functional film 29.

[0145] The substrate 12 can be, for example, a resin substrate made of a resin material such as polyimide, or a glass substrate. In the present embodiment, in order to make the display device 30 a flexible display device, the case of using a resin substrate made of a resin material such as polyimide as the substrate 12 is taken as an example for explanation, but it is not limited thereto. In the case where the display device 30 is a non-flexible display device, a glass substrate can be used as the substrate 12.

[0146] The barrier layer 3 is a layer that prevents foreign substances such as water and oxygen from entering the thin film transistor TR, the first light-emitting element 5R, the second light-emitting element 5G, and the third light-emitting element 5B. For example, it can be composed of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a stacked film of these layers formed by CVD.

[0147] The transistor TR portion of the thin film transistor layer 4 including the transistor TR includes a semiconductor film SEM and doped semiconductor films SEM’·SEM”, an inorganic insulating film 16, a gate electrode G, an inorganic insulating film 19, an inorganic insulating film 20, a source electrode S and a drain electrode D, and a planarization film 21. The portion other than the transistor TR portion of the thin film transistor layer 4 including the transistor TR includes the inorganic insulating film 16, the inorganic insulating film 19, the inorganic insulating film 20, and the planarization film 21.

[0148] The semiconductor films SEM·SEM′·SEM" can also be composed of, for example, low-temperature polycrystalline silicon (LTPS) or an oxide semiconductor (such as a semiconductor of the In-Ga-Zn-O type). In the present embodiment, the case where the transistor TR is a top-gate structure is illustrated as an example, but it is not limited thereto, and the transistor TR can also be a bottom-gate structure.

[0149] The gate electrode G, the source electrode S, and the drain electrode D are composed of, for example, a single-layer film or a stacked film of a metal containing at least one of aluminum, tungsten, molybdenum, tantalum, chromium, titanium, and copper.

[0150] The inorganic insulating films 16, 19, and 20 can be composed of, for example, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a stacked film thereof formed by CVD.

[0151] The planarization film 21 can be composed of, for example, an organic material such as polyimide or acrylic that can be coated, or can be formed as an inorganic film.

[0152] The first light-emitting element 5R included in the red sub-pixel RSP includes an anode 22 that is a layer above the planarization film 21, a functional layer 24R including a red light-emitting layer, and a cathode 25. The second light-emitting element 5G included in the green sub-pixel GSP includes an anode 22 that is a layer above the planarization film 21, a functional layer 24G including a green light-emitting layer, and a cathode 25. The blue light-emitting element 5B included in the blue sub-pixel BSP includes an anode 22 that is a layer above the planarization film 21, a functional layer 24B including a blue light-emitting layer, and a cathode 25. In addition, an insulating bank 23 that covers the edge of the anode 22 can be formed, for example, by patterning through photolithography after coating an organic material such as polyimide or acrylic, or can be formed as an inorganic film.

[0153] Therefore, according to the display device 30, carrier balance, external quantum efficiency (EQE), and reliability can be improved.

[0154] 〔Supplementary Note〕The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. Embodiments obtained by appropriately combining technical means separately disclosed in different embodiments are also included in the technical scope of the present invention. Moreover, new technical features can be formed by combining the technical methods separately disclosed in each embodiment. Industrial Applicability

[0155] The present disclosure can be utilized in light-emitting elements, display devices, and methods for forming light-emitting elements. Explanation of Reference Numerals

[0156] 1, 1A, 1b, 1c, 1d, 1e, 1f, 1g Light-emitting element 5R First light-emitting element 5G Second light-emitting element 5B Third light-emitting element 7, 7a Hole transport layer 8, 8’, 8” First part or second part 9, 9a Electron transport layer 10 Electron transport material (carrier transport material) 11 Hole transport material (carrier transport material) 17 Quantum dot 18a Continuous first compound (first matrix) 18b Continuous second compound (second matrix) 18c Continuous third compound (third matrix) 22 Anode 24R Functional layer including red light-emitting layer 24G Functional layer including green light-emitting layer 24B Functional layer including a blue light-emitting layer 25 Cathode 30 Display device 38 Light-emitting layer E Electron H Hole RSP Red sub-pixel GSP Green sub-pixel BSP Blue sub-pixel DA Display area

Claims

1. A light-emitting element, characterized in that, comprising: an anode, a cathode, and a light-emitting layer disposed between the anode and the cathode, wherein the light-emitting layer includes a plurality of quantum dots, a continuous compound disposed around each of the plurality of quantum dots, and a charge transport material having charge transport properties.

2. The light-emitting element according to claim 1, characterized in that, the continuous compound is one or more matrices selected from inorganic compounds, organic polymer compounds, and organic-inorganic hybrid compounds.

3. The light-emitting element according to claim 1, characterized in that, the continuous compound is a matrix of an inorganic compound, and the matrix of the inorganic compound contains the charge transport material.

4. The light-emitting element according to any one of claims 1 to 3, characterized in that, the charge transport material having charge transport properties is a hole transport material having hole transport properties, the light-emitting layer includes a first part and a second part, the first part is arranged closer to the anode than the second part, and the concentration of the hole transport material having hole transport properties contained in the first part is higher than the concentration of the hole transport material having hole transport properties contained in the second part.

5. The light-emitting element according to any one of claims 1 to 3, characterized in that, the charge transport material having charge transport properties is an electron transport material having electron transport properties, the light-emitting layer includes a first part and a second part, the first part is arranged closer to the anode than the second part, and the concentration of the electron transport material having electron transport properties contained in the second part is higher than the concentration of the electron transport material having electron transport properties contained in the first part.

6. The light-emitting element according to any one of claims 1 to 3, characterized in that, the charge transport material having charge transport properties is a hole transport material having hole transport properties, the light-emitting layer includes a first part and a second part, the first part is arranged closer to the anode than the second part, and the concentration of the hole transport material having hole transport properties contained in the second part is higher than the concentration of the hole transport material having hole transport properties contained in the first part.

7. The light-emitting element according to any one of claims 1 to 3, characterized in that, the charge transport material having charge transport properties is an electron transport material having electron transport properties, the light-emitting layer includes a first part and a second part, the first part is arranged closer to the anode than the second part, and the concentration of the electron transport material having electron transport properties contained in the first part is higher than the concentration of the electron transport material having electron transport properties contained in the second part.

8. The light-emitting element according to any one of claims 1 to 3, characterized in that, the charge transport material having charge transport properties is composed of multiple components, and a part of the charge transport material having multiple charge transport properties is a hole transport material having hole transport properties, The remaining part of the carrier transport material having various carrier transport properties is an electron transport material having electron transport properties. The light-emitting layer includes a first part and a second part. The first part is arranged closer to the anode than the second part. The concentration of the hole transport material having hole transport properties contained in the first part is higher than the concentration of the hole transport material having hole transport properties contained in the second part. The concentration of the electron transport material having electron transport properties contained in the second part is higher than the concentration of the electron transport material having electron transport properties contained in the first part.

9. The light-emitting element according to any one of claims 4, 6, and 8, wherein, The hole transport material having hole transport properties is nanoparticles containing at least one metal oxide of Ni, Mg, Mo, Cu, Co, Cr, and Ti.

10. The light-emitting element according to any one of claims 4, 6, and 8, wherein, The hole transport material having hole transport properties is nanoparticles of nickel oxide.

11. The light-emitting element according to any one of claims 4, 6, and 8, wherein, The hole transport material having hole transport properties is an organic monomer having hole transport properties.

12. The light-emitting element according to any one of claims 5, 7, and 8, wherein, The nanoparticles having electron transport properties are nanoparticles containing at least one of Zn, Mg, Ti, Si, Sn, W, Ta, Ba, Zr, Al, Y, and Hf.

13. The light-emitting element according to any one of claims 5, 7, and 8, wherein, The nanoparticles having electron transport properties are nanoparticles of zinc oxide or zinc magnesium oxide.

14. The light-emitting element according to any one of claims 5, 7, and 8, wherein, The nanoparticles having electron transport properties are an organic monomer having electron transport properties.

15. The light-emitting element according to any one of claims 1 to 14, wherein, A hole functional layer is provided between the anode and the light-emitting layer, An electron functional layer is provided between the cathode and the light-emitting layer.

16. The light-emitting element according to claim 15, wherein, The hole functional layer includes at least one of a hole transport layer and a hole injection layer, and the electron functional layer includes at least one of an electron transport layer and an electron injection layer.

17. A display device, wherein, comprising: A first light-emitting element that emits a first color light; A second light-emitting element that emits a second color light whose emission peak wavelength is shorter than the first color light; and A third light-emitting element that emits a third color light whose emission peak wavelength is shorter than the second color light, The third light-emitting element is the light-emitting element according to any one of claims 1 to 16.

18. A method for forming a light-emitting layer, wherein, At least a part of a light-emitting layer is formed using a first solution, wherein the first solution contains a plurality of quantum dots, a precursor of the continuous compound that forms a continuous compound around each of the plurality of quantum dots, a carrier transport material having carrier transport properties, and a solvent.

19. The method for forming a light-emitting layer according to claim 18, wherein, it includes: a first step of forming a part of the light-emitting layer using the first solution; and a second step of forming another part of the light-emitting layer using a second solution, wherein the second solution is prepared such that only the content of the carrier transport material in the first solution is less than the content of the carrier transport material in the second solution, by performing the first step before or after the second step, laminating a part of the light-emitting layer and another part of the light-emitting layer.

20. The method for forming a light-emitting layer according to claim 19, wherein, the second solution does not contain the carrier transport material.

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