Light emitting element and display device

Abstract

A light emitting element (2) comprising an EML (8) and an HTL (6), wherein the EML (8) comprises a base material (16) and a plurality of QDs (14) and the base material (16) includes a parent compound including at least one type of first group VI element as a main component and includes at least one type of second group VI element having a smaller periodic number than the first group VI element. The total concentration of the second group VI elements in the base material is within a range from 1×1016 atoms / cm3 to 1×1020 atoms / cm3 inclusive.

Description

Light-emitting element and display device

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

[0002] Light-emitting devices that use quantum dots as light-emitting materials in their light-emitting layers generally have a greater number of electrons injected than holes injected into the light-emitting layer, resulting in problems of excessive electron supply and insufficient holes. Furthermore, organic ligands are generally used on the surfaces of quantum dots to protect the quantum dots and improve their dispersibility in solvents. However, organic ligands made of organic substances are prone to degradation, resulting in reduced reliability.

[0003] Non-Patent Document 1 discloses quantum dots protected with sulfides instead of organic ligands. By inorganicizing the light-emitting layer by protecting the quantum dots with sulfides in this way, it is possible to eliminate organic substances that are prone to deterioration, thereby improving reliability.

[0004] InP-Quantum-Dot-in-ZnS-Matrix Solids for Thermal and Air Stability, Chemical Material, 2020, 32, 22, 9584-9590

[0005] However, even if the light-emitting layer is made inorganic, the electron excess remains.

[0006] One aspect of the present disclosure has been made in consideration of the above-mentioned problems, and its purpose is to provide a light-emitting element and a display device that are highly reliable, can improve the carrier balance between holes and electrons, and have excellent light-emitting characteristics.

[0007] In order to solve the above problems, a light-emitting element according to one aspect of the present disclosure includes a light-emitting layer and a hole transport layer provided adjacent to the light-emitting layer, wherein the light-emitting layer includes a base material containing at least one inorganic compound and a plurality of quantum dots, the base material including, as the inorganic compound, a base compound containing at least one first group VI element as a main component, and at least one second group VI element having a smaller periodic number than the first group VI element contained in the base compound, and a total concentration of the second group VI element in the base material is 1×10１６ atoms / cm ３ That's it, 1 x 10 ２０ atoms / cm ３ It is within the following range:

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

[0009] According to one embodiment of the present disclosure, it is possible to provide a light-emitting element and a display device that are highly reliable, can improve the carrier balance between holes and electrons, and have excellent light-emitting properties.

[0010] 1 is a cross-sectional view showing a schematic configuration of a light-emitting device according to embodiment 1. FIG. 2 is a cross-sectional view showing an example of a schematic configuration of a quantum dot and its vicinity in the light-emitting device shown in FIG. 1. FIG. 3 is a cross-sectional view showing a state in which adjacent quantum dots are approaching each other in the light-emitting device shown in FIG. 1. FIG. 4 is a schematic view showing an example of a band structure of each functional layer when the functional layers between the anode and the cathode in the light-emitting device shown in FIG. 1 are in an isolated state. FIG. 5 is a schematic view showing an example of a band structure of each functional layer when the functional layers shown in FIG. 4 are bonded together and band-shifted so that the Fermi levels coincide. FIG. 6 is a schematic view showing an example of a band structure of each functional layer when the functional layers shown in FIG. 6 are bonded together and band-shifted so that the Fermi levels coincide. FIG. 7 is a graph showing the J-V characteristics of the light-emitting device according to embodiment 1 and the J-V characteristics of the comparative light-emitting device. FIG. 8 is a graph showing the light-emitting characteristics of the light-emitting device according to embodiment 1 and the light-emitting characteristics of the comparative light-emitting device. FIG. 9 is another graph showing the light-emitting characteristics of the light-emitting device according to embodiment 1 and the light-emitting characteristics of the comparative light-emitting device. 16 is a flowchart illustrating an example of a manufacturing method for the light-emitting element according to embodiment 1. It is a cross-sectional view illustrating a ligand substitution step shown in FIG. 11. It is a cross-sectional view illustrating a schematic configuration of a quantum dot dispersion liquid used in forming the light-emitting element according to embodiment 1. It is a cross-sectional view illustrating a process of an example of a method for forming a light-emitting layer of the light-emitting element according to embodiment 1. It is a cross-sectional view illustrating a schematic configuration of a light-emitting element according to embodiment 2. It is a schematic view illustrating an example of a band structure of each functional layer when a second group VI element is mixed only in a first portion of a first light-emitting layer and each functional layer between an anode and a cathode is in an isolated state in the light-emitting element shown in FIG. 15. It is a schematic view illustrating an example of a band structure of each functional layer in a state where the functional layers shown in FIG. 16 are joined and band-shifted so that the Fermi levels coincide. It is a cross-sectional view illustrating an example of a schematic configuration of a light-emitting element according to a modified example of embodiment 2. It is a plan view illustrating a configuration example of a display device according to embodiment 3.

[0011] [Embodiment 1] One embodiment of the present disclosure will be described in detail below. Note that, hereinafter, the expression "A to B" regarding two numbers A and B means "greater than or equal to A and less than or equal to B" unless otherwise specified. Furthermore, hereinafter, a layer formed in a process earlier than a layer to be compared will be referred to as a "lower layer," and a layer formed in a process later than a layer to be compared will be referred to as an "upper layer."

[0012] Furthermore, in this disclosure, "organic material" or "organic compound" refers to a substance in which carbon is the center of the atomic bond, and "inorganic material" or "inorganic compound" refers to a substance other than organic. Therefore, in this disclosure, it is preferable to consider "inorganic material" or "inorganic compound" to refer to a substance in which carbon is not involved in the atomic bond. It may also be a substance in which carbon is not involved in the center of the atomic bond. Furthermore, it does not exclude the possibility of considering it as a substance without a carbon chain.

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

[0014] (Schematic configuration of light-emitting element) The light-emitting element according to this embodiment includes a light-emitting layer and a hole transport layer provided adjacent to the light-emitting layer, and the light-emitting layer includes a base material containing at least one inorganic compound and a plurality of quantum dots.

[0015] In the following, an example will be described in which the light-emitting element has a conventional structure in which an anode is a lower electrode and a cathode is an upper electrode, and includes functional layers, a hole transport layer, a light-emitting layer, and an electron transport layer, between the anode and the cathode. In the present disclosure, the layers between the anode and the cathode are collectively referred to as functional layers.

[0016] However, the light-emitting element according to this embodiment is not limited thereto, and may have, as functional layers, a light-emitting layer and a hole transport layer provided adjacent to the light-emitting layer. Furthermore, the light-emitting element according to this embodiment may have, for example, an inverted structure in which a cathode is a lower electrode and an anode is an upper electrode.

[0017] Hereinafter, the light-emitting layer may be referred to as "EML," the hole transport layer may be referred to as "HTL," and the electron transport layer may be referred to as "ETL." Quantum dots may also be referred to as "QD."

[0018] Fig. 1 is a cross-sectional view showing a schematic configuration of a light-emitting element 2 according to this embodiment. Fig. 2 is a cross-sectional view showing an example of a schematic configuration of a QD 14 and its vicinity in the light-emitting element 2 shown in Fig. 1. Fig. 3 is a cross-sectional view showing a state in which adjacent QDs 14 are close to each other in the light-emitting element 2 shown in Fig. 1.

[0019] As shown in FIG. 1 , the light-emitting element 2 according to this embodiment has, for example, a configuration in which an anode 4, a HTL 6, an EML 8, an ETL 10, and a cathode 12 are provided in this order from the lower layer side (e.g., the side of a support such as a substrate, not shown). Each layer from the anode 4 to the cathode 12 is generally supported by a substrate serving as a support. Although not shown and not described, the light-emitting element 2 may also include a functional layer, not shown, other than the HTL 6, the EML 8, and the ETL 10 between the anode 4 and the cathode 12. For example, the light-emitting element 2 may also include a hole-injection layer, which has hole-transport properties and promotes the injection of holes from the anode 4 to the HTL 6, between the anode 4 and the HTL 6. Hereinafter, the hole-injection layer may be referred to as "HIL."

[0020] At least one of the anode 4 and the cathode 12 is a translucent electrode. Either the anode 4 or the cathode 12 may be a so-called reflective electrode that is light-reflective. The light-emitting element 2 can extract light from the translucent electrode side.

[0021] For example, if the light-emitting element 2 is a top-emission type light-emitting element that emits light from the upper electrode side, a translucent electrode is used for the upper electrode and a reflective electrode is used for the lower electrode, whereas if the light-emitting element 2 is a bottom-emission type light-emitting element that emits light from the lower electrode side, a translucent electrode is used for the lower electrode and a reflective electrode is used for the lower electrode.

[0022] The translucent electrode is made of a conductive material that transmits visible light, such as ITO (indium tin oxide), IZO (indium zinc oxide), ZnO, AZO (aluminum-doped zinc oxide, also known as ZAO), BZO (boron-doped zinc oxide), or FTO (fluorine-doped tin oxide).

[0023] The reflective electrode is preferably made of a conductive material having a high reflectance for visible light, such as a metal such as Al, Cu, Au, Ag, or MgAg, or an alloy containing such a metal.

[0024] The HTL 6 contains a hole transport material and is capable of transporting holes (h ＋ , see FIG. 5 below) to the EML 8. As the hole-transporting material, an organic or inorganic material that has been conventionally used in a QLED (quantum dot light-emitting diode), which is a light-emitting element containing QDs, or an OLED (organic light-emitting diode), can be used.

[0025] Examples of the organic material for HTL6 include conductive compounds such as 4,4'-bis(carbazol-9-yl)biphenyl (CBP), polyphenylene vinylene (PPV), a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT:PSS), poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl)diphenylamine)]) (TFB), and polyvinylcarbazole (PVK).

[0026] Examples of inorganic materials for HTL6 include molybdenum oxide, NiO, and Cr. ２ O ３ , MgO, MgZnO, LaNiO３ , or W.O. ３ In particular, a material having a large electron affinity and ionization potential is suitable as the material for HTL6.

[0027] The ETL 10 contains an electron transport material and is capable of transporting electrons (e － , see FIG. 5 below) to the EML 8. Examples of the electron transport material include TiO ２ In addition, organic or inorganic materials conventionally employed in QLEDs or OLEDs can be used.

[0028] The organic material for the ETL 10 can be, for example, a conductive compound such as tris(8-quinolinol)aluminum complex (Alq3), bathocuproine (BCP), or (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) (t-Bu-PBD).

[0029] Examples of inorganic materials that can be used for the ETL 10 include metal oxides such as ZnO, AZO, ITO, In—Ga—Zn—O-based semiconductors (e.g., indium gallium zinc oxide), and electrides. In particular, materials with low electron affinity are suitable for the ETL 10.

[0030] The EML 8 includes a host material 16 containing at least one inorganic compound and a plurality of QDs 14. In this disclosure, removing the organic ligands and embedding the QDs 14 in the host material 16 containing the inorganic compound is referred to as mineralizing the EML 8. The EML 8 containing the host material 16 containing the inorganic compound may also be referred to as mineralized EML 8.

[0031] In the EML 8, holes transported from the anode 4 and electrons transported from the cathode 12 recombine, and the resulting excitons emit light during the transition from the conduction band level to the valence band level of the QDs 14. The EML 8 contains nano-sized QDs 14 as the light-emitting material, which correspond to the emission color.

[0032] QD14s are dots with a maximum particle width of 100 nm or less. QD14s are generally sometimes referred to as semiconductor nanoparticles because their composition is derived from semiconductor materials. QD14s are also generally sometimes referred to as inorganic nanoparticles because their composition is derived from inorganic materials. QD14s are also sometimes referred to as nanocrystals because their structure has, for example, a specific crystalline structure.

[0033] The shape of the QD14 is not particularly limited as long as it satisfies the above-mentioned maximum width, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). For example, the shape may be a polygonal cross-sectional shape, a rod-like three-dimensional shape, a branch-like three-dimensional shape, a three-dimensional shape with an uneven surface, or a combination thereof.

[0034] QD14 may contain at least one metal element, such as Cd, Zn, In, Sb, Al, Si, Ga, Pb, Ge, or Mg. Alternatively, QD14 may be a semiconductor material that combines at least one metal element with a nonmetal element, such as S, Te, Se, N, P, or As.

[0035] QD14 may be formed of only a core, or may be a two-component, three-component, or four-component core. Alternatively, QD14 may have a core-shell structure including a core 14C and a shell 14S, as shown in Figure 2, or may be a core-shell or core-multishell structure.

[0036] As shown in FIG. 2 , when a QD14 includes a shell 14S, a core 14C is located at the center, and the shell 14S is provided on the surface of the core 14C. While it is desirable for the shell 14S to cover the entire core 14C, it is not necessary for the shell 14S to completely cover the core 14C. The shell 14S may be formed on only a portion of the surface of the core 14C. A QD14 can be said to have a core-shell structure if, upon observing a cross-section of the QD14, it is clear that the shell 14S is formed on only a portion of the surface of the core 14C, or if it is clear that the shell 14S surrounds the core 14C. Therefore, it is sufficient to determine from a cross-section of the QD14 that the shell 14S covers the entire core 14C. The cross-sectional observation can be performed, for example, using a scanning transmission electron microscope (STEM) or a transmission electron microscope (TEM).

[0037] The QDs 14 may also include doped nanoparticles or have a compositionally graded structure. The shell 14S may be formed as a solid solution on the surface of the core 14C. In Figure 2, the boundary between the core 14C and the shell 14S is shown by a dotted line, indicating that the boundary between the core 14C and the shell 14S may or may not be identifiable by analysis. The shell 14S may be formed in multiple layers.

[0038] The core 14C and shell 14S of the QD 14 may contain materials used for the core and shell materials of conventionally known QDs. The core 14C may be composed of, for example, Si, Ge, CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, ZnTe, CdSeTe, GaInP, ZnSeTe, etc. The shell 14S may be composed of, for example, CdS, ZnS, CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, AIP, etc. For example, if the shell 14S contains ZnSSe, the ZnSSe contained in the shell 14S may be ZnS. ｘ Se １－ｘ(0≦x≦1) When the QDs 14 have a core-shell structure, examples of the materials of the QDs 14 (combinations of the materials of the core 14C and shell 14S) include ZnSe / ZnS, InP / ZnS, CdSe / CdS, CdSe / ZnSe, and CIGS / ZnS.

[0039] It is preferable that the compositions shown by chemical formulas in this disclosure are stoichiometric, but this does not exclude non-stoichiometric compositions.

[0040] The emission wavelength of QD14 can be varied by adjusting the particle size, composition, etc. QD14 is a QD that emits visible light, and by appropriately adjusting the particle size and composition of QD14, it is possible to control the emission wavelength from the blue wavelength region to the red wavelength region.

[0041] The core 14C of the QD 14 is a light-emitting material that has a valence band level and a conduction band level and emits light by recombination of holes in the valence band level and electrons in the conduction band level. The light emitted from the QD 14 has a narrow spectrum due to the quantum confinement effect, making it possible to obtain light with a relatively deep chromaticity.

[0042] The QDs 14 in the EML 8 do not need to be arranged regularly as shown in Fig. 1 , and the QDs 14 may be included in the EML 8 in a disordered manner. Furthermore, in the EML 8, the QDs 14 may be in a state where a host material 16 is formed between adjacent QDs 14 as shown in Fig. 1 , and the QDs 14 are not close to each other, or the EML 8 may include two or more QDs 14 that are close to each other as shown in Fig. 3. The thickness of the EML 8 may be approximately 1 nm or more and 100 nm or less, and preferably approximately 10 nm or more and 60 nm or less.

[0043] In this disclosure, the term "base material" refers to a material that contains and holds other substances, and can be referred to as a matrix material, a substrate, or a filler. In other words, in this disclosure, the term "base material 16" refers to a material that contains and holds QDs 14. The base material 16 is an element that constitutes the membrane in which QDs 14 are distributed, and as shown in FIG. 1, it is one of the components of the EML 8 that contains multiple QDs 14. The base material 16 may be solid at room temperature.

[0044] The base material 16 may be filled in the EML 8. Focusing on two of the multiple QDs 14 as shown in FIG. 1 , the base material 16 may fill the space between the two QDs 14 (i.e., the region Y (space) between the two QDs 14). If the two QDs are a first QD 14a and a second QD 14b, the region Y is the region enclosed in a cross-sectional view by two lines (common external tangents) tangent to the outer peripheries of the first QD 14a and the second QD 14b and the opposing outer peripheries of the first QD 14a and the second QD 14b.

[0045] Note that FIG. 1 illustrates an example in which the QDs 14 are embedded in the base material 16 at intervals. However, as described above, in the EML 8, adjacent QDs 14 may be spaced apart or may be close to each other. As shown in FIG. 3, even if adjacent first QDs 14a and second QDs 14b are close to each other, a region Y (space) may exist between the first QDs 14a and second QDs 14b. Even if the first QDs 14a and second QDs 14b are close to each other, the base material 16 may fill the region Y (space) between the first QDs 14a and second QDs 14b.

[0046] Therefore, the host material 16 may fill regions (spaces) in the EML8 other than those occupied by the QDs 14. Therefore, the host material 16 may fill regions (spaces) in the EML8 other than those occupied by the QDs 14. The EML8 has a QD group (quantum dot group) including a plurality of QDs 14, and the host material 16 may fill regions (spaces) in the EML8 other than those occupied by the QD group. Here, three or more QDs 14 are collectively referred to as a QD group. The host material 16 may fill regions (spaces) in the EML8 other than those occupied by the plurality of QDs 14. The outer edges (top and bottom surfaces) of the EML8 may be covered with the host material 16. Alternatively, a portion of the host material 16 may extend from the outer edge of the EML8, and the QDs 14 may be positioned away from the outer edge of the EML8. The outer edge of the EML8 may not be formed solely by the host material 16, and some of the QDs 14 may be exposed from the host material 16. The base material 16 may refer to the portion of the EML 8 excluding the QDs 14 .

[0047] The matrix 16 may contain multiple QDs 14. The matrix 16 may be configured to fill the spaces between the multiple QDs 14 (i.e., the spaces formed between the multiple QDs 14). The matrix 16 may partially or completely fill the spaces between the multiple QDs 14.

[0048] The base material 16 has a thickness of 1000 nm along the surface direction perpendicular to the layer thickness direction. ２ The base material 16 may include a continuous film having an area of ​​at least 1000 nm. A continuous film means a film that is not separated in one plane by a material other than the material that constitutes the continuous film. The continuous film may be an integrated film that is seamlessly connected by chemical bonds of the materials that constitute the base material 16.

[0049] The base material 16 may contain the same material as the shells 14S contained in each of the multiple QDs 14. In other words, the shells 14S may contain the same material as the matrix compound of the base material 16. When the shells 14S contain the same material as the matrix compound of the base material 16, the shells 14S and the matrix compound of the base material 16 are continuously connected, thereby improving the quality of the base material 16.

[0050] In this manner, when the base material 16 contains the same material as the shell 14S, the average distance between adjacent cores 14C (core-to-core distance) may be 3 nm or more, or even 5 nm or more, to avoid contact between the QDs 14 and aggregation of the QDs 14. Alternatively, the average distance between adjacent cores 14C may be 0.5 times or more the average core diameter. The core-to-core distance is the average distance between adjacent cores in a space containing 20 cores. The core-to-core distance should be kept wider than the distance when the shells 14S are in contact with each other. The average core diameter is the average core diameter of 20 cores 14C in a cross-sectional observation of a space containing 20 cores. The core diameter can be the diameter of a circle having the same area as the core area in cross-sectional observation.

[0051] The concentration of the matrix 16 in the EML8 is, for example, the area ratio occupied by the matrix 16 in the cross section of the EML8. The concentration of the matrix 16 may be 10% or more and 90% or less, or 30% or more and 70% or less, when observing the cross section of the EML8. The concentration of the matrix 16 may be measured, for example, from the area ratio obtained by image processing of the cross section of the EML8. When the QD14 has a core-shell structure, the concentration of the shell 14S may be 1% or more and 50% or less. When the shell 14S and the matrix 16 are made of the same material (same composition) and are indistinguishable from each other, the concentration of the combined region of the shell 14S and the matrix 16 may be within the range obtained by adding the range of the concentration of the shell 14S to the range of the concentration of the matrix 16. The ratio of the core 14C, shell 14S, and matrix 16 of the QD14 may be appropriately adjusted so that the sum of these is 100% or less. In this way, when the shell 14S and the base material 16 cannot be distinguished from each other, the shell 14S may be considered as a part of the base material 16.

[0052] The EML 8 may be composed of a plurality of QDs 14 and a host material 16. When the EML 8 is analyzed, the intensity of carbon detected due to the chain structure may be below noise.

[0053] The material of the base material 16 preferably has a wider band gap (hereinafter referred to as "Eg") than the material of the QD 14. For example, as described above, if the QD 14 has a core 14C and a shell 14S, the Eg of the base material 16 is preferably larger than the Eg of either the core 14C or the shell 14S.

[0054] Recombination of carriers (electrons and holes) injected into QD 14 occurs mainly in core 14C. Shell 14S has the function of suppressing the occurrence of defects or dangling bonds in core 14C and reducing the recombination of carriers undergoing a deactivation process. When Eg of base material 16 is larger than Eg of core 14C or shell 14S, the exciton confinement effect in core 14C is high, and excitons generated by carrier recombination or light absorption in core 14C are less likely to diffuse into base material 16, thereby improving the luminous efficiency of light-emitting element 2.

[0055] Note that the Eg of the base material 16 may be equal to or smaller than the Eg of the shell 14S, provided that it is larger than the Eg of the core 14C. However, it is preferable that the Eg of the base material 16 be larger than the Eg of the shell 14S. In this case, the exciton confinement effect in the core 14C is enhanced, which suppresses the diffusion of excitons from the QD 14 to the base material 16 and further improves the luminous efficiency.

[0056] The base material 16 contains at least one inorganic compound. The inorganic compound (inorganic material) constituting the base material 16 may be a semiconductor material or an insulating material.

[0057] It should be noted that the base material 16 may be made of any material as long as its main material is an inorganic compound, and it is not excluded that a material different from the inorganic compound used as the main material may be added as an additive.

[0058] The base material 16 includes, as the inorganic compound, a base compound containing at least one group VI element (first group VI element) as a main component, and also includes a group VI element (second group VI element) having a smaller periodic number than the first group VI element. Note that the base material 16 may also contain a substance different from the base compound, for example, as an additive.

[0059] In this disclosure, the notation of element group numbers using Roman numerals is based on the old IUPAC system, and Group VI elements include Group VIA elements and Group VIB elements. Therefore, Group VI elements refer to Group 6 elements and Group 16 elements in the notation based on the new IUPAC system. In this disclosure, the notation of element group numbers using Arabic numerals indicates the notation based on the new IUPAC system. The group numbers in the old IUPAC system correspond to the formal number of valence electrons.

[0060] Specific examples of Group VIA elements include, in ascending order of periodic number, Cr (chromium), Mo (molybdenum), W (tungsten), and Sg (seaborgium).Specific examples of Group VIB elements include, in ascending order of periodic number, O (oxygen), S (sulfur), Se (selenium), Te (tellurium), Po (polonium), and Lv (livermorium).Note that O belongs to the second period, S belongs to the third period, Cr and Se belong to the fourth period, Mo and Te belong to the fifth period, W and Po belong to the sixth period, and Sg and Lv belong to the seventh period.

[0061] When the first Group VI element belongs to the nth period (m is an integer of 2 or more), the second Group VI element is a Group VI element belonging to the m-kth period (k is an integer of 1 or more and m-1 or less).

[0062] The matrix compound is preferably a II-VI compound. Group II elements include Group IIA elements and Group IIB elements, and refer to Group 2 elements and Group 12 elements. In the present disclosure, the II-VI compound may contain a Group II element and a Group VI element in a composition ratio of approximately 1:1, or may contain a Group VI element relative to the Group II element in a ratio of more than 1:1. In other words, the matrix compound may contain a II-VI compound in which the Group VI element is in excess.

[0063] Examples of the matrix compound include compounds containing one or more Group II elements selected from magnesium (Mg), zinc (Zn), cadmium (Cd), and mercury (Hg), and one or more Group VI elements selected from O, S, Se, and Te.

[0064] To maintain or strengthen the confinement of excitons in the core 14C of the QD14, the host compound desirably has an Eg equal to or wider than that of the core 14C or shell 14S of the QD14, as described above, and more desirably has an Eg equal to or wider than that of the shell 14S. Furthermore, to improve the quality of the host material 16, it is desirable that the shell 14S of the QD14 and the crystalline host material 16 are continuously connected. Alternatively, the shell 14S of the QD14 and the host material 16 may be formed as amorphous (non-crystalline). For this reason, the host compound is preferably a II-VI compound typically used for the shell of a QD, and it is desirable to use the same material as the shell 14S of the QD14 for the host material 16, particularly the host compound.

[0065] The first group VI element may be any group VI element other than O, but is preferably at least one selected from the group consisting of S, Se, and Te. Among II-VI compounds, S, Se, and Te are generally used in the shells of QDs and are particularly suitable as host compounds. As described above, the host material 16 includes at least one host compound primarily composed of a first group VI element, as well as a second group VI element having a smaller periodic number than the first group VI element. O is excluded from the first group VI elements because it has the smallest periodic number among the group VI elements.

[0066] Examples of II-VI compounds include magnesium sulfide (MgS), magnesium selenide (MgSe), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), cadmium selenide (CdSe), cadmium telluride (CdTe), mercury sulfide (HgS), mercury selenide (HgSe), mercury telluride (HgTe), cadmium selenium sulfide (CdSeS), and cadmium selenium telluride (CdS eTe), cadmium sulfur telluride (CdSTe), zinc selenium sulfide (ZnSeS), zinc selenium telluride (ZnSeTe), zinc tellurium sulfide (ZnTeS), mercury selenium sulfide (HgSeS), tellurium compounds mercury selenium (HgSeTe), mercury sulfur telluride (HgSTe), cadmium zinc sulfide (CdZnS), cadmium zinc selenide (CdZnSe), cadmium zinc telluride (CdZnTe), cadmium sulfide water Silver (CdHgS), cadmium mercury selenide (CdHgSe), cadmium mercury telluride (CdHgTe), mercury zinc sulfide (HgZnS), mercury zinc selenide (HgZnSe), mercury zinc telluride (HgZnTe), magnesium zinc selenide (MgZnSe), magnesium zinc sulfide (MgZnS), mercury zinc tellurium sulfide (HgZnTeS), cadmium zinc selenium sulfide (CdZnSeS), cadmium telluride Examples of such compounds include zinc selenium (CdZnSeTe), cadmium zinc sulfur telluride (CdZnSTe), cadmium mercury selenium sulfide (CdHgSeS), cadmium mercury selenium telluride (CdHgSeTe), cadmium mercury sulfur telluride (CdHgSTe), mercury zinc selenium sulfide (HgZnSeS), mercury zinc selenium telluride (HgZnSeTe), mercury zinc sulfur telluride (HgZnSTe), and mixtures thereof. Thus, the II-VI compounds are not limited to binary compounds, but may also be ternary or quaternary compounds. The chemical formulas in parentheses following the compound names are representative examples. As mentioned above, the composition ratios described in the chemical formulas are preferably stoichiometric, with the actual compound composition conforming to the chemical formula, but are not necessarily stoichiometric.

[0067] As shown in the above example, the II-VI group compound used in the matrix compound may include, for example, a metal sulfide. In particular, the shell 14S is often ZnS. As mentioned above, it is desirable to use the same material as the shell 14S of the QD 14 for the matrix compound. Therefore, when the shell 14S is ZnS, ZnS is preferably used for the matrix compound. The band gap of ZnS is 3.6 eV.

[0068] However, this embodiment is not limited to this. Generally, metal sulfides containing a metal element M other than Zn, such as ZnMS, are also suitable for use in the shell of QDs, similar to ZnS. Therefore, the II-VI group compound used for the host compound may be a metal sulfide containing a metal element M other than Zn, such as ZnMS. The metal element M is preferably one higher in the periodic table than Zn, such as Mg or Li.

[0069] In this way, the base material 16 may be a mixed crystal of a metal sulfide containing a first element and a metal sulfide containing a second element, or the base material 16 may be a mixed crystal abc in which a compound ac consisting of elements a and c is mixed with a compound bc consisting of elements b and c. When the base material 16 includes a mixed crystal of a metal sulfide containing a first element and a metal sulfide containing a second element as the base compound, for example, the first element may be Zn, and the second element may be Mg or Li (lithium).

[0070] Thus, the host material 16 may contain Mg or Li, or a mixture of Mg and Li. Mg and Li belong to a higher period with a smaller period number than Mg. Therefore, when either or both of Mg and Li are contained at a compositional level, the Eg of the host material 16 increases, suppressing the current flowing outside the QDs 14. Therefore, by including at least one of Mg and Li in the host material 16, the efficiency of hole injection into the QDs 14 can be improved, further improving the luminous efficiency.

[0071] It is desirable that Mg and Li are contained at a composition level in the base material 16. In other words, it is desirable that Mg and Li form a part of the composition of the base material 16. Therefore, when the base material 16 contains at least one of Mg and Li, the lower limit of the total concentration of Mg and Li contained in the base material 16 is 1×10 ２１ atoms / cm ３ On the other hand, when the base material 16 contains, for example, a mixed crystal ZnMgS of ZnS and MgS, or a mixed crystal ZnLiS of ZnS and LiS, the crystal systems of MgS and LiS are different from those of ZnS, and therefore the upper limit of the ZnS-based Mg or Li, or the total composition of Mg and Li in the base material 16 is 10%. Therefore, in terms of concentration, when the base material 16 contains at least one of Mg and Li, the upper limit of the total concentration of Mg and Li contained in the base material 16 is 1×10 ２２ atoms / cm ３ Therefore, when the base material 16 contains at least one of Mg and Li, the total concentration of Mg and Li contained in the base material 16 is 1×10 ２１ atoms / cm ３ That's it, 1 x 10 ２２ atoms / cm ３ It is desirable that the following:

[0072] The second VI group element is a dopant mixed (doped) into the base compound as an impurity element (additive), and the total concentration of the second VI group element in the base material 16 is 1×10 １６ atoms / cm ３ That's it, 1 x 10 ２０ atoms / cm ３ It is within the following range:

[0073] As described above, the second group VI element is a group VI element having a smaller periodic number than the first group VI element. Therefore, when the matrix compound is, for example, ZnS as described above, the group VI element S belongs to the third period, and therefore, the second group VI element is O, a group VI element belonging to the second period. In this case, the matrix 16 contains two group VI elements, S and O, as the group VI elements. Of course, when the first group VI element is, for example, Se, which belongs to the fourth period, the second group VI element may be O, which belongs to the second period, or S, which belongs to the third period. In this case, the matrix 16 may contain two group VI elements, Se and S, or Se and O, as the group VI elements, or may contain three group VI elements, Se, S, and O. Furthermore, when the first group VI element is, for example, Te belonging to the fifth period, the second group VI element may be O belonging to the second period, S belonging to the third period, or Se belonging to the fourth period. In this case, the base material 16 may contain, as the group VI elements, two types of group VI elements, namely Te and Se, Te and S, or Te and O, or may contain two types of group VI elements, namely Te, Se, and S, or Te, Se, and O, or Te, S, and O. Furthermore, when the first group VI element is, for example, Te belonging to the fifth period, the base material 16 may contain three types of group VI elements, namely Te, Se, and S, or Te, Se, and O, or Te, S, and O, or may contain four types of group VI elements, namely Te, Se, S, and O.

[0074] The second group VI element is not particularly limited as long as it is a group VI element having a smaller periodic number than the first group VI element. As described above, the base material 16 may contain the first group VI element and the second group VI element, and may contain three or more types of group VI elements as long as it contains two or more types of group VI elements.

[0075] It should be noted that the structure of the base material 16 can be observed in a cross section of the EML 8 with a width of about 100 nm, and it is sufficient to know that it has the above-described structure; it is not necessary that the above-described structure be observed throughout the entire EML 8.

[0076] When a different element that is in the same group as the constituent elements of the matrix compound (i.e., the same group in the periodic table) and has a smaller periodic number than the constituent elements is mixed (doped) into the matrix 16 as an impurity element, some of the constituent elements of the matrix compound are substituted with the different element. In other words, when a different element that has the same valence electron configuration as the constituent elements of the matrix compound and a large electronegativity (indicating the ease with which electrons are attracted) (in other words, a small ionic radius) is mixed into the matrix 16, some of the constituent elements are substituted with the different element.

[0077] Therefore, when a second Group VI element that is one or more periods higher than the first Group VI element contained in the matrix compound is mixed into the matrix 16, a portion of the first Group VI element contained in the matrix compound is replaced with the second Group VI element. Because the second Group VI element has a smaller period number than the first Group VI element, it has a valence orbital and the same number of valence electrons as the first Group VI element of the matrix compound, a larger electronegativity, and a smaller ionic radius than the first Group VI element. Therefore, even when the second Group VI element is mixed into the matrix 16, the matrix remains electrically neutral and the conduction type does not change. However, the second Group VI element has a larger electronegativity than the first Group VI element, and therefore is more likely to attract electrons around the second Group VI element. As a result, free electrons present in the parent compound are bound around the added second Group VI element, causing uncertainty in the wave function, resulting in broadening of the wave function. Energy levels (electron trap levels) resulting from excitons bound to the second Group VI element, which is an impurity element, corresponding to this broadening of the wave function appear within the band gap of the parent compound. Such energy levels (electron trap levels) bound by impurity atoms with the same valence electron configuration are called isoelectronic levels, isoelectronic traps, or isoelectronic bands.

[0078] In this way, when the base material 16 is doped with the second group VI element, a portion of the first group VI element in the base compound is replaced with the second group VI element, which locally changes the state of valence electrons and forms an isoelectronic level (isoelectronic band) within the band gap of the base compound.

[0079] Fig. 4 is a schematic diagram showing an example of the band structure of each functional layer (HTL6, EML8, and ETL10) between the anode 4 and the cathode 12 in the light-emitting device 2 shown in Fig. 1 when the functional layer is in an isolated state (in other words, when each functional layer is in isolation). Fig. 5 is a schematic diagram showing an example of the band structure of each functional layer when the functional layers shown in Fig. 4 are joined and band-shifted so that their Fermi levels coincide. Note that Figs. 4 and 5 show, as an example, the band structure of each functional layer when the base material 16 of the EML8, which uses ZnS as the base compound, is doped with O as a second Group VI element (O-doped).

[0080] For comparison, FIGS. 6 and 7 show the band structures of each functional layer in a comparative light-emitting device having the same configuration as the light-emitting device 2 shown in FIG. 1 , except that the host material 16 of the EML 8 is not doped with impurities. FIG. 6 is a schematic diagram showing an example of the band structure of each functional layer (HTL6, EML8, and ETL10) between the anode 4 and the cathode 12 in an isolated state in a comparative light-emitting device having an EML 8′ containing a host material 16 not doped with impurity elements and QDs 14. FIG. 7 is a schematic diagram showing an example of the band structure of each functional layer in a state where the functional layers shown in FIG. 6 are bonded together and band-shifted so that their Fermi levels are aligned. That is, in FIGS. 5 and 7 , the Fermi levels of the functional layers are aligned to compare the energy levels.

[0081] The effect obtained by the base material 16 containing the second Group VI element will be described below using the case where O is doped as the second Group VI element as described above as an example.

[0082] As mentioned above, O is a Group VI element, just like S in the parent compound, and is a higher element than S in the periodic table. Therefore, O has a valence orbital and the same number of valence electrons as S in the parent compound, but its electronegativity is greater than that of S, and its ionic radius is smaller than that of S. O, which replaces S by doping, locally changes the state of the valence electrons, creating an isoelectronic trap level.

[0083] This isoelectronic trap level is formed in the band gap of the parent compound of EML8 at a position close to the conduction band minimum (CBM) and has a density of states at least equivalent to the doped O concentration. Therefore, as shown in FIGS. 4 and 5, the isoelectronic trap level E Ｔ When O is doped, the band gap of EML8 is equivalently narrowed, and the CBM of EML8 is effectively deepened. Ｆ The Fermi level E Ｆ is the level at which the probability of electron existence is 1 / 2. Fermi level E Ｆ In the case of an intrinsic semiconductor, the Fermi level E Ｆ is half the level effectively deepened by O doping from the band gap of ZnS (in other words, the isoelectronic level E Ｔ The band gap shifts to a deeper position by 1 / 2 of the amount of reduction of the band gap equivalently reduced by the O doping. Since O has the same valence as S and the free electron density does not change due to O doping, the base material 16 maintains its intrinsic carrier density, and the Fermi level E of the EML Ｆ is the distance between the valence band edge (VBM) of EML8 and the O isoelectronic level E Ｔ In addition, the isoelectronic band of O in ZnS has a density of states that is approximately the same as the density of added O, so that the injected carriers can be transported.

[0084] On the other hand, as shown in FIGS. 6 and 7, when O doping is not performed, the Fermi level difference between the EML8 and the HTL6 is small and the junction shift of each functional layer is small, so that the hole injection barrier is high.

[0085] Therefore, as shown in Fig. 5, by doping with O, the band shift and bending occurring at the junction between HTL6 and inorganic EML8 are smaller than in the comparative light-emitting device shown in Fig. 7. Therefore, in Light-Emitting Device 2, as shown in Fig. 5, the hole injection barrier to inorganic EML8 as seen from HTL6 is lowered compared to the comparative light-emitting device shown in Fig. 7, improving the hole injection efficiency. On the other hand, as shown in Figs. 5 and 7, the electron injection efficiency is the same whether or not O is doped.

[0086] Light-emitting devices using QDs as the light-emitting material generally have a higher electron injection rate than hole injection rate in the EML, resulting in problems of excessive electron supply and hole shortage. Even if the EML8 is made inorganic by the host material 16, the electron excess remains. Therefore, improving the hole injection efficiency improves the carrier balance in the inorganic EML8, thereby improving the external quantum efficiency (EQE).

[0087] Therefore, as described above, the light-emitting device 2 includes the EML 8 and the HTL 6 provided adjacent to the EML 8, the EML 8 includes the host material 16 containing at least one type of inorganic compound and a plurality of QDs 14, the host material 16 includes, as the inorganic compound, at least one type of host compound containing a first group VI element as a main component, and also includes a second group VI element having a smaller periodic number than the first group VI element, and the total concentration of the second group VI element in the host material 16 is 1×10 １６ atoms / cm ３ That's it, 1 x 10 ２０ atoms / cm ３ By ensuring that the content is within the following range, the carrier balance between holes and electrons can be improved, and a light-emitting element 2 with excellent light-emitting properties can be provided.

[0088] According to this embodiment, as described above, the total concentration of the second group VI element in the base material 16 is 1×10 １６ atoms / cm ３ When the second group VI element is mixed in such a manner as described above, the second group VI element forms an isoelectronic trap level E Ｔ Form.

[0089] The concentration is determined so that the second Group VI element does not reach the isoelectronic trap level E Ｔ The total concentration of the second group VI element in the base material 16 is 1×10 １６ atoms / cm ３ That's it, 1 x 10 ２０ atoms / cm ３By doping the second group VI element within the following range, the top of the valence band of the HTL6 and the top of the valence band of the EML8 become closer, the hole injection barrier from the HTL6 to the EML8 becomes smaller, and the hole injection efficiency improves.

[0090] However, when the total concentration of the second group VI element in the base material 16 reaches the composition level of the base compound that constitutes the base material 16, the valence orbital energy of the second group VI element affects the interatomic bonds.

[0091] For example, as described above, when the parent compound is ZnS and the second VI group element is O, the energy of the valence electron orbitals is O>S for both the p orbital and the s orbital. Therefore, if O is at the composition level of the parent compound, the band shifts in the direction of shallowing the CBM. As a result, the band gap of the parent crystal expands. In such a situation, the Fermi level E Ｆ Since the thickness of the HTL layer 6 is shifted shallower, the injection layer barrier to the inorganic EML layer 8 is enlarged, suppressing hole injection.

[0092] Therefore, the total concentration of the second group VI element in the base material 16 is 1×10 , which is a concentration less than the composition of the base compound so as not to exceed the range of impurity level concentration (so-called doping concentration). ２０ atoms / cm ３ It is required to be within the following range.

[0093] In this way, when the second Group VI element is O, the upper limit of the O concentration below the composition of the parent compound is 1×10 ２０ atoms / cm ３ (composition 0.1%). O is at the isoelectronic trap level E Ｔ The lower limit of the concentration for forming １６ atoms / cm ３ Therefore, as described above, the total concentration of the second group VI element in the base material 16 is 1×10 １６ atoms / cm ３ That's it, 1 x 10 ２０ atoms / cm ３ It is mixed into the base material 16 so as to be within the following range.

[0094] The total concentration of the first group VI element in the base material 16 is preferably 10 times or more greater than the total concentration of the second group VI element in the base material 16. ５ It is more desirable to have it more than twice as large.

[0095] The first group VI element is contained in the base material 16 at a composition level, so that the total concentration of the first group VI element in the base material 16 is at least 1×10 ２１ atoms / cm ３ In addition, the base material 16 is 1 × 10 ２１ atoms / cm ３ The elements contained in the base material 16 are the main components of the base material 16. In other words, the base material 16 contains 1×10 ２１ atoms / cm ３ The elements contained above are the main components of the matrix compound. The main component is not limited to one type of element. The matrix 16 may contain two or more types of first group VI elements as the main component. The matrix 16 may also contain a group II element as the main component. The group II element may be one of the main components or may not be the main component. The matrix 16 may have a concentration of 1×10 ２０ atoms / cm ３ Over 1x10 ２１ atoms / cm ３ The base material 16 may contain elements other than the first group VI element and the second group VI element at a composition level within a range of less than 10 ...

[0096] On the other hand, the total concentration of the second group VI element in the base material 16 is at most 1×10 ２０ atoms / cm ３ Therefore, the total concentration of the first group VI element in the base material 16 is 10 times or more greater than the total concentration of the second group VI element in the base material 16. Note that the total concentration of the second group VI element in the base material 16 is an impurity concentration as described above, and taking into consideration the detection limit, it is 1×10 １６ atoms / cm ３ Since the lower limit is 10.times.10, the total concentration of the first group VI element in the base material 16 is 10.times.10 lower than the total concentration of the second group VI element in the base material 16.times.10５ It is more desirable to have it more than twice as large.

[0097] As described above, the base material 16 is doped with O as an impurity, and the incorporation of O into the crystal of the base compound can be determined from the chemical shift of O in element concentration analysis using an electron probe microanalyzer (EPMA). In this way, the doping of the second Group VI element into the base material 16 as an impurity can be determined by EPMA.

[0098] The total concentration of the second group VI element in the base material 16 can be measured by secondary ion mass spectrometry (SIMS). The concentration can also be measured by Auger electron spectroscopy (AES). The lower limit of detection accuracy is SIMS (ppm) < AES (%), and SIMS has 10,000 times higher detection accuracy than AES. The lower limit of spatial resolution is AES (30 nm) < SIMS (200 nm). SIMS has a coarser spatial resolution, 6.7 times higher than AES, but SIMS can also perform analysis on a scale much smaller than one pixel. Therefore, although AES can be used to measure the concentration, SIMS is more preferable due to its high detection accuracy.

[0099] Furthermore, in this embodiment, since the organic ligands are removed by mineralization, it can be determined that the second Group VI element detected by SIMS, EPMA, etc. is not derived from an organic substance but has been added to the base material 16.

[0100] FIG. 8 is a graph showing the J-V characteristics of the light-emitting element 2 according to the present embodiment, in which the base material 16 having ZnS as the base compound is doped with O, and the J-V characteristics of the light-emitting element for comparison, in which the base material 16 having ZnS as the base compound is not doped with O.

[0101] 8, the solid line shows the J-V characteristics of the relationship between the voltage applied to the light-emitting element 2 and the current flowing through the light-emitting element 2 via the junction between HTL6, EML8, and ETL10, as indicated by I in Fig. 1. The dashed line shows the J-V characteristics of the relationship between the voltage applied to the comparative light-emitting element and the current flowing through the comparative light-emitting element via the junction between HTL6, EML8, and ETL10 in the comparative light-emitting element.

[0102] From Figure 8, it can be seen that by doping the base material 16 with O, the current rise voltage of the light-emitting element 2 is reduced by about 1 V compared to the current rise voltage of the comparative light-emitting element, and the slope becomes steeper.

[0103] In general, the current flowing in the light-emitting element exhibits a steeper slope as the injected carriers radiatively recombine more efficiently. As described above, the current I flowing in the light-emitting element 2 via the junctions of the HTL 6, EML 8, and ETL 10 contributes to the radiative recombination of carriers.

[0104] Therefore, from the results shown in FIG. 8, it can be inferred that by doping the base material 16 with O, carriers are efficiently injected into the inorganic EML 8, and the radiative recombination efficiency of the injected carriers is improved.

[0105] 9 and 10 are graphs showing the light-emitting characteristics of the light-emitting element 2 according to this embodiment, in which the base material 16 having ZnS as the base compound is doped with O, and the light-emitting characteristics of the comparative light-emitting element, in which the base material 16 having ZnS as the base compound is not doped with O.

[0106] 9, the solid line indicates the relationship between the current density applied to the light-emitting element 2 and the external quantum efficiency (EQE) as the light-emitting characteristic, and the dashed line indicates the relationship between the current density applied to the comparative light-emitting element and the EQE as the light-emitting characteristic. In Fig. 10, the solid line indicates the relationship between the voltage applied to the light-emitting element 2 and the EQE as the light-emitting characteristic, and the dashed line indicates the relationship between the voltage applied to the comparative light-emitting element and the EQE as the light-emitting characteristic.

[0107] As shown in FIG. 9, the maximum value of the EQE (peak EQE) for the comparative light-emitting element is about 5%, whereas the peak EQE for the light-emitting element 2 is about 12%. This means that the EQE is significantly improved by doping the base material 16 with O. This light-emitting characteristic is consistent with the prediction from the J-V characteristics shown in FIG. 8. Furthermore, the current density at which the peak EQE is shown is 1 mA / cm for the comparative light-emitting element. ２ while for Light-emitting element 2 it was 10 mA / cm ２ This suggests that carriers have been injected to a level that matches the radiative recombination rate of the QDs 14 contained in the inorganic EML 8. This result indicates that almost all of the current flowing through the light-emitting element 2 is injected into the EML 8 without waste and contributes to light emission.

[0108] Furthermore, as shown in Figure 10, the voltage at which the peak EQE of light-emitting element 2 shows is shifted by about 2 V to the lower voltage side compared to the comparative light-emitting element, indicating that the carrier injection loss has been significantly reduced.

[0109] The base material 16 may further contain at least one halogen element. For example, as shown in Fig. 2, the base material 16 may contain halide ions 16H having at least one of fluoride ions, chloride ions, bromide ions, and iodide ions.

[0110] The halogen element binds to the unpaired electron of the host compound to stabilize it, thereby passivating defects in the host material 16. Here, "passivating defects in the host material 16" means that the unpaired electron is used to bond with the halogen element, so that the defects no longer function as non-radiative centers or carrier traps. Furthermore, as shown in FIG. 2, the presence of halide ions 16H near the surface of the QD14 improves the dispersibility of the QD14. Therefore, it is desirable for the host material 16 to contain a halogen element. The area near the surface of the QD14 may be within a range approximately the thickness of the shell 14S.

[0111] The base material 16 may contain 1 atomic % or more of halogen elements. The total concentration of halogen elements in the base material 16 is 1×10１６ atoms / cm ３ The total concentration of halogen elements in the base material 16 is preferably 1×10 １９ atoms / cm ３ It is desirable that the following:

[0112] The halogen elements need only be contained in the base material 16 to an extent that they fill defects in the base material 16. The total concentration of the halogen elements in the base material 16 need only be significantly lower than the composition of the base material 16, and if the total concentration of the halogen elements in the base material 16 reaches the composition level of the base material 16, the properties of the base material 16 may change. Furthermore, if halogen elements that are not incorporated into the composition of the base material 16 are present at a high density, there is a high possibility that the quality of the base material 16 will be significantly degraded.

[0113] For this reason, (i) as described above, the total concentration of halogen elements in the base material 16 must be set lower than the composition level of the base material 16, and (ii) the planar defect density of heteroepitaxially grown GaN / sapphire, which has a high defect density, is 1×10 ９ / cm ２ (iii) the temperature at which the base material 16 is synthesized is significantly lower than the general semiconductor growth temperature; (iv) a II-VI compound that is prone to group IV deficiency is used as the base compound; and (v) the defect area density in the base material 16 is at least 1×10 １０ / cm ２ Considering this, the total concentration of halogen elements in the base material 16 is estimated to be on the order of 1×10 １６ atoms / cm ３ That's it, 1 x 10 １９ atoms / cm ３ It is desirable that the following:

[0114] The concentration of halide ions 16H near each QD 14 in the EML 8 is preferably higher than the concentration of halide ions 16H further away from the QD 14. For example, the vicinity of a QD 14 may be within 1 nm of the outermost surface of the QD 14.

[0115] 2, the average total concentration of halogen atoms within a distance DA of 1 nm from the outer surface of the shell 14S, which is the outermost surface of the QD14, may be higher than the average total concentration of halogen atoms at other positions. In this case, the average total concentration of halogen atoms within the distance DA of 1 nm may be 10% or more higher, 50% or more higher, or 100% or more higher than the average total concentration of halogen atoms at other positions. Such a concentration distribution can be confirmed, for example, by elemental mapping using cross-sectional TEM-EDX (transmission electron microscope-energy dispersive X-ray spectroscopy).

[0116] Note that "other positions" here can also be referred to as positions where no QD14 is present within 1 nm. Multiple QD14s are contained within the EML8. Therefore, the above value can be considered to be a comparison between the average total halogen atom concentration within a 1 nm radius around each QD14 in the EML8 and the average total halogen atom concentration in the EML8 that is more than 1 nm away from any QD14.

[0117] In other words, it is preferable that the average value of the total concentration of halogen elements in the region within 1 nm from the outermost surface of each of the multiple QDs 14 in the base material 16 is higher than the average value of the total concentration of the halogen elements in the region in the base material 16 that is more than 1 nm away from the outermost surface of each of the multiple QDs 14, and may be, for example, 10% or more, 50% or more, or 100% or more higher.

[0118] This can further improve the dispersibility of the QDs 14, and can form an EML 8 with a more uniform thickness.

[0119] The host material 16 can include halide ions by forming the EML 8 using a QD dispersion that includes a halogen element and QDs 14 .

[0120] (Method for Manufacturing the Light-Emitting Element 2) Next, a method for manufacturing the light-emitting element 2 according to this embodiment will be described below with reference to Fig. 11. Fig. 11 is a flowchart showing an example of the method for manufacturing the light-emitting element 2 according to this embodiment.

[0121] As shown in FIG. 11 , in the method for manufacturing the light-emitting device 2 according to this embodiment, first, an anode 4 is formed on a substrate 3 serving as a support (step S1, anode formation step), as shown in FIG. 14 below. Next, an HTL 6 is formed (step S2, HTL formation step). In parallel, a QD dispersion is prepared (prepared) (step S11, QD dispersion preparation step). Next, an EML 8 is formed using the QD dispersion (step S3, EML formation step). Next, an ETL 10 is formed (step S4, ETL formation step). Next, a cathode 12 is formed (step S5, cathode formation step). This completes the manufacture of the light-emitting device 2.

[0122] The anode 4 is formed in step S1 and the cathode 12 is formed in step S5 by, for example, vapor deposition or sputtering.

[0123] The HTL 6 is formed in step S2 and the ETL 10 is formed in step S4 by, for example, vacuum deposition, sputtering, a coating method using a colloidal solution, a sol-gel method, or the like.

[0124] Before explaining step S3, step S11 will be explained in more detail.

[0125] (Step S11) The QD dispersion preparation step of step S11 includes a ligand substitution step (step S21) of substituting the ligand coordinated to the QDs 14.

[0126] In many cases, synthesized or commercially obtained QDs have organic ligands coordinated as ligands. Commercially available QDs are generally provided in the form of a QD dispersion containing an organic ligand. The organic ligand is used as a dispersant to improve the dispersibility of QDs in the QD dispersion, and is also used to improve the surface stability and storage stability of QDs. Furthermore, QDs are synthesized, for example, by a wet method, and the particle size of QDs is controlled by coordinating organic ligands to the surface of the QDs. Therefore, QD dispersions synthesized by a wet method contain the organic ligands used in the synthesis of QDs. Therefore, in this embodiment, a ligand substitution process is carried out to substitute the ligands coordinated to QDs in order to mineralize EML8.

[0127] In this embodiment, the QD dispersion contains, for example, halide ion-coordinated QDs, and the ligand substitution step involves substituting the organic ligand with the halide ion, thereby coordinating the halide ion to the QDs.

[0128] A method for substituting the organic ligands coordinated to the QD 14 with halide ions 16H will be described below with reference to FIG.

[0129] 12 is a cross-sectional schematic diagram illustrating the ligand substitution process (step S21) shown in FIG. 11 . As shown in FIG. 12 , in the ligand substitution process, a first solution 20 containing dissolved halide ions 16H and a second solution 22 containing dispersed QDs 14 coordinated with carbon chains CC as organic ligands are first poured into a container 18 (step S21a). The first solution 20 contains a first solvent 24 in which halide ions 16H are soluble, and the second solution 22 contains a second solvent 26 in which carbon chains CC are soluble. For example, the second solvent 26 has a different polarity from the first solvent 24 and a lower specific gravity than the first solvent 24. A separation liquid 28 having a specific gravity and polarity between the first solvent 24 and the second solvent 26 may be poured into the container 18 to more clearly distinguish the boundary between the first solution 20 and the second solution 22.

[0130] The first solvent 24 may contain at least one organic solvent selected from the group consisting of, for example, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N-methylformamide (NMF), formamide, N,N'-dimethylpropyleneurea, dimethylacetamide, N-methylpyrrolidone, gamma-butyrolactone, propylene carbonate, acetonitrile, 2-methoxyethanol, methyl acetate, ethyl acetate, ethyl formate, methyl formate, tetrahydrofuran, diethyl ether, tetrahydrothiophene, and diethyl sulfide. In this case, the first solvent 24 effectively disperses both the QDs 14 coordinated with halide ions 16H and the precursor of the base material 16. The first solvent 24 may also be a polar solvent with a higher polarity than the second solvent 26. The first solvent 24 may be prepared by dispersing, for example, zinc chloride, sodium chloride, hydrochloric acid, or the like in NMF, DMF, DMSO, or the like. The second solvent 26 is preferably, for example, toluene, hexane, octane, octadecene, etc. The second solvent 26 is preferably a non-polar solvent that is immiscible with the first solvent 24.

[0131] The carbon chain CC may be a carbon chain commonly used as a ligand for QDs. Because the second solvent 26 is a solvent in which the carbon chain CC is soluble, the QDs 14 coordinated with the carbon chain CC are easily dispersed in the second solution 22. Furthermore, the first solution 20 contains an excess amount of halide ions 16H that exceeds the amount of halide ions 16H that can coordinate to the QDs 14. The concentration of halide ions 16H in the first solvent 24 is preferably 0.01 mol / L or higher, and more preferably 0.1 mol / L or higher.

[0132] Next, the container 18 containing the first solution 20 and the second solution 22 is vibrated at high speed by a stirrer to mix the first solution 20 and the second solution 22 (step S21b). To improve the efficiency of the mixing, a stir bar may be placed in the container 18. In other words, the process of mixing the first solution 20 and the second solution 22 is a process of treating the QDs 14 with the halide ions 16H, and in particular, a process of producing QDs 14 coordinated with the halide ions 16H.

[0133] As described above, the first solution 20 contains an excess of halide ions 16H. Generally, when two or more types of ligands are contained in a solution in which QDs are dispersed, the ligands coordinated to the QDs are in equilibrium with each other among the ligands in the solution. Therefore, when the first solution 20 and the second solution 22 are stirred, at least a portion of the ligands coordinated to the QDs 14 are replaced by halide ions 16H from the carbon chains CC.

[0134] For example, in step S21b, the solution in container 18 is stirred for at least one minute. Alternatively, the solution in container 18 may be stirred for one hour at a temperature of 25°C and a frequency of 10 vibrations per minute. Under these conditions, it can be said that there is a sufficiently high probability that the ligands coordinated to the QDs 14 in container 18 have been replaced with halide ions 16H. Furthermore, it is more desirable to stir the solution in container 18 in an atmosphere of nitrogen, argon, or the like, so that atmospheric water or oxygen does not mix with the solution in container 18.

[0135] 12 , a third solution 30 in which QD14 coordinated with halide ions 16H is dispersed in first solvent 24, and a fourth solution 32 in which carbon chains CC are dissolved in second solvent 26 are obtained in container 18. As a result, QD14 coordinated with halide ions 16H is obtained in third solution 30. The stirring may be completed when ultraviolet light or the like is irradiated onto the liquid in container 18 and it is confirmed that the luminescent liquid layer has shifted from the top to the bottom of container 18.

[0136] Next, a QD dispersion step (step S22) is performed in which the QDs 14 coordinated with the halide ions 16H and the precursor of the base material 16 are dispersed in a solvent, thereby producing a QD dispersion liquid containing the QDs 14 coordinated with the halide ions 16H, the precursor of the base material 16, and the solvent, which is used to form the EML 8 in step S3.

[0137] FIG. 13 is a cross-sectional view showing a schematic configuration of the QD dispersion liquid 38 used to form the light-emitting element 2 according to this embodiment, which is manufactured in step S22.

[0138] In step S22, for example, subsequent to step S21, only the third solution 30 is extracted from the container 18 using a dropper or the like. Then, this extracted third solution 30 is mixed with a precursor solution in which a precursor 36, which is a precursor of the base material 16, is dispersed in, for example, the first solvent 24, in a container 34 shown in Fig. 13. As a result, as shown in Fig. 13, the QDs 14 coordinated with the halide ions 16H and the precursor 36 are dispersed in, for example, the first solvent 24, and a QD dispersion 38 containing the QDs 14, the precursor 36, and the first solvent 24 is produced (prepared).

[0139] The precursor solution may be injected into the container 18 before the third solution 30 is injected, or the precursor solution may be injected into the container 18 after or simultaneously with the injection of the third solution 30. The order of adding (injecting) the third solution 30 and the precursor solution is not particularly limited.

[0140] The precursor 36 contains a first Group VI element. When the first Group VI element is S and the matrix compound is, for example, a metal sulfide such as ZnS as described above, the precursor 36 may contain, as a Group II element source containing a Group II element, at least one metal source containing a Group II element as a metal element, for example, selected from the group consisting of metal acetates, metal nitrates, and metal halides.

[0141] In this case, the precursor 36 may contain, as the first Group VI element source containing the first Group VI element, at least one sulfur source containing sulfur as the first Group VI element, for example, selected from the group consisting of thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N′-dimethylthiourea, tetramethylthiourea, and thioacetamide.

[0142] Furthermore, the precursor 36 may contain a metal complex in which thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N'-dimethylthiourea, tetramethylthiourea, or thioacetamide is coordinated to a metal element (for example, a metal atom).

[0143] The second group VI element may be contained in the precursor 36, or may be contained in, for example, the first solvent 24 in which the precursor 36 is dispersed, or may be added after the third solution 30 and the precursor solution are mixed together. The method for doping the second group VI element into the base material 16 is not particularly limited.

[0144] When the base material 16 contains O as the second group VI element, O can be mixed into the base material 16 by, for example, adjusting the pH of the QD dispersion liquid 38 so that the pH of the QD dispersion liquid 38 becomes slightly acidic, for example, about pH 6.5. To adjust the pH of the QD dispersion liquid 38, an acid may be added. A small amount of acid may be added to slightly lower the pH and reduce the OH concentration. － By slightly increasing the concentration, a small amount of O can be mixed into the base material 16 .

[0145] The amount of acid required for pH adjustment can be determined by the following formula (1): pH is calculated by the following formula (1): Z = (N x n x Q x 10 ５ ) / (60 × W × D) ... (1) n (H ＋ Just take the common logarithm of the concentration.

[0146] In the formula (1), Z represents the required amount of acid (mL), N represents 1 gram equivalent of acid (g), and n represents the target H ＋ Q is the total amount of solvent (m ３ For example, when the first solvent 24 is used as the solvent as described above, Q represents the total amount of the first solvent 24. W represents the concentration (wt%) of the acid. D represents the specific gravity of the acid.

[0147] Examples of the acid include hydrochloric acid (HCl), sulfuric acid (H ２ SO ４ ), phosphoric acid (H ３ P.O. ４ ) or the like can be used. Among these acids, HCl, which does not contain P, S, or the like, is preferably used. HCl is composed only of elements contained in the precursor 36 for mineralization and the first solvent 24, so that no different elements are mixed into the base material 16.

[0148] Adding an acid in this manner changes the pH of the first solvent 24, which in turn changes the pH of the QD dispersion 38. Changing the pH of the QD dispersion 38 also changes the reaction of the precursor 36. Therefore, when adjusting the pH of the QD dispersion 38 by lowering the pH of the QD dispersion 38 with an acid, it is desirable to change the reaction temperature depending on the pH, or, if the reaction temperature is not changed, to extend the reaction time. This allows the layer thickness of the mineralized EML 8 to be maintained constant.

[0149] When the base material 16 contains a group VI element other than O as the second group VI element, for example, a precursor 36 containing a second group VI element source at the above-mentioned impurity concentration may be used to mix the second group VI element other than O into the base material 16. Alternatively, a compound of the same group II element as the group II element source contained in the precursor 36 may be dispersed in the first solvent 24 together with the precursor 36 as a compound containing the second group VI element. By dispersing the plurality of QDs 14, the precursor 36 containing the first group VI element, the compound containing the second group VI element, and the first solvent 24, the concentration of the second group VI element in the base material 16 becomes 1×10 １６ atoms / cm ３ That's it, 1 x 10 ２０ atoms / cm ３ The QD dispersion 38 may be prepared to contain the following ranges:

[0150] Next, step S3 will be described in more detail.

[0151] (Step S3) FIG. 14 is a cross-sectional view showing an example of a method for forming the EML 8. In FIG.

[0152] As shown in FIG. 14 by S2, at the completion of step S2, the substrate 3, the anode 4, and the HTL 6 are formed.

[0153] In step S3, first, the QD dispersion 38 produced in step S11 is applied onto the HTL 6. This forms a coating layer 8A containing the QD dispersion 38 as a coating film on the HTL 6 (step S31, QD dispersion application step).

[0154] The coating film may be formed by any method, such as bar coating, spin coating, or ink jet printing.

[0155] Next, the coating layer 8A is baked (heated) or the like to remove the first solvent 24 contained in the coating layer 8A, and the coating layer 8A is dried (step S32, solvent removal step).

[0156] As an example, in step S32, after step S31, the layered structure from the substrate 3 to the coating layer 8A is heated at a temperature of 80°C to 500°C for at least one minute to dry the coating layer 8A. As the coating layer 8A dries, the precursor 36 is denatured (crystallized). This results in the formation of a matrix 16 that contains a matrix compound primarily composed of at least one first group VI element and at least one second group VI element at the impurity level concentration (so-called doping concentration) described above. This results in the formation of an EML 8 on the HTL 6, which includes the matrix 16 containing the first and second group VI elements and the QDs 14.

[0157] The concentration of the second Group VI element in the EML 8 mineralized by such a procedure can be quantified by, for example, SIMS, as described above. For example, the precursor 36 may contain zinc acetate (ZnC ４ H ６ O ４ ) was used as the sulfur source, and thiourea (CH ４ N ２ The EML8 was formed by using ZnS as the matrix compound and O as the second Group VI element using dimethyl sulfoxide as the first solvent 24 and HCl as the acid, adjusting the pH of the QD dispersion 38 to, for example, pH 6.5. The concentration of O in the resulting EML8 was measured by SIMS and found to be 1×10 １６ atoms / cm ３ The fact that O, the second Group VI element, is doped as an impurity can be determined by evaluating the chemical shift of O using EPMA. In addition, since the organic ligands are removed by mineralization, it can be determined that the O detected by SIMS and EPMA is not derived from organic matter but is added to the base material 16.

[0158] The O concentration is at an impurity level (so-called doping concentration) with respect to the base material 16 and does not reach the composition of the base compound. Ｔ The concentration is equal to or greater than that required to form

[0159] Therefore, in this case, O is trapped at the isoelectronic trap level E in the band gap of the parent compound ZnS. Ｔ As a result, as described above, the CBM of HTL6 and the CBM of EML8 approach each other, the hole injection barrier from HTL6 to EML8 is reduced, and the hole injection efficiency is improved. As a result, the carrier balance between holes and electrons is improved, and as shown in FIGS. 8 to 10, a light-emitting element 2 with excellent light-emitting characteristics can be obtained.

[0160] Furthermore, as described above, when halide ions 16H are coordinated to shell 14S of QD 14, QD 14 has high dispersibility in polar solvents and is less likely to precipitate. Furthermore, the coordination of halide ions 16H to shell 14S of QD 14 suppresses aggregation of QD 14 that occurs when precursor 36 reacts with the surface of QD 14, allowing the dispersibility of QD 14 to be maintained for a long period of time.

[0161] Furthermore, as the drying of the first solvent 24 in the QD dispersion 38 progresses from step S31 to step S32, the concentration of QD14 in the QD dispersion 38 increases. However, as described above, if halide ions 16H are coordinated to the shells 14S of the QD14, the precipitation of the QD14 before the precursor 36 is deposited on the HTL 6 can be suppressed. Therefore, the coordination of halide ions 16H to the shells 14S of the QD14 allows the formation of an EML 8 that is smoother and in which the QD14 are more uniformly dispersed.

[0162] As described above, in step S32, the stack from the substrate 3 to the coating layer 8A is heated to, for example, 80°C to 500°C to form the EML 8. Therefore, it is preferable that all layers from the anode 4 to the coating layer 8A are formed of layers made of inorganic materials. It is more preferable that all layers from the anode 4 to the cathode 12 are formed of layers made of inorganic materials.

[0163] 1 illustrates an example in which the anode 4 is the lower electrode, the cathode 12 is the upper electrode, and the EML 8 is provided on the HTL 6. However, the present disclosure is not limited to this example.

[0164] The light-emitting element 2 may have the cathode 12 as a lower electrode, the anode 4 as an upper electrode, and the HTL 6 provided on the EML 8. Therefore, the light-emitting element 2 may have a configuration in which, for example, the cathode 12, the ETL 10, the EML 8, the HTL 6, and the anode 4 are provided in this order from the lower layer side (for example, the support side (not shown), such as the substrate 3).

[0165] In this case, the stacking order of the light-emitting element 2 is reversed from that of the light-emitting element 2 shown in FIG. Therefore, when manufacturing such a light-emitting element 2, first, a cathode 12 is formed on a substrate 3 serving as a support (step S5, cathode formation step). Next, an ETL 10 is formed (step S4, ETL formation step). In parallel, a QD dispersion is manufactured (prepared) (step S11, QD dispersion manufacturing step). Next, an EML 8 is formed using the QD dispersion (step S3, EML formation step). Next, a HTL 6 is formed (step S2, HTL formation step). Next, an anode 4 is formed (step S1, anode formation step). In this manner, the light-emitting element 2 is manufactured.

[0166] Also in this case, the light-emitting element 2 may have a functional layer (not shown) between the anode 4 and the cathode 12 in addition to the HTL 6 , EML 8 , and ETL 10 .

[0167] Second Embodiment (Schematic Configuration of Light-Emitting Element 2) FIG. 15 is a cross-sectional view showing a schematic configuration of a light-emitting element 2 according to this embodiment.

[0168] As shown in FIG. 15, the light-emitting element 2 includes an ETL 10 provided adjacent to the EML 8 on the opposite side of the EML 8 from the HTL 6 .

[0169] In the light-emitting device 2 according to this embodiment, the total concentration of the second group VI element in the base material 16 on the side closer to the HTL 6 than the center in the thickness direction of the EML 8 is higher than the total concentration of the second group VI element in the base material 16 on the side closer to the electron transport layer than the center in the thickness direction of the EML 8. Therefore, in the EML8 of the light-emitting device 2 according to this embodiment, the base material 16 has a first portion P1 having a relatively high total concentration of the second group VI element and a second portion P2 having a relatively low total concentration of the second group VI element.

[0170] For example, as shown in FIG. 15 , the EML 8 may have a stacked configuration of a first EML 8 a in which the total concentration of the second group VI element in the base material 16 is relatively high, and a second EML 8 b in which the total concentration of the second group VI element in the base material 16 is relatively low.

[0171] For example, the EML 8 may include a first EML 8a adjacent to the HTL 6, and a second EML 8b provided between the first EML 8a and the ETL 10, adjacent to the first EML 8a and the ETL 10. In this case, the base material 16 of the first EML 8a is the first portion P1, and the base material 16 of the second EML 8b is the second portion P2. However, this is not limiting, and for example, as shown in FIG. 18 , an intermediate layer may be provided between the first EML 8a and the second EML 8b.

[0172] The light-emitting element 2 shown in FIG. 15 has, as an example, a configuration in which an anode 4, an HTL 6, an EML 8 consisting of a first EML 8 a and a second EML 8 b provided on the first EML 8 a, an ETL 10, and a cathode 12 are provided in this order from the lower layer side (for example, the support side (not shown), such as the substrate 3).

[0173] The first EML 8a and the second EML 8b have the same thickness and the same configuration except for the difference in the total concentration of the second group VI element in the base material 16, as described above. The total thickness of the first EML 8a and the second EML 8b may be greater than the thickness of the EML 8 according to Embodiment 1, but is preferably the same as the thickness of the EML 8 according to Embodiment 1. The thickness of the EML 8 is designed to optimize the light extraction efficiency. Therefore, even when the EML 8 is divided into the first EML 8a and the second EML 8b, the highest luminous efficiency can be obtained by not changing the overall thickness of the EML 8 from the optimal thickness.

[0174] The sum of the concentrations of the second group VI elements in the base material 16 closer to the HTL 6 than the center of the EML 8 in the thickness direction is 1×10 １９ atoms / cm ３ That's it, 1 x 10 ２０ atoms / cm ３ Therefore, the total concentration of the second group VI element in the first portion P1 in the first EML 8a may be within the range of 1×10 １９ atoms / cm ３ That's it, 1 x 10 ２０ atoms / cm ３ It may be within the following range:

[0175] The sum of the concentrations of the second group VI elements in the base material 16 on the side closer to the ETL 10 than the center of the EML 8 in the thickness direction is 1×10 １６ atoms / cm ３ That's it, 1 x 10 １８ atoms / cm ３ Therefore, the total concentration of the second group VI element in the second portion P2 in the second EML 8b may be within the range of 1×10 １９ atoms / cm ３ That's it, 1 x 10 ２０ atoms / cm ３ However, as described above, it is a prerequisite that the condition (sum of the concentrations of the second group VI elements in the first portion P1)>(sum of the concentrations of the second group VI elements in the second portion P2 in the second EML 8b) is satisfied.

[0176] However, this embodiment is not limited to this. The second group VI element may be mixed only in the base material 16 on a side closer to the HTL 6 than the center in the thickness direction of the EML 8. Therefore, the second group VI element may be mixed only in the second EML 8b of the first EML 8a and the second EML 8b, or the second group VI element may be mixed only in the first portion P1 of the first portion P1 and the second portion P2.

[0177] In this case, the second group VI element may be mixed over a thickness that is half the thickness of the EML8.

[0178] In either case, as described above, the concentration of the second group VI element is relatively high on the side closer to the HTL 6 than to the center in the thickness direction of the EML 8, thereby improving the hole injection efficiency and further improving the EQE.

[0179] Furthermore, as described above, when the total concentration of the second group VI element closer to the HTL6 is relatively high, diffusion of the second group VI element from the EML8 to the HTL6 occurs over time. For example, when the second group VI element is O as described above, O diffuses from the EML8 to the HTL6 over time, suppressing oxygen vacancies in the HTL6. When the above-described HIL is provided between the HTL6 and the anode 4, O diffused from the EML8 to the HTL6 diffuses into the HIL over time, suppressing oxygen vacancies in the HTL6 and the HIL. In particular, in the HIL made of an inorganic material, oxygen vacancies are the source of free electrons, so suppressing oxygen vacancies can suppress the disruption of hole transport due to oxygen vacancies. As a result, a highly reliable light-emitting element 2 can be obtained.

[0180] Fig. 16 is a schematic diagram showing an example of the band structure of each functional layer in the light-emitting device 2 shown in Fig. 15 when the second group VI element is mixed only in the first portion P1 of the first EML 8a and the functional layers (HTL6, first EML 8a, second EML 8b, and ETL10) between the anode 4 and the cathode 12 are in an isolated state. Fig. 17 is a schematic diagram showing an example of the band structure of each functional layer in a state where the functional layers shown in Fig. 16 are bonded and band-shifted so that the Fermi levels are aligned. Note that Figs. 15 and 16 also show, as an example, the band structure of each functional layer when only the first portion P1 of the matrix 16 of the EML 8, which uses ZnS as the matrix compound, is doped with O as the second group VI element (O-doping).

[0181] As shown in FIGS. 15 and 16 , in the light-emitting device 2 according to this embodiment, the O concentration in the first EML 8 a is higher than the O concentration in the second EML 8 b, and the Fermi level E Ｆ The VBM of EML8 and the isoelectronic level of O, E Ｔ Therefore, the hole injection barrier to the first EML 8a as seen from the HTL 6 is lowered, and the hole injection efficiency is improved. As a result, the EQE can be further improved as described above.

[0182] (Method for Manufacturing Light-Emitting Element 2) In this embodiment, QDs 14 are applied in two separate applications in step S3. Specifically, in step S11, two types of QD dispersion liquids 38 with different content ratios of the second Group VI element are prepared as the QD dispersion liquids 38, and in step S3, steps S31 and S32 are repeated twice using each of the QD dispersion liquids 38.

[0183] When the second group VI element is O and only the first portion P1 in the first EML 8a is doped with O, an acid needs to be added only to the QD dispersion 38 used to form the first EML 8a.

[0184] When the second group VI element is O and the first portion P1 in the first EML 8 a and the second portion P2 in the second EML 8 b each contain O as the second group VI element, the concentration of acid added to the QD dispersion 38 used to form the second EML 8 b can be made lower than the concentration of acid added to the QD dispersion 38 used to form the first EML 8 a. Alternatively, the amount of acid added to the QD dispersion 38 used to form the second EML 8 b can be made lower than the amount of acid added to the QD dispersion 38 used to form the first EML 8 a.

[0185] (Modification) The total concentration of the second group VI element in the base material 16 may decrease toward the ETL 10 in the thickness direction of the EML 8. However, in this case, the total concentration of the second group VI element in the base material 16 does not need to decrease linearly toward the ETL 10, but may decrease in steps. The total concentration of the second group VI element in the base material 16 may change continuously or stepwise.

[0186] In the present disclosure, the phrase "the total concentration of the second group VI element in the base material 16 decreases toward the ETL 10 in the thickness direction of the EML 8" includes both a case in which the total concentration of the second group VI element in the base material 16 decreases linearly toward the ETL 10 in the thickness direction of the EML 8, and a case in which the total concentration of the second group VI element decreases stepwise toward the ETL 10.

[0187] In either case, when the EML 8 is divided into a side closer to the HTL 6 and a side farther from the center of the EML 8 in the thickness direction (i.e., the ETL 10 side), the sum of the concentrations of the second group VI elements in the base material 16 on the side closer to the HTL 6 than the center of the EML 8 in the thickness direction is 1×10 １９ atoms / cm ３ That's it, 1 x 10 ２０ atoms / cm ３ The sum of the concentrations of the second group VI elements in the base material 16 on the side closer to the ETL 10 than the center of the EML 8 in the thickness direction may be within the range of 1×10 １６ atoms / cm ３ That's it, 1 x 10 １８ atoms / cm ３ It may be within the following range:

[0188] FIG. 18 is a cross-sectional view showing an example of a schematic configuration of a light-emitting element 2 according to this modification.

[0189] FIG. 18 shows, as an example, a case in which the EML 8 has a configuration in which a first EML 8 a′, a second EML 8 b′, and a third EML 8 c′ are stacked in this order from the HTL 6 side, and the total concentration of the second group VI element in the base material 16 decreases stepwise.

[0190] 18 , the EML8 of the light-emitting element 2 includes a base material 16 including a first portion P11, a second portion P12, and a third portion P13, each having a different total concentration of the second group VI element. The total concentration of the second group VI element in the second portion P12 is smaller than that in the first portion P11, and the total concentration of the second group VI element in the third portion P13 is smaller than that in the second portion P12. In this case, the base material 16 of the first EML 8 a′ corresponds to the first portion P11, the base material 16 of the second EML 8 b′ corresponds to the second portion P12, and the base material 16 of the third EML 8 c′ corresponds to the third portion P13.

[0191] The first EML 8a', the second EML 8b', and the third EML 8c' have the same thickness and the same configuration except for the difference in the total concentration of the second group VI element in the base material 16, as described above. The total thickness of the first EML 8a', the second EML 8b', and the third EML 8c' may be greater than the thickness of the EML 8 according to Embodiment 1, but is preferably the same as the thickness of the EML 8 according to Embodiment 1. In this case, the highest luminous efficiency can be obtained.

[0192] In this case, too, as described above, the concentration of the second group VI element is relatively higher on the side closer to the HTL 6 than on the side closer to the ETL 10, thereby improving the hole injection efficiency and further increasing the EQE.

[0193] Also in this case, since the total concentration of the second group VI element closer to the HTL 6 is relatively large, for example, when the second group VI element is O as described above, O diffuses from the EML 8 to the HTL 6 over time, suppressing oxygen vacancies in the HTL 6. Therefore, a light-emitting element 2 with high reliability can be obtained.

[0194] 18 , in step S3, QDs 14 are applied three times. Specifically, in step S11, three types of QD dispersions 38 with different content ratios of the second group VI element are prepared as the QD dispersions 38, and in step S3, steps S31 and S32 are repeated three times using each of the QD dispersions 38. Note that in this case, the base material 16 of the third EML 8c′ closest to the ETL 10 does not necessarily need to contain the second group VI element.

[0195] To gradually decrease the total concentration of the second group VI element in the base material 16 toward the ETL 10 in the thickness direction of the EML 8, for example, when the second group VI element is O, the concentration of acid added to the QD dispersion 38 used to form the EML closer to the ETL 10 may be gradually decreased compared to the concentration of acid added to the QD dispersion 38 used to form the EML closer to the HTL 6. Alternatively, the amount of acid added to the QD dispersion 38 used to form the EML closer to the ETL 10 may be gradually decreased compared to the amount of acid added to the QD dispersion 38 used to form the EML closer to the HTL 6.

[0196] Alternatively, in step S31, while the QD dispersion 38 is continuously supplied and applied onto the HTL 6, acid of different concentrations may be dropped (supplied) in multiple batches, or the amount of acid dropped may be varied and the acid may be dropped (supplied) in multiple batches. For example, by carefully controlling the amount of acid dropped, or by gradually diluting the acid to decrease its concentration, the total concentration of the second Group VI element in the base material 16 can be gradually decreased (i.e., continuously changed).

[0197] [Embodiment 3] The light-emitting element 2 can be suitably used as a light source for a light-emitting device such as a display device or a lighting device. The light-emitting device may include at least one light-emitting element 2. The following description will be given taking as an example a case where the light-emitting element 2 is used as a light source for a display device.

[0198] Fig. 19 is a plan view showing an example of the configuration of a display device according to this embodiment. As shown in Fig. 19, the display device 100 includes a display unit 15 including a plurality of sub-pixels X, and a driver circuit 25 that drives the display unit 15. For example, the sub-pixels X include the light-emitting element 2 and pixel circuit 5 described in the first or second embodiment. The display device 100 may also be a lighting device.

[0199] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0200] 2 Light-emitting element 6 HTL (hole transport layer) 8 EML (light-emitting layer) 10 ETL (electron transport layer) 16 Base material 14 QD (quantum dot) 14C Core 14S Shell 16H Halide ion 100 Display device

Claims

1. A light-emitting layer and a hole transport layer provided adjacent to the light-emitting layer, the light-emitting layer includes a host material including at least one inorganic compound and a plurality of quantum dots; The base material is The inorganic compound includes at least one base compound mainly composed of a first Group VI element, at least one second Group VI element having a smaller periodic number than the first Group VI element contained in the parent compound; The total concentration of the second group VI element in the base material is 1×10 １６ atoms / cm ３ That's it, 1 x 10 ２０ atoms / cm ３ A light-emitting device characterized in that:

2. 2. The light-emitting device according to claim 1, wherein the host compound is a II-VI compound.

3. 3. The light-emitting device according to claim 1, wherein the first Group VI element is at least one element selected from the group consisting of S, Se, and Te.

4. The quantum dot has a core and a shell, The light-emitting device according to claim 1 or 2, wherein the shell comprises the same material as the host compound.

5. The quantum dot has a core and a shell, 3. The light-emitting device according to claim 1, wherein the band gap of the base material is larger than the band gap of the core or the shell.

6. The light-emitting device according to claim 5 , wherein the band gap of the base material is larger than the band gap of the shell.

7. 5. The light-emitting device according to claim 4, wherein the average distance between the cores of adjacent quantum dots is 3 nm or more.

8. 3. The light-emitting device according to claim 1, wherein the second VI group element is O.

9. The total concentration of the first group VI element in the base material is 10 times higher than the total concentration of the second group VI element in the base material. ５ 3. The light-emitting device according to claim 1, wherein the thickness of the light-emitting device is at least twice as large as that of the light-emitting device according to claim 1.

10. an electron transport layer provided adjacent to the light emitting layer on the opposite side of the light emitting layer to the hole transport layer, 3. The light-emitting element according to claim 1, wherein a total concentration of the second group VI element in the base material on a side closer to the hole transport layer than a center in the thickness direction of the light-emitting layer is greater than a total concentration of the second group VI element in the base material on a side closer to the electron transport layer than a center in the thickness direction of the light-emitting layer.

11. 11. The light-emitting device according to claim 10, wherein the total concentration of the second group VI element in the base material decreases toward the electron transport layer in the thickness direction of the light-emitting layer.

12. the total concentration of the second Group VI element in the base material on a side closer to the hole transport layer than the center in the thickness direction of the light emitting layer is 1×10 １９ atoms / cm ３ That's it, 1 x 10 ２０ atoms / cm ３ Within the following range: the total concentration of the second Group VI element in the base material on a side closer to the electron transport layer than the center in the thickness direction of the light emitting layer is 1×10 １６ atoms / cm ３ That's it, 1 x 10 １８ atoms / cm ３ 11. The light-emitting device according to claim 10, wherein the range is as follows:

13. 11. The light-emitting device according to claim 10, wherein the second Group VI element is mixed only in the base material on a side closer to the hole transport layer than the center in the thickness direction of the light-emitting layer.

14. 14. The light-emitting device according to claim 13, wherein the second group VI element is mixed over a thickness that is half the thickness of the light-emitting layer.

15. 3. The light-emitting device according to claim 1, wherein the base material further contains at least one halogen element.

16. The total concentration of the halogen elements in the base material is 1×10 １６ atoms / cm ３ The light-emitting element according to claim 15,

17. The total concentration of the halogen elements in the base material is 1×10 １９ atoms / cm ３ 17. The light-emitting device according to claim 16, wherein:

18. The light-emitting element according to claim 15, characterized in that the average value of the total concentration of the halogen element in the region of the base material within 1 nm from the outermost surface of each of the plurality of quantum dots is 10% or more higher than the average value of the total concentration of the halogen element in the region of the base material that is more than 1 nm away from the outermost surface of each of the plurality of quantum dots.

19. 3. The light-emitting device according to claim 1, wherein the base material contains at least one of Mg and Li.

20. 3. The light-emitting device according to claim 1, wherein the base material is filled between the quantum dots in the light-emitting layer.

21. The base material is 1000 nm thick in a plane direction perpendicular to the thickness direction of the light emitting layer. ２ 3. The light-emitting device according to claim 1, further comprising a continuous film having an area of ​​at least one of the above.

22. The light-emitting device according to claim 1 , wherein the plurality of quantum dots are dispersed in the base material.

23. 3. The light-emitting device according to claim 1, wherein the quantum dots are encapsulated in the base material.

24. A display device comprising the light-emitting device according to claim 1 or 2.