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

Abstract

A light-emitting element (1) includes an anode (11), a cathode (15), and an EML (13) including a QD (21) and an MX (22). The MX has a first region containing an inorganic compound (23) and a second region containing an inorganic compound (24) in a direction along a straight line (L1) penetrating an outer edge portion (13a) on the anode side and an outer edge portion (13b) on the cathode side in the EML, and the concentration of the inorganic compound (23) in the first region differs from the concentration of the inorganic compound (24) in the second region by a certain degree or more.

Description

Technical Field

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

[0002] Patent document 1 discloses a quantum dot device that has a quantum dot layer including luminescent quantum dots and non-luminescent quantum dots in order to improve luminescent properties. It is disclosed that the shell of the luminescent quantum dots has a larger band gap than the core, thereby exerting a quantum confinement effect and emitting light. Prior art Patent document: U.S. Patent Application Publication No. 2019 / 280232 Summary of the invention Problem to be solved

[0004] However, organic ligands such as oleic acid are arranged in these quantum dots in Patent Document 1. Organic ligands composed of organic substances have problems such as low stability and easy detachment, which leads to a decrease in light emission characteristics and a decrease in reliability.

[0005] Therefore, if an inorganic medium is used instead of an organic ligand to cover the periphery of the quantum dot, the quantum dot can be firmly protected. However, when the periphery of the quantum dot is uniformly covered with an inorganic medium, in order to exert the quantum confinement effect, if an inorganic compound with a large band gap is used as the inorganic medium, the injection efficiency of holes and electron carriers into the quantum dot decreases, which becomes the cause of the reduction in luminous efficiency.

[0006] One aspect of the present disclosure has been made in view of the above-mentioned problems, and an object thereof is to provide a light-emitting element and a display device having high stability, high luminous efficiency and high reliability, and a method for manufacturing the light-emitting element. Technical solutions to solve problems

[0007] In order to solve the above-mentioned problem, one aspect of the present disclosure involves a light-emitting element comprising a first electrode and a second electrode, and a light-emitting layer arranged between the first electrode and the second electrode, the light-emitting layer comprising a plurality of quantum dots and a matrix material, the matrix material comprising a first inorganic compound and a second inorganic compound, the matrix material having a first region comprising at least the first inorganic compound and a second region comprising at least the second inorganic compound in a straight line direction passing through a first outer edge portion on the first electrode side and a second outer edge portion on the second electrode side in the light-emitting layer, the second region being arranged closer to the second outer edge portion than the first region, and a concentration of the first inorganic compound in the first region differs from a concentration of the first inorganic compound in the second region by more than a certain amount.

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

[0009] In order to solve the above-mentioned problems, a method for manufacturing a light-emitting element according to one embodiment of the present disclosure is provided, wherein the light-emitting element comprises a first electrode and a second electrode, and a light-emitting layer arranged between the first electrode and the second electrode, the light-emitting layer comprising a plurality of quantum dots and a matrix material, the matrix material comprising a first inorganic compound and a second inorganic compound, the matrix material having a first region comprising at least the first inorganic compound and a second region comprising at least the second inorganic compound in a straight line direction penetrating a first outer edge portion on the first electrode side and a second outer edge portion on the second electrode side in the light-emitting layer, the second region being arranged closer to the second outer edge portion than the first region, and a concentration of the first inorganic compound in the first region differs from a concentration of the first inorganic compound in the second region by a certain amount or more, the manufacturing method comprising a step of forming the light-emitting layer, the step of forming the light-emitting layer comprising: (1) a step of applying a quantum dot dispersion liquid, wherein the step of applying a first inorganic compound precursor comprising the plurality of quantum dots, a first inorganic compound precursor, a halide ion and a first solvent and wherein the first inorganic compound precursor is thermally decomposed to form a first region; (1) a first film forming step, heating the film of the quantum dot dispersion at a temperature higher than the thermal decomposition temperature of the precursor of the first inorganic compound to thermally decompose at least a portion of the precursor of the first inorganic compound and remove the first solvent, thereby forming a first film including the plurality of quantum dots and a matrix material containing the first inorganic compound; (2) a first inorganic compound precursor solution supplying step, supplying a second inorganic compound precursor solution onto the first film, the second inorganic compound precursor solution containing the second inorganic compound precursor and a second solvent, the second inorganic compound precursor thermally decomposes to form the second inorganic compound; and (3) a second inorganic compound forming step, heating the second inorganic compound precursor solution supplied in the second inorganic compound precursor solution supplying step at a temperature higher than the thermal decomposition temperature of the second inorganic compound precursor to thermally decompose at least a portion of the second inorganic compound precursor and remove the second solvent, thereby forming a matrix material containing the second inorganic compound. Effects of the Invention

[0010] According to one embodiment of the present disclosure, a light-emitting element and a display device having high stability, high luminous efficiency and high reliability, and a method for manufacturing a light-emitting element can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1This is a cross-sectional view showing an example of a schematic configuration of a light emitting element according to the first embodiment. Figure 2 Yes means Figure 1 A cross-sectional view showing an example of a schematic structure of a quantum dot and its vicinity in the light-emitting element shown. Figure 3 Yes means Figure 1 A cross-sectional view showing a state in which adjacent quantum dots are close to each other in a light-emitting element shown. Figure 4 This is a cross-sectional view schematically showing a state of carrier injection in a comparative light-emitting element in which the periphery of a quantum dot is uniformly covered with a matrix material composed of an inorganic compound. Figure 5 Yes means Figure 4 A diagram showing the energy band structure of each functional layer in a comparative light-emitting element is shown. Figure 6 This is a cross-sectional view schematically showing a state of carrier injection in the light-emitting element of the first embodiment when the first inorganic compound is indium sulfide and the second inorganic compound is magnesium sulfide. Figure 7 Yes means Figure 6 A diagram showing the energy band structure of each functional layer in the light-emitting element shown. Figure 8 This is a cross-sectional view showing an example of a measurement direction of the concentrations of the first inorganic compound and the second inorganic compound along an arbitrary straight line in the light-emitting layer of the light-emitting element according to the first embodiment. Fig. 9 It is measured using X-ray photoelectron spectroscopy Figure 8 A graph showing the concentration distribution of indium sulfide and zinc sulfide in the light-emitting layer. Fig.10 This is a cross-sectional view showing another example of the measurement direction of the concentrations of the first inorganic compound and the second inorganic compound along an arbitrary straight line in the light-emitting layer of the light-emitting element according to the first embodiment. Fig.11 Measured using XPS Fig.10 Graph showing the concentration distribution of indium sulfide and zinc sulfide in the light-emitting layer. Fig.12 It is an explanatory diagram of a method of studying the concentration distribution in the film thickness direction of the first inorganic compound and the second inorganic compound contained in the light-emitting layer of the light-emitting element of the first embodiment using a cross-sectional TEM / EDX method. Fig.13 This is another explanatory diagram of a method of studying the concentration distributions of the first inorganic compound and the second inorganic compound in the film thickness direction contained in the light-emitting layer of the light-emitting element of the first embodiment using the cross-sectional TEM / EDX method. Fig.14Measured using cross-sectional TEM / EDX method Fig.12 Graph showing the concentration distribution of indium sulfide and zinc sulfide in the thickness direction of the light-emitting layer. Fig.15 This is a cross-sectional view of another example of the schematic structure of the light emitting element according to the first embodiment. Fig.16 This is a cross-sectional view of still another example of the schematic structure of the light emitting element according to the first embodiment. Fig.17 This is a cross-sectional view of still another example of the schematic structure of the light emitting element according to the first embodiment. Fig.18 This is a cross-sectional view of still another example of the schematic structure of the light emitting element according to the first embodiment. Fig.19 This is a cross-sectional view of still another example of the schematic structure of the light emitting element according to the first embodiment. Fig. 20 This is a cross-sectional view of still another example of the schematic structure of the light emitting element according to the first embodiment. Fig.21 This is a cross-sectional view of still another example of the schematic structure of the light emitting element according to the first embodiment. Fig. 22 This is a flowchart showing the method for manufacturing the light emitting element according to the first embodiment. Fig.23 It is used to illustrate Fig. 22 Schematic cross-sectional view of the ligand replacement step in the quantum dot dispersion production process shown. Fig.24 It is a schematic cross-sectional view showing the steps after the ligand replacement step in the quantum dot dispersion production process. Fig.25 It is shown Fig. 22 FIG. 1 is a cross-sectional view showing an example of a part of the step of forming the light-emitting layer. Fig.26 is a schematic diagram of a reaction scheme for producing the first inorganic compound described above. Fig. 27 This is a graph showing the TGA measurement results of the thermal decomposition of zinc xanthate. Fig.28 This is a graph showing the measurement results obtained by using a film thickness step meter when forming the first film of the light-emitting element of this embodiment. Fig.29 It is shown in Fig. 22 A cross-sectional view showing an example of formation of a first layer formed in the first film formation step shown. Fig.30 It is shown in Fig. 22 A cross-sectional view showing another formation example of the first layer formed in the first film formation step shown. Fig.31 It is shown in Fig. 22 A cross-sectional view showing still another formation example of the first layer formed in the first film forming step shown. Fig.32 It is shown Fig. 22 FIG. 1 is a cross-sectional view showing an example of a part of the step of forming the light-emitting layer. Fig.33 It is shown Fig. 22 Another step cross-sectional view of an example of a part of the step of forming the light emitting layer shown. Fig.34 This is a diagram showing a reaction scheme for forming a metal sulfide from a precursor of the metal sulfide when the base material contains the metal sulfide as an inorganic compound. Fig.35 This is a cross-sectional view showing an example of a schematic configuration of a light emitting element according to a modification of the first embodiment. Fig.36 It is a cross-sectional view showing an example of a possible structure of a light emitting element according to the second embodiment. Fig.37 This is a flowchart of an example of a method for manufacturing a light emitting element according to the second embodiment. Fig.38 It is a plan view of a configuration example of a display device according to a third embodiment. DETAILED DESCRIPTION

[0012] [First embodiment] Hereinafter, one embodiment of the present disclosure will be described in detail. In addition, in the following, the description of "A to B" for two numbers A and B means "A or more and B or less" unless otherwise specified. In addition, in the following, a layer formed by a process before the layer of the comparison object is referred to as a "lower layer", and a layer formed by a process after the layer of the comparison object is referred to as an "upper layer".

[0013] In addition, below, for the convenience of description, the same reference numerals are given to the components having the same functions as the components described previously, and the description thereof will not be repeated. In the embodiments described later, the differences from the embodiments described previously are described. Unless otherwise specified, the same deformation as the embodiments described previously can of course be performed.

[0014] (Schematic Structure of Light Emitting Element) The light-emitting element of this embodiment includes a first electrode and a second electrode, and a light-emitting layer disposed between the first electrode and the second electrode, wherein the light-emitting layer includes a plurality of quantum dots and a matrix material. In addition, hereinafter, the light-emitting layer is sometimes referred to as "EML", the quantum dots are referred to as "QD", and the matrix material is referred to as "MX".

[0015] One of the first electrode and the second electrode is an anode, and the other is a cathode. In the present invention, the layer between the first electrode and the second electrode is called a functional layer. The functional layer includes at least EML.

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

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

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

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

[0020] The anode 11 is an electrode that supplies holes to the EML 13 by applying a voltage. The cathode 15 is an electrode that supplies electrons to the EML 13 by applying a voltage. The anode 11 and the cathode 15 each include a conductive material, and are connected to a power source (eg, a DC power source) not shown to apply a voltage therebetween.

[0021] At least one of the anode 11 and the cathode 15 is a light-transmitting electrode. In addition, either the anode 11 or the cathode 15 may be a so-called reflective electrode having light reflectivity. The light-emitting element 1 can extract light from the light-transmitting electrode side.

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

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

[0024] In the reflective electrode, it is preferred to use a conductive light reflective material with high reflectivity of visible light, such as a metal such as aluminum (Al), copper (Cu), gold (Au), silver (Ag), or an alloy containing these metals such as magnesium-silver alloy (MgAg). In addition, the reflective electrode can also be formed by stacking a layer composed of the above-mentioned light-transmitting material and a layer composed of the above-mentioned light-reflective material.

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

[0026] Examples of organic materials used in HTL 12 include poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl))diphenylamine)] (TFB), poly(4-butyltriphenylamine) (p-TPD), 4,4'-bis(carbazole-9-yl)biphenyl (CBP), polyphenylene vinylene (PPV), and a composite compound of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT:PSS). S), poly (4, 9-dioctylfluorenyl) -2, 7-diyl (4, 4'-bis (carbazole-9-yl) biphenyl (CBP), polyphenylene vinylene (PPV), a composite compound of poly (3, 4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT), TFB (poly [(9, 9-dioctylfluorenyl-2, 7-diyl) -co- (4, 4'- (N-4-sec-butylphenyl)) diphenylamine]) or polyvinyl carbazole (PVK) and the like.

[0027] As the inorganic material used in HTL12, for example, metal oxides such as molybdenum oxide (MoO2, MoO3), nickel oxide (NiO), chromium oxide (Cr2O3), magnesium oxide (MgO), magnesium zinc oxide (MgZnO), lanthanum nickelate (LaNiO3) or tungsten oxide (WO3) can be cited. In particular, as the material of HTL12, a material with large electron affinity and ionization potential is preferred.

[0028] The ETL 14 is a charge transport layer containing an electron transport material and having an electron transport function of transporting electrons injected from the cathode 15 to the EML 13. As the electron transport material, for example, organic materials or inorganic materials conventionally used in ETLs such as QLEDs and OLEDs can be used.

[0029] Examples of the organic material used in the ETL 14 include conductive compounds such as tris(8-hydroxyquinoline)aluminum complex (Alq3), bathocuproin (BCP), or 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (t-Bu-PBD).

[0030] Examples of the inorganic material used for the ETL 14 include metal oxides such as zinc oxide (ZnO), aluminum zinc oxide (AlZnO), lithium zinc oxide (LiZnO), and magnesium zinc oxide (MgZnO). In particular, the material of the ETL 14 is preferably a material with a low electron affinity.

[0031] EML13 includes a plurality of QD21 and MX22. ​​In EML13, holes transported from anode 11 and electrons transported from cathode 15 recombine, and the excitons generated thereby migrate from the conduction band energy level of QD21 to the valence band energy level, thereby emitting light. EML13 includes nano-sized QD21 corresponding to the luminescent color as a luminescent material.

[0032] QD21 is a point where the maximum width of the particle is less than 100nm. Since QD21 is usually composed of semiconductor materials, it is sometimes called semiconductor nanoparticles. In addition, since QD21 is usually composed of inorganic materials, it is sometimes called inorganic nanoparticles. In addition, the structure of QD21, for example, has a specific crystal structure, and is sometimes called nanocrystals.

[0033] The shape of QD21 is not particularly limited as long as it is within the range that satisfies the above-mentioned maximum width, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). For example, it can be a polygonal cross-sectional shape, a rod-shaped three-dimensional shape, a branch-shaped three-dimensional shape, a three-dimensional shape with concave and convex surfaces, or a combination thereof.

[0034] QD21 may also include at least one metal element. Examples of the metal element included in QD21 include Cd, Zn, In, Sb, Al, Si, Ga, Pb, Ge, and Mg. In addition, QD21 may also be a semiconductor material formed by combining at least one metal element with a non-metal element such as S, Te, Se, N, P, and As.

[0035] QD21 can be formed by only the nucleus, or can be a two-component nucleus, a three-component nucleus, or a four-component nucleus. Figure 2 As shown, QD 21 may have a core-shell structure including a core 21C and a shell 21S, or may be a core-shell type or a core-multi-shell type.

[0036] like Figure 2 As shown, in the case where QD21 includes a shell 21S, there is a core 21C in the center, and the shell 21S is arranged on the surface of the core 21C. The shell 21S preferably covers the entire core 21C, but the shell 21S does not need to completely cover the core 21C. The shell 21S can also be formed on a portion of the surface of the core 21C. If QD21 is judged to have a shell 21S formed on a portion of the surface of the core 21C in a cross section of the QD21, or it is judged that the shell 21S surrounds the core 21C, it can be said that it has a core-shell structure. Therefore, as long as it can be judged by observing a cross section of QD21 that the shell 21S covers the entire core 21C. In addition, the above-mentioned cross-sectional observation can be performed, for example, by a scanning transmission electron microscope (STEM) or a transmission electron microscope (TEM).

[0037] In addition, the QD 21 may include doped nanoparticles, or may have a structure with a gradient composition. In addition, the shell 21S may be formed in a state of being solid-solution-coated on the surface of the core 21C. Figure 2 In FIG. 1 , the boundary between the core 21C and the shell 21S is indicated by a dotted line, which means that the present invention is applicable regardless of whether the boundary between the core 21C and the shell 21S can be confirmed by analysis. The shell 21S may be formed into multiple layers.

[0038] QD21 may also include materials used for core materials and shell materials of QDs known in the past in the respective materials of the core 21C and the shell 21S. The core 21C may be composed of Si, Ge, CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, ZnTe, CdSeTe, GaInP, ZnSeTe, etc. The shell 21S may be composed of CdS, ZnS, CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, AIP, etc. As an example, when the shell 21S contains ZnSSe, the ZnSSe contained in the shell 21S may also be ZnSxSe1-x (0≤x≤1). When QD21 has a core-shell structure, examples of the material of QD21 (combination of core 21C / shell 21S materials) include ZnSe / ZnS, InP / ZnS, CdSe / CdS, CdSe / ZnSe, CIGS / ZnS, and the like.

[0039] It should be noted that the compositions expressed as chemical formulae in the present disclosure are representative examples, and the composition ratios described in the chemical formulae are ideal as long as the composition of the actual compound is stoichiometric as shown in the chemical formulae. The composition ratio described in the chemical formula is preferably a stoichiometric ratio in which the composition of the actual compound is completely consistent with the chemical formula, but this does not exclude cases other than stoichiometric ratio.

[0040] QD21 can change the emission wavelength in various ways by adjusting the particle size, composition, etc. QD21 is a QD that emits visible light, and the emission wavelength can be controlled to be in the blue to red wavelength range by appropriately adjusting the particle size and composition of QD21.

[0041] The core 21C of QD21 has a valence band energy level and a conduction band energy level, and is a luminescent material that emits light by recombination of holes in the valence band energy level and electrons in the conduction band energy level. Since the light emitted from QD21 has a narrow spectrum due to the quantum confinement effect, light with a deep chromaticity can be obtained.

[0042] Also, QD21 in EML13 does not need to be Figure 1 QD21 may be arranged regularly as shown in FIG. 1 , or may be included in EML13 in an unordered manner. Figure 1 As shown in FIG. 1 , MX22 is formed between adjacent QD21, and the state in which QD21 are not close to each other can also be as shown in FIG. Figure 3 The EML 13 shown includes two or more QDs 21 close to each other. The layer thickness of the EML 13 can be the same as in the conventional method and is not particularly limited.

[0043] MX22 is MX with an inorganic compound (inorganic medium) as a main material, and as an inorganic compound, contains at least two or more inorganic compounds including an inorganic compound 23 and an inorganic compound 24. In addition, the inorganic compound 23 is described as the first inorganic compound and the inorganic compound 24 is described as the second inorganic compound below, but the present embodiment is not limited to this. In addition, MX22 can also be an inorganic MX (inorganic matrix material) composed of an inorganic compound.

[0044] In the present invention, MX represents a component that contains and holds other substances, and can be called a base material, a substrate, or a filling material. That is, in the present invention, MX22 refers to a component that includes and holds QD21. MX22 is an element that constitutes a film in which QD21 is dispersed, such as Figure 1 As shown in FIG. 1 , MX 22 is one of the components of EML 13 including a plurality of QDs 21. Furthermore, MX 22 may be solid at room temperature.

[0045] MX22 can also be filled in EML13. Figure 1 As shown, focusing on two QD21 among the plurality of QD21, MX22 may also be filled between the two QD21 (i.e., the region Y (space) between the two QD21). If the two QD21 are set as the first QD21a and the second QD21b, the region Y is a region surrounded by two straight lines (common external tangent lines) tangent to the outer peripheries of the first QD21a and the second QD21b in cross-sectional observation, and the corresponding outer peripheries of the first QD21a and the second QD21b.

[0046] And, in Figure 1 In the example, the case where the QDs 21 are buried in the MX 22 at intervals is shown. However, as described above, in the EML 13, the adjacent QDs 21 may be not close to each other, or may be close to each other. Figure 3 As shown, even if the adjacent first QD21a and second QD21b are close, there can be area Y (space) between these first QD21a and second QD21b. Even if these first QD21a and second QD21b are close, MX22 can fill the area Y (space) between these first QD21a and second QD21b.

[0047] Therefore, in EML13, MX22 can fill the area (space) other than QD21. Therefore, in EML13, MX22 can also fill the area (space) other than QD21. EML13 has a QD group (quantum dot group) including multiple QD21, and MX22 can also fill the area (space) other than the QD group of EML13. Here, more than three QD21 are collectively referred to as QD groups. In EML13, MX22 can also fill the area (space) other than multiple QD21. Figure 1 As shown, the outer edge 13a (first outer edge) on the anode 11 side and the outer edge 13b (second outer edge) on the cathode 15 side in the EML 13 can be covered with MX22. ​​In addition, it can also be configured that: the outer edge 13a or the outer edge 13b of the EML 13 has a portion of MX22, and QD21 is located at a position away from at least one of the outer edge 13a and the outer edge 13b of the EML 13. However, the configuration of the light emitting element 1 is not limited to the above configuration, and at least one of the outer edge 13a and the outer edge 13b of the EML 13 may not only be formed by MX22, but a part of QD21 may be exposed from MX22. ​​MX22 can also represent a portion other than QD21 in the EML 13.

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

[0049] MX22 may include a plurality of QDs 21. MX22 may be formed to fill spaces between the plurality of QDs 21 (ie, to form spaces between the plurality of QDs 21). MX22 may partially or completely fill spaces between the plurality of QDs 21.

[0050] MX22 may also include a 1000 nm 2 A continuous film having an area of ​​1000 mm or more. A continuous film refers to a film that is not separated on a plane by materials other than the material constituting the continuous film. A continuous film may also be an integrated film that is continuously connected by chemical bonds of the materials constituting MX22.

[0051] MX22 may be formed of a material different from the shell 21S included in each of the multiple QD21, or may include the same material as the shell 21S. In other words, the shell 21S may only include a material different from at least one inorganic compound included in MX22, or may include the same material as at least one inorganic compound included in MX22. ​​In the case where the shell 21S includes the same material as at least one inorganic compound contained in MX22, the above-mentioned inorganic compound may be either an inorganic compound 23, an inorganic compound 24, or an inorganic compound other than these inorganic compounds 23 and inorganic compounds 24. In the case where the shell 21S includes the same material as at least one inorganic compound contained in MX222, the carrier confinement effect is high, the diffusion of excitons from QD21 to MX22 can be suppressed, and the luminous efficiency is improved. In addition, since the shell 21S is continuously connected to at least one inorganic compound contained in MX22, the quality of MX22 can be improved.

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

[0053] The concentration of MX22 in EML13 is, for example, the area ratio occupied by MX22 in the cross section of EML13. In the cross-sectional observation of EML13, the concentration of the above-mentioned MX22 can be more than 10% and less than 90%, or more than 30% and less than 70%. The concentration of the above-mentioned MX22 can be measured, for example, based on the area ratio in the image processing in the cross-sectional observation of EML13. In the case where QD21 is a core-shell structure, the concentration of shell 21S can be more than 1% and less than 50%. Shell 21S and MX22 are composed of the same material (same composition). When shell 21S and MX22 cannot be distinguished, the concentration of the area where shell 21S and MX22 are combined can be within the numerical range obtained by adding the numerical range of the concentration of MX22 to the numerical range of the concentration of shell 21S. The ratio of the core 21C of QD21 to the shell 21S and MX22 can be appropriately adjusted so that the total of these is less than 100%. In this way, when the case 21S and the MX22 cannot be distinguished, the case 21S may be made a part of the MX22.

[0054] EML 13 may be composed of a plurality of QDs 21 and MX 22. When analyzing EML 13, the intensity of carbon detected by the chain structure may be below noise.

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

[0056] The recombination of carriers (electrons and holes) injected into QD21 is mainly generated in the core 21C. The shell 21S has the function of suppressing the generation of defects or dangling bonds in the core 21C and reducing the recombination of carriers that have undergone the deactivation process. When the Eg of MX22 is greater than the Eg of the core 21C or the shell 21S, the confinement effect of the excitons to the core 21C is high, and the recombination of carriers in the core 21C or the excitons generated by light absorption is difficult to diffuse to MX22, which can improve the luminous efficiency of the light-emitting element 1.

[0057] Furthermore, as long as the Eg of at least one inorganic compound contained in MX22 is greater than the Eg of the core 21C, it may be equal to or smaller than the Eg of the shell 21S. However, it is preferred that the Eg of at least one inorganic compound contained in MX22 is greater than the Eg of the shell 21S. In this case, the core 21C has a higher blocking effect on excitons, suppresses the diffusion of excitons from QD21 to MX22, and can further improve the luminous efficiency.

[0058] At least one inorganic compound (inorganic material) contained in MX22 may be a semiconductor material or an insulator material. As at least one inorganic compound contained in MX22, for example, metal sulfide can be preferably cited. The precursor of metal sulfide is thermally decomposed at a relatively low temperature, and the control of Eg is easy. Therefore, MX22 preferably contains metal sulfide as an inorganic compound, and as inorganic compound 23 and inorganic compound 24, metal sulfide is preferably used.

[0059] Examples of the metal sulfides include tin sulfide (SnS2), indium sulfide (In2S3), zinc sulfide (ZnS), aluminum sulfide (Al2S3), beryllium sulfide (BeS), germanium sulfide (GeS2), barium sulfide (BaS), calcium sulfide (CaS), and magnesium sulfide (MgS).

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

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

[0062] It is sufficient that MX22 contains at least two or more inorganic compounds including the inorganic compound 23 and the inorganic compound 24, and the addition of a material different from these inorganic compounds as an additive is not excluded.

[0063] As described above, the EML 13 is filled with MX22 around the QD 21. In this way, the light emitting element 1 protects the periphery of the QD 21 with MX22 by covering the periphery of the QD 21 with MX22.

[0064] Compared with organic ligands, MX containing an inorganic compound as an inorganic medium is difficult to peel off from QD21, and by covering the periphery of QD21 with MX22, QD can be firmly protected. Therefore, EML13 includes MX22 containing an inorganic compound, thereby being able to improve the stability of EML13 compared to the case where an organic ligand is used in EML13. In addition, the degradation of QD21 can be suppressed, and the light-emitting characteristics and reliability of the light-emitting element 1 can be improved.

[0065] However, when the periphery of QD21 is uniformly covered with an inorganic compound, if an inorganic compound with a large Eg is used as the inorganic compound, the injection efficiency of holes and electron carriers into QD21 is reduced, which becomes a cause of reduced luminous efficiency. Therefore, in this embodiment, as described above, two or more inorganic compounds containing inorganic compounds 23 and inorganic compounds 24 are used in MX22 to change the composition of MX22 in the layer thickness direction of EML13. Thus, the energy level of MX22 is changed on the HTL12 side and the ETL14 side.

[0066] In the direction of the straight line L1 penetrating the outer edge portion 13a and the outer edge portion 13b in the EML 13, the MX 22 has a first region containing at least an inorganic compound 23 and a second region containing at least an inorganic compound 24. The second region is arranged closer to the outer edge portion 13b than the first region. The concentration of the inorganic compound 23 in the first region differs from the concentration of the inorganic compound 23 in the second region by a certain degree or more. For example, the concentration of the inorganic compound 23 in the first region and the concentration of the inorganic compound 23 in the second region are expected to differ by 20% or more.

[0067] That is, MX22 has, in the direction of the straight line L1: (1) a first region, which contains at least an inorganic compound 23; (2) a second region, which contains at least an inorganic compound 24, and is disposed at a position closer to the outer edge portion 13b than the first region, and the concentration of the inorganic compound 23 in the first region differs from the concentration of the inorganic compound 23 by a certain degree or more. Furthermore, since the concentration of the inorganic compound 23 in the second region differs from the concentration of the inorganic compound 23 in the first region by a certain degree or more, the concentration of the inorganic compound 24 in the second region also differs from the concentration of the inorganic compound 24 in the first region by a certain degree or more.

[0068] Furthermore, in the direction of the straight line L1 penetrating the outer edge portion 13 a and the outer edge portion 13 b in the EML 13 , the MX 22 has a first region containing at least the inorganic compound 23 and a second region containing at least the inorganic compound 24 .

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

[0070] Figure 1 In the figure, an example is shown in which MX22 includes a first layer 22a containing an inorganic compound 23 as a main component as a first region and includes a second layer 22b containing an inorganic compound 24 as a main component as a second region.

[0071] Furthermore, in cross-sectional observation of the EML 13 , unless there is any particular limitation or contradiction, the structure of the MX22 can be observed in a width of about 100 nm and a desired structure can be observed. The desired structure does not need to be observed in the entire EML 13 .

[0072] Figure 4 2 is a cross-sectional view schematically showing the state of carrier injection in a comparative light-emitting element 101 in which the periphery of QD 21 is uniformly covered with MX122 composed of an inorganic compound 23. Figure 4 In the diagram, arrows are used to indicate the number of holes (h+) and electrons (e-). Figure 4In the figure, illustrations other than HTL 12, EML 113 and ETL 14 are omitted. Figure 5 It is shown Figure 4 FIG. 1 is a diagram showing the energy band structure of each functional layer in a light-emitting element 101 for comparison.

[0073] The light emitting element 101 for comparison has the same structure as that of the light emitting element 101 except that the light emitting element 101 is replaced with the light emitting element 101 and the light emitting element 101 is covered with the light emitting element 101 around the QD 21 by using the light emitting element 101 formed by the inorganic compound 23 instead of the light emitting element 101. Figure 1 The light emitting element 1 shown has the same structure.

[0074] exist Figure 4 In the figure, for example, the anode 11 is made of ITO, the HTL 12 is made of P-TPD, the ETL 14 is made of ZnMgO, and the cathode 15 is made of Al. In such a light emitting element 101, Figure 4 and Figure 5 As shown, when zinc sulfide (ZnS) is used as the inorganic compound 23 and the periphery of QD 21 is uniformly covered with ZnS, the balance of electrons and holes in EML 113 is, for example, about 6: 4. Therefore, in this case, electrons are excessive and holes are insufficient, carrier balance is reduced, and luminous efficiency and reliability are reduced.

[0075] Therefore, in the case where there is an excess of electrons and a shortage of holes, in order to improve the carrier balance, it is preferred to reduce the amount of electrons injected into EML113 or increase the amount of holes injected. In the present embodiment, in the case where there is an excess of electrons and a shortage of holes, (I) as the inorganic compound 23, an inorganic compound having an element composition ratio with an energy level or characteristic that easily promotes hole injection is used compared to the inorganic compound 24, or (II) as the inorganic compound 24, an inorganic compound having an element composition ratio with an energy level or characteristic that easily suppresses electron injection is used. By satisfying at least one of the above (I) and (II), a light-emitting element 1 that adjusts carrier balance, has high stability, and has high luminous efficiency and reliability can be provided.

[0076] Therefore, as described above, in the case where electrons are excessive and holes are insufficient, for example, as the inorganic compound 24, it is preferable to use an inorganic compound having an Eg larger than that of the inorganic compound 23. In other words, as the inorganic compound 23, it is preferable to use an inorganic compound having an Eg smaller than that of the inorganic compound 24. In this case, the injection of electrons can be suppressed to adjust the carrier balance, thereby improving the luminous efficiency and reliability.

[0077] In addition, as described above, when electrons are in excess and holes are insufficient, for example, as the inorganic compound 23, it is preferable to use an inorganic compound having a hole mobility greater than that of the inorganic compound 24. In other words, as the inorganic compound 24, it is preferable to use an inorganic compound having a hole mobility less than that of the inorganic compound 23. In this case, holes are easily injected to adjust the carrier balance, and the luminous efficiency and reliability can be improved.

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

[0079] If the charge e and the mean free time T are assumed to be constant, the smaller the effective mass, the higher the carrier mobility.

[0080] Therefore, when it is desired to improve the hole injection property, an inorganic compound having a larger Eg than ZnS used as the material of the shell 21S of the QD 21 and a smaller hole effective mass is generally used for the inorganic compound 23 .

[0081] Table 1 shows an example of Eg and effective mass of a metal sulfide having a relatively high hole transporting property as an inorganic compound having a relatively high hole transporting property. Table 2 shows an example of Eg and effective mass of a metal sulfide having a relatively low hole transporting property as an inorganic compound having a relatively low hole transporting property. Table 1

[0082] Table 2 Inorganic compounds (metal sulfides) Eg(eV) Effective mass <![CDATA[GeS2]]> 3.52 0.88 B S 3.90 2.30 CaS 5.78 1.24 MgS 6.39 0.95 Therefore, as described above, in the case of excess electrons and insufficient holes, for example, (a) the inorganic compound 23 is indium sulfide (InS), and the inorganic compound 24 may be magnesium sulfide (MgS). Alternatively, (b) the inorganic compound 23 is zinc sulfide (ZnS), and the inorganic compound 24 may be magnesium sulfide (MgS). Alternatively, (c) the inorganic compound 23 is indium sulfide (InS), and the inorganic compound 24 may be zinc sulfide (ZnS). It should be noted that as the above-mentioned indium sulfide (InS), for example, In2S3 can be listed.

[0083] In this way, in the case of excess electrons and insufficient holes, for example, by changing MX22 (specifically, inorganic compound 23) on the HTL12 side to MX22 whose main component is an inorganic compound with a smaller Eg than MX22 (specifically, inorganic compound 24) on the ETL14 side and a high hole mobility (small effective hole mass), hole injection can be promoted and the excess electrons can be adjusted. In addition, for example, by changing MX22 on the ETL14 side to MX22 whose main component is an inorganic compound with a larger Eg than MX22 on the HTL12 side and a low carrier mobility (large effective mass), electron injection can be suppressed and the insufficient holes can be adjusted.

[0084] Figure 6 As an example, it is a cross-sectional view schematically showing (a) the state of carrier injection in the light-emitting element 1 when the inorganic compound 23 is indium sulfide (In2S3) and the inorganic compound 24 is magnesium sulfide (MgS). Figure 6 In FIG. 1 , illustrations other than HTL 12, EML 13, and ETL 14 are omitted. Figure 6 In FIG. 1 , as in the light emitting element 101 , an example is shown in which the anode 11 is made of ITO, the HTL 12 is made of p-TPD, the ETL 14 is made of ZnMgO, and the cathode 15 is made of Al. Figure 6 In, also with Figure 4 Likewise, the numbers of holes (h+) and electrons (e-) are shown by arrows. Figure 7 Yes means Figure 6 The energy band structure of each functional layer in the light emitting element 1 is shown in FIG. Figure 7 In FIG. 1 , for comparison, the band structure of zinc sulfide (ZnS) is also shown.

[0085] like Figure 6 as well as Figure 7 As shown, by providing a first layer 22a having In2S3 with a smaller Eg than ZnS as a main component on the HTL12 side, hole injection into QD21 can be promoted compared to the case where QD21 is covered with only ZnS. In addition, by providing a second layer 22b having MgS with a larger Eg than ZnS as a main component on the ETL14 side, electron injection into QD21 can be suppressed compared to the case where QD21 is covered with only ZnS. In this case, the balance between electrons and holes in EML13 can be improved to approximately 5:5, and the carrier balance can be adjusted.

[0086] And, in Figure 6In the example, (a) the case where the inorganic compound 23 is In2S3 and the inorganic compound 24 is MgS is described. However, even in the case where (b) the inorganic compound 23 is ZnS and the inorganic compound 24 is MgS, and (c) the inorganic compound 23 is InS such as In2S3 and the inorganic compound 24 is ZnS, the balance between electrons and holes can be improved to about 5:5.

[0087] On the other hand, in the case where electrons are insufficient and holes are in excess, in order to improve the carrier balance, it is preferred to reduce the amount of hole injection or increase the amount of electron injection. Therefore, in the case where electrons are insufficient and holes are in excess, (i) as the inorganic compound 23, an inorganic compound having an element composition ratio with an energy level or characteristic that is easy to suppress holes is used compared to the inorganic compound 24, or (ii) as the inorganic compound 24, an inorganic compound having an element composition ratio with an energy level or characteristic that is easy to promote electron injection is used. By satisfying at least one of the above conditions (i) and (ii), a light-emitting element 1 that adjusts carrier balance, has high stability, and has high luminous efficiency and reliability can be provided.

[0088] Therefore, as described above, in the case where electrons are insufficient and holes are excessive, for example, as the inorganic compound 23, it is preferable to use an inorganic compound having an Eg larger than that of the inorganic compound 24. In other words, as the inorganic compound 24, it is preferable to use an inorganic compound having an Eg smaller than that of the inorganic compound 23. In this case, the injection of holes can be suppressed to adjust the carrier balance, thereby improving the luminous efficiency and reliability.

[0089] In addition, as described above, in the case where electrons are insufficient and holes are excessive, for example, as the inorganic compound 24, it is preferable to use an inorganic compound having a greater electron mobility than the inorganic compound 23. In other words, as the inorganic compound 23, it is preferable to use an inorganic compound having a smaller electron mobility than the inorganic compound 24. In this case, electrons are easily injected, carrier balance is adjusted, and luminous efficiency and reliability can be improved.

[0090] Therefore, in the case where electrons are insufficient and holes are excessive, by changing, for example, MX22 on the ETL14 side to MX22 whose main component is an inorganic compound with a smaller Eg than MX22 on the HTL12 side and a high electron mobility (small electron effective mass), electron injection can be promoted and excess holes can be adjusted. In addition, by changing, for example, MX22 on the HTL12 side to MX22 whose main component is an inorganic compound with a larger Eg than MX22 on the ETL14 side and a low electron mobility (large electron effective mass), electron injection can be promoted and excess holes can be adjusted.

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

[0092] Therefore, as an inorganic compound with a relatively high hole transport property, an example of Eg and effective mass of an inorganic compound other than metal sulfide with a relatively high hole transport property is shown in Table 3. In addition, as an inorganic compound with a relatively low hole transport property, an example of Eg and effective mass of an inorganic compound other than metal sulfide with a relatively low hole transport property is shown in Table 4. Table 3

[0093] Table 4 Inorganic compounds Eg(eV) Effective mass BeSe 3.60 0.47 CaSe 4.86 0.69 MgSe 5.63 0.12 For example, different inorganic compounds have different energy levels as shown in Tables 1 to 4. Therefore, according to the present embodiment, by changing the composition of MX22 in the first region and the second region as described above, the hole and electron transport capabilities can be changed.

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

[0095] Thus, according to this embodiment, MX22 contains the inorganic compound 23 and the inorganic compound 24. By changing the concentration of the inorganic compound 23 and the inorganic compound 24 in MX22 between the outer edge portion 13a and the outer edge portion 13b of the EML 13, the carrier balance can be adjusted and the luminous efficiency can be improved. Therefore, according to this embodiment, a light-emitting element 1 with high stability, high luminous efficiency and high reliability can be provided.

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

[0097] In the analysis based on non-destructive test (such as XPS analysis), the amount of constituent elements and element ratios in the inorganic compound are basically detected in a dispersed manner. For example, when the inorganic compound contained in MX22 is ZnS, Zn and S are detected separately in the analysis based on non-destructive test. In this case, the detected elements are Zn:S=1:1. Therefore, it can be known that the inorganic compound contained in the first region is ZnS.

[0098] On the other hand, for example, MX22 contains two inorganic compounds, both of which are sulfides. In this case, if the inorganic compounds contained in MX22 are ZnS and In2S3, the elements detected by the above analysis are three elements: Zn, In, and S. In this case, if the concentration of ZnS is equal to the concentration of In2S3 (that is, if ZnS:In2S3=1:1), it is detected as Zn:In:S=1:2:4.

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

[0100] In addition, in this case, for example, it is possible to confirm whether the above-mentioned inorganic compound is ZnS or ZnO based on the energy of the chemical bond detected by the above-mentioned detection method (inspection method), and it is also possible to combine the above-mentioned detection method and other detection methods. As the above-mentioned detection method, as described above, it is most preferred to analyze based on XPS, but as an analysis method inferior to XPS, it is also possible to use a cross-sectional TEM (transmission electron microscope) and an EDX (energy dispersive X-ray spectrometry) cross-sectional TEM / EDX method. For example, it is also possible to analyze by combining inspection methods such as XPS and cross-sectional TEM / EDX method. In addition, as the next preferred analysis method in the cross-sectional TEM / EDX method, it is possible to analyze in the form of crystals such as XRD (X-ray diffraction setting), for example, it is also possible to analyze by combining inspection methods such as XPS and XRD.

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

[0102] When XPS is used in the measurement of the above concentration, the measurement is performed at multiple measurement depths in the depth direction of EML 13. XPS sputters and etches the sample by accelerating Ar (argon) ions to several hundred V to several kV, and on the other hand, by irradiating the exposed sample surface with X-rays, the kinetic energy of the photoelectrons emitted from the sample surface is measured. Thus, the composition and chemical bond state of the elements constituting the sample surface are analyzed.

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

[0104] Figure 8 1 is a cross-sectional view showing an example of the measurement direction of the concentration of the inorganic compound 23 and the inorganic compound 24 along an arbitrary straight line L1 in the EML 13. Figure 8 In the figure, QD21 is omitted for the sake of illustration. Figure 8 In the figure, MX22 is shown as an example, in which MX22 includes a first layer 22a whose main component is an inorganic compound 23 as a first region, and includes a second layer 22b whose main component is an inorganic compound 24 as a second region, wherein the inorganic compound 23 is InS and the inorganic compound 24 is ZnS. Figure 8 In FIG. 1 , in order to indicate the measurement direction, the straight line L1 is indicated by an arrow.

[0105] Fig. 9 It means using XPS along Figure 8 The straight line L1 shown is measured, Figure 8 1 is a graph showing the concentration distribution of InS (e.g., In2S3) and ZnS in the EML 13 shown. Also, for ease of explanation and illustration, Fig. 9 The measurement result is shown as an example when QD21 does not exist on the arbitrary straight line L1. However, when QD21 exists on the straight line L1, the concentrations of the inorganic compound 23 and the inorganic compound 24 can be obtained by supplementation. Fig. 9 In the measurement time and along Figure 8 The measured depth (measured distance) of the straight line L1 shown is proportional. Fig. 9 In , the measurement time can be replaced by the measurement depth (measurement distance) along the straight line L1.

[0106] like Fig. 9As shown, by XPS analysis, the elements in any measurement depth (measurement distance) in the EML 13 (in other words, the elements in any measurement surface) can be quantified. For example, the ZnS concentration can be calculated by the following formula: ZnS concentration (= Zn element concentration) = (Zn element amount) / {(Zn element amount) + (In element amount)} The Zn element concentration can be calculated. Similarly, the InS concentration can be calculated by the following formula: InS concentration (=In element concentration) = (In element amount) / {(Zn element amount) + (In element amount)} Calculated as the In element concentration.

[0107] As described above, from the element concentration at an arbitrary measurement depth (measurement distance) in the EML 13 , the concentration distribution of each inorganic compound at an arbitrary measurement depth (measurement distance) in the EML 13 can be studied.

[0108] from Fig. 9 The measurement results shown show that there is a boundary between the inorganic compound 23 (InS) and the inorganic compound 24 (ZnS) in EML13. In other words, it is known that there is a portion in EML13 where the concentrations of the inorganic compound 23 (InS) and the inorganic compound 24 (ZnS) are equal. This shows that there are regions of different inorganic compounds in EML13. Figure 8 , the case where MX22 is completely divided into the first region and the second region is shown, but the present invention is not limited thereto. For example, the first region is a region whose main component is the inorganic compound 23, and the second region is a region whose main component is the inorganic compound 24. Therefore, the first region and the second region do not necessarily need to be completely in contact with each other, and may exist with a gap therebetween.

[0109] In addition, if there is a portion in the first region where the concentration of the inorganic compound 23 differs by a certain degree (e.g., 20%) or more, that is, if the concentration of the inorganic compound 23 exists at, for example, 100% and 80%, it is considered that the concentration of the inorganic compound 23 in the portion changes greatly. Therefore, it can be considered that there is a boundary in the portion. In addition, similarly, if there is a portion in the second region where the concentration of the inorganic compound 24 differs by a degree (e.g., 20%) or more, it can be considered that there is a boundary in the portion. In addition, if there is a portion in the first region where the concentration of the inorganic compound 23 differs by a certain degree (e.g., 20%) or more, and there is a portion in the second region where the concentration of the inorganic compound 24 differs by a certain degree (e.g., 20%) or more, it can also be considered that there is a boundary. It can be seen from this that there are regions with different inorganic compounds in EML13.

[0110] Fig.101 is a cross-sectional view showing another example of the measurement direction of the concentration of the inorganic compound 23 and the inorganic compound 24 along the arbitrary straight line L1 in the EML 13. Fig.10 In the figure, the QD21 is omitted for the sake of illustration. Fig.10 MX22 is also shown as an example. In MX22, the first region includes a first layer 22a whose main component is an inorganic compound 23, and the second region includes a second layer 22b whose main component is an inorganic compound 24. The inorganic compound 23 is InS, and the inorganic compound 24 is ZnS. Fig.10 In order to indicate the measurement direction, the straight line L1 is indicated by an arrow.

[0111] Fig.11 It means using XPS along Fig.10 The straight line L1 shown is measured, Fig.10 The concentration distribution of InS and ZnS in EML13 is shown in FIG. Fig.11 In FIG. 1 , for the convenience of explanation and illustration, the measurement result in the case where the QD 21 does not exist on the arbitrary straight line L1 is also shown as an example.

[0112] It can be seen that in the same measurement method, the direction of the straight line L1, that is, the invasion path of Ar ions and X-rays can be Figure 8 As shown, perpendicular to the EML13 layer, it can also be as shown Fig.10 As shown, it is inclined relative to the layer of EML13.

[0113] In the present embodiment, the concentration distribution of the inorganic compound in the EML 13 can be measured by the above method using XPS. However, in the present embodiment, it is not limited thereto, and the concentration distribution of the inorganic compound contained in the EML 13 can also be measured using a cross-sectional TEM / EDX method. Furthermore, the measurement result using XPS is preferred over the measurement result using a cross-sectional TEM / EDX method. Fig.12 and Fig.13 1 is an explanatory diagram showing a method for studying the concentration distribution of the inorganic compound 23 and the inorganic compound 24 in the film thickness direction contained in the EML 13 using the cross-sectional TEM / EDX method. Fig.12 as well as Fig.13 In the figure, the QD21 is omitted for the sake of illustration. Fig.12 as well as Fig.13 In the figure, MX22 is shown as an example, in which MX22 includes a first layer 22a with an inorganic compound 23 as a main component as a first region, and includes a second layer 22b with an inorganic compound 24 as a main component as a second region, the inorganic compound 23 is InS, and the inorganic compound 24 is ZnS. Fig.13 In order to indicate the measurement direction, the straight line L1 is indicated by an arrow.

[0114] When the concentration distribution of the inorganic compound 23 and the inorganic compound 24 in the film thickness direction contained in the EML 13 is studied using the cross-sectional TEM / EDX method, first, Fig.12 As shown in FIG. 1 , the light emitting element 1 is processed by FIB (Focused Ion Beam) processing or the like to form a cross section of the EML 13 along the layer thickness direction of the EML 13. Fig.13 As shown, the cross section of EML13 was observed by cross-sectional TEM, and EDX was used to observe the cross section of EML13 in the direction perpendicular to the layer thickness direction (the direction perpendicular to the straight line L1). Fig.13 The dotted line shown is divided into multiple parts for scanning, and the number of each element contained in the MX22 part of each scanned measurement line is counted. If the device has a counting function for the number of elements on the measurement line, this function can be used to implement the counting, and if it is not implemented by image analysis from the scanning image of EDX. In this way, the amount (concentration) of the elements of each inorganic compound distributed along the straight line L1 direction in the above-mentioned cross section of EML13 can be quantified. In this case, the scanning area using EDX (i.e., the scanning area using X-rays) in the above-mentioned cross section becomes the size and shape of each measurement line. Therefore, in this case, each measurement line is also the same shape.

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

[0116] Fig.14 The cross-sectional TEM / EDX method is used to measure the Fig.12 The concentration distribution of InS and ZnS in the film thickness direction (the direction of the straight line L1) of EML13 is shown in FIG. Fig.14 As described above, , represents the concentrations of InS and ZnS in MX22.

[0117] As described above, the light emitting element 1 of this embodiment includes, as an example, the first layer 22a containing the inorganic compound 23 as the first region and the second layer 22b containing the inorganic compound 24 as the second region.

[0118] The inorganic compound 23 and the inorganic compound 24 are mutually infiltrated and mixed at the boundary surface between the first layer 22a and the second layer 22b, so that Fig. 9 , Fig.11 and Fig.14 As shown, a concentration distribution occurs in the layer thickness direction of the EML 13 .

[0119] At this time, the concentration of the inorganic compound 23 may be changed continuously or in steps in the direction of the straight line L1. Similarly, the concentration of the inorganic compound 24 may be changed continuously or in steps in the direction of the straight line L1.

[0120] When a medium with a large Eg is inserted into the interface of a layer adjacent to the EML 13 in the EML 13, all carriers need to cross the potential barrier of the above-mentioned medium. However, by changing the concentration of the inorganic compound 23 or the inorganic compound 24 continuously or in stages, the injection barrier of the carrier can be changed in stages, and carrier injection can be easily performed compared to the case of crossing a large injection barrier at one time. Therefore, as described above, in the EML 13, by giving the inorganic compound 23 and the inorganic compound 24 a concentration distribution, the driving voltage can also be reduced.

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

[0122] In addition, EML 13 preferably includes a region where the concentration of inorganic compound 23 in MX22 is 80% or more within a range of at least 1 nm from outer edge 13a. Thus, MX22 near outer edge 13a is formed of a relatively uniform component, and carriers are easily injected from anode 11 side into QD 21 near outer edge 13a.

[0123] Similarly, EML 13 preferably includes a region where the concentration of inorganic compound 24 in MX22 is 80% or more within a range of at least 1 nm from outer edge 13b. Thus, MX22 near outer edge 13b is formed of a relatively uniform component, and carriers are easily injected from cathode 15 side into QD 21 near outer edge 13b.

[0124] As described above, when the EML 13 includes a region where the concentration of the inorganic compound 23 in the MX 22 is 80% or more within a range of at least 1 nm from the outer edge portion 13a, for example Figure 1 As shown in FIG. 1 , the outer edge portion 13a is preferably covered with MX22. ​​Similarly, when the EML 13 includes a region where the concentration of the inorganic compound 24 in MX22 is 80% or more within a range of at least 1 nm from the outer edge portion 13b, for example, Figure 1 As shown in FIG. 1 , the outer edge 13b is preferably covered with MX22. ​​That is, it is preferable that a part of MX22 is provided from the outer edge 13a and the outer edge 13b of the EML 13, and QD21 is located at a position away from the outer edge 13a and the outer edge 13b of the EML 13.

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

[0126] Therefore, the boundary surface between the first region and the second region may intersect with a plurality of QDs 21. For example, Figure 1 In the light emitting element 1 shown, the EML 13 includes a QD array 21L (quantum dot array) in the thickness direction of the EML 13 . The QD array 21L (quantum dot array) is a plurality of QDs 21 arranged in a direction perpendicular to the thickness direction of the EML 13 . Figure 1 In the light-emitting element 1 shown, the interface 22I between the first layer 22a and the second layer 22b intersects with the QD column 21L.

[0127] The light-emitting element 1 can change the concentration of each inorganic compound contained in MX 22 within the thickness range of one QD 21 in the layer thickness direction of EML 13. Figure 1 As shown, even when QD21 is stacked in only one column in the thickness direction of EML13, when QD21 is stacked in only one (i.e., one layer) in the thickness direction of EML13, or when QD21 is not stacked neatly, the carrier balance can be adjusted to improve the luminous efficiency.

[0128] Furthermore, as described above, in the EML 13 , an inorganic compound having an arbitrary Eg is in direct contact with each of the QDs 21 at an arbitrary ratio, so that the inorganic compound can be more effectively affected.

[0129] And, as mentioned above, Figure 1 This is an example of a schematic configuration of the light emitting element 1 of this embodiment. The light emitting element 1 of this embodiment is not limited to Figure 1 The composition shown. Figure 15 to Figure 21 This is a cross-sectional view showing another example of the schematic configuration of the light emitting element 1 according to the present embodiment. Figure 15 to Figure 21 In the figure, illustrations other than HTL 12 , EML 13 , and ETL 14 are omitted.

[0130] like Fig.15 As shown, the QD array 21L may be arranged in multiple rows (e.g., 2 rows) in the thickness direction of the EML 13. That is, the QD 21 may be stacked in multiple layers in the thickness direction of the EML 13. In this case, the interface 22I between the first layer 22a and the second layer 22b may be as shown in FIG. Figure 1 As shown in FIG. 1 , the QD array 21L on the HTL 12 side, in other words, on the bottom layer, may also intersect. Fig.15 As shown in FIG. 2 , the interface 221 between the first layer 22a and the second layer 22b may intersect with the QD column 21L on the upper side (ETL14 side) of the QD column 21L in the bottom layer. Fig.15 As shown, when the QD 21 is stacked in two layers, the interface 221 between the first layer 22 a and the second layer 22 b may be provided at the 1.5th layer of each QD 21 .

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

[0132] In addition, if Fig.17 As shown, the EML 13 may have a structure in which a plurality of QD columns 21L are stacked in the layer thickness direction of the EML 13 , but the interface 22I between the first layer 22 a and the second layer 22 b is not clearly distinguished.

[0133] In addition, the QDs 21 may not be included in the EML 13 in a state where they are arranged as the QD columns 21L. Fig.18As shown, QD21 may be stacked in a complex manner in EML13. In this case, the interface 22I between the first layer 22a and the second layer 22b may intersect with the QD column 21L on the upper side (ETL14 side) than the QD column 21L of the bottom layer. For example, in the case where QD21 is stacked in two layers, the interface 22I between the first layer 22a and the second layer 22b may be provided in the 1.5th layer of each QD21. Although not shown in the figure, the above-mentioned boundary surface 22I may of course intersect with the QD column 21L on the HTL12 side, in other words, the bottom layer.

[0134] In addition, if Fig.19 As shown, the EML 13 may have a structure including the QD 21 only in the first layer 22a and not in the second layer 22b. Fig. 20 As shown, the second layer 22b may also include at least a portion of QDs 21. Fig.19 The case where QD21 is complexly stacked in EML13, the interface 22I between the first layer 22a and the second layer 22b is not clearly separated, and QD21 is included only in the first layer 22a and not in the second layer 22b is illustrated as an example. Fig. 20 In the figure, the case where QD21 is complexly stacked in EML13, the interface 22I between the first layer 22a and the second layer 22b is not clearly distinguished, and there is a portion where the interface 22I of the first layer 22a and the second layer 22b intersects with the QD column 21L of the bottom layer, and there is also a portion where the interface 22I of the first layer 22a and the second layer 22b intersects with the QD column 21L on the upper side (ETL14 side) compared to the QD column 21L of the bottom layer is illustrated as an example.

[0135] In addition, if Fig.21 As shown, the EML 13 may have a gradient in the concentration of a plurality of inorganic compounds, and the concentration of each inorganic compound may gradually change from the outer edge portion 13 a to the outer edge portion 13 b to have an element gradient.

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

[0137] In addition, if As shown, QD 21 may be exposed from MX 22 in at least one of the outer edge portion 13 a and the outer edge portion 13 b of the EML 13 .

[0138] For example, Figures 18 to 20As shown, a part of MX22 may be located from at least one of the outer edge portion 13a and the outer edge portion 13b of the EML 13, and QD21 may be located at a position away from at least one of the outer edge portion 13a and the outer edge portion 13b.

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

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

[0141] like Figure 2 As shown in FIG. 1 , since the halide ions 31a exist near the surface of QD 21, the dispersibility of QD 21 is improved. Therefore, it is preferable that MX22 contains a halogen element. In addition, the thickness of the shell 21S can be set to the vicinity of the surface of QD 21.

[0142] In addition, the halogen element is combined with the unpaired electrons of the inorganic compound constituting Mx22 to stabilize. Therefore, by including the halogen element in MX22, the defects of MX22 can be passivated. In addition, here, "passivating the defects of MX22" means that the unpaired electrons are used to combine with the halogen element, so the defects no longer function as non-luminescent centers or carrier traps.

[0143] MX22 may contain halogen elements of 1 atomic % or more. The concentration of halide ions 31a near each QD21 is preferably higher than the concentration of halide ions 31a on the surrounding side. For example, the vicinity of a certain QD21 within a range of 1 nm from the outermost surface of the QD21 may be set as the vicinity of the quantum dot.

[0144] So, for example Figure 2As shown, in the periphery of QD21, the average value of the total concentration of halogen atoms within a distance DA of 1 nm from the outermost surface of the QD21, i.e., the outer surface of the shell 21S, may be higher than the average value of the total concentration of halogen atoms at other positions. In this case, the average value of the total concentration of halogen atoms within the distance DA of 1 nm may be higher than the average value of the total concentration of halogen atoms at other positions by 10% or more, or by 50% or more, or by 100% or more. Such a concentration distribution can be confirmed, for example, by element mapping based on cross-sectional TEM-EDX (transmission electron microscopy-energy dispersive X-ray spectroscopy).

[0145] Here, "other positions" can also be said to be positions where there is no QD21 within 1 nm. EML13 contains multiple QD21. Therefore, the above value can also be a value when the average value of the concentration of the total amount of halogen atoms within 1 nm around each QD21 in EML13 is compared with the average value of the concentration of the total amount of halogen atoms in the portion where any QD21 in EML13 is more than 1 nm away.

[0146] That is, it is preferred that the average value of the concentration of the total of halogen elements in an area within 1 nm from the outermost surface of each of the multiple QD21 in Mx22 is higher than the average value of the concentration of the total of the halogen elements in an area more than 1 nm away from the outermost surface of each of the above-mentioned multiple QD21 in Mx22, and can be, for example, greater than 10%, or greater than 50%, or greater than 100%.

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

[0148] By forming the EML 13 using a QD dispersion liquid containing a halogen element and the QDs 21 , the MX 22 may contain halide ions.

[0149] (Method for Manufacturing Light Emitting Element 1) Below, refer to Figure 22 to Figure 34 A method for manufacturing the light emitting element 1 according to this embodiment will be described. Fig. 22 This is a flowchart showing an example of a method for manufacturing the light emitting element 1 according to the present embodiment.

[0150] like Fig. 22As shown, in the manufacturing method of the light-emitting element 1 of the present embodiment, first, an anode 11 is formed on a substrate serving as a support (step S1, anode forming process). Then, HTL 12 is formed (step S2, hole transport layer (HTL) forming process). In addition, a QD dispersion is manufactured (adjusted) in parallel (step S11, quantum dot (QD) dispersion manufacturing process). Then, EML 13 is formed using the above-mentioned QD dispersion (step S3, light-emitting layer (EML) forming process). Then, ETL 14 is formed (step S4, electron transport layer (ETL) forming process). Then, a cathode 15 is formed (step S5, cathode forming process). Thus, the above-mentioned light-emitting element 1 is manufactured.

[0151] In the formation of the anode 11 in step S1 and the formation of the cathode 15 in step S5 , for example, a vapor deposition method, a sputtering method, or the like is used.

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

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

[0154] (Step S11) The QD dispersion liquid preparation process of step S11 is as follows: Fig.23 As shown, the process includes a ligand replacement step (step S21) of replacing the ligand coordinated to QD21. Fig.23 It is a schematic cross-sectional view for explaining the ligand replacement step (step S21 ) in step S11 .

[0155] In the QDs synthesized or obtained commercially, in most cases, an organic ligand (hereinafter, for the sake of convenience, referred to as a "first organic ligand") is used as a ligand. Commercially available QDs are generally provided in the state of a QD dispersion containing a first organic ligand as a ligand. The first organic ligand is used as a dispersant to improve the dispersibility of the QDs in the QD dispersion, and is also used to improve the surface stability and storage stability of the QDs. In addition, the synthesis of QDs uses, for example, a wet method, and the particle size of the QDs is controlled by aligning the first organic ligand to the surface of the QD. Therefore, the QD dispersion synthesized by the wet method contains, for example, a first organic ligand used for the synthesis of QDs. Such a first organic ligand is sometimes used directly, and sometimes replaced with a desired first organic ligand depending on the type of solvent, etc. In either case, the EML obtained by coating a QD dispersion containing a first organic ligand commonly used as an organic ligand and then drying it contains the above-mentioned first organic ligand.

[0156] In this embodiment, in order to invalidate the EML 13, a ligand replacement step is performed in which the first organic ligand coordinated to the QD 21 is replaced with the second organic ligand thermally decomposed by heating and the halide ion 31a. The organic ligand that is a precursor of MX22 is used as the second ligand.

[0157] Below, refer to Fig.23 , a method of replacing the first organic ligand coordinated to QD 21 with the second organic ligand and the halide ion 31a is described.

[0158] like Fig.23 As shown, in the above-mentioned ligand replacement process, first, a ligand solution 30 and a QD dispersion liquid 40 are injected into a container 61, wherein the ligand solution 30 contains dissolved halide ions 31a and an organic ligand 32 as a second organic ligand, and the QD dispersion liquid 40 contains dispersed QD21 coordinated by an organic ligand 41 as a first organic ligand (step S21a).

[0159] The halide ions 31a are supplied, for example, as metal halide 31. The metal halide 31 exists as halide ions 31a as anions and metal ions 31b as cations. Of these halide ions 31a and metal ions 31b, halide ions 31a are negatively charged and are therefore attracted to the positively charged surface of QD 21 as a halogen ligand.

[0160] As the halide ion 31a of the anion, for example, there are fluoride ions (F - ), chloride ion (C1 - ), bromide ion (Br - ), iodide ion (I - )wait.

[0161] Examples of the metal ion 31b as the cation include Li + 、Na + , K + , Rb + , Cs + 、Be 2+ Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ 、Zn 2+ 、Al 3+ , Ga 3+ 、In 3+ Sn 2+ , Pb 2+ wait.

[0162] The organic ligand 32 is not particularly limited as long as it is a compound that is thermally decomposed by heating, contains at least one of the elements contained in the inorganic compound 23, and is a precursor of MX22. ​​As the organic ligand 32, for example, xanthogenic acid is preferably used. In addition, as materials that can be used as the organic ligand 32, thiourea, thioacetamide, dithiocarboxylic acid, dithiocarbamic acid, trithiocarbonic acid, dimethylthiourea, and tertiary mercaptan can be cited.

[0163] As an example, the inorganic compound 23 is ZnS, the organic ligand 41 is a chloride ion (Cl2) in which the halide ion 31a is used. - ) and the case where the organic ligand 32 is replaced by xanthogenic acid is described as an example. Xanthogenic acid is a part of the precursor of MX22 (ZnS precursor) and is used as a part of the S (sulfur) source of ZnS.

[0164] Fig.23 As an example, the metal halide 31 is ZnCl2, and the halide ion 31a is Cl - 、Metal ion 31b is Zn 2+ , organic ligand 32 is xanthate ( Fig.23 The case of (indicated by "Xan") is used as an example for illustration.

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

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

[0167] As described above, the organic ligand 41 may be a carbon chain generally used as a ligand of QD. Since the solvent 42 is a solvent in which the organic ligand 41 is soluble, the QD 21 coordinated by the organic ligand 41 is easily dispersed in the QD dispersion 40 .

[0168] In addition, an excess of halide ions 31a exceeding the amount of halide ions 31a that can be coordinated to QD21 and an excess of organic ligands 32 exceeding the amount of organic ligands 32 that can be coordinated to QD21 are dissolved in the ligand solution 30. For example, more than 0.1 mol / l of halide ions 31a and more than 0.1 mol / l of organic ligands 32 may be dissolved in the ligand solution 30. In addition, in the ligand solution 30, the molar ratio of the dissolved amount of halide ions 31a to the dissolved amount of organic ligands 32 may be 3:1.

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

[0170] Here, as described above, the ligand solution 30 contains an excess of halide ions 31a and an excess of organic ligands 32. Generally speaking, when the solution in which the QD is dispersed contains two or more ligands, the ligands coordinated to the QDs are in equilibrium between the ligands in the solution. Therefore, when the ligand solution 30 and the QD dispersion 40 are stirred, at least a portion of the ligands coordinated to the QD21 are replaced by the halide ions 31a and the organic ligands 32 from the organic ligands 41.

[0171] Therefore, by the above stirring, Fig.23 As shown in step S21 b , in the container 61 , a QD dispersion 51 in which QDs 21 coordinated with halide ions 31 a and organic ligands 32 are dispersed in the solvent 33 and a ligand solution 52 in which the organic ligands 41 are dissolved in the solvent 42 can be obtained.

[0172] In summary, QD21 coordinated with halide ions 31a and organic ligands 32 is obtained in QD dispersion 51. The stirring may be considered complete when ultraviolet rays are irradiated on the liquid in container 61 and a light-emitting liquid layer is confirmed to move from the upper side of container 61 to the lower side.

[0173] Then, if Fig.23As shown in step S21c, only the QD dispersion liquid 51 is extracted from the container 61 and transferred to the container 62.

[0174] Fig.24 It is a schematic cross-sectional view showing the process after step S21 of step S11.

[0175] like Fig.24 As shown, when the inorganic compound 23 is ZnS, after step S21c, the QD dispersion 51 extracted in step S21c and zinc xanthate as the precursor 34 of MX22 (ZnS precursor) are mixed in the container 62 (step S22). Fig.24 In the above, Zn(EtXan)2 represents zinc xanthate. Zinc xanthate is used as a part of the S (sulfur) source of ZnS and a Zn (zinc) source.

[0176] Thus, the chloride ion (Cl1 - ) and QD21 of xanthate as an organic ligand 32 used as a precursor, and zinc xanthate as a part of the S source and a precursor 34 of the Zn source are dispersed in, for example, a solvent 33 as a first solvent for dispersion or dissolution. Thus, a QD dispersion 53 (see FIG. 5 ) containing QD21, xanthate and zinc xanthate as precursors (ZnS precursors) of the inorganic compound 23 (MX22), halide ions 31a, and the solvent 33 is prepared (liquid preparation). Fig.25 S31).

[0177] When the halide ions 31 a are used as ligands, the quantum yield (QY) of the obtained light-emitting element 1 is slightly lower than that of the case where an organic ligand is used.

[0178] However, as described above, by using halide ions 31a as ligands, QD21 can be dispersed in a polar solvent. Figure 2 As shown, for example, when the halide ion 31a is coordinated to the shell 21S of QD21, the dispersibility of QD21 in the polar solvent is high, and it is difficult to precipitate QD21. In addition, by coordinating the halide ion 31a to the shell 21S of QD21, the aggregation of QD21 caused by the precursor reaction of MX222 on the surface of QD21 can be suppressed, and the dispersibility of QD21 can be maintained for a long time.

[0179] On the other hand, the dispersibility of QD21 in a polar solvent using xanthogenic acid as an organic ligand is low compared to the case of using a halogen ligand. However, by using xanthogenic acid as a ligand, the QY of the obtained light-emitting element 1 can be improved.

[0180] Next, step S3 will be described.

[0181] (Step S3) Fig.25 1 is a process cross-sectional view showing an example of a part of the EML forming process (step S3). Fig.25 The substrate as a support and the anode 11 are omitted in the figure.

[0182] like Fig.25 As shown, in step S3, first, the QD dispersion 53 manufactured in step S11 is coated on the HTL 12. As described above, the QD dispersion 53 contains a plurality of QDs 21, xanthogenic acid and zinc xanthogenic acid as precursors of the inorganic compound 23 (first inorganic compound), halide ions 31a, and a solvent 33 as a first solvent. And, Fig.25 In the formula, Xan represents xanthate, Zn(EtXan)2 represents zinc xanthate, and Cl - Indicates the halide ions 31a. Thus, a coating film of the QD dispersion liquid 53 is formed on the HTL 12 (step S31, quantum dot dispersion liquid coating step).

[0183] In addition, as a method for forming a coating film, for example, any method such as a bar coating method, a spin coating method, and an ink jet method can be appropriately selected.

[0184] Next, the xanthogenic acid and zinc xanthogenic acid precursors of the inorganic compound 23 are heated to a temperature higher than the thermal decomposition temperature (e.g. Fig.26 As shown, the coating of the QD dispersion 53 is heated at 150-200° C. As a result, at least a portion of the precursor of the inorganic compound 23 is thermally decomposed, and the solvent 33 is removed. As a result, a first film of MX22 containing the inorganic compound 23 and a plurality of QDs 21 constituting the first layer 22a is formed (step S32, first film forming step).

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

[0186] like Fig.26 As shown, zinc xanthate has a structure in which Zn is bonded to xanthate. Xanthate and zinc xanthate are precursors of the inorganic compound 23, and these xanthate and zinc xanthate are thermally decomposed by heating, and the organic components are gasified, while Zn and S are combined to form ZnS. In this way, the QD dispersion 53 is formed into a bulk inorganic compound 23 by thermal decomposition of the precursor of the inorganic compound 23. In addition, when nanoparticles of an inorganic compound are used as the inorganic compound, there are many gaps and the above-mentioned purpose cannot be achieved.

[0187] Fig. 27 This is a graph showing the measurement results based on TGA (thermogravimetric analysis) indicating the thermal decomposition property of zinc xanthate (Zn(EtXan)2).

[0188] like Fig. 27 As shown in FIG. 1 , when the mass of zinc xanthate before heating is set to 100 wt %, zinc xanthate is thermally decomposed by heating, and the organic components are gasified, so that the mass gradually decreases. Fig. 27 As shown, zinc xanthate is used in e.g. The molten metal was thermally decomposed to a great extent, and the mass was reduced to less than 40 wt % of the mass before heating.

[0189] Fig.28 It is a graph showing the measurement results using a film thickness step meter when the first film is formed. Fig.28 In FIG. 1 , the horizontal axis represents the scanning distance, and the vertical axis represents the film thickness (step). Fig.28 The graph shows the change in the film thickness of the first layer 22a of MX22 when the coating film of the QD dispersion liquid 53 is heated at 100°C, 125°C, and 175°C, respectively, when p-TPD is used as the HTL 12, THF is used as the solvent 33, and ZnS is used as the inorganic compound 23.

[0190] like Fig. 27 As shown in FIG. 1 , if the heating temperature exceeds 125°C, the zinc xanthate is greatly thermally decomposed, the mass is reduced, and the volume is reduced accordingly, so that Fig.28 As shown, the film thickness of the first layer 22a of MX22 is reduced. In particular, when the coating film of the QD dispersion liquid 53 is heated at 175°C, which is much higher than the thermal decomposition point of zinc xanthate, the entire coating film is decomposed, and the mass and film thickness are greatly reduced.

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

[0192] Figure 29 to Figure 31 Each of them is a cross-sectional view showing an example of formation of the first layer 22 a formed in step S32 .

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

[0194] Therefore, by adjusting the concentration of the precursor of the inorganic compound 23 contained in the QD dispersion 53, Figure 1 At the boundary surface 221 between the first layer 22a and the second layer 22b shown in FIG. 1 , an outer edge portion of the MX22 containing the inorganic compound 23 intersects with the QD array 21L, and can form, for example Fig.29 The first layer 22a is shown.

[0195] According to this embodiment, Fig.29As shown, the concentration of, for example, the inorganic compound 23 contained in MX22 can be changed within the thickness range of one QD21 in the thickness direction of the EML13. Therefore, even when, for example, only one QD21 is stacked in the thickness direction of the EML13, the carrier balance can be adjusted to improve the luminous efficiency.

[0196] In addition, in step S32, for example, if the inorganic compound 23 has good adhesion to the QD 21, the inorganic compound 23 is formed around the QD 21, and then the overall volume of the first layer 22a is reduced. In this case, by adjusting the concentration of the precursor of the inorganic compound 23 and controlling the mass reduction (film thickness reduction) of the precursor of the inorganic compound 23, it is possible to form, for example Fig.30 or Fig.31 The first layer 22a is shown.

[0197] Fig.32 as well as Fig.33 Each of them is a process cross-sectional view showing an example of a part of the process of forming the EML (step S3). Fig.32 and Fig.33 As an example, in Fig.29 The case where the second layer 22b is formed on the first layer 22a is illustrated as an example.

[0198] In this way, if the QD dispersion 53 containing QD21 and xanthogenic acid and zinc xanthogenic acid as precursors of the inorganic compound 23 is applied on, for example, HTL12, which serves as a base layer and heated, the xanthogenic acid and zinc xanthogenic acid around QD21 are decomposed. Thus, ZnS is formed as the inorganic compound 23, and the area around QD21 is covered with ZnS, forming a part of MX22. ​​At this time, as described above, by adjusting the concentration of the precursor of the inorganic compound 23, only the area around QD21 can be covered with the inorganic compound 23, or the area around QD21 can be covered with the inorganic compound 23.

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

[0200] The inorganic compound precursor solution 54 contains a precursor of the inorganic compound 24 and a solvent 55 (second solvent) that dissolves the inorganic compound 24. The solvent 55 can be the same solvent as the solvent exemplified as the first solvent. Fig.32 In the figure, the inorganic compound 24 is magnesium sulfide (MgS), and magnesium xanthate is used as a precursor of the inorganic compound 24. Fig.32 In the above, Mg(EtXan)2 represents magnesium xanthate. Thus, a coating film of the inorganic compound precursor solution 54 is formed on the first film.

[0201] The inorganic compound precursor solution 54 may be supplied onto the first film without particular limitation. The inorganic compound precursor solution 54 may be spread on the first film or applied on the first film by bar coating, spin coating, ink jet coating, or the like.

[0202] Next, the inorganic compound precursor solution 54 supplied in the above step S33 is heated at a temperature higher than the thermal decomposition temperature of the precursor of the inorganic compound 24, so that at least a portion of the precursor of the inorganic compound 24 is thermally decomposed, and the solvent 55 is removed. The magnesium xanthate used as the precursor of the inorganic compound 24 is also thermally decomposed by heating, similarly to the zinc xanthate, so that the organic components are gasified, and the mass gradually decreases. Accordingly, the volume decreases, and the film thickness of the second layer 22b of MX22 is reduced. As a result, as Fig.33 As shown, MX22 containing the inorganic compound 24 as a main component is formed as the second layer 22b (step S34, second inorganic compound forming step). Thus, the EML 13 including the QDs 21 and the first layer 22a and the second layer 22b as MX22 is formed.

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

[0204] Magnesium xanthate is a precursor of the inorganic compound 24. Magnesium xanthate is thermally decomposed by heating, and the organic component is gasified, while Mg and S are combined to form MgS. In this way, the inorganic compound precursor solution 54 forms a bulk inorganic compound 24 by thermally decomposing the precursor of the inorganic compound 24.

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

[0206] And, if Fig.26As shown, the inorganic compound is ZnS. When ZnS is used as a precursor of the inorganic compound, Fig.34 M is Zn. In addition, the inorganic compound is InS (for example, In2S3). When indium xanthate is used as a precursor of the inorganic compound, M is In (indium). Indium xanthate serves as a S source and an In source of InS.

[0207] (Variation Example) exist Figure 1 In the embodiment, the case where the anode 11 is a lower electrode, the cathode 15 is an upper electrode, and the EML 13 is provided on the HTL 12 is exemplified. However, the present disclosure is not limited thereto.

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

[0209] The light emitting element 1 can be Figure 1 As shown, it has a conventional structure, or it can be Fig.35 As shown, it has an inverter structure.

[0210] Fig.35 The light emitting element 1 shown has the following structure: the cathode 15 is a lower electrode, the anode 11 is an upper electrode, and the HTL 12 is arranged on the EML 13. Fig.35 As shown, the light emitting element 1 may have a structure in which a cathode 15 , an ETL 14 , an EML 13 , an HTL 12 , and an anode 11 are provided in order from the lower layer side (eg, the support side of the substrate not shown).

[0211] In this case, if Fig.35 As shown, the stacking order of the light emitting element 1 is Figure 1 The light-emitting element 1 shown is the opposite. Therefore, when manufacturing such a light-emitting element 1, first, a cathode 15 is formed on a substrate serving as a support (step S5, cathode forming process). Then, ETL 14 is formed (step S4, ETL forming process). In addition, a QD dispersion is manufactured (adjusted) in parallel (step S11, QD dispersion manufacturing process). Then, EML 13 is formed using the QD dispersion (step S3, EML forming process). Then, HTL 12 is formed (step S2, HTL forming process). Then, a cathode 11 is formed (step S1, cathode forming process). Thus, the light-emitting element 1 is manufactured.

[0212] In this case, the inorganic compound 24 is used as the first inorganic compound, and the inorganic compound 23 is used as the second inorganic compound. Therefore, in step S11, a QD dispersion containing a precursor of the inorganic compound 24 instead of the precursor of the inorganic compound 23 is manufactured. Therefore, as the first solvent contained in the above-mentioned QD dispersion, for example, when the inorganic compound 24 is MgS, for example, a QD dispersion containing QD21, xanthogenic acid and magnesium xanthogenic acid as a precursor (MgS precursor) of the inorganic compound 24 (MX22), halide ions 31a, and a solvent (first solvent) for dispersing or dissolving them can be manufactured.

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

[0214] [Second embodiment] Fig.36 It is a cross-sectional view showing an example of a schematic configuration of the light emitting element 1 according to the present embodiment.

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

[0216] Fig.36 MX22 shown contains, in addition to the inorganic compound 23 and the inorganic compound 24, the inorganic compound 25 as an inorganic compound.

[0217] therefore, Fig.36 In the light-emitting element 1 shown, in the direction of the straight line L1 penetrating the outer edge 13a and the outer edge 13b in the EML 13, the MX 22 has a first region containing at least an inorganic compound 23, a second region containing at least an inorganic compound 24, and a third region containing at least an inorganic compound 25. The second region is disposed on the outer edge 13b side relative to the first region. The third region is disposed on the outer edge 13b side relative to the second region.

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

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

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

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

[0222] Furthermore, the first region is formed by sandwiching the second region between the first region and the third region, so that the penetration degree of the inorganic compound 24 into the first region is different from the penetration degree of the inorganic compound 25 into the first region. Therefore, in the first region, the concentration of the inorganic compound 24 is different from the concentration of the inorganic compound 25, and the concentration of the inorganic compound 24 is higher than the concentration of the inorganic compound 25. Similarly, the third region is formed by sandwiching the second region between the third region and the first region, so that the penetration degree of the inorganic compound 24 into the third region is different from the penetration degree of the inorganic compound 23 into the third region. Therefore, in the third region, the concentration of the inorganic compound 24 is different from the concentration of the inorganic compound 23, and the concentration of the inorganic compound 24 is higher than the concentration of the inorganic compound 23. However, in the second region, the inorganic compound 23 and the inorganic compound 25 may be the same concentration.

[0223] In addition, in the first embodiment, the concentration of the inorganic compound 23, the concentration of the inorganic compound 24, and the concentration of the inorganic compound 25 can be controlled by using Fig.12 and Fig.13 The measurements were performed in the same manner as described.

[0224] exist Fig.36 In the figure, an example is shown in which MX22 includes a first layer 22a having an inorganic compound 23 as a first region, a second layer 22b having an inorganic compound 24 as a second region, and a third layer 22c having an inorganic compound 25 as a third region. Fig.36In the example, the EML 13 is provided with a QD column 21L in the layer thickness direction of the EML 13, and the QD column 21L is arranged with a plurality of QDs 21 in a direction perpendicular to the layer thickness direction of the EML 13, and the interface 22I between the first layer 22a and the second layer 22b and the interface 22B between the second layer 22b and the third layer 22c respectively intersect with the QD column 21L. However, the present embodiment is not limited thereto. In the present embodiment, for example, Figure 15 to Figure 21 As shown, QD 21 may be stacked in multiple layers in the thickness direction of EML 13, and the boundary surfaces of the layers may not be clearly distinguished.

[0225] In addition, in the present embodiment, EML 13 preferably includes a region where the concentration of inorganic compound 23 in MX 22 is 80% or more within a range of at least 1 nm from outer edge 13a. As described above, by forming MX 22 near outer edge 13a with a relatively uniform composition, carriers are easily injected from the anode 11 side into QD 21 near outer edge 13a.

[0226] In addition, in the present embodiment, EML 13 preferably includes a region where the concentration of inorganic compound 25 in MX 22 is 80% or more within a range of at least 1 nm from outer edge 13 b. As described above, MX 22 near outer edge 13 b is formed of a relatively uniform component, so that carriers are easily injected from cathode 15 side into QD 21 near outer edge 13 b.

[0227] In this embodiment, for example, when electrons are excessive and holes are insufficient, in order to improve carrier balance, it is preferable to reduce the amount of electrons injected into the EML 13 or increase the amount of holes injected.

[0228] Therefore, as described above, in the case where electrons are in excess and holes are insufficient, for example, an inorganic compound having an Eg greater than that of the inorganic compound 23 is preferably used as the inorganic compound 24, and an inorganic compound having an Eg greater than that of the inorganic compound 24 is preferably used as the inorganic compound 25. In other words, an inorganic compound having an Eg smaller than that of the inorganic compound 24 is preferably used as the inorganic compound 23, and an inorganic compound having an Eg smaller than that of the inorganic compound 25 is preferably used as the inorganic compound 24. In this case, the injection of electrons can be suppressed to adjust the carrier balance, thereby improving the luminous efficiency and reliability.

[0229] In addition, as described above, when electrons are in excess and holes are insufficient, for example, an inorganic compound having a hole mobility greater than that of the inorganic compound 24 is preferably used as the inorganic compound 23, and an inorganic compound having an electron mobility less than that of the inorganic compound 24 is preferably used as the inorganic compound 25. In this case, holes are easily injected, and on the other hand, the injection of electrons is suppressed to adjust the carrier balance, which can improve the luminous efficiency and reliability.

[0230] Therefore, as described above, in the case of excess electrons and insufficient holes, for example, the inorganic compound 23 is indium sulfide (InS), the inorganic compound 24 is zinc sulfide (ZnS), and the inorganic compound 25 is magnesium sulfide (MgS). In this case, the indium sulfide (InS) may be, for example, In2S3.

[0231] Thus, in the case of excess electrons and insufficient holes, for example, by changing MX22 (specifically, inorganic compound 23) on the HTL12 side to MX22 whose main component is an inorganic compound with a smaller Eg than MX22 (specifically, inorganic compound 25) on the ETL14 side and a high hole mobility (small effective hole mass), hole injection can be promoted and the excess electrons can be adjusted. In addition, for example, by changing MX22 on the ETL14 side to MX22 whose main component is an inorganic compound with a larger Eg than MX22 on the HTL12 side and a low electron mobility (large effective electron mass), electron injection can be suppressed and the insufficient holes can be adjusted.

[0232] On the other hand, when electrons are insufficient and holes are excessive, for example, an inorganic compound having an Eg greater than that of the inorganic compound 24 is preferably used as the inorganic compound 23, and an inorganic compound having an Eg greater than that of the inorganic compound 24 is preferably used as the inorganic compound 25. In other words, an inorganic compound having an Eg smaller than that of the inorganic compound 23 is preferably used as the inorganic compound 24, and an inorganic compound having an Eg smaller than that of the inorganic compound 24 is preferably used as the inorganic compound 25. In this case, the injection of holes can be suppressed to adjust the carrier balance, thereby improving the luminous efficiency and reliability.

[0233] In addition, as described above, when electrons are insufficient and holes are excessive, for example, an inorganic compound having an electron mobility greater than that of the inorganic compound 23 is preferably used as the inorganic compound 24, and an inorganic compound having an electron mobility greater than that of the inorganic compound 24 is preferably used as the inorganic compound 25. In this case, electrons are easily injected, carrier balance is adjusted, and luminous efficiency and reliability can be improved.

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

[0235] The method for manufacturing the light emitting element 1 of the present embodiment is the same as the method for manufacturing the light emitting element 1 of the first embodiment except for the following points.

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

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

[0238] As described above, as the inorganic compound 23, for example, indium sulfide (e.g., In2S3) can be used. As the inorganic compound 24, for example, zinc sulfide (ZnS) can be used. As the inorganic compound 25, for example, magnesium sulfide (MgS) can be used. In this case, xanthogenic acid and indium xanthogenic acid are used as precursors of the inorganic compound 23. In addition, zinc xanthogenic acid is used as a precursor of the inorganic compound 24. In addition, magnesium xanthogenic acid is used as a precursor of the inorganic compound 25. The reaction scheme is as follows: Fig.34 shown.

[0239] Next, the third inorganic compound precursor solution supplied in the above step S35 is heated at a temperature above the thermal decomposition temperature of the precursor of the inorganic compound 25, so that at least a portion of the precursor of the inorganic compound 25 is thermally decomposed, and the above third solvent is removed. Thus, as the third layer 22c, MX22 containing the inorganic compound 25 as the main component is formed (step S36, third inorganic compound forming step). Thus, EML13 containing QD21 and containing the first layer 22a, the second layer 22b and the third layer 22c as MX22 is formed.

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

[0241] Furthermore, in the present embodiment, although the case where MX22 contains three inorganic compounds is described as an example, the present embodiment is not limited thereto. MX22 may contain, for example, four or more inorganic compounds.

[0242] [Third embodiment] The light emitting element 1 can be preferably used as a light source of a light emitting device such as a display device or a lighting device. A light emitting device can include at least one light emitting element 1. Hereinafter, a case where the light emitting element 1 is used as a light source of a display device will be described as an example.

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

[0244] The present disclosure is not limited to the above-mentioned embodiments, and various changes can be made within the scope of the claims. The embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. Moreover, new technical features can be formed by combining the technical methods disclosed in each embodiment.

[0245] 1. 100 light emitting elements 11 Anode 15 Cathode 13, 13A, 13B EML (luminescent layer) 13a, 13b outer edge 21 QD (Quantum Dot) 21L QD array (quantum dot array) 21C Core 21S Shell 22MX (base material) 22I, 22B boundary surface 23, 24, 25 Inorganic compounds 31a Halide ions 33 solvent (first solvent) 34 Precursor 53 QD dispersion (quantum dot dispersion) 54 Inorganic compound precursor solution (second inorganic compound precursor solution) 55 solvent (second solvent) 70 Display device L1 Straight Line

Claims

1. A light-emitting element comprising a first electrode, a second electrode, and a light-emitting layer disposed between the first electrode and the second electrode, characterized in that: The light-emitting layer comprises a plurality of quantum dots and a matrix material, The matrix material comprises a first inorganic compound and a second inorganic compound, The base material has a first region containing at least the first inorganic compound and a second region containing at least the second inorganic compound in a straight line direction penetrating a first outer edge portion on the first electrode side and a second outer edge portion on the second electrode side in the light-emitting layer, The second region is disposed closer to the second outer edge than the first region. The concentration of the first inorganic compound in the first region and the concentration of the first inorganic compound in the second region differ by a certain amount or more.

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

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

4. The light emitting element according to any one of claims 1 to 3, wherein A boundary surface between the first region and the second region intersects the plurality of quantum dots.

5. The light-emitting element according to any one of claims 1 to 4, wherein The light-emitting layer comprises at least one quantum dot array in the thickness direction of the light-emitting layer, wherein the quantum dot array is a plurality of quantum dots arranged in a direction perpendicular to the thickness direction of the light-emitting layer. The base material includes, as the first region, a first layer having the first inorganic compound as a main component, and as the second region, a second layer having the second inorganic compound as a main component, A boundary surface between the first layer and the second layer intersects the quantum dot array.

6. The light-emitting element according to any one of claims 1 to 4, wherein A concentration of the first inorganic compound in the first region is greater than a concentration of the second inorganic compound in the first region, and a concentration of the second inorganic compound in the second region is greater than a concentration of the first inorganic compound in the second region.

7. The light emitting element according to claim 6, wherein: The first electrode is an anode, The second electrode is a cathode, The band gap of the second inorganic compound is greater than the band gap of the first inorganic compound.

8. The light emitting element according to claim 6, wherein: The first electrode is an anode, The second electrode is a cathode, The band gap of the first inorganic compound is greater than the band gap of the second inorganic compound.

9. The light emitting element according to claim 6, wherein: The first electrode is an anode, The second electrode is a cathode, The hole mobility of the first inorganic compound is greater than the hole mobility of the second inorganic compound.

10. The light emitting element according to claim 6, wherein The first electrode is an anode, The second electrode is a cathode, The electron mobility of the second inorganic compound is greater than the electron mobility of the first inorganic compound.

11. The light-emitting element according to any one of claims 1 to 10, wherein The first inorganic compound and the second inorganic compound are metal sulfides.

12. The light emitting element according to any one of claims 1 to 8 and 10, wherein: The first inorganic compound is indium sulfide, The second inorganic compound is magnesium sulfide.

13. The light emitting element according to any one of claims 1 to 8 and 10, wherein The first inorganic compound is zinc sulfide, The second inorganic compound is magnesium sulfide.

14. The light emitting element according to any one of claims 1 to 8 and 10, wherein: The first inorganic compound is indium sulfide, The second inorganic compound is zinc sulfide.

15. The light-emitting element according to any one of claims 1 to 14, wherein The light-emitting layer includes a region where the concentration of the second inorganic compound in the matrix material is 80% or more within a range of at least 1 nm from the second outer edge portion.

16. The light-emitting element according to any one of claims 1 to 14, wherein The matrix material further comprises a third inorganic compound, The base material further has a third region in the linear direction, and the third region contains at least the third inorganic compound. The third region is disposed closer to the second outer edge portion than the second region. The concentration of the third inorganic compound in the third region is different from the concentration of the third inorganic compound in at least one of the first region and the second region by a certain amount or more.

17. The light emitting element according to claim 7, wherein: The matrix material further contains a third inorganic compound having a larger band gap than the second inorganic compound, The base material further has a third region in the linear direction, and the third region contains at least the third inorganic compound. The third region is disposed closer to the second outer edge portion than the second region. A concentration of the third inorganic compound in the third region is higher than concentrations of the third inorganic compound in the first region and the second region.

18. The light emitting element according to claim 8, wherein The matrix material further contains a third inorganic compound having a smaller band gap than the second inorganic compound, The base material further has a third region in the linear direction, and the third region contains at least the third inorganic compound. The third region is disposed closer to the second outer edge portion than the second region. A concentration of the third inorganic compound in the third region is higher than concentrations of the third inorganic compound in the first region and the second region.

19. The light emitting element according to claim 9, wherein The matrix material further contains a third inorganic compound having an electron mobility smaller than that of the second inorganic compound, The base material further has a third region in the linear direction, and the third region contains at least the third inorganic compound. The third region is disposed closer to the second outer edge portion than the second region. A concentration of the third inorganic compound in the third region is higher than concentrations of the third inorganic compound in the first region and the second region.

20. The light emitting element according to claim 10, wherein The matrix material further contains a third inorganic compound having an electron mobility greater than that of the second inorganic compound, The base material further has a third region in the linear direction, and the third region contains at least the third inorganic compound. The third region is disposed closer to the second outer edge portion than the second region. A concentration of the third inorganic compound in the third region is higher than concentrations of the third inorganic compound in the first region and the second region.

21. The light emitting element according to any one of claims 16, 17 and 19, wherein: The first inorganic compound is indium sulfide, The second inorganic compound is zinc sulfide, The third inorganic compound is magnesium sulfide.

22. The light emitting element according to any one of claims 16 to 21, wherein The light-emitting layer includes a region where the concentration of the third inorganic compound in the matrix material is 80% or more within a range of at least 1 nm from the second outer edge portion.

23. The light-emitting element according to any one of claims 1 to 22, wherein The quantum dot has a core and a shell, The at least one inorganic compound contained in the matrix material has a band gap larger than a band gap of the core or the shell.

24. The light emitting element according to claim 23, wherein The average distance between the cores of adjacent quantum dots is greater than or equal to 3 nm.

25. The light-emitting element according to any one of claims 1 to 24, wherein The matrix material is filled between the plurality of quantum dots of the light emitting layer.

26. The light-emitting element according to any one of claims 1 to 25, wherein The base material has a continuous film, and the continuous film has a thickness of 1000 nm in a plane direction perpendicular to the thickness direction of the light-emitting layer. 2 The area above.

27. The light-emitting element according to any one of claims 1 to 26, wherein The plurality of quantum dots are dispersed in the matrix material.

28. The light-emitting element according to any one of claims 1 to 27, wherein The plurality of quantum dots are contained in the matrix material.

29. The light-emitting element according to any one of claims 1 to 28, wherein The matrix material further contains a halogen element.

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

31. The light-emitting element according to claim 29 or 30, characterized in that: The average value of the total concentration of the halogen elements in the region within 1 nm from the outermost surface of each of the multiple quantum dots in the matrix material is more than 10% higher than the average value of the total concentration of the halogen elements in the region more than 1 nm from the outermost surface of each of the multiple quantum dots in the matrix material.

32. A display device, characterized in that: A light-emitting element according to any one of claims 1 to 31.

33. A method for manufacturing a light emitting element, The light emitting element comprises: a first electrode and a second electrode; and a light-emitting layer, arranged between the first electrode and the second electrode, the light-emitting layer comprising a plurality of quantum dots and a matrix material, the matrix material comprising a first inorganic compound and a second inorganic compound, the matrix material having a first region comprising at least the first inorganic compound and a second region comprising at least the second inorganic compound in a straight line direction passing through a first outer edge portion on the first electrode side and a second outer edge portion on the second electrode side in the light-emitting layer, the second region being arranged closer to the second outer edge portion than the first region, and a concentration of the first inorganic compound in the first region differing from a concentration of the first inorganic compound in the second region by a certain amount or more, The manufacturing method is characterized in that The manufacturing method includes a light emitting layer forming step of forming the light emitting layer. The light emitting layer forming step comprises: A quantum dot dispersion coating step, which includes coating the quantum dot dispersion and forming a coating film of the quantum dot dispersion, wherein the quantum dot dispersion includes the plurality of quantum dots, the first inorganic compound precursor, halide ions and a first solvent, and the first inorganic compound precursor is thermally decomposed to form the first inorganic compound; A first film forming step of heating the coating of the quantum dot dispersion at a temperature higher than the thermal decomposition temperature of the precursor of the first inorganic compound to thermally decompose at least a portion of the precursor of the first inorganic compound and remove the first solvent, thereby forming a first film including the plurality of quantum dots and a matrix material including the first inorganic compound; A second inorganic compound precursor solution supplying step, which supplies the second inorganic compound precursor solution onto the first film, wherein the second inorganic compound precursor solution comprises the second inorganic compound precursor and a second solvent, and the second inorganic compound precursor is thermally decomposed to form the second inorganic compound; A second inorganic compound forming step is performed, wherein the second inorganic compound precursor solution supplied in the second inorganic compound precursor solution supplying step is heated at a temperature above the thermal decomposition temperature of the second inorganic compound precursor, so as to thermally decompose at least a portion of the second inorganic compound precursor and remove the second solvent, thereby forming a matrix material containing the second inorganic compound.

34. The method for manufacturing a light emitting element according to claim 33, wherein: In the light-emitting layer forming process, the concentration of the precursor of the first inorganic compound contained in the quantum dot dispersion is adjusted in such a way that there is at least one quantum dot column in the thickness direction of the light-emitting layer and an outer edge portion of the matrix material containing the first inorganic compound in the first film intersects with the quantum dot column, wherein the quantum dot column refers to the plurality of quantum dots arranged in a direction perpendicular to the thickness direction of the light-emitting layer.

35. The method for manufacturing a light emitting element according to claim 33 or 34, wherein: The matrix material further comprises a third inorganic compound, The light emitting layer forming step comprises: A third inorganic compound precursor solution supplying step, wherein the third inorganic compound precursor solution is supplied to the base material containing the second inorganic compound, wherein the third inorganic compound precursor solution contains the third inorganic compound precursor and a third solvent, and the third inorganic compound precursor is thermally decomposed to form the third inorganic compound; A third inorganic compound forming step is performed, wherein the third inorganic compound precursor solution supplied in the third inorganic compound precursor solution supplying step is heated at a temperature above the thermal decomposition temperature of the third inorganic compound precursor, so as to thermally decompose at least a portion of the third inorganic compound precursor and remove the third solvent, thereby forming a matrix material containing the third inorganic compound.

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