Light-emitting element, display device

Abstract

A light-emitting element according to the present invention comprises a first electrode and a second electrode that are opposite each other and a light-emitting layer that is provided between the first electrode and the second electrode. The light-emitting layer includes a plurality of quantum dots, a medium portion that fills the space between the plurality of quantum dots, and an adduct that is positioned at at least a portion of the periphery of the quantum dots.

Description

Light-emitting element, display device

[0001] The present disclosure relates to a light-emitting element containing quantum dots as a light-emitting material, and a display device including the light-emitting element.

[0002] To improve durability, research is being conducted into covering quantum dots with silica (silicon oxide). Non-Patent Document 1 discloses a structure in which quantum dots are covered with silica having an organic ring structure introduced therein.

[0003] "Blue-Emitting InP / GaP / ZnS Quantum Dots with Enhanced Stability by Siloxane Capping: Implication for Electroluminescent Devices" (ACS Appl. Nano Mater. 2022, 5, 2801-2811)

[0004] Non-Patent Document 1 attempts to improve the carrier injection efficiency by π electrons by introducing an organic ring structure into silica, but the carrier injection is still insufficient.

[0005] A light-emitting element according to one aspect of the present disclosure comprises opposing first and second electrodes and a light-emitting layer disposed between the first and second electrodes, the light-emitting layer including a plurality of quantum dots, a medium portion filling the spaces between the plurality of quantum dots, and an additive located at least partially around the quantum dots.

[0006] A light emitting device capable of improving carrier injection into quantum dots is achieved.

[0007] 1 is a diagram showing a schematic side cross-sectional view of a display device according to an embodiment and a schematic diagram showing a medium portion filling the spaces between quantum dots. FIG. 1 is a schematic diagram of a display device according to an embodiment. FIG. 2 is a schematic enlarged view of a quantum dot and its periphery in a cross section of a light-emitting layer according to an embodiment. FIG. 3 is a schematic enlarged view of a quantum dot and its periphery in a cross section of a light-emitting layer according to a comparative embodiment. FIG. 4 is a graph showing a band diagram of a light-emitting layer according to a comparative embodiment and a probability of electrons being present at each position in the light-emitting layer. FIG. 5 is a graph showing a band diagram of a light-emitting layer according to an embodiment and a graph showing a probability of electrons being present at each position in the light-emitting layer. FIG. 6 is a graph showing the relationship between the film thickness of an additive according to an embodiment and the probability of electrons leaking out of quantum dots. FIG. 7 is a graph showing the relationship between the film thickness of an additive according to an embodiment and the probability of electrons transmitting through the additive. FIG. 8 is another graph showing the relationship between the film thickness of an additive according to an embodiment and the probability of electrons transmitting through the additive. FIG. 9 is a schematic diagram showing the arrangement of atoms at the interface between quantum dots and a sulfide semiconductor according to a comparative embodiment. FIG. 10 is a schematic diagram showing the arrangement of atoms at the interface between quantum dots, an additive, and a sulfide semiconductor according to an embodiment. FIG. 11 is a flowchart showing a method for manufacturing a display device according to an embodiment. FIG. 12 is a schematic process diagram for explaining the preparation of a quantum dot structure in the method for manufacturing a display device according to an embodiment. 1A to 1C are cross-sectional views illustrating steps in a method for forming a light-emitting layer according to an embodiment of the present invention;

[0008] [Embodiments] <Display Device: Overview> Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that in each drawing, similar components are denoted by the same reference numerals and description thereof will be omitted.

[0009] 2 is a schematic diagram of a display device according to this embodiment. The display device 1 is a device that can be used, for example, as a display for a television, a smartphone, or the like. The display device 1 includes a display unit 30 including a plurality of sub-pixels X, and a driver circuit 40 that drives the plurality of sub-pixels X. At least one of the plurality of sub-pixels X includes a light-emitting element 2 and a pixel circuit 50 that drives the light-emitting element 2. The display device 1 displays an image on the display unit 30 by controlling light emission from each of the plurality of light-emitting elements 2 formed in the display unit 30 via the driver circuit 40 and the pixel circuit 50.

[0010] The structure of the display unit 30 of the display device 1, particularly the structure of the light-emitting element 2, will be described in more detail with reference to FIG. 1 . A schematic cross-sectional side view 101 in FIG. 1 is a schematic cross-sectional side view of the display device 1 according to an embodiment of the present disclosure. In particular, the schematic cross-sectional side view 101 illustrates a cross section perpendicular to the display surface of the display device 1 and passing through the light-emitting element 2. Schematic views 102 and 103 in FIG. 1 are schematic views illustrating the sulfide semiconductor 16 filling the spaces between quantum dots 18, which will be described later. In particular, the schematic views 102 and 103 respectively illustrate two examples of a set P of two quantum dots 18 and a region (space) K between them, as shown in the schematic cross-sectional side view 101. In particular, the schematic views 102 and 103 respectively illustrate set P1 and set P2, which are examples of sets of quantum dots 18A and 18B.

[0011] As shown in the schematic side cross-sectional view 101, the display device 1 according to this embodiment includes a display unit 30 including the above-described light-emitting element 2 and a substrate 3, and the light-emitting element 2 is provided on the substrate 3. The display device 1 has a structure in which the layers of the light-emitting element 2 are stacked on the substrate 3 on which, for example, TFTs (Thin Film Transistors) (not shown) are formed as pixel circuits 50. In this specification, the direction from the light-emitting element 2 of the display device 1 to the substrate 3 is referred to as the "downward direction," and the direction opposite to the downward direction is referred to as the "upward direction."

[0012] The light-emitting element 2 includes, on an anode 4 as a first electrode, a hole transport layer 6, a light-emitting layer 8, an electron transport layer 10, and a cathode 12 as a second electrode, in this order from bottom to top. The anode 4 of the light-emitting element 2 is electrically connected to the TFT of the substrate 3.

[0013] <Outline of Light-Emitting Element> The structure of each layer of the light-emitting element 2 will be described in more detail below.

[0014] The anode 4 and the cathode 12 contain a conductive material and are electrically connected to the hole transport layer 6 and the electron transport layer 10, respectively.

[0015] At least one of the anode 4 and the cathode 12 is a transparent electrode that transmits visible light. Examples of transparent electrodes that can be used include ITO (indium tin oxide), IZO (indium zinc oxide), ZnO, AZO (aluminum-doped zinc oxide, also known as ZAO), BZO (boron-doped zinc oxide), and FTO (fluorine-doped tin oxide). The transparent electrode may be formed by a sputtering method or the like. Alternatively, either the anode 4 or the cathode 12 may contain a metal material, and preferred metal materials are Al, Cu, Au, Ag, or Mg, which have high reflectivity for visible light, or alloys of these.

[0016] The hole transport layer 6 is a layer that transports holes from the anode 4 to the light-emitting layer 8. The material of the hole transport layer 6 can be an organic or inorganic material that has been conventionally used in quantum dot-containing light-emitting devices or organic EL light-emitting devices. Examples of organic materials that can be used for the hole transport layer 6 include conductive compounds such as 4,4'-bis(carbazol-9-yl)biphenyl (CBP), polyphenylene vinylene (PPV), a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT-PSS), poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-4-sec-butylphenyl)diphenylamine)]) (TFB), and polyvinylcarbazole (PVK). Examples of inorganic materials that can be used for the hole transport layer 6 include molybdenum oxide, NiO, Cr ２ O ３ , MgO, MgZnO, LaNiO３ , MoO ３ , or W.O. ３ In particular, as the material for the hole transport layer 6, a material having a large electron affinity and ionization potential is suitable.

[0017] The electron transport layer 10 is a layer that transports electrons from the cathode 12 to the light-emitting layer 8. The electron transport layer 10 is made of a material such as TiO ２ In addition, organic or inorganic materials conventionally employed in quantum dot-containing light-emitting devices or organic EL light-emitting devices can be used. Examples of organic materials that can be used for the electron transport layer 10 include conductive compounds such as tris(8-quinolinol)aluminum complex (Alq3), bathocuproine (BCP), and (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) (t-Bu-PBD). Examples of inorganic materials that can be used for the electron transport layer 10 include metal oxides such as ZnO, ZAO, ITO, InGaZnO, and electride. Materials with low electron affinity are particularly suitable for the electron transport layer 10.

[0018] In this embodiment, the hole transport layer 6 and the electron transport layer 10 can be formed by vacuum deposition, sputtering, or a coating method using a colloidal solution using the above-mentioned materials. The light-emitting element 2 may also include a hole injection layer between the anode 4 and the hole transport layer 6, or an electron injection layer between the cathode 12 and the electron transport layer 10. The light-emitting element 2 may also include an intermediate layer between the hole transport layer 6 and the light-emitting layer 8, or between the electron transport layer 10 and the light-emitting layer 8. The hole injection layer, electron injection layer, and intermediate layer may all be formed by the same method as the hole transport layer 6 or the electron transport layer 10.

[0019] <Light-Emitting Layer> In this embodiment, the light-emitting layer 8 includes a plurality of quantum dot structures 14 and a sulfide semiconductor 16 as a medium portion. Each quantum dot structure 14 includes a quantum dot 18 and an addition 20 located around at least a portion of the quantum dot 18.

[0020] In this disclosure, "surrounding" refers to a region extending around an object (here, quantum dots 18), and the distance from the object is not particularly limited. However, "surrounding" may refer to a region extending outward from the surface of an object over a given width, or may refer to a region from quantum dots 18 having a width approximately equal to or less than the distance between adjacent quantum dots 18. Furthermore, "located around" does not necessarily mean continuously surrounding an object, but also includes cases where the object is intermittently surrounded, and cases where the object is located in only a portion of the region extending around the object.

[0021] The specific configuration of the light-emitting layer 8 will be described in more detail with reference to Fig. 3. Fig. 3 is a schematic enlarged view of one quantum dot structure 14 and its surroundings in the cross section of the light-emitting layer 8 shown in Fig. 1, and in particular, is an enlarged view of region A shown in Fig. 1.

[0022] 3, each quantum dot 18 has a core / shell structure, including a core 18C and a shell 18S formed around the core 18C. In this embodiment, recombination of electrons and holes injected into the quantum dot 18 occurs mainly in the core 18C. The shell 18S has the function of suppressing the occurrence of defects or dangling bonds in the core 18C and reducing the recombination of carriers that undergo a deactivation process.

[0023] The core 18C and shell 18S of the quantum dot 18 may contain materials used for the core and shell of conventionally known core / shell quantum dots. In this embodiment, the core 18C is made of InP and the shell 18S is made of ZnS. However, the quantum dot 18 may also have a core / shell structure of CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, ZnSe / ZnS, or CIGS / ZnS. The shell 18S may be formed of multiple layers containing multiple different materials.

[0024] The core 18C of the quantum dot 18 is a light-emitting material that has a valence band level and a conduction band level and emits light by recombination of holes in the valence band level and electrons in the conduction band level. The light emitted from the quantum dot 18 has a narrow spectrum due to the quantum confinement effect, making it possible to obtain light with a relatively deep chromaticity.

[0025] The quantum dots 18 have a particle size of about 1 to 100 nm. The wavelength of light emitted from the quantum dots 18 can be controlled by the particle size. In particular, since the quantum dots 18 have a core / shell structure, the wavelength of light emitted from the quantum dots 18 can be controlled by controlling the particle size of the cores 18C. Therefore, by controlling the particle size of the cores 18C of the quantum dots 18, the wavelength of light emitted by the display device 1 can be controlled.

[0026] In this embodiment, the addition 20 may be located, for example, all around the quantum dot 18. For example, as shown in Fig. 3 , in any cross section passing through any quantum dot 18, the addition 20 may be located all around the quantum dot 18. Here, "the addition 20 is located all around the quantum dot 18" may mean that the addition 20 is located over 90% or more of the periphery of the quantum dot 18. Furthermore, as shown in Fig. 3 , the surface of the quantum dot 18 and the addition 20 may be in contact, or the addition 20 and the sulfide semiconductor 16 may be in contact.

[0027] The band gap of the additive 20 is wider than the band gap of the constituent material of the quantum dot 18. When the quantum dot 18 has a core and a shell surrounding the core, the band gap of the additive 20 is wider than the band gap of the constituent material of the shell. Also, the band gap of the additive 20 is wider than the band gap of the constituent material of the sulfide semiconductor 16. For example, the additive 20 may include an oxide insulator, and in particular, may include oxygen atoms.

[0028] In the present disclosure, the term "atom" does not only mean an atom existing as a single atom, but also includes an atom existing in the form of a molecule having two or more atoms including the atom and another atom, an atom existing in the form of a complex, an atom existing in the form of a compound, or an atom existing in the form of an ion, and does not limit the form of existence. In other words, an oxygen atom includes an atom existing in the form of a compound having an oxygen atom, and an atom existing in the form of an oxygen ion. It is preferable that the oxygen atom be able to be identified as an oxygen element by analysis, regardless of the form of existence.

[0029] For example, the additive 20 may be an inorganic material. For example, the additive 20 may be silicon oxide (SiO ２ ), and zinc sulfide (ZnS). In addition, the additive 20 may contain, for example, titanium oxide (TiO ２ ), aluminum oxide (Al ２ O ３ ), boron oxide (B ２ O ３ ), phosphorus oxide (P ２ O ５ ), germanium oxide (GeO ２ ), hafnium oxide (HfO ２ ), zinc oxide (ZnO), zirconium oxide (ZrO ２ ), tellurium oxide (TeO ２ ), bismuth oxide (Bi ２ O ３ ), vanadium oxide (V ２ O ５ ), antimony oxide (Sb ２ O ５ The compound may contain one or more selected from the group consisting of lead oxide (PbO), lead oxide (PbO), and copper oxide (CuO). The chemical formulas written in parentheses after the compound names are representative examples. The composition ratios written in the chemical formulas may be stoichiometric, but do not necessarily have to be stoichiometric.

[0030] The band gap of the additive 20 containing any of the above-mentioned materials tends to be larger than the band gaps of the sulfide semiconductor 16 and the quantum dots 18. Therefore, for reasons described below, the additive 20 containing any of the above-mentioned materials increases the probability of generating excitons in the core 18C of the light-emitting layer 8, improving the luminous efficiency of the quantum dots 18.

[0031] The addition 20 may have a solid portion. This configuration can enhance the effect of the addition 20 in protecting the quantum dots 18. In the present disclosure, "solid" may refer to I. the size of the missing region being 5 nm or less. For example, if it is confirmed in cross-sectional observation that the maximum width of the missing region is 5 nm or less, the component having the cross-section can be said to be solid. In the present disclosure, "solid" may also refer to II. the volume of the addition 20 in the light-emitting layer 8 being 9 times or more the volume of the void. Alternatively, in the present disclosure, "solid" may also refer to III. the absence of a region lacking a constituent element of the addition 20, or a region so small that it can be ignored. For a component to be solid, it is sufficient that it satisfies the above condition I. However, it is sufficient to satisfy condition II only if it cannot be identified by I, and it is sufficient to satisfy condition III only if it cannot be identified by II. In the cross-sectional observation, it is sufficient to confirm the cross-section of a region 100 nm wide. The maximum thickness of the solid portion of the addition 20 may be 1 nm or less, and the minimum thickness may be 0.1 nm or more.

[0032] Hereinafter, unless otherwise specified, the "thickness of the addition 20" refers to the thickness of the solid portion of the addition 20. Furthermore, the thickness of the addition 20 in this embodiment refers to the size in the radial direction from the quantum dot 18 as the center, and particularly refers to the thickness in the normal direction to the surface of the quantum dot 18.

[0033] The additive 20 may also be a dense discontinuous film having at least one discontinuity. The "discontinuity" may be a region where one or more of the constituent elements of the additive 20 are missing, and typically has a size of more than 8 nm. The discontinuity may penetrate the additive 20 three-dimensionally. Furthermore, when the additive 20 for one quantum dot 18 is composed of multiple parts that are separate and independent from each other, the discontinuity may include a gap between the multiple parts. A "dense discontinuous film" may mean a film that has discontinuities and where the regions other than the discontinuities are dense. The additive 20 may include a continuous film with a non-uniform thickness.

[0034] The additive 20 may be porous and may include a continuous film surrounding the quantum dots 18 at a cross section through the quantum dots 18. With this configuration, the additive 20 protects the quantum dots 18, and carriers can be injected into the quantum dots 18 through the pores of the additive 20. The porous pores may be regions lacking one or more of the constituent elements of the additive 20, and typically have a size of more than 5 nm and not more than 8 nm. The pores may penetrate the additive 20 three-dimensionally.

[0035] The quantum dot structures 14 in the light-emitting layer 8 do not need to be arranged regularly as shown in Fig. 1, and the quantum dot structures 14 may be included in the light-emitting layer 8 in a disordered manner. In the light-emitting layer 8 shown in Fig. 1, a sulfide semiconductor 16 and an additive 20, which will be described later, are formed between two quantum dots 18, and the quantum dots 18 are not in contact with each other. However, this is not a limitation, and the light-emitting layer 8 may include two or more quantum dots 18 that are in contact with each other. The film thickness of the light-emitting layer 8 may be approximately 1 nm to 100 nm.

[0036] In this embodiment, the sulfide semiconductor 16 contained in the light emitting layer 8 may contain a metal sulfide, such as zinc sulfide (ZnS), gallium sulfide (Ga ２ S ３ ), magnesium sulfide (MgS), cadmium sulfide (CdS), tin sulfide (SnS ２ ), indium sulfide (In ２ S ３The sulfide semiconductor 16 may include at least one of ZnTeS, ZnMgS, and manganese sulfide (MnS). ２ , ZnGa ２ S ４ , MgGa ２ S ４ In this embodiment, a case will be described in which the light emitting layer 8 is an integrated film of a sulfide semiconductor 16 containing ZnS and the quantum dot structure 14. In this way, the sulfide semiconductor 16 protects the quantum dot structure 14, thereby improving the reliability of the light emitting layer 8.

[0037] However, light-emitting layer 8 may contain metal sulfides or metal oxides other than sulfide semiconductor 16, as long as the injection of carriers from each charge transport layer to quantum dots 18 and the transmission of visible light are not hindered. The metal sulfides or metal oxides other than sulfide semiconductor 16 in light-emitting layer 8 may be less than 50 atomic %, more preferably 30 atomic % or less, and even more preferably 10 atomic % or less.

[0038] The sulfide semiconductor 16 according to this embodiment fills the spaces between the quantum dots 18. In other words, the light-emitting layer 8 includes the sulfide semiconductor 16 as a medium portion that fills the spaces between the quantum dots 18.

[0039] Note that, "the sulfide semiconductor 16 filling the spaces between the quantum dots 18" means that the sulfide semiconductor 16 fills at least the region K between the quantum dots 18A and 18B, as shown in the schematic diagram 102 of the set P1 in FIG. 1 . The region K is a region surrounded by two lines (common circumscribing lines) tangent to the peripheries of the quantum dots 18A and 18B and the opposing peripheries of the quantum dots 18A and 18B in the cross section of the light-emitting layer 8. Therefore, as shown in the schematic diagram 103 of the set P2 in FIG. 1 , the region K can exist even if the quantum dots 18A and 18B are close to each other, and the sulfide semiconductor 16 fills the region K.

[0040] The expression "the sulfide semiconductor 16 fills the spaces between the quantum dots 18" does not necessarily mean that the region K between the quantum dots 18A and 18B is entirely composed of the sulfide semiconductor 16. For example, the region K between the quantum dots 18A and 18B may contain the above-described additive 20, and may also contain a material, such as a ligand, different from the material of the sulfide semiconductor 16. Specifically, for example, the light-emitting layer 8 may contain an organic ligand that is added to improve the dispersibility of the quantum dots 18 in a solution used for coating and that coordinates to the outer surfaces of the quantum dots 18 in the solution. In this case, in the light-emitting layer 8, from the viewpoint of improving the reliability of the light-emitting layer 8, the weight ratio of the organic ligand to the total weight including the region K may be less than 5%, for example.

[0041] The sulfide semiconductor 16 may fill the region of the light-emitting layer 8 other than the region where the quantum dots 18 are formed. For example, the outer edge (upper and lower surfaces) of the light-emitting layer 8 may be covered with the sulfide semiconductor 16. Alternatively, the light-emitting layer 8 may be configured such that a portion of the sulfide semiconductor 16 extends from the outer edge, with the quantum dots 18 positioned away from the outer edge. The outer edge of the light-emitting layer 8 may not be formed solely of the sulfide semiconductor 16, and some of the quantum dots 18 may be exposed from the sulfide semiconductor 16. The sulfide semiconductor 16 may refer to the portion of the light-emitting layer 8 excluding the plurality of quantum dots 18.

[0042] The sulfide semiconductor 16 is formed at a position in the thickness direction of the light emitting layer 8 so as to have a thickness of 1000 nm in a plane perpendicular to the thickness direction. ２ In the light-emitting layer 8, the quantum dot structure 14 may be encapsulated in a continuous film of the sulfide semiconductor 16, in other words, the quantum dots 18 may be encapsulated in a continuous film of the sulfide semiconductor 16. In this case, the composition of the additive 20 may be different from the composition of the sulfide semiconductor 16.

[0043] For example, when 60% or more of the surface of 80% or more of the quantum dot structures 14 constituting the light-emitting layer 8 is in contact with the continuous film of the sulfide semiconductor 16, it can be said that the quantum dot structures 14 included in the light-emitting layer 8 are encapsulated in the sulfide semiconductor 16. In this way, the quantum dot structures 14 encapsulated in the sulfide semiconductor 16, in other words, the light-emitting layer 8 including the quantum dots 18 encapsulated in the sulfide semiconductor 16, improves the light-emitting characteristics and extends the lifetime.

[0044] The light-emitting layer 8 has a thickness of 1000 nm or less in a plane direction perpendicular to the film thickness direction at any position in the film thickness direction. ２ The light-emitting layer 8 may contain one or more quantum dot structures 14 per layer. In this case, the light-emitting layer 8 generally contains a sufficient concentration of quantum dots 18 to function as the light-emitting layer of a light-emitting device.

[0045] The band gap of the sulfide semiconductor 16 contained in the light-emitting layer 8 may be larger than the band gap of the material of the core 18C of the quantum dot 18. In this case, excitons generated by carrier recombination or light absorption in the core 18C of the quantum dot 18 are less likely to diffuse into the sulfide semiconductor 16, and the light-emitting properties of the quantum dot 18 are less likely to be impaired.

[0046] As will be described later, when the light-emitting layer 8 is formed from a quantum dot dispersion liquid containing quantum dots 18, a drying step of drying the quantum dot dispersion liquid by heating may be included. Here, in the drying step, for example, the laminate containing the quantum dot dispersion liquid applied onto the hole transport layer 6 is heated to 80°C to 500°C. Therefore, in this embodiment, from the viewpoint of the heat resistance of the light-emitting element 2, all of the layers provided in the light-emitting element 2, from the anode 4 to the cathode 12, may be formed from inorganic layers.

[0047] The effects of the light-emitting element 2 according to this embodiment will be described by comparing it with a light-emitting element according to a comparative embodiment. The light-emitting element according to the comparative embodiment has the same configuration as the light-emitting element 2 according to this embodiment, except that it includes a light-emitting layer 8A instead of the light-emitting layer 8 according to this embodiment.

[0048] A light-emitting layer 8A according to a comparative example will be described with reference to Fig. 4. Fig. 4 is a schematic cross-sectional side view of the light-emitting layer 8A, and in particular, is an enlarged view of a quantum dot structure 14A (described later) and its surroundings.

[0049] The light-emitting layer 8A has the same configuration as the light-emitting layer 8, except that it includes a quantum dot structure 14A instead of the quantum dot structure 14. The quantum dot structure 14A has the same configuration as the quantum dot structure 14, except that it does not include the additive 20. Therefore, in the light-emitting layer 8A, the sulfide semiconductor 16 fills the spaces between the multiple quantum dots 18, and the sulfide semiconductor 16 and the shells 18S of the quantum dots 18 are in contact with each other.

[0050] Problems that arise in the light-emitting element according to the comparative example will be described with reference to Fig. 5. Fig. 5 shows a band diagram 501 of the light-emitting layer 8A and a graph 502 showing the probability of electrons existing at each position in the light-emitting layer 8A.

[0051] In the band diagram 501, the upper side on the paper is the higher energy side, and the band gap at each position on a line passing through approximately the center of the quantum dot 18 is shown. In the graph 502, the vertical axis represents the square of the absolute value of the wave function of the electron injected into the core 18C of the quantum dot 18, in other words, the probability of the electron's existence, and the horizontal axis represents each position on the above-mentioned line. Each position in the band diagram 501 corresponds to each position in the graph 502.

[0052] As shown in band diagram 501, the band gap of core 18C is smaller than the band gap of shell 18S. This reduces the diffusion of electrons injected into core 18C to shell 18S. However, as shown in graph 502, electrons injected into core 18C have the highest probability of remaining in core 18C, but may diffuse toward shell 18S due to the broadening of the wave function.

[0053] Furthermore, in this embodiment, the shell 18S and the sulfide semiconductor 16 are both made of zinc sulfide, and therefore the shell 18S and the sulfide semiconductor 16 have approximately the same band gap, as shown in the band diagram 501. Therefore, there is virtually no barrier to electron injection from the shell 18S to the sulfide semiconductor 16, and electrons diffuse more easily from the shell 18S to the sulfide semiconductor 16 than from the core 18C to the shell 18S.

[0054] For this reason, as shown in graph 502, in quantum dot structure 14A of light-emitting layer 8A, there is a possibility that electrons injected into core 18C may leak out to sulfide semiconductor 16. The integral value on the further periphery of quantum dot 18 than the boundary between sulfide semiconductor 16 and shell 18S in graph 502 corresponds to the seepage probability EX, which is the probability that electrons injected into core 18C will leak out of quantum dot 18. When the seepage probability EX increases, the probability of generating excitons in core 18C decreases, and the luminous efficiency of quantum dot 18 decreases.

[0055] The effects of the light-emitting element 2 according to this embodiment will be described with reference to Fig. 6. Fig. 6 shows a band diagram 601 of the light-emitting layer 8 and a graph 602 showing the probability of electrons existing at each position in the light-emitting layer 8.

[0056] In the band diagram 601, as in the band diagram 501, the upper side on the paper is the higher energy side, and the band gaps at each position on a line passing through approximately the center of the quantum dot 18 are shown. The definitions of the vertical and horizontal axes in the graph 602 are the same as those of the vertical and horizontal axes in the graph 502. Each position in the band diagram 601 corresponds to each position in the graph 602.

[0057] Since the additive 20 is located at least partially around the quantum dot 18, a barrier exists in the transport of electrons from the inside to the outside of the quantum dot 18. In particular, as shown in the band diagram 601, in this embodiment, the band gap of the additive 20 is larger than the band gap of the shell 18S. In this case, in the light-emitting layer 8, a barrier exists for electron injection from the shell 18S to the additive 20. Furthermore, in this embodiment, the band gap of the additive 20 is larger than the band gap of the sulfide semiconductor 16. In this case, if the band gap of the sulfide semiconductor 16 is also larger than the band gap of the shell 18S, the barrier for electron injection from the shell 18S to the additive 20 becomes even larger.

[0058] For this reason, as shown in graph 602, the presence probability of electrons injected into core 18C rapidly decreases in the direction from core 18C toward the sulfide semiconductor 16. Therefore, in the quantum dot structure 14 of the light-emitting layer 8, the probability that electrons injected into core 18C will leak to the sulfide semiconductor 16 decreases. In particular, as shown in graph 602, the seepage probability EX in this embodiment is smaller than the seepage probability EX in the comparative example. Therefore, in the light-emitting layer 8 according to this embodiment, the probability that electrons injected into core 18C will remain in core 18C increases.

[0059] In particular, as described above, the additive 20 contains oxygen atoms. Generally, substances containing oxygen atoms, including oxide insulators, have a larger band gap than semiconductors that do not contain oxygen atoms. Therefore, the additive 20 containing oxygen atoms is likely to have a larger band gap than the constituent material of the quantum dots 18, further reducing the seepage probability EX.

[0060] When the additives 20 are positioned all around the quantum dots 18 in the quantum dot structure 14, an electron injection barrier from the shell 18S to the additives 20 exists in almost all paths through which carriers can move from the inside to the outside of the quantum dots 18. Therefore, when the additives 20 are positioned all around the quantum dots 18 in the quantum dot structure 14, the seepage probability EX in the light-emitting layer 8 is further reduced.

[0061] The relationship between the thickness of the addition 20 in each quantum dot structure 14 of the light-emitting layer 8 according to this embodiment and the probability EX of electrons leaking out from the core 18C will be described with reference to Fig. 7. Fig. 7 is a graph showing the relationship between the thickness of the addition 20 in the quantum dot structure 14 and the probability EX of electrons leaking out from the core 18C. In Fig. 7, the vertical axis represents the probability EX of electrons leaking out from the core 18C, and the horizontal axis represents the thickness of the addition 20 in units of nm. In Fig. 7, a thickness of 0 for the addition 20 means that the quantum dot structure 14 substantially does not have the addition 20.

[0062] 7, when the thickness of the addition 20 is 0.1 nm or more, the seepage probability EX in the quantum dot structure 14 is reduced to less than 1 / 6 compared to when there is no addition 20. Furthermore, when the thickness of the addition 20 is 0.2 nm, the seepage probability EX is further reduced compared to when the thickness of the addition 20 is 0.1 nm. From the viewpoint of sufficiently reducing the seepage probability EX, the thickness of the addition 20 may be 0.1 nm or more.

[0063] For the same reason as described above, a barrier also exists for the transport of holes from the inside to the outside of the quantum dot 18. Furthermore, when the band gap of the additive 20 is larger than the band gap of the shell 18S, a barrier for hole injection from the shell 18S to the additive 20 also exists in the light-emitting layer 8, similar to a barrier for electron injection. Therefore, in the quantum dot structure 14 of the light-emitting layer 8, the probability that holes injected into the core 18C will leak into the sulfide semiconductor 16 is reduced, and in the light-emitting layer 8, the probability that holes injected into the core 18C will remain in the core 18C is improved.

[0064] As a result, in the light-emitting element 2 according to this embodiment, the probability that carriers including electrons and holes injected into the core 18C of the light-emitting layer 8 continue to remain in the core 18C is increased. Therefore, in the light-emitting element 2, the probability of generating excitons in the core 18C of the light-emitting layer 8 is increased, and the luminous efficiency of the quantum dots 18 is improved.

[0065] As shown in the band diagram 601, the band gap of the additive 20 is larger than the band gap of the sulfide semiconductor 16. Therefore, in the light-emitting layer 8, there is a barrier to carrier injection from the sulfide semiconductor 16 to the additive 20. However, because the thickness of the solid portion of the additive 20 is 1 nm or less, carriers injected from the charge transport layer into the sulfide semiconductor 16 pass through the additive 20 due to the tunneling effect and are injected into the quantum dots 18.

[0066] The relationship between the thickness of the additive 20 in each quantum dot structure 14 of the light-emitting layer 8 according to this embodiment and the probability of carrier transmission through the additive 20 will be described with reference to FIGS. 8 and 9. FIGS. 8 and 9 are graphs showing the relationship between the thickness of the additive 20 in the quantum dot structure 14 and the probability of electron transmission through the additive 20. In FIGS. 8 and 9, the vertical axis represents the probability that electrons injected from the sulfide semiconductor 16 into the quantum dot 18 transmit through the additive 20 by the tunneling effect, and the horizontal axis represents the thickness of the additive 20 in units of nm. In FIGS. 8 and 9, a thickness of 0 for the additive 20 means that the quantum dot structure 14 does not substantially have the additive 20. FIG. 8 shows a graph showing the relationship between the thickness of the additive 20 in the quantum dot structure 14 and the probability of electron transmission through the additive 20. ２ 9 shows the case where the additive 20 is made of ZrO ２ This shows the case where

[0067] 8 and 9, when the quantum dot structure 14 does not have the additive 20, the probability that the electrons will transmit through the additive 20 is substantially 100%. Furthermore, as the thickness of the additive 20 that the quantum dot structure 14 has increases, the probability that the electrons will transmit through the additive 20 decreases.

[0068] However, as shown in FIG. 8, the additive 20 is SiO ２ In the case where the thickness of the addition 20 is 1 nm or less, the probability that electrons will pass through the addition 20 is greater than 10%. ２In this case, if the thickness of the additive 20 is 1 nm or less, the probability that electrons will transmit through the additive 20 is 60% or more. From the above, from the viewpoint of improving the probability that electrons will transmit through the additive 20 and be injected from the sulfide semiconductor 16 into the quantum dots 18, the thickness of the additive 20 may be 1 nm or less.

[0069] In general, the probability that an electron located in the first layer will pass through the second layer and be injected into another layer increases as the difference between the LUMO of the first layer and the LUMO of the second layer decreases. When the sulfide semiconductor 16 is made of zinc sulfide (ZnS), the difference in LUMO between the sulfide semiconductor 16 and the additive 20 becomes smaller when the additive 20 is made of SiO ２ When it consists of ZrO ２ Therefore, the probability that electrons will pass through the addition 20 is smaller when the addition 20 is made of SiO ２ When it consists of ZrO ２ Therefore, from the viewpoint of improving the probability that electrons are transmitted through the additive 20 and injected from the sulfide semiconductor 16 into the quantum dots 18, the additive 20 is preferably made of ZrO ２ may include:

[0070] The probability that holes are injected from the sulfide semiconductor 16 into the quantum dots 18 through the additive 20 also increases as the thickness of the additive 20 decreases. Therefore, the light-emitting layer 8 according to this embodiment increases the probability that carriers including holes from the hole transport layer 6 and electrons from the electron transport layer 10 are injected from the sulfide semiconductor 16 into the quantum dots 18 through the additive 20. Therefore, in the light-emitting element 2, the probability of generating excitons in the cores 18C of the light-emitting layer 8 increases, and the luminous efficiency of the quantum dots 18 improves.

[0071] Other effects achieved by the light-emitting element 2 according to this embodiment will be described with reference to Fig. 10 and Fig. 11. Fig. 10 is a schematic diagram showing the arrangement of atoms at the interface between the quantum dots 18 and the sulfide semiconductor 16 according to a comparative embodiment. Fig. 11 is a schematic diagram showing the arrangement of atoms at the interface between the quantum dots 18, the additive 20, and the sulfide semiconductor 16 according to this embodiment.

[0072] 10 and 11 , the sulfide semiconductor 16 and the shell 18S of the quantum dot 18 according to the comparative example and the present embodiment have a structure in which Zn atoms and S atoms are regularly arranged and bonded to each other, and the core 18C of the quantum dot 18 has a structure in which In atoms and P atoms are regularly arranged and bonded to each other.

[0073] Here, the lattice constant of ZnS is 5.420 Å, and the lattice constant of InP is 5.869 Å. In other words, the interatomic distance of ZnS is shorter than the interatomic distance of InP. Therefore, when the shell 18S is epitaxially grown on the surface of the core 18C, the shell 18S grows while being subjected to compressive strain. Therefore, near the interface with the core 18C, the distance between the Zn atoms and the S atoms of the shell 18S is extended to approximately the interatomic distance of the InP of the core 18C.

[0074] In the comparative example, when the sulfide semiconductor 16 grows epitaxially on the surface of the shell 18S, the sulfide semiconductor 16 also grows while being subjected to compressive strain. Therefore, near the interface with the shell 18S, the distance between the Zn atom and the S atom of the sulfide semiconductor 16 according to the comparative example is extended to approximately the interatomic distance of the InP in the core 18C.

[0075] From the surface of the core 18C to a thickness equal to the critical thickness CT, the distance between the Zn atoms and the S atoms in the sulfide semiconductor 16 is maintained at approximately the interatomic distance of the InP in the core 18C. However, at a position from the surface of the core 18C beyond the critical thickness CT, the Zn atoms and the S atoms in the sulfide semiconductor 16 are unable to absorb the stress caused by distortion, and dislocations occur in the structure of the Zn atoms and the S atoms in the sulfide semiconductor 16. Therefore, at a position from the surface of the core 18C beyond the critical thickness CT, the distance between the Zn atoms and the S atoms in the sulfide semiconductor 16 is compressed to approximately the interatomic distance in simple ZnS.

[0076] Therefore, in the sulfide semiconductor 16 according to the comparative example, a mismatch occurs in the arrangement of Zn atoms and S atoms between the vicinity of the shell 18S and a position distant from the shell 18S. In particular, defects such as dangling bonds may occur between Zn atoms and S atoms at a position distant from the surface of the core 18C by the critical thickness CT, in other words, at a position where a dislocation occurs in the structure of Zn atoms and S atoms in the sulfide semiconductor 16. The energy of excitons generated by the recombination of carriers injected into the quantum dots 18 may transfer to the defects, which may cause a deactivation process. In particular, because the defects occur near the surface of the quantum dots 18, the energy of excitons generated in the core 18C is likely to transfer to the defects.

[0077] On the other hand, as shown in FIG. 11, in the light-emitting layer 8 according to this embodiment, SiO ２ Therefore, in the light-emitting layer 8, an interface between the sulfide semiconductor 16 and the additive 20, and an interface between the shell 18S and the additive 20 are formed.

[0078] In this embodiment, when the additive 20 grows on the surface of the shell 18S, the SiO ２ absorbs the compressive strain to some extent, thereby reducing the mismatch in atomic arrangement between the shell 18S and the additive 20. For the same reason, the mismatch in atomic arrangement between the sulfide semiconductor 16 and the additive 20 is also reduced.

[0079] As described above, the formation of the additive 20 between the sulfide semiconductor 16 and the shell 18S reduces dislocations occurring in the structure of Zn atoms and S atoms in the sulfide semiconductor 16, regardless of the difference in the interatomic distance between the sulfide semiconductor 16 and the shell 18S. Therefore, the light-emitting layer 8 according to this embodiment reduces defects occurring near the surfaces of the quantum dots 18. Therefore, in the light-emitting element 2, the probability of generating excitons in the cores 18C of the light-emitting layer 8 increases, improving the luminous efficiency of the quantum dots 18.

[0080] In order to reduce the mismatch in atomic arrangement between the shell 18S and the additive 20 and between the sulfide semiconductor 16 and the additive 20, the additive 20 may contain an oxide, in particular, SiO ２ and ZnS, and in particular may contain a mixture of both. In other words, from the viewpoint of reducing the mismatch of the atomic arrangement described above, the additive 20 may contain SiO ２ and a material contained in at least one of the shell 18S and the sulfide semiconductor 16. Furthermore, when the thickness of the shell 18S is smaller than the critical thickness CT, the interatomic distance in the shell 18S is more likely to be maintained at any position, and mismatch in the atomic arrangement between the shell 18S and the additive 20 is further reduced.

[0081] Furthermore, when the surface of the quantum dot 18 and the additive 20 are in contact with each other, the additive 20 more efficiently reduces the mismatch in the atomic arrangement between the shell 18S and the additive 20. In addition, when the additive 20 and the sulfide semiconductor 16 are in contact with each other, the additive 20 more efficiently reduces the mismatch in the atomic arrangement between the sulfide semiconductor 16 and the additive 20.

[0082] <Outline of Manufacturing Method of Display Device> A manufacturing method of the display device 1 according to this embodiment will be described with reference to Fig. 12. Fig. 12 is a flowchart for explaining the manufacturing method of the display device 1 according to this embodiment.

[0083] In the manufacturing method of the display device 1 according to this embodiment, first, the substrate 3 is formed (step S2). The substrate 3 may be formed by forming a TFT on a glass substrate in alignment with the position where the anode 4 of the light-emitting element 2 is to be formed.

[0084] Next, the anode 4 is formed (step S4). The anode 4 may be formed by depositing a conductive material by, for example, sputtering, as described above. Next, the hole transport layer 6 is formed (step S6). The hole transport layer 6 may be formed by, for example, vacuum deposition, sputtering, or a coating method using a colloidal solution, as described above.

[0085] <Synthesis of Quantum Dot Dispersion Liquid> Next, the light-emitting layer 8 is formed. In this embodiment, an example will be described in which a quantum dot dispersion liquid containing the quantum dot structures 14 is synthesized, and the quantum dot dispersion liquid is applied and then dried to obtain the light-emitting layer 8.

[0086] In this embodiment, for example, preparation of the quantum dot structure 14 (step S8) is performed as a pre-step of the step of synthesizing the quantum dot dispersion liquid containing the quantum dot structure 14.

[0087] FIG. 13 is a cross-sectional view illustrating the steps for preparing the quantum dot structure 14 described above. In preparing the quantum dot structure 14, first, a first liquid L1 and a second liquid L2 were prepared as shown in step S8-2 of FIG. 13 . The first liquid L1 was prepared by dispersing quantum dots 18 coordinated with organic ligands in octane. The first liquid L1 may be used directly in a subsequent step, or the first liquid L1 may be centrifuged to separate the quantum dots 18 coordinated with organic ligands, and the quantum dots 18 may be re-dispersed in pure octane to be used as a new first liquid L1 in a subsequent step. The second liquid L2 was prepared by dissolving TMOS in NMF. The concentration of TMOS in the second liquid L2 was 0.02 mol / L.

[0088] Next, the first liquid L1 and the second liquid L2 shown in step S8-2 of FIG. 13 were thoroughly stirred and mixed. During the stirring process, the TMOS around the quantum dots 18 reacted in the second liquid L2, synthesizing silicon oxide. Because the reaction occurred near room temperature, the crystal system of the silicon oxide was trigonal. The ZnS in the shell of the quantum dots QD and the silicon oxide have different crystal systems and significantly different lattice constants. Therefore, a large lattice mismatch occurs between the ZnS in the shell of the quantum dots QD and the silicon oxide grown thereon. Furthermore, the melting point of silicon oxide is 1710°C. For this reason, silicon oxide synthesized in contact with the quantum dots QD at a temperature much lower than the melting point of over 1000°C, such as near room temperature, is difficult to grow into a single crystal and is likely to become polycrystalline, amorphous, or porous. In addition, some silicon elements bond with hydroxyl groups (-OH) and / or some silicon oxide is converted into water (H ２O), silicic acid was synthesized. The inorganic film containing silicon oxide and silicic acid was arranged as an adduct 20 at least partially around the quantum dots QD, as shown in step S8-4 of FIG. 13 . Furthermore, the organic ligands coordinated to the quantum dots 18 were released, and the adducts 20 were formed around the quantum dots 18, causing the quantum dots 18 to move from the first liquid L1 to the second liquid L2. As a result, a quantum dot structure 14 was prepared in the second liquid L2 in step S8.

[0089] Next, a quantum dot dispersion liquid L3 shown in Fig. 14 is prepared (step S10). Fig. 14 is a schematic diagram showing the quantum dot dispersion liquid L3 prepared in a container C.

[0090] In step S10, first, the first liquid L1 is removed from the mixed solution of the first liquid L1 and the second liquid L2 mixed in step S8, and ethyl acetate is added to the remaining second liquid L2 to precipitate and separate the quantum dot structure 14. Then, the quantum dot structure 14 is dispersed in ethanol. Other alcohols such as methanol and IPA may be used instead of ethanol. The alcohol converts silicon oxide and silicic acid into water (H ２ O) can be removed to prevent water from corroding the quantum dots 18.

[0091] The quantum dot structure 14 was again precipitated and separated using ethyl acetate, and dispersed in a solvent 22 such as alcohol. Furthermore, a precursor 24 of the sulfide semiconductor 16 was dispersed in the solvent 22. As a result, in step S10, a quantum dot dispersion liquid L3 is prepared in which a plurality of quantum dot structures 14, each including quantum dots 18 and an adduct 20 formed around at least a portion of the quantum dots 18, are dispersed in the solvent 22, as shown in FIG.

[0092] The precursor 24 of the sulfide semiconductor 16 contained in the quantum dot dispersion liquid L3 may contain, for example, a metal acetate, a metal nitrate, or a metal halide as a metal source, and at least one of thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N'-dimethylthiourea, tetramethylthiourea, and thioacetamide as a sulfur source. Alternatively, the precursor 24 may contain a metal complex in which thiourea, N-methylthiourea, 1,3-dimethylthiourea, N,N'-dimethylthiourea, tetramethylthiourea, or thioacetamide is coordinated to a metal atom.

[0093] Since silicon oxide and silicic acid easily retain water, it is desirable to repeat the alcohol dehydration of the quantum dot structure 14 multiple times by precipitating and separating the quantum dot structure 14 with ethyl acetate and dispersing it in the solvent 22. For example, the alcohol dehydration may be performed twice.

[0094] <Formation of Light-Emitting Layer> Next, a method for applying the quantum dot dispersion liquid L3 and forming the light-emitting layer 8 from the quantum dot dispersion liquid L3 will be described in detail with reference to Fig. 15. Fig. 15 is a cross-sectional view showing the steps in the method for forming the light-emitting layer 8.

[0095] 15 , at the completion of step S6, the substrate 3, anode 4, and hole transport layer 6 are formed. In this embodiment, the quantum dot dispersion L3 prepared in steps S8 and S10 is applied onto the hole transport layer 6 (step S12). In other words, step S12 is a process of applying the quantum dot dispersion L3 to a laminate including the substrate 3, anode 4, and hole transport layer 6, which serves as the substrate. As a result, a coating layer 26 including the quantum dot dispersion L3 is formed on the hole transport layer 6.

[0096] The quantum dot dispersion liquid L3 may be applied by, for example, a spin coating method in which the quantum dot dispersion liquid L3 is applied onto the hole transport layer 6 while rotating a laminate from the substrate 3 to the hole transport layer 6. Alternatively, the quantum dot dispersion liquid L3 may be applied using an existing thin film formation method such as an inkjet method.

[0097] Following application of the quantum dot dispersion liquid L3, the laminate from the substrate 3 to the coating layer 26 is heated at a temperature of 80° C. to 500° C. for one minute or longer to dry the coating layer 26 (step S14). As the coating layer 26 dries, the precursor 24 crystallizes to form the sulfide semiconductor 16. As a result, a light-emitting layer 8 is formed on the hole transport layer 6, as shown in FIG.

[0098] In step S14 according to this embodiment, the laminate from the anode 4 to the coating layer 26 is heated to 80° C. to 500° C. to form the light-emitting layer 8. For this reason, it is more preferable that all layers from the anode 4 to the cathode 12 are formed of inorganic layers.

[0099] 12 , the electron transport layer 10 is then formed (step S16). The electron transport layer 10 may be formed by, for example, vacuum deposition, sputtering, or a coating method using a colloidal solution, as described above. The cathode 12 is then formed (step S18). The cathode 12 may be formed by depositing a conductive material by, for example, sputtering, as described above.

[0100] In this manner, the light-emitting element 2 according to this embodiment is formed, and the manufacturing process of the display device 1 is completed. Note that the manufacturing method of the display device 1 according to this embodiment may also include the steps of forming the hole injection layer, the electron injection layer, and the intermediate layer described above. Furthermore, following step S18, a capping layer or the like may be formed on the cathode 12, thereby forming the capping layer or the like on the light-emitting element 2.

[0101] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0102] REFERENCE SIGNS LIST 1 display device 2 light-emitting element 3 substrate 4 anode (first electrode) 8 light-emitting layer 12 cathode (second electrode) 16 sulfide semiconductor (medium portion) 18 quantum dot 20 additive

Claims

1. A light-emitting element comprising: a first electrode and a second electrode facing each other; and a light-emitting layer provided between the first electrode and the second electrode, the light-emitting layer including a plurality of quantum dots; a medium portion filling the spaces between the plurality of quantum dots; and an addition located around at least a portion of the quantum dots.

2. The light-emitting device according to claim 1, wherein the additive contains an oxygen atom.

3. The light-emitting device according to claim 1 or 2, wherein the additive is positioned around the entire periphery of the quantum dot in any cross section passing through the quantum dot.

4. The light-emitting element according to any one of claims 1 to 3, wherein the surface of the quantum dot and the additive are in contact with each other.

5. The light-emitting element according to any one of claims 1 to 4, wherein the additional material and the medium portion are in contact with each other.

6. The light-emitting element according to any one of claims 1 to 5, wherein the additive includes a solid portion.

7. The light-emitting device according to claim 6, wherein the maximum thickness of the solid portion of the additive in the normal direction to the surface of the quantum dot is 1 nm or less.

8. The light-emitting device according to claim 6 or 7, wherein the minimum thickness of the solid portion of the additive in the normal direction to the surface of the quantum dot is 0.1 nm or more.

9. The light-emitting element according to any one of claims 1 to 8, wherein the additive contains at least one of silicon oxide and zinc sulfide.

10. The light-emitting device according to any one of claims 1 to 9, wherein the additive comprises at least one selected from the group consisting of silicon oxide, titanium oxide, aluminum oxide, boron oxide, phosphorus oxide, germanium oxide, hafnium oxide, zinc oxide, zirconium oxide, tellurium oxide, bismuth oxide, vanadium oxide, antimony oxide, lead oxide, and copper oxide.

11. The light-emitting element according to any one of claims 1 to 10, wherein the medium portion contains a metal sulfide.

12. The light-emitting device according to claim 11, wherein the metal sulfide comprises at least one of zinc sulfide, gallium sulfide, magnesium sulfide, cadmium sulfide, tin sulfide, indium sulfide, and manganese sulfide.

13. The light-emitting element according to any one of claims 1 to 12, wherein the medium portion has a continuous film containing the quantum dots.

14. 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 light-emitting device according to claim 13 , having an area of ​​at least 100 nm.

15. The light-emitting device according to any one of claims 1 to 14, wherein the band gap of the additive is larger than the band gap of the quantum dots.

16. The light-emitting device according to any one of claims 1 to 15, wherein the band gap of the additive is larger than the band gap of the medium portion.

17. A display device comprising a plurality of light-emitting elements according to any one of claims 1 to 16.

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