Light-emitting element and method for manufacturing same, display device, NANO metal oxide particle group, dispersion liquid for NANO metal oxide particles, and method for manufacturing NANO metal oxide particles

Abstract

A light-emitting element (30) includes an anode (2), a cathode (5), a light-emitting layer (EM) provided between the anode (2) and the cathode (5), and an electronic functional layer (4) provided between the cathode (5) and the light-emitting layer (EM). The electronic functional layer (4) includes a plurality of nano metal oxide particles each comprising a core that contains: a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf; a second element that is a metalloid element or an element selected from, among nonmetallic elements, elements excluding elemental hydrogen, elemental oxygen, and group 18 elements; elemental zinc; and elemental oxygen.

Description

Light-emitting element and manufacturing method thereof, display device, metal oxide nanoparticle group, dispersion of metal oxide nanoparticles, and manufacturing method of metal oxide nanoparticles

[0001] One aspect of the present disclosure relates to a light-emitting element, a method for manufacturing a light-emitting element, a display device, a group of metal oxide nanoparticles, a dispersion of metal oxide nanoparticles, and a method for manufacturing metal oxide nanoparticles.

[0002] In recent years, various display devices equipped with light-emitting elements have been developed, and in particular, display devices equipped with OLEDs (Organic Light Emitting Diodes) or QLEDs (Quantum dot Light Emitting Diodes) have attracted much attention because of their ability to achieve low power consumption, thinness, high image quality, and the like.

[0003] Patent Document 1 describes an OLED or QLED having electronic functional layers, such as an electron transport layer or an electron injection layer, formed solely from zinc oxide nanoparticles or magnesium zinc oxide nanoparticles.

[0004] Japan Special Table No. 2021-521586

[0005] However, as disclosed in Patent Document 1, electronic functional layers such as electron transport layers and electron injection layers formed solely from zinc oxide nanoparticles or magnesium zinc oxide nanoparticles do not have high resistance to the cathode formation process, for example, a vapor deposition process or a sputtering process, in the cathode formation process, which is a subsequent process of forming the electronic functional layer, and it has been reported that even the light-emitting layer, which is the layer below the electronic functional layer, is damaged after the cathode formation process, resulting in a significant decrease in luminous efficiency. Zinc oxide nanoparticles or magnesium zinc oxide nanoparticles have a relatively large particle size variation, which causes the electronic functional layer formed solely from zinc oxide nanoparticles or magnesium zinc oxide nanoparticles to lack density, resulting in insufficient protection of the light-emitting layer, which is the layer below the electronic functional layer.

[0006] Therefore, it has been considered to form electronic functional layers such as electron transport layers and electron injection layers using a material obtained by mixing zinc oxide nanoparticles or magnesium zinc oxide nanoparticles with a polymer organic material such as PVP (polyvinylpyrrolidone), which is expected to function as a binder. However, an organic-inorganic hybrid electronic functional layer obtained by mixing zinc oxide nanoparticles or magnesium zinc oxide nanoparticles with a polymer organic material has very poor stability, and there are problems such as phase separation between the organic material and the inorganic material during the process of forming the electronic functional layer. Although a slight improvement in density can be achieved compared to an electronic functional layer formed only with zinc oxide nanoparticles or magnesium zinc oxide nanoparticles, a satisfactory level of density is still not achieved due to the large variation in particle size inherent in the zinc oxide nanoparticles or magnesium zinc oxide nanoparticles. Therefore, a light-emitting device having an organic-inorganic hybrid electronic functional layer cannot achieve a satisfactory level of luminous efficiency.

[0007] An object of one aspect of the present disclosure is to provide a group of metal oxide nanoparticles with small particle size and particle size variation, a method for producing metal oxide nanoparticles, a light-emitting device with high luminous efficiency, and a method for producing the same.

[0008] In order to solve the above-mentioned problems, the light-emitting device of the present disclosure includes an anode, a cathode, a light-emitting layer provided between the anode and the cathode, and an electronic functional layer provided between the cathode and the light-emitting layer, wherein the electronic functional layer includes a plurality of metal oxide nanoparticles each having a core including a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, a second element which is an element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a semi-metallic element, zinc, and oxygen.

[0009] In order to solve the above-mentioned problems, the display device of the present disclosure includes a plurality of the light-emitting elements.

[0010] In order to solve the above-mentioned problems, the metal oxide nanoparticles of the present disclosure are a group of metal oxide nanoparticles each comprising a core containing a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, a second element which is an element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a metalloid element, zinc, and oxygen.

[0011] In order to solve the above-mentioned problems, the dispersion of metal oxide nanoparticles of the present disclosure contains the above-mentioned metal oxide nanoparticles and a solvent.

[0012] In order to solve the above-mentioned problems, the method for producing metal oxide nanoparticles of the present disclosure provides a reaction apparatus including: a micromixer that mixes and discharges a first precursor of metal oxide nanoparticles containing a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, which are supplied from the outside; a second precursor of metal oxide nanoparticles containing a second element that is an element selected from non-metal elements excluding hydrogen, oxygen, and Group 18 elements or a metalloid element; a third precursor of metal oxide nanoparticles containing zinc; and a reactant; a microchannel having one end that is a supply end and the other end that is a discharge end, and through which the fluid discharged from the micromixer is supplied from the supply end; and a microreactor that controls the reaction conditions in at least a portion of the microchannel, to produce metal oxide nanoparticles composed of a core containing the first element, the second element, zinc, and oxygen.

[0013] In order to solve the above-mentioned problems, the method for manufacturing a light-emitting element of the present disclosure includes an anode formation step of forming an anode, a cathode formation step of forming a cathode which is performed after the anode formation step, a light-emitting layer formation step of forming a light-emitting layer which is performed between the anode formation step and the cathode formation step, and an electronic function layer formation step of forming an electronic function layer which is performed between the light-emitting layer formation step and the cathode formation step, wherein in the electronic function layer formation step, the electronic function layer is formed which contains metal oxide nanoparticles manufactured by the method for manufacturing metal oxide nanoparticles.

[0014] According to one aspect of the present disclosure, it is possible to provide a group of metal oxide nanoparticles with small particle size and small particle size variation, a method for producing metal oxide nanoparticles, a light emitting device with high luminous efficiency, and a method for producing the same.

[0015] 1 is a plan view showing a schematic configuration of a display device of Embodiment 1. FIG. 2 is a cross-sectional view showing a schematic configuration of a light-emitting device provided in the display device of Embodiment 1 shown in FIG. 1. FIG. 3 is a diagram showing an example of a method for manufacturing the light-emitting device shown in FIG. 2. FIG. 4 is a diagram showing a schematic configuration of a reaction apparatus used in a process for manufacturing metal oxide nanoparticles contained in an electronic functional layer provided in the light-emitting device shown in FIG. 2. FIG. 5 is a diagram showing an example of process conditions in a process for manufacturing metal oxide nanoparticles using the reaction apparatus shown in FIG. 4. FIG. 6 is a diagram for explaining a process for manufacturing metal oxide nanoparticles using the reaction apparatus shown in FIG. 4. FIG. 7 is a diagram for explaining a recovery process of metal oxide nanoparticles performed after manufacturing metal oxide nanoparticles using the reaction apparatus shown in FIG. 4. FIG. 7 is a diagram showing the results of FT-IR of metal oxide nanoparticles contained in an electronic functional layer provided in the light-emitting device shown in FIG. 2. FIG. 8 is a diagram showing the particle size distribution of metal oxide nanoparticles contained in an electronic functional layer provided in the light-emitting device shown in FIG. 2. FIG. 9 is a diagram showing the relationship between current density and luminance for each of the light-emitting devices of Reference Example 1 and Reference Example 2. FIG. 10 is a diagram showing the relationship between current density and luminance for each of the light-emitting devices of Example 1 and Comparative Example 1.

[0016] The following describes an embodiment of the present disclosure with reference to Figures 1 to 11. For the sake of convenience, components having the same functions as those described in a specific embodiment will be denoted by the same reference numerals, and their description may be omitted.

[0017] First Embodiment FIG. 1 is a plan view showing a schematic configuration of a display device 1 according to a first embodiment.

[0018] As shown in Fig. 1, the display device 1 includes a frame area NDA and a display area DA. The display area DA of the display device 1 includes a plurality of pixels PIX, each of which includes a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP. In this embodiment, a case in which one pixel PIX is configured with a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP will be described as an example, but this is not limiting. For example, one pixel PIX may include subpixels of other colors in addition to the red subpixel RSP, the green subpixel GSP, and the blue subpixel BSP.

[0019] FIG. 2 is a cross-sectional view showing a schematic configuration of the light-emitting element 30 provided in the display device 1 of the first embodiment shown in FIG.

[0020] The red sub-pixel RSP provided in the display area DA of the display device 1 includes a red light-emitting element in which the light-emitting layer EM is a red light-emitting layer in the light-emitting element 30 shown in Figure 2, the green sub-pixel GSP provided in the display area DA of the display device 1 includes a green light-emitting element in which the light-emitting layer EM is a green light-emitting layer in the light-emitting element 30 shown in Figure 2, and the blue sub-pixel BSP provided in the display area DA of the display device 1 includes a blue light-emitting element in which the light-emitting layer EM is a blue light-emitting layer in the light-emitting element 30 shown in Figure 2.

[0021] 2 , the light-emitting element 30 includes an anode 2, a cathode 5, an emitting layer EM provided between the anode 2 and the cathode 5, an electronic functional layer 4 provided between the cathode 5 and the emitting layer EM, and a hole functional layer 3 provided between the anode 2 and the emitting layer EM. In this embodiment, the light-emitting element 30 is described by taking as an example a case where it includes the hole functional layer 3, but the present invention is not limited to this, and the hole functional layer 3 may be omitted as appropriate.

[0022] The hole functional layer 3 may include at least one of a hole transport layer (HTL) and a hole injection layer (HIL). The hole injection layer (HIL) may be, for example, a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT:PSS), NiO particles, MoO ３The hole transport layer (HTL) can be formed using, for example, poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl))diphenylamine)] (TFB), N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-benzidine (poly-TPD), polyvinylcarbazole (PVK), 4,4′-bis(carbazol-9-yl)biphenyl (CBP), NiO particles, or the like.

[0023] In this embodiment, the electronic functional layer 4 is described as a single layer that functions as an electron transport layer (ETL), an electron injection layer (EIL), and a hole blocking layer (HBL). However, this is not limiting, and the electronic functional layer 4 may include, for example, two or more layers selected from the electron transport layer (ETL), the electron injection layer (EIL), and the hole blocking layer (HBL). In this embodiment, as shown in FIG. 2 , the electronic functional layer 4 is provided so as to be in contact with both the cathode 5 and the light-emitting layer EM.

[0024] As shown in FIG. 2 , the electronic functional layer 4 provided between the cathode 5 and the light-emitting layer EM contains a plurality of metal oxide nanoparticles each having a core including a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf; a second element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a metalloid element; zinc; and oxygen. That is, the metal oxide nanoparticles contained in the electronic functional layer 4 are core-structured nanoparticles consisting solely of a core containing the first element, the second element, zinc, and oxygen. Core-structured nanoparticles differ from core / shell-structured nanoparticles having a core and a shell outside the core, each shell having a different composition from the core, in that they do not have a shell with a different composition from the core. Examples of metalloid elements include B, Si, Ge, As, Sb, and Te. Furthermore, the metal oxide nanoparticles contained in the electronic functional layer 4 are nanoparticles with a core structure formed by a competitive reaction between molecules containing the first element, molecules containing the second element, and molecules containing zinc, and each core contains only the first element, the second element, zinc, and oxygen. Therefore, the particle size is unlikely to increase, and the particle size and particle size variation are small. Therefore, an electronic functional layer 4 containing a plurality of metal oxide nanoparticles with such small particle size and particle size variation, or an electronic functional layer 4 composed of a plurality of metal oxide nanoparticles with such small particle size and particle size variation, can achieve high density and high resistance to the cathode 5 formation process, such as a vapor deposition process or sputtering process, in the cathode 5 formation process, which is a subsequent process of forming the electronic functional layer 4. Therefore, a light-emitting element 30 including the electronic functional layer 4 can achieve high luminous efficiency.

[0025] The fact that the metal oxide nanoparticles contained in the electronic functional layer 4 are nanoparticles with a core structure consisting only of a core of a single composition can be confirmed, for example, using time-of-flight secondary ion mass spectrometry (TOF-SIMS), or by performing elemental analysis while etching the metal oxide nanoparticles little by little from the outside.

[0026] The second element, which is an element or a metalloid element selected from the non-metal elements described above excluding hydrogen, oxygen, and Group 18 elements, may be any of B, C, N, F, Si, P, S, Cl, Ge, As, Se, Br, Sb, Te, I, and At, and the second element described above may be any of B, Si, Ge, As, Sb, Te, C, N, P, and S.

[0027] It is preferable that, in a unit volume of the metal oxide nanoparticles contained in the electronic functional layer 4, the amount of oxygen element is greater than the amount of the first element, the amount of the second element, and the amount of zinc element, respectively, and that the amount of the second element and the amount of zinc element are each greater than the amount of the first element.

[0028] In this embodiment, the metal oxide nanoparticles contained in the electronic function layer 4 are nanoparticles with a core structure consisting of a single core composed of Mg as the first element, Si as the second element, zinc, and oxygen. The metal oxide nanoparticles contained in the electronic function layer 4 in this embodiment contain Zn—O bonds, Mg—O bonds, and Si—O bonds.

[0029] A portion of a cross section cut along the thickness direction of the electronic functional layer 4 contains 10×N metal oxide nanoparticles (N is a natural number greater than or equal to 2) containing Mg as the first element and Si, zinc, and oxygen as the second elements. When the particle sizes of the 10×N metal oxide nanoparticles are arranged in ascending order, the particle size of the 5×Nth metal oxide nanoparticle is preferably 1.8 nm or less, and the difference between the particle size of the 9×Nth metal oxide nanoparticle and the particle size of the Nth metal oxide nanoparticle is preferably 2.1 nm or less. The particle sizes of the 10×N metal oxide nanoparticles can be measured, for example, using a scanning transmission electron microscope (STEM). The particle size of the 5×Nth metal oxide nanoparticle refers to the particle size of the metal oxide nanoparticle that corresponds to 50% (median) of the particle sizes of the 10×N metal oxide nanoparticles arranged in ascending order. The particle size of the 9×Nth metal oxide nanoparticle refers to the particle size of the metal oxide nanoparticle that corresponds to 90% of the particle sizes of the 10×N metal oxide nanoparticles arranged in ascending order. The particle size of the Nth metal oxide nanoparticle means the particle size of the metal oxide nanoparticle that corresponds to 10% of the particle sizes of the 10×N metal oxide nanoparticles arranged in ascending order.

[0030] In this embodiment, the light-emitting layer EM included in the light-emitting element 30 shown in FIG. 2 is described as an example containing quantum dots (QDs). However, this is not limited thereto and the light-emitting layer may also contain an organic light-emitting material. The quantum dots (QDs) may have, for example, a core structure, a core / shell structure, a core / shell / shell structure, or a shell structure with a continuously varying core / shell ratio. The core portion may be composed of, for example, Si or C in the case of a unicomponent system; CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, or ZnTe in the case of a ternary system; CdSeTe, GaInP, or ZnSeTe in the case of a quaternary system; or AIGS in the case of a quaternary system. In the case of a binary system, the shell portion can be composed of, for example, CdS, CdTe, CdSe, ZnS, ZnSe, ZnTe, etc., and in the case of a ternary system, the shell portion can be composed of, for example, CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, AIP, etc.

[0031] 2 may be a top-emission type or a bottom-emission type. The light-emitting element 30 has a forward-laid structure in which the cathode 5 is disposed as an upper layer than the anode 2. To form the light-emitting element 30 as a top-emission type, the anode 2 may be formed from an electrode material that reflects visible light, and the cathode 5 may be formed from an electrode material that transmits visible light. To form the light-emitting element 30 as a bottom-emission type, the anode 2 may be formed from an electrode material that transmits visible light, and the cathode 5 may be formed from an electrode material that reflects visible light.

[0032] The electrode material that reflects visible light is not particularly limited as long as it can reflect visible light and has electrical conductivity. Examples of the electrode material that reflects visible light include metal materials such as Al, Mg, Li, and Ag, alloys of the metal materials, laminates of the metal materials and transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), and laminates of the alloys and the transparent metal oxides.

[0033] On the other hand, the electrode material that transmits visible light is not particularly limited as long as it can transmit visible light and has conductivity, and examples thereof include transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), thin films made of metal materials such as Al and Ag, and nanowires made of metal materials such as Al and Ag.

[0034] 3A to 3C are diagrams showing an example of a method for manufacturing the light emitting element 30 shown in FIG.

[0035] 2 has a sequentially stacked structure in which the cathode 5 is disposed above the anode 2, and can be manufactured by performing, in this order, an anode formation step S1 to form the anode 2, a hole functional layer formation step S2 to form the hole functional layer 3, a light-emitting layer formation step S3 to form the light-emitting layer EM, an electronic functional layer formation step S4 to form the electronic functional layer 4, and a cathode formation step S5 to form the cathode 5. In the electronic functional layer formation step S4, the electronic functional layer 4 is formed, which includes a plurality of metal oxide nanoparticles each having a core including a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, a second element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements, or a metalloid element, zinc, and oxygen, which are manufactured by a method for manufacturing metal oxide nanoparticles described later. In this embodiment, as shown in FIG. 3, only the electronic function layer formation step S4 is performed between the light-emitting layer formation step S3 and the cathode formation step S5, and as shown in FIG. 2, the electronic function layer 4 is provided so as to be in contact with both the cathode 5 and the light-emitting layer EM.

[0036] FIG. 4 is a diagram showing a schematic configuration of a reaction apparatus 10 used in a process for producing metal oxide nanoparticles contained in the electronic functional layer 4 provided in the light-emitting element 30 shown in FIG. 2 . FIG. 5 is a diagram showing an example of process conditions in a process for producing metal oxide nanoparticles using the reaction apparatus 10 shown in FIG. 4 . FIG. 6 is a diagram for explaining a process for producing metal oxide nanoparticles using the reaction apparatus 10 shown in FIG. 4 . FIG. 7 is a diagram for explaining a metal oxide nanoparticle recovery process performed after producing metal oxide nanoparticles using the reaction apparatus 10 shown in FIG. 4 . FIG. 8 is a diagram showing the results of FT-IR of metal oxide nanoparticles contained in the electronic functional layer 4 provided in the light-emitting element 30 shown in FIG. 2 . FIG. 9 is a diagram showing the particle size distribution of metal oxide nanoparticles contained in the electronic functional layer 4 provided in the light-emitting element 10 shown in FIG. 2 .

[0037] Metal oxide nanoparticles having a core structure consisting only of a core containing a first element selected from the above-mentioned Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, a second element which is an element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a semi-metallic element, zinc, and oxygen, can be produced using, for example, a reaction apparatus including a micromixer, a microchannel, and a microreactor.

[0038] The reaction apparatus includes a micromixer that mixes and discharges a first precursor of metal oxide nanoparticles containing a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, a second precursor of metal oxide nanoparticles containing a second element which is an element selected from non-metal elements excluding hydrogen, oxygen, and Group 18 elements or a semi-metal element, a third precursor of metal oxide nanoparticles containing zinc, and a reactant, all of which are supplied from the outside; a microchannel having one end which is a supply end and the other end which is a discharge end, and to which the fluid discharged from the micromixer is supplied from the supply end; and a microreactor that controls the reaction conditions in at least a portion of the microchannel.

[0039] In this embodiment, the reaction apparatus described above is the reaction apparatus 10 shown in FIG. 4 , and metal oxide nanoparticles having a core structure consisting only of a core containing a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, a second element which is an element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a metalloid element, zinc, and oxygen will be described as an example, but the present invention is not limited to this.

[0040] As shown in FIG. 4 , the reaction apparatus 10 includes a micromixer including a first micromixer 16 including a first supply port Inlet1, a second supply port Inlet2, and a first outlet Outlet1, and a second micromixer 19 including a third supply port Inlet3, a fourth supply port Inlet4, and a second outlet Outlet2, and the fluid discharged from the first outlet Outlet1 is supplied from the third supply port Inlet3, and the fluid discharged from the second outlet Outlet2 is supplied from the supply end of the microchannel 20. The reaction apparatus 10 further includes a first supply unit 11 configured to supply a first solution containing a first precursor of metal oxide nanoparticles containing a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, a third precursor of metal oxide nanoparticles containing zinc, and a first solvent to one of the first supply port Inlet1, the second supply port Inlet2, and the fourth supply port Inlet4 at a first flow rate; a second supply unit 12 that supplies a second solution containing the reactant and a second solvent at a second flow rate to another one of the first supply port Inlet 1, the second supply port Inlet 2, and the fourth supply port Inlet 4, and a third supply unit 13 that supplies a third solution containing a second precursor of metal oxide nanoparticles containing a second element, the second element being a semi-metallic element or an element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements, and a third solvent at a third flow rate to still another one of the first supply port Inlet 1, the second supply port Inlet 2, and the fourth supply port Inlet 4. As shown in FIG. 4 , the reaction apparatus 10 includes a microchannel 20 having one end serving as a supply end and the other end serving as a discharge end, to which a fluid discharged from the second discharge port Outlet 2 of the second micromixer 19 is supplied from the supply end, and a microreactor 21 that controls reaction conditions in at least a portion of the microchannel 20.

[0041] A method for producing metal oxide nanoparticles having a core structure consisting of only a core containing a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, a second element which is an element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a metalloid element, zinc, and oxygen, using a reaction apparatus 10 shown in FIG. 4, includes the steps of: (1) preparing a first precursor of the metal oxide nanoparticles containing the first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, such as magnesium acetate; and (2) preparing a third precursor of the metal oxide nanoparticles containing zinc, such as zinc acetate. A first solution containing, for example, dimethyl sulfoxide (DMSO) as a polar solvent serving as a first solvent, is supplied from a first supply unit 11 to a first supply port Inlet 1 at a first flow rate. A first solution containing, for example, tetramethylammonium hydroxide (for example, TMAH.5H), which is an alkaline reactant, is supplied as a reactant. ２ A second solution containing, as a second solvent, for example, ethanol, which is an alcohol-based solvent, is supplied from the second supply unit 12 to the second supply port Inlet 2 at a second flow rate, and a second precursor of metal oxide nanoparticles containing a second element, which is an element selected from non-metal elements excluding hydrogen, oxygen, and Group 18 elements, or a semi-metal element, is supplied from the second supply unit 12 to the second supply port Inlet 2 at a second flow rate, and a second precursor of metal oxide nanoparticles containing, as a second precursor, ... tetraalkoxysilane, for example, tetraethoxysilane (TEOS(Tetraethyl orthosilicate) and a third solvent, for example, ethanol, which is an alcohol-based solvent, from a third supply unit 13 to a fourth supply port Inlet 4 at a third flow rate; and a second step of recovering, from the discharge end of the microchannel 20, a dispersion of metal oxide nanoparticles having a core structure composed only of a core containing a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, a second element which is an element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a semi-metallic element, zinc, and oxygen.

[0042] 4 , the reaction apparatus 10 further includes a first supply flow path 14 connecting a first supply port Inlet 1 of the first micromixer 16 to an outlet of the first supply unit 11, a second supply flow path 15 connecting a second supply port Inlet 2 of the first micromixer 16 to an outlet of the second supply unit 12, a third supply flow path 17 connecting a first outlet Outlet 1 of the first micromixer 16 to a third supply port Inlet 3 of the second micromixer 19, a fourth supply flow path 18 connecting a fourth supply port Inlet 4 of the second micromixer 19 to an outlet of the third supply unit 13, and a recovery unit 22 for recovering a fluid discharged from an outlet end of the microchannel 20. The first supply flow path 14 and the second supply flow path 15 are preferably the same supply flow path having the same flow path diameter and flow path length, and the third supply flow path 17 and the fourth supply flow path 18 are preferably the same supply flow path having the same flow path diameter and flow path length. Although not shown, when the outlet of the first supply unit 11 is directly connected to the first supply port Inlet 1 of the first micromixer 16, the reaction apparatus 10 does not need to have the first supply flow path 14, when the outlet of the second supply unit 12 is directly connected to the second supply port Inlet 2 of the first micromixer 16, the reaction apparatus 10 does not need to have the second supply flow path 15, when the outlet of the third supply unit 13 is directly connected to the fourth supply port Inlet 4 of the second micromixer 19, the reaction apparatus 10 does not need to have the fourth supply flow path 18, and when the first outlet Outlet 1 of the first micromixer 16 and the third supply port Inlet 3 of the second micromixer 19 are directly connected, the reaction apparatus 10 does not need to have the third supply flow path 17. Furthermore, the reaction apparatus 10 does not need to have the recovery unit 22, and in this case, the user of the reaction apparatus 10 can prepare the recovery unit 22. The microreactor 21 that controls the reaction conditions in at least a part of the microchannel 20 controls, for example, the temperature of a part of the microchannel 20 to an optimum temperature for the reaction of the fluid flowing in the microchannel 20 .In this embodiment, as described above, magnesium acetate is used as the first precursor, tetraethoxysilane (TEOS (Tetraethyl orthosilicate)) is used as the second precursor, and zinc acetate is used as the third precursor. Therefore, for example, ZnOH and MgOH are generated in the first micro mixer 16, and for example, ZnOH, MgOH, and Si(OH) are generated in the second micro mixer 19. Ｘ (OC ２ H ５ ) ４－Ｘ (X=0, 1, 2, 3, 4) is produced, and in a part of the microchannel 20 where the reaction conditions are controlled by the microreactor 21, ZnOH, MgOH and Si(OH) Ｘ (OC ２ H ５ ) ４－Ｘ (X=0, 1, 2, 3, 4) dehydration reactions occur competitively among them. Therefore, for example, metal oxide nanoparticles produced using the reaction apparatus 10 shown in Fig. 4 are metal oxide nanoparticles with a core structure consisting only of a core containing the first element, the second element, zinc element, and oxygen element, and are not nanoparticles with a core / shell structure having a core and a shell provided outside the core with a different composition from the core. As described above, since the dehydration reaction mainly occurs in the microchannel 20, the first solution is supplied from the first supply unit 11 at a first flow rate to one of the first supply port Inlet 1, the second supply port Inlet 2, and the fourth supply port Inlet 4, the second solution is supplied from the second supply unit 12 at a second flow rate to the other of the first supply port Inlet 1, the second supply port Inlet 2, and the fourth supply port Inlet 4, and the third solution is supplied from the third supply unit 13 at a third flow rate to yet another of the first supply port Inlet 1, the second supply port Inlet 2, and the fourth supply port Inlet 4.

[0043] 4 , the reactor 10 includes a T-shaped first micromixer 16 and a T-shaped second micromixer 19 in a plan view, and a flow microreactor-type special reaction field utilizing turbulence can be realized by the T-shaped first micromixer 16 and the T-shaped second micromixer 19 in a plan view. In this embodiment, an example is described in which the reactor 10 includes a T-shaped first micromixer 16 and a T-shaped second micromixer 19 in a plan view, but this is not limited thereto. The reactor 10 may include, for example, a V-shaped micromixer in a plan view instead of at least one of the T-shaped first micromixer 16 and the T-shaped second micromixer 19. A V-shaped micromixer in a plan view can also realize a flow microreactor-type special reaction field utilizing turbulence. Furthermore, the reaction apparatus 10 may be provided with, for example, a linear micromixer instead of at least one of the T-shaped first micromixer 16 and the T-shaped second micromixer 19. The linear micromixer can realize a special reaction field of a flow microreactor type in which fluids supplied from two supply ports flow in parallel.

[0044] As shown in FIG. 5, in the first solution described above, Mg ２＋ and Zn ２＋ The amounts of zinc acetate and magnesium acetate were adjusted so that the concentration ratio of the two was 15:85, and the amounts of zinc acetate and magnesium acetate and the amount of dimethyl sulfoxide (DMSO) as the first solvent were adjusted so that the concentration of the first solution was 0.1 M. In addition, in the second solution described above, tetramethylammonium hydroxide (e.g., TMAH.5H) was added so that the concentration of the second solution was 0.25 M. ２ The amounts of MgO and the second solvent, ethanol, were adjusted. ２＋ and Zn ２＋and tetramethylammonium hydroxide (e.g., TMAH.5H) in a second solution. ２ The molar ratio of tetraethoxysilane (TEOS (Tetraethyl orthosilicate)) to the third solvent (ethanol) was adjusted to 1:1.3. In addition, in the third solution described above, the amounts of tetraethoxysilane (TEOS (Tetraethyl orthosilicate)) and the third solvent (ethanol) were adjusted so that the concentration of the third solution was 0.169 M. The flow rates of the first solution, the second solution, and the third solution can be appropriately determined taking into account the amount of metal oxide nanoparticles to be obtained as the final product. In this embodiment, the flow rates of the first solution were 12.6 ml, the second solution was 6.552 ml, and the third solution was 16 ml. In order to set the supply time of the first solution from the first supply unit 11, the supply time of the second solution from the second supply unit 12, and the supply time of the third solution from the third supply unit 13 to 84 minutes, the first supply unit 11 supplied the first solution at a first flow rate, for example, 9 ml / h, the second supply unit 12 supplied the second solution at a second flow rate, for example, 4.68 ml / h, and the third supply unit 13 supplied the third solution at a third flow rate, for example, 11.5 ml / h.

[0045] As shown in FIG. 6 , the method for producing metal oxide nanoparticles includes, as described above, step S11 of preparing a first solution having a predetermined concentration A (0.1 M in this embodiment), a second solution having a predetermined concentration B (0.25 M in this embodiment), and a third solution having a predetermined concentration C (0.169 M in this embodiment); step S12 of supplying the first solution to the first supply port Inlet 1 of the first micromixer 16 at a predetermined flow rate D (9 mL / h in this embodiment), supplying the second solution to the second supply port Inlet 2 of the first micromixer 16 at a predetermined flow rate E (4.68 mL / h in this embodiment), and supplying the third solution to the fourth supply port Inlet 4 of the second micromixer 19 at a predetermined flow rate F (11.5 mL / h in this embodiment); and step S13 of recovering the produced dispersion of ultranano-sized oxide nanoparticles containing Mg, Zn, and Si from the discharge end of the microchannel 20. In step S13 of recovering the dispersion of ultranano-sized oxide nanoparticles containing Mg, Zn, and Si, it is preferable to separately recover the fluid discharged from the discharge end of the microchannel 20 during the initial fixed period and the final fixed period, and to recover only the fluid discharged from the discharge end of the microchannel 20 during an intermediate period other than the above periods as a dispersion of ultranano-sized oxide nanoparticles containing Mg, Zn, and Si.

[0046] As shown in Fig. 7, the method for producing metal oxide nanoparticles preferably further includes step S21 of transferring the dispersion of ultranano-sized oxide nanoparticles containing Mg, Zn, and Si recovered in step S13 shown in Fig. 6 to a centrifuge tube and adding a poor solvent (e.g., ethyl acetate) to precipitate ultranano-sized oxide nanoparticles containing Mg, Zn, and Si, step S22 of separating the solids from the solution by centrifugation, and step S23 of removing the supernatant (e.g., a mixture of the reaction products, dimethyl sulfoxide (DMSO) and ethanol (EtOH)). By including the metal oxide nanoparticle recovery step shown in Fig. 7, the method for producing metal oxide nanoparticles can obtain a dispersion of ultranano-sized oxide nanoparticles containing Mg, Zn, and Si from which impurities have been removed. 7 , the method for producing metal oxide nanoparticles may further include a step S24 of removing the solution including the supernatant and redispersing the solids (ultranano-sized oxide nanoparticles containing Mg, Zn, and Si) in a solvent (e.g., ethanol or butanol) to prepare a redispersion of ultranano-sized oxide nanoparticles containing Mg, Zn, and Si. This method can obtain a redispersion of ultranano-sized oxide nanoparticles containing Mg, Zn, and Si redispersed in a desired specific solvent. Furthermore, in the step of preparing the redispersion, an organic ligand such as monoethanolamine (MEA) may be further added to further improve dispersibility.

[0047] As shown in FIG. 8, the FT-IR results of the ultranano-sized oxide nanoparticles containing Mg, Zn, and Si contained in the electronic functional layer 4 provided in the light-emitting element 30 shown in FIG. 2 showed absorption at wavenumbers corresponding to Zn—O bonds, Mg—O bonds, and Si—O bonds, respectively, and it was confirmed that the ultranano-sized oxide nanoparticles containing Mg, Zn, and Si contain Zn—O bonds, Mg—O bonds, and Si—O bonds.

[0048] The particle size distribution of the metal oxide nanoparticles produced using the reaction apparatus 10 shown in Fig. 4, i.e., the redispersion of the ultranano-sized oxide nanoparticles containing Mg, Zn, and Si described above, was measured and the results are shown in Fig. 9. The redispersion here is a solution in which ultranano-sized oxide nanoparticles containing Mg, Zn, and Si are dispersed in ethanol, which is a solvent.

[0049] As shown in Figure 9, the particle size of the metal oxide nanoparticles at particle size-based cumulative 50% (D50) in the redispersion of ultranano-sized oxide nanoparticles containing Mg, Zn, and Si was 1.76 nm, which was 1.80 nm or less. Furthermore, the difference between the particle size of the metal oxide nanoparticles at particle size-based cumulative 90% (D90) in the redispersion of ultranano-sized oxide nanoparticles containing Mg, Zn, and Si and the particle size of the metal oxide nanoparticles at particle size-based cumulative 10% (D10) was 2.05 nm, which was 2.10 nm or less. The particle size distribution shown in Figure 9 was measured by DLS (dynamic light scattering) using a Nanotrac wave II manufactured by Microtaract.

[0050] In this embodiment, ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si are produced using the reaction apparatus 10 under the conditions shown in FIG. 5 , and as described above, the particle size of the metal oxide nanoparticles at 50% cumulative particle size (D50) is 1.76 nm, and the difference between the particle size of the metal oxide nanoparticles at 90% cumulative particle size (D90) and the particle size of the metal oxide nanoparticles at 10% cumulative particle size (D10) is 2.05 nm, but this is not limited to these values. For example, by adjusting the above-mentioned first flow rate, second flow rate, and third flow rate so that the supply time of the first solution from the first supply unit 11, the supply time of the second solution from the second supply unit 12, and the supply time of the third solution from the third supply unit 13 are all longer or shorter than 84 minutes, the time that the fluid discharged from the second outlet Outlet 2 of the second micromixer 19 remains in a part of the microchannel 20 where the reaction conditions are controlled by the microreactor 21 can be adjusted, and therefore, it is possible to obtain ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si in which the particle size value of metal oxide nanoparticles at particle size cumulative 50% (D50) is, for example, 4 nm or less, and the difference between the particle size of metal oxide nanoparticles at particle size cumulative 90% (D90) and the particle size of metal oxide nanoparticles at particle size cumulative 10% (D10) is, for example, 3 nm or less.

[0051] Although not shown, the particle size of the metal oxide nanoparticles at particle size cumulative 50% (D50) in the dispersion of ultranano-sized oxide nanoparticles containing Mg, Zn, and Si recovered in step S13 shown in Fig. 6 was also 1.80 nm or less. In addition, the difference between the particle size of the metal oxide nanoparticles at particle size cumulative 90% (D90) and the particle size of the metal oxide nanoparticles at particle size cumulative 10% (D10) in the dispersion of ultranano-sized oxide nanoparticles containing Mg, Zn, and Si recovered in step S13 shown in Fig. 6 was also 2.10 nm or less.

[0052] As described above, the ultranano-sized oxide nanoparticles containing Mg, Zn, and Si have small particle sizes and small particle size variations, which are produced using the reaction apparatus 10. The reason why ultranano-sized oxide nanoparticles containing Mg, Zn, and Si with small particle sizes and small particle size variations can be produced in this way is thought to be due to the fact that the first solution, the second solution, and the third solution react while constantly flowing to produce oxide nanoparticles with an ultranano-sized core structure containing Mg, Zn, and Si, and that the competitive reactions between molecules containing Mg, molecules containing Si, and molecules containing Zn produce oxide nanoparticles with an ultranano-sized core structure containing Mg, Zn, and Si.

[0053] 10 is a diagram showing the relationship between current density and luminance, i.e., the general luminous efficiency, of the light-emitting element of Reference Example 1 and the light-emitting element of Reference Example 2. Note that, although the results using a red light-emitting element are shown as an example here, similar results can be obtained with green and blue light-emitting elements.

[0054] The light-emitting element (red light-emitting element) of Reference Example 1 shown in FIG. 10 is a light-emitting element in which an anode made of Ag, a hole injection layer made of nickel oxide nanoparticles, a hole transport layer made of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl))diphenylamine)] (TFB), a light-emitting layer containing InP as red-emitting quantum dots, an electron transport layer which is an electronic functional layer made of zinc oxide nanoparticles, and a cathode made of ITO (indium tin oxide) are stacked in this order.

[0055] Since zinc oxide nanoparticles are metal oxide nanoparticles containing only zinc element, they have a larger particle size and particle size variation than the above-mentioned ultranano-sized oxide nanoparticles containing Mg, Zn, and Si. Therefore, the electron transport layer, which is an electronic functional layer formed from such zinc oxide nanoparticles provided in the light-emitting element (red light-emitting element) of Reference Example 1, lacks density and is therefore not highly resistant to the cathode formation process, for example, the vapor deposition process or sputtering process, in the cathode formation process, which is a process subsequent to the electron transport layer formation process. After the cathode formation process, even the light-emitting layer below the electron transport layer is damaged, resulting in a significant decrease in luminous efficiency. Therefore, as shown in Figure 10, the light-emitting element (red light-emitting element) of Reference Example 1 does not achieve a satisfactory luminous efficiency.

[0056] On the other hand, the light-emitting element (red light-emitting element) of Reference Example 2 shown in FIG. 10 is a light-emitting element in which an anode made of Ag, a hole injection layer made of nickel oxide nanoparticles, a hole transport layer made of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl))diphenylamine)] (TFB), a light-emitting layer containing InP as red-emitting quantum dots, an electron transport layer which is an electronic functional layer made of a material in which zinc oxide nanoparticles and PVP (polyvinylpyrrolidone) are mixed, and a cathode made of ITO (indium tin oxide) are laminated in this order. In the light-emitting element (red light-emitting element) of Reference Example 1 and the light-emitting element (red light-emitting element) of Reference Example 2, the film thickness of each layer was the same, and the layers other than the electron transport layer, which was the electronic functional layer, namely the anode, the hole injection layer, the hole transport layer, the light-emitting layer containing red-light-emitting quantum dots, and the cathode, were each formed using the same material with the same composition.

[0057] The electron transport layer serving as the electronic functional layer of Comparative Example 2, which is formed from a material comprising a mixture of zinc oxide nanoparticles and PVP (polyvinylpyrrolidone), has slightly improved density compared to the electron transport layer serving as the electronic functional layer of Comparative Example 1, and a red light-emitting device including the electron transport layer serving as the electronic functional layer of Comparative Example 2 can achieve a slightly improved luminous efficiency, as shown in Fig. 10 . However, an organic-inorganic hybrid electron transport layer such as the electron transport layer serving as the electronic functional layer of Comparative Example 2, which is formed from a material comprising a mixture of zinc oxide nanoparticles and PVP (polyvinylpyrrolidone), is very unstable and suffers from problems such as phase separation between the organic material and the inorganic material during the process of forming the electron transport layer. In addition, due to the influence of the large variation in particle size inherent in the zinc oxide nanoparticles, a satisfactorily high density is still not achieved, and a red light-emitting device including the electron transport layer serving as the electronic functional layer of Comparative Example 2 cannot achieve a satisfactorily high luminous efficiency.

[0058] 11 is a diagram showing the relationship between current density and luminance, i.e., the general luminous efficiency, of the light-emitting element of Example 1 and the light-emitting element of Comparative Example 1. Note that, although the results using a blue light-emitting element are shown here as an example, similar results can be obtained with red and green light-emitting elements.

[0059] The light-emitting element (blue light-emitting element) of Comparative Example 1 shown in FIG. 11 is a light-emitting element in which an anode made of Ag, a hole injection layer made of nickel oxide nanoparticles, a hole transport layer made of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl))diphenylamine)] (TFB), a light-emitting layer containing ZnSe as blue-emitting quantum dots, an electron transport layer which is an electronic functional layer of Comparative Example 2 made of a material in which zinc oxide nanoparticles and PVP (polyvinylpyrrolidone) are mixed, and a cathode made of ITO (indium tin oxide) are laminated in this order.

[0060] The light-emitting element (blue light-emitting element) of Comparative Example 1 shown in FIG. 11 does not provide a satisfactorily high luminous efficiency for the same reasons as the light-emitting element (red light-emitting element) of Reference Example 2 shown in FIG.

[0061] The light-emitting element (blue light-emitting element) of Example 1 shown in FIG. 11 is a light-emitting element in which an anode made of Ag, a hole injection layer made of nickel oxide nanoparticles, a hole transport layer made of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl))diphenylamine)] (TFB), a light-emitting layer containing ZnSe as blue-emitting quantum dots, an electron transport layer which is the electronic functional layer 4 of Example 1 formed of the above-mentioned oxide nanoparticles having an ultranano-sized core structure containing Mg, Zn, and Si, and a cathode made of ITO (indium tin oxide) are laminated in this order. In the light-emitting element (blue light-emitting element) of Comparative Example 1 and the light-emitting element (blue light-emitting element) of Example 1, the film thickness of each layer was the same, and each of the layers other than the electron transport layer, which is an electronic functional layer, namely, the anode, the hole injection layer, the hole transport layer, the light-emitting layer containing blue-light-emitting quantum dots, and the cathode, were formed using the same material with the same composition.

[0062] 11 , the blue light-emitting device including the electron transport layer as the electronic functional layer 4 of Example 1 achieved a significantly improved and satisfactorily high luminous efficiency compared to the blue light-emitting device including the electron transport layer as the electronic functional layer of Comparative Example 2. The ultranano-sized oxide nanoparticles containing Mg, Zn, and Si contained in the electron transport layer as the electronic functional layer 4 have small particle size and particle size variation, can achieve high density, and are highly resistant to the cathode formation process, such as a vapor deposition process or sputtering process, in the cathode formation step, which is a step subsequent to the step of forming the electron transport layer, and thus the light-emitting device including the electron transport layer as the electronic functional layer 4 can achieve high luminous efficiency.

[0063] The metal oxide nanoparticle group includes a core containing a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, a second element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a metalloid element, and zinc and oxygen. The metal oxide nanoparticles may have a particle size of 1.80 nm or less at a particle size cumulative 50% (D50) and a difference between the particle size of the metal oxide nanoparticles at a particle size cumulative 90% (D90) and the particle size of the metal oxide nanoparticles at a particle size cumulative 10% (D10) of 2.10 nm or less. The second element may be any of B, Si, Ge, As, Sb, Te, C, N, P, and S. Preferably, the amount of oxygen in a unit volume of the metal oxide nanoparticles is greater than the amount of the first element, the amount of the second element, and the amount of zinc, and the amount of the second element and the amount of zinc are each greater than the amount of the first element. The first element may be Mg, and the second element may be Si. In this case, the metal oxide nanoparticles contain Zn—O bonds, Mg—O bonds, and Si—O bonds.

[0064] In the present embodiment, the electronic function layer 4 is formed using a dispersion of metal oxide nanoparticles containing a solvent and a group of metal oxide nanoparticles, the group of metal oxide nanoparticles comprising a core containing a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf produced using the reaction apparatus 10, a second element which is an element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a semi-metallic element, zinc, and oxygen. However, the present invention is not limited to this, and the metal oxide nanoparticles produced using the reaction apparatus 10 or the above-mentioned dispersion of metal oxide nanoparticles can also be used in the field of electronic materials other than electronic function layers or in other technical fields.

[0065] [Additional Notes] 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.

[0066] The present disclosure can be used in a light-emitting element, a method for manufacturing a light-emitting element, a display device, a group of metal oxide nanoparticles, a dispersion of metal oxide nanoparticles, and a method for manufacturing metal oxide nanoparticles.

[0067] REFERENCE SIGNS LIST 1 display device 2 anode 3 hole functional layer 4 electron functional layer 5 cathode 10 reactor 11 first supply section 12 second supply section 13 third supply section 14 first supply flow path 15 second supply flow path 16 first micromixer 17 third supply flow path 18 fourth supply flow path 19 second micromixer 20 microchannel 21 microreactor 22 recovery section 30 light-emitting element EM light-emitting layer RSP red subpixel GSP green subpixel BSP blue subpixel PIX pixel DA display area NDA frame area Inlet1 first supply port Inlet2 second supply port Inlet3 third supply port Inlet4 fourth supply port Outlet1 first outlet Outlet2 second outlet

Claims

1. A light-emitting device comprising: an anode; a cathode; a light-emitting layer provided between the anode and the cathode; and an electronic functional layer provided between the cathode and the light-emitting layer, wherein the electronic functional layer comprises a plurality of metal oxide nanoparticles each having a core comprising a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf; a second element which is an element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements, or a semi-metallic element; zinc; and oxygen.

2. The light-emitting element according to claim 1, wherein the second element is any one of B, Si, Ge, As, Sb, Te, C, N, P, and S.

3. The light-emitting element described in claim 1 or 2, wherein, in a unit volume of the metal oxide nanoparticles, the amount of oxygen element is greater than the amount of the first element, the amount of the second element, and the amount of zinc element, and the amount of the second element and the amount of zinc element are each greater than the amount of the first element.

4. The light-emitting element according to claim 1, wherein the first element is Mg, and the second element is Si.

5. The light-emitting device of claim 4, wherein the metal oxide nanoparticles include Zn—O bonds, Mg—O bonds, and Si—O bonds.

6. The light-emitting element described in claim 4 or 5, wherein, in a part of a cross section cut along the thickness direction of the electronic functional layer containing 10×N metal oxide nanoparticles (N is a natural number of 2 or more), when the particle diameters of the 10×N metal oxide nanoparticles are arranged in ascending order, the particle diameter of the 5×Nth metal oxide nanoparticle is 1.8 nm or less.

7. The light-emitting device according to claim 6, wherein the difference between the particle size of the 9×Nth metal oxide nanoparticle and the particle size of the Nth metal oxide nanoparticle is 2.1 nm or less.

8. The light-emitting device according to any one of claims 1 to 7, wherein the electronically functional layer is in contact with both the cathode and the light-emitting layer.

9. A display device comprising a plurality of light-emitting elements according to any one of claims 1 to 8.

10. A group of metal oxide nanoparticles comprising a group of metal oxide nanoparticles each having a core including a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, a second element which is an element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements, or a semi-metallic element, zinc, and oxygen.

11. The group of metal oxide nanoparticles according to claim 10, wherein the second element is any one of B, Si, Ge, As, Sb, Te, C, N, P, and S.

12. A group of metal oxide nanoparticles according to claim 10 or 11, wherein, in a unit volume of the metal oxide nanoparticles, the amount of oxygen element is greater than the amount of the first element, the amount of the second element, and the amount of zinc element, and the amount of the second element and the amount of zinc element are each greater than the amount of the first element.

13. A group of metal oxide nanoparticles according to any one of claims 10 to 12, wherein the first element is Mg, and the second element is Si.

14. The group of metal oxide nanoparticles according to claim 13, wherein the metal oxide nanoparticles contain Zn—O bonds, Mg—O bonds, and Si—O bonds.

15. A group of metal oxide nanoparticles according to claim 13 or 14, wherein the particle size of the metal oxide nanoparticles at particle size cumulative 50% (D50) is 1.8 nm or less, and the difference between the particle size of the metal oxide nanoparticles at particle size cumulative 90% (D90) and the particle size of the metal oxide nanoparticles at particle size cumulative 10% (D10) is 2.1 nm or less.

16. A dispersion of metal oxide nanoparticles comprising the metal oxide nanoparticles according to any one of claims 10 to 15 and a solvent.

17. A method for producing metal oxide nanoparticles, comprising: producing metal oxide nanoparticles having a core containing the first element, the second element, zinc, and oxygen, using a reaction apparatus including: a micromixer that mixes and discharges a first precursor of metal oxide nanoparticles containing a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, which are supplied from the outside; a second precursor of metal oxide nanoparticles containing a second element which is an element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a metalloid element; a third precursor of metal oxide nanoparticles containing zinc; and a reactant; a microchannel having one end which is a supply end and the other end which receives the fluid discharged from the micromixer; and a microreactor that controls the reaction conditions in at least a portion of the microchannel.

18. The method for producing metal oxide nanoparticles according to claim 17, wherein the micromixer comprises a first micromixer including a first supply port, a second supply port, and a first outlet, and a second micromixer including a third supply port, a fourth supply port, and a second outlet, wherein the fluid discharged from the first outlet is supplied from the third supply port, and the fluid discharged from the second outlet is supplied from the supply end of the microchannel, and the reaction apparatus comprises: a first supply unit that supplies a first solution containing the first precursor, the third precursor, and a first solvent at a first flow rate to one of the first supply port, the second supply port, and the fourth supply port; a second supply unit that supplies a second solution containing the reactant and a second solvent at a second flow rate to another of the first supply port, the second supply port, and the fourth supply port; and a third supply unit that supplies a third solution containing the second precursor and a third solvent at a third flow rate to yet another of the first supply port, the second supply port, and the fourth supply port.

19. A method for producing metal oxide nanoparticles according to claim 18, comprising: a first step of supplying the first solution containing magnesium acetate as the first precursor, zinc acetate as the third precursor, and a polar solvent as the first solvent from the first supply unit to the first supply port, supplying the second solution containing the reactant and an alcohol-based solvent as the second solvent from the second supply unit to the second supply port, and supplying the third solution containing tetraalkoxysilane as the second precursor and an alcohol-based solvent as the third solvent from the third supply unit to the fourth supply port; and a second step of recovering a dispersion of metal oxide nanoparticles composed of cores containing the first element, the second element, zinc element, and oxygen element from the discharge end of the microchannel.

20. A method for producing metal oxide nanoparticles according to claim 19, comprising: a third step of transferring the dispersion of metal oxide nanoparticles recovered in the second step to a centrifuge tube and adding a poor solvent to precipitate the metal oxide nanoparticles; a fourth step of separating the solid matter from the solution by centrifugation; a fifth step of removing the solution including the supernatant; and a sixth step of preparing a redispersion of the metal oxide nanoparticles by redispersing the solid matter in a solvent.

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