Method for producing metal oxide nanoparticles, metal oxide nanoparticle dispersion liquid, reaction device, light emitting element, display device, methods for producing light emitting element and display device, and metal oxide nanoparticle group

Abstract

This reaction device (10) comprises: a micromixer (15) which includes a first supply port (Inlet 1), a second supply port (Inlet 2), and a discharge port (Outlet); a first supply unit (11) which supplies a first solution that contains a precursor of metal oxide nanoparticles which contain a first metal element, a precursor of metal oxide nanoparticles which contain a second metal element that is different from the first metal element, and a first solvent to the first supply port (Inlet 1) at a first flow rate; a second supply unit (12) which supplies a second solution that contains a reactant and a second solvent to the second supply port (Inlet 2) at a second flow rate; a microchannel (16) in which one end serves as a supply end and the other end serves as a discharge end, and a fluid discharged from the discharge port (Outlet) is supplied from the supply end; and a microreactor (17) which controls at least some of the reaction conditions for the microchannel (16).

Description

Method for producing metal oxide nanoparticles and dispersion, reaction device, light-emitting element and display device and method for producing the same, metal oxide nanoparticle group

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

[0002] Patent Document 1 discloses a technique for producing metal oxide nanoparticles by a liquid phase deposition method.

[0003] Japanese Patent Publication No. 2008-44826

[0004] The technique for producing metal oxide nanoparticles by a liquid phase precipitation method disclosed in Patent Document 1 is a technique suitable for producing metal oxide nanoparticles containing only one type of metal element, but is not suitable for producing metal oxide nanoparticles containing two or more different types of metal elements.

[0005] One aspect of the present disclosure aims to provide a method for producing metal oxide nanoparticles containing two or more different metal elements, which have a small particle size and small particle size variation, and a reaction apparatus for producing such metal oxide nanoparticles.

[0006] In order to solve the above-mentioned problems, the reaction apparatus of the present disclosure includes: a micromixer including a first supply port, a second supply port, and an outlet port; a first supply unit that supplies a first solution containing a precursor of metal oxide nanoparticles containing a first metal element, a precursor of metal oxide nanoparticles containing a second metal element different from the first metal element, and a first solvent at a first flow rate to one of the first supply port and the second supply port; a second supply unit that supplies a second solution containing a reactant and a second solvent at a second flow rate to the other of the first supply port and the second supply port; a microchannel having one end that is a supply end and the other end that is a discharge end, and through which a fluid discharged from the discharge port of the micromixer is supplied; and a microreactor that controls reaction conditions in at least a part of the microchannel.

[0007] In order to solve the above-mentioned problems, the method for producing metal oxide nanoparticles of the present disclosure produces metal oxide nanoparticles containing the first metal element and the second metal element using a reaction apparatus including: a micromixer including a first supply port, a second supply port, and an outlet; a first supply unit that supplies a first solution containing a precursor of metal oxide nanoparticles containing a first metal element, a precursor of metal oxide nanoparticles containing a second metal element different from the first metal element, and a first solvent at a first flow rate to one of the first supply port and the second supply port; a second supply unit that supplies a second solution containing a reactant and a second solvent at a second flow rate to the other of the first supply port and the second supply port; a microchannel having one end that is a supply end and the other end that is a discharge end, and through which a fluid discharged from the discharge port of the micromixer is supplied; and a microreactor that controls reaction conditions in at least a part of the microchannel.

[0008] 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, a light-emitting layer formation step of forming a light-emitting layer which is carried out 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 carried out 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 containing metal oxide nanoparticles manufactured by the method for manufacturing metal oxide nanoparticles.

[0009] In order to solve the above-mentioned problems, the manufacturing method of the display device according to the present disclosure includes a step of forming a plurality of light-emitting elements by the manufacturing method of the light-emitting element.

[0010] In order to solve the above-mentioned problems, the light-emitting element 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 including a first metal element and a second metal element different from the first metal element, and in a part of a cross section cut along the thickness direction of the electronic functional layer including 10×N metal oxide nanoparticles (N is a natural number of 2 or more), 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 3.5 nm or less, and the difference in particle size between the 9×Nth metal oxide nanoparticle and the Nth metal oxide nanoparticle is 3 nm or less.

[0011] In order to solve the above-mentioned problems, the display device of the present disclosure includes a plurality of the light-emitting elements.

[0012] In order to solve the above-mentioned problems, the group of metal oxide nanoparticles of the present disclosure comprises a group of metal oxide nanoparticles containing a first metal element and a second metal element different from the first metal element, wherein the particle size of the metal oxide nanoparticles at particle size cumulative 50% (D50) is 3.5 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 3 nm or less.

[0013] 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.

[0014] According to one aspect of the present disclosure, a method for producing metal oxide nanoparticles containing two or more different metal elements, which have small particle size and small particle size variation, and a reaction apparatus for producing such metal oxide nanoparticles, etc. can be provided.

[0015] 1. It is a plan view showing a schematic configuration of a display device of embodiment 1. It is a cross-sectional view showing a schematic configuration of a light-emitting element provided in the display device of embodiment 1 shown in FIG. 1. It is a diagram showing an example of a method for manufacturing the light-emitting element shown in FIG. 2. It is a diagram showing a schematic configuration of a reaction apparatus used in a process of manufacturing metal oxide nanoparticles contained in an electronic functional layer provided in the light-emitting element shown in FIG. 2. It is a diagram showing an example of process conditions in a process of manufacturing metal oxide nanoparticles using the reaction apparatus shown in FIG. 4. It is a diagram for explaining a process of manufacturing metal oxide nanoparticles using the reaction apparatus shown in FIG. 4. It is a diagram for explaining a metal oxide nanoparticle recovery process performed after manufacturing metal oxide nanoparticles using the reaction apparatus shown in FIG. 4. It is a diagram showing a particle size distribution of metal oxide nanoparticles manufactured using the reaction apparatus shown in FIG. 4. It is a diagram showing the energy levels of the valence band top (VBM) and the conduction band bottom (CBM) of an electronic functional layer containing metal oxide nanoparticles manufactured using the reaction apparatus shown in FIG. 4, and the energy levels of the valence band top (VBM) and the conduction band bottom (CBM) of an electronic functional layer containing metal oxide nanoparticles manufactured using the reaction apparatus shown in FIG. 13. 14 is a diagram comparing the device characteristics of an EOD (electro only device) having an electronic functional layer containing metal oxide nanoparticles manufactured using the reaction apparatus shown in FIG. 4 with the device characteristics of an EOD (electro only device) having an electronic functional layer containing metal oxide nanoparticles manufactured by the batch method shown in FIG. 13. FIG. 15 is a diagram showing the device characteristics of a HOD (hole only device) having a hole functional layer provided in the light-emitting device shown in FIG. 2. FIG. 16 is a diagram showing a schematic configuration of another reaction apparatus that can be used in a process of manufacturing metal oxide nanoparticles contained in an electronic functional layer provided in the light-emitting device shown in FIG. 2. FIG. 17 is a diagram showing a schematic configuration of a reaction apparatus used in a process of manufacturing metal oxide nanoparticles by a batch method. FIG. 18 is a diagram showing the particle size distribution of metal oxide nanoparticles manufactured using the reaction apparatus shown in FIG. 13. FIG. 19 is a cross-sectional view showing a schematic configuration of a light-emitting device provided in a display device of embodiment 2. FIG. 20 is a cross-sectional view showing a schematic configuration of a light-emitting device provided in a display device of embodiment 3.

[0016] The following describes embodiments of the present disclosure with reference to Figures 1 to 16. For the sake of convenience, components having the same functions as those described in specific embodiments 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 ３ The 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, a case where the electronic functional layer 4 functions as an electron transport layer (ETL), an electron injection layer (EIL), and a hole blocking layer (HBL) in one layer will be described as an example, but the present invention is not limited thereto. For example, the electronic functional layer 4 may function as an electron transport layer (ETL) and a hole blocking layer (HBL) as described in Embodiment 2, or may function only as an electron injection layer (EIL) as described in Embodiment 3. As described above, in this embodiment, the electronic functional layer 4 functions as an electron transport layer (ETL), an electron injection layer (EIL), and a hole blocking layer (HBL) in one layer. Therefore, in the light-emitting element 30 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] The electronic functional layer 4 includes a plurality of metal oxide nanoparticles each including a first metal element and a second metal element different from the first metal element. As will be described later, the metal oxide nanoparticles including the first metal element and the second metal element included in the electronic functional layer 4 are metal oxide nanoparticles produced using, for example, a reaction apparatus 10 shown in FIG. 4 , and therefore have small particle sizes and small variations in particle sizes.

[0025] 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 the first metal element and the second metal element. 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 3.5 nm or less, and the difference between the particle size of the 9×Nth metal oxide nanoparticle and the particle size of the Nth nanoparticle is 3 nm or less. Preferably, the particle size of the 5×Nth metal oxide nanoparticle is 3.2 nm or less, and the difference between the particle size of the 9×Nth metal oxide nanoparticle and the particle size of the Nth nanoparticle is 2.5 nm or less. More preferably, the particle size of the 5×Nth metal oxide nanoparticle is 2.9 nm or less, and the difference between the particle size of the 9×Nth metal oxide nanoparticle and the particle size of the Nth nanoparticle is 2 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 5xNth metal oxide nanoparticle means the particle size of the metal oxide nanoparticle that corresponds to 50% (median) when the particle sizes of the 10xN metal oxide nanoparticles are arranged in ascending order. The particle size of the 9xNth metal oxide nanoparticle means the particle size of the metal oxide nanoparticle that corresponds to 90% when the particle sizes of the 10xN metal oxide nanoparticles are 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% when the particle sizes of the 10xN metal oxide nanoparticles are arranged in ascending order.

[0026] In this embodiment, the metal oxide nanoparticles contained in the electronic function layer 4 are magnesium zinc oxide nanoparticles, the first metal element contained in the metal oxide nanoparticles is Zn, and the second metal element is Mg, but this is not limiting. For example, the first metal element and the second metal element in the metal oxide nanoparticles contained in the electronic function layer 4 may be different elements selected from Zn, Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Cu, Co, Mn, and Hf.

[0027] 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.

[0028] The light-emitting element 30 shown in FIG. 2 may be a top-emission type or a bottom-emission type. The light-emitting element 30 has a forward stack structure in which the cathode 5 is disposed above the anode 2. Therefore, to form 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 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. On the other hand, although not shown, the light-emitting element provided in the display device 1 may have an inverted stack structure in which the anode is disposed above the cathode. In this case, to form a top-emission type, the cathode may be formed from an electrode material that reflects visible light, and the anode may be formed from an electrode material that transmits visible light. To form a bottom-emission type, the cathode may be formed from an electrode material that transmits visible light, and the anode may be formed from an electrode material that reflects visible light.

[0029] 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.

[0030] 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.

[0031] 3A to 3C are diagrams showing an example of a method for manufacturing the light emitting element 30 shown in FIG.

[0032] 2 has a sequentially stacked structure in which the cathode 5 is disposed above the anode 2, and therefore 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. This is not a limitation, and a method for manufacturing a light-emitting device may include an anode formation step to form the anode 2, a cathode formation step to form the cathode 5, a light-emitting layer formation step to form the light-emitting layer EM, which is performed between the anode formation step and the cathode formation step, and an electronic functional layer formation step to form the electronic functional layer 4, which is performed between the light-emitting layer formation step and the cathode formation step. In the electronic functional layer formation step, the electronic functional layer 4 may be formed, which includes metal oxide nanoparticles containing the first metal element and the second metal element. The metal oxide nanoparticles containing the first metal element and the second metal element contained in the electronic functional layer 4 are metal oxide nanoparticles produced using, for example, a reaction apparatus 10 as shown in Figure 4, as described below, and therefore have small particle size and particle size variation.

[0033] In this embodiment, the electronic functional layer 4 functions as an electron transport layer (ETL), an electron injection layer (EIL), and a hole blocking layer (HBL) in one layer. Therefore, in the light-emitting element 30 shown in FIG. 2 , the electronic functional layer 4 may be provided so as to be in contact with both the cathode 5 and the light-emitting layer EM, and only the electronic functional layer formation step is performed between the light-emitting layer formation step and the cathode formation step.

[0034] As described above, the display device 1 shown in FIG. 1 includes a plurality of light-emitting elements, and therefore the manufacturing method of the display device 1 includes a step of forming a plurality of light-emitting elements, for example, by the manufacturing method of the light-emitting element 30 shown in FIG. 3.

[0035] 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 particle size distribution of metal oxide nanoparticles produced using the reaction apparatus 10 shown in FIG. 4 . FIG. 9 is a diagram showing the energy levels of the valence band top (VBM) and the conduction band bottom (CBM) of the electronic functional layer 4 containing metal oxide nanoparticles produced using the reaction apparatus 10 shown in FIG. 4 , and the energy levels of the valence band top (VBM) and the conduction band bottom (CBM) of the electronic functional layer of Comparative Example 1 containing metal oxide nanoparticles produced by the batch method shown in FIG. 13 . FIG. 10 is a diagram comparing the device characteristics of an EOD (electro-only device) having an electronic functional layer 4 containing metal oxide nanoparticles produced using the reaction apparatus 10 shown in FIG. 4 with the device characteristics of an EOD (electro-only device) having an electronic functional layer of Comparative Example 1 containing metal oxide nanoparticles produced by the batch method shown in FIG. 13 . FIG. 11 is a diagram showing the device characteristics of a HOD (hole-only device) having a hole functional layer 3 provided in the light-emitting element 30 shown in FIG. 2 . FIG. 12 is a diagram showing the schematic configuration of another reaction apparatus 20 that can be used in the process of producing metal oxide nanoparticles contained in the electronic functional layer 4 provided in the light-emitting element 30 shown in FIG. 2 . FIG. 13 is a diagram showing the schematic configuration of a reaction apparatus 100 used in the process of producing metal oxide nanoparticles by the batch method. FIG. 14 is a diagram showing the particle size distribution of metal oxide nanoparticles produced using the reaction apparatus 100 shown in FIG. 13 .

[0036] 4 , the reaction apparatus 10 includes: a micromixer 15 including a first supply port Inlet1, a second supply port Inlet2, and an outlet Outlet; a first supply unit 11 that supplies a first solution containing a precursor of metal oxide nanoparticles containing a first metal element, a precursor of metal oxide nanoparticles containing a second metal element different from the first metal element, and a first solvent at a first flow rate to one of the first supply port Inlet1 and the second supply port Inlet2 (in this embodiment, the first supply port Inlet1); a second supply unit 12 that supplies a second solution containing a reactant and a second solvent at a second flow rate to the other of the first supply port Inlet1 and the second supply port Inlet2 (in this embodiment, the second supply port Inlet2); a microchannel 16 having one end that is a supply end and the other end that is a discharge end, to which a fluid discharged from the discharge port Outlet of the micromixer 15 is supplied from the supply end; and a microreactor 17 that controls the reaction conditions of at least a part of the microchannel 16. In this embodiment, as a method for producing metal oxide nanoparticles containing the first metal element and the second metal element, for example, a reaction apparatus 10 is used to produce metal oxide nanoparticles containing the first metal element and the second metal element, but this is not limited to this, and for example, a reaction apparatus 20 shown in Figure 12 may be used to produce metal oxide nanoparticles containing the first metal element and the second metal element.

[0037] As shown in FIG. 4 , the reaction apparatus 10 further includes a first supply flow path 13 connecting a first supply port (Inlet 1) of the micromixer 15 to an outlet of the first supply unit 11, a second supply flow path 14 connecting a second supply port (Inlet 2) of the micromixer 15 to an outlet of the second supply unit 12, and a recovery unit 18 for recovering a fluid discharged from an outlet end of the microchannel 16. The first supply flow path 13 and the second supply flow path 14 are identical supply flow paths having the same flow path diameter and 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 micromixer 15, the reaction apparatus 10 does not need to include the first supply flow path 13. When the outlet of the second supply unit 12 is directly connected to the second supply port (Inlet 2) of the micromixer 15, the reaction apparatus 10 does not need to include the second supply flow path 14. Furthermore, the reaction device 10 does not necessarily have to include the recovery unit 18. In this case, the user of the reaction device 10 may prepare the recovery unit 18. The microreactor 17, which controls the reaction conditions of at least a part of the microchannel 16, controls the temperature of a part of the microchannel 16 to an optimum temperature for the reaction of the fluid flowing in the microchannel 16, for example.

[0038] In this embodiment, in the reaction apparatus 10 shown in Figure 4, the first metal element in the precursor of metal oxide nanoparticles containing a first metal element and the precursor of metal oxide nanoparticles containing a second metal element contained in the first solution are Zn, the second metal element is Mg, and the metal oxide nanoparticles are magnesium zinc oxide nanoparticles.However, this is not limited to this, and the first metal element and the second metal element may each be different elements selected from Zn, Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Cu, Co, Mn, and Hf.

[0039] 4, the reaction device 10 is provided with a micromixer 15 that is T-shaped in a plan view, and a flow microreactor-type special reaction field that utilizes turbulence can be realized by the T-shaped micromixer 15 in a plan view. In this embodiment, the reaction device 10 is described using an example in which it is provided with a T-shaped micromixer 15 in a plan view, but this is not limiting, and the reaction device 10 may be provided with, for example, a V-shaped micromixer in a plan view, and a flow microreactor-type special reaction field that utilizes turbulence can also be realized by a V-shaped micromixer in a plan view.

[0040] In this embodiment, magnesium zinc oxide nanoparticles are produced using a reaction apparatus 10. As shown in FIG. 4 , the first solution supplied from the first supply unit 11 to the first supply port Inlet 1 of the micromixer 15 via the first supply flow path 13 contains zinc acetate as a precursor of metal oxide nanoparticles containing a first metal element, magnesium acetate as a precursor of metal oxide nanoparticles containing a second metal element, and dimethyl sulfoxide (DMSO) as a first solvent. However, the present invention is not limited to this. For example, zinc acetate dihydrate may be used as the precursor of metal oxide nanoparticles containing the first metal element, and magnesium acetate tetrahydrate may be used as the precursor of metal oxide nanoparticles containing a second metal element. A polar solvent other than dimethyl sulfoxide (DMSO) may also be used as the first solvent. The second solution supplied from the second supply unit 12 to the second supply port Inlet 2 of the micromixer 15 via the second supply flow path 14 contains tetramethylammonium hydroxide (e.g., TMAH.5H), which is an alkaline reactant, as a reactant. ２The following description will be given of an example in which the second solution contains ethanol, an alcohol-based solvent, as the second solvent, but is not limited to this. The second solution may contain alkaline reactants such as tetramethylammonium hydroxide (e.g., TMAH.5H ２ In addition, the second solvent contained in the second solution may be any solvent other than ethanol as long as it is an alcohol-based solvent. Note that, for example, ZnOH and MgOH are generated in the micromixer 15, and a dehydration reaction between ZnOH and MgOH occurs in a part of the microchannel 16 where the reaction conditions are controlled by the microreactor 17.

[0041] 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. ２The molar ratio of the first solution to the second solution (MgO) was adjusted to 1:1.3. The flow rates of the first solution and the second solution can be appropriately determined taking into consideration the amount of magnesium zinc oxide nanoparticles to be obtained as the final product. In this embodiment, the flow rate of the first solution was 12.6 ml, and the flow rate of the second solution was 6.552 ml. In order to set the supply time of the first solution from the first supply unit 11 and the supply time of the second solution from the second supply unit 12 to 84 minutes, the first supply unit 11 supplied the first solution at a first flow rate, for example, 9 ml / h, and the second supply unit 12 supplied the second solution at a second flow rate, for example, 4.68 ml / h. In this embodiment, the first solution contained Mg ２＋ and Zn ２＋ The amounts of zinc acetate and magnesium acetate are adjusted so that the concentration ratio is 15:85. Therefore, as magnesium zinc oxide nanoparticles, for example, Zn ０．８５ Mg ０．１５ I was able to get O.

[0042] 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) and a second solution having a predetermined concentration B (0.25 M in this embodiment), step S12 of supplying the first solution to a first supply port Inlet 1 of the micromixer 15 at a predetermined flow rate C (9 ml / h in this embodiment) and supplying the second solution to a second supply port Inlet 2 of the micromixer 15 at a predetermined flow rate D (4.68 ml / h in this embodiment), and step S13 of discharging the ultranano-sized magnesium zinc oxide nanoparticles (e.g., ZnO) generated from the outlet end of the microchannel 16. ０．８５ Mg ０．１５ and a step S13 of recovering the dispersion liquid of O).

[0043] As shown in Fig. 7, the method for producing metal oxide nanoparticles preferably further includes step S21 of transferring the dispersion of magnesium zinc oxide nanoparticles 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 magnesium zinc oxide nanoparticles, step S22 of separating the solid matter 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 produce magnesium zinc oxide nanoparticles (e.g., Zn) from which impurities have been removed. ０．８５ Mg ０．１５ In addition, in step S23 shown in FIG. 7, the method for producing metal oxide nanoparticles includes removing the solution including the supernatant and redispersing the solid content in a solvent (e.g., ethanol or butanol) to obtain a dispersion of magnesium zinc oxide nanoparticles (e.g., Zn ０．８５ Mg ０．１５ In this method, the magnesium zinc oxide nanoparticles (e.g., ZnO) redispersed in a desired specific solvent are prepared. ０．８５ Mg ０．１５ In the step of preparing the redispersion, an organic ligand such as monoethanolamine (MEA) may be further added to further improve dispersibility.

[0044] The metal oxide nanoparticles produced using the reaction apparatus 10 shown in FIG. 4, i.e., the above-mentioned magnesium zinc oxide nanoparticles (e.g., Zn ０．８５ Mg ０．１５ The particle size distribution was measured using a redispersion of magnesium zinc oxide nanoparticles (e.g., ZnO). The redispersion was performed using a redispersion of magnesium zinc oxide nanoparticles (e.g., ZnO). The results are shown in FIG. ０．８５ Mg ０．１５ O) is dispersed in ethanol as a solvent.

[0045] As shown in FIG. 8, magnesium zinc oxide nanoparticles (e.g., Zn ０．８５ Mg ０．１５The particle size of the metal oxide nanoparticles at particle size-based cumulative 50% (D50) in the redispersion of magnesium zinc oxide nanoparticles (e.g., ZnO) was 2.88 nm, which was 2.9 nm or less. ０．８５ Mg ０．１５ The difference between the particle size of the metal oxide nanoparticles at particle size-based cumulative 90% (D90) and the particle size of the metal oxide nanoparticles at particle size-based cumulative 10% (D10) in the redispersion of 1.0 was 1.89 nm, which was 2 nm or less. The particle size distributions shown in Figures 8 and 14 were measured by DLS (dynamic light scattering) using a Nanotrac wave II manufactured by Microtaract.

[0046] In this embodiment, magnesium zinc oxide nanoparticles are produced using the reaction apparatus 10 under the conditions shown in Figure 5, and as described above, the particle size of the metal oxide nanoparticles at particle size cumulative 50% (D50) is 2.88 nm, 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 1.89 nm, but this is not limited to these values. For example, by adjusting the above-mentioned first flow rate and second flow rate so that the supply time of the first solution from the first supply unit 11 and the supply time of the second solution from the second supply unit 12 are both longer than 84 minutes, for example, 100 to 120 minutes, it is possible to obtain magnesium zinc oxide nanoparticles in which the particle size of metal oxide nanoparticles at particle size cumulative 50% (D50) is 3.5 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 3 nm or less.

[0047] Although not shown, the magnesium zinc oxide nanoparticles (e.g., Zn) recovered in step S13 shown in FIG. ０．８５ Mg ０．１５ The particle size of the metal oxide nanoparticles at particle size-based cumulative 50% (D50) in the dispersion of magnesium zinc oxide (MgO) was also 2.9 nm or less. ０．８５ Mg ０．１５The difference between the particle size of the metal oxide nanoparticles at particle size-based cumulative 90% (D90) and the particle size of the metal oxide nanoparticles at particle size-based cumulative 10% (D10) in the dispersion of O) was also 2 nm or less.

[0048] As described above, the magnesium zinc oxide nanoparticles produced using the reaction apparatus 10 have small particle sizes and small particle size variations. The reason why magnesium zinc oxide nanoparticles 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 and the second solution react while constantly flowing to produce the magnesium zinc oxide nanoparticles, and that the first solution contains a precursor of metal oxide nanoparticles containing a first metal element and a precursor of metal oxide nanoparticles containing a second metal element.

[0049] In this embodiment, magnesium zinc oxide nanoparticles were produced using the reaction apparatus 10 shown in Fig. 4, but the present invention is not limited to this, and magnesium zinc oxide nanoparticles may also be produced using a reaction apparatus 20 shown in Fig. 12. The reaction apparatus 20 shown in Fig. 12 differs from the reaction apparatus 10 shown in Fig. 4 in that it is equipped with a micromixer 25 that is linear in plan view. By providing the reaction apparatus 20 with the micromixer 25 that is linear in plan view, it is possible to realize a flow microreactor-type special reaction field in which the first solution and the second solution both flow as parallel flows.

[0050] As shown in FIG. 13, magnesium zinc oxide nanoparticles (e.g., Zn ０．８５ Mg ０．１５ The reaction apparatus 100 used in the process for producing magnesium zinc oxide nanoparticles (e.g., ZnO) comprises a supply unit 101, a supply flow path 102, and a reaction bath 103. 12.6 ml of the first solution described above was placed in the reaction bath 103 in advance, and while stirring, 6.552 ml of the second solution described above was supplied from the supply unit 101 to the reaction bath 103 via the supply flow path 102 at a flow rate of 4.68 ml / h for 84 minutes. Stirring was then continued for 90 minutes or more. Magnesium zinc oxide nanoparticles (e.g., ZnO) produced by such a batch method were prepared. ０．８５ Mg ０．１５In the manufacturing process of magnesium zinc oxide nanoparticles (e.g., ZnO), the reaction starts from the moment the second solution is supplied. However, immediately after the last second solution is supplied, it is necessary to continue stirring for a while in order to ensure the reaction time of the last second solution. Even if stirring is continued for a while, it is inevitable that there will be a difference between the reaction time of the first second solution and the reaction time of the last second solution. ０．８５ Mg ０．１５ Therefore, it is inevitable that the particle size of the particles (O) will vary widely.

[0051] Magnesium zinc oxide nanoparticles (e.g., Zn) produced using the reaction apparatus 100 shown in FIG. ０．８５ Mg ０．１５ The particle size distribution results of magnesium zinc oxide nanoparticles (e.g., ZnO) produced using the reactor 100 are shown in Figure 14. ０．８５ Mg ０．１５ The particle size of the metal oxide nanoparticles at particle size-based cumulative 50% (D50) in the dispersion of magnesium zinc oxide (e.g., ZnO) was 6.9 nm. ０．８５ Mg ０．１５ In the case of O), it is believed that the particle size and particle size variation become large due to the influence of the reasons mentioned above.

[0052] As shown in FIG. 9, magnesium zinc oxide nanoparticles (e.g., Zn ０．８５ Mg ０．１５ The energy level of the valence band minimum (VBM) of the electronic functional layer 4 containing magnesium zinc oxide (ZnO) was −7.25 eV, the energy level of the conduction band minimum (CBM) was −3.41 eV, and the band gap was 3.84 eV. On the other hand, the energy level of the magnesium zinc oxide nanoparticles (e.g., ZnO) produced by the batch method shown in FIG. ０．８５ Mg ０．１５ The electronic functional layer of Comparative Example 1 containing SiO had a valence band maximum (VBM) energy level of −7.24 eV, a conduction band minimum (CBM) energy level of −3.48 eV, and a band gap of 3.76 eV.

[0053] 9 , the energy level (−7.25 eV) of the valence band upper limit (VBM) of the electronic functional layer 4 is not significantly different from the energy level (−7.24 eV) of the valence band upper limit (VBM) of the electronic functional layer of Comparative Example 1. Therefore, when the electronic functional layer 4 functions as an electron transport layer (ETL), an electron injection layer (EIL), and a hole blocking layer (HBL) in one layer, as in this embodiment, the injection barrier of holes from the light-emitting layer EM to the electronic functional layer 4 can be maintained high, and therefore the electronic functional layer 4 can also be suitably used as a hole blocking layer (HBL).

[0054] As shown in FIG. 10, magnesium zinc oxide nanoparticles (e.g., Zn ０．８５ Mg ０．１５ 13. The EOD (electro only device) is provided with an electronic functional layer 4 containing magnesium zinc oxide nanoparticles (e.g., ZnO) and the EOD is provided with an electronic functional layer 4 containing magnesium zinc oxide nanoparticles (e.g., ZnO) produced by a batch method as shown in FIG. ０．８５ Mg ０．１５ In each of the EODs (electro-only devices) having the electronic functional layer of Comparative Example 1 containing ITO (indium tin oxide), the current density of the EOD (electro-only device) having the electronic functional layer 4 at a predetermined voltage value within the range of voltage values ​​actually used is smaller than the current density of the EOD (electro-only device) having the electronic functional layer of Comparative Example 1. The EOD (electro-only device) having the electronic functional layer 4 is made of ITO (indium tin oxide) as an anode, a light-emitting layer containing CdSe, and magnesium zinc oxide nanoparticles (e.g., ZnO) produced using the reaction apparatus 10 shown in FIG. ０．８５ Mg ０．１５ On the other hand, an EOD (electro only device) having an electronic functional layer of Comparative Example 1 was formed by laminating an ITO (indium tin oxide) as an anode, a light-emitting layer containing CdSe, and magnesium zinc oxide nanoparticles (e.g., ZnO) produced by the batch method shown in FIG. 13 . ０．８５Mg ０．１５ The electronic functional layer of Comparative Example 1 containing ZnO and ITO (indium tin oxide) as a cathode were laminated in this order.

[0055] 11 , the device characteristics of a hole-only device (HOD) including the hole functional layer 3 provided in the light-emitting element 30 shown in FIG. 2 , i.e., the current density relative to a predetermined voltage value within a range of voltage values ​​actually used, show the same tendency as the device characteristics of an electro-only device (EOD) including the electronic functional layer 4 shown in FIG. 10 , i.e., the current density relative to a predetermined voltage value within a range of voltage values ​​actually used. In this embodiment, the hole functional layer 3 used is a laminated film in which a hole injection layer (HIL) formed from conventional NiO particles and a hole transport layer (HTL) formed from poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl))diphenylamine)] (TFB) are laminated in this order from the anode 2 side. The HOD (hole only device) was formed by laminating, in this order, ITO (indium tin oxide) as an anode, a hole functional layer 3, a light-emitting layer containing CdSe, and ITO (indium tin oxide) as a cathode.

[0056] The current density of an EOD (electro only device) having an electronic functional layer 4 for a predetermined voltage value within the range of voltage values ​​actually used shown in Figure 10 is similar to the current density of an HOD (hole only device) having a hole functional layer 3 for a predetermined voltage value within the range of voltage values ​​actually used shown in Figure 11, so a good carrier balance can be achieved in the light-emitting element 30 having the electronic functional layer 4 and the hole functional layer 3.

[0057] As described above, in a group of metal oxide nanoparticles comprising a group of metal oxide nanoparticles containing a first metal element and a second metal element different from the first metal element, the particle size of the metal oxide nanoparticles at particle size cumulative 50% (D50) is 3.5 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 3 nm or less. In a group of metal oxide nanoparticles comprising a group of metal oxide nanoparticles containing a first metal element and a second metal element different from the first metal element, it is preferable that the particle size of the metal oxide nanoparticles at particle size cumulative 50% (D50) is 3.2 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 2.5 nm or less, and it is even more preferable that the particle size of the metal oxide nanoparticles at particle size cumulative 50% (D50) is 2.9 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 nm or less. The first metal element and the second metal element may be different elements selected from Zn, Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Cu, Co, Mn, and Hf, and the first metal element may be Zn, the second metal element may be Mg, and the metal oxide nanoparticles may be magnesium zinc oxide nanoparticles.

[0058] In this embodiment, an example has been described in which the electronic functional layer 4 is formed using a dispersion of metal oxide nanoparticles containing a solvent and a group of metal oxide nanoparticles consisting of a group of metal oxide nanoparticles containing a first metal element and a second metal element different from the first metal element, which are produced using the reaction device 10 or the reaction device 20. However, this is not limited to this, and the group of metal oxide nanoparticles produced using the reaction device 10 or the reaction device 20 or the dispersion of the above-mentioned metal oxide nanoparticles can also be used in the field of electronic materials other than electronic functional layers, or in other technical fields.

[0059] Second Embodiment FIG. 15 is a cross-sectional view showing a schematic configuration of a light-emitting element 40 provided in a display device of a second embodiment.

[0060] 15 , in a light-emitting element 40, an electronic functional layer 4 and an electron injection layer 6 are provided in this order from the light-emitting layer EM side between the light-emitting layer EM and the cathode 5. In the light-emitting element 40, the electronic functional layer 4 functions as an electron transport layer (ETL) and a hole blocking layer (HBL). Since the light-emitting element 40 also has the electronic functional layer 4 between the light-emitting layer EM and the cathode 5, it is possible to achieve improvements in carrier balance and luminous efficiency.

[0061] Third Embodiment FIG. 16 is a cross-sectional view showing a schematic configuration of a light-emitting element 50 provided in a display device according to a third embodiment.

[0062] 16 , in the light-emitting element 50, an electron transport layer 7 and an electronic functional layer 4 are provided in this order from the light-emitting layer EM side between the light-emitting layer EM and the cathode 5. In the light-emitting element 50, the electronic functional layer 4 functions as an electron injection layer (EIL). Since the light-emitting element 50 also has the electronic functional layer 4 between the light-emitting layer EM and the cathode 5, it is possible to achieve improvements in carrier balance and luminous efficiency.

[0063] [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.

[0064] The present disclosure can be used in a method for producing metal oxide nanoparticles, a reaction apparatus, a light-emitting device and a display device and methods for producing the same, a group of metal oxide nanoparticles, and a dispersion of metal oxide nanoparticles.

[0065] REFERENCE SIGNS LIST 1 display device 2 anode 3 hole functional layer 4 electron functional layer 5 cathode 6 electron injection layer 7 electron transport layer 10, 20 reaction device 11 first supply section 12 second supply section 13 first supply flow path 14 second supply flow path 15, 25 micromixer 16 microchannel 17 microreactor 18 recovery section 30, 40, 50 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 Outlet outlet

Claims

1. A reaction apparatus comprising: a micromixer including a first supply port, a second supply port, and an outlet; a first supply unit that supplies a first solution containing a precursor of metal oxide nanoparticles containing a first metal element, a precursor of metal oxide nanoparticles containing a second metal element different from the first metal element, and a first solvent at a first flow rate to one of the first supply port and the second supply port; a second supply unit that supplies a second solution containing a reactant and a second solvent at a second flow rate to the other of the first supply port and the second supply port; a microchannel having one end that is a supply end and the other end that is a discharge end, and through which a fluid discharged from the discharge port of the micromixer is supplied; and a microreactor that controls reaction conditions in at least a portion of the microchannel.

2. The reaction apparatus according to claim 1, wherein the first metal element and the second metal element are different elements selected from the group consisting of Zn, Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Cu, Co, Mn, and Hf.

3. The reaction device according to claim 1 or 2, wherein the first metal element is Zn, the second metal element is Mg, and the metal oxide nanoparticles are magnesium zinc oxide nanoparticles.

4. A reaction device according to any one of claims 1 to 3, wherein the micromixer is T-shaped or V-shaped in plan view.

5. A reaction device according to any one of claims 1 to 3, wherein the micromixer has a linear shape in a plan view.

6. A method for producing metal oxide nanoparticles comprising the first metal element and the second metal element, using a reaction apparatus comprising: a micromixer including a first supply port, a second supply port, and an outlet; a first supply unit that supplies a first solution comprising a precursor of metal oxide nanoparticles comprising a first metal element, a precursor of metal oxide nanoparticles comprising a second metal element different from the first metal element, and a first solvent at a first flow rate to one of the first supply port and the second supply port; a second supply unit that supplies a second solution comprising a reactant and a second solvent at a second flow rate to the other of the first supply port and the second supply port; a microchannel having one end that is a supply end and the other end that is a discharge end, the microchannel receiving the fluid discharged from the discharge port of the micromixer from the supply end; and a microreactor that controls reaction conditions in at least a portion of the microchannel.

7. A method for producing metal oxide nanoparticles according to claim 6, comprising: a first step including a step of supplying the first solution from the first supply unit to one of the first supply port and the second supply port, and a step of supplying the second solution containing the reactant and an alcohol-based solvent as the second solvent from the second supply unit to the other of the first supply port and the second supply port; and a second step of recovering a dispersion of the metal oxide nanoparticles containing the first metal element and the second metal element from the discharge end of the microchannel.

8. The method for producing metal oxide nanoparticles described in claim 7, wherein the particle size of the metal oxide nanoparticles at particle size-based cumulative 50% (D50) in the dispersion of the metal oxide nanoparticles recovered in the second step is 2.9 nm or less.

9. A method for producing metal oxide nanoparticles as described in claim 8, wherein 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) in the dispersion of the metal oxide nanoparticles recovered in the second step is 2 nm or less.

10. A method for producing metal oxide nanoparticles according to any one of claims 7 to 9, wherein the first metal element is Zn, the second metal element is Mg, the metal oxide nanoparticles are magnesium zinc oxide nanoparticles, the first solution contains zinc acetate as a precursor of metal oxide nanoparticles containing the first metal element, magnesium acetate as a precursor of metal oxide nanoparticles containing the second metal element, and a polar solvent as the first solvent, and the second solution contains an alkaline reactant as the reactant.

11. The method for producing metal oxide nanoparticles according to claim 10, wherein the alkaline reactant contained in the second solution is tetramethylammonium hydroxide (TMAH), and the polar solvent contained in the first solution is dimethyl sulfoxide (DMSO).

12. A method for producing metal oxide nanoparticles according to any one of claims 7 to 11, 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 solids from the solution by centrifugation; and a fifth step of removing the supernatant.

13. The method for producing metal oxide nanoparticles according to claim 12, wherein the fifth step comprises a sixth step of removing the solution including the supernatant liquid, and redispersing the solid content in a solvent to prepare a redispersion of the metal oxide nanoparticles.

14. The method for producing metal oxide nanoparticles according to claim 13, wherein in the sixth step, a redispersion liquid of the metal oxide nanoparticles containing an organic ligand is prepared.

15. The method for producing metal oxide nanoparticles according to claim 14, wherein the particle size of the metal oxide nanoparticles at particle size-based cumulative 50% (D50) in the redispersion of the metal oxide nanoparticles is 2.9 nm or less.

16. The method for producing metal oxide nanoparticles according to claim 15, wherein 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) in the redispersion of the metal oxide nanoparticles is 2 nm or less.

17. A method for manufacturing a light-emitting element, comprising: an anode formation step for forming an anode; a cathode formation step for forming a cathode; a light-emitting layer formation step for forming a light-emitting layer, which is carried out between the anode formation step and the cathode formation step; and an electronic function layer formation step for forming an electronic function layer, which is carried out 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 containing metal oxide nanoparticles manufactured by the method for manufacturing metal oxide nanoparticles described in any one of claims 6 to 16.

18. The method for manufacturing a light-emitting element according to claim 17, wherein only the electronic functional layer forming step is carried out between the light-emitting layer forming step and the cathode forming step.

19. A method for manufacturing a display device, comprising the step of forming a plurality of light-emitting elements by the method for manufacturing a light-emitting element according to claim 17 or 18.

20. 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 comprising a first metal element and a second metal element different from the first metal element, and wherein in a part of a cross section taken along the thickness direction of the electronic functional layer comprising 10×N metal oxide nanoparticles (N is a natural number of 2 or more), 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 3.5 nm or less, and the difference in particle size between the 9×Nth metal oxide nanoparticle and the Nth metal oxide nanoparticle is 3 nm or less.

21. The light-emitting element described in claim 20, wherein the particle size of the 5×Nth metal oxide nanoparticle is 2.9 nm or less, and the difference in particle size between the 9×Nth metal oxide nanoparticle and the Nth metal oxide nanoparticle is 2 nm or less.

22. The light-emitting element according to claim 20 or 21, wherein the first metal element and the second metal element are different elements selected from Zn, Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Cu, Co, Mn, and Hf.

23. A light-emitting element according to any one of claims 20 to 22, wherein the first metal element is Zn, the second metal element is Mg, and the metal oxide nanoparticles are magnesium zinc oxide nanoparticles.

24. The light-emitting device according to any one of claims 20 to 23, wherein the electronically functional layer is in contact with both the cathode and the light-emitting layer.

25. A display device comprising a plurality of light-emitting elements according to any one of claims 20 to 24.

26. A group of metal oxide nanoparticles comprising a group of metal oxide nanoparticles containing a first metal element and a second metal element different from the first metal element, wherein the particle size of the metal oxide nanoparticles at particle size cumulative 50% (D50) is 3.5 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 3 nm or less.

27. A group of metal oxide nanoparticles according to claim 26, wherein the particle size of the metal oxide nanoparticles at particle size cumulative 50% (D50) is 2.9 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 nm or less.

28. A group of metal oxide nanoparticles according to claim 26 or 27, wherein the first metal element and the second metal element are different elements selected from Zn, Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Cu, Co, Mn, and Hf.

29. A group of metal oxide nanoparticles according to any one of claims 26 to 28, wherein the first metal element is Zn, the second metal element is Mg, and the metal oxide nanoparticles are magnesium zinc oxide nanoparticles.

30. A dispersion of metal oxide nanoparticles comprising the metal oxide nanoparticles according to any one of claims 26 to 29 and a solvent.

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