WO2025215817A1 - 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 - Google Patents

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

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.

In recent years, a variety of display devices equipped with light-emitting elements have been developed, and display devices equipped with OLEDs (Organic Light Emitting Diodes) or QLEDs (Quantum Dot Light Emitting Diodes) in particular have attracted considerable attention due to their ability to achieve low power consumption, thinness, and high image quality.

Patent Document 1 describes an OLED or QLED equipped with 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.

Japan Special Table No. 2021-521586

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, such as the vapor deposition or sputtering process, that occurs in the cathode formation step, which is a subsequent step in forming the electronic functional layer. It has been reported that even the light-emitting layer below the electronic functional layer is damaged after the cathode formation step, resulting in a significant decrease in luminous efficiency. Zinc oxide nanoparticles or magnesium zinc oxide nanoparticles have relatively large particle size variations, and as a result, electronic functional layers formed solely from zinc oxide nanoparticles or magnesium zinc oxide nanoparticles lack density, resulting in insufficient protection of the light-emitting layer below the electronic functional layer.

Therefore, it is conceivable to form electronic functional layers such as electron transport layers and electron injection layers using a material in which zinc oxide nanoparticles or magnesium zinc oxide nanoparticles are mixed with a polymeric organic material such as PVP (polyvinylpyrrolidone), which is expected to function as a binder. However, organic-inorganic hybrid electronic functional layers in which zinc oxide nanoparticles or magnesium zinc oxide nanoparticles are mixed with a polymeric organic material are very unstable, and problems such as phase separation between the organic and inorganic materials occur during the process of forming the electronic functional layer. While slight improvements in density can be achieved compared to electronic functional layers 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 zinc oxide nanoparticles or magnesium zinc oxide nanoparticles. Therefore, there is a problem in that a satisfactory level of luminous efficiency cannot be achieved even in light-emitting devices equipped with an organic-inorganic hybrid electronic functional layer.

One aspect of the present disclosure aims to provide metal oxide nanoparticles with small particle size and particle size variation, a method for manufacturing metal oxide nanoparticles, a light-emitting element with high luminous efficiency, and a method for manufacturing the same.

In order to solve the above problems, the light-emitting device of the present disclosure has the following features:
an anode;
a cathode;
a light-emitting layer disposed between the anode and the cathode;
an electronic functional layer disposed between the cathode and the light-emitting layer;
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.

In order to solve the above problems, the display device of the present disclosure comprises:
A display device comprising a plurality of the light-emitting elements.

In order to solve the above problems, the metal oxide nanoparticles of the present disclosure are
The nanoparticles are made of 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.

In order to solve the above problems, the dispersion of metal oxide nanoparticles of the present disclosure has the following features:
The metal oxide nanoparticles and a solvent are included.

In order to solve the above-mentioned problems, the method for producing metal oxide nanoparticles of the present disclosure includes the steps of:
a micromixer that mixes and discharges a first precursor of metal oxide nanoparticles that contains 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 that contains 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 that contains zinc, and a reactant, all of which are supplied from the outside;
a microchannel having a supply end at one end and a discharge end at the other end, the microchannel receiving the fluid discharged from the micromixer 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 having a core that contains the first element, the second element, zinc, and oxygen.

In order to solve the above-mentioned problems, the method for manufacturing a light-emitting element according to the present disclosure includes the steps of:
an anode formation step of forming an anode;
a cathode forming step of forming a cathode, which is performed after the anode forming step;
a light-emitting layer forming step of forming a light-emitting layer, which is carried out between the anode forming step and the cathode forming step;
an electronic functional layer forming step of forming an electronic functional layer, which is performed between the light-emitting layer forming step and the cathode forming step;
In the electronic functional layer forming step, the electronic functional layer is formed, which contains metal oxide nanoparticles produced by the method for producing metal oxide nanoparticles.

One aspect of the present disclosure provides metal oxide nanoparticle groups and methods for producing metal oxide nanoparticles with small particle size and particle size variation, as well as light-emitting devices with high luminous efficiency and methods for producing the same.

1 is a plan view showing a schematic configuration of a display device according to a first embodiment. 2 is a cross-sectional view showing a schematic configuration of a light-emitting element provided in the display device of the first embodiment shown in FIG. 1. FIG. 3A to 3C are diagrams illustrating an example of a method for manufacturing the light-emitting element shown in FIG. 2. 3 is a diagram showing a schematic configuration of a reaction apparatus used in a process for producing metal oxide nanoparticles contained in an electronic functional layer provided in the light-emitting element shown in FIG. 2. FIG. FIG. 5 is a diagram showing an example of process conditions in a process for producing metal oxide nanoparticles using the reaction apparatus shown in FIG. 4. FIG. 5 is a diagram illustrating a process for producing metal oxide nanoparticles using the reaction apparatus shown in FIG. 4. FIG. 5 is a diagram illustrating a recovery step of metal oxide nanoparticles that is carried out after producing metal oxide nanoparticles using the reaction apparatus shown in FIG. 4. FIG. 3 is a diagram showing the results of FT-IR of metal oxide nanoparticles contained in an electronic functional layer provided in the light-emitting element shown in FIG. 2. 3 is a diagram showing the particle size distribution of metal oxide nanoparticles contained in an electronic functional layer provided in the light-emitting element shown in FIG. 2. FIG. 10 is a graph showing the relationship between current density and luminance of each of the light-emitting elements of Reference Example 1 and Reference Example 2. FIG. 1 is a diagram showing the relationship between current density and luminance of the light-emitting element of Example 1 and the light-emitting element of Comparative Example 1. FIG.

The following describes an embodiment of the present disclosure with reference to Figures 1 to 11. For ease of explanation, 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.

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

As shown in FIG. 1, the display device 1 has a frame area NDA and a display area DA. The display area DA of the display device 1 has 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, an example is described in which one pixel PIX is composed of a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP, but this is not limiting. For example, one pixel PIX may include subpixels of other colors in addition to the red subpixel RSP, green subpixel GSP, and blue subpixel BSP.

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

The red subpixel 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 in the light-emitting element 30 shown in FIG. 2 is a red light-emitting layer, the green subpixel 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 in the light-emitting element 30 shown in FIG. 2 is a green light-emitting layer, and the blue subpixel 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 in the light-emitting element 30 shown in FIG. 2 is a blue light-emitting layer.

As shown in FIG. 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 as including the hole functional layer 3 as an example, but this is not limiting, and the hole functional layer 3 may be omitted as appropriate.

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 formed using, for example, a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT:PSS), NiO particles, _MoO3 particles, or the like. 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.

In this embodiment, an example will be described in which the electronic functional layer 4 is a single layer that functions as an electron transport layer (ETL), an electron injection layer (EIL), and a hole blocking layer (HBL), but this is not limited to this. For example, the electronic functional layer 4 may include two or more layers selected from an electron transport layer (ETL), an electron injection layer (EIL), and a 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.

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 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 semi-metallic element; zinc; and oxygen. In other words, the metal oxide nanoparticles contained in the electronic functional layer 4 are nanoparticles with a core structure consisting only of a core containing the first element, the second element, zinc, and oxygen. Core-structured nanoparticles differ from core/shell nanoparticles having a core and a shell with a different composition from the core in that they do not have a shell with a different composition from the core. Examples of semi-metallic elements include B, Si, Ge, As, Sb, and Te. Furthermore, the metal oxide nanoparticles contained in the electronic function 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 composed only of a core containing the first element, the second element, zinc, and oxygen. Therefore, their particle size is unlikely to increase in size, and their particle size and particle size variation are small. Therefore, an electronic function layer 4 containing a plurality of metal oxide nanoparticles with such small particle size and particle size variation, or an electronic function 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 function layer 4. Therefore, a light-emitting element 30 including the electronic function layer 4 can achieve high luminous efficiency.

In addition, whether 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 using, for example, time-of-flight secondary ion mass spectrometry (TOF-SIMS), or by performing elemental analysis while gradually etching the metal oxide nanoparticles from the outside.

The second element, which is an element or semimetal element selected from the non-metal elements mentioned 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 mentioned above may be any of B, Si, Ge, As, Sb, Te, C, N, P, and S.

In a unit volume of the metal oxide nanoparticles contained in the electronic functional layer 4, the amount of oxygen element is preferably 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 preferably greater than the amount of the first element.

In this embodiment, the metal oxide nanoparticles contained in the electronic function layer 4 are described as an example of nanoparticles with a core structure consisting of only a core of a single composition 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.

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, it is preferable that the particle size of the 5×Nth metal oxide nanoparticle is 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 nanoparticle is 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 means the particle size of the metal oxide nanoparticle that is 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 means the particle size of the metal oxide nanoparticle that is 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 x N metal oxide nanoparticles arranged in ascending order.

In this embodiment, the light-emitting layer EM provided in the light-emitting element 30 shown in FIG. 2 is described as an example containing quantum dots (QDs), but 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; for example, CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, or ZnTe in the case of a ternary system; for example, CdSeTe, GaInP, or ZnSeTe; and for example, 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, it can be composed of, for example, CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, AIP, etc.

The light-emitting element 30 shown in Figure 2 may be either a top-emission type or a bottom-emission type. The light-emitting element 30 has a stacked structure in which the cathode 5 is disposed above the anode 2. To make it a top-emission type, the anode 2 should be formed from an electrode material that reflects visible light, and the cathode 5 should be formed from an electrode material that transmits visible light. To make it a bottom-emission type, the anode 2 should be formed from an electrode material that transmits visible light, and the cathode 5 should be formed from an electrode material that reflects visible light.

The electrode material that reflects visible light is not particularly limited as long as it can reflect visible light and is conductive, but examples include metal materials such as Al, Mg, Li, and Ag, alloys of these metal materials, laminates of these metal materials and transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), and laminates of these alloys and these transparent metal oxides.

On the other hand, electrode materials that transmit visible light are not particularly limited as long as they are transparent to visible light and conductive, but examples 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 or Ag, and nanowires made of metal materials such as Al or Ag.

Figure 3 shows an example of a method for manufacturing the light-emitting element 30 shown in Figure 2.

2 has a sequentially stacked structure in which the cathode 5 is disposed above the anode 2, and can be manufactured by performing the following steps in this order: anode formation process S1 to form the anode 2; hole functional layer formation process S2 to form the hole functional layer 3; light-emitting layer formation process S3 to form the light-emitting layer EM; electronic functional layer formation process S4 to form the electronic functional layer 4; and cathode formation process S5 to form the cathode 5. In the electronic functional layer formation process 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, which are manufactured by the metal oxide nanoparticle manufacturing method described below; a second element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a semimetallic element; zinc; and oxygen. 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.

FIG. 4 is a diagram showing the schematic configuration of a reaction apparatus 10 used in the process of producing metal oxide nanoparticles contained in the electronic function layer 4 of the light-emitting element 30 shown in FIG. 2. FIG. 5 is a diagram showing an example of process conditions for the process of producing metal oxide nanoparticles using the reaction apparatus 10 shown in FIG. 4. FIG. 6 is a diagram illustrating the process of producing metal oxide nanoparticles using the reaction apparatus 10 shown in FIG. 4. FIG. 7 is a diagram illustrating the 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 function layer 4 of 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 function layer 4 of the light-emitting element 10 shown in FIG. 2.

Metal oxide nanoparticles having a core structure consisting only of 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.

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 that is an element selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a semi-metallic element, a third precursor of metal oxide nanoparticles containing zinc, and a reactant, all supplied from the outside; a microchannel having a supply end on one side and a discharge end on the other side, and into 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.

In this embodiment, the reaction apparatus described above is the reaction apparatus 10 shown in FIG. 4, and an example will be given of the production of 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 selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a metalloid element, zinc, and oxygen, but the present invention is not limited to this.

As shown in Figure 4, the reaction apparatus 10 is equipped with 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 third solvent and 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, to yet another one of the first supply port Inlet 1, the second supply port Inlet 2, and the fourth supply port Inlet 4 at a third flow rate. As shown in FIG. 4 , the reaction apparatus 10 includes a microchannel 20 having one end as a supply end and the other end 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 the reaction conditions in at least a portion of the microchannel 20.

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 tetramethylammonium hydroxide (e.g., TMAH.5H 2 O), an alkaline reactant, as a reactant, and ethanol, an alcoholic solvent, as a second solvent, is supplied from a second supply unit 12 to a second supply port Inlet 2 at a second flow _rate . A second precursor of metal oxide nanoparticles containing a second element, which is an element selected from nonmetallic elements excluding hydrogen, oxygen, and Group 18 elements, or a semimetallic element, is supplied from a first supply unit 11 to a first supply port Inlet 1 at a first flow rate. 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.

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 produced in the first micromixer 16, and for example, ZnOH, MgOH, and Si(OH) _X (OC ₂ H ₅ ) _4-X (X = 0, 1, 2, 3, 4) are produced in the second micromixer 19. In a part of the microchannel 20 where the reaction conditions are controlled by the microreactor 21, dehydration reactions between ZnOH, MgOH, and Si(OH) _X (OC ₂ H ₅ ) _4-X (X = 0, 1, 2, 3, 4) occur competitively. 4 , the metal oxide nanoparticles produced using the reaction apparatus 10 shown in FIG. 4 are core-structured metal oxide nanoparticles composed solely of a core containing the first element, the second element, zinc, and oxygen, and are not core/shell nanoparticles having a core and a shell with a different composition from the core. As described above, since the dehydration reaction occurs primarily in the microchannel 20, the first solution may be 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 may be 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 may be supplied from the third supply unit 13 at a third 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.

As shown in FIG. 4, the reactor 10 includes a T-shaped first micromixer 16 and a T-shaped second micromixer 19 in a planar view. The T-shaped first micromixer 16 and the T-shaped second micromixer 19 can realize a flow microreactor-type special reaction field that utilizes turbulence in a planar view. In this embodiment, the reactor 10 includes a T-shaped first micromixer 16 and a T-shaped second micromixer 19 in a planar view. However, this is not limited to this. The reactor 10 may include, for example, a V-shaped micromixer in a planar 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 planar view can also realize a flow microreactor-type special reaction field that utilizes turbulence. Furthermore, the reaction apparatus 10 may be equipped 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. A linear micromixer can realize a special reaction field of the flow microreactor type in which fluids supplied from two supply ports flow in parallel.

As shown in FIG. 5 , in the first solution described above, the amounts of zinc acetate and magnesium acetate were adjusted so that the concentration ratio of Mg ²⁺ to Zn ²⁺ 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 the second solution, the amounts of tetramethylammonium hydroxide (e.g., TMAH.5H ₂ O) and ethanol, which is the second solvent, were adjusted so that the concentration of the second solution would be 0.25 M. Furthermore, as shown in FIG. 5, the molar ratio of Mg ²⁺ and Zn ²⁺ in the first solution to tetramethylammonium hydroxide (e.g., TMAH.5H ₂ O) in the second solution was adjusted to 1:1.3. In the third solution, tetraethoxysilane (TEOS (Tetraethyl The amounts of the first solution, the second solution, and the third solvent, ethanol, were adjusted. 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 6.552 mL, and the third solution 16 mL. To set the supply time of the first solution from the first supply unit 11, the second solution from the second supply unit 12, and 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, e.g., 9 mL/h, the second supply unit 12 supplied the second solution at a second flow rate, e.g., 4.68 mL/h, and the third supply unit 13 supplied the third solution at a third flow rate, e.g., 11.5 mL/h.

As shown in Figure 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 dispersion of ultranano-sized oxide nanoparticles containing Mg, Zn, and Si produced 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.

As shown in Figure 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 Figure 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 reactants dimethyl sulfoxide (DMSO) and ethanol (EtOH)). By including the metal oxide nanoparticle recovery step shown in Figure 7 in the method for producing metal oxide nanoparticles, a dispersion of ultranano-sized oxide nanoparticles containing Mg, Zn, and Si from which impurities have been removed can be obtained. Furthermore, the method for producing metal oxide nanoparticles may further include step S24 of removing the solution containing 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 in step S23 shown in FIG. 7 . This method allows for the production of 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 added to further improve dispersibility.

As shown in Figure 8, the FT-IR results for the ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si contained in the electronic function layer 4 of the light-emitting element 30 shown in Figure 2 showed absorption at the wavenumbers corresponding to Zn-O bonds, Mg-O bonds, and Si-O bonds, respectively, confirming that the ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si contain Zn-O bonds, Mg-O bonds, and Si-O bonds.

Figure 9 shows the results of measuring the particle size distribution using a redispersion of metal oxide nanoparticles produced using the reaction apparatus 10 shown in Figure 4, i.e., the ultranano-sized oxide nanoparticles containing Mg, Zn, and Si described above. Note that 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.

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

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 Figure 5. As described above, the particle size of metal oxide nanoparticles at 50% cumulative particle size (D50) is 1.76 nm, and the difference between the particle size of metal oxide nanoparticles at 90% cumulative particle size (D90) and the particle size of metal oxide nanoparticles at 10% cumulative particle size (D10) is 2.05 nm, but this is not limited to this. For example, by adjusting the first flow rate, second flow rate, and third flow rate described above 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 portion of the microchannel 20 where the reaction conditions are controlled by the microreactor 21 can be adjusted. This makes it possible to obtain ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si in which the particle size 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.

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

As described above, the ultranano-sized oxide nanoparticles containing Mg, Zn, and Si produced using the reaction apparatus 10 have small particle sizes and particle size variations. The ability to produce ultranano-sized oxide nanoparticles containing Mg, Zn, and Si with small particle sizes and particle size variations is believed to be due to the fact that the first solution, second solution, and third solution constantly flow and react to produce oxide nanoparticles with an ultranano-sized core structure containing Mg, Zn, and Si, and 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.

Figure 10 shows the relationship between current density and luminance for the light-emitting element of Reference Example 1 and the light-emitting element of Reference Example 2, i.e., the approximate luminous efficiency. Note that while the results using a red light-emitting element are shown here as an example, similar results can be obtained with green and blue light-emitting elements.

The light-emitting element (red light-emitting element) of Reference Example 1 shown in Figure 10 is a light-emitting element formed in this order: 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 that is an electronic functional layer made of zinc oxide nanoparticles; and a cathode made of ITO (indium tin oxide).

Because zinc oxide nanoparticles are metal oxide nanoparticles containing only zinc element, they have a larger particle size and particle size variation than the ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si described above. Therefore, the electron transport layer, which is an electronic functional layer formed from such zinc oxide nanoparticles and 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, such as the vapor deposition or sputtering process, that occurs in the cathode formation step, which is a step that follows the electron transport layer formation step. After the cathode formation step, even the light-emitting layer below the electron transport layer is damaged, resulting in a significant decrease in luminous efficiency. As a result, as shown in Figure 10, the light-emitting element (red light-emitting element) of Reference Example 1 does not achieve satisfactory luminous efficiency.

On the other hand, the light-emitting element (red light-emitting element) of Reference Example 2 shown in Figure 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) are stacked in this order, 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 that is a mixture of zinc oxide nanoparticles and PVP (polyvinylpyrrolidone), and a cathode made of ITO (indium tin oxide). 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, each layer was formed to have the same film thickness, and each of the layers other than the electron transport layer, which is the electronic functional layer (anode, hole injection layer, hole transport layer, light-emitting layer containing red-emitting quantum dots, and cathode) was formed using the same material with the same composition.

The electron transport layer, which is the electronic functional layer of Comparative Example 2 and is formed from a material that is a mixture of zinc oxide nanoparticles and PVP (polyvinylpyrrolidone), has slightly improved density compared to the electron transport layer, which is the electronic functional layer of Comparative Example 1. As shown in Figure 10, a red light-emitting device equipped with the electron transport layer, which is the electronic functional layer of Comparative Example 2, can achieve a slightly improved luminous efficiency. However, an organic-inorganic hybrid electron transport layer, such as the electron transport layer, which is the electronic functional layer of Comparative Example 2 and is formed from a material that is a mixture of zinc oxide nanoparticles and PVP (polyvinylpyrrolidone), is very unstable and suffers from problems such as phase separation between the organic and inorganic materials during the electron transport layer formation process. Furthermore, due to the large variation in particle size inherent in the zinc oxide nanoparticles, it is still not possible to achieve a satisfactorily high density. Therefore, a red light-emitting device equipped with the electron transport layer, which is the electronic functional layer of Comparative Example 2, cannot achieve a satisfactorily high luminous efficiency.

Figure 11 shows the relationship between current density and luminance for the light-emitting element of Example 1 and the light-emitting element of Comparative Example 1, i.e., the approximate luminous efficiency. Note that while 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.

The light-emitting element (blue light-emitting element) of Comparative Example 1 shown in Figure 11 is a light-emitting element formed in this order: 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 of Comparative Example 2, made of a material mixture of zinc oxide nanoparticles and PVP (polyvinylpyrrolidone); and a cathode made of ITO (indium tin oxide).

The light-emitting element of Comparative Example 1 (blue light-emitting element) shown in Figure 11 does not achieve a satisfactorily high luminous efficiency for the same reasons as the light-emitting element of Reference Example 2 (red light-emitting element) shown in Figure 10.

The light-emitting element (blue light-emitting element) of Example 1 shown in Figure 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 electronic functional layer 4 of Example 1 made of oxide nanoparticles with an ultra-nano-sized core structure containing Mg, Zn, and Si as described above, and a cathode made of ITO (indium tin oxide) are stacked 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, each layer was formed to have the same film thickness, and each of the layers other than the electron transport layer, which is the electronic functional layer (anode, hole injection layer, hole transport layer, light-emitting layer containing blue-emitting quantum dots, and cathode) were formed using the same materials with the same composition.

As shown in Figure 11, the blue light-emitting device having 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 having the electron transport layer as the electronic functional layer of Comparative Example 2. The ultra-nano-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, allowing for high density and high resistance to the cathode formation process, such as the 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 light-emitting devices having the electron transport layer as the electronic functional layer 4 can achieve high luminous efficiency.

The metal oxide nanoparticle group is composed of 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 selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a metalloid element; and zinc and oxygen. The particle size of the metal oxide nanoparticles at a cumulative 50% (D50) particle size may be 1.80 nm or less, and the difference between the particle size of the metal oxide nanoparticles at a cumulative 90% (D90) particle size and the particle size of the metal oxide nanoparticles at a cumulative 10% (D10) particle size may be 2.10 nm or less. The second element may be any of B, Si, Ge, As, Sb, Te, C, N, P, and S. Furthermore, it is preferable that, per 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 that the amount of the second element and the amount of zinc element are each greater than the amount of the first element. Furthermore, the first element may be Mg and the second element may be Si, in which case the metal oxide nanoparticles contain Zn—O bonds, Mg—O bonds, and Si—O bonds.

In this 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 selected from non-metallic elements excluding hydrogen, oxygen, and Group 18 elements or a metalloid element, and zinc and oxygen. However, this 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 and in other technical fields.

[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.

The present disclosure can be used in light-emitting devices, methods for manufacturing light-emitting devices, display devices, metal oxide nanoparticle groups, dispersions of metal oxide nanoparticles, and methods for manufacturing metal oxide nanoparticles.

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 (20)

an anode;
a cathode;
a light-emitting layer disposed between the anode and the cathode;
an electronic functional layer disposed between the cathode and the light-emitting layer;
The electronic functional layer comprises 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. The light-emitting element described in claim 1, wherein the second element is any one of B, Si, Ge, As, Sb, Te, C, N, P, and S. 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,
The light-emitting element according to claim 1 , wherein the amount of the second element and the amount of the zinc element are each greater than the amount of the first element. the first element is Mg,
The light-emitting device according to claim 1 , wherein the second element is Si. The light-emitting element described in claim 4, wherein the metal oxide nanoparticles contain Zn-O bonds, Mg-O bonds, and Si-O bonds. In a part of a cross section cut along the thickness direction of the electronic functional layer, the cross section contains 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 light-emitting device according to claim 4 or 5, wherein the particle diameter of the 5×Nth metal oxide nanoparticle is 1.8 nm or less. The light-emitting element described in claim 6, wherein the difference in particle size between the 9xNth metal oxide nanoparticle and the Nth metal oxide nanoparticle is 2.1 nm or less. A light-emitting element described in any one of claims 1 to 7, wherein the electronic functional layer is in contact with both the cathode and the light-emitting layer. A display device comprising a plurality of light-emitting elements according to any one of claims 1 to 8. 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. The group of metal oxide nanoparticles described in claim 10, wherein the second element is any one of B, Si, Ge, As, Sb, Te, C, N, P, and S. 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,
The group of metal oxide nanoparticles according to claim 10 or 11, wherein the amount of the second element and the amount of zinc element are each greater than the amount of the first element. the first element is Mg,
The group of metal oxide nanoparticles according to claim 10 , wherein the second element is Si. The group of metal oxide nanoparticles described in claim 13, wherein the metal oxide nanoparticles contain Zn-O bonds, Mg-O bonds, and Si-O bonds. The particle size of the metal oxide nanoparticles at particle size-based cumulative 50% (D50) is 1.8 nm or less;
15. The group of metal oxide nanoparticles according to claim 13 or 14, wherein 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) is 2.1 nm or less. A dispersion of metal oxide nanoparticles comprising the metal oxide nanoparticles described in any one of claims 10 to 15 and a solvent. a micromixer that mixes and discharges a first precursor of metal oxide nanoparticles that contains 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 that contains 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 that contains zinc, and a reactant, all of which are supplied from the outside;
a microchannel having a supply end at one end and a discharge end at the other end, the microchannel receiving the fluid discharged from the micromixer from the supply end;
a microreactor that controls the reaction conditions in at least a portion of the microchannel, to produce metal oxide nanoparticles having a core that contains the first element, the second element, zinc, and oxygen. the micromixer includes a first micromixer including a first supply port, a second supply port, and a first discharge port, and a second micromixer including a third supply port, a fourth supply port, and a second discharge port;
The fluid discharged from the first outlet is supplied from the third supply port,
the fluid discharged from the second outlet is supplied to the supply end of the microchannel;
The reactor 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 one of the first supply port, the second supply port, and the fourth supply port;
18. The method for producing metal oxide nanoparticles according to claim 17, further comprising: 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 one of the first supply port, the second supply port, and the fourth supply port. 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;
a second step of recovering a dispersion of metal oxide nanoparticles composed of a core containing the first element, the second element, zinc element, and oxygen element from the discharge end of the microchannel. a third step of transferring the dispersion of the 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 and 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 content in a solvent.