Light emitting element, display device, method for manufacturing light emitting element, and method for manufacturing metal oxide nanoparticles

Abstract

A light emitting element (11) includes an anode (2), a cathode (5), a light emitting layer (EM) provided between the anode (2) and the cathode (5), a hole functional layer (3) provided between the anode (2) and the light emitting layer (EM), and an electron functional layer (4a) provided between the cathode (5) and the light emitting layer (EM). The hole functional layer (3) contains first metal oxide nanoparticles, and the electron functional layer (4a) contains second metal oxide nanoparticles. The first metal oxide nanoparticles are composed of a plurality of Ni atoms, a plurality of oxygen atoms, and a plurality of Fe atoms, the number of which is smaller than the number of the Ni atoms. The second metal oxide nanoparticles contain a first metal element and a second metal element different from the first metal element.

Description

Light-emitting element, display device, method for manufacturing a light-emitting element, and method for manufacturing metal oxide nanoparticles 【0001】 One aspect of this disclosure relates to a light-emitting element, a display device, a method for manufacturing a light-emitting element, and a method for manufacturing metal oxide nanoparticles. 【0002】 In recent years, various display devices equipped with light-emitting elements have been developed, and in particular, display devices equipped with OLEDs (Organic Light Emitting Diodes) or QLEDs (Quantum Dot Light Emitting Diodes) have attracted considerable attention due to their ability to achieve low power consumption, thin design, and high image quality. 【0003】 In the field of OLEDs or QLEDs, a configuration is well known in which at least one of a hole injection layer and a hole transport layer is provided between the anode and the light-emitting layer as a hole functional layer. For example, Patent Document 1 describes using a nickel oxide thin film as the hole injection layer, and bonding an organic molecule having an electron-withdrawing group, such as trifluoromethylbenzoic acid, trifluoromethylphenylacetic acid, or trifluorobutyl acid, to the surface of the nickel oxide thin film in order to improve the hole injection properties of the hole injection layer. 【0004】 International Publication No. 2018 / 001372 【0005】 However, as disclosed in Patent Document 1, when organic molecules are bonded to the surface of a nickel oxide thin film as a hole injection layer, there is a problem that the inclusion of a large amount of organic molecules leads to a decrease in reliability. 【0006】 One aspect of this disclosure aims to provide a method for producing metal oxide nanoparticles having good reliability, good hole injection characteristics, and good hole transport characteristics, a light-emitting element with high external quantum efficiency and a method for producing the same, and a display device equipped with a light-emitting element with high external quantum efficiency. 【0007】The present disclosure provides a method for producing metal oxide nanoparticles in order to solve the above-mentioned problems, comprising the steps of: preparing a mixed solution of a first precursor containing Ni atoms, a second precursor containing Fe atoms, and a solvent; adjusting the pH of the mixed solution to obtain a hydroxide intermediate containing the Ni atoms and the Fe atoms; removing by-products from the hydroxide intermediate; drying the hydroxide intermediate from which the by-products have been removed; pulverizing the dried hydroxide intermediate; and heat-treating the fine particles of the pulverized hydroxide intermediate. 【0008】 To solve the above problems, the present disclosure provides 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; an emissive layer formation step performed between the anode formation step and the cathode formation step for forming an emissive layer; and a hole functional layer formation step performed between the emissive layer formation step and the anode formation step for forming a hole functional layer, wherein the hole functional layer formation step includes a first metal oxide nanoparticle manufactured by the method for manufacturing metal oxide nanoparticles. 【0009】 To solve the above 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, a hole functional layer provided between the anode and the light-emitting layer and containing first metal oxide nanoparticles, and an electronic functional layer provided between the cathode and the light-emitting layer and containing second metal oxide nanoparticles, wherein the first metal oxide nanoparticles are composed of a plurality of Ni atoms, a plurality of oxygen atoms, and a number of Fe atoms less than the number of Ni atoms, and the second metal oxide nanoparticles include a first metal element and a second metal element different from the first metal element. 【0010】 The display device of this disclosure includes the light-emitting element in order to solve the aforementioned problems. 【0011】According to one aspect of this disclosure, a method for producing metal oxide nanoparticles having good reliability, good hole injection characteristics, and good hole transport characteristics, a light-emitting element with high external quantum efficiency and a method for producing the same, and a display device equipped with a light-emitting element with high external quantum efficiency can be provided. 【0012】Figure 1 is a plan view showing the schematic configuration of the display device of Embodiment 1. Figure 1 is a cross-sectional view showing the schematic configuration of the light-emitting element provided in the display device of Embodiment 1. Figure 2 is a cross-sectional view showing the schematic configuration of the hole functional layer provided in the light-emitting element. Figure 2 is a diagram for explaining the manufacturing method of the forward-facing light-emitting element. Figure 2 is a diagram for explaining the manufacturing method of the inverted-facing light-emitting element. Figure 3 is a diagram for explaining the manufacturing method of the first metal oxide nanoparticles. Figure 3 is a diagram showing the schematic manufacturing method of the first metal oxide nanoparticles. Figure 6 and Figure 7 are diagrams showing the X-ray diffraction (XRD) measurement results of the first metal oxide nanoparticles manufactured by the manufacturing methods shown. Figure 6 and Figure 7 are diagrams showing the particle size distribution of the first metal oxide nanoparticles manufactured by the manufacturing methods shown. Figure 6 and Figure 7 are diagrams comparing the element characteristics of a Hole Only Device (HOD) equipped with a hole injection layer containing the first metal oxide nanoparticles manufactured by the manufacturing methods shown in Figures 6 and Figure 7 with the element characteristics of a Hole Only Device (HOD) equipped with a hole injection layer containing nickel oxide nanoparticles, which is a comparative example. Figures 6 and 7 show a comparison of the transmittance of a hole injection layer containing first metal oxide nanoparticles manufactured by the manufacturing method shown in Figures 6 and 7, and the transmittance of a hole injection layer containing nickel oxide nanoparticles, which is a comparative example. Figure 2 shows the relationship between the current density and external quantum efficiency (EQE) of a light-emitting element and a light-emitting element equipped with a hole injection layer containing nickel oxide nanoparticles, which is a comparative example. Figure 13 shows a schematic cross-sectional view of a light-emitting element of Embodiment 2, which comprises a hole functional layer containing first metal oxide nanoparticles and an electronic functional layer containing second metal oxide nanoparticles. Figure 14 shows a schematic view of the reactor used in the process of manufacturing the second metal oxide nanoparticles contained in the electronic functional layer of the light-emitting element shown in Figure 13. Figure 14 shows an example of process conditions in the process of manufacturing second metal oxide nanoparticles using the reactor shown in Figure 14. Figure 14 shows a diagram to explain the process of manufacturing second metal oxide nanoparticles using the reactor shown in Figure 14. Figure 14 shows a diagram to explain the process of recovering second metal oxide nanoparticles after manufacturing them using the reactor shown in Figure 14. Figure 4 shows the particle size distribution of second metal oxide nanoparticles manufactured using the reactor shown in Figure 4.Figure 14 shows the energy levels of the upper valence band (VBM) and lower conduction band (CBM) of an electronically functional layer containing second metal oxide nanoparticles manufactured using the reactor shown in Figure 14, and the energy levels of the upper valence band (VBM) and lower conduction band (CBM) of an electronically functional layer containing second metal oxide nanoparticles manufactured by a comparative example batch method. Figure 13 shows a schematic configuration of another reactor that can be used in the process of manufacturing second metal oxide nanoparticles contained in the electronically functional layer of the light-emitting element shown in Figure 13. Figure 23 shows the relationship between current density and external quantum efficiency (EQE) in the light-emitting element shown in Figure 2, Figure 13, and Figure 22. Figure 3 shows a schematic cross-sectional view of the light-emitting element of Embodiment 3, which comprises a hole functional layer containing first metal oxide nanoparticles and an electronically functional layer containing second metal oxide nanoparticles. Figure 24 shows a schematic configuration of a reactor used in the process of manufacturing second metal oxide nanoparticles contained in the electronically functional layer of the light-emitting element shown in Figure 22. Figure 23 shows an example of process conditions in the process of manufacturing second metal oxide nanoparticles using the reactor shown in Figure 23. This figure illustrates the process of producing second metal oxide nanoparticles using the reaction apparatus shown in Figure 23. This figure illustrates the process of recovering second metal oxide nanoparticles after they have been produced using the reaction apparatus shown in Figure 23. This figure shows the FT-IR results of second metal oxide nanoparticles contained in the electronic functional layer of the light-emitting element shown in Figure 22. This figure shows the particle size distribution of second metal oxide nanoparticles contained in the electronic functional layer of the light-emitting element shown in Figure 22. 【0013】 The embodiments of this disclosure will be described below with reference to Figures 1 to 28. For the sake of convenience, in the following description, components having the same function as those described in a particular embodiment will be denoted by the same reference numerals, and their descriptions may be omitted. 【0014】 [Embodiment 1] Figure 1 is a plan view showing the schematic configuration of the display device 1 of Embodiment 1. 【0015】As shown in Figure 1, the display device 1 comprises a frame area NDA and a display area DA. The display area DA of the display device 1 is provided with a plurality of pixels PIX, and each pixel PIX includes a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP. In this embodiment, the case in which one pixel PIX is composed of a red subpixel RSP, a green subpixel GSP, and a blue subpixel BSP is described as an example, but it is not limited to this. 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. 【0016】 Figure 2 is a cross-sectional view showing a schematic configuration of the light-emitting element 10 provided in the display device 1 of Embodiment 1 shown in Figure 1. 【0017】 Each of the red subpixels RSP, green subpixel GSP, and blue subpixel BSP provided in the display area DA of the display device 1 includes the light-emitting element 10 shown in Figure 2. Specifically, the red subpixel RSP includes a red light-emitting element in which the light-emitting layer EM provided in the light-emitting element 10 shown in Figure 2 is a red light-emitting layer; the green subpixel GSP includes a green light-emitting element in which the light-emitting layer EM provided in the light-emitting element 10 shown in Figure 2 is a green light-emitting layer; and the blue subpixel BSP includes a blue light-emitting element in which the light-emitting layer EM provided in the light-emitting element 10 shown in Figure 2 is a blue light-emitting layer. 【0018】 As shown in Figure 2, the light-emitting element 10 includes an anode 2, a cathode 5, a light-emitting layer EM provided between the anode 2 and the cathode 5, and a hole functional layer 3 provided between the anode 2 and the light-emitting layer EM. In this embodiment, the case in which the light-emitting element 10 further includes an electronic functional layer 4 between the cathode 5 and the light-emitting layer EM is described as an example, but the embodiment is not limited to this, and the electronic functional layer 4 may be omitted as appropriate. 【0019】 Figure 3 is a cross-sectional view showing the schematic configuration of the hole functional layer 3 provided in the light-emitting element 10 shown in Figure 2. 【0020】In this embodiment, as shown in Figure 3, the hole functional layer 3 is constructed by stacking a hole injection layer 3HI and a hole transport layer 3HT in that order from the anode 2 side. The hole injection layer 3HI contains a first metal oxide nanoparticle 20 composed of a plurality of Ni atoms, a plurality of oxygen atoms, and a plurality of Fe atoms in a number less than the number of Ni atoms. 【0021】 As described above, in this embodiment, the hole functional layer 3 is composed of a hole injection layer 3HI and a hole transport layer 3HT, and the case in which only the hole injection layer 3HI contains the first metal oxide nanoparticles 20 has been explained as an example. However, the embodiment is not limited to this, and as long as the hole functional layer 3 contains the first metal oxide nanoparticles 20, the hole functional layer 3 may be composed of only the hole injection layer 3HI, only the hole transport layer 3HT, or both the hole injection layer 3HI and the hole transport layer 3HT. 【0022】 The hole transport layer 3HT may be formed using an organic material such as 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), or polyvinylcarbazole (PVK), or it may be formed using an inorganic material. In this embodiment, the hole transport layer 3HT was formed using poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB). 【0023】 The electronic functional layer 4 only needs to include at least one of an electron transport layer and an electron injection layer. If it includes both an electron transport layer and an electron injection layer, the electron injection layer and the electron transport layer are stacked in this order from the cathode 5 side. 【0024】The electron transport layer may be formed using an organic material such as 2,2',2"-(1,3,5-benzintriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi), or it may be formed using an inorganic material such as ZnO nanoparticles or nanoparticles of an oxide containing Zn and Mg. In this embodiment, the electronic functional layer 4 is composed solely of an electron transport layer, and the electron transport layer is formed of ZnO nanoparticles. 【0025】 The electron injection layer can be formed using, for example, alkali metals or alkaline earth metals such as aluminum, strontium, calcium, lithium, cesium, magnesium oxide, aluminum oxide, strontium oxide, lithium oxide, lithium fluoride, magnesium fluoride, strontium fluoride, calcium fluoride, barium fluoride, cesium fluoride, polymethyl methacrylate, sodium polystyrene sulfonate, alkali metals or alkaline earth metals, oxides of alkali metals or alkaline earth metals, fluorides of alkali metals or alkaline earth metals, or organic complexes of alkali metals. 【0026】 Figure 4 is a diagram illustrating the manufacturing method of the light-emitting element 10 with a forward-facing structure shown in Figure 2. Figure 5 is a diagram illustrating the manufacturing method of the light-emitting element with an inverted-facing structure. 【0027】The light-emitting element 10 shown in Figure 2 may be either a top-emission type or a bottom-emission type. In this embodiment, the case in which the light-emitting element 10 shown in Figure 2 has a forward-facing structure in which the cathode 5 is positioned above the anode 2 will be described as an example. The forward-facing light-emitting element 10 shown in Figure 2 can be manufactured by performing the following steps in order, as shown in Figure 4: step S11 to form the anode 2, step S12 to form the hole functional layer 3, step S13 to form the light-emitting layer EM, step S14 to form the electronic functional layer 4, and step S15 to form the cathode 5. The invention is not limited to this, and although not shown, the light-emitting element may also have an inverted-facing structure in which the anode 2 is positioned above the cathode 5. The inverted-facing light-emitting element can be manufactured by performing the following steps in order, as shown in Figure 5: step S21 to form the cathode 5, step S22 to form the electronic functional layer 4, step S23 to form the light-emitting layer EM, step S24 to form the hole functional layer 3, and step S25 to form the anode 2. As in this embodiment, in order to make the forward-facing light-emitting element 10 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. In order to make the forward-facing light-emitting element 10 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. On the other hand, in order to make the inverted-facing light-emitting element a top-emission type, the cathode 5 should be formed from an electrode material that reflects visible light and the anode 2 should be formed from an electrode material that transmits visible light. In order to make the inverted-facing light-emitting element a bottom-emission type, the cathode 5 should be formed from an electrode material that transmits visible light and the anode 2 should be formed from an electrode material that reflects visible light. 【0028】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 metallic materials such as Al, Mg, Li, and Ag, or alloys of the metallic materials, or laminates of the metallic material and transparent metal oxides (e.g., indium tin oxide, indium zinc oxide, indium gallium zinc oxide, etc.), or laminates of the alloy and the transparent metal oxide. 【0029】 On the other hand, the electrode material that transmits visible light is not particularly limited as long as it can transmit visible light and is 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 and Ag, or nanowires made of metal materials such as Al and Ag. 【0030】 In this embodiment, in order to realize a top-emission type light-emitting element 10, the anode 2 is formed from a laminate of an indium tin oxide film, an Ag film, and another indium tin oxide film, which are electrode materials that reflect visible light, and the cathode 5 is formed from a nanowire made of Ag, which is an electrode material that transmits visible light. 【0031】 The light-emitting layer EM provided in the light-emitting element 10 shown in Figure 2 may be a light-emitting layer containing quantum dots, or a light-emitting layer containing an organic light-emitting material. A light-emitting element 10 equipped with a light-emitting layer containing quantum dots is a QLED (Quantum dot Light Emitting Diode), and a light-emitting element 10 equipped with a light-emitting layer containing an organic light-emitting material is an OLED (Organic Light Emitting Diode). 【0032】Quantum dots such as red-emitting quantum dots in the red-emitting layer, green-emitting quantum dots in the green-emitting layer, and blue-emitting quantum dots in the blue-emitting layer may have, for example, a core structure, a core / shell structure, a core / shell / shell structure, or a shell structure with continuously changing core / ratio. The shell may cover a portion of the core, but it is preferable that it completely covers the core. The core of the quantum dot may contain one or more selected from, for example, Si, Ge, CdSe, CdS, CdTe, InP, GaP, InN, ZnSe, ZnS, ZnTe, CdSeTe, GaInP, and ZnSeTe. The quantum dot shell may include one or more selected from, for example, CdS, ZnS, CdSSe, CdTeSe, CdSTe, ZnSSe, ZnSTe, ZnTeSe, and AgInP (AIP), and may be selected to have a lattice constant close to that of the core and a larger band gap than the core. 【0033】 Figure 6 is a diagram illustrating the manufacturing method of the first metal oxide nanoparticles 20 shown in Figure 3. Figure 7 is a schematic diagram showing the manufacturing method of the first metal oxide nanoparticles 20 shown in Figure 3. Figure 8 is a diagram showing the X-ray diffraction (XRD) measurement results of the first metal oxide nanoparticles 20 shown in Figure 3. Figure 9 is a diagram showing the particle size distribution of the first metal oxide nanoparticles 20 manufactured by the manufacturing methods shown in Figures 6 and 7. 【0034】 As shown in Figure 6, the method for producing the first metal oxide nanoparticles 20 shown in Figure 3 includes the steps of: S1 preparing a mixed solution of a first precursor containing Ni atoms, a second precursor containing Fe atoms, and a solvent; S2 adjusting the pH of the mixed solution to obtain a hydroxide intermediate containing Ni atoms and Fe atoms; S3 removing by-products from the hydroxide intermediate; S4 drying the hydroxide intermediate from which the by-products have been removed; S5 pulverizing the dried hydroxide intermediate; and S6 heat treating the pulverized hydroxide intermediate fine particles. 【0035】 As shown in Figure 7, in step S1, which prepares a mixed solution of a first precursor containing Ni atoms, a second precursor containing Fe atoms, and a solvent, for example, the first precursor may be nickel nitrate (Ni(NO)).３ ) ２ ) The hexahydrate of is used as the second precursor, and iron nitrate (Fe(NO ３ )) ３ ) The nonahydrate of can be used as the solvent, and water can be used. In this embodiment, for example, nickel nitrate (Ni(NO ３ )) ２ ) with a molar concentration M (= mol / L) adjusted to 2.5 M or more and 5 M or less, an aqueous solution of the hexahydrate of, to the aqueous solution, (the number of moles of the nonahydrate of the additional iron nitrate (Fe(NO ３ )) ３ )) / (the number of moles of the hexahydrate of nickel nitrate (Ni(NO ３ )) ２ )) in the aqueous solution + the number of moles of the nonahydrate of the additional iron nitrate (Fe(NO ３ )) ３ )) × 100 (%) has a value of 0.1% or more and 20% or less, and the nonahydrate of iron nitrate (Fe(NO ３ )) ３ )) is added and stirred to prepare a mixed solution. 【0036】 As shown in FIG. 7, in step S2 of adjusting the pH of the mixed solution to obtain a hydroxide intermediate containing Ni atoms and Fe atoms, for the mixed solution, the pH is adjusted to 9 or more and 12 or less. For example, an aqueous NaOH solution is added and stirred to obtain a suspension of Fe-Ni-OH, which is a slurry-like hydroxide intermediate containing Ni atoms and Fe atoms. 【0037】Subsequently, as shown in Figures 6 and 7, by performing the following steps in order: step S3 to remove by-products from the suspension of Fe-Ni-OH, which is the hydroxide intermediate; step S4 to dry the hydroxide intermediate from which the by-products have been removed; and step S5 to pulverize the dried hydroxide intermediate, fine particles of the dried hydroxide intermediate Fe-Ni-OH can be obtained. In step S3 to remove by-products from the suspension of Fe-Ni-OH, which is the hydroxide intermediate, for example, one or more centrifugations and one or more washes with water may be performed. In step S4 to dry the hydroxide intermediate from which the by-products have been removed, the solid content of the hydroxide intermediate can be obtained by drying the slurry-like hydroxide intermediate at a temperature of 20°C or higher and 80°C or freeze-drying at a temperature of less than 0°C. In step S5, which involves grinding the dried hydroxide intermediate, the solid portion of the hydroxide intermediate may be ground using a grinding device (e.g., a hand mill) until it reaches a predetermined size to obtain fine particles of Fe-Ni-OH, which is the hydroxide intermediate in powder form. Furthermore, after step S5, which involves grinding the dried hydroxide intermediate, a classification step may be performed to obtain fine particles of a predetermined size or smaller. In this embodiment, the solid portion of the hydroxide intermediate was ground in a mortar until its particle size was approximately 200 μm or less. 【0038】 Subsequently, in step S6, which involves heat-treating the fine hydroxide intermediate particles after pulverization as shown in Figures 6 and 7, the first metal oxide nanoparticles 20, which are composed of multiple Ni atoms, multiple oxygen atoms, and multiple Fe atoms in a number less than the number of Ni atoms, are heated in air at a temperature of 230°C or higher and 300°C or lower, i.e., calcination. Ｘ Ni （１－Ｘ） Nanoparticles can be obtained that consist of a compound represented by O (Fe is the element iron, Ni is the element nickel, O is the element oxygen, and X is less than 0.5). As mentioned above, in this embodiment, (additional iron nitrate (Fe (NO) ３ ) ３ ) molar number of xuhydrate (nickel nitrate (Ni(NO) in the aqueous solution) / (the number of moles of xuhydrate) / (nickel nitrate (Ni(NO) in the aqueous solution) ３ )２ The number of moles of hexahydrate of ) + the additional amount of iron nitrate (Fe(NO) ３ ) ３ The value of (moles of ) of the nonahydrate of ) × 100 (%) should be between 0.1% and 20%. ３ ) ３ Since the nonahydrate of ) is added, Fe Ｘ Ni （１－Ｘ） Nanoparticles can be obtained that consist of a compound represented by O (Fe is the element iron, Ni is the element nickel, O is the element oxygen, and X is between 0.001 and 0.2). 【0039】 In the manufacturing method of the light-emitting element 10 with a forward-facing structure shown in Figure 4, step S12 for forming the hole functional layer, or in the manufacturing method of the light-emitting element with an inverted-facing structure shown in Figure 5, step S24 for forming the hole functional layer may be formed by creating a hole functional layer containing first metal oxide nanoparticles 20 produced by the metal oxide nanoparticle manufacturing method described above, based on Figures 6 and 7. 【0040】 Figure 8 shows the X-ray diffraction (XRD) measurement results of the first metal oxide nanoparticles 20 manufactured by the manufacturing methods shown in Figures 6 and 7. Figure 9 shows the particle size distribution of the first metal oxide nanoparticles 20 manufactured by the manufacturing methods shown in Figures 6 and 7. Figure 10 is a comparison of the element characteristics of a Hole Only Device (HOD) equipped with a hole injection layer 3HI containing the first metal oxide nanoparticles 20 manufactured by the manufacturing methods shown in Figures 6 and 7, and the element characteristics of a Hole Only Device (HOD) equipped with a hole injection layer containing nickel oxide nanoparticles, which is a comparative example. Figure 11 is a comparison of the transmittance of the hole injection layer 3HI containing the first metal oxide nanoparticles 20 manufactured by the manufacturing methods shown in Figures 6 and 7, and the transmittance of the hole injection layer containing nickel oxide nanoparticles, which is a comparative example. Figure 12 is a relationship between the current density and external quantum efficiency (EQE) of the light-emitting element 10 shown in Figure 2 and the light-emitting element 100 equipped with a hole injection layer containing nickel oxide nanoparticles, which is a comparative example. 【0041】 In the X-ray diffraction (XRD) measurement of the first metal oxide nanoparticle 20 shown in Figure 8, the first metal oxide nanoparticle 20 is defined as FeＸ Ni （１－Ｘ） Nanoparticles composed of a compound represented by O (Fe is iron, Ni is nickel, O is oxygen, and X = 0.05) were used. As shown in Figure 8, Fe Ｘ Ni （１－Ｘ） X-ray diffraction (XRD) measurements of nanoparticles composed of the compound represented by O (Fe is iron, Ni is nickel, O is oxygen, and X = 0.05) were equivalent to those of FeNiO (standard in the figure) in the database, and the average crystallite size was 4.42 nm. 【0042】 In the measurement of the particle size distribution shown in Figure 9, the first metal oxide nanoparticle 20 is Fe Ｘ Ni （１－Ｘ） Nanoparticles composed of a compound represented by O (Fe is iron, Ni is nickel, O is oxygen, and X = 0.05) were used, and the particle size distribution was measured while these nanoparticles were dispersed in water. As shown in Figure 9, the particle size distribution was as follows: the particle size of the first metal oxide nanoparticle 20 at 50% cumulative particle size (D50) was 16.1 nm, the particle size of the first metal oxide nanoparticle 20 at 90% cumulative particle size (D90) was 30.35 nm, and the particle size of the first metal oxide nanoparticle 20 at 95% cumulative particle size (D95) was 43.73 nm. The particle size distributions shown in Figures 9, 18, and 28 were measured using DLS (dynamic light scattering), and were measured using a Nanotrac waveII manufactured by Microtaract. 【0043】 The Hole Only Device (HOD) shown in Figure 10, which includes a hole injection layer 3HI containing first metal oxide nanoparticles 20, comprises an indium tin oxide (ITO) film and the first metal oxide nanoparticles 20, Fe Ｘ Ni （１－Ｘ）A hole injection layer 3HI with a thickness of 50 nm to 60 nm, composed of nanoparticles of a compound represented by O (Fe is iron, Ni is nickel, O is oxygen, and X = 0.05), a light-emitting layer EM containing quantum dots, and an Ag film were laminated in this order. On the other hand, the comparative example shown in Figure 10, a Hole Only Device (HOD) equipped with a hole injection layer containing nickel oxide nanoparticles, was manufactured to have the same configuration as the Hole Only Device (HOD) equipped with the hole injection layer 3HI containing the first metal oxide nanoparticles 20 described above, except that it is equipped with a hole injection layer with a thickness of 50 nm to 60 nm, composed of NiO nanoparticles, instead of the hole injection layer 3HI. As shown in Figure 10, the element characteristics of the Hole Only Device (HOD) equipped with a hole injection layer 3HI containing the first metal oxide nanoparticles 20 (shown by a dotted line in the figure) are shown by a solid line in the figure. Compared to the element characteristics of the comparative example Hole Only Device (HOD) equipped with a hole injection layer containing nickel oxide nanoparticles (shown by a solid line in the figure), the Hole Only Device (HOD) achieves a higher current density at a lower voltage. This indicates that the hole injection capability and hole transport capability of the hole injection layer 3HI containing the first metal oxide nanoparticles 20 are significantly improved compared to the hole injection capability and hole transport capability of the comparative example hole injection layer containing nickel oxide nanoparticles. 【0044】 As shown in Figure 11, the first metal oxide nanoparticle 20 is Fe Ｘ Ni （１－Ｘ） The transmittance in the visible light region of a hole injection layer 3HI with a thickness of 50 nm to 60 nm, composed of nanoparticles of a compound represented by O (Fe is iron, Ni is nickel, O is oxygen, and X = 0.05), is significantly improved compared to the transmittance in the visible light region of a hole injection layer with a thickness of 50 nm to 60 nm, which is a comparative example composed of NiO nanoparticles. Therefore, in a light-emitting element equipped with a hole injection layer 3HI containing the first metal oxide nanoparticles 20, the light extraction efficiency can be improved. 【0045】The light-emitting element 10 shown in Figure 2, which includes a hole injection layer 3HI containing the first metal oxide nanoparticles 20 shown in Figure 12, realizes a bottom emission type light-emitting element, and has an indium tin oxide (ITO) film as the anode 2 and the first metal oxide nanoparticles 20 Fe Ｘ Ni （１－Ｘ） The device was manufactured by stacking the following in this order: a hole injection layer 3HI with a thickness of 50 nm or more and 60 nm or less, composed of nanoparticles made of a compound represented by O (Fe is iron, Ni is nickel, O is oxygen, and X = 0.05); a hole transport layer 3HT composed of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB); an emissive layer EM containing quantum dots; an electronic functional layer 4 composed of ZnO nanoparticles; and an Ag film as a cathode 5. On the other hand, the comparative example shown in Figure 12, a bottom-emission type light-emitting element 100 equipped with a hole injection layer containing nickel oxide nanoparticles, was manufactured to have the same configuration as the light-emitting element 10 shown in Figure 2, which is equipped with a hole injection layer 3HI containing the first metal oxide nanoparticles 20 described above, except that instead of the hole injection layer 3HI, it is equipped with a hole injection layer made of NiO nanoparticles with a film thickness of 50 nm or more and 60 nm or less. As shown in Figure 12, it can be confirmed that at the same current density, the external quantum efficiency (EQE) of the light-emitting element 10 is higher than the external quantum efficiency (EQE) of the comparative example light-emitting element 100. 【0046】As described above, the first metal oxide nanoparticles 20 produced by the method for manufacturing metal oxide nanoparticles described above, based on Figures 6 and 7, can achieve good reliability, good hole injection characteristics, and good hole transport characteristics. Furthermore, when a hole functional layer 3 containing the first metal oxide nanoparticles 20 is provided, a light-emitting element 10 with high external quantum efficiency (EQE) can be realized, and a display device 1 equipped with a light-emitting element 10 with high external quantum efficiency (EQE) can be realized. Moreover, according to the method for manufacturing a light-emitting element 10 that includes a hole functional layer formation step of forming a hole functional layer 3 containing the first metal oxide nanoparticles 20 produced by the method for manufacturing metal oxide nanoparticles described above, based on Figures 6 and 7, a light-emitting element 10 with high external quantum efficiency (EQE) can be realized. Furthermore, the first metal oxide nanoparticles 20 are Fe Ｘ Ni （１－Ｘ） In the case of a light-emitting element equipped with a hole-functional layer 3 containing a film composed of nanoparticles made of a compound represented by O (Fe is iron, Ni is nickel, O is oxygen, and X is between 0.001 and 0.2), the light extraction efficiency can be improved. 【0047】 [Embodiment 2] The light-emitting element 11 of Embodiment 2 differs from the light-emitting element 10 of Embodiment 1, which has the electronic functional layer 4 described above, in that it has an electronic functional layer 4a containing a second metal oxide nanoparticle, which will be described later. 【0048】 Figure 13 is a cross-sectional view showing a schematic configuration of a light-emitting element 11 of Embodiment 2, which comprises a hole functional layer 3 containing first metal oxide nanoparticles 20 and an electronic functional layer 4a containing second metal oxide nanoparticles. 【0049】As shown in Figure 13, the light-emitting element 11 includes an anode 2, a cathode 5, a light-emitting layer EM provided between the anode 2 and the cathode 5, a hole functional layer 3 provided between the anode 2 and the light-emitting layer EM, and an electronic functional layer 4a provided between the cathode 5 and the light-emitting layer EM. The hole functional layer 3 includes the first metal oxide nanoparticles 20 described in Embodiment 1, which are composed of a plurality of Ni atoms, a plurality of oxygen atoms, and a plurality of Fe atoms in a number less than the number of Ni atoms. The electronic functional layer 4a includes second metal oxide nanoparticles which include a first metal element and a second metal element different from the first metal element. 【0050】 The first metal oxide nanoparticles 20 contained in the hole functional layer 3 provided in the light-emitting element 11 are Fe Ｘ Ni （１－Ｘ） It is preferable that the compound is composed of O (where Fe is the element iron, Ni is the element nickel, O is the element oxygen, and X is between 0.001 and 0.2). 【0051】 The hole functional layer 3 provided in the light-emitting element 11 preferably includes a hole injection layer 3HI containing first metal oxide nanoparticles 20 and a hole transport layer 3HT provided between the hole injection layer 3HI and the light-emitting layer EM, as shown in Figure 3. 【0052】 In this embodiment, the case in which the electronic functional layer 4a functions as an electron transport layer (ETL), an electron injection layer (EIL), and a hole blocking layer (HBL) in a single layer is described as an example, but it is not limited to this. For example, the electronic functional layer 4a may function as an electron transport layer (ETL) and a hole blocking layer (HBL), or the electronic functional layer 4a may function only as an electron injection layer (EIL). As described above, in this embodiment, since the electronic functional layer 4a functions as an electron transport layer (ETL), an electron injection layer (EIL), and a hole blocking layer (HBL) in a single layer, in the light-emitting element 11 shown in Figure 13, the electronic functional layer 4a is provided so as to be in contact with both the cathode 5 and the light-emitting layer EM. 【0053】The electronic functional layer 4a contains second metal oxide nanoparticles comprising a first metal element and a second metal element different from the first metal element. The second metal oxide nanoparticles containing the first metal element and the second metal element contained in the electronic functional layer 4a are second metal oxide nanoparticles manufactured using, for example, a reaction apparatus 30 as shown in Figure 14, as described later, and therefore have small particle size and particle size variation. 【0054】 A portion of a cross-section cut along the thickness direction of the electronic functional layer 4a contains 10 × N (where N is a natural number of 2 or more) second metal oxide nanoparticles containing the first metal element and the second metal element, and when the particle sizes of the 10 × N second metal oxide nanoparticles are arranged in ascending order, the particle size of the 5 × Nth second metal oxide nanoparticle is 3.5 nm or less, and the difference between the particle size of the 9 × Nth second metal oxide nanoparticle and the particle size of the Nth second metal oxide nanoparticle is 3 nm or less. Preferably, the particle size of the 5 × Nth second metal oxide nanoparticle is 3.2 nm or less, and the difference between the particle size of the 9 × Nth second metal oxide nanoparticle and the particle size of the Nth second metal oxide nanoparticle is 2.5 nm or less. More preferably, the particle size of the 5 × Nth second metal oxide nanoparticle is 2.9 nm or less, and the difference between the particle size of the 9 × Nth second metal oxide nanoparticle and the particle size of the Nth second metal oxide nanoparticle is 2 nm or less. The particle size of the 10 × N second metal oxide nanoparticles can be measured, for example, using a scanning transmission electron microscope (STEM). The particle size of the 5 × Nth second metal oxide nanoparticle represents the particle size of the second metal oxide nanoparticle that corresponds to 50% (median) when the particle sizes of the 10 × N second metal oxide nanoparticles are arranged in ascending order. The particle size of the 9 × Nth second metal oxide nanoparticle represents the particle size of the second metal oxide nanoparticle that corresponds to 90% when the particle sizes of the 10 × N second metal oxide nanoparticles are arranged in ascending order. The particle size of the Nth second metal oxide nanoparticle represents the particle size of the second metal oxide nanoparticle that corresponds to 10% when the particle sizes of the 10 × N second metal oxide nanoparticles are arranged in ascending order. 【0055】In this embodiment, the case in which the second metal oxide nanoparticles contained in the electronic functional layer 4a are magnesium zinc oxide nanoparticles, the first metal element contained in the second metal oxide nanoparticles is Zn, and the second metal element is Mg will be described as an example, but the embodiment is not limited to this. For example, the first metal element and the second metal element in the second metal oxide nanoparticles contained in the electronic functional layer 4a may be different elements selected from Zn, Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Cu, Co, Mn, and Hf. 【0056】 The manufacturing method for the light-emitting element 11 shown in Figure 13 includes an electronic functional layer formation step for forming an electronic functional layer 4a, which is performed between an emissive layer formation step for forming an emissive layer EM and a cathode formation step for forming a cathode 5. In the electronic functional layer formation step, an electronic functional layer 4a containing a second metal oxide nanoparticle is formed. The second metal oxide nanoparticle containing the first metal element and the second metal element in the electronic functional layer 4a is, as will be described later, a second metal oxide nanoparticle manufactured using, for example, a reaction apparatus 30 as shown in Figure 14, and therefore has small particle size and particle size variation. 【0057】Figure 14 shows a schematic configuration of a reactor 30 used in the process of producing second metal oxide nanoparticles contained in the electronic functional layer 4a of the light-emitting element 11 shown in Figure 13. Figure 15 shows an example of process conditions in the process of producing second metal oxide nanoparticles using the reactor 30 shown in Figure 14. Figure 16 is a diagram illustrating the process of producing second metal oxide nanoparticles using the reactor 30 shown in Figure 14. Figure 17 is a diagram illustrating the process of recovering second metal oxide nanoparticles after they have been produced using the reactor 30 shown in Figure 14. Figure 18 shows the particle size distribution of second metal oxide nanoparticles produced using the reactor 30 shown in Figure 14. Figure 19 shows the energy levels of the upper valence band (VBM) and lower conduction band (CBM) of an electronic functional layer 4a containing second metal oxide nanoparticles manufactured using the reactor 30 shown in Figure 14, and the energy levels of the upper valence band (VBM) and lower conduction band (CBM) of an electronic functional layer containing second metal oxide nanoparticles manufactured by a comparative example batch method. Figure 20 shows a schematic configuration of another reactor 40 that can be used in the process of manufacturing second metal oxide nanoparticles contained in the electronic functional layer 4a provided in the light-emitting element 11 shown in Figure 13. 【0058】As shown in Figure 14, the reaction apparatus 30 includes a micromixer 35 including a first inlet 1, a second inlet 2, and an outlet, and a first supply unit 31 that supplies a first solution containing a first precursor of second metal oxide nanoparticles containing a first metal element, a second precursor of second 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 inlet 1 and the second inlet 2, in this embodiment, the first inlet 1. The micromixer includes a first inlet 1 and a second inlet 2, and in this embodiment, a second supply unit 32 that supplies a second solution containing a reactant and a second solvent at a second flow rate to the other end, the second inlet 2, a microchannel 36 in which one end is a supply end and the other end is a discharge end, and the fluid discharged from the outlet of the micromixer 35 is supplied from the supply end, and a microreactor 37 that controls the reaction conditions of at least a part of the microchannel 36. In this embodiment, as a method for producing second metal oxide nanoparticles containing the first metal element and the second metal element, for example, a reaction apparatus 30 is used to produce second metal oxide nanoparticles containing the first metal element and the second metal element, but the invention is not limited to this, and for example, a reaction apparatus 40 shown in Figure 20 may be used to produce second metal oxide nanoparticles containing the first metal element and the second metal element. 【0059】As shown in Figure 14, the reaction apparatus 30 further includes a first supply channel 33 connecting the first inlet 1 of the micromixer 35 and the outlet of the first supply unit 31, a second supply channel 34 connecting the second inlet 2 of the micromixer 35 and the outlet of the second supply unit 32, and a recovery unit 38 for recovering the fluid discharged from the outlet end of the microchannel 36. The first supply channel 33 and the second supply channel 34 are the same supply channel with the same channel diameter and channel length. Although not shown, if the outlet of the first supply unit 31 is directly connected to the first inlet 1 of the micromixer 35, the reaction apparatus 30 does not need to have the first supply channel 33, and if the outlet of the second supply unit 32 is directly connected to the second inlet 2 of the micromixer 35, the reaction apparatus 30 does not need to have the second supply channel 34. Furthermore, the reaction apparatus 30 does not necessarily have to be equipped with a recovery unit 38; in this case, the user of the reaction apparatus 30 may prepare the recovery unit 38. The microreactor 37, which controls the reaction conditions of at least a portion of the microchannels 36, for example controls a portion of the microchannels 36 to the optimal temperature for the reaction of the fluid flowing through the microchannels 36. 【0060】 In this embodiment, as an example, in the reaction apparatus 30 shown in Figure 14, the first metal element in the first precursor of the second metal oxide nanoparticles containing the first metal element and the second precursor of the second metal oxide nanoparticles containing the second metal element in the first solution is Zn, the second metal element is Mg, and the second metal oxide nanoparticles are magnesium zinc oxide nanoparticles. However, the embodiment 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. 【0061】As shown in Figure 14, the reaction apparatus 30 is equipped with a T-shaped micromixer 35 in a plan view, and a special flow microreactor type reaction field utilizing turbulence can be realized by the T-shaped micromixer 35 in a plan view. In this embodiment, the case in which the reaction apparatus 30 is equipped with a T-shaped micromixer 35 in a plan view is described as an example, but it is not limited to this, and the reaction apparatus 30 may be equipped with a V-shaped micromixer in a plan view, for example, and a special flow microreactor type reaction field utilizing turbulence can also be realized by the V-shaped micromixer in a plan view. 【0062】 In this embodiment, magnesium zinc oxide nanoparticles are produced using the reaction apparatus 30. As shown in Figure 14, the first solution supplied from the first supply unit 31 to the first supply port Inlet 1 of the micromixer 35 via the first supply channel 33 contains zinc acetate as the first precursor of the second metal oxide nanoparticles containing the first metal element, magnesium acetate as the second precursor of the second metal oxide nanoparticles containing the second metal element, and dimethyl sulfoxide (DMSO) as the first solvent. This is described as an example, but is not limited to this. For example, zinc acetate dihydrate may be used as the first precursor of the second metal oxide nanoparticles containing the first metal element, or magnesium acetate tetrahydrate may be used as the second precursor of the second metal oxide nanoparticles containing the second metal element. A polar solvent other than dimethyl sulfoxide (DMSO) may also be used as the first solvent. Furthermore, the second solution supplied from the second supply unit 32 to the second supply port Inlet 2 of the micromixer 35 via the second supply channel 34 contains tetramethylammonium hydroxide (for example, TMAH·5H), which is an alkaline reactant, as a reactant. ２We will explain using the example of a case in which the solution contains (O) and ethanol, an alcohol-based solvent, as the second solvent, but it is not limited to this. As for the reactant included in the second solution, if it is an alkaline reactant, tetramethylammonium hydroxide (for example, TMAH·5H) is used. ２ Other solvents can also be used, and as the second solvent in the second solution, any alcohol-based solvent other than ethanol can be used. In the micromixer 35, for example, ZnOH and MgOH are generated, and in a part of the microchannel 36 where the reaction conditions are controlled by the microreactor 37, a dehydration reaction between ZnOH and MgOH occurs. 【0063】 As shown in Figure 15, 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 was 15:85. The amounts of zinc acetate and magnesium acetate, as well as the amount of dimethyl sulfoxide (DMSO), the first solvent, were also adjusted so that the concentration of the first solution was 0.1 M. Furthermore, 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 O) and the second solvent, ethanol, were adjusted. Furthermore, as shown in Figure 15, the amount of Mg in the first solution ２＋ and Zn ２＋ And, tetramethylammonium hydroxide (e.g., TMAH·5H) in the second solution. ２The molar ratio of O) was adjusted to 1:1.3. Considering the amount of magnesium oxide zinc nanoparticles to be obtained as the final product, the flow rate of the first solution and the flow rate of the second solution can be appropriately determined. In this embodiment, the flow rate of the first solution was set to 12.6 ml and the flow rate of the second solution was set to 6.552 ml. In order to make the supply time of the first solution from the first supply unit 31 and the supply time of the second solution from the second supply unit 32 both 84 minutes, the first supply unit 31 supplied the first solution at a first flow rate, for example, 9 ml / h, and the second supply unit 32 supplied the second solution at a second flow rate, for example, 4.68 ml / h. In this embodiment, the first solution contains 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 oxide zinc nanoparticles, for example, Zn ０．８５ Mg ０．１５ We were able to obtain O. 【0064】 As shown in Figure 16, the method for producing the second metal oxide nanoparticles is as described above: Step S31 of preparing a first solution of predetermined concentration A, 0.1 M in this embodiment, and a second solution of predetermined concentration B, 0.25 M in this embodiment; Step S32 of supplying the first solution to the first inlet 1 of the micromixer 35 at a predetermined flow rate C, 9 ml / h in this embodiment, and supplying the second solution to the second inlet 2 of the micromixer 35 at a predetermined flow rate D, 4.68 ml / h in this embodiment; and Ultra-nano-sized magnesium-zinc oxide nanoparticles (e.g., Zn) generated from the discharge end of the microchannel 36. ０．８５ Mg ０．１５ The process includes step S33 of recovering the dispersion of O). 【0065】As shown in Figure 17, it is preferable that the method for producing second metal oxide nanoparticles further includes the steps of: transferring the dispersion of magnesium-zinc nanoparticles recovered in step S33 shown in Figure 16 to a centrifuge tube and adding a poor solvent (e.g., ethyl acetate) to precipitate ultra-nano-sized magnesium-zinc nanoparticles in step S41; separating the solid and solution by centrifugation in step S42; and removing the supernatant (e.g., a mixture of the reactants dimethyl sulfoxide (DMSO) and ethanol (EtOH)) in step S43. The method for producing second metal oxide nanoparticles includes the step of recovering second metal oxide nanoparticles shown in Figure 17, thereby removing impurities and other contaminants from magnesium-zinc nanoparticles (e.g., Zn ０．８５ Mg ０．１５ A dispersion of O) can be obtained. Furthermore, in the method for producing the second metal oxide nanoparticles, in step S43 shown in Figure 17, the solution containing the supernatant is removed, and the solid content is redispersed in a solvent (e.g., ethanol or butanol) to obtain magnesium oxide zinc nanoparticles (e.g., Zn ０．８５ Mg ０．１５ The method may further include the step of preparing a redispersion of O). In this method, magnesium oxide zinc nanoparticles (e.g., Zn) are redispersed in a specific solvent of choice. ０．８５ Mg ０．１５ A redispersion of O) can be obtained. Furthermore, in the process of preparing the redispersion described above, an organic ligand such as monoethanolamine (MEA) may be added to further improve dispersibility. 【0066】 The second metal oxide nanoparticles produced using the reaction apparatus 30 shown in Figure 14, i.e., the magnesium zinc oxide nanoparticles (for example, Zn) described above. ０．８５ Mg ０．１５ Figure 18 shows the results of measuring the particle size distribution using the redispersion solution of (O). Note that the redispersion solution here is magnesium oxide zinc nanoparticles (e.g., Zn ０．８５ Mg ０．１５ This is a solution obtained by dispersing O) in ethanol, which is the solvent. 【0067】 As shown in Figure 18, magnesium oxide zinc nanoparticles (e.g., Zn ０．８５ Mg０．１５ In the redispersion of O), the particle size of the second metal oxide nanoparticles, which represent 50% cumulative particle size (D50), was 2.88 nm, and was 2.9 nm or less. Also, magnesium oxide zinc nanoparticles (e.g., Zn ０．８５ Mg ０．１５ In the redispersion of O), the difference between the particle size of the second metal oxide nanoparticles at 90% cumulative particle size (D90) and the particle size of the second metal oxide nanoparticles at 10% cumulative particle size (D10) was 1.89 nm, which is less than or equal to 2 nm. 【0068】 In this embodiment, magnesium zinc oxide nanoparticles are produced using the reaction apparatus 30 under the conditions shown in Figure 15. As described above, the particle size of the second metal oxide nanoparticle with a particle size-based cumulative total of 50% (D50) was 2.88 nm, and the difference between the particle size of the second metal oxide nanoparticle with a particle size-based cumulative total of 90% (D90) and the particle size of the second metal oxide nanoparticle with a particle size-based cumulative total of 10% (D10) was 1.89 nm, but this is not limited to this. For example, by adjusting the first and second flow rates described above so that the supply time of the first solution from the first supply unit 31 and the supply time of the second solution from the second supply unit 32 are both longer than 84 minutes, for example, to 100 to 120 minutes, magnesium zinc oxide nanoparticles can be obtained in which the particle size of the second metal oxide nanoparticles with a particle size-based cumulative 50% (D50) is 3.5 nm or less, and the difference between the particle size of the second metal oxide nanoparticles with a particle size-based cumulative 90% (D90) and the particle size of the second metal oxide nanoparticles with a particle size-based cumulative 10% (D10) is 3 nm or less. 【0069】 Although not shown in the figure, magnesium oxide zinc nanoparticles (for example, Zn) recovered in step S33 shown in Figure 16. ０．８５ Mg ０．１５ The particle size of the second metal oxide nanoparticles, which is the cumulative 50% (D50) of the particle size in the dispersion of O), was also 2.9 nm or less. Furthermore, the magnesium oxide zinc nanoparticles (e.g., Zn) recovered in step S33 shown in Figure 16 ０．８５ Mg ０．１５The difference between the particle size of the second metal oxide nanoparticles, which represent 90% of the particle size based on cumulative particle size (D90), and the particle size of the metal oxide nanoparticles, which represent 10% of the particle size based on cumulative particle size (D10), in dispersion O) was also 2 nm or less. 【0070】 As described above, the magnesium zinc oxide nanoparticles produced using the reaction apparatus 30 have small particle size and small particle size variation. It is believed that the ability to produce magnesium zinc oxide nanoparticles with small particle size and small particle size variation is due to the fact that the first solution and the second solution react while constantly flowing, generating magnesium zinc oxide nanoparticles, and that the first solution contains a first precursor of a second metal oxide nanoparticle containing a first metal element and a second precursor of a second metal oxide nanoparticle containing a second metal element. 【0071】 In this embodiment, magnesium oxide zinc nanoparticles were produced using the reaction apparatus 30 shown in Figure 14, but the invention is not limited to this, and magnesium oxide zinc nanoparticles may also be produced using the reaction apparatus 40 shown in Figure 20. The reaction apparatus 40 shown in Figure 20 differs from the reaction apparatus 30 shown in Figure 14 in that, in plan view, it is equipped with a linear micromixer 45. By providing the linear micromixer 45 in the reaction apparatus 40 in plan view, a special flow microreactor type reaction field can be realized in which both the first solution and the second solution flow in parallel. 【0072】 Although not shown in the diagram, magnesium oxide zinc nanoparticles (e.g., Zn) are produced by a batch method. ０．８５ Mg ０．１５ In the process of producing O), 12.6 ml of the first solution was placed in the reaction apparatus beforehand, and while stirring, 6.552 ml of the second solution was supplied at a flow rate of, for example, 4.68 ml / h for 84 minutes. After that, stirring was continued for 90 minutes or more. Magnesium oxide zinc nanoparticles (e.g., Zn) are produced by this batch method. ０．８５ Mg ０．１５In the manufacturing process of (O), the reaction proceeds from the moment the above-described second solution is supplied. However, immediately after the last second solution is supplied, it is necessary to continue stirring for a while to ensure the reaction time of the last-supplied second solution. Even if stirring is continued in this way, variation between the reaction time of the second solution supplied at the beginning and the reaction time of the second solution supplied at the end is inevitable, and it is unavoidable that the particle size variation of magnesium zinc oxide nanoparticles (for example, Zn ０．８５ Mg ０．１５ O) produced by the batch method becomes large. The particle size distribution of magnesium zinc oxide nanoparticles (for example, Zn ０．８５ Mg ０．１５ O) produced by the batch method is such that the particle size of the metal oxide nanoparticles at a cumulative 50% by particle size standard (D50) in the dispersion of magnesium zinc oxide nanoparticles (for example, Zn ０．８５ Mg ０．１５ O) was 6.9 nm. In the case of magnesium zinc oxide nanoparticles (for example, Zn ０．８５ Mg ０．１５ O) produced by the batch method, it is considered that the particle size and the variation in particle size become large due to the influence of the above reasons. 【0073】 As shown in FIG. 19, the energy level of the valence band top (VBM) of the electronic functional layer 4a containing magnesium zinc oxide nanoparticles (for example, Zn ０．８５ Mg ０．１５ O) produced using the reaction apparatus 30 shown in FIG. 14 was -7.25 eV, the energy level of the conduction band bottom (CBM) was -3.41 eV, and its band gap was 3.84 eV. On the other hand, the energy level of the valence band top (VBM) of the electronic functional layer of Comparative Example 1 containing magnesium zinc oxide nanoparticles (for example, Zn ０．８５ Mg ０．１５ O) produced by the above-described batch method was -7.24 eV, the energy level of the conduction band bottom (CBM) was -3.48 eV, and its band gap was 3.76 eV. 【0074】On the other hand, as shown in Figure 19, the energy level of the upper valence band (VBM) of the electronic functional layer 4a (-7.25 eV) is not significantly different from the energy level of the upper valence band (VBM) of the electronic functional layer in Comparative Example 1 (-7.24 eV). Therefore, as in this embodiment, when the electronic functional layer 4a functions as an electron transport layer (ETL), electron injection layer (EIL), and hole blocking layer (HBL) in a single layer, a high barrier for hole injection from the light-emitting layer EM to the electronic functional layer 4a can be maintained, making it suitable for use as a hole blocking layer (HBL). 【0075】 The external quantum efficiency (EQE) results for the light-emitting element 11 (Embodiment 2) shown in Figure 13 will be explained later in Embodiment 3, based on Figure 21, along with the external quantum efficiency (EQE) results for the light-emitting element 12 shown in Figure 22. 【0076】 [Embodiment 3] The light-emitting element 12 of Embodiment 3 differs from the light-emitting element 10 of Embodiment 1, which has the electronic functional layer 4 described above, and the light-emitting element 11 of Embodiment 2, which has the electronic functional layer 4a described above, in that it has an electronic functional layer 4b containing a second metal oxide nanoparticle, which will be described later. 【0077】 Figure 22 is a cross-sectional view showing a schematic configuration of a light-emitting element 12 of Embodiment 3, which comprises a hole functional layer 3 containing first metal oxide nanoparticles 20 and an electronic functional layer 4b containing second metal oxide nanoparticles. 【0078】 As shown in Figure 22, the light-emitting element 12 includes an anode 2, a cathode 5, a light-emitting layer EM provided between the anode 2 and the cathode 5, a hole functional layer 3 provided between the anode 2 and the light-emitting layer EM, and an electronic functional layer 4b provided between the cathode 5 and the light-emitting layer EM. The hole functional layer 3 includes the first metal oxide nanoparticles 20 described in Embodiment 1, which are composed of a plurality of Ni atoms, a plurality of oxygen atoms, and a plurality of Fe atoms in a number less than the number of Ni atoms. The electronic functional layer 4b includes second metal oxide nanoparticles containing a first metal element and a second metal element different from the first metal element. 【0079】In this embodiment, the case in which the electronic functional layer 4b functions as an electron transport layer (ETL), an electron injection layer (EIL), and a hole blocking layer (HBL) in a single layer is described as an example, but it is not limited to this, and for example, the electronic functional layer 4b may comprise two or more layers selected from the electron transport layer (ETL), the electron injection layer (EIL), and the hole blocking layer (HBL). In this embodiment, as shown in Figure 22, the electronic functional layer 4b is provided so as to be in contact with both the cathode 5 and the light-emitting layer EM. 【0080】As shown in Figure 22, the electronic functional layer 4b provided between the cathode 5 and the light-emitting layer EM contains a second metal oxide nanoparticle composed of a core containing a first element, which is a first metallic element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf; a second element, which is a nonmetallic element excluding hydrogen, oxygen, and group 18 elements, or a metalloid element; and the second metallic element, zinc, and oxygen. In other words, the second metal oxide nanoparticle contained in the electronic functional layer 4b is a core-structure nanoparticle composed only of a core containing the first element, the second element, zinc, and oxygen. The core-structure nanoparticle differs from a core / shell-structure nanoparticle, which has a core and a shell provided outside the core with a different composition, in that it does not have a shell provided with a different composition from the core. Note that metalloid elements refer to, for example, B, Si, Ge, As, Sb, and Te. Furthermore, the second metal oxide nanoparticles contained in the electronic functional layer 4b are nanoparticles with a core structure composed only of a core containing the first element, the second element, zinc, and oxygen, formed by a competitive reaction between a molecule containing the first element, a molecule containing the second element, and a molecule containing zinc. Therefore, the particle size is inherently small, and the particle size and particle size variation are small. Consequently, an electronic functional layer 4b containing multiple second metal oxide nanoparticles with small particle size and particle size variation, or an electronic functional layer 4b composed of multiple second metal oxide nanoparticles with small particle size and particle size variation, can achieve high density and high resistance to the cathode 5 deposition process, such as a vapor deposition process or a sputtering process, in the cathode 5 formation process, which is a post-process of the electronic functional layer 4b formation process. As a result, the light-emitting element 12 equipped with the electronic functional layer 4b can achieve high external quantum efficiency (EQE). 【0081】 Furthermore, the fact that the second metal oxide nanoparticles contained in the electronic functional layer 4b are nanoparticles with a core structure composed only of a single-composition core can be confirmed, for example, using time-of-flight secondary ion mass spectrometry (TOF-SIMS), or by performing elemental analysis while gradually etching the second metal oxide nanoparticles from the outside. 【0082】 The second element, which is selected from the nonmetallic elements excluding hydrogen, oxygen, and the Group 18 elements mentioned above, or is a metalloid element, 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. 【0083】 In a unit volume of the second metal oxide nanoparticles contained in the electronic functional layer 4b, it is preferable that the amount of oxygen is greater than the amount of the first element, the amount of the second element, and the amount of zinc, and that the amount of the second element and the amount of zinc are each greater than the amount of the first element. 【0084】 In this embodiment, we will describe, as an example, the case in which the second metal oxide nanoparticles contained in the electronic functional layer 4b are nanoparticles with a core structure composed only of a single-composition core made up of Mg as the first element, Si as the second element, zinc, and oxygen. The second metal oxide nanoparticles contained in the electronic functional layer 4b in this embodiment include Zn-O bonds, Mg-O bonds, and Si-O bonds. 【0085】 A portion of a cross-section cut along the thickness direction of the electronic functional layer 4b contains 10 × N (where N is a natural number of 2 or more) second metal oxide nanoparticles, each containing Mg as the first element, Si as the second element, zinc, and oxygen. When the particle sizes of the 10 × N second metal oxide nanoparticles are arranged in ascending order, it is preferable that the particle size of the 5 × Nth second metal oxide nanoparticle is 1.8 nm or less, and the difference between the particle size of the 9 × Nth second metal oxide nanoparticle and the particle size of the Nth second metal oxide nanoparticle is 2.1 nm or less. 【0086】The manufacturing method for the light-emitting element 12 shown in Figure 22 includes an electronic functional layer formation step for forming an electronic functional layer 4b, which is performed between an emissive layer formation step for forming an emissive layer EM and a cathode formation step for forming a cathode 5. In the electronic functional layer formation step, an electronic functional layer 4b containing second metal oxide nanoparticles is formed. The second metal oxide nanoparticles containing the first metal element and the second metal element in the electronic functional layer 4b are second metal oxide nanoparticles manufactured using, for example, a reaction apparatus 50 as shown in Figure 23, as will be described later, and therefore have small particle size and particle size variation. 【0087】 Figure 23 shows a schematic configuration of a reactor 50 used in the process of producing second metal oxide nanoparticles contained in the electronic functional layer 4b of the light-emitting element 12 shown in Figure 22. Figure 24 shows an example of process conditions in the process of producing second metal oxide nanoparticles using the reactor 50 shown in Figure 23. Figure 25 is a diagram illustrating the process of producing second metal oxide nanoparticles using the reactor 50 shown in Figure 23. Figure 26 is a diagram illustrating the recovery process of second metal oxide nanoparticles performed after producing second metal oxide nanoparticles using the reactor 50 shown in Figure 23. Figure 27 shows the FT-IR results of second metal oxide nanoparticles contained in the electronic functional layer 4b of the light-emitting element 12 shown in Figure 22. Figure 28 shows the particle size distribution of second metal oxide nanoparticles contained in the electronic functional layer 4b of the light-emitting element 12 shown in Figure 22. 【0088】 A second metal oxide nanoparticle having a core structure composed only of a core containing a first element, which is a first metallic 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 a nonmetallic element excluding hydrogen, oxygen, and group 18 elements, or a metalloid element; and the second metallic element, zinc, and oxygen, can be manufactured, for example, using a reaction apparatus including a micromixer, microchannels, and a microreactor. 【0089】The reaction apparatus includes a micromixer that mixes and discharges a reactant, a first precursor of second metal oxide nanoparticles containing a first element which is a first metal element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, a second precursor of second metal oxide nanoparticles containing a second element which is a nonmetal element selected from elements excluding hydrogen, oxygen, and group 18 elements, or a metalloid element, a third precursor of second metal oxide nanoparticles containing a zinc element which is the second metal element, and a reactant, supplied from the outside; a microchannel, one end of which is a supply end and the other end of which is a discharge end, and the fluid discharged from the micromixer is supplied from the supply end; and a microreactor that controls the reaction conditions of at least a portion of the microchannel. 【0090】 In this embodiment, as an example, we will describe the production of metal oxide nanoparticles with a core structure consisting only of a core containing a first element, which is a first metallic element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf; a second element, which is a nonmetallic element excluding hydrogen, oxygen, and group 18 elements, or a metalloid element; and the second metallic element, zinc, and oxygen. However, we are not limited to this example. 【0091】As shown in Figure 23, the reaction apparatus 50 includes a micromixer comprising a first micromixer 56 including a first inlet 1, a second inlet 2, and a first outlet 1, and a second micromixer 59 including a third inlet 3, a fourth inlet 4, and a second outlet 2. Fluid discharged from the first outlet 1 is supplied from the third inlet 3, and fluid discharged from the second outlet 2 is supplied from the supply end of the microchannel 60. Furthermore, the reaction apparatus 50 includes a first supply unit 51 that supplies a first solution containing a first precursor of second 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 second metal oxide nanoparticles containing a zinc element, and a first solvent at a first flow rate to one of the first supply ports Inlet 1, the second supply port Inlet 2, and the fourth supply port Inlet 4. In one of the other inlets 4, there is a second supply unit 52 that supplies a second solution containing the reactant and a second solvent at a second flow rate, and in yet another one of the first inlet 1, second inlet 2, and fourth inlet 4, there is a third supply unit 53 that supplies a third solution containing a second precursor of a second metal oxide nanoparticle, which is an element selected from nonmetallic elements excluding hydrogen, oxygen, and group 18 elements, or a metalloid element, and a third solvent at a third flow rate. As shown in Figure 23, the reaction apparatus 50 includes a microchannel 60 in which one end is a supply end and the other end is a discharge end, and the fluid discharged from the second discharge outlet 2 of the second micromixer 59 is supplied from the supply end, and a microreactor 61 that controls the reaction conditions of at least a portion of the microchannel 60. 【0092】A method for producing second 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 selected from nonmetallic elements excluding hydrogen, oxygen, and group 18 elements, or a metalloid element, zinc, and oxygen, using the reaction apparatus 50 shown in Figure 23, wherein the first precursor of the second metal oxide nanoparticles containing the first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf is, for example, magnesium acetate, and the third precursor of the second metal oxide nanoparticles containing zinc is, for example, zinc acetate. A first solution containing an acetate and a polar solvent, such as dimethyl sulfoxide (DMSO), is supplied from the first supply unit 51 to the first supply port Inlet 1 at a first flow rate, and a reactant is added, for example, an alkaline reactant such as tetramethylammonium hydroxide (e.g., TMAH·5H). ２ A second solution containing O) and, as a second solvent, for example, ethanol, which is an alcohol-based solvent, is supplied from the second supply unit 52 to the second supply port Inlet 2 at a second flow rate. A second metal oxide nanoparticle containing a second element selected from nonmetallic elements excluding hydrogen, oxygen, and group 18 elements, or a metalloid element, is used as a second precursor, for example, tetraethoxysilane (TEOS(Tetraethyl)), which is a tetraalkoxysilane. The process includes: a first step of supplying a third solution containing orthosilicate and, for example, ethanol, an alcohol-based solvent, as a third solvent from a third supply unit 53 to a fourth supply port Inlet 4 at a third flow rate; and a second step of recovering a dispersion of second 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 a nonmetallic element excluding hydrogen, oxygen, and group 18 elements, or a metalloid element, zinc, and oxygen. 【0093】As shown in Figure 23, the reaction apparatus 50 further includes a first supply channel 54 connecting the first inlet 1 of the first micromixer 56 to the outlet of the first supply unit 51, a second supply channel 55 connecting the second inlet 2 of the first micromixer 56 to the outlet of the second supply unit 52, a third supply channel 57 connecting the first outlet 1 of the first micromixer 56 to the third inlet 3 of the second micromixer 59, a fourth supply channel 58 connecting the fourth inlet 4 of the second micromixer 59 to the outlet of the third supply unit 53, and a recovery unit 62 for recovering the fluid discharged from the discharge end of the microchannel 60. Preferably, the first supply channel 54 and the second supply channel 55 are the same supply channel with the same channel diameter and channel length, and preferably the third supply channel 57 and the fourth supply channel 58 are the same supply channel with the same channel diameter and channel length. Although not shown in the diagram, if the outlet of the first supply unit 51 is directly connected to the first supply port Inlet 1 of the first micromixer 56, the reaction apparatus 50 does not need to have a first supply channel 54; if the outlet of the second supply unit 52 is directly connected to the second supply port Inlet 2 of the first micromixer 56, the reaction apparatus 50 does not need to have a second supply channel 55; if the outlet of the third supply unit 53 is directly connected to the fourth supply port Inlet 4 of the second micromixer 59, the reaction apparatus 50 does not need to have a fourth supply channel 58; and if the first outlet Outlet 1 of the first micromixer 56 and the third supply port Inlet 3 of the second micromixer 59 are directly connected, the reaction apparatus 50 does not need to have a third supply channel 57. Furthermore, the reaction apparatus 50 does not need to have a recovery unit 62; in this case, the user of the reaction apparatus 50 may prepare the recovery unit 62. Furthermore, the microreactor 61, which controls the reaction conditions of at least a portion of the microchannel 60, for example controls a portion of the microchannel 60 to the optimal temperature for the reaction of the fluid flowing through the microchannel 60.In this embodiment, as described above, Magnesium Acetate is used as the first precursor, Tetraethyl orthosilicate (TEOS) is used as the second precursor, and Zinc Acetate is used as the third precursor. Therefore, in the first micromixer 56, for example, ZnOH and MgOH are generated. In the second micromixer 59, for example, ZnOH, MgOH, and Si(OH). Ｘ (OC ２ H ５ ) ４－Ｘ (X = 0, 1, 2, 3, 4) are generated. In a part of the microchannel 60 where the reaction conditions are controlled by the microreactor 61, ZnOH, MgOH, and Si(OH). Ｘ (OC ２ H ５ ) ４－Ｘ (X = 0, 1, 2, 3, 4) undergo a dehydration reaction with each other competitively as a competing reaction. Therefore, for example, the second metal oxide nanoparticles produced using the reaction apparatus 50 shown in FIG. 23 are second metal oxide nanoparticles having a core structure composed only of a core containing the first element, the second element, the zinc element, and the oxygen element, and do not become nanoparticles having a core / shell structure having a shell provided with a composition different from that of the core on the outside of the core. As described above, since the dehydration reaction mainly occurs in the microchannel 60, the first solution is supplied from the first supply unit 51 at the first flow rate to one of the first supply port Inlet1, the second supply port Inlet2, and the fourth supply port Inlet4, and the second solution is supplied from the second supply unit 52 at the second flow rate to another one of the first supply port Inlet1, the second supply port Inlet2, and the fourth supply port Inlet4, and the third solution is supplied from the third supply unit 53 at the third flow rate to yet another one of the first supply port Inlet1, the second supply port Inlet2, and the fourth supply port Inlet4. 【0094】As shown in Figure 23, the reaction apparatus 50 is equipped with a T-shaped first micromixer 56 and a T-shaped second micromixer 59 in a plan view, and a flow microreactor type special reaction field utilizing turbulence can be realized by the T-shaped first micromixer 56 and the T-shaped second micromixer 59 in a plan view. In this embodiment, the case in which the reaction apparatus 50 is equipped with a T-shaped first micromixer 56 and a T-shaped second micromixer 59 in a plan view is described as an example, but it is not limited to this, and the reaction apparatus 50 may be equipped with, for example, a V-shaped micromixer in a plan view instead of at least one of the T-shaped first micromixer 56 and the T-shaped second micromixer 59, and a flow microreactor type special reaction field utilizing turbulence can also be realized by a V-shaped micromixer in a plan view. Furthermore, the reaction apparatus 50 may also include, for example, a linear micromixer instead of at least one of the T-shaped first micromixer 56 and the T-shaped second micromixer 59. A linear micromixer can realize a special reaction field of the flow microreactor type in which the fluids supplied from the two supply ports flow in parallel. 【0095】 As shown in Figure 24, 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 was 15:85. The amounts of zinc acetate and magnesium acetate, as well as the amount of dimethyl sulfoxide (DMSO), the first solvent, were also adjusted so that the concentration of the first solution was 0.1 M. Furthermore, 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 O) and the second solvent, ethanol, were adjusted. Furthermore, as shown in Figure 24, the amount of Mg in the first solution ２＋ and Zn ２＋And, tetramethylammonium hydroxide (e.g., TMAH·5H) in the second solution. ２ The molar ratio of (O) was adjusted to 1:1.3. In addition, in the third solution described above, the amounts of tetraethoxysilane (TEOS (Tetraethyl orthosilicate)) and the third solvent, ethanol, were adjusted so that the concentration of the third solution was 0.169 M. Considering the amount of the final product, the second metal oxide nanoparticles, the flow volumes of the first solution, the second solution, and the third solution can be appropriately determined. In this embodiment, the flow volume of the first solution was set to 12.6 ml, the flow volume of the second solution to 6.552 ml, and the flow volume of the third solution to 16 ml. In order to make the supply time of the first solution from the first supply unit 51, the supply time of the second solution from the second supply unit 52, and the supply time of the third solution from the third supply unit 53 all 84 minutes, the first supply unit 51 supplied the first solution at a first flow rate, for example, 9 ml / h; the second supply unit 52 supplied the second solution at a second flow rate, for example, 4.68 ml / h; and the third supply unit 53 supplied the third solution at a third flow rate, for example, 11.5 ml / h. 【0096】As shown in Figure 25, the method for producing the second metal oxide nanoparticles includes, as described above, a step S51 of preparing a first solution of predetermined concentration A, 0.1 M in this embodiment, a second solution of predetermined concentration B, 0.25 M in this embodiment, and a third solution of predetermined concentration C, 0.169 M in this embodiment; a step S52 of supplying the first solution to the first inlet 1 of the first micromixer 56 at a predetermined flow rate D, 9 ml / h in this embodiment, the second solution to the second inlet 2 of the first micromixer 56 at a predetermined flow rate E, 4.68 ml / h in this embodiment, the third solution to the fourth inlet 4 of the second micromixer 59 at a predetermined flow rate F, 11.5 ml / h in this embodiment; and a step S53 of recovering a dispersion of ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si generated from the discharge end of the microchannel 60. In step S53, which involves recovering a dispersion of ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si, it is preferable to recover separately the fluid discharged from the discharge end of the microchannel 60 during an initial period and a final period, and to recover only the fluid discharged from the discharge end of the microchannel 60 during intermediate periods other than those mentioned above as a dispersion of ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si. 【0097】As shown in Figure 26, the method for producing the second metal oxide nanoparticles preferably further includes the steps of: transferring the dispersion of ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si recovered in step S53 shown in Figure 25 to a centrifuge tube and adding a poor solvent (e.g., ethyl acetate) to precipitate the ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si in step S61; separating the solids from the solution by centrifugation in step S62; and removing the supernatant (e.g., a mixture of the reactants dimethyl sulfoxide (DMSO) and ethanol (EtOH)) in step S63. By including the second metal oxide nanoparticle recovery step shown in Figure 26, the method for producing the second metal oxide nanoparticles can be obtained from which impurities have been removed, such as the dispersion of ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si. Furthermore, the method for producing the second metal oxide nanoparticles may further include step S64, in which, in step S63 shown in Figure 26, the solution containing the supernatant is removed, and the solid components (ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si) are redispersed in a solvent (e.g., ethanol or butanol) to prepare a redispersion solution of ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si. In this method, a redispersion solution of ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si, redispersed in a desired specific solvent, can be obtained. In addition, in the step of preparing the redispersion solution described above, an organic ligand such as monoethanolamine (MEA) may be further added to further improve dispersibility. 【0098】 As shown in Figure 27, the FT-IR results for ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si in the electronic functional layer 4b of the light-emitting element 12 shown in Figure 22 showed absorption at wavenumbers corresponding to Zn-O bonds, Mg-O bonds, and Si-O bonds, respectively. This confirmed that the ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si contain Zn-O bonds, Mg-O bonds, and Si-O bonds. 【0099】Figure 28 shows the results of measuring the particle size distribution using a redispersion solution of the second metal oxide nanoparticles produced using the reaction apparatus 50 shown in Figure 23, i.e., the ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si as described above. The redispersion solution here is a solution in which ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si are dispersed in ethanol, which is the solvent. 【0100】 As shown in Figure 28, the particle size of the second metal oxide nanoparticles at 50% cumulative particle size (D50) in the redispersion of ultra-nanosized oxide nanoparticles containing Mg, Zn, and Si was 1.76 nm, which is 1.80 nm or less. Furthermore, the difference between the particle size of the second metal oxide nanoparticles at 90% cumulative particle size (D90) and the particle size of the second metal oxide nanoparticles at 10% cumulative particle size (D10) in the redispersion of ultra-nanosized oxide nanoparticles containing Mg, Zn, and Si was 2.05 nm, which is 2.10 nm or less. 【0101】In this embodiment, ultra-nanosized oxide nanoparticles containing Mg, Zn, and Si are produced using the reaction apparatus 50 under the conditions shown in Figure 24. As described above, the particle size of the second metal oxide nanoparticle with a particle size-based cumulative percentage of 50% (D50) was 1.76 nm, and the difference between the particle size of the second metal oxide nanoparticle with a particle size-based cumulative percentage of 90% (D90) and the particle size of the second metal oxide nanoparticle with a particle size-based cumulative percentage of 10% (D10) was 2.05 nm, but this is not limited to this. For example, by adjusting the first, second, and third flow rates described above so that the supply time of the first solution from the first supply unit 51, the supply time of the second solution from the second supply unit 52, and the supply time of the third solution from the third supply unit 53 are all longer or shorter than 84 minutes, the time that the fluid discharged from the second outlet 2 of the second micromixer 59 remains in a part of the microchannel 60 whose reaction conditions are controlled by the microreactor 61 can be adjusted. As a result, ultra-nanosized oxide nanoparticles containing Mg, Zn, and Si can be obtained in which the particle size of the second metal oxide nanoparticles at particle size 50% cumulative (D50) is, for example, 4 nm or less, and the difference between the particle size of the second metal oxide nanoparticles at particle size 90% cumulative (D90) and the particle size of the second metal oxide nanoparticles at particle size 10% cumulative (D10) is, for example, 3 nm or less. 【0102】 Although not shown in the diagram, the particle size of the second metal oxide nanoparticles at 50% cumulative particle size (D50) in the dispersion of ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si recovered in step S53 shown in Figure 25 was also 1.80 nm or less. Furthermore, the difference between the particle size of the second metal oxide nanoparticles at 90% cumulative particle size (D90) and the particle size of the second metal oxide nanoparticles at 10% cumulative particle size (D10) in the dispersion of ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si recovered in step S53 shown in Figure 25 was also 2.10 nm or less. 【0103】As described above, the ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si produced using the reaction apparatus 50 have small particle size and small particle size variation. It is thought that the ability to produce ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si with small particle size and small particle size variation is due to the fact that the first solution, second solution, and third solution react while constantly flowing, generating oxide nanoparticles with an ultra-nano-sized core structure containing Mg, Zn, and Si, and that the competitive reaction between molecules containing Mg, molecules containing Si, and molecules containing Zn also generates oxide nanoparticles with an ultra-nano-sized core structure containing Mg, Zn, and Si. 【0104】 Figure 21 shows the current density (mA / cm²) of the light-emitting elements 10, 11, and 12 of Embodiments 1 to 3. ２ This figure shows the results of the external quantum efficiency (EQE) and the emission factor. The light-emitting element 10 shown in Figure 21 (illustrated in Figures 2 and 3) is a top-emission type light-emitting element, and in order to realize a top-emission type light-emitting element, it has a laminated film of an indium tin oxide (ITO) film as the anode 2, an Ag film and an indium tin oxide (ITO) film, and first metal oxide nanoparticles 20 Fe Ｘ Ni （１－Ｘ） The device has a structure in which a hole injection layer 3HI with a thickness of 50 nm to 60 nm is made up of nanoparticles composed of a compound represented by O (Fe is iron, Ni is nickel, O is oxygen, and X = 0.05), a hole transport layer 3HT made up of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] (TFB) is stacked in this order, an emissive layer EM containing quantum dots, an electronic functional layer 4 made up of ZnO nanoparticles, and an indium tin oxide (ITO) film as the cathode 5. On the other hand, the light-emitting element 11 shown in Figure 21 (illustrated in Figure 13) has a structure in which magnesium oxide zinc nanoparticles (for example, Zn) are used instead of the electronic functional layer 4 made up of ZnO nanoparticles. ０．８５ Mg ０．１５Except for having an electronic functional layer 4a composed of (O), it has the same configuration as the light-emitting element 10 described above. Also, the light-emitting element 12 shown in Figure 21 (illustrated in Figure 22) has an electronic functional layer 4 composed of ZnO nanoparticles and magnesium oxide zinc nanoparticles (for example, Zn ０．８５ Mg ０．１５ The configuration is the same as that of the light-emitting element 10 and 11, except that instead of the electronic functional layer 4a composed of O), it has an electronic functional layer 4b composed of ultra-nano-sized oxide nanoparticles containing Mg, Zn, and Si. As shown in Figure 21, 10 mA / cm ２ At the following current densities, it can be confirmed that the external quantum efficiency (EQE) of each of the light-emitting elements 11 and 12 is higher than that of the light-emitting element 10. 【0105】 [Additional Notes] This disclosure is not limited to the embodiments described above, 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 this disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. 【0106】 This disclosure can be used in light-emitting devices, display devices, methods for manufacturing light-emitting devices, and methods for manufacturing metal oxide nanoparticles. 【0107】1 Display device 2 Anode 3 Hole functional layer 3HT Hole transport layer 3HI Hole injection layer 4 Electronic functional layer 4a, 4b Electronic functional layer containing second metal oxide nanoparticles 5 Cathode 10, 11, 12 Light-emitting element 20 First metal oxide nanoparticles 30, 40, 50 Reactor 31, 51 First supply unit 32, 52 Second supply unit 33, 54 First supply channel 34, 55 Second supply channel 35, 45 Micromixer 36, 60 Microchannel 37, 61 Microreactor 38, 62 Recovery unit 53 Third supply unit 56 First micromixer 57 Third supply channel 58 Fourth supply channel 59 Second micromixer Inlet 1 First supply port Inlet 2 Second supply port Inlet 3 Third supply port Inlet 3 Third supply port Outlet Outlet 1: First Outlet 2: Second Outlet EM: Emitting Layer PIX: Pixel RSP: Red Subpixel GSP: Green Subpixel BSP: Blue Subpixel DA: Display Area NDA: Border Area

Claims

1. A method for producing metal oxide nanoparticles, comprising the steps of: preparing a mixed solution of a first precursor containing Ni atoms, a second precursor containing Fe atoms, and a solvent; adjusting the pH of the mixed solution to obtain a hydroxide intermediate containing the Ni atoms and the Fe atoms; removing by-products from the hydroxide intermediate; drying the hydroxide intermediate from which the by-products have been removed; pulverizing the dried hydroxide intermediate; and heat-treating the fine particles of the pulverized hydroxide intermediate.

2. The method for producing metal oxide nanoparticles according to claim 1, wherein the first precursor is nickel nitrate hexahydrate, the second precursor is iron nitrate nonahydrate, and the solvent is water.

3. The method for producing metal oxide nanoparticles according to claim 1 or 2, wherein in the step of obtaining the hydroxide intermediate, the pH is adjusted to 9 or higher and 12 or lower.

4. The method for producing metal oxide nanoparticles according to any one of claims 1 to 3, wherein the heat treatment step is performed at a temperature of 230°C or higher and 300°C or lower.

5. The method for producing metal oxide nanoparticles according to any one of claims 1 to 4, wherein in the step of drying the hydroxide intermediate, the hydroxide intermediate is dried at a temperature of 20°C or higher and 80°C or freeze-dried at a temperature of less than 0°C.

6. A method for manufacturing an light-emitting element, comprising: an anode formation step for forming an anode; a cathode formation step for forming a cathode; an emissive layer formation step performed between the anode formation step and the cathode formation step for forming an emissive layer; and a hole functional layer formation step performed between the emissive layer formation step and the anode formation step for forming a hole functional layer, wherein in the hole functional layer formation step, the hole functional layer is formed, the hole functional layer containing first metal oxide nanoparticles manufactured by the method for manufacturing metal oxide nanoparticles described in any one of claims 1 to 5.

7. The process includes an electronic functional layer formation step performed between the light-emitting layer formation step and the cathode formation step, wherein the electronic functional layer is formed in the electronic functional layer formation step, and the electronic functional layer includes a second metal oxide nanoparticle, the second metal oxide nanoparticles include 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 first precursor of the second metal oxide nanoparticles containing a first metal element, a second precursor of the second 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, and a microchannel in which one end is a supply end and the other end is an outlet end, and the fluid discharged from the outlet of the micromixer is supplied from the supply end, The method for manufacturing a light-emitting element according to claim 6, wherein the metal oxide nanoparticles are produced using a reaction apparatus that includes a microreactor for controlling the reaction conditions of at least a portion of the microchannels, and the nanoparticles contain the first metal element and the second metal element.

8. The process includes an electronic functional layer formation step performed between the light-emitting layer formation step and the cathode formation step, wherein the electronic functional layer is formed in the electronic functional layer formation step, and the electronic functional layer includes a second metal oxide nanoparticle, the second metal oxide nanoparticle is supplied from the outside, a first precursor of the second metal oxide nanoparticle containing a first element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, a second precursor of the second metal oxide nanoparticle containing a second element which is an element selected from nonmetal elements excluding hydrogen, oxygen, and group 18 elements or a metalloid element, a third precursor of the second metal oxide nanoparticle containing zinc, and a reactant, a micromixer that mixes and discharges these, and a microchannel in which one end is a supply end and the other end is a discharge end, the fluid discharged from the micromixer is supplied from the supply end, A method for manufacturing a light-emitting element according to claim 6, wherein the metal oxide nanoparticle is manufactured using a reaction apparatus that includes a microreactor for controlling the reaction conditions of at least a portion of the microchannel, and is composed of a core comprising the first element, the second element, the zinc element, and the oxygen element.

9. A light-emitting element comprising: an anode; a cathode; a light-emitting layer provided between the anode and the cathode; a hole functional layer provided between the anode and the light-emitting layer, containing first metal oxide nanoparticles; and an electronic functional layer provided between the cathode and the light-emitting layer, containing second metal oxide nanoparticles, wherein the first metal oxide nanoparticles are composed of a plurality of Ni atoms, a plurality of oxygen atoms, and a number of Fe atoms less than the number of Ni atoms, and the second metal oxide nanoparticles contain a first metal element and a second metal element different from the first metal element.

10. The first metal oxide nanoparticle is composed of the compound shown in the following (Chemical Formula 1), Fe Ｘ Ni （１－Ｘ） O (Chemical Formula 1) The light-emitting element according to claim 9, wherein in (Chemical Formula 1), Fe is an iron element, Ni is a nickel element, O is an oxygen element, and X is 0.001 or more and 0.2 or less.

11. The light-emitting element according to claim 9 or 10, wherein the hole functional layer comprises a hole injection layer containing the first metal oxide nanoparticles and a hole transport layer provided between the hole injection layer and the light-emitting layer.

12. A light-emitting element according to any one of claims 9 to 11, wherein, in a portion of a cross section cut along the thickness direction of the electronically functional layer containing 10 × N second metal oxide nanoparticles (where N is a natural number of 2 or more), when the particle sizes of the 10 × N second metal oxide nanoparticles are arranged in ascending order, the particle size of the 5 × Nth second metal oxide nanoparticle is 3.5 nm or less, and the difference between the particle size of the 9 × Nth second metal oxide nanoparticle and the particle size of the Nth second metal oxide nanoparticle is 3 nm or less.

13. The light-emitting element according to claim 12, wherein the particle size of the 5th × Nth second metal oxide nanoparticle is 2.9 nm or less, and the difference between the particle size of the 9th × Nth second metal oxide nanoparticle and the particle size of the Nth second metal oxide nanoparticle is 2 nm or less.

14. The light-emitting element according to claim 12 or 13, wherein the first metal element and the second metal element are each different elements selected from Zn, Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Cu, Co, Mn, and Hf.

15. The light-emitting element according to any one of claims 12 to 14, wherein the first metal element is Zn, the second metal element is Mg, and the second metal oxide nanoparticles are magnesium zinc oxide nanoparticles.

16. The light-emitting element according to any one of claims 9 to 11, wherein the second metal oxide nanoparticle is composed of a core, the core comprises a first element which is the first metal element, the second metal element, the second element, and an oxygen element, the first element being any element selected from Mg, Ti, Sn, W, Ta, Ba, Zr, Al, Y, Co, Cu, Mn, and Hf, the second metal element being the zinc element, and the second element being an element selected from nonmetal elements excluding hydrogen, oxygen, and group 18 elements, or a metalloid element.

17. The light-emitting element according to claim 16, wherein the second element is any of B, Si, Ge, As, Sb, Te, C, N, P, and S.

18. The light-emitting element according to claim 16 or 17, wherein, in a unit volume of the second metal oxide nanoparticle, the amount of oxygen is greater than the amount of the first element, the amount of the second element, and the amount of zinc, and the amount of the second element and the amount of zinc are each greater than the amount of the first element.

19. The light-emitting element according to any one of claims 16 to 18, wherein the first element is Mg and the second element is Si.

20. The light-emitting element according to claim 19, wherein the second metal oxide nanoparticle comprises a Zn-O bond, a Mg-O bond, and a Si-O bond.

21. The light-emitting element according to claim 19 or 20, wherein, in a portion of a cross section cut along the thickness direction of the electronically functional layer containing 10 × N second metal oxide nanoparticles (where N is a natural number of 2 or more), when the particle sizes of the 10 × N second metal oxide nanoparticles are arranged in ascending order, the particle size of the 5 × Nth second metal oxide nanoparticle is 1.8 nm or less.

22. The light-emitting element according to claim 21, wherein the difference between the particle size of the 9 × Nth second metal oxide nanoparticle and the particle size of the Nth second metal oxide nanoparticle is 2.1 nm or less.

23. The light-emitting element according to any one of claims 9 to 22, wherein the electronic functional layer is in contact with both the cathode and the light-emitting layer.

24. A display device comprising a light-emitting element according to any one of claims 9 to 23.

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