Surface-coated metal oxide fine particles, metal oxide fine particle dispersion, method for producing surface-coated metal oxide fine particles, method for producing a metal oxide fine particle laminated film

Abstract

The present invention provides surface-coated metal oxide nanoparticles that can be sufficiently dispersed in a non-aqueous solvent. [Solution] Surface-coated metal oxide fine particles, wherein the surface of fine particles made of a metal oxide is coated with a coating compound, characterized in that the ratio A / B of the weight A of the coating compound to the weight B of the metal oxide fine particles is in the range of 0.001 to 0.2. Preferably, the coating compound has one or more functional groups selected from alkyl groups, alkoxy groups, acyl groups, carboxyl groups, phosphoryl groups, sulfo groups, amino groups, and nitro groups.

Description

[Technical Field]

[0001] This invention relates to surface-coated metal oxide fine particles used, for example, when forming conductive films, metal oxide fine particle dispersions, methods for producing surface-coated metal oxide fine particles, and methods for producing metal oxide fine particle laminated films. [Background technology]

[0002] Recently, perovskite solar cells, which use perovskite films, have been proposed as a type of thin-film solar cell. These perovskite solar cells come in both forward and reverse structures. In the reverse structure of a perovskite solar cell, an electron transport layer is formed stacked on top of the perovskite layer.

[0003] Conventionally, in inverted perovskite solar cells, the electron transport layer is often made of organic materials such as PCBM (phenyl C61 methyl butyrate) or C60 deposited on the perovskite layer. However, the aforementioned organic materials used in the electron transport layer are extremely expensive, which significantly impacts the cost of the device. Furthermore, these organic materials have limitations in terms of durability against temperature, humidity, and oxidation, potentially preventing stable long-term use. Therefore, there was a desire to use inorganic materials as electron transport layers, which are considered to be cheaper and more stable than organic materials.

[0004] Inorganic electron transport layers are often formed using n-type oxide semiconductors such as TiO2, SnO2, and ZnO. In dry deposition, the initial cost of manufacturing equipment is very high, making it difficult to implement. Furthermore, as mentioned above, in inverted perovskite solar cells, it is necessary to deposit an electron transport layer on the perovskite layer. However, when attempting to dry deposit the electron transport layer on the perovskite layer, sputter damage can occur to the perovskite layer, impairing its power generation capacity. Additionally, the limited heating temperature can result in a film with low crystallinity, leading to poor electron conductivity and high resistance. For various reasons depending on the deposition method, it has been difficult to produce solar cells with high photoelectric conversion efficiency (PCE) over large areas.

[0005] On the other hand, wet deposition is superior to dry deposition in terms of the cost of introducing manufacturing equipment and the hurdles to scaling up to large areas, making it an excellent method for mass production. However, this requires a dispersion liquid for coating as a material, and inverted perovskite solar cells have only been used on a research scale. This is because, in the case of inverted perovskite solar cells, the electron transport layer material must be coated on the perovskite layer, and if the solvent does not have low corrosiveness (solubility) of the perovskite layer, the properties will be severely degraded.

[0006] In particular, it is known that moisture has a high corrosive effect on the perovskite layer, and even with the selection of an appropriate solvent, performance degrades if moisture is absorbed. Furthermore, tin oxide tends to disperse poorly in non-corrosive solvents, resulting in the inability to form a dense and uniform coating film through aggregation of tin oxide nanoparticles, thus failing to achieve power generation performance. Even when a dispersant is selected to disperse the material in the solvent to resolve this issue, some component of the dispersant impairs the performance, such as being corrosive to the perovskite layer or significantly increasing the film resistance. Therefore, it is believed that no superior non-aqueous dispersion for electron transport material coating has been mass-produced.

[0007] Here, Patent Document 1 discloses the use of a dispersion (Nanograde N-21X, manufactured by Avantama) in which aluminum-doped zinc oxide particles (AZO) are dispersed in isopropyl alcohol (IPA). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2023-036564 [Overview of the project] [Problems that the invention aims to solve]

[0009] Incidentally, conventional metal oxide nanoparticle dispersions are known to disperse metal oxide nanoparticles by using components that are corrosive to the perovskite layer. These metal oxide nanoparticle dispersions were diluted several tens of times before coating to reduce their corrosiveness, and then the coating time was shortened to minimize damage to the perovskite layer and allow for film formation. Such metal oxide fine particle dispersions require rapid film formation and can only be deposited using methods that complete film formation quickly, such as spin coaters. They are not suitable for use in die coaters or other methods that are suitable for coating large areas. Furthermore, because the perovskite layer is dispersed by adding corrosive components (dispersants), it causes degradation of the solar cell performance, making it difficult to achieve high conversion efficiency.

[0010] Furthermore, the isopropyl alcohol (IPA) dispersion of aluminum-doped zinc oxide particles (AZO) described in Patent Document 1 could not contain a large number of particles, making it impossible to efficiently and stably form a conductive film with excellent conductivity. In addition, it is sold as a reagent, making industrial use difficult.

[0011] This invention has been made in view of the circumstances described above, and aims to provide surface-coated metal oxide fine particles that can be sufficiently dispersed in a non-aqueous solvent, a metal oxide fine particle dispersion in which these surface-coated metal oxide fine particles are dispersed, and the above-mentioned method for producing surface-coated metal oxide fine particles and method for producing a metal oxide fine particle laminate film. [Means for solving the problem]

[0012] To solve the above problems, the inventors conducted diligent research and found that, instead of dispersing tin oxide by adding an erosive component (dispersant) to the perovskite layer, it is possible to sufficiently disperse metal oxide nanoparticles in a non-aqueous solvent by chemically treating the surface of the tin oxide nanoparticles. By treating the nanoparticles before dispersion and then proceeding to the dispersion process, the amount of components other than tin oxide can be reduced, resulting in a tin oxide dispersion that is less likely to degrade the properties of solar cells. Furthermore, it was found that the type of solvent in which dispersion can occur can be changed depending on the type of surface treatment.

[0013] The present invention is based on the above-described findings, and the surface-coated metal oxide fine particles of the present invention in aspect 1 are surface-coated metal oxide fine particles in which the surface of the metal oxide fine particles is coated with a coating compound, characterized in that the ratio A / B of the weight A of the coating compound to the weight B of the metal oxide fine particles is in the range of 0.001 or more and 0.2 or less.

[0014] According to the surface-coated metal oxide fine particles of embodiment 1 of the present invention, the surface of the metal oxide fine particles is coated with a coating compound, and the ratio A / B of the weight A of the coating compound to the weight B of the metal oxide fine particles is in the range of 0.001 to 0.2, so that they can be well dispersed in a non-aqueous solvent.

[0015] The surface-coated metal oxide fine particles of Embodiment 2 of the present invention are the surface-coated metal oxide fine particles of Embodiment 1 of the present invention, wherein the coating compound has any one or more functional groups selected from an alkyl group, an alkoxy group, an acyl group, a carboxyl group, a phosphoryl group, a sulfo group, an amino group, and a nitro group.

[0016] According to the surface-coated metal oxide fine particles of Embodiment 2 of the present invention, since the coating compound has any one or more functional groups selected from an alkyl group, an alkoxy group, an acyl group, a carboxyl group, a phosphoryl group, a sulfo group, an amino group, and a nitro group, it is possible to disperse more favorably in a non-aqueous solvent. By coating with these functional groups, the polarity of tin oxide can be reduced and it can be easily dispersed in an organic solvent.

[0017] The surface-coated metal oxide fine particles of Embodiment 3 of the present invention are the surface-coated metal oxide fine particles of Embodiment 1 or Embodiment 2 of the present invention, wherein the coating compound has a compound having any one or more functional groups selected from an alkyl group, an alkoxy group, an acyl group, a carboxyl group, a phosphoryl group, a sulfo group, and a nitro group and a compound having an amino group.

[0018] According to the surface-coated metal oxide fine particles of Embodiment 3 of the present invention, since the coating compound has a compound having any one or more functional groups selected from an alkyl group, an alkoxy group, a carboxyl group, a phosphoryl group, a sulfo group, a nitro group, and a halogen and a compound having an amino group, it is possible to disperse more favorably in a non-aqueous solvent.

[0019] The surface-coated metal oxide fine particles of Embodiment 4 of the present invention are the surface-coated metal oxide fine particles of any one of Embodiments 1 to 3 of the present invention, and are characterized in that the median diameter is 20 nm or less.

[0020] According to the surface-coated metal oxide fine particles of Aspect 4 of the present invention, since the median diameter is 20 nm or less, a relatively thin conductive film (metal oxide fine particle laminated film) can be formed.

[0021] The surface-coated metal oxide fine particles of Aspect 5 of the present invention are characterized in that, among the surface-coated metal oxide fine particles of any one of Aspects 1 to 4 of the present invention, the metal oxide is tin oxide.

[0022] According to the surface-coated metal oxide fine particles of Aspect 5 of the present invention, since the metal oxide is tin oxide, a conductive film (metal oxide fine particle laminated film) having excellent conductivity can be formed.

[0023] The metal oxide fine particle dispersion of Aspect 6 of the present invention is characterized in that any one of the surface-coated metal oxide fine particles of Aspects 1 to 5 is dispersed in an organic solvent having an acid dissociation constant of 15.1 or more.

[0024] According to the metal oxide fine particle dispersion of Aspect 6 of the present invention, since any one of the surface-coated metal oxide fine particles of Aspects 1 to 5 is dispersed in an organic solvent having an acid dissociation constant of 15.1 or more, the surface-coated metal oxide fine particles will be sufficiently dispersed, and a uniform conductive film (metal oxide fine particle laminated film) can be formed.

[0025] The metal oxide fine particle dispersion of Aspect 7 of the present invention is characterized in that, in the metal oxide fine particle dispersion of Aspect 6 of the present invention, the organic solvent having an acid dissociation constant of 15.1 or more is an alcohol-based solvent having 4 or more carbon atoms.

[0026] According to the metal oxide fine particle dispersion of Aspect 7 of the present invention, since the organic solvent having an acid dissociation constant of 15.1 or more is an alcohol-based solvent having 4 or more carbon atoms, the surface-coated metal oxide fine particles can be surely dispersed.

[0027] The metal oxide fine particle dispersion of embodiment 8 of the present invention is characterized in that the water content is 100 mass sppm or less, in the metal oxide fine particle dispersion of embodiment 6 or embodiment 7 of the present invention.

[0028] According to the metal oxide fine particle dispersion of embodiment 8 of the present invention, since the water content is 100 mass sppm or less, deterioration of the perovskite layer can be suppressed even when it is applied directly onto the perovskite layer.

[0029] A method for producing surface-coated metal oxide fine particles according to aspect 9 of the present invention is a method for producing surface-coated metal oxide fine particles according to claims 1 to 5, comprising a surface treatment step of coating the surface of metal oxide fine particles with a coating compound, wherein in the surface treatment step, 5 × 10 4 This method is characterized by being carried out under reduced pressure (below Pa) and at a temperature between 0°C and 200°C, and by removing the generated water.

[0030] According to the method for producing surface-coated metal oxide fine particles in aspect 9 of the present invention, the surface treatment step of coating the surface of the metal oxide fine particles with a coating compound is performed in 5 × 10 4 The system is designed to be carried out under reduced pressure of less than Pa and at a temperature between 0°C and 200°C, and to remove the generated water, thus enabling the efficient production of surface-coated metal oxide nanoparticles.

[0031] A method for producing surface-coated metal oxide fine particles in aspect 10 of the present invention is characterized in that, in the method for producing surface-coated metal oxide fine particles in aspect 9 of the present invention, excess coating compound that was not adsorbed on the surface of the metal oxide fine particles is removed.

[0032] According to the metal oxide fine particle dispersion of embodiment 10 of the present invention, the configuration removes excess coating compound that was not adsorbed on the surface of the metal oxide fine particles, thereby suppressing the deterioration of the perovskite layer due to excess coating compound.

[0033] The method for producing a metal oxide microparticle laminated film according to aspect 11 of the present invention is characterized by comprising a coating step of coating a metal oxide microparticle dispersion according to any one of aspects 6 to 8 of the present invention.

[0034] According to the method for manufacturing a metal oxide microparticle laminated film of aspect 11 of the present invention, since it includes a coating step of coating a metal oxide microparticle dispersion of any one of aspects 6 to 8 of the present invention, an electron transport layer (metal oxide microparticle laminated film) can be stably formed on a perovskite layer. [Effects of the Invention]

[0035] According to the present invention, it is possible to provide surface-coated metal oxide fine particles that can be sufficiently dispersed in a non-aqueous solvent, a metal oxide fine particle dispersion in which these surface-coated metal oxide fine particles are dispersed, and the above-mentioned method for producing surface-coated metal oxide fine particles and method for producing a metal oxide fine particle laminate film. [Brief explanation of the drawing]

[0036] [Figure 1] This is a schematic diagram illustrating a perovskite solar cell equipped with a metal oxide nanoparticle multilayer film, which is an embodiment of the present invention. [Figure 2] This is a schematic diagram illustrating a surface-coated metal oxide fine particle, which is an embodiment of the present invention. [Figure 3] This flowchart shows an example of a method for producing surface-coated metal oxide fine particles, which is an embodiment of the present invention. [Figure 4] This flowchart shows an example of a method for manufacturing a metal oxide nanoparticle laminated film, which is an embodiment of the present invention. [Modes for carrying out the invention]

[0037] The following describes embodiments of the present invention, including surface-coated metal oxide fine particles, metal oxide fine particle dispersions, a method for producing surface-coated metal oxide fine particles, and a method for producing a metal oxide fine particle laminated film, with reference to the attached drawings. The embodiments described below are provided specifically to better illustrate the spirit of the invention and do not limit the present invention unless otherwise specified.

[0038] In this embodiment of the present invention, surface-coated metal oxide fine particles are dispersed in a solvent to form a metal oxide fine particle dispersion. Furthermore, the metal oxide microparticle dispersion, which is an embodiment of the present invention, can be used, for example, when forming a metal oxide microparticle laminated film used as a conductive layer.

[0039] Furthermore, the metal oxide nanoparticle laminated film, which is an embodiment of the present invention, can be used, for example, as an electron transport layer in a perovskite solar cell shown in Figure 1. In this embodiment, the perovskite solar cell 10 has a structure in which an ITO film 12, a hole transport layer 13, a perovskite layer 14, an electron transport layer 15, and a back electrode 16 are stacked on the surface of a glass substrate 11, as shown in Figure 1, for example.

[0040] In the metal oxide nanoparticle laminated film constituting the electron transport layer 13, the film thickness is specified to be within the range of 10 nm to 500 nm. Therefore, in the metal oxide microparticle dispersion of this embodiment, it is required to form a thin and precise layered metal oxide microparticle film. Furthermore, the layered metal oxide microparticle film is required to have excellent conductivity as a conductive material.

[0041] The conductivity of a metal oxide microparticle laminate is greatly influenced by the number of contact points between the metal oxide microparticles in the laminate. Therefore, to improve conductivity, it is necessary to deposit the metal oxide microparticle laminate so that the metal oxide microparticles are uniformly arranged. In addition, it is necessary to reduce the electrical resistance between the metal oxide microparticles. Furthermore, in perovskite solar cells, the perovskite layer degrades significantly due to water, so it is necessary to sufficiently reduce the moisture content in the metal oxide nanoparticle multilayer film. In particular, when depositing an electron transport layer (metal oxide nanoparticle multilayer film) stacked on top of the perovskite layer, if the metal oxide nanoparticle dispersion contains moisture, the perovskite layer may degrade.

[0042] <Surface coated metal oxide fine particles> Therefore, in the surface-coated metal oxide fine particles 20 of this embodiment, as shown in Figure 2, the structure comprises metal oxide fine particles 21 and a coating compound 22 that coats the surface of the metal oxide fine particles 21. In this embodiment, the surface-coated metal oxide fine particles 20 have a ratio A / B of the weight A of the coating compound 22 to the weight B of the metal oxide fine particles 21, which is within the range of 0.001 to 0.2.

[0043] Here, if the ratio A / B of the weight A of the coating compound 22 to the weight B of the metal oxide nanoparticles 21 in the surface-coated metal oxide nanoparticles 20 is less than 0.001, there is a risk that the metal oxide nanoparticles may not be sufficiently dispersed in the non-aqueous solvent. On the other hand, if the ratio A / B of the weight A of the coating compound 22 to the weight B of the metal oxide nanoparticles 21 in the surface-coated metal oxide nanoparticles 20 exceeds 0.2, there is a risk that the excess coating compound 22 will increase the resistance and impair the performance of the solar cell. In addition, depending on the type of excess coating compound, there is a risk that it may erode the perovskite layer.

[0044] Based on the above, in this embodiment, the ratio A / B of the weight A of the coating compound 22 to the weight B of the metal oxide fine particles 21 in the surface-coated metal oxide fine particles 20 is set to a range of 0.001 or more and 0.2 or less. Furthermore, the lower limit of the ratio A / B between the weight A of the coating compound 22 and the weight B of the metal oxide fine particles 21 in the surface-coated metal oxide fine particles 20 is preferably 0.0025 or more, and more preferably 0.005 or more. On the other hand, the upper limit of the ratio A / B between the weight A of the coating compound 22 and the weight B of the metal oxide fine particles 21 in the surface-coated metal oxide fine particles 20 is preferably 10 or less, and more preferably 5 or less.

[0045] Furthermore, in the surface-coated metal oxide fine particles 20 of this embodiment, it is preferable that the coating compound 22 has one or more functional groups selected from alkyl groups, alkoxy groups, acyl groups, carboxyl groups, phosphoryl groups, sulfo groups, amino groups, and nitro groups. For example, alkyl groups may be attached as alkoxy groups by being deposited via oxygen on the tin oxide side during coating. Another example is the acetyl group, a type of acyl group, which may be attached in the form of acetyloxy, with an additional oxygen atom. Other functional groups may also be attached with oxygen added via oxygen on the tin oxide side, and the presence or absence of oxygen is not distinguished in the description. For example, when a methyl group is described, it is assumed that a methoxy group with oxygen attached is also included.

[0046] Furthermore, in the surface-coated metal oxide fine particles 20 of this embodiment, it is preferable that the coating compound 22 comprises a compound having one or more functional groups selected from alkyl groups, alkoxy groups, carboxyl groups, phosphoryl groups, sulfo groups, and nitro groups, and a compound having an amino group. Furthermore, it is preferable to appropriately select the surface functional groups contained in the coating compound 22 depending on the type of non-aqueous solvent. For example, when the non-aqueous solvent is 1-hexanol, it is preferable to have methyl groups, ethyl groups, acetyl groups, amino groups, nitro groups, etc., as surface functional groups.

[0047] Furthermore, in the surface-coated metal oxide fine particles 20 of this embodiment, it is preferable that the median diameter is 20 nm or less. Furthermore, the median diameter is more preferably 10 nm or less, and more preferably 5 nm or less. There is no particular lower limit to the median diameter, but it is practically 1 nm or more.

[0048] Furthermore, in the surface-coated metal oxide fine particles 20 of this embodiment, the metal oxide constituting the metal oxide fine particles 21 is preferably tin oxide.

[0049] <Method for producing surface-coated metal oxide fine particles> Next, a method for producing surface-coated metal oxide fine particles according to this embodiment will be described. In the method for producing surface-coated metal oxide fine particles according to this embodiment, as shown in Figure 3, the process comprises a metal oxide fine particle generation step S01 and a surface treatment step S02.

[0050] (Metal oxide fine particle generation step S01) First, metal oxide nanoparticles 21 are synthesized. For example, if the metal oxide nanoparticles 21 are tin oxide nanoparticles, they can be synthesized as follows. A tin oxide suspension is prepared by adding an aqueous sodium hydroxide solution dropwise to an aqueous tin chloride solution. By centrifuging the resulting tin oxide suspension, a tin oxide paste containing metal oxide fine particles is obtained. Ammonia water is added dropwise to the obtained tin oxide paste to form an aqueous dispersion of tin oxide. Modified alcohol is added to this dispersion and dried. This yields metal oxide fine particles 21.

[0051] (Surface treatment process S02) Next, the surface of the obtained metal oxide nanoparticles 21 is coated with a coating compound. For example, in the case of acetylation, a reagent such as acetic acid is mixed with the metal oxide nanoparticles, and 5 × 10 4 The surface treatment is performed under reduced pressure of less than Pa and at a temperature of 0°C to 200°C, and the water generated is removed while the coating compound is adsorbed onto the surface of the metal oxide fine particles 21. Furthermore, it is preferable to remove any excess coating compound that was not adsorbed onto the surface of the metal oxide fine particles 21.

[0052] Here, in the surface treatment process S02, 5 × 10 4 By performing the procedure under reduced pressure below Pa, it becomes possible to promote the evaporation and removal of excess coating compounds that do not adsorb onto the surface of the metal oxide fine particles 21. Furthermore, the pressure in the surface treatment step S02 is preferably 5000 Pa or less, and more preferably 1000 Pa or less. There is no particular lower limit to the pressure in the surface treatment step S02, but it is practically 0.67 Pa or more.

[0053] Furthermore, by keeping the temperature within the range of 0°C to 200°C in the surface treatment process S02, the surface treatment can be performed efficiently, and the temperature degradation of the metal oxide fine particles 21 themselves can be suppressed. The lower limit of the temperature in the surface treatment step S02 is preferably 70°C or higher, and more preferably 100°C or higher. On the other hand, the upper limit of the temperature in the surface treatment step S02 is preferably 200°C or lower, and more preferably 160°C or lower. The lower limit temperature is determined by the boiling point and reaction rate of the treatment agent, and is selected at a temperature below the boiling point that provides a sufficient reaction rate. The upper limit temperature is determined by the ease of aggregation and grain growth of oxide nanoparticles, and is selected at a temperature that does not hinder dispersion in subsequent processes and does not cause significant grain growth.

[0054] Through the process described above, the surface-coated metal oxide fine particles 20 of this embodiment are manufactured.

[0055] <Metal oxide fine particle dispersion> Next, the metal oxide microparticle dispersion according to this embodiment will be described. In the metal oxide microparticle dispersion according to this embodiment, the surface-coated metal oxide microparticles according to this embodiment are dispersed in an organic solvent with an acid dissociation constant of 15.1 or higher. In organic solvents with a low acid dissociation constant, depending on the compatibility with the coating compound, there may be erosive properties towards the perovskite layer. Here, the organic solvent with an acid dissociation constant of 15.1 or higher is preferably an alcohol-based solvent having 4 or more carbon atoms.

[0056] Furthermore, in the metal oxide fine particle dispersion of this embodiment, the water content is preferably 100 mass sppm or less. The water content can be reduced to 100 mass sppm or less by dehydration treatment using molecular sieves or the like. The water content of the metal oxide fine particle dispersion is preferably 100 massppm or less, and more preferably 20 massppm or less. While there is no particular lower limit to the water content of the metal oxide fine particle dispersion, it is practically 1 massppm or more.

[0057] In this embodiment, the metal oxide fine particle dispersion is produced by adding and mixing an organic solvent with an acid dissociation constant of 15.1 or higher to the surface-coated metal oxide fine particles of this embodiment. Furthermore, there are no particular restrictions on the mixing method, and existing mixing methods such as bead mills can be appropriately selected and applied.

[0058] <Method for manufacturing a layered film of metal oxide microparticles> Next, an example of a method for manufacturing a metal oxide microparticle laminated film using the metal oxide microparticle dispersion of this embodiment will be explained using the flow chart in Figure 4.

[0059] (Solid concentration adjustment step S11) First, a metal oxide fine particle dispersion according to this embodiment is prepared, and the solid content concentration in the metal oxide fine particle dispersion is adjusted to be within the range of 1 mass% to 20 mass%. Furthermore, the solid content concentration in the metal oxide fine particle dispersion is preferably 1 mass% or more, and more preferably 1.5 mass% or more. In addition, the solid content concentration in the metal oxide fine particle dispersion is preferably 10 mass% or less, and more preferably 5 mass% or less.

[0060] (Coating process S12) Next, a dispersion of metal oxide fine particles with adjusted solid content is coated onto the substrate using a spin coating apparatus. In this coating process S12, the spin coating conditions are preferably set to a rotation speed of 500 rpm or more and 5000 rpm or less, and a coating time of 5 seconds or more and 60 seconds or less. Furthermore, the thickness of the coating film is preferably set to a range of 20 nm or more and 500 nm or less.

[0061] (Heating process S13) Next, the coating film (a dispersion of coated metal oxide microparticles) is heated to remove the solvent and form a layered metal oxide microparticle film. In this heating step S13, the heating conditions are preferably such that the heating temperature is within the range of 100°C to 400°C and the heating time is within the range of 1 minute to 30 minutes.

[0062] Through the steps described above, the metal oxide nanoparticle laminated film of this embodiment is formed.

[0063] In this embodiment of surface-coated metal oxide fine particles 20, which has the above configuration, the surface of the metal oxide fine particles 21 is coated with a coating compound 22, and the ratio A / B of the weight A of the coating compound 22 to the weight B of the metal oxide fine particles 21 is in the range of 0.001 to 0.2, so that it can be dispersed well in a non-aqueous solvent. Therefore, it is possible to construct a metal oxide nanoparticle dispersion that enables the stable formation of a metal oxide nanoparticle laminated film in which metal oxide nanoparticles are uniformly stacked on a perovskite layer.

[0064] In the surface-coated metal oxide fine particles 20 of this embodiment, if the coating compound 22 has one or more functional groups selected from alkyl groups, alkoxy groups, acyl groups, carboxyl groups, phosphoryl groups, sulfo groups, amino groups, and nitro groups, the surface-coated metal oxide fine particles 20 can be dispersed even more effectively in a non-aqueous solvent.

[0065] In the surface-coated metal oxide fine particles 20 of this embodiment, if the coating compound 22 has a compound having one or more functional groups selected from alkyl groups, alkoxy groups, acyl groups, carboxyl groups, phosphoryl groups, sulfo groups, and nitro groups, and a compound having an amino group, then the surface-coated metal oxide fine particles 20 can be dispersed even more effectively in a non-aqueous solvent.

[0066] In the surface-coated metal oxide nanoparticles 20 of this embodiment, when the median diameter is 20 nm or less, a relatively thin conductive film (metal oxide nanoparticle laminated film) can be formed.

[0067] In the surface-coated metal oxide fine particles 20 of this embodiment, if the metal oxide constituting the metal oxide fine particles 21 is tin oxide, a conductive film (metal oxide fine particle laminated film) with excellent conductivity can be formed.

[0068] In the metal oxide microparticle dispersion of this embodiment, the surface-coated metal oxide microparticles 20 of this embodiment are dispersed in an organic solvent with an acid dissociation constant of 15.1 or higher. As a result, the surface-coated metal oxide microparticles 20 are sufficiently dispersed, and a uniform conductive film (metal oxide microparticle laminated film) can be formed.

[0069] In the metal oxide fine particle dispersion of this embodiment, if the organic solvent with an acid dissociation constant of 15.1 or higher is an alcohol-based solvent having 4 or more carbon atoms, the surface-coated metal oxide fine particles 20 of this embodiment can be reliably dispersed.

[0070] In this embodiment of the metal oxide fine particle dispersion, if the water content is 100 mass sppm or less, the deterioration of the perovskite layer can be suppressed even when it is directly applied onto the perovskite layer.

[0071] In the method for producing surface-coated metal oxide fine particles according to this embodiment, the surface treatment step S02 in which the surface of the metal oxide fine particles 21 is coated with a coating compound 22 is performed in 5 × 10 4 The system is configured to be carried out under reduced pressure of Pa or less and at a temperature of 0°C to 200°C, and to remove the generated water, so that surface-coated metal oxide fine particles 20 can be produced efficiently.

[0072] In the method for producing surface-coated metal oxide fine particles according to this embodiment, if the configuration is such that excess coating compound 22 that was not adsorbed on the surface of the metal oxide fine particles 21 is removed, the deterioration of the perovskite layer due to the excess coating compound 22 can be suppressed.

[0073] In the method for manufacturing a metal oxide microparticle laminated film according to this embodiment, a coating step is included in which the metal oxide microparticle dispersion according to this embodiment is applied, so that an electron transport layer (metal oxide microparticle laminated film) can be stably formed on the perovskite layer.

[0074] Although one embodiment of the present invention has been described above, the present invention is not limited thereto and can be modified as appropriate without departing from the technical spirit of the invention. In this embodiment, the metal oxide nanoparticle laminated film was described as constituting the electron transport layer of the perovskite solar cell shown in Figure 1, but it may be used in other applications not limited to this. [Examples]

[0075] The verification experiments conducted to confirm the effectiveness of the present invention will be described. In the following examples and comparative examples of the present invention, alkyl groups may be attached as alkoxy groups by being attached via oxygen on the tin oxide side during coating. As another example, an acetyl group, which is a type of acyl group, may be attached in the form of acetyloxy, with an additional oxygen atom attached. Other functional groups may also be attached with oxygen added via oxygen on the tin oxide side, and the presence or absence of oxygen is not distinguished in the description. For example, when a methyl group is mentioned, it is also intended to include a methoxy group with oxygen attached.

[0076] (Examples 1-8 of the present invention, Comparative Examples 2,3) A sodium hydroxide solution was added dropwise to a tin chloride solution, and the resulting tin oxide suspension was washed multiple times (8 times) using a centrifuge to obtain a tin oxide paste. A water ammonia solution was added dropwise to the washed tin oxide paste to prepare an aqueous dispersion of tin oxide. Denatured alcohol was added to this aqueous dispersion of tin oxide and it was dried.

[0077] Subsequently, surface treatment agents having the functional groups shown in Table 1 were added, and the metal oxide fine particles were surface-treated under the atmosphere and treatment temperature conditions shown in Table 1 to form a coated compound having one or more functional groups selected from alkyl groups, alkoxy groups, carboxyl groups, acyl groups, amino groups, nitro groups, and halogen groups, thereby producing surface-coated metal oxide fine particles. At this time, the total content of the functional groups was adjusted to be within the range shown in Table 1.

[0078] A dispersion of metal oxide fine particles was obtained by adding the non-aqueous solvents shown in Table 1 to these surface-coated metal oxide fine particles so that the tin oxide concentration in the dispersion was 4 mass%, and then mixing with a bead mill.

[0079] (Comparative Example 1) A dispersion of metal oxide fine particles was obtained by adding the non-aqueous solvents shown in Table 1 to untreated metal oxide fine particles so that the tin oxide concentration in the dispersion was 4 mass%, and then mixing the mixture with a bead mill.

[0080] (Laminated film of metal oxide microparticles) The solid content concentration of the aforementioned metal oxide fine particle dispersion was adjusted to 2 mass%. A dispersion of metal oxide fine particles with adjusted solid content was spin-coated onto a 50mm x 50mm glass substrate using a spin coater (Mikasa Corporation, model: MS-A150) at 1000 rpm for 20 seconds to form a coating film. A layered film of metal oxide nanoparticles was formed on a glass substrate with a coated film by heating it on a hot plate at 100°C for 5 minutes.

[0081] The surface-coated metal oxide nanoparticles, metal oxide nanoparticle dispersions, and metal oxide nanoparticle laminated films obtained as described above were evaluated for each item using the following methods.

[0082] (Total content of functional groups in coated compounds) Measurements were taken using a TG-DTA (NETZSCH STA-2500) by heating from room temperature to 600°C at a heating rate of 10°C / min. A dry air atmosphere was used, and the total content of functional groups in the coated compound was measured by the weight loss up to approximately 500°C, excluding the weight loss due to water removal (weight loss from room temperature to approximately 140°C).

[0083] (Primary particle size of metal oxide nanoparticles) Metal oxide nanoparticles dispersed in a solvent were imaged at a magnification of 200,000x using a transmission electron microscope (JEOL Ltd., model: JEM-2010F). The captured image was obtained by measuring the particle size of 100 particles using software (product name: Image J) and calculating the average.

[0084] (Secondary particle size of metal oxide nanoparticles) The obtained tin oxide particle dispersion was diluted to 0.5 mass% with the same solvent as the dispersion medium, and the secondary particle size was measured using a particle size distribution analyzer (Malvern Zetasizer nano).

[0085] (Evaluation of solar cell characteristics) The photovoltaic conversion characteristics of the fabricated photovoltaic conversion device were measured by a method conforming to the output measurement method of silicon crystal solar cells in JIS C8913:1998. The results are shown in Table 1. Specifically, a solar simulator (SMO-250III type manufactured by Spectral Instruments Co., Ltd.) combined with an air mass filter equivalent to AM1.5G was adjusted to a light intensity of 100 mW / cm2 with a secondary reference Si solar cell as the light source for measurement. While irradiating the test sample of the perovskite solar cell (the photovoltaic conversion device of Example 1) with light, the I-V curve characteristics were measured using a source meter (Model 2400 general-purpose source meter manufactured by Keithley Instruments Inc.). The short-circuit current (Isc), open-circuit voltage (Voc), fill factor (FF), and the short-circuit current density (Jsc) according to Equation 1 below, and the photovoltaic conversion efficiency (PCE) according to Equation 2 were obtained.

[0086] Equation 1: Short-circuit current density (Jsc; mA / cm 2 ) = Isc (mA) / effective light-receiving area S (cm 2 ) Equation 2: Photovoltaic conversion efficiency (PCE; %) = Voc (V) × Jsc (mA / cm 2 ) × FF × 100 / 100 (mW / cm 2 )

[0087] Here, as an evaluation of the solar cell characteristics, those that do not operate as a battery are marked as "×", those with a maximum photovoltaic conversion efficiency of 12% or more but with variations are marked as "△-〇", those with a maximum photovoltaic conversion efficiency stably at 12% or more are marked as "〇", and those with a maximum photovoltaic conversion efficiency stably at 15% or more are marked as "◎".

[0088]

Table 1

[0089]

Table 2

[0090] In Comparative Example 1, the surface was not coated with the coating compound and could not be sufficiently dispersed in the non-aqueous solvent. As a result, a uniform electron transport layer could not be formed, and the solar cell performance was "X". In Comparative Example 2, the ratio A / B of the weight A of the coating compound to the weight B of the metal oxide fine particles was less than 0.001, and it was not possible to sufficiently disperse it in the non-aqueous solvent. As a result, a uniform electron transport layer could not be formed, and the solar cell performance was "X". In Comparative Example 3, the ratio A / B of the weight A of the coating compound to the weight B of the metal oxide fine particles exceeded 0.2, making it impossible to sufficiently disperse them in the non-aqueous solvent. As a result, a uniform electron transport layer could not be formed, and the solar cell performance was "X".

[0091] In Examples 1-14 of the present invention, the ratio A / B of the weight A of the coating compound to the weight B of the metal oxide fine particles was within the range of 0.001 to 0.2, allowing for sufficient dispersion in a non-aqueous solvent. As a result, a uniform electron transport layer could be formed, and the solar cell performance was "△-〇" or better, which was superior to that of Comparative Examples 1-3. In particular, in Examples 1, 7, and 8 of the present invention, the solar cell performance was rated as "〇", and in Example 2-6 of the present invention, the solar cell performance was rated as "◎", confirming that the solar cell performance is particularly excellent.

[0092] As described above, it has been confirmed that the present invention provides surface-coated metal oxide fine particles that can be sufficiently dispersed in a non-aqueous solvent, a metal oxide fine particle dispersion in which these surface-coated metal oxide fine particles are dispersed, and the above-mentioned method for producing surface-coated metal oxide fine particles and method for producing a metal oxide fine particle laminate film.

Claims

1. Surface-coated metal oxide nanoparticles in which the surface of the metal oxide nanoparticles is coated with a coating compound, Surface-coated metal oxide fine particles characterized in that the ratio A / B of the weight A of the coating compound to the weight B of the metal oxide fine particles is within the range of 0.001 to 0.

2.

2. The surface-coated metal oxide fine particles according to claim 1, characterized in that the coating compound has one or more functional groups selected from alkyl groups, alkoxy groups, acyl groups, carboxyl groups, phosphoryl groups, sulfo groups, amino groups, and nitro groups.

3. The surface-coated metal oxide fine particles according to claim 1, characterized in that the coating compound comprises a compound having one or more functional groups selected from alkyl, alkoxy, acyl, carboxyl, phosphoryl, sulfo, and nitro groups, and a compound having an amino group.

4. The surface-coated metal oxide fine particles according to claim 1, characterized in that the median diameter is 20 nm or less.

5. The surface-coated metal oxide fine particles according to claim 1, characterized in that the metal oxide is tin oxide.

6. A dispersion of metal oxide fine particles characterized in that the surface-coated metal oxide fine particles described in any one of claims 1 to 5 are dispersed in an organic solvent having an acid dissociation constant of 15.1 or higher.

7. The metal oxide fine particle dispersion according to claim 6, characterized in that the organic solvent with an acid dissociation constant of 15.1 or higher is an alcohol-based solvent having 4 or more carbon atoms.

8. The metal oxide fine particle dispersion according to claim 6, characterized in that the water content is 100 mass ppm or less.

9. A method for producing surface-coated metal oxide fine particles according to any one of claims 1 to 5, The process includes a surface treatment step in which the surface of metal oxide fine particles is coated with a coating compound, and in the surface treatment step, 5 × 10 ４ A method for producing surface-coated metal oxide fine particles, characterized by carrying out the process under reduced pressure of Pa or less and at a temperature of 0°C to 200°C, and removing the generated water.

10. A method for producing surface-coated metal oxide fine particles according to claim 9, characterized in that excess coating compound that did not adsorb onto the surface of the metal oxide fine particles is removed.

11. A method for producing a metal oxide microparticle laminated film, characterized by comprising a coating step of coating the metal oxide microparticle dispersion described in claim 6.

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