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

Abstract

The present invention pertains to surface-coated metal oxide fine particles in each of which the surface of a fine particle formed of a metal oxide is coated with a coating compound, and which are 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 0.001-0.2. The coating compound preferably has one or more functional groups selected from among alkyl groups, alkoxy groups, acyl groups, a carboxyl group, a phosphoryl group, a sulfo group, an amino group, and a nitro group.

Description

Surface-coated metal oxide nanoparticles, metal oxide nanoparticle dispersion, method for producing surface-coated metal oxide nanoparticles, and method for producing a metal oxide nanoparticle laminated film.

[0001] This invention relates to surface-coated metal oxide fine particles used, for example, when forming conductive films, a dispersion of metal oxide fine particles, a method for producing surface-coated metal oxide fine particles, and a method for producing a metal oxide fine particle laminate. This application claims priority based on Japanese Patent Application No. 2025-007047, filed in Japan on January 17, 2025, the contents of which are incorporated herein by reference.

[0002] Recently, perovskite solar cells using perovskite films have been proposed as thin-film solar cells. These perovskite solar cells come in 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, 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, these organic materials used for the electron transport layer are very expensive, which significantly impacts the cost of the device. Furthermore, these organic materials have durability issues against temperature, humidity, and oxidation, and there is a risk that they cannot be used stably for long periods. Therefore, there has been a desire to use inorganic materials as electron transport layers, which are considered to be cheaper and more stable than organic materials.

[0004] As an inorganic material-based electron transport layer, TiO ２ , SnO ２These are often deposited using n-type oxide semiconductors such as ZnO. However, dry deposition has a tendency to be difficult to implement due to the high cost of introducing manufacturing equipment. 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, or the limited heating temperature can result in a film with low crystallinity, poor electron conductivity, and high resistance. For various reasons depending on the deposition method, it has been difficult to manufacture solar cells with high photoelectric conversion efficiency (PCE) over a large area.

[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 large-area deposition, making it an excellent method for mass production. However, it requires a dispersion liquid for coating as a material, and has only been used on a research scale for inverted perovskite solar cells. 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 erosive (solubility) towards 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 solvents that do not corrode, and the aggregation of tin oxide nanoparticles prevents the formation of a dense and uniform coating film, resulting in a failure to obtain power generation performance. Even when a dispersant is selected to disperse in the solvent to resolve this, some component of the dispersant impairs performance, such as corroding the perovskite layer or significantly increasing film resistance. For this reason, 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).

[0008] Japanese Patent Application Publication No. 2023-036564 (A)

[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 during film formation. Such metal oxide nanoparticle dispersions require film formation to be completed in a short time, and can only be formed using methods that complete film formation in a short time, such as spin coaters, making them difficult to use for film formation with die coaters, which are suitable for coating large areas. Furthermore, because the dispersion is achieved by adding components (dispersants) that are corrosive to the perovskite layer, it causes degradation of 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.

[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 has been made based on the above-described findings, and the surface-coated metal oxide fine particles of the present invention in embodiment 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 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 characterized in that, in the surface-coated metal oxide fine particles of embodiment 1 of the present invention, 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.

[0016] According to the surface-coated metal oxide fine particles of embodiment 2 of the present invention, since 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, it is possible to disperse them even better in non-aqueous solvents. By coating with these functional groups, the polarity of the metal oxide fine particles can be reduced, making them easier to disperse in organic solvents.

[0017] The surface-coated metal oxide fine particles of embodiment 3 of the present invention are characterized in that, in the surface-coated metal oxide fine particles of embodiment 1 or embodiment 2 of the present invention, the coating compound comprises 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.

[0018] According to the surface-coated metal oxide fine particles of embodiment 3 of the present invention, the coating compound has a compound having one or more functional groups selected from alkyl groups, alkoxy groups, carboxyl groups, phosphoryl groups, sulfo groups, nitro groups, and halogens, and a compound having an amino group, so that it can be dispersed even better in a non-aqueous solvent.

[0019] The surface-coated metal oxide fine particles of embodiment 4 of the present invention are characterized in that, in any one of embodiments 1 to 3 of the present invention, the metal oxide is tin oxide.

[0020] According to the surface-coated metal oxide nanoparticles of embodiment 4 of the present invention, since the metal oxide is tin oxide, a conductive film (metal oxide nanoparticle laminated film) with excellent conductivity can be formed.

[0021] The metal oxide fine particle dispersion of embodiment 5 of the present invention is characterized in that one of the surface-coated metal oxide fine particles from embodiments 1 to 4 is dispersed in an organic solvent with an acid dissociation constant of 15.1 or higher.

[0022] According to the metal oxide microparticle dispersion of Embodiment 5 of the present invention, since any one of the surface-coated metal oxide microparticles from Embodiments 1 to 4 is dispersed in an organic solvent with an acid dissociation constant of 15.1 or higher, the surface-coated metal oxide microparticles are sufficiently dispersed, and a uniform conductive film (metal oxide microparticle laminated film) can be formed.

[0023] The metal oxide fine particle dispersion of embodiment 6 of the present invention is characterized in that, in the metal oxide fine particle dispersion of embodiment 5 of the present invention, the organic solvent with an acid dissociation constant of 15.1 or higher is an alcohol-based solvent having 4 or more carbon atoms.

[0024] According to the metal oxide fine particle dispersion of embodiment 6 of the present invention, the organic solvent with an acid dissociation constant of 15.1 or higher is an alcohol-based solvent having 4 or more carbon atoms, so that the surface-coated metal oxide fine particles can be reliably dispersed.

[0025] The metal oxide fine particle dispersion of embodiment 7 of the present invention is characterized in that, in the metal oxide fine particle dispersion of embodiment 5 or embodiment 6 of the present invention, the water content is 100 mass ppm or less.

[0026] According to the metal oxide fine particle dispersion of embodiment 7 of the present invention, since the water content is 100 mass ppm or less, deterioration of the perovskite layer can be suppressed even when it is applied directly onto the perovskite layer.

[0027] A method for producing surface-coated metal oxide fine particles according to embodiment 8 of the present invention is a method for producing surface-coated metal oxide fine particles according to any one of embodiments 1 to 4, 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 The process is carried out under reduced pressure (Pa or less) and at a temperature between 0°C and 200°C, and is characterized by the removal of the generated water.

[0028] According to the method for producing surface-coated metal oxide fine particles in embodiment 8 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 ４The process is carried out under reduced pressure below Pa and at a temperature between 0°C and 200°C, and the generated water is removed, allowing for the efficient production of surface-coated metal oxide fine particles.

[0029] The method for producing surface-coated metal oxide fine particles according to aspect 9 of the present invention is characterized by removing excess coating compound that was not adsorbed on the surface of the metal oxide fine particles.

[0030] According to the metal oxide fine particle dispersion of embodiment 9 of the present invention, the configuration removes excess coating compounds that were not adsorbed on the surface of the metal oxide fine particles, thereby suppressing the deterioration of the perovskite layer due to excess coating compounds.

[0031] The method for producing a metal oxide microparticle laminated film according to aspect 10 of the present invention is characterized by comprising a coating step of coating a metal oxide microparticle dispersion according to any one of aspects 5 to 5 of the present invention.

[0032] According to the method for manufacturing a metal oxide microparticle laminated film of embodiment 10 of the present invention, since it includes a coating step of coating a metal oxide microparticle dispersion of any one of embodiments 5 to 7 of the present invention, an electron transport layer (metal oxide microparticle laminated film) can be stably formed on a perovskite layer.

[0033] 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.

[0034] This is a schematic diagram of a perovskite solar cell equipped with a metal oxide nanoparticle multilayer film according to an embodiment of the present invention. This is a schematic diagram of surface-coated metal oxide nanoparticles according to an embodiment of the present invention. This is a flowchart showing an example of a method for manufacturing surface-coated metal oxide nanoparticles according to an embodiment of the present invention. This is a flowchart showing an example of a method for manufacturing a metal oxide nanoparticle multilayer film according to an embodiment of the present invention.

[0035] 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.

[0036] The surface-coated metal oxide fine particles according to the embodiment of the present invention are dispersed in a solvent to form a metal oxide fine particle dispersion. Furthermore, the metal oxide fine particle dispersion according to the embodiment of the present invention is used, for example, when forming a metal oxide fine particle laminated film used as a conductive layer.

[0037] Furthermore, the metal oxide nanoparticle laminated film, which is an embodiment of the present invention, is 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 laminated on the surface of a glass substrate 11, as shown in Figure 1.

[0038] In the metal oxide nanoparticle laminated film constituting the electron transport layer 13, the film thickness is within the range of 10 nm to 500 nm. Therefore, in the metal oxide nanoparticle dispersion of this embodiment, it is required to form the metal oxide nanoparticle laminated film thinly and precisely. Furthermore, the metal oxide nanoparticle laminated film is required to have excellent conductivity as a conductive material.

[0039] The conductivity of the metal oxide particle laminated film is significantly affected by the number of contact points between the metal oxide particles in the metal oxide particle laminated film. Therefore, in order to improve the conductivity, it is necessary to form the metal oxide particle laminated film so that the metal oxide particles are uniformly arranged. In addition, it is necessary to reduce the electrical resistance between the metal oxide particles. In a perovskite solar cell, since the perovskite layer is significantly deteriorated by water, it is necessary to sufficiently reduce the moisture contained in the metal oxide particle laminated film. In particular, when forming the electron transport layer (metal oxide particle laminated film) so as to be laminated on the perovskite layer, if the metal oxide particle dispersion contains moisture, the perovskite layer may deteriorate.

[0040] <Surface-coated metal oxide particles> Therefore, in the surface-coated metal oxide particles 20 of the present embodiment, as shown in FIG. 2, it has a structure having metal oxide particles 21 and a coating compound 22 that coats the surface of the metal oxide particles 21. And in the surface-coated metal oxide particles 20 of the present embodiment, the ratio A / B of the weight A of the coating compound 22 to the weight B of the metal oxide particles 21 is within the range of 0.001 or more and 0.2 or less.

[0041] Here, when the ratio A / B of the weight A of the coating compound 22 to the weight B of the metal oxide particles 21 in the surface-coated metal oxide particles 20 is less than 0.001, there is a possibility that the metal oxide particles cannot be sufficiently dispersed in the non-aqueous solvent. On the other hand, when the ratio A / B of the weight A of the coating compound 22 to the weight B of the metal oxide particles 21 in the surface-coated metal oxide particles 20 exceeds 0.2, there is a possibility that the excessive coating compound 22 increases the resistance value and impairs the performance as a solar cell. In addition, an excessive amount of the coating compound may erode the perovskite layer depending on the type.

[0042] From the above, in the present 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 in the range of 0.001 or more and 0.2 or less. In addition, the lower limit of 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 preferably 0.0025 or more, and more preferably 0.005 or more. On the other hand, the upper limit of 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 preferably 10 or less, and more preferably 5 or less.

[0043] Further, in the surface-coated metal oxide fine particles 20 of the present embodiment, the coating compound 22 preferably has 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. For example, the alkyl group may adhere as an alkoxy group by adhering through oxygen on the tin oxide side when coating. As another example, an acetyl group, which is a kind of acyl group, may adhere in the form of acetyloxy in which one more oxygen is attached. Other functional groups may also adhere in a form in which oxygen is added by oxygen on the tin oxide side, and the description is not distinguished by the presence or absence of oxygen. When a methyl group is described as an example, it shall include a methoxy group with oxygen attached.

[0044] Furthermore, in the surface-coated metal oxide fine particles 20 of the present embodiment, the coating compound 22 preferably has a compound having one or more functional groups selected from an alkyl group, an alkoxy group, a carboxyl group, a phosphoryl group, a sulfo group, and a nitro group and a compound having an amino group. In addition, it is preferable to appropriately select the surface functional groups contained in the coating compound 22 according to the type of the non-aqueous solvent. For example, when the non-aqueous solvent is 1-hexanol, it is preferable to have a methyl group, an ethyl group, an acetyl group, an amino group, a nitro group, etc., as the surface functional groups.

[0045] 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.

[0046] <Method for Manufacturing Surface-Coated Metal Oxide Fine Particles> Next, the method for manufacturing surface-coated metal oxide fine particles according to this embodiment will be described. In the method for manufacturing 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.

[0047] (Metal Oxide Microparticle Production Process S01) First, metal oxide microparticles 21 are synthesized. Here, for example, if the metal oxide microparticles 21 are tin oxide microparticles, they can be synthesized as follows: A tin oxide suspension is produced by adding an aqueous sodium hydroxide solution dropwise to an aqueous tin chloride solution. A tin oxide paste containing metal oxide microparticles is obtained by centrifuging the obtained tin oxide suspension. Ammonia water is added dropwise to the obtained tin oxide paste to make an aqueous dispersion of tin oxide. Modified alcohol is added to this dispersion and dried. This gives the metal oxide microparticles 21.

[0048] (Surface treatment step S02) Next, the surface of the obtained metal oxide fine particles 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 fine particles, 5 × 10 ４ Surface treatment is performed under reduced pressure of Pa or less and at a temperature of 0°C to 200°C, while adsorbing the coating compound onto the surface of the metal oxide fine particles 21 and removing the water generated. It is preferable to remove any excess coating compound that was not adsorbed onto the surface of the metal oxide fine particles 21.

[0049] Here, in the surface treatment step S02, 5 × 10 ４ By performing the process under reduced pressure of Pa or less, it is 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. 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 substantially 0.67 Pa or higher.

[0050] Furthermore, by setting the temperature in the surface treatment step S02 within the range of 0°C to 200°C, 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 has a sufficient reaction rate. The upper limit temperature is determined by the ease of aggregation and grain growth of the oxide nanoparticles, and is selected at a temperature that does not hinder dispersion in subsequent processes and does not cause significant grain growth.

[0051] Through the process described above, the surface-coated metal oxide fine particles 20 of this embodiment are manufactured.

[0052] <Metal Oxide Microparticle 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. The acid dissociation constant may be 15.3 or higher, or 15.5 or higher, although it is not particularly limited. Furthermore, there is no particular upper limit to the acid dissociation constant, but it is substantially 18 or lower. Here, as the organic solvent with an acid dissociation constant of 15.1 or higher, it is preferable to use an alcohol-based solvent with 4 or more carbon atoms. The number of carbon atoms may be 6 or higher, or 8 or higher, although it is not particularly limited. Furthermore, there is no particular upper limit to the number of carbon atoms, but it is substantially 10 or lower.

[0053] Furthermore, in the metal oxide fine particle dispersion of this embodiment, the water content is preferably 100 mass ppm or less. The water content can be reduced to 100 mass ppm or less by dehydration treatment using molecular sieves or the like. The water content in the metal oxide fine particle dispersion is preferably 100 mass ppm or less, and more preferably 20 mass ppm or less. There is no particular lower limit to the water content in the metal oxide fine particle dispersion, but it is substantially 1 mass ppm or more.

[0054] In this embodiment, the metal oxide fine particle dispersion is produced by adding an organic solvent with an acid dissociation constant of 15.1 or higher to the surface-coated metal oxide fine particles of this embodiment and mixing them. There are no particular restrictions on the mixing method, and existing mixing methods such as bead mills can be appropriately selected and applied.

[0055] <Method for Manufacturing a Metal Oxide Microparticle Laminated Film> 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.

[0056] (Solid content 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%. Preferably, the solid content concentration in the metal oxide fine particle dispersion is 1 mass% or more, and more preferably 1.5 mass% or more. Furthermore, preferably, the solid content concentration in the metal oxide fine particle dispersion is 10 mass% or less, and more preferably 5 mass% or less.

[0057] (Coating process S12) Next, a metal oxide fine particle dispersion with adjusted solid content is coated onto the substrate using a spin coating apparatus. The conditions for spin coating in this coating process S12 are preferably 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. The thickness of the coated film is preferably within the range of 20 nm or more and 500 nm or less.

[0058] (Heating step S13) Next, the coated film (coated metal oxide fine particle dispersion) is heated to remove the solvent and form a metal oxide fine particle laminated film. In this heating step S13, it is preferable 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.

[0059] Through the steps described above, the metal oxide nanoparticle laminated film of this embodiment is formed.

[0060] In this embodiment of surface-coated metal oxide fine particles 20, 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 fine particle dispersion that can stably form a metal oxide fine particle laminated film in which metal oxide fine particles are uniformly laminated on a perovskite layer.

[0061] 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.

[0062] 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, alkoxy, acyl, carboxyl, phosphoryl, sulfo, 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.

[0063] In the surface-coated metal oxide fine particles 20 of this embodiment, when 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.

[0064] 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.

[0065] 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.

[0066] In this embodiment of the metal oxide fine particle dispersion, if the water content is 100 mass ppm or less, the deterioration of the perovskite layer can be suppressed even when it is directly applied onto the perovskite layer.

[0067] 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 process is carried out under reduced pressure of Pa or less and at a temperature of 0°C to 200°C, and the generated water is removed, so surface-coated metal oxide fine particles 20 can be produced efficiently.

[0068] 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.

[0069] 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.

[0070] 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 thereto.

[0071] The following describes the verification experiments conducted to confirm the effectiveness of the present invention. In the examples and comparative examples of the present invention described below, alkyl groups may be attached as alkoxy groups by attaching 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 described, it is also intended to include a methoxy group with oxygen attached.

[0072] (Examples 1-8 of the present invention, Comparative Examples 2 and 3) An aqueous solution of sodium hydroxide was added dropwise to an aqueous solution of tin chloride, and the resulting tin oxide suspension was washed multiple times (8 times) in a centrifuge to obtain a tin oxide paste. After washing, aqueous ammonia was added dropwise to the tin oxide paste to prepare an aqueous dispersion of tin oxide. Modified alcohol was added to this aqueous dispersion of tin oxide and dried.

[0073] 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.

[0074] 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.

[0075] (Comparative Example 1) A metal oxide fine particle dispersion was obtained by adding the non-aqueous solvent shown in Table 1 to metal oxide fine particles that had not undergone surface treatment, so that the tin oxide concentration in the dispersion was 4 mass%, and then mixing with a bead mill.

[0076] (Laminated metal oxide microparticle film) The solid content concentration of the metal oxide microparticle dispersion was adjusted to 2 mass%. The metal oxide microparticle dispersion with the adjusted solid content was spin-coated onto a 50 mm x 50 mm glass substrate using a spin coater (Mikasa Corporation model name: MS-A150) at 1000 rpm for 20 seconds to form a coated film. The glass substrate with the coated film was heated on a hot plate at 100°C for 5 minutes to form a laminated metal oxide microparticle film.

[0077] 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.

[0078] (Total content of functional groups in the coated compound) The measurement was performed using a TG-DTA (NETZSCH STA-2500) by raising the temperature from room temperature to 600°C at a heating rate of 10°C / min. Dry air was used as the atmosphere, 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).

[0079] (Primary particle size of metal oxide nanoparticles) Metal oxide nanoparticles dispersed in a solvent were photographed at a magnification of 200,000x using a transmission electron microscope (JEOL Ltd., model name: JEM-2010F). The primary particle size was determined by measuring the particle size of 100 particles from the captured image using software (product name: Image J) and calculating the average.

[0080] (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 (Zetasizer nano, Malvern).

[0081] (Evaluation of Solar Cell Characteristics) The photovoltaic conversion characteristics of the fabricated photovoltaic conversion element were measured by a method conforming to the output measurement method of silicon crystalline solar cells in JIS C8913:1998. The results are shown in Table 1. Specifically, a solar simulator (Spectra Instruments Co., Ltd. model SMO-250III) combined with an air mass filter equivalent to AM1.5G was adjusted to a light intensity of 100 mW / cm² using a secondary reference Si solar cell as the measurement light source. While irradiating the test sample of the perovskite solar cell (the photovoltaic conversion element of Example 1) with light, the I-V curve characteristics were measured using a source meter (Keithley Instruments Inc., model 2400 general-purpose source meter). 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.

[0082] 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 )

[0083] Here, as the evaluation of solar cell characteristics, those that do not operate as a battery are rated as "D", those with a maximum photovoltaic conversion efficiency of 12% or more but with variations are rated as "C", those with a maximum photovoltaic conversion efficiency stably at 12% or more are rated as "B", and those with a maximum photovoltaic conversion efficiency stably at 15% or more are rated as "A".

[0084]

[0085]

[0086] 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 "D". In Comparative Example 2, the ratio A / B of the weight of the coating compound A to the weight of the metal oxide fine particles B was less than 0.001, and it 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 "D". In Comparative Example 3, the ratio A / B of the weight of the coating compound A to the weight of the metal oxide fine particles B exceeded 0.2, and it 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 "D".

[0087] In Examples 1-18 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, achieving a solar cell performance of "C" or higher, which was superior to that of Comparative Examples 1-3. In particular, in Examples 1, 4, and 7-9 of the present invention, the solar cell performance was "B," and in Examples 2, 3, 5, and 6, the solar cell performance was "A," confirming particularly excellent solar cell performance.

[0088] 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 fine particles, wherein 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.

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 groups, alkoxy groups, acyl groups, carboxyl groups, phosphoryl groups, sulfo groups, 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 metal oxide is tin oxide.

5. 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 4 are dispersed in an organic solvent having an acid dissociation constant of 15.1 or higher.

6. The metal oxide fine particle dispersion according to claim 5, 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.

7. The metal oxide fine particle dispersion according to claim 5, characterized in that the water content is 100 mass ppm or less.

8. A method for producing surface-coated metal oxide fine particles according to any one of claims 1 to 4, comprising a surface treatment step of coating the surface of the metal oxide fine particles with a coating compound, wherein the surface treatment step is carried out under reduced pressure of 5 × 10⁴ Pa or less and at a temperature of 0°C to 200°C, and the generated water is removed.

9. The method for producing surface-coated metal oxide fine particles according to claim 8, characterized in that excess coating compound that was not adsorbed on the surface of the metal oxide fine particles is removed.

10. 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 5.

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