Tin oxide particle dispersion and method for producing tin oxide particle laminated film

Abstract

Provided are: a tin oxide particle dispersion in which tin oxide particles are dispersed in a solvent, from which it is possible to form a tin oxide particle laminated film having excellent conductivity as a result of the tin oxide particles being arranged uniformly, and which is characterized by having a zeta potential of -35 mV or less at pH 10; and a method for producing a tin oxide particle laminated film. The tin oxide particles may be doped with a different element. The different element is preferably one or more selected from antimony, fluorine, and phosphorus. The primary particle size of the tin oxide particles is preferably in the range of 1.5-100 nm.

Description

Tin oxide particle dispersion and method for producing tin oxide particle laminated film

[0001] This invention relates to a tin oxide particle dispersion liquid that can be used, for example, when forming a conductive film, and a method for manufacturing a tin oxide particle laminate film using this tin oxide particle dispersion liquid. This application claims priority based on Japanese Patent Application No. 2023-163348, filed on September 26, 2023, the contents of which are incorporated herein by reference.

[0002] Because tin oxide has relatively good electrical conductivity, tin oxide particle laminated films having a structure in which tin oxide particles are laminated are used as conductive materials for conductive layers in various devices. To improve specific properties of tin oxide particle laminated films, materials in which various elements are doped into tin oxide have also been proposed. The above-mentioned tin oxide particle laminated films are formed by coating and drying a tin oxide particle dispersion liquid in which tin oxide particles are dispersed.

[0003] In the above-mentioned tin oxide particle laminate film, the number of contact points between tin oxide particles affects the conductivity. Therefore, it is necessary to form a tin oxide particle laminate film in which tin oxide particles are uniformly arranged. Therefore, for example, Patent Document 1 proposes a film formation technique using spin coating in a gas flow. In Patent Document 1, the vapor pressure is controlled during film formation to adjust the drying rate of the dispersion, thereby forming a uniform tin oxide particle laminate film.

[0004] Japanese Patent Publication No. 64-027667 (A)

[0005] Recently, the application of the above-mentioned tin oxide particle laminated film as, for example, the electron transport layer of perovskite solar cells has been considered. The electron transport layer of perovskite solar cells has a very thin film thickness of the nanometer order, making it even more difficult to form a uniform film with excellent conductivity. Furthermore, with the trend toward smaller size and thinner devices, there is a demand for thin and uniform tin oxide particle laminated films that serve as conductive layers.

[0006] In order to form a uniform tin oxide particle laminate film, it is necessary for the tin oxide particles to be dispersed without agglomeration during the film formation process using a tin oxide particle dispersion. Here, when the applied tin oxide particle dispersion is heated, the dispersant contained in the tin oxide particle dispersion volatilizes, and the tin oxide particles may aggregate. Furthermore, if a nonvolatile dispersant is added, the nonvolatile dispersant may be present between the tin oxide particles, reducing the number of contact points between the tin oxide particles and potentially reducing conductivity.

[0007] The present invention has been made in view of the above-mentioned circumstances, and aims to provide a tin oxide particle dispersion capable of forming a tin oxide particle laminated film having excellent conductivity in which tin oxide particles are uniformly arranged, and a method for producing a tin oxide particle laminated film.

[0008] In order to solve the above problems, the present inventors conducted extensive research and discovered that by keeping the zeta potential of a tin oxide particle dispersion low in a basic solvent, the electrical repulsion between the tin oxide particles increases, allowing the tin oxide particles to be uniformly dispersed without agglomeration, and making it possible to form a tin oxide particle laminated film with excellent conductivity.

[0009] The present invention has been made based on the above findings, and a tin oxide particle dispersion liquid according to Aspect 1 of the present invention is a tin oxide particle dispersion liquid in which tin oxide particles are dispersed in a solvent, and is characterized in that the zeta potential at pH 10 is −35 mV or less.

[0010] According to the tin oxide particle dispersion of Aspect 1 of the present invention, the zeta potential at pH 10 is kept low, at −35 mV or less, so that when this tin oxide particle dispersion is coated, the tin oxide particles are uniformly dispersed without agglomeration. Therefore, even if the dispersant volatilizes when a coating film of the tin oxide particle dispersion is heat-treated, agglomeration of the tin oxide particles is suppressed, and the tin oxide particles are uniformly arranged. Furthermore, there is no need to add a non-volatile dispersant, and the presence of the non-volatile dispersant between the tin oxide particles can be suppressed. Therefore, the number of contact points between the tin oxide particles is ensured, making it possible to form a tin oxide particle laminated film with excellent conductivity.

[0011] A tin oxide particle dispersion liquid of Aspect 2 of the present invention is characterized in that the tin oxide particles are doped with a different element in the tin oxide particle dispersion liquid of Aspect 1. According to the tin oxide particle dispersion liquid of Aspect 2 of the present invention, the tin oxide particles are doped with a different element, which makes it possible to adjust the properties of the tin oxide particles and form a tin oxide particle laminate film that meets required properties.

[0012] A tin oxide particle dispersion liquid of Aspect 3 of the present invention is characterized in that, in the tin oxide particle dispersion liquid of Aspect 2, the different element is one or more elements selected from antimony, fluorine, and phosphorus. According to the tin oxide particle dispersion liquid of Aspect 3 of the present invention, the different element is one or more elements selected from antimony, fluorine, and phosphorus, so that the properties of the tin oxide particles can be adjusted and a tin oxide particle laminate film can be formed according to required properties.

[0013] A tin oxide particle dispersion liquid of Aspect 4 of the present invention is the tin oxide particle dispersion liquid of any one of Aspects 1 to 3, characterized in that the primary particle diameter of the tin oxide particles is in the range of 1.5 nm to 100 nm. According to the tin oxide particle dispersion liquid of Aspect 4 of the present invention, the primary particle diameter of the tin oxide particles is in the range of 1.5 nm to 100 nm, and therefore a tin oxide particle laminated film having a thickness on the order of nanometers can be stably formed.

[0014] A method for producing a tin oxide particle laminate film according to Aspect 5 of the present invention is characterized by including a coating step of applying the tin oxide particle dispersion liquid according to any one of Aspects 1 to 4. The method for producing a tin oxide particle laminate film according to Aspect 5 of the present invention includes a coating step of applying the tin oxide particle dispersion liquid according to any one of Aspects 1 to 4. Because the method for producing a tin oxide particle laminate film according to Aspect 5 of the present invention includes a coating step of applying the tin oxide particle dispersion liquid according to any one of Aspects 1 to 4, the tin oxide particles are uniformly arranged, making it possible to form a tin oxide particle laminate film with excellent conductivity.

[0015] The present invention can provide a tin oxide particle dispersion capable of forming a tin oxide particle laminated film in which tin oxide particles are uniformly arranged and which has excellent electrical conductivity, and a method for producing a tin oxide particle laminated film.

[0016] 1 is a schematic explanatory diagram of a perovskite solar cell provided with a tin oxide particle laminate film according to an embodiment of the present invention; 2 is a flow chart showing an example of a method for producing a tin oxide particle dispersion liquid according to an embodiment of the present invention; 3 is a flow chart showing an example of a method for producing a tin oxide particle laminate film according to an embodiment of the present invention;

[0017] Hereinafter, a tin oxide particle dispersion liquid and a method for producing a tin oxide particle laminate film according to embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following embodiments are specifically described to provide a better understanding of the gist of the invention, and unless otherwise specified, do not limit the present invention.

[0018] A tin oxide particle dispersion according to an embodiment of the present invention is used, for example, in forming a tin oxide particle laminated film used as a conductive layer. The tin oxide particle laminated film according to an embodiment of the present invention is used, for example, as an electron transport layer of a perovskite solar cell shown in Fig. 1. As shown in Fig. 1, a perovskite solar cell 10 has a structure in which an ITO film 12, an electron transport layer 13, a perovskite layer 14, a hole transport layer 15, and a back electrode 16 are laminated on the surface of a glass substrate 11.

[0019] The tin oxide particle laminate film constituting the electron transport layer 13 has a thickness in the range of 10 nm to 100 nm. Therefore, the tin oxide particle dispersion liquid of this embodiment is required to form a thin and precise tin oxide particle laminate film. Furthermore, as a conductive material, the tin oxide particle laminate film is required to have excellent conductivity.

[0020] The conductivity of a tin oxide particle laminate film is greatly affected by the number of contact points between tin oxide particles in the tin oxide particle laminate film. Therefore, in order to improve the conductivity, the tin oxide particle laminate film must be formed so that the tin oxide particles are uniformly arranged. Therefore, in the tin oxide particle dispersion liquid of this embodiment, the zeta potential at pH 10 is set to −35 mV or less.

[0021] Here, we will explain the zeta potential. Metal oxides such as tin oxide have a surface potential when dispersed in water. In this metal oxide aqueous dispersion, the potential of the sliding surface where liquid flow begins in the electric double layer consisting of an ion fixing layer and an ion diffusion layer formed around the metal oxide particles is called the zeta potential. The magnitude of this zeta potential depends on the surface condition of the metal oxide and the pH of the solution, and the value of the zeta potential of tin oxide stabilizes at a pH of 10 or higher.

[0022] Here, a dispersion of tin oxide in water typically has a zeta potential of approximately −35 mV to −25 mV at pH 10. In contrast, the tin oxide particle dispersion of this embodiment is configured, as described above, to have a relatively low zeta potential of −35 mV or less at pH 10. While not particularly limited, the zeta potential at pH 10 may be −40 mV or less or −45 mV or less. Furthermore, while not particularly limited, the zeta potential at pH 10 may be −100 mV or more, −80 mV or more, or −60 mV or more. The solvent may be a polar or nonpolar solvent, such as ethanol, 2-propanol, 1-hexanol, toluene, chlorobenzene, or a mixture thereof. By setting the zeta potential at pH 10 low, the electrical repulsion between the tin oxide particles suppresses aggregation of the tin oxide particles, resulting in uniform dispersion. Therefore, even if the dispersant volatilizes during the heating process of the applied tin oxide particle dispersion and the liquid becomes closer to neutral, the tin oxide particles remain dispersed without agglomerating, even without the use of a non-volatile dispersant, making it possible to coat a uniform film.

[0023] Furthermore, in the tin oxide particle dispersion liquid of this embodiment, the tin oxide particles may be doped with a different element other than Sn and O. The content of the different element is preferably in the range of 10,000 ppm by mass to 100,000 ppm by mass. Although not particularly limited, the content of the different element may be in the range of 20,000 ppm by mass to 90,000 ppm by mass, or in the range of 30,000 ppm by mass to 800,000 ppm by mass. The doped different element is preferably one or more elements selected from antimony, fluorine, and phosphorus.

[0024] Furthermore, in the tin oxide particle dispersion liquid of this embodiment, the primary particle diameter of the tin oxide particles is preferably in the range of 1.5 nm to 100 nm. The primary particle diameter of the tin oxide particles is more preferably 1.8 nm or more, and even more preferably 2.0 nm or more. The primary particle diameter of the tin oxide particles is more preferably 50 nm or less, and even more preferably 10 nm or less.

[0025] Next, an example of a method for producing a tin oxide particle dispersion liquid according to this embodiment will be described with reference to the flow chart of FIG.

[0026] (Raw material suspension generation step S01) A water-soluble alkali metal stannate (potassium stannate trihydrate in this embodiment) is dissolved in ion-exchanged water as a tin raw material to generate a base solution. An acid solution is added dropwise to this base solution and allowed to stand to generate a raw material suspension. In this raw material suspension generation step S01, it is preferable to mix the solution while stirring at a dropping rate in the range of 15 mL / min to 100 mL / min. By increasing the mixing rate of the acid solution and the base solution (increasing the dropping rate, stirring with a stirrer or vortex mixer during mixing, or mixing the solution in a flow path using a jet flow), it becomes possible to arrange stannate ions (derived anions) on the particle surfaces. It is also preferable to set the standing time in the range of 1 day to 14 days.

[0027] (Stock material liquid production step S02) Next, ammonia water is added to the obtained raw material suspension to produce a stock material liquid. In this stock material liquid production step S02, it is preferable that the ammonia concentration in the added ammonia water is in the range of 0.2 mass% to 28 mass%.

[0028] (Synthesis step S03) Next, the raw material solution is placed in a sealed container and heated to produce a tin oxide particle dispersion. Here, in the synthesis step S03, it is preferable to set the synthesis temperature T in the range of 20° C. to 280° C., the reaction time H in the range of 0.1 hours to 120 hours, and the product T×H of the synthesis temperature T and the synthesis time H in the range of 20 to 8000.

[0029] The above-described steps result in the formation of a tin oxide particle dispersion liquid according to this embodiment. This tin oxide particle dispersion liquid has a zeta potential of −35 mV or less at pH 10.

[0030] Next, an example of a method for producing a tin oxide particle laminated film using the tin oxide particle dispersion liquid according to this embodiment will be described with reference to the flow chart of FIG.

[0031] (Solid content concentration adjustment step S11) First, a tin oxide particle dispersion liquid according to this embodiment is prepared, and the solid content concentration in the tin oxide particle dispersion liquid is adjusted using ion-exchanged water so that it falls within the range of 2 mass% to 20 mass%. The solid content concentration in the tin oxide particle dispersion liquid is preferably 5 mass% or more, and more preferably 8 mass% or more. The solid content concentration in the tin oxide particle dispersion liquid is preferably 18 mass% or less, and more preferably 15 mass% or less.

[0032] (Coating step S12) Next, the tin oxide particle dispersion liquid with the adjusted solid content concentration is coated onto a substrate using a spin coater. The spin coating conditions in this coating step S12 are preferably a rotation speed of 500 rpm or more and 3000 rpm or less, and a coating time of 5 seconds or more and 60 seconds or less. The thickness of the coating film is preferably 20 nm or more and 100 nm or less.

[0033] (Heating step S13) Next, the coating film (the coated tin oxide particle dispersion) is heated to remove the solvent and form a tin oxide particle laminate film. The heating conditions in this heating step S13 are preferably a heating temperature in the range of 100° C. to 400° C. and a heating time in the range of 1 minute to 10 minutes.

[0034] The above-described steps result in the formation of a tin oxide particle laminate film according to this embodiment, which has an average film thickness in the range of 10 nm to 100 nm, a standard deviation of the film thickness in the range of 3 nm to 40 nm, and a coefficient of variation CV of the film thickness of 50% or less.

[0035] The tin oxide particle dispersion liquid of this embodiment configured as described above has a low zeta potential of −35 mV or less at pH 10, so that when this tin oxide particle dispersion liquid is coated, the tin oxide particles are uniformly dispersed without agglomeration. Therefore, even if the dispersant volatilizes when a coating film of the tin oxide particle dispersion liquid is heat-treated, agglomeration of the tin oxide particles is suppressed, and the tin oxide particles are uniformly arranged. Furthermore, there is no need to add a non-volatile dispersant, and the presence of the non-volatile dispersant between the tin oxide particles can be suppressed. This ensures the number of contact points between the tin oxide particles, making it possible to form a tin oxide particle laminated film with excellent conductivity.

[0036] Furthermore, in the tin oxide particle dispersion liquid of this embodiment, when the tin oxide particles are doped with a different element, it is possible to form a tin oxide particle laminate film according to the desired characteristics, depending on the type and content of the different element to be doped. Here, when the different element is one or more selected from antimony, fluorine, and phosphorus, it is possible to form a tin oxide particle laminate film with particularly excellent conductivity.

[0037] Furthermore, in the tin oxide particle dispersion liquid of this embodiment, when the primary particle diameter of the tin oxide particles is within the range of 1.5 nm to 100 nm, the tin oxide particles are uniformly dispersed, even when a tin oxide particle laminate film is formed with a thickness on the nanometer order, and it becomes possible to stably form a tin oxide particle laminate film with a uniform thickness.

[0038] The method for producing a tin oxide particle laminate film of this embodiment includes a coating step S12 in which the tin oxide particle dispersion of this embodiment is applied. This makes it possible to form a tin oxide particle laminate film in which the tin oxide particles are uniformly arranged and which has excellent conductivity.

[0039] While 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 tin oxide particle laminated film has been described as constituting the electron transport layer of the perovskite solar cell shown in Figure 1, but the present invention is not limited thereto and may be used for other purposes.

[0040] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0041] (Invention Example) In this invention example, potassium stannate trihydrate was used as the tin raw material (base raw material). A base solution was obtained by dissolving 1.99 g of potassium stannate trihydrate in 10 g of ion-exchanged water. An acid solution containing the acid raw material shown in Table 1 was added dropwise to this base solution at a rate of 1 mL / min, and the mixture was allowed to stand for 3 days to obtain a raw material suspension. 7.0 g of 1.4 mass % ammonia water was added to the raw material suspension to obtain a raw material solution. This raw material solution was placed in a sealed container and heated under the synthesis conditions shown in Table 1 to obtain a tin oxide particle dispersion.

[0042] In Example 10 of the present invention, 0.180 g of antimony (III) chloride was added to the base solution, and then an acid solution was added dropwise to the base solution to dope with Sb. In Example 11 of the present invention, 0.108 g of phosphorus trichloride was added to the base solution, and then an acid solution was added dropwise to the base solution to dope with P. In Example 12 of the present invention, 0.025 g of tin (IV) fluoride was added to the base solution, and then an acid solution was added dropwise to the base solution to dope with F. In Example 13 of the present invention, 0.180 g of antimony (III) chloride and 0.108 g of phosphorus trichloride were added to the base solution, and then an acid solution was added dropwise to the base solution to dope with F and P.

[0043] Comparative Example In this comparative example, tin(IV) chloride pentahydrate was used as the tin raw material (acid raw material). 1.80 g of tin(IV) chloride pentahydrate was dissolved in 5.2 g of ion-exchanged water to obtain an acid solution. A base solution containing the base raw material shown in Table 1 was added dropwise to this acid solution at a rate of 1 mL / min, and the mixture was allowed to stand for 3 days to obtain a raw material suspension. 7.0 g of 1.4 mass% ammonia water was added to the raw material suspension to obtain a raw material solution. This raw material solution was placed in a sealed container and heated under the synthesis conditions shown in Table 1 to obtain a tin oxide particle dispersion.

[0044] (Tin oxide particle laminate film) The above-mentioned tin oxide particle dispersion was diluted with ion-exchanged water to a solids concentration of 8 mass%. The diluted tin oxide particle dispersion was spin-coated onto a 50 mm x 50 mm glass substrate using a spin coater (Mikasa Co., Ltd., model: MS-A150) at 500 rpm for 60 seconds to form a coating film. The glass substrate with the coating film formed thereon was heated on a hot plate at 100°C for 3 minutes to form a tin oxide particle laminate film.

[0045] The tin oxide particle dispersion liquid and the tin oxide particle laminated film obtained as described above were evaluated for various items by the following methods. The evaluation results are shown in Table 1.

[0046] (Zeta potential) The tin oxide dispersion was diluted to 1.0 mass% with ion-exchanged water, and then 0.1 mol / L of hydrochloric acid was added to adjust the pH to 10.0. This was used as a sample, and the zeta potential was measured using a particle size distribution analyzer (Malvern Zetasizer nano). The measurement was performed three times, and the average value was taken as the zeta potential value at pH 10.

[0047] (Primary particle diameter of tin oxide particles) The tin oxide particles dispersed in a solvent were photographed at a magnification of 200,000 times using a transmission electron microscope (manufactured by JEOL Ltd., model name: JEM-2010F). The photographed image was used with software (product name: Image J) to measure the particle diameters of 100 particles and calculate the average.

[0048] (Conductivity of Tin Oxide Particle Laminated Film) The resistance of the tin oxide particle laminated film obtained as described above was measured using a surface resistance measuring device (product number: Loresta AP MCP-T400, probe: ASP probe (four-needle), manufactured by Mitsubishi Chemical Corporation).

[0049]

[0050] In Comparative Example 1, the zeta potential at pH 10 was −31.8 mV, and the electrical resistance of the tin oxide particle laminated film was 6.31×10 ７ In Comparative Example 2, the zeta potential at pH 10 was −33.8 mV, and the electrical resistance of the tin oxide particle laminated film was 4.18×10 ７ The value was high at Ω, indicating poor conductivity.

[0051] In contrast, in Examples 1 to 13 of the present invention, the zeta potential at pH 10 was −35 mV or less, and the electrical resistance of the tin oxide particle laminated film was 9.44×10 ６ The value was low at Ω or less, indicating excellent conductivity.

[0052] As described above, it has been confirmed that the present invention can provide a tin oxide particle dispersion capable of forming a tin oxide particle laminate film in which tin oxide particles are uniformly arranged and which has excellent conductivity, and a method for producing a tin oxide particle laminate film.

[0053] According to the present invention, it is possible to provide a tin oxide particle dispersion capable of forming a tin oxide particle laminated film having excellent electrical conductivity in which tin oxide particles are uniformly arranged, and a method for producing a tin oxide particle laminated film.

Claims

1. A tin oxide particle dispersion liquid in which tin oxide particles are dispersed in a solvent, characterized in that the zeta potential at pH 10 is -35 mV or less.

2. The tin oxide particle dispersion according to claim 1, wherein the tin oxide particles are doped with a different element.

3. The tin oxide particle dispersion liquid according to claim 2, wherein the different element is one or more elements selected from the group consisting of antimony, fluorine and phosphorus.

4. The tin oxide particle dispersion liquid according to claim 1, characterized in that the primary particle diameter of the tin oxide particles is within the range of 1.5 nm to 100 nm.

5. A method for producing a tin oxide particle laminate film, comprising a coating step of coating a tin oxide particle dispersion liquid according to any one of claims 1 to 4.

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