Titanium oxide powder, titanium oxide dispersion, and method for producing a titanium oxide film

Abstract

The present invention provides titanium oxide powder, titanium oxide dispersion, and a method for producing a titanium oxide film, all of which exhibit particularly excellent conductivity. [Solution] The color of the powder is L * a * b * In the color space, L * If the range is between 50 and 85, a * If the value is within the range of -5.00 or more and -1.95 or less, b * The present invention is characterized by having a pH within the range of -20 to -5. The present invention is characterized by comprising a coating step of coating a titanium oxide dispersion in which the titanium oxide powder of the present invention is dispersed in a dispersion medium. It is preferable that the titanium oxide is co-doped with a pentavalent metal and a trivalent metal. It is preferable that the pentavalent metal is niobium. It is preferable that the trivalent metal is a metallic element of the third period of the periodic table.

Description

Technical Field

[0001] The present invention relates to, for example, titanium oxide powder, a titanium oxide dispersion liquid used when forming a conductive film, and a method for manufacturing a titanium oxide film.

Background Art

[0002] Since titanium oxide has relatively good conductivity, it is used as a conductive material such as an antistatic agent, an electron transport layer of a solar cell, and a conductive layer in various devices. Here, in the above-mentioned titanium oxide, in order to further improve conductivity, for example, in Patent Document 1, titanium oxide doped with niobium has been proposed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, for example, in the electron transport layer of a perovskite solar cell, further improvement in conductivity is required. For this reason, as the titanium oxide constituting the electron transport layer, one having excellent conductivity more than ever is required.

[0005] This invention has been made in view of the above-described circumstances, and an object thereof is to provide a titanium oxide powder, a titanium oxide dispersion liquid, and a method for manufacturing a titanium oxide film that are particularly excellent in conductivity.

Means for Solving the Problems

[0006] In order to solve the above problems, as a result of intensive studies by the present inventors, in niobium-doped titanium oxide, in order to generate free electrons and improve conductivity, it is necessary to dope a pentavalent metal (niobium). However, since it mainly contains tetravalent titanium as a metal element, even if a pentavalent metal (niobium) is added to titanium oxide, the pentavalent metal (niobium) becomes stable, so there is a possibility that sufficient free electrons cannot be generated. Therefore, by adding a trivalent metal element together with the pentavalent metal (niobium), it was found that the pentavalent metal (niobium) can be stably doped and the conductivity is improved. In the titanium oxide in which the pentavalent metal (niobium) is sufficiently doped in this way, the plasma frequency becomes shorter and it exhibits blue color.

[0007] The titanium oxide powder of Aspect 1 of the present invention is made based on the above findings, and the color of the powder is L * a * b * In the color space, L * is in the range of 50 or more and 85 or less, a * is in the range of -5.00 or more and -1.95 or less, and b * is in the range of -20 or more and -5 or less.

[0008] According to the titanium oxide powder of Aspect 1 of the present invention, the color of the powder is L * a * b * In the color space, L * is in the range of 50 or more and 85 or less, a * is in the range of -5.00 or more and -1.95 or less, and b * is in the range of -20 or more and -5 or less, so it exhibits blue color. Such titanium oxide powder is sufficiently doped with a pentavalent metal, sufficient free electrons are generated, and it has excellent conductivity.

[0009] The titanium oxide powder of Aspect 2 of the present invention is characterized in that in the titanium oxide powder of Aspect 1 of the present invention, a pentavalent metal and a trivalent metal are co-doped in the titanium oxide. According to the titanium oxide powder of embodiment 2 of the present invention, since the titanium oxide is co-doped with a pentavalent metal and a trivalent metal, the pentavalent metal is stably doped, making it possible to reliably improve the conductivity of the titanium oxide powder.

[0010] The titanium oxide powder of embodiment 3 of the present invention is characterized in that, in the titanium oxide powder of embodiment 2 of the present invention, the pentavalent metal is niobium. According to the titanium oxide powder of embodiment 3 of the present invention, since the pentavalent metal doped into the titanium oxide powder is niobium, it is possible to reliably improve the conductivity of the titanium oxide powder.

[0011] The titanium oxide powder of embodiment 4 of the present invention is characterized in that, in the titanium oxide powder of embodiment 2 or embodiment 3 of the present invention, the trivalent metal is a metallic element of the third period of the periodic table. According to the titanium oxide powder of embodiment 4 of the present invention, since the trivalent metal is a metal element of the third period of the periodic table, the pentavalent metal is doped more stably, making it possible to reliably improve the conductivity of the titanium oxide powder.

[0012] The titanium dioxide dispersion of embodiment 5 of the present invention is characterized in that titanium dioxide powder according to any one of embodiments 1 to 4 of the present invention is dispersed in a dispersion medium. According to the titanium oxide dispersion of embodiment 5 of the present invention, since the titanium oxide powder described in any one of embodiments 1 to 4 of the present invention is dispersed in the dispersion medium, a titanium oxide film with particularly excellent conductivity can be formed.

[0013] A method for producing a titanium oxide film according to aspect 6 of the present invention is a method for producing a titanium oxide film, characterized in that it comprises a coating step of coating the titanium oxide dispersion according to aspect 5 of the present invention. According to the method for producing a titanium oxide film of embodiment 6 of the present invention, since it includes a coating step of coating the titanium oxide dispersion of embodiment 5 of the present invention, it can be made of titanium oxide powder with excellent conductivity, and it is possible to form a titanium oxide film with particularly excellent conductivity. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide titanium oxide powder, titanium oxide dispersion, and a method for producing a titanium oxide film, all of which have particularly excellent conductivity. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram illustrating a perovskite solar cell equipped with a titanium oxide film formed using titanium oxide powder, which is an embodiment of the present invention. [Figure 2] This is a flow chart showing an example of a method for producing titanium oxide powder and titanium oxide dispersion, which are embodiments of the present invention. [Figure 3] This is a flow chart showing an example of a method for manufacturing a titanium oxide film, which is an embodiment of the present invention. [Modes for carrying out the invention]

[0016] The following describes embodiments of the present invention, specifically the production methods for titanium oxide powder and titanium oxide films, with reference to the attached drawings. The embodiments described below are provided to better illustrate the spirit of the invention and do not limit the present invention unless otherwise specified.

[0017] The titanium oxide powder, according to an embodiment of the present invention, is used, for example, when forming a titanium oxide film used as a conductive layer. Furthermore, the titanium oxide 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.

[0018] The titanium oxide film constituting the electron transport layer 15 has a film thickness within the range of 10 nm to 100 nm. In this embodiment, the titanium oxide film is required to be a conductive material with excellent conductivity.

[0019] The conductivity of a titanium oxide film depends particularly on the conductivity of the titanium oxide itself that makes up the film. In titanium oxide, it is effective to generate free electrons by stably doping it with a pentavalent metal. Furthermore, in titanium oxide sufficiently doped with a pentavalent metal, the plasma frequency becomes shorter, resulting in a blue color.

[0020] Therefore, in the titanium oxide powder of this embodiment, the color of the powder is L * a * b * In the color space, L * If the range is between 50 and 85, a * If the value is within the range of -5.00 or more and -1.95 or less, b * It is said to be within the range of -20 to -5.

[0021] Here, L * a * b * A color space is a color system that represents the colors of objects, and is defined in JIS Z 8781-4. * a * b * In the color space, brightness is L * , chromaticity which indicates hue and saturation * ,b * It is represented as follows. Lightness L * This indicates brightness, L * A higher value results in a whiter (lighter) color, L * A smaller value results in a darker (blacker) color. chromaticity a * ,b * This indicates the direction of the color, +a * The red direction, -a * It is in the direction of green, and +b* Yellow direction, -b * The blue line indicates the direction.

[0022] In the titanium oxide powder of this embodiment, the brightness L * Since the value is set within the range of 50 to 85, the colors become more vibrant. Also, chromaticity a * If the color temperature is within the range of -5.00 to -1.95, chromaticity b * Since it is within the range of -20 to -5, it will appear blue.

[0023] Note that the brightness L in titanium dioxide powder * It is preferable that the value is 52 or higher, and more preferably 55 or higher. Also, the brightness L in titanium dioxide powder * It is preferable that the value be 80 or less, and more preferably 65 or less. Furthermore, the chromaticity a in titanium dioxide powder * It is preferable that the chromaticity a in titanium dioxide powder be -4.95 or higher, and more preferably -4.90 or higher. * It is preferable that the value is -2.00 or less, and more preferably -3.00 or less. Furthermore, chromaticity b in titanium dioxide powder * It is preferable that the chromaticity b in titanium dioxide powder be -19.00 or higher, and more preferably -18.00 or higher. * It is preferable that it be -7.00 or less, and more preferably -15.00 or less.

[0024] Furthermore, in the titanium oxide powder of this embodiment, it is preferable that the titanium oxide is co-doped with a pentavalent metal and a trivalent metal. Doping titanium oxide with a pentavalent metal generates free electrons, improving its conductivity. Furthermore, co-doping with a trivalent metal along with the pentavalent metal ensures stable doping of the pentavalent metal.

[0025] In this embodiment, the titanium oxide powder is preferably composed of niobium, which is a pentavalent metal. Furthermore, in the titanium oxide powder of this embodiment, it is preferable that the trivalent metal is a metallic element of the third period of the periodic table.

[0026] Next, an example of a method for producing the titanium dioxide powder and titanium dioxide dispersion according to this embodiment will be explained using the flow chart in Figure 2.

[0027] (Raw material suspension generation process S01) A titanium raw material containing tetravalent titanium, a compound containing a trivalent metal, and a compound containing a pentavalent metal are weighed in a predetermined proportion and dissolved in deionized water. Examples of titanium raw materials include titanium(IV) chloride, titanium tetraisopropoxide, and titanium glycolic acid complexes. Examples of compounds containing trivalent metals include titanium(III) chloride, scandium(III) chloride hexahydrate, and yttrium acetate. Furthermore, examples of compounds containing pentavalent metals include niobium(V) chloride, vanadium(V) chloride, and antimony(V) chloride.

[0028] (Heat treatment process S02) The raw material suspension obtained as described above is heat-treated under the following conditions: heating temperature: 70°C to 300°C, holding time at the heating temperature: 0.25 hours to 48 hours. This produces titanium dioxide powder (dark blue titanium dioxide) as described in this embodiment.

[0029] (Dispersion process S03) After the obtained titanium dioxide powder is centrifuged multiple times with alcohol, an inorganic acid is added and ultrasonic irradiation is performed to produce a titanium dioxide dispersion in which the titanium dioxide powder is dispersed in a dispersion medium.

[0030] Next, an example of a method for producing a titanium oxide film (electron transport layer 15) using the titanium oxide dispersion according to this embodiment will be explained using the flow chart in Figure 3.

[0031] (Titanium dioxide concentration adjustment process S11) First, prepare the titanium dioxide dispersion according to this embodiment, and adjust the titanium dioxide concentration in the dispersion so that it is within the range of 0.5 mass% to 5.0 mass%. Furthermore, the titanium dioxide concentration in the titanium dioxide dispersion is preferably 0.6 mass% or higher, and more preferably 0.8 mass% or higher. In addition, the titanium dioxide concentration in the titanium dioxide dispersion is preferably 2.0 mass% or lower, and more preferably 1.5 mass% or lower.

[0032] (Coating process S12) Next, a titanium dioxide dispersion with an adjusted titanium dioxide concentration is applied to the substrate using a spin coating apparatus. In this coating process S12, the spin coating conditions are preferably set to a rotation speed of 200 rpm or more and 2000 rpm or less, and a coating time of 3 seconds or more and 120 seconds or less. Furthermore, the thickness of the coating film is preferably set to a range of 10 nm or more and 100 nm or less.

[0033] (Heating process S13) Next, the coating film (coated titanium oxide dispersion) is heated to remove the dispersion medium and form a titanium oxide film (electron transport layer 15). 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 20 minutes to 180 minutes.

[0034] Through the steps described above, the titanium oxide film (electron transport layer 15) of this embodiment is formed. In this embodiment, the titanium oxide film (electron transport layer 15) has an average film thickness within the range of 10 nm to 100 nm.

[0035] According to the titanium oxide powder of this embodiment, which has the above configuration, the color of the powder is L * a * b * In the color space, L * If the range is between 50 and 85, a * If the value is within the range of -5.00 or more and -1.95 or less, b * Since the ion is within the range of -20 to -5, it will exhibit a blue color. Such titanium oxide powder is sufficiently doped with pentavalent metal, generates a sufficient amount of free electrons, and has excellent conductivity.

[0036] In the titanium oxide powder of this embodiment, when a pentavalent metal and a trivalent metal are co-doped into the titanium oxide, the pentavalent metal is stably doped, making it possible to reliably improve the conductivity of the titanium oxide powder.

[0037] In the titanium oxide powder of this embodiment, when the pentavalent metal is niobium, it is possible to reliably improve the conductivity of the titanium oxide powder.

[0038] In the titanium oxide powder of this embodiment, if the trivalent metal is a metal element of the third period of the periodic table, the pentavalent metal becomes even more stable in doping, making it possible to reliably improve the conductivity of the titanium oxide powder.

[0039] According to the titanium dioxide dispersion of this embodiment, since the titanium dioxide powder of this embodiment is dispersed in the dispersion medium, it is possible to form a titanium dioxide film with particularly excellent conductivity.

[0040] The method for manufacturing a titanium oxide film according to this embodiment includes a coating step S12 in which the titanium oxide dispersion according to this embodiment is applied, making it possible to form a titanium oxide film with particularly excellent conductivity.

[0041] 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 titanium oxide film is 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]

[0042] The verification experiments conducted to confirm the effectiveness of the present invention will be described.

[0043] (Titanium dioxide powder) As shown in Table 1, titanium raw materials containing tetravalent titanium, compounds containing trivalent metals (trivalent metal compounds), and compounds containing pentavalent metals (pentavalent metal compounds) were weighed and dissolved in 15 mL of deionized water. The obtained raw material suspension was sealed in an autoclave having an inner cylinder made of a fluorine compound and heat-treated under the conditions shown in Table 1. This yielded titanium oxide powders for Examples 1-6 and Comparative Examples 1 and 2 of the present invention.

[0044] (Titanium oxide film) The titanium dioxide powder described above was centrifuged three times with methanol-modified alcohol, and then 30 mL of 0.1 mol / L hydrochloric acid was added and ultrasonic irradiation was performed to obtain a titanium dioxide dispersion. The titanium dioxide concentration in this titanium dioxide dispersion was adjusted to 1.0 mass%, and a coating film was formed by spin-coating it onto a 50 mm x 50 mm glass substrate using a spin coater (Mikasa Corporation, model name: MS-A150) at 800 rpm for 60 seconds. A titanium oxide film was formed on a glass substrate with a coated film by heating it on a hot plate at 120°C for 3 minutes.

[0045] Then, the titanium oxide powders and titanium oxide films of Examples 1 to 6 and Comparative Examples 1 and 2 obtained as described above were evaluated for each item using the following method.

[0046] (Color of titanium dioxide powder) The color of the obtained titanium dioxide powder was evaluated using a color meter (SM-T, manufactured by Suga Test Instruments Co., Ltd.). The powder is sealed in a 15mm diameter aperture, and light from a D65 light source is shone at a 10° angle. The L of the powder is then measured from the reflected light. * a * , b * The result was calculated.

[0047] (Conductivity of titanium oxide film) The titanium oxide film obtained as described above was subjected to resistance testing using a surface resistance meter (model number: Loresta AP MCP-T400, probe: ASP probe (four-needle), manufactured by Mitsubishi Chemical Corporation).

[0048] [Table 1]

[0049] [Table 2]

[0050] In Comparative Example 1, the powder was not doped with trivalent metal, and the color of the powder was L * a * b * In the color space, L * ga 92.62, a * -1.78, b * The value was -3.18, and it did not exhibit a blue color. Furthermore, the resistance value of the deposited titanium oxide film was 7.11 × 10⁻⁶. 7 It had a high impedance of Ω, indicating poor conductivity. In Comparative Example 2, the powder was not doped with a pentavalent metal, and the color of the powder was L * a * b * In the color space, L * 88.26, a * -1.64, b * The value was -4.69, and it did not exhibit a blue color. Furthermore, the resistance value of the deposited titanium oxide film was 6.33 × 10⁻⁶. 7 It had a high impedance of Ω, indicating poor conductivity.

[0051] In contrast, in Examples 1 to 6 of the present invention, the color of the powder is L * a * b * In the color space, L * If the range is between 50 and 85, a * If the value is within the range of -5.00 or more and -1.95 or less, b * The value was within the range of -20 to -5, and was blue in color. The resistivity of the deposited titanium oxide film is 1.69 × 10⁻⁶. 7 It had a low impedance of less than ohms and excellent conductivity.

[0052] As described above, it has been confirmed that the present invention can provide titanium oxide powder with particularly excellent conductivity and a method for producing a titanium oxide film.

Claims

1. The color of the powder is L ＊ a ＊ b ＊ In the color space, L ＊ If the range is between 50 and 85, a ＊ If the value is within the range of -5.00 or more and -1.95 or less, b ＊ Titanium oxide powder characterized in that the temperature is within the range of -20 to -5.

2. The titanium oxide powder according to claim 1, characterized in that titanium oxide is co-doped with a pentavalent metal and a trivalent metal.

3. The titanium oxide powder according to claim 2, characterized in that the pentavalent metal is niobium.

4. The titanium oxide powder according to claim 2, characterized in that the trivalent metal is a metallic element of the third period of the periodic table.

5. A titanium dioxide dispersion characterized in that titanium dioxide powder according to any one of claims 1 to 4 is dispersed in a dispersion medium.

6. A method for producing a titanium oxide film, A method for producing a titanium oxide film, characterized by comprising a coating step of coating the titanium oxide dispersion described in claim 5.

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