Conductive film and method for manufacturing the same

Abstract

To provide: a conductive film that is excellent in conductivity and can be stably deposited even on a surface of an organic material; and a method for manufacturing the conductive film.SOLUTION: A conductive film includes tin oxide nanoparticles 21 and tin hydroxide 24, and a proportion of tin hydroxide is in a range of 0.01-0.15 in terms of weight ratio. The tin hydroxide 24 is preferably present so as to fill a cavity between the tin oxide nanoparticles 21. The tin hydroxide 24 is preferably present on a tin oxide nanoparticle layer formed by lamination of the tin oxide nanoparticles 21.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This invention relates to a conductive film and a method for manufacturing the conductive film.

Background Art

[0002] Tin oxide particles are used as a conductive film for antistatic agents, electron transport layers of solar cells, etc. For example, in the electron transport layer of a perovskite solar cell, a tin oxide particle laminated film formed using a tin oxide particle dispersion is used. However, in a conductive film produced using a tin oxide particle dispersion, a decrease in conductivity due to interfacial resistance between tin oxide particles, interfacial resistance on the surface of the conductive film, and interfacial resistance caused by voids between particles cannot be avoided. Note that while film formation by coating a tin oxide particle dispersion is easy, it is generally less conductive than a sputtered film.

[0003] On the other hand, as described in Patent Document 1, it is possible to form a conductive film by a method other than coating and drying a particle dispersion using tin alkoxide, but a high-energy process such as MOCVD is required for film formation. In order to produce a highly conductive conductive film from such an organotin compound, it is necessary to convert it to crystalline tin oxide. Referring to the crystallization of tin oxide by the coprecipitation method shown in Patent Document 2, it is necessary to heat up to about 600 ° C to obtain crystalline tin oxide from tin hydroxide or tin alkoxide.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, for example, when forming a conductive film as an electron transport layer of a perovskite solar cell, since the perovskite solar cell is formed on a substrate made of a material with low heat resistance such as an organic film or an organometallic compound, it was not possible to form a conductive film using the above-described tin alkoxide. Further, for example, when forming a conductive film as an electron transport layer of a perovskite solar cell, it is required to have even better conductivity.

[0006] The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a conductive film that is excellent in conductivity and can be stably formed on the surface of an organic material, and a method for manufacturing the conductive film.

Means for Solving the Problems

[0007] As a result of intensive studies by the present inventors to solve the above problems, it has been found that by coating a tin oxide nanoparticle dispersion liquid and a tin alkoxide solution and drying this, a conductive film excellent in conductivity can be formed.

[0008] The conductive film of Aspect 1 of the present invention is based on the above finding, and has tin oxide nanoparticles and tin hydroxide, and the ratio of the tin hydroxide is in the range of 0.01 or more and 0.15 or less by weight ratio. According to the conductive film of Aspect 1 of the present invention, since it has tin oxide nanoparticles and tin hydroxide, and the ratio of the tin hydroxide is in the range of 0.01 or more and 0.15 or less by weight ratio, the tin hydroxide reduces the interfacial resistance between the tin oxide nanoparticles, the interfacial resistance on the surface of the conductive film, and the interfacial resistance caused by the voids between the tin oxide nanoparticles, and is excellent in conductivity.

[0009] The conductive film of Aspect 2 of the present invention is characterized in that, in the conductive film of Aspect 1 of the present invention, the tin hydroxide is present so as to fill the voids between the tin oxide nanoparticles. According to the conductive film of Embodiment 2 of the present invention, since the tin hydroxide is present so as to fill the gaps between the tin oxide nanoparticles, the interfacial resistance due to the gaps between the tin oxide nanoparticles is surely lowered by the amorphous tin hydroxide, and the conductivity is particularly excellent.

[0010] The conductive film of Embodiment 3 of the present invention is characterized in that, in the conductive film of Embodiment 1 or Embodiment 2 of the present invention, the tin hydroxide is present on the tin oxide nanoparticle layer formed by laminating the tin oxide nanoparticles. According to the conductive film of Embodiment 3 of the present invention, since the tin hydroxide is present on the tin oxide nanoparticle layer formed by laminating the tin oxide nanoparticles, the interfacial resistance on the surface of the conductive film is surely lowered, and the conductivity is particularly excellent.

[0011] The conductive film of Embodiment 4 of the present invention is characterized in that, in any one of the conductive films of Embodiments 1 to 3 of the present invention, the primary particle diameter of the tin oxide nanoparticles is in the range of 1.5 nm or more and 10.0 nm or less. According to the conductive film of Embodiment 4 of the present invention, since the primary particle diameter of the tin oxide nanoparticles is in the range of 1.5 nm or more and 10.0 nm or less, a relatively thin and highly conductive film can be obtained.

[0012] The conductive film of Embodiment 5 of the present invention is characterized in that, in any one of the conductive films of Embodiments 1 to 4 of the present invention, the tin oxide nanoparticles are doped with a hetero element. According to the conductive film of Embodiment 5 of the present invention, since the tin oxide nanoparticles are doped with a hetero element, the characteristics of the tin oxide nanoparticles can be adjusted, and a conductive film according to the required characteristics can be obtained.

[0013] The conductive film of Embodiment 6 of the present invention is characterized in that, in the conductive film of Embodiment 5 of the present invention, the hetero element is one or more selected from antimony, fluorine, and phosphorus. According to the conductive film of Aspect 6 of the present invention, since the different element is one or more selected from antimony, fluorine, and phosphorus, the characteristics of the tin oxide nanoparticles can be adjusted, and a conductive film according to required characteristics can be obtained.

[0014] The method for manufacturing a conductive film according to Aspect 7 of the present invention is a method for manufacturing a conductive film for manufacturing any one of the conductive films of Aspects 1 to 6 of the present invention, and includes a coating step of coating a tin alkoxide or a tin aminoalkoxide and a tin oxide nanoparticle dispersion liquid, and a heating step of heating the coated tin alkoxide or the tin aminoalkoxide and the tin oxide nanoparticle dispersion liquid at a temperature of 200°C or lower. According to the method for manufacturing a conductive film of Aspect 7 of the present invention, since a tin alkoxide or a tin aminoalkoxide and a tin oxide nanoparticle dispersion liquid are coated and heated at a temperature of 200°C or lower, sufficient conductivity can be ensured even when drying and firing are performed under low-temperature conditions, and it becomes possible to stably form a conductive film on the surface of an organic material.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a conductive film excellent in conductivity and capable of stably forming a film on the surface of an organic material, and a method for manufacturing the conductive film.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0017] Hereinafter, a conductive film according to an embodiment of the present invention and a method for manufacturing the conductive film will be described with reference to the accompanying drawings. Note that each of the embodiments shown below is specifically described to better understand the gist of the invention, and does not limit the present invention unless otherwise specified.

[0018] The conductive film 20 according to an embodiment of the present invention is used, for example, as an electron transport layer of the perovskite solar cell shown in FIG. 1. In the present 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 (conductive film 20), and a back electrode 16 are laminated on the surface of a substrate 11, as shown in FIG. 1 for example. In the conductive film 20 constituting the electron transport layer 15, the film thickness is in the range of 10 nm or more and 100 nm or less.

[0019] Here, in the present embodiment, the substrate 11 is a transparent substrate made of an organic material. Therefore, in the conductive film 20 according to the present embodiment, it is possible to stably form a film on the substrate 11 made of an organic material, and as the electron transport layer 15, it is required to be particularly excellent in conductivity.

[0020] Therefore, in the conductive film 20 according to the present embodiment, as shown in FIG. 2, it has tin oxide nanoparticles 21 and tin hydroxide 24, and the ratio of tin hydroxide 24 is in the range of 0.01 or more and 0.15 or less by weight ratio. Note that, in the conductive film 20, the lower limit of the ratio of tin hydroxide 24 is preferably 0.02 or more, and more preferably 0.03 or more. On the other hand, the upper limit of the ratio of tin hydroxide 24 in the conductive film 20 is preferably 0.10 or less, and more preferably 0.05 or less.

[0021] In the present embodiment, as shown in FIG. 2, the structure is such that tin oxide nanoparticles 21 are dispersed in the mother phase of tin hydroxide 24, and tin hydroxide 24 exists so as to fill the gaps between the tin oxide nanoparticles 21. Note that, in the present embodiment, the conductive film 20 is composed of tin oxide nanoparticles 21 and tin hydroxide 24. Further, in the present embodiment, tin hydroxide 24 is preferably amorphous.

[0022] Here, in the conductive film 20 according to the present embodiment, the primary particle diameter of the tin oxide nanoparticles 21 is preferably in the range of 1.5 nm or more and 10.0 nm or less. Note that the lower limit of the primary particle diameter of the tin oxide nanoparticles 21 is preferably 1.6 nm or more, and more preferably 1.8 nm or more. On the other hand, the upper limit of the primary particle diameter of the tin oxide nanoparticles 21 is preferably 5 nm or less, and more preferably 3 nm or less.

[0023] Further, in the conductive film 20 according to the present embodiment, the tin oxide nanoparticles 21 may be doped with a foreign element other than Sn and O. Note that the content of the foreign element is preferably in the range of 10000 mass ppm or more and 100000 mass ppm or less. Note that, as the foreign element to be doped, it is preferable to use one or more selected from antimony, fluorine, and phosphorus.

[0024] Next, the manufacturing method of the conductive film according to the present embodiment will be described with reference to the flowcharts of FIGS. 3 to 5. In the manufacturing method of the conductive film according to the present embodiment, as shown in FIG. 3, it includes a tin oxide nanoparticle dispersion preparation step S01, a tin alkoxide solution preparation step S02, a liquid mixing step S03, a coating step S04, and a heating step S05.

[0025] (Tin Oxide Nanoparticle Dispersion Preparation Step S01) First, the tin oxide nanoparticle dispersion preparation step S01 will be described with reference to the flowchart of FIG. 4. In the tin oxide nanoparticle dispersion preparation step S01, as shown in FIG. 4, a raw material suspension generation step S11, a raw material solution generation step S12, and a synthesis step S13 are provided.

[0026] In the raw material suspension generation step S11, tin(IV) chloride pentahydrate is dissolved in ion-exchanged water to produce an acid solution. Also, potassium stannate trihydrate is dissolved in ion-exchanged water to produce a base solution. The acid solution is dropped into this base solution and allowed to stand to produce a raw material suspension. In this raw material suspension generation step S11, it is preferable to mix while stirring within a range where the dropping rate is 15 mL / min or more and 100 mL / min or less. 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, performing liquid mixing in a flow path using a jet flow), it becomes possible to arrange anions derived from stannate ions on the particle surface. Also, it is preferable that the standing time is within a range of 1 day or more and 14 days or less.

[0027] In the raw material solution generation step S12, ammonia water is added to the raw material suspension obtained in the raw material suspension generation step S11 to produce a raw material solution. In this raw material solution generation step S12, it is preferable that the ammonia concentration in the added ammonia water is within a range of 0.2 mass% or more and 28 mass% or less.

[0028] In the synthesis step S13, the raw material solution obtained in the raw material solution generation step S12 is placed in a sealed container and heat-treated to produce a tin oxide nanoparticle dispersion. Here, it is preferable that the synthesis temperature T in the synthesis step S13 is within a range of 20°C or more and 280°C or less, the synthesis time H is within a range of 0.1 hour or more and 120 hours or less, and the product of the synthesis temperature T and the synthesis time H, T×H, is within a range of 20 or more and 8000 or less.

[0029] (Tin alkoxide solution preparation step S02) Next, the tin alkoxide solution preparation step S02 will be described with reference to the flowchart of FIG. 5. In the tin alkoxide solution preparation step S02, as shown in FIG. 5, a raw material preparation step S21, a dissolution step S22, and a precipitate removal step S23 are provided.

[0030] In the raw material preparation step S21, a tin raw material (a compound containing tin) and an alkoxide raw material are prepared. Here, as the alkoxide raw material, one containing an alkali metal is used. Here, as the tin raw material, tin(IV) chloride pentahydrate, tin(IV) chloride anhydride, tin(II) chloride dihydrate, tin(II) chloride anhydride, etc. can be used. Further, as the alkoxide raw material, sodium methoxide, sodium ethoxide, sodium isopropoxide, potassium methoxide, potassium ethoxide, lithium ethoxide, etc. can be used.

[0031] In the dissolution step S22, the above-mentioned tin raw material (a compound containing tin) and alkoxide raw material weighed at a predetermined ratio are added to a solvent and dissolved, and then left standing for a certain period of time. The standing time is preferably in the range of 12 hours or more and 168 hours or less. At this time, the tin raw material and the alkoxide raw material containing an alkali metal react to form tin alkoxide.

[0032] In the precipitate removal step S23, the precipitate is removed from the standing solution to recover the supernatant (liquid component). Thereby, the tin alkoxide solution according to the present embodiment can be obtained.

[0033] (Liquid mixing step S03) The tin oxide nanoparticle dispersion and the tin alkoxide solution obtained as described above are mixed at a predetermined ratio to obtain a mixed raw material liquid. At this time, the solid content concentration in the mixed raw material liquid is adjusted to be in the range of 3 mass% or more and 25 mass% or less. Note that the solid content concentration in the mixed raw material liquid is preferably 4 mass% or more, more preferably 5 mass% or more. Also, the solid content concentration in the mixed raw material liquid is preferably 22 mass% or less, more preferably 18 mass% or less.

[0034] (Coating step S04) Next, the mixed raw material liquid is applied onto the substrate. Although there is no particular limitation on the coating method, in this embodiment, the mixed raw material liquid is coated onto the substrate by a spin coater. In the coating step S04, when coating with a spin coater, the spin coating conditions are preferably within a range of 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. Also, the thickness of the coating film is preferably within a range of 10 nm or more and 100 nm or less.

[0035] (Heating step S05) Next, the coating film (the coated tin oxide nanoparticle dispersion and the tin alkoxide solution) is heated to remove the solvent, and drying and firing are performed to form a conductive film. The heating conditions in this heating step S05 are preferably within a range of a heating temperature of 15°C or more and 200°C or less, and a heating time of 1 minute or more and 120 minutes or less.

[0036] Through the above-described respective steps, the conductive film 20 according to this embodiment is formed.

[0037] According to the conductive film 20 of this embodiment configured as described above, since it is composed of tin oxide nanoparticles 21 and amorphous tin hydroxide 24, the interface resistance between the tin oxide nanoparticles 21, the interface resistance on the surface of the conductive film 20, and the interface resistance caused by the voids between the tin oxide nanoparticles 21 are low due to the tin hydroxide 24, and it has excellent conductivity.

[0038] In the conductive film 20 according to this embodiment, as shown in FIG. 2, when tin hydroxide 24 exists so as to fill the gaps between the tin oxide nanoparticles 21, the interface resistance caused by the gaps between the tin oxide nanoparticles 21 is surely reduced by the tin hydroxide 24, and the conductivity is particularly excellent.

[0039] In the conductive film 20 according to this embodiment, when the primary particle diameter of the tin oxide nanoparticles 21 is in the range of 1.5 nm or more and 10.0 nm or less, a relatively thin and highly conductive conductive film can be obtained.

[0040] In the conductive film 20 according to this embodiment, when the tin oxide nanoparticles 21 are doped with a foreign element, the characteristics of the tin oxide nanoparticles 21 can be adjusted, and the conductive film 20 can be made to meet the required characteristics. Here, when the foreign element is one or more selected from antimony, fluorine, and phosphorus, it is possible to form a conductive film 20 having particularly excellent conductivity.

[0041] According to the method for manufacturing the conductive film 20 of this embodiment, since it includes a liquid mixing step S03 of mixing a tin oxide nanoparticle dispersion liquid and a tin alkoxide solution to obtain a mixed raw material liquid, a coating step S04 of coating the mixed raw material liquid, and a heating step S05 of heating the coated mixed raw material liquid, sufficient conductivity can be ensured even when drying and firing are performed under low-temperature conditions, and it becomes possible to stably form a conductive film on the surface of an organic material.

[0042] As described above, one embodiment of the present invention has been described, but the present invention is not limited to this, and can be appropriately modified without departing from the technical idea of the invention. In this embodiment, the conductive film has been described as constituting the electron transport layer of the perovskite solar cell shown in FIG. 1, but it may be used for other applications not limited to this.

[0043] Furthermore, in the present embodiment, as shown in FIG. 2, the structure is such that tin oxide nanoparticles 21 are dispersed in the matrix phase of tin hydroxide 24, and although it has been described that tin hydroxide 24 exists so as to fill the gaps between the tin oxide nanoparticles 21, it is not limited thereto. For example, as shown in FIG. 6, amorphous tin hydroxide 24 may exist on a tin oxide nanoparticle layer 22 formed by laminating tin oxide nanoparticles 21. Also, the structure shown in FIG. 2 and the structure shown in FIG. 6 may be mixed.

[0044] Here, in the conductive film 20 shown in FIG. 6, as shown in the flowchart shown in FIG. 7, a first coating step S101 of coating a tin oxide nanoparticle dispersion, a second coating step S102 of coating a tin alkoxide solution so as to laminate the coated tin oxide nanoparticle dispersion, and a heating step S103 of heating the coated tin oxide nanoparticle dispersion and the tin alkoxide solution can form a film.

Example

[0045] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0046] (Example 1 of the present invention) 0.86 g of tin(IV) chloride pentahydrate was dissolved in 5.27 g of ion-exchanged water (solution A). Also, 1.00 g of potassium stannate trihydrate was dissolved in 5 g of ion-exchanged water (solution B). Solution B was dropped into solution A at a rate of 5 mL / min and left standing for 3 days to obtain a raw material suspension. The raw material suspension was centrifuged (18,000 rpm, 60 min) to remove the supernatant water. 9 mL of acetic acid was added to the obtained tin oxide paste to obtain a transparent dispersion. After adding 2 g of molecular sieves (3A) to this dispersion to remove the moisture contained in the paste, it was sealed in an autoclave and heated at 250°C for 2 hours to obtain a transparent tin oxide acetic acid dispersion.

[0047] Also, 0.74 g of sodium ethoxide was weighed and dissolved in 10 mL of ethanol (Solution C). Also, 0.74 g of tin(IV) chloride was weighed and dissolved in 10 mL of ethanol (Solution D). Solution C was added dropwise to Solution D, and after standing, the precipitate was removed to prepare a tin(IV) ethoxide ethanol solution.

[0048] (Film formation of conductive film) 10 g of tin oxide acetic acid dispersion and 2 g of tin(IV) ethoxide ethanol solution were mixed to obtain a mixed raw material solution. This mixed raw material solution was spin-coated on a 50 mm × 50 mm glass substrate using a spin coater (manufactured by Mikasa Co., Ltd., model name: MS-A150) under the conditions of 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 conductive film.

[0049] (Examples 2 - 7 of the present invention, Comparative Examples 1 and 2) Conductive films of Examples 2 - 7 of the present invention and Comparative Examples 1 and 2 were obtained by the same procedure as in Example 1 of the present invention. At this time, the ratio of tin hydroxide was adjusted by changing the mixing ratio of the tin oxide acetic acid dispersion and the tin(IV) ethoxide ethanol solution. In Example 5 of the present invention, antimony(III) chloride was added to Solution A, and then Solution B was added dropwise to Solution A to dope Sb. In Example 6 of the present invention, phosphorus trichloride was added to Solution A, and then Solution B was added dropwise to Solution A to dope P. Furthermore, in Example 7 of the present invention, tin(IV) fluoride was added to Solution A, and then Solution B was added dropwise to Solution A to dope F.

[0050] For Examples 1 - 7 of the present invention and Comparative Examples 1 and 2 obtained as described above, each item was evaluated by the following methods.

[0051] (Primary particle size of tin oxide nanoparticles) Regarding the tin oxide nanoparticles in the conductive film, photographs were taken at a magnification of 200,000 times using a transmission electron microscope (manufactured by JEOL Ltd., model name: JEM - 2010F). The particle size of 100 particles in the captured image was measured by software (product name: Image J), and the average was calculated to obtain the result.

[0052] (Ratio of tin hydroxide) 10 mg of the above conductive film was weighed, and thermogravimetric measurement was performed using a thermogravimetric analyzer (TG-DTA STA2500 manufactured by Netzsch) under the conditions of a temperature range of 20 to 600 °C, a heating rate of 10 °C / min, and an argon atmosphere. From the results, the ratio X of tin hydroxide in the conductive film was calculated by the following formula. Note that the weight loss rate when all the materials in the conductive film are tin hydroxide is 19.3%. X = c / 19.3 c = 1 - a / b Residual thermogravimetric rate at 600 °C: a Residual thermogravimetric rate at 100 °C: b Weight loss rate from 100 °C to 600 °C: c

[0053] (Conductivity of the conductive film) For the conductive film obtained as described above, the resistance was measured using a surface resistance meter (product number: Loresta AP, probe: ASP probe (four needles), manufactured by Mitsubishi Chemical Corporation).

[0054]

Table 1

[0055] In Comparative Example 1, the ratio of tin hydroxide in the conductive film was as low as 0.001, and the electrical resistance value of the formed conductive film increased. In Comparative Example 2, the ratio of tin hydroxide in the conductive film was as high as 0.250, and the electrical resistance value of the formed conductive film was too large to be measured. On the other hand, in Invention Examples 1 to 7 in which the ratio of tin hydroxide in the conductive film was within the scope of the present invention, the electrical resistance value was sufficiently low and the conductivity was excellent.

[0056] As described above, according to the present invention, it has been confirmed that it is possible to provide a conductive film having excellent conductivity and capable of being stably formed on the surface of an organic material, and a method for manufacturing the conductive film.

Claims

1. A conductive film comprising tin oxide nanoparticles and tin hydroxide, the ratio of the tin hydroxide being in the range of 0.01 to 0.15 in weight ratio.

2. 2. The conductive film according to claim 1, wherein the tin hydroxide is present so as to fill gaps between the tin oxide nanoparticles.

3. 2. The conductive film according to claim 1, wherein the tin hydroxide is present on a tin oxide nanoparticle layer formed by stacking the tin oxide nanoparticles.

4. 2. The conductive film according to claim 1, wherein the primary particle diameter of the tin oxide nanoparticles is within a range of 1.5 nm to 10.0 nm.

5. The conductive film according to claim 1 , wherein the tin oxide nanoparticles are doped with a different element.

6. 6. The conductive film according to claim 5, wherein the different element is one or more elements selected from the group consisting of antimony, fluorine and phosphorus.

7. A method for producing the conductive film according to any one of claims 1 to 6, comprising the steps of: A method for producing a conductive film, comprising: a coating step of coating a tin alkoxide or tin aminoalkoxide and a tin oxide nanoparticle dispersion; and a heating step of heating the coated tin alkoxide or tin aminoalkoxide and the tin oxide nanoparticle dispersion at a temperature of 200°C or lower.

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