JP2010251310A - Method for preparing carbon paste for screen printing of counter electrode of dye-sensitized solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparing carbon paste for screen printing of an counter electrode of a dye-sensitized solar cell, the carbon paste being capable of preparing a carbon counter electrode on FTO (Fluorine-doped Tin Oxide) glass by screen printing, forming uniform particles, and reducing the film thickness dependency of the counter electrode. <P>SOLUTION: In preparing screen printing carbon paste for a counter electrode of a dye-sensitized solar cell, terpineol is used as a solvent. A carbon counter electrode can be prepared by screen printing using the carbon paste. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode.

(1. Introduction)
In recent years, energy resources have been reviewed due to global warming and fossil fuel reserves, and solar power generation is attracting attention as one of them. Sunlight is inexhaustible, there is no danger of exhaustion like fossil fuels, and there is no increase in CO ₂ . The solar energy that reaches the earth changes to heat on the earth's surface and sea surface, and part of it becomes an energy source that generates wind, waves, and ocean currents. Furthermore, if fossil fuels are of the same quality, solar energy is accumulated in the ground. If there is a technology that can convert 100% of the solar energy that falls on the entire earth, the world's annual energy consumption can be covered in just one hour [Non-Patent Document 1]. From the viewpoint of reducing carbon dioxide, it is also said that a 1 m ² solar cell (assuming a conversion efficiency of 10%) corresponds to a 54 m ² afforestation. From these, it can be seen that sunlight is promising as primary energy [Non-Patent Document 1]. Solar power generation contributes to power load leveling because it generates a lot of power during the daytime when demand for electricity is the highest, and solar energy is an area-distributed system, so it has the advantage of reducing energy loss due to transportation. However, silicon-based solar cells, which are currently mainstream, still have many problems such as high production costs, and solar cells with lower cost and higher efficiency are required.

  Therefore, development of non-silicon-based solar cells such as thin-film silicon solar cells and CIS (copper-indium) based on a reduced amount of silicon is underway. Among them, new organic solar cells called “Gretzel cells” or “dye-sensitized solar cells” do not use silicon, and their materials and manufacturing processes are cheaper and less expensive than other solar cells. It is attracting attention as a cost solar cell [Non-patent Document 2].

FIG. 1 shows the structure and operating principle of a dye-sensitized solar cell. When a titanium oxide paste is printed on a conductive glass substrate (FTO lath) 101 and baked, a mesoporous titanium oxide electrode is formed. When it is immersed in a dye solution, the dye is fixed to the titanium oxide surface by an ester bond. A nitrile electrolyte solution 105 containing iodine redox (I ⁻ / I ₃ ⁻ ) interposed between the photoelectrode 102 and a counter electrode 104 produced by vapor deposition of Pt on a conductive glass substrate 103. Inject. Thus, the dye-sensitized solar cell 106 is completed. The dye fixed on the titanium oxide surface absorbs sunlight and changes from a ground state (HOMO) to an excited state (LUMO), and electrons in the excited state are injected into the conduction band of titanium oxide to enter the conductive glass substrate 101. Arrive. Thereafter, the electrons move to the counter electrode 104 via the external connection 107 and reduce I ₃ ⁻ on the Pt surface of the counter electrode 104. The produced I ⁻ moves through the electrolyte solution 105 to the photoelectrode 102 and reduces the oxidized dye. This is a cycle of electrons. In this way, it can be produced relatively easily under atmospheric pressure, and the raw materials are not subject to resource restrictions, so that inexpensive production is possible [Non-patent Document 3].

  Not only that, dye-sensitized solar cells have unique characteristics such as good power generation characteristics in low light, colorfulness, etc., and applications that make use of these have been developed. For example, it is possible to reduce the weight and make flexible by converting the substrate into a resin, adapting it to mobile power supplies and sports / outdoor products, and developing the market.

The historical background of the dye-sensitized solar cell will be described. In 1887, James Moser et al. Reported the charge transfer phenomenon from photoexcited dye to semiconductor, which became the principle of dye-sensitized solar cells. In 1976, a dye-sensitized solar cell using a porous ZnO electrode was announced, and various researches on the dye-sensitized solar cell have been conducted thereafter. The basis for the development of efficiency of the dye-sensitized solar cell has been associated with nanocrystalline TiO ₂ thin film having a high porosity. The photoelectric effect of the porous TiO ₂ thin film has been enhanced together with a photosensitizing dye having a high light absorption coefficient. Therefore, the manufacturing technology of the TiO ₂ film is an important element for realizing high efficiency. Currently, several research institutions have reported conversion efficiencies of more than 10%. The current highest efficiency is 11.2% with N719 dye reported by Prof. Gratzel et al. Regarding other dyes, Sharp Corporation reports 11.1% using Black dye. Research institutions reporting efficiencies of 10% or higher are summarized in Table 1 [Non-Patent Document 3].

  Table 1 below shows the performance and research institutions of dye-sensitized solar cells for which conversion efficiency of 10% or more is reported.

  As described above, Pt is currently used for the counter electrode of the dye-sensitized solar cell. However, since Pt is expensive, it is desired to develop a counter electrode without using Pt. As one of them, a carbon counter electrode is being studied. The active point of carbon black is located at the crystal edge, and has more crystal edges than carbon nanotubes and graphite. For this reason, several studies on the purification of carbon paste using carbon black have been conducted. Murakami et al.'S research succeeded in achieving performance close to the Pt counter electrode by refining a carbon paste using an aqueous solvent and using it as a counter electrode [Non-patent Document 4]. In addition, Easawamoothi Ramasamy et al. Refined the carbon paste using the viscose method, and also realized performance close to the Pt counter electrode [Non-patent Document 5].

Jun Uchida, Koji Segawa, Shogo Ito. Chemical engineering. , 71 (2007), 429. Toward the practical application of dye-sensitized solar cells Yuki Saito. Chemical engineering. 71 (2007), 452. Development of electrolyte and counter electrode materials for dye-sensitized solar cells Hironori Arakawa. Chemical engineering. 71 (2007), 424. Current status and issues of research and development of dye-sensitized solar cells TN Murakami, S. Ito, Q. Wang, MK Nazeeruddin, T. Bessho, I. Cesar, P. Liska, RH Baker, P. Comte, P. Pechy, M. Graetzel, J Electrochem Soc., 153 (12) , (2006) A2255. E Ramasamy, W. J. Lee, D. Y. Lee, J. S. Song., APPLIED PHYSICS LETTERS., 90 (2007) 173103. S. Ito, T. N. Murakami, P. Comte, P. Liska, C. Graetzel, M. K. Nazeeruddin, M. Graetzel., Thin Solid Films, 516 (2008), 4613.

  However, when these carbon pastes are applied to FTO glass, a doctor blade method must be performed, which is not efficient from the viewpoint of mass production. If it becomes possible to use screen printing, mass production is possible, which can be said to be a great advantage not found in the Pt counter electrode where screen printing is impossible. Regarding the research on the carbon paste for screen printing, there is no mention of a detailed report example of its production method.

  Therefore, in this experiment, a carbon paste that can be used for screen printing was prepared, a dye-sensitized solar cell was assembled using a carbon counter electrode using the paste, and the characteristics were measured.

  Accordingly, an object of the present invention is to solve the above-mentioned problem, and it is possible to produce a carbon counter electrode on FTO glass by screen printing, the particles become uniform, and the film thickness dependence of the counter electrode becomes small. The object is to provide a method for producing a carbon paste for screen printing of a sensitized solar cell counter electrode.

  In order to achieve the above object, the present invention is configured as follows.

  According to the first aspect of the present invention, a carbon powder and a metal semiconductor are used, and a high-boiling solvent and a low-boiling solvent are added thereto to obtain a dispersion, and the dispersion is distilled to remove the low-boiling solvent. Thus, a carbon paste for screen printing of a dye-sensitized solar cell counter electrode, characterized in that a carbon paste is obtained, is provided.

According to a second aspect of the present invention, there is provided the method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to the first aspect, wherein the metal semiconductor is a colloid of TiO ₂ .

  According to a third aspect of the present invention, there is provided a method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to the first or second aspect, wherein the high boiling point solvent is α-terpineol.

  According to a fourth aspect of the present invention, there is provided the method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to any one of the first to third aspects, wherein the low boiling point solvent is ethanol.

According to the fifth aspect of the present invention, TiO ₂ colloid is added to carbon powder and ground in a mortar,
Add Ti (OCH (CH ₃ ) ₂ ) ₄ and isopropanol to water with stirring, add nitric acid, and then stir while heating to obtain a white and transparent colloid of TiO ₂ ,
To the carbon powder ground in the mortar, gradually add ethanol while gradually grinding,
Next, stirring is repeated several times,
Then, add α-terpineol, add ethyl cellulose, and stir every time they are added,
The method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to any one of the first to fourth aspects, in which ethanol is removed from the dispersion thus obtained to obtain a carbon paste, is provided.

According to the sixth aspect of the present invention, 6 g of carbon powder is prepared, 9 g of TiO ₂ colloid is added thereto and ground in a mortar,
Prepare 75 mL of water, add 12.5 mL Ti (OCH (CH ₃ ) ₂ ) ₄ and 2 mL isopropanol with stirring, add 0.6 mL of 65% nitric acid, and heat at 80 ° C. While stirring for 8 hours to obtain a white and transparent TiO ₂ colloid,
The carbon powder ground in a mortar is further ground with ethanol until the total amount reaches about 150 mL, and then transferred to a tall beaker.
Next, put a magnetic stir bar and stir for 1 minute with a magnetic stirrer.
Then, the mixture is stirred with an ultrasonic homogenizer, and for the ultrasonic homogenizer, the irradiation time is 2 seconds, the irradiation stop time is 2 seconds, and 1 minute is performed.
Stirring with a magnetic stirrer and ultrasonic homogenizer is repeated three times alternately,
Thereafter, 20 g of α-terpineol was added, 30 g of ethyl cellulose was added, and each time they were added, the mixture was stirred with a magnetic stirrer and an ultrasonic homogenizer.
The method for preparing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to the fifth aspect is characterized in that ethanol is removed from the dispersion thus obtained by an evaporator to obtain a carbon paste.

  According to a seventh aspect of the present invention, there is provided the method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to any one of the first to sixth aspects, wherein the carbon powder is graphite.

  According to the method for producing a screen-printed carbon paste for a dye-sensitized solar cell counter electrode according to the present invention, a carbon-printed carbon paste and a metal semiconductor are used for producing a screen-printed carbon paste for a dye-sensitized solar cell counter electrode. A solvent and a low-boiling solvent are added to obtain a dispersion, and the dispersion is distilled to remove the low-boiling solvent. In the carbon paste thus produced, a carbon counter electrode can be produced on FTO glass by screen printing, the particles are uniform, and the film thickness dependence of the counter electrode is reduced. More specifically, terpineol can be used as a solvent.

It is explanatory drawing which shows the structure of the dye-sensitized solar cell concerning one Embodiment of this invention. It is explanatory drawing explaining the process of cutting a transparent electrode. It is explanatory drawing explaining the process wash | cleaned by ultrasonic cleaning. It is explanatory drawing explaining the process of heat-processing the surface with an oven toaster. It is an explanatory view for explaining a step of performing a TiCl ₄ treatment. It is explanatory drawing explaining the process wash | cleaned with water and ethanol. It is explanatory drawing explaining the process of performing screen printing. It is explanatory drawing explaining the process of putting in an electric furnace and sintering. It is explanatory drawing explaining the process of putting in an electric furnace and sintering. It is a flowchart which shows the preparation procedures of the carbon paste using terpineol. It is a perspective view which shows the assembly of a cell. It is a figure which shows the visual comparison of the counter electrode by the carbon paste using terpineol, and the counter electrode by the carbon paste using an aqueous solvent. It is a figure which shows the image which image | photographed with SEM the carbon electrode formed with the carbon paste using the terpineol at the time of magnification 150 times. It is a figure which shows the image which image | photographed the carbon electrode formed with the carbon paste using the water solvent at the time of 150 time magnification by SEM. It is a figure which shows the image which image | photographed the carbon electrode formed with the carbon paste using the terpineol at the time of magnification of 30000 times with SEM. It is a figure which shows the image which image | photographed by SEM the carbon electrode formed with the carbon paste using the water solvent in the case of 30000 times magnification. It is a graph which shows the comparison of the IV curve in each counter electrode. It is a graph which shows the IV curve in each film thickness. It is a graph which shows the curve of the impedance in each film thickness. It is an equivalent circuit diagram used for fitting. It is a graph which shows the comparison of the impedance of a paste.

  Embodiments according to the present invention will be described below in detail based on the drawings and experiments.

(2. Experiment)
2.1. Materials and equipment used Valerontrile (Aldrich) was purified by vacuum distillation. 4-tert-butylpyridine (Tokyo Chemical Industry Co., Ltd.), acetonitrile (Wako Pure Chemical Industries, Ltd.), guanidiniumthiocyanate (Kishida Chemical Co., Ltd.) and H ₂ PtCl ₆ (Tokyo Chemical Industry Co., Ltd.) were used as they were. H ₂ O was purified by distillation and filtration. TiCl ₄ (Aldrich) was used by diluting the stock solution to 2M at 0 ° C. A plate for screen printing (Seritech Co., Ltd.) and a squeegee (NEWLONG) are used for the production of the electrodes. Moreover, a solar simulator (YAMASITA DENSO) (AM1.5,100mW cm ^<-2 >) is used for the measurement of a photoelectric characteristic.

2.2. Preparation of electrode First, FTO glass (Nippon Sheet Glass Co., Ltd., thickness 4 mm) is prepared as the conductive glass of the photoelectrode, cut into a 7.5 × 2.5 cm square, and ultrasonicated for 20 minutes using a synthetic detergent. Wash. Thereafter, the surface is washed with water and ethanol (Kanto Chemical Co., Inc.), placed in an oven toaster, and the surface is heated at 250 ° C. for 15 minutes. Then, the FTO glass substrate is immersed in a 40 mM TiCl ₄ aqueous solution at 70 ° C. for 30 minutes, taken out, and then rinsed with water and ethanol. A screen-printed TiO ₂ paste (18NR, JGC Catalysts & Chemicals Co., Ltd.) with a particle size of 20 nm was applied on an FTO substrate in an area of 5 × 5 mm square, labeled with a clean box, and then at 125 ° C. for 4 minutes. dry. This operation is repeated until the film thickness reaches 12-14 μm. Thereafter, a TiO ₂ paste having a particle size of 400 nm is screen-printed to form a light scattering layer. This film thickness is about 4-5 μm. Then, the electrode is placed in an electric furnace (AS ONE), dried at 450 ° C. for 15 minutes, and sintered. It is taken out from the electric furnace, soaked again in 40 mM TiCl ₄ solution at 70 ° C. for 30 minutes, taken out, rinsed with water and ethanol, dried at 450 ° C. for 30 minutes and sintered. This is immersed in an N719 dye solution at 40 ° C. for 3 hours to obtain an electrode [Non-patent Document 6]. A series of steps is shown in FIGS. 2A to 2H.

2A to 2H show a process for manufacturing a TiO ₂ electrode.

In FIG. 2A, the transparent electrode is cut. In FIG. 2B, cleaning is performed by ultrasonic cleaning. In FIG. 2C, the surface is heat-treated with an oven toaster. In FIG. 2D, a TiCl ₄ process is performed. In FIG. 2E, wash with water and ethanol. In FIG. 2F, screen printing is performed. In FIGS. 2G and 2H, it is sintered in an electric furnace.

2.3. Production of Carbon Paste A method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to this embodiment uses carbon powder and a metal semiconductor, and a high-boiling solvent and a low-boiling solvent for these carbon powder and metal semiconductor. Is added to obtain a dispersion, and then the dispersion is distilled to remove the low boiling point solvent, thereby obtaining a carbon paste.

  Here, a low boiling point solvent is a solvent that volatilizes at room temperature and dries in seconds. A high boiling point solvent does not volatilize at room temperature, and is heated to a temperature higher than room temperature (high temperature) or air is refluxed. It refers to a solvent that does not dry unless it is let down or decompressed. A solvent is required to form and maintain the state of the paste, but if a high boiling point solvent is not used, the state of the paste changes at the beginning and end of screen printing due to volatilization, resulting in uniform printing. Can not. However, if only a high boiling point solvent is used, the dispersibility of the carbon powder is poor at the time of carbon paste production. The solvent may be distilled off. That is, the criterion for low and high boiling points is whether volatilization occurs at room temperature.

As an example of the metal semiconductor, a TiO ₂ colloid can be used. As an example of the high boiling point solvent, α-terpineol can be used. As an example of the low boiling point solvent, ethanol can be used. As an example of the carbon powder, graphite can be used. More specifically, Ti (OCH (CH ₃ ) ₂ ) ₄ and isopropanol are added to water while stirring, nitric acid is added, and stirring is performed while heating. Thus, a white and transparent TiO ₂ colloid is obtained.

Next, the TiO ₂ colloid is added to the carbon powder and ground in a mortar.

  Next, the carbon powder ground in the mortar is further ground while gradually adding ethanol.

  The stirring is then repeated several times.

  Thereafter, α-terpineol is added, ethylcellulose is added, and stirring is performed each time they are added.

  Ethanol is removed from the dispersion thus obtained to obtain a carbon paste.

  Furthermore, the carbon paste preparation method for screen printing will be described in more detail below.

  FIG. 3 shows a procedure for producing a carbon paste using terpineol.

First, 6 g of carbon powder (Printex L, Degussa) is prepared, and 9 g of TiO ₂ colloid is added thereto and ground in a mortar.

Here, the production method of the TiO ₂ colloid to be used is as follows. Prepare 75 mL of water and add to it 12.5 mL of Ti (OCH (CH ₃ ) ₂ ) ₄ and 2 mL of isopropanol with stirring. Then, after adding 0.6 mL of 65% nitric acid, the mixture is stirred for 8 hours while heating at 80 ° C. to obtain a white and transparent TiO ₂ colloid.

  The carbon powder ground in the mortar is ground further while gradually adding ethanol until the total amount reaches about 150 mL, and transferred to a tall beaker.

  Next, a magnetic stirrer is put and stirred with a magnetic stirrer (IKA) for 1 minute.

  And it stirs with an ultrasonic homogenizer (Vibra cell 72408, Bioblock scientific). For the ultrasonic homogenizer, the irradiation time is 2 seconds and the irradiation stop time is 2 seconds.

  Agitation with a magnetic stirrer and ultrasonic homogenizer is repeated three times alternately.

  Thereafter, 20 g of α-terpineol (Tokyo Chemical Industry Co., Ltd.) is added, and 30 g of ethyl cellulose (Tokyo Chemical Industry Co., Ltd.) is added. Each time they are added, they are stirred with a magnetic stirrer and an ultrasonic homogenizer.

  The dispersion thus obtained is subjected to an evaporator to remove ethanol to obtain a carbon paste.

For comparison, a carbon paste using an aqueous solvent is also prepared. A carbon water paste is obtained by adding ₂ mL of TiO ₂ colloid, 4 mL of water, and 2 mL of 10% Triton X-100 aqueous solution to 1.3 g of carbon powder and grinding in a mortar [Non-Patent Document 4].

2.4. Preparation of counter electrode FTO glass (Nippon Sheet Glass Co., Ltd., thickness 2 mm) is prepared as a counter electrode, cut into a 7.5 × 2.5 cm square in the same manner as the electrode preparation, and a diameter of about 1 mm with a hand drill (U-hoby). Make a hole. This is ultrasonically cleaned with a synthetic detergent for 20 minutes. Then, it is immersed in a 40 mM TiCl ₄ aqueous solution at 70 ° C. for 30 minutes, taken out, and washed with water and ethanol. This is put into an oven toaster and the surface is heated at 250 ° C. for 15 minutes. Then, a carbon paste is applied on the FTO glass with an area of 5 × 5 mm square by screen printing and dried at 125 ° C. for 4 minutes. At this time, in order to change the film thickness, the number of times of applying the paste is changed to 7.8 μm, 26.4 μm, and 46.6 μm, respectively. Thereafter, this is put in an electric furnace, dried at 450 ° C. for 15 minutes and sintered to obtain a carbon electrode.

For comparison, a Pt electrode is also produced. FTO glass is cut into 1.5 × 1.5 cm squares, which are also drilled with a hand drill. This is washed with water and 0.1 M HCL ethanol solution and ultrasonically washed with acetone for 15 minutes. Thereafter, the remaining organic impurities were removed by heating at 450 ° C. for 15 minutes, and a drop of H ₂ PtCl ₆ solution (2 mg of Pt in 1 ml of ethanol) was applied to coat the Pt catalyst on the FTO glass. A Pt electrode is obtained by heating at 450 ° C. for [min.

2.5. Assembling the cell The TiO ₂ electrode is taken up from the dye solution, and this and the carbon electrode are assembled in a sandwich to obtain a cell of the dye-sensitized solar cell. The assembly of the cell is shown in FIG.

First, a TiO ₂ electrode (TiO ₂ layer) 1 and a carbon electrode (carbon layer) 2 face each other, and a hot melt film (for example, a commercial product such as Surlyn (registered trademark) 1702, TAMAPOLY) 3 is sandwiched between them. The TiO ₂ electrode 1 and the carbon electrode 2 are bonded by heating with a hot plate. At this time, it is necessary to bond the TiO ₂ layer 1 and the carbon layer 2 so as not to shift. The film 3 used here is cut with a Thomson blade so that the width is 1 mm and the opening 3 a is about 2 mm larger than the TiO ₂ layer 1. And the hole 4 of a counter electrode is sealed with another hot-melt film 5, and the hole 5a is opened in the film 5 using a needle | hook. The hot melt film 5 used here is a 5 × 5 mm square cut into a square. A drop of the electrolyte is dropped into the hole 5a, put into the cell by reverse vacuum transfer, and the hole is sealed again with another hot melt film 6 and a cover glass 7. Finally, solder is applied to the ends of the FTO glasses 8 and 9 of the electrode and the counter electrode, and the cell is completed. A cell using a Pt electrode as a counter electrode is produced in the same procedure.

The electrolyte used was 0.6M BMII solution, 0.03M I ₂ , 0.10M guanidinium thiocynate and 0.5M 4-tert butylpyridine with acetonitrile and valeronitrile. (Valerontrile) mixed solution (volume ratio 85:15) [Non-Patent Document 6].

2.6. Measurement of photoelectric characteristics An assembled cell is covered with a mask, and an external bias is applied in the state of irradiating light with a solar simulator, and the IV curve and cell performance (current density JSC, open-circuit voltage VOC, fill factor FF, The efficiency η) is measured. Impedance is also measured with an impedance measuring instrument (BioLogic). The mask is used by making a 6 x 6 mm square hole in black vinyl tape and sticking it to the cell.

(3. Results and discussion)
First, a visual comparison was made between a counter electrode made of carbon paste using terpineol (see the left side of FIG. 5) and a counter electrode made of carbon paste using an aqueous solvent (see the right side of FIG. 5). This is shown in FIG.

  From FIG. 5, it is possible to form a carbon layer on FTO glass by screen printing with a carbon paste using terpineol (see the left side of FIG. 5), but with a carbon paste using an aqueous solvent, a carbon layer is formed. It can be seen that the shape of this is collapsed and is unsuitable for use in screen printing (see the right side of FIG. 5). In general, it is useful to use screen printing for the production of the counter electrode, so that it can also be applied to screen printing. The carbon paste using terpineol is superior to the carbon paste using an aqueous solvent.

  Images taken by SEM of these carbon electrodes are shown in FIGS. 6A to 6D.

  6A and 6B are 150 times magnification, and FIGS. 6C and 6D are 30000 times magnification. 6A and 6C are terpineols, and FIGS. 6B and 6D are carbon pastes using an aqueous solvent.

  6A and 6B are images obtained by photographing a counter electrode of carbon paste using terpineol and a counter electrode of carbon paste using an aqueous solvent at a magnification of 150 times, respectively. The carbon paste using terpineol is uniformly applied to the FTO glass (see FIG. 6A), but the carbon paste using the aqueous solvent is non-uniform and the carbon layer is uneven (see FIG. 6B). . 6C and 6D are photographs of each carbon electrode with a magnification of 30000 times. In the carbon paste using terpineol, the particles are uniform (see FIG. 6C), but in the carbon paste using a water solvent, the particles are aggregated and are not uniform (see FIG. 6D).

  From the above, it can be seen that the carbon paste using terpineol is useful as described above. Pt counter electrode (see graph of “Pt” in FIG. 7), counter electrode by carbon paste using terpineol (see graph of “Carbon terpineol” in FIG. 7), counter electrode by carbon paste using water solvent (“Carbon in FIG. 7) Each photoelectric characteristic was measured about the graph of water. Table 2 shows a comparison between them. Moreover, the IV curve is shown in FIG.

  That is, Table 2 shows a comparison of cell performance at each electrode.

  FIG. 7 shows a comparison of IV curves at each counter electrode.

  The respective efficiencies were 6.942% for the Pt counter cell, 6.408% for the carbon paste counter electrode using terpineol, and 7.123% for the carbon electrode counter electrode using the aqueous solvent. Comparing these, the carbon paste using terpineol is about 0.5% less efficient than the Pt electrode, but the efficiency has not dropped so much, and it can fully substitute for the Pt electrode. Is considered possible.

  Subsequently, when the carbon paste was applied on the FTO glass, the photoelectric characteristics when the film thickness was changed were measured. The respective values are shown in Table 3. That is, Table 3 shows the cell performance at each film thickness.

  Further, FIG. 8 shows an IV curve and FIG. 9 shows an impedance curve of these cells. For the impedance curve, the results of the cell with the Pt counter electrode were also measured for comparison, and are shown in the figure.

  FIG. 8 shows an IV curve at each film thickness.

  FIG. 9 shows an impedance curve at each film thickness.

  From Table 3, even if the film thickness of the carbon layer is changed, there is no significant change in efficiency. The efficiency η of the dye-sensitized solar cell is expressed by the following formula 1 (Equation 1).

When the film thickness is increased, the open circuit voltage V _OC and the short-circuit current density J _SC are decreased, but conversely, since the fill factor FF is increased, it is considered that the efficiency η did not change as a result. From FIG. 9, it can be seen that as the film thickness is increased, the shape of the impedance curve approaches the curve of the cell impedance by the Pt counter electrode. These impedance curves were fitted by an equivalent circuit. An equivalent circuit used for this fitting is shown in FIG. Further, Table 4 shows impedance values obtained by fitting, and Table 5 shows carbon counter electrode values using an aqueous solvent for comparison. FIG. 10 shows a comparison of these values as a graph.

  FIG. 11 shows a comparison of paste impedances.

Table 4 shows the impedance _Rct with respect to the film thickness of the carbon paste using terpineol.

Table 5 shows the impedance _Rct with respect to the film thickness of the carbon paste by the water solvent [Non-Patent Document 4].

First, the equivalent circuit shown in FIG. 10 will be briefly described. R _S and R _ct in the figure are resistance elements. Next, CPE, which is an abbreviation for Constant Phase Element. The impedance Z of this element can be obtained by the following equation 2 (Equation 2).

  The values of P and T in Equation 2 (Equation 2) are components reflecting resistance and capacitance due to the roughness of the surface of the electrode with respect to impedance. As can be seen from Equation 2 (Equation 2) above, if the value of P is 1, this element acts as a capacitor.

  When attention is paid to FIG. 11, the impedance of the carbon counter electrode by the carbon paste using terpineol is less dependent on the film thickness than that of the carbon paste using the water solvent. From this fact, it was confirmed that the carbon paste using terpineol was more useful than the carbon paste of the water solvent.

(4. Conclusion)
In this experiment, we succeeded in producing a screen-printed carbon paste for the dye-sensitized solar cell counter electrode. Terpineol was used as a solvent for this carbon paste. With this carbon paste, the carbon counter electrode could be produced by screen printing, but with the carbon paste using the previously reported aqueous solvent, the carbon layer could not be well formed on the FTO glass even after screen printing, and the particle uniformity Also, the carbon paste particles using terpineol were uniform, whereas the carbon paste using water solvent was aggregated and the particles were not uniform. When impedance was measured, the counter electrode of the carbon paste of terpineol was less dependent on the film thickness than that of the aqueous solvent. From the above, it was confirmed that the carbon paste using terpineol is more useful than the carbon paste using an aqueous solvent.

  It is to be noted that, by appropriately combining arbitrary embodiments of the various embodiments described above, the effects possessed by them can be produced.

  The method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to the present invention can produce a carbon counter electrode on FTO glass by screen printing, the particles are uniform, and the film thickness dependence of the counter electrode is reduced. It is useful as a counter electrode of a dye-sensitized solar cell capable of mass production.

Claims (7)

  Using carbon powder and a metal semiconductor, a high-boiling solvent and a low-boiling solvent were added thereto to obtain a dispersion, and the dispersion was distilled to remove the low-boiling solvent to obtain a carbon paste. A method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode, characterized by: The method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to claim 1, wherein the metal semiconductor is a colloid of TiO ₂ .   The method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to claim 1, wherein the high boiling point solvent is α-terpineol.   The method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to any one of claims 1 to 3, wherein the low boiling point solvent is ethanol. Add Ti (OCH (CH ₃ ) ₂ ) ₄ and isopropanol to water with stirring, add nitric acid, and then stir while heating to obtain a white and transparent colloid of TiO ₂ ,
The TiO ₂ colloid thus obtained is added to carbon powder and ground in a mortar.
The carbon powder ground in the mortar is further ground while gradually adding ethanol,
Next, stirring is repeated several times,
Then, add α-terpineol, add ethyl cellulose, and stir every time they are added,
The method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to any one of claims 1 to 4, wherein ethanol is removed from the dispersion thus obtained to obtain a carbon paste. Prepare 75 mL of water, add 12.5 mL Ti (OCH (CH ₃ ) ₂ ) ₄ and 2 mL isopropanol with stirring, add 0.6 mL of 65% nitric acid, and heat at 80 ° C. While stirring for 8 hours to obtain a white and transparent TiO ₂ colloid,
9 g of the TiO ₂ colloid thus obtained is added to 6 g of the prepared carbon powder and ground in a mortar.
The carbon powder ground in the mortar is further ground while gradually adding ethanol until the total amount is about 150 mL, transferred to a tall beaker,
Next, put a magnetic stir bar and stir for 1 minute with a magnetic stirrer.
Then, the mixture is stirred with an ultrasonic homogenizer, and for the ultrasonic homogenizer, the irradiation time is 2 seconds, the irradiation stop time is 2 seconds, and 1 minute is performed.
Stirring with a magnetic stirrer and ultrasonic homogenizer is repeated three times alternately,
Thereafter, 20 g of α-terpineol was added, 30 g of ethyl cellulose was added, and each time they were added, the mixture was stirred with a magnetic stirrer and an ultrasonic homogenizer.
6. The method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to claim 5, wherein the dispersion thus obtained is subjected to an evaporator to remove ethanol to obtain a carbon paste.   The method for producing a carbon paste for screen printing of a dye-sensitized solar cell counter electrode according to any one of claims 1 to 6, wherein the carbon powder is graphite.