JP6641667B2 - Coating liquid, structure for solar cell, solar cell, and method for manufacturing structure for solar cell - Google Patents

Description

  The present invention relates to a coating liquid for forming a porous semiconductor electrode, a structure for a solar cell, a solar cell, and a method for manufacturing a structure for a solar cell.

  Dye-sensitized solar cells are examples of solar cells that have relatively low production energy and are advantageous in reducing costs. Dye-sensitized solar cells consist of a transparent substrate made of glass or the like, a conductive transparent thin film, a porous semiconductor electrode, a photosensitizing compound (sensitizing dye, etc.), and an electrolyte containing an oxidation-reduction pair (electrolyte solution, etc.). , And a counter electrode are sequentially stacked. By making the semiconductor electrode holding the sensitizing dye porous, the specific surface area is increased several hundred times to 1,000 times, and a large amount of the sensitizing dye is retained, so that a large photocurrent can be obtained. This is a feature (for example, see Non-Patent Documents 1 and 2).

  Generally, a porous semiconductor electrode for a dye-sensitized solar cell is prepared by formulating a dispersion liquid containing semiconductor nanocrystal particles and a binder into a coating liquid having adjusted viscosity, and applying this to a substrate by a method such as screen printing. After that, the binder is removed by heating and baking to obtain a porous body. Titanium oxide is often used as semiconductor nanocrystal particles.

  The principle of power generation of a dye-sensitized solar cell is as follows: 1) The photosensitizing compound fixed on the surface of the semiconductor electrode absorbs external light such as sunlight to be in an excited state. 2) This emits electrons to the semiconductor electrode. 3) The emitted electrons diffuse and move through the semiconductor electrode and arrive at the conductive transparent substrate. 4) Move from the conductive substrate to the counter electrode via an external circuit. 5) Oxidation in the electrolyte at the counter electrode. This is based on a cycle in which the reduced pair is reduced, and 6) the reduced form moves in the electrolytic solution and reaches the dye, and the photosensitized compound which has emitted electrons is reduced and returned to the ground state. By repeating this cycle, power is continuously generated while the light is irradiated.

  In view of such a power generation principle, the porous structure formed in the semiconductor electrode needs to have an appropriate surface area and an appropriate pore size at the same time. That is, in order to increase sunlight absorption, which is the starting point of the power generation cycle, the larger the amount of the sensitizing dye is, the more advantageous it is. Therefore, it is preferable that the area of the semiconductor electrode surface which is the dye fixing surface is large. On the other hand, in order for the redox couple in the electrolyte to return the dye to the ground state and complete the power generation cycle, the electrolyte is sufficiently filled in the pores in the porous structure, and the electrolyte and the dye come into contact with each other. Need to be. If the pores are too narrow, the electrolyte cannot penetrate sufficiently and the pores are not filled. Therefore, the pores having a diameter such that the liquid penetration depth due to the capillary phenomenon is substantially the same as the primary particle diameter constituting the semiconductor electrode. Holes need to be built. In particular, this problem becomes remarkable when the viscosity of the electrolyte is high and it is difficult to penetrate into the pores.

  The pore structure in the semiconductor electrode is primarily due to the fact that after a coating liquid containing semiconductor nanocrystal particles is applied to the substrate, the binder disappears due to heating and the remaining nanocrystal particles form a film. It is formed by creating a gap between them. In this case, the larger the particle size, the larger the pore size formed, but the surface area per unit volume decreases accordingly. Therefore, it is difficult to have an appropriate surface area and an appropriate pore size at the same time simply by forming pores by gaps between particles.

  There have been proposals to solve the above problems. A particulate material (hereinafter, referred to as a heat-dissipating material) that burns and disappears by heating at the same level as or less than ordinary heating and sintering, and at the time of disappearance gives pores having a diameter larger than a gap formed by contact between particles. ) As an additive of a coating solution. For example, there are Patent Documents 1 to 4. For example, in Patent Literature 1, polystyrene particles having an average particle diameter of 100 nm to 1,000 nm or carbon nanotubes having an average particle diameter of 50 nm are added to a titanium oxide paste as a heat-dissipating material. This controls the pore size and porosity formed in the titanium oxide electrode film after firing. In Patent Literature 4, a crosslinking agent having at least one kind of an oxypropylene unit or an oxytetramethylene unit and having two or more polymerizable unsaturated groups is reacted with a monomer having a polymerizable unsaturated group. The obtained acrylic resin is used as a heat extinguishing material. As a result, pores of about 200 to 1,000 nm are formed.

  On the other hand, a process called titanium tetrachloride treatment is often performed on a porous semiconductor electrode for a dye-sensitized solar cell (for example, see Non-Patent Document 3). This is to apply a coating solution containing titanium oxide particles as semiconductor nanocrystals to a substrate, make it porous by heating and baking, then immerse it in an aqueous solution of titanium tetrachloride, and adsorb titanium tetrachloride molecules on the surface of the porous film, After that, it is dried and fired. By this treatment, the electrical connection between the titanium oxide particles is improved, a reverse electron transfer prevention layer is formed between the titanium oxide porous film and the conductive transparent substrate, and between the titanium oxide porous film and the conductive transparent substrate. It is thought that the power generation performance of the dye-sensitized solar cell is improved because the mechanical strength of the dye increases.

  However, the aqueous solution of titanium tetrachloride used for titanium tetrachloride treatment is strongly acidic and generates hydrochloric acid during heating and firing, so it is necessary to introduce acid-resistant equipment to industrially perform this treatment. This leads to an increase in cost. In addition, the addition of these processes requires extra manufacturing time, and lowers productivity, which also results in an increase in manufacturing cost.

  Therefore, attempts have been made to add a titanium oxide precursor to a coating solution for forming a titanium oxide electrode to achieve the same performance improvement at the time of titanium tetrachloride treatment without performing the treatment (for example, see Patent Literature 5-6). For example, in Patent Document 5, by adding an organic titanium chelate complex to a coating solution, the coating solution is applied, dried, and fired to increase the photocurrent and open-end voltage of the dye-sensitized solar cell. I have. Further, in Patent Document 6, by adding peroxo-modified titanium oxide particles to a coating liquid, a favorable conductive path is formed without performing titanium tetrachloride treatment.

  The present invention makes it possible to sufficiently fill a semiconductor electrode with a high-viscosity electrolyte solution, and furthermore, to reduce the mechanical strength between the semiconductor electrode and the conductive transparent substrate which occurs at that time. It is an object of the present invention to provide a coating liquid for forming a porous semiconductor electrode which can be suppressed without performing a chemical treatment and has excellent power generation performance.

In order to achieve this object, the present inventors have conducted intensive studies, and as a structural material for forming a semiconductor electrode, in addition to titanium oxide nanocrystal particles, contain titanium oxide nanoamorphous particles, and furthermore, specific heat annihilation particles It has been found that the above problems can be solved by using a coating liquid containing.
That is, the present invention provides a coating liquid containing a semiconductor structural material, a binder resin, heat-dissipating particles, and a dispersion solvent for forming a porous semiconductor electrode, wherein the semiconductor structural material is titanium oxide nanocrystal particles. And titanium oxide nano-amorphous particles, wherein the heat-destructible particles are polymethyl methacrylate having a weight average molecular weight (Mw) of 30,000 or more and 45,000 or less and a glass transition temperature (Tg) of 80 ° C. or more and 95 ° C. or less. It is a coating liquid characterized by the following.

  By using the coating liquid of the present invention, it is possible to sufficiently fill the semiconductor electrode with the high-viscosity electrolytic solution, and at the same time, the mechanical strength between the semiconductor electrode and the conductive transparent substrate is generated. Can be suppressed without performing any additional processing, and a porous semiconductor electrode having excellent power generation performance can be formed.

FIG. 1 shows an example in which the adhesion of the titanium oxide electrode obtained in Example 1 and Comparative Example 1 to an FTO substrate was measured using a peel strength measuring device.

Hereinafter, the present invention will be described in detail.
When a high-viscosity electrolytic solution or a solid electrolyte is used in mind, the pore size formed only by the disappearance of the binder in the semiconductor electrode is insufficient to fill these electrolytes. In order to allow the electrolyte or the like to be sufficiently filled in the semiconductor electrode, a heat-dissipating material is added. The resulting porous structure is less sparse as compared to the case where no heat-dissipating material is added, so that a problem occurs in that the mechanical strength between the titanium oxide porous film and the conductive transparent substrate is reduced. Therefore, it is necessary to add a treatment for increasing the mechanical strength like the titanium tetrachloride treatment, but the titanium tetrachloride treatment has the above-mentioned industrial problems.
The present invention has been devised to solve these problems.
The coating liquid of the present invention contains a heat-extinguishing material in order to enable a high-viscosity electrolyte or the like to be sufficiently filled in a semiconductor electrode. The resulting porous structure is less sparse than when no heat extinguishing material is added. However, in the coating liquid of the present invention, the titanium oxide nano-amorphous particles disposed between the titanium oxide nano-crystal particles and the conductive transparent substrate provide a binding action. This increases the mechanical strength between the two without the need for a special additional treatment, such as titanium tetrachloride treatment, and reduces the time, energy, and processing equipment required for such additional treatment. it can. In addition, the electric connection between the semiconductor nanocrystal particles can be improved by converting the nanoamorphous particles arranged between the titanium oxide nanocrystal particles into titanium oxide crystals after firing. Together with these effects, a semiconductor electrode suitable for a high-viscosity electrolytic solution can be obtained simply and with a low energy process.

  In the present invention, a coating containing titanium oxide nanocrystal particles (1) and titanium oxide nanoamorphous particles (2) as semiconductor structural materials, heat-destructible particles (3), a binder resin (4), and a dispersion solvent (5). A working liquid (6) is prepared.

(1) Titanium oxide nanocrystal particles The titanium oxide nanocrystal particles used in the present invention are not particularly limited, and known titanium oxide nanocrystal particles can be used.
The average primary particle size of the titanium oxide nanocrystal particles is preferably from 1 nm to 500 nm, more preferably from 20 nm to 135 nm. When the primary particle diameter is 1 nm or more, the semiconductor porous film is not excessively densified even when the heat-destructible particles are added, and the pore diameter formed in the porous film is not reduced. There is no problem that the penetration or filling of the electrolyte is restricted. On the other hand, when the primary particle diameter is 500 nm or less, the surface area contained in the semiconductor porous film does not decrease, and the amount of the adsorbed dye can be sufficiently secured.
The content of the titanium oxide nanocrystal particles in the coating liquid is preferably 5 to 50% by mass, and more preferably 10 to 30% by mass.

It is desirable that the titanium oxide nanocrystal particles be deagglomerated from several tens to several hundreds of nanometers as necessary. The method of loosening the aggregation is not particularly limited as long as it can give an impact force exceeding the aggregation force, and a known method can be used. Agglomeration can be loosened either in the liquid phase or in the gas phase.
As a method of loosening agglomeration in the gas phase, a method of applying a mechanical impact force to agglomerated particles, such as a jet mill, a hammer mill, a roller mill, a pin mill, a vibration mill, or a method of disintegrating by a shear stress between the agglomerated particles and the mill wall The method can be selected.
As a method of loosening the aggregation in the liquid phase, a collision method using ceramic beads, such as a bead mill, or a crushing method using shear stress between the beads and the mill wall surface can be selected. It is also possible to select a method in which ceramic beads are not used, by applying a high-pressure pump to accelerate the dispersion liquid, accelerating the dispersion liquid, or applying an impact force by causing the dispersion liquid to collide with the collision member. A method in which the dispersion liquid is pressurized and accelerated by a high-pressure pump to give an impact force due to shear stress generated between the dispersion liquid and the wall surface when passing through the flow path at a high speed. A method of applying an impact force by shearing stress with the vessel wall or bottom surface, or a method of irradiating a dispersion liquid with ultrasonic waves to apply an impact force based on a cavitation phenomenon.

(2) Titanium oxide nano-amorphous particles The titanium oxide nano-amorphous particles used in the present invention are not particularly limited, and known ones can be used.
The equivalent circle diameter of the titanium oxide nanoamorphous particles is preferably 20% or less of the average primary particle diameter of the titanium oxide nanocrystal particles (1). When the content is 20% or less, the probability that the diameter of the titanium oxide nano-amorphous particles exceeds the geometric diameter formed by the close packing of the titanium oxide nano-crystal particles does not increase, that is, between titanium oxide nano-crystal particles or oxidation. There is no possibility that nano-amorphous particles not arranged between the titanium nano-crystal particles and the conductive substrate are generated at a certain ratio or more. By setting the content to 20% or less, a sufficient ratio of titanium oxide nanoamorphous particles can be arranged at a desired position.

  Further, when a titanium oxide precursor such as the organic titanium chelate or peroxo-modified titanium oxide particles described in the background art is added, if the conversion of these precursors to titanium oxide is incomplete, it is not added. On the contrary, there is a problem that the conductivity is lowered. However, the titanium oxide nanoamorphous particles themselves have conductivity, and even if the conversion to semiconductor nanocrystals is incomplete, they do not prevent the conductivity. This means that restrictions on the firing temperature and time in the manufacturing process are reduced, and a power generation performance above a certain level can be obtained without necessarily performing strict temperature and time management. Therefore, the production yield of the dye-sensitized solar cell can be improved by the present invention.

(3) Heat-extinguishing particles The heat-extinguishing particles used in the present invention burn and extinguish when fired at about 500 ° C. in air, which is a normal firing atmosphere for a coating film, and have a weight average molecular weight (Mw). Is a polymethyl methacrylate having a glass transition temperature (Tg) of from 80 ° C to 95 ° C.
In order to ensure sufficient power generation efficiency, the connectivity of the pores in the semiconductor electrode is also indispensable. For that purpose, it is important that the Mw and Tg of the heat annihilation particles are within the above ranges. By using polymethyl methacrylate having Mw and Tg within this range, the heat-dissipating particles are softened and deformed, burn, and disappear in the course of temperature rise in baking at about 500 ° C. The pores formed thereby have improved connectivity compared to the case without such deformation, and a more desirable structure for injecting and penetrating the high-viscosity electrolyte solution into the inside of the semiconductor porous electrode. It has become.
The particle size of the heat annihilating particles is preferably from 10 nm to less than 2,000 nm, more preferably from 50 nm to less than 1,000 nm. Heat-extinguishing particles are added for the purpose of expanding the pores formed in the semiconductor porous electrode film to a size that allows the electrolyte to sufficiently penetrate, so that the size can be adjusted to the target pore size. desirable. When the particle size of the heat annihilation particles is 10 nm or more, the pores formed by the annihilation of the particles become 10 nm or more, which can be larger than the pore diameter formed when the heat annihilation particles are not added. On the other hand, when the particle size of the heat annihilating particles is less than 2,000 nm, excessively large pores are not formed for the purpose, the arrangement of the sensitizing dye is not reduced, and the power generation performance is reduced. I will not let you.

(4) Binder resin The binder resin is added to adjust the coating property of the liquid, and has a thickening effect, is dissolved in a solvent, and is dissolved in air, which is a normal firing atmosphere for a coating film. There is no particular limitation as long as it burns and disappears during firing at about 500 ° C.
For example, polyethylene glycol, polyvinyl alcohol, ethyl cellulose and the like can be mentioned.

(5) Dispersion solvent The dispersion solvent is not particularly limited as long as the components (1) to (4) contained in the coating liquid can be appropriately dispersed and the dispersion state can be maintained. is not.
For example, water, alcohol solvents such as methanol, ethanol, isopropyl alcohol and α-terpineol, ketone solvents such as acetone, methyl ethyl ketone or methyl isobutyl ketone, and ester solvents such as ethyl formate, ethyl acetate and n-butyl acetate. , Diethyl ether, dimethoxyethane, tetrahydrofuran, dioxolan, or dioxane, etc .; ether solvents, N, N-dimethylformamide, N, N-dimethylacetamide, or amide solvents such as N-methyl-2-pyrrolidone, dichloromethane, chloroform , Bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene, fluorobenzene, bromobenzene, iodobenzene, Or a halogenated hydrocarbon solvent such as 1-chloronaphthalene, n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene, toluene, o-xylene, m And hydrocarbon solvents such as -xylene, p-xylene, ethylbenzene and cumene. These can be used alone or as a mixed solvent of two or more.

  In addition to the above (1) to (5), other components can be mixed as necessary within the scope of the object of the present invention. Such components include, for example, a dispersant for stabilizing the dispersibility of the titanium oxide nanocrystal particles and the heat-destructible resin, more specifically, an acid such as hydrochloric acid, nitric acid, and acetic acid, and polyoxyethylene (10) octyl. Surfactants such as phenyl ether; chelating agents such as acetylacetone, 2-aminoethanol, and ethylenediamine;

(6) Coating liquid The coating liquid is obtained by uniformly mixing the components (1) to (4) and the dispersion solvent of (5).
In addition, at the time of mixing, titanium oxide nanocrystal particles, titanium oxide nanoamorphous particles, a heat-destructible resin, and a binder are each prepared in advance as a dispersion or a solvent solution dispersed in a solvent, and these may be mixed. preferable. In this case, a preferable solvent can be selected from the above-mentioned dispersion solvents. In addition, titanium oxide nano-amorphous particles are prepared by reacting a titanate ester such as titanium tetraisopropoxide as a precursor thereof with an acid in an aqueous system, and then dispersing by replacing water with a solvent such as ethanol. It is preferred to prepare a liquid.
When mixing these dispersions or solvent solutions, based on the coating liquid,
(1) 5 to 50% by mass, preferably 10 to 30% by mass of titanium oxide nanocrystal particles,
(2) titanium oxide nano-amorphous particles 0.25 to 2.5% by mass, preferably 0.5 to 1.5% by mass,
(3) heat-extinguishing particles 1 to 25% by mass, preferably 2 to 15% by mass,
(4) 1 to 25% by mass, preferably 2 to 15% by mass of a binder resin,
(5) It is preferable to mix so that the ratio of the solvent for dispersion and the balance may be the same.
In particular, the mass ratio of the titanium oxide crystal particles to the nano-amorphous particles is preferably 100: 1 to 100: 20. The purpose of the addition of the nano-amorphous particles is to provide mechanical strength between the titanium oxide crystal particles and the conductive transparent substrate, but to achieve the intended function sufficiently by setting the mass ratio to 100: 1 or more. Can be. On the other hand, by setting the mass ratio to 100: 20 or less, a decrease in the power generation capability caused by the low conductivity of the amorphous particles is limited, and it is possible to simultaneously provide the mechanical strength and maintain the power generation performance.
The mixing method is not particularly limited as long as a uniform mixing effect can be obtained.
Specific examples include a stirring blade type mixer, a three-roll mill, a stirrer, a ball mill, a paint conditioner, a sand mill, an attritor, a disperser, a jet mill, and an ultrasonic dispersion.
Further, at the time of mixing, heating, cooling, pressurizing or depressurizing may be performed.

The structure for a solar cell of the present invention has a semiconductor electrode derived from the coating liquid of the present invention on a substrate (conductive transparent substrate) on which a transparent electron collecting electrode is disposed.
The type of substrate is not particularly limited as long as it is made of a material transparent to visible light and has a certain mechanical strength. For example, glass, a transparent plastic plate, a transparent plastic film, an inorganic transparent crystal Are used.
The electron collecting electrode is not particularly limited as long as it is a conductive substance that is transparent to visible light, and a known material used for a usual photoelectric conversion element or a liquid crystal panel can be used.
For example, indium-tin oxide (hereinafter, referred to as ITO), fluorine-doped tin oxide (hereinafter, referred to as FTO), antimony-doped tin oxide (hereinafter, referred to as ATO), and the like can be mentioned. May be.
The thickness of the electron collecting electrode is preferably from 5 nm to 100 μm, more preferably from 50 nm to 10 μm.
In addition, a known material in which the electron collecting electrode and the base material are integrated can be used. For example, FTO coated glass, ITO coated glass, zinc oxide: aluminum coated glass, FTO coated transparent plastic film, ITO coated transparent film Plastic films and the like.

The solar cell structure of the present invention can be manufactured by forming a porous semiconductor electrode by applying the coating liquid of the present invention on a conductive transparent substrate and baking the coating liquid.
The method for applying the coating liquid is not particularly limited, and the coating can be performed according to a known method.
For example, a printing method, a dipping method, a spray method, a wire bar method, a spin coating method, a roller coating method, a blade coating method, a gravure coating method, or the like can be used. As a printing method, various methods such as letterpress, offset, gravure, intaglio, rubber plate, screen printing and the like can be used.
The firing method is not particularly limited, and a known method such as a muffle furnace can be used.
There is no particular limitation on the range of the firing temperature, but if the temperature is too high, the resistance of the electron collecting electrode increases, or the base material is melted, so that the temperature is preferably 30 to 700 ° C, more preferably 100 to 600 ° C. . The firing time is not particularly limited, but is preferably 10 minutes to 10 hours.
After firing, for example, chemical plating using an aqueous solution of titanium tetrachloride or a mixed solution with an organic solvent may be used to increase the surface area of the semiconductor nanocrystal particles and increase the efficiency of electron injection from the photosensitizing compound to the semiconductor fine particles. Electrochemical plating using an aqueous solution of titanium chloride may be performed.

  The method for manufacturing a structure for a solar cell according to the present invention enables a high-viscosity electrolytic solution to be sufficiently filled in a semiconductor electrode, and furthermore, a machine generated between the semiconductor electrode and the conductive transparent substrate. Since a decrease in the mechanical strength can be suppressed without performing any special additional treatment, a semiconductor electrode having excellent power generation performance and suitable for a high-viscosity electrolytic solution can be obtained simply and with a low energy process.

The solar cell of the present invention contains the solar cell structure, a photosensitizing compound, and a solid electrolyte.
The photosensitizing compound and solid electrolyte are not particularly limited, and known compounds can be used.

  The excellent effects of the present invention will be described with the following representative examples. Note that the present description is for specifically explaining the effects of the invention, and does not limit the content of the invention.

[Example 1]
A solution composed of 10 parts by mass of titanium oxide and 90 parts by mass of ethanol was prepared by adding the titanium oxide aggregate (the titanium oxide nanocrystal particles (1), the average primary particle diameter of 21 nm) to ethanol. This was stirred with a magnetic stirrer for 16 hours, so that the titanium oxide aggregate was well wetted in advance.
The solution prepared in this manner is irradiated with an ultrasonic wave having a frequency of 40 kHz for 30 minutes by using an ultrasonic homogenizer (Sonifier SLPe 40 manufactured by BRANSON) to give an impact force derived from cavitation, thereby obtaining a titanium oxide aggregate. Was dispersed to obtain a titanium oxide nanocrystal dispersion.
When the volume-based particle size distribution of the obtained dispersion was measured by a laser diffraction particle size distribution analyzer (LA-950, manufactured by Horiba, Ltd.), the volume average median diameter (D50) was 120 nm.

Also, a solution consisting of 15.9 parts by mass of titanium tetraisopropoxide, 3.3 parts by mass of acetic acid and 80.8 parts by mass of water was stirred and mixed, and a mixture of 65% nitric acid and 1.5% by mass of the original solution was added thereto. In addition, after stirring and mixing, the mixture was kept at 80 ° C. for 4 hours. The solution thus prepared was irradiated with an ultrasonic wave having a frequency of 40 kHz for 10 minutes using an ultrasonic homogenizer, and then treated with a centrifugal separator (Himac CP-NX manufactured by Hitachi Koki), and the supernatant water was discarded. An ethanol dispersion (titanium oxide nanoamorphous dispersion) containing nanoamorphous titanium oxide ((the titanium oxide nanoamorphous particles (2)) was obtained by adding the same amount of ethanol as the discarded water. After drying at 120 ° C. for 30 minutes using a hot air dryer (Yamato Kagaku DS400) and comparing the masses before and after drying, the dispersion contained 4.5% by mass of nanoamorphous titanium oxide.
The obtained dispersion was observed with a transmission electron microscope (TEM, JEM-2100 manufactured by JEOL Ltd.), and particles in the visual field at a magnification of 200,000 were analyzed by image processing software (Image Pro Plus manufactured by Media Cybernetics). The average equivalent circle diameter of the titanium oxide nanoamorphous particles was 3.5 nm.

On the other hand, an aggregate composed of polymethyl methacrylate A fine particles having an average primary particle diameter of 60 nm (the heat-destructible particles (3)) was prepared. The weight average molecular weight (Mw) of the polymethyl methacrylate A fine particles determined by gel permeation chromatography (HLC-8220 manufactured by Tosoh Corporation) was 31,500, and a differential scanning calorimeter (Seiko Instruments Inc.) The glass transition temperature (Tg) determined by DSC6200) was 85 ° C.
The polymethyl methacrylate A fine particles were charged into ethanol to prepare a solution comprising 20 parts by mass of polymethyl methacrylate A fine particles and 80 parts by mass of ethanol. This was stirred with a magnetic stirrer for 2 hours, so that the polymethyl methacrylate A aggregate was well wetted in advance.
The solution prepared in this manner is irradiated with ultrasonic waves having a frequency of 40 kHz for 5 minutes using the ultrasonic homogenizer to give an impact force derived from cavitation, and the polymethyl methacrylate A aggregate is dispersed therein. A methyl methacrylate A dispersion was obtained.

The titanium oxide nanocrystal dispersion, titanium oxide nanoamorphous dispersion, and polymethyl methacrylate A dispersion prepared as described above were mixed while being stirred with a magnetic stirrer. At this time, the titanium oxide nanocrystals and the titanium oxide nanoamorphous after mixing were mixed at a mass ratio of 95: 5. Thereafter, ethyl cellulose (manufactured by Kanto Kagaku Co., Ltd., toluene: ethanol = viscosity of a 5% solution in a 80:20 solvent at 25 ° C. = 45 cP) as a binder and α-terpineol (manufactured by Kanto Kagaku Co., Ltd.) as a solvent were added. Then, after stirring with a magnetic stirrer for 1 hour, ethanol was removed with a rotary evaporator to obtain a coating liquid having a viscosity suitable for screen printing (the coating liquid (6)).
The amount of each of the coating liquids was adjusted so that the amount of titanium oxide was 15% by mass, the amount of polymethyl methacrylate A was 5% by mass, and the amount of the binder was 7% by mass after removing the ethanol solvent after the application.

This coating solution was applied by screen printing to a glass substrate having FTO (F-doped Tin Oxide) formed on its surface, and then baked at 500 ° C. for 60 minutes in air to form a porous semiconductor electrode.
The adhesion of the obtained titanium oxide semiconductor electrode to the FTO film was measured by a peel strength measuring device (SAICAS manufactured by Daipla Wintes). A borazon cutting blade (blade width 1.0 mm) was used for the measurement. The titanium oxide film formed on the FTO film is cut obliquely at a horizontal speed of 2.0 μm / sec and a vertical speed of 0.1 μm / sec. By moving the cutting blade only in the direction, the force applied to the cutting blade during peeling was measured, and the peel strength was calculated.
Further, the titanium oxide semiconductor electrode formed by the above method was adjusted to 0.5 mM as a ruthenium complex with an N719 dye (cis-bis (isothiocyanato) bis (2,2′-bipyridyl-4,4′-dicarboxylate). A) Ruthenium (II) -bis-tetra-n-butylammonium (manufactured by Solaronix) (the above-mentioned photosensitizing compound) in a mixed solution of acetonitrile / t-butanol (1: 1 by volume) at room temperature for 2 days in a dark place. To allow the photosensitizing compound to be adsorbed on the surface of the semiconductor electrode.

A 1-ethyl-3-methylimidazolinium dicyanamide (Sigma-Aldrich Co., Ltd.) was prepared by dissolving the following compound (1) of a proprietary compound in a chlorobenzene (10% solid content) solution on a semiconductor electrode supporting a photosensitizing compound. , 27 mM) and a solution obtained by adding 4-t-butylpyridine (55 mM, manufactured by Across Corporation) were added dropwise and air-dried. Furthermore, a solution obtained by adding 1-ethyl-3-methylimidazolinium dicyanamide (Sigma Aldrich, 5 mM) to a chlorobenzene (2% solid content) solution in which the following compound (2) of the in-house synthesized product is dissolved. Was formed by spin coating to form a solid electrolyte-containing material. 100 nm of gold was vacuum-deposited on this to form a counter electrode, and a solar cell was produced.
IV measurement of the manufactured solar cell was performed, and the conversion efficiency was calculated. IV measurement was performed under simulated sunlight irradiation (AM 1.5, 100 mW / cm ² , 25 ° C.).

[Comparative Example 1]
A coating liquid was prepared in the same manner as in Example 1, except that the titanium oxide nanoamorphous particles (2) were not added to the coating liquid. Further, using this coating liquid, a semiconductor electrode and a solar cell were produced in the same manner as in Example 1, and the peel strength and the conversion efficiency were calculated.

[Example 2]
A coating liquid was prepared in the same manner as in Example 1 except that titanium oxide nanocrystal particles having an average primary particle diameter of 133 nm were used as the titanium oxide nanocrystal particles (1). Further, using this coating liquid, a semiconductor electrode and a solar cell were produced in the same manner as in Example 1, and the peel strength and the conversion efficiency were calculated.

[Example 3]
As a titanium oxide nanocrystal particle (1), a titanium oxide nanocrystal particle having an average primary particle diameter of 18 nm is used. A solution composed of 10 parts by mass of the present titanium oxide nanocrystal particle and 90 parts by mass of ethanol is prepared, and then treated with a paint shaker for 48 hours. A coating liquid was prepared in the same manner as in Example 1, except that a titanium oxide nanocrystal dispersion was thereby obtained. Further, using this coating liquid, a semiconductor electrode and a solar cell were produced in the same manner as in Example 1, and the peel strength and the conversion efficiency were calculated.

[Example 4]
A coating liquid was prepared in the same manner as in Example 1 except that titanium oxide nanocrystal particles having an average primary particle diameter of 140 nm were used as the titanium oxide nanocrystal particles (1). Further, using this coating liquid, a semiconductor electrode and a solar cell were produced in the same manner as in Example 1, and the peel strength and the conversion efficiency were calculated.

[Example 5]
As in Example 1, except that a solution consisting of titanium tetraisopropoxide, acetic acid, and water was stirred and mixed, nitric acid was added thereto, and the mixture was stirred and mixed, and kept at 80 ° C. for 8 hours to obtain titanium oxide nanoamorphous particles. To prepare a coating solution. At this time, the average circle equivalent diameter determined from the TEM image was 4.4 nm. Further, using this coating liquid, a semiconductor electrode and a solar cell were produced in the same manner as in Example 1, and the peel strength and the conversion efficiency were calculated.

[Comparative Example 2]
A solution composed of titanium tetraisopropoxide, acetic acid, and water is stirred and mixed, nitric acid is added to the solution, and after stirring and mixing, the mixture is kept at 80 ° C. for 4 hours, and then water is further added, and the mixture is kept in an autoclave at 250 ° C. for 12 hours Then, a coating liquid was prepared in the same manner as in Example 1, except that hydrothermal synthesis was performed to obtain anatase titanium oxide particles. At this time, the average circle equivalent diameter determined from the TEM image was 12.5 nm. Further, using this coating liquid, a semiconductor electrode and a solar cell were produced in the same manner as in Example 1, and the peel strength and the conversion efficiency were calculated.

[Comparative Example 3]
A coating liquid was prepared in the same manner as in Example 1, except that polymethyl methacrylate B fine particles were used as the heat annihilating particles. Further, using this coating liquid, a semiconductor electrode and a solar cell were produced in the same manner as in Example 1, and the peel strength and the conversion efficiency were calculated. The weight average molecular weight (Mw) of polymethyl methacrylate B fine particles determined by gel permeation chromatography (HLC-8220 manufactured by Tosoh Corporation) was 27,000, and a differential scanning calorimeter (manufactured by Seiko Instruments Inc.) The glass transition temperature (Tg) determined by DSC 6200) was 75 ° C.

[Comparative Example 4]
A coating liquid was prepared in the same manner as in Example 1 except that polymethyl methacrylate C fine particles were used as the heat annihilating particles. Further, using this coating liquid, a semiconductor electrode and a solar cell were produced in the same manner as in Example 1, and the peel strength and the conversion efficiency were calculated. The weight average molecular weight (Mw) of the polymethyl methacrylate C fine particles determined by the gel permeation chromatography was 48,400, and the glass transition temperature (Tg) determined by the differential scanning calorimeter was 99 ° C.

The adhesion was evaluated as the mechanical strength of the titanium oxide electrode obtained in Example 1 and Comparative Example 1 with respect to the FTO substrate. FIG. 1 shows the results of the peel strength measured by using a peel strength measuring device as the adhesion. From this result, it can be seen that in Example 1 in which the titanium oxide nanoamorphous particles were added, the adhesion was improved as compared with Comparative Example 1 in which the titanium oxide nanoamorphous particles were not added.
Table 1 below shows the results of the peel strength measured using a peel strength measuring device as the adhesion of the titanium oxide electrodes obtained in Examples 1 to 5 and Comparative Examples 1 and 2 to the FTO substrate. From these results, Examples 1 to 5 in which the titanium oxide nanoamorphous particles were added were Comparative Examples 1 in which the titanium oxide nanoamorphous particles were not added, or Comparative Examples in which the titanium oxide nanoamorphous particles were converted into anatase crystals by hydrothermal synthesis. It can be seen that the adhesion is improved as compared with 2.

Table 1 below shows conversion efficiencies when solar cells were produced using the coating liquids obtained in Examples 1 to 5 and Comparative Examples 1 and 2. The solar cells obtained in Examples 1 to 5 have sufficient adhesion between the titanium oxide electrode and the FTO electrode, and optimal pores for filling the solid electrolyte are uniformly formed in the semiconductor electrode film. As a result, good conversion efficiency is obtained. In particular, Examples 1 and 2 in which the average primary particle size of the titanium oxide used was in the range of 20 nm to 135 nm, and the equivalent circle diameter of the titanium oxide nanoamorphous particles was 20% or less of the average primary particle size of the titanium oxide nanocrystal particles. In No. 2, high conversion efficiency was obtained. On the other hand, in Comparative Examples 1 and 2, although pores for filling the solid electrolyte were formed, the adhesion between the titanium oxide electrode and the FTO electrode was insufficient. Peeling occurs. Therefore, only lower conversion efficiency can be obtained as compared with the first to fifth embodiments. In the titanium oxide electrodes obtained in Comparative Examples 1 and 2, the titanium tetrachloride treatment conventionally used is indispensable, and a semiconductor electrode suitable for a solid electrolyte can be obtained only by drying and baking the coating liquid. Can not do.

  In addition, Table 2 below shows the peel strength to the FTO substrate when a titanium oxide electrode was produced and the conversion efficiency when a solar cell was produced using the coating liquids obtained in Example 1 and Comparative Examples 3 and 4. Show. In Example 1, polymethyl methacrylate A was used as the heat annihilating particles, whereas in Comparative Examples 3 and 4, polymethyl methacrylates B and C were used, respectively. This is an effect obtained when the weight average molecular weight and glass transition temperature of polymeryl methacrylate A are in appropriate ranges. That is, since polymethyl methacrylate B has an excessively low glass transition temperature, the heat-extinguishing particles are excessively softened. On the other hand, polymethyl methacrylate C has an excessively high glass transition temperature, so that the connectivity of pores obtained by disappearance is insufficient. Therefore, neither of Comparative Examples 3 and 4 has a more desirable structure for injecting and penetrating the high-viscosity electrolyte solution into the inside of the semiconductor porous electrode.

As described above, according to the present invention, pores are formed so as to sufficiently fill a semiconductor electrode with a high-viscosity electrolytic solution, and the adhesion between the semiconductor electrode and the conductive transparent substrate required at the time of filling is improved. Thus, it was possible to provide a solar cell structure excellent in power generation performance because it could be provided without performing any additional processing.

Japanese Patent No. 4887664 JP 2010-118158 A JP 2011-181281 A JP 2012-072234 A Japanese Patent No. 4808560 JP 2012-28302 A

Nature, 353 (1991) 737. J. Am. Chem. Soc. , 115 (1993) 6382. J. Phys. Chem. B. 110 (2006) 19191

Claims (6)

  For forming a porous semiconductor electrode, a semiconductor structure material, a binder resin, a heat-extinguishing particles, and a coating solution containing a dispersion solvent, wherein the semiconductor structure material is titanium oxide nanocrystalline particles and titanium oxide nanoamorphous particles. Wherein the heat-extinguishing particles are polymethyl methacrylate having a weight average molecular weight (Mw) of 30,000 or more and 45,000 or less and a glass transition temperature (Tg) of 80 ° C. or more and 95 ° C. or less. Coating liquid.   The coating liquid according to claim 1, wherein the average primary particle size of the titanium oxide nanocrystal particles is 20 nm or more and 135 nm or less.   The coating liquid according to claim 1, wherein a circle equivalent diameter of the titanium oxide nanoamorphous particles is 20% or less of an average primary particle diameter of the titanium oxide nanocrystal particles. 4.   A structure for a solar cell, comprising a semiconductor electrode derived from the coating liquid according to claim 1 on a conductive transparent substrate.   A solar cell comprising the solar cell structure according to claim 4, a photosensitizing compound, and a solid electrolyte.   A method for producing a structure for a solar cell, comprising forming a porous semiconductor electrode on a conductive transparent substrate using the coating liquid according to claim 1.