JP5332358B2 - Coating solution for reverse electron prevention layer formation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating liquid capable of forming a backward electron preventive layer of high backward current preventive effect having high durability against an electrolyte, on a surface of an electrode substrate used in a dye-sensitized solar battery, by screen printing of high production efficiency. <P>SOLUTION: The coating liquid is a liquid of forming the backward electron preventive layer on the surface of the electrode substrate, and comprises an organic solvent solution containing, as a solute, a metal compound capable of forming a metal oxide by heat treatment, wherein the organic solvent solution contains a solute stabilizer and has 10 cP or more of viscosity at 25&deg;C. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a coating solution for forming a reverse electron prevention layer, and more particularly to a coating solution used for forming a reverse electron prevention layer provided on the electrode substrate surface of a dye-sensitized solar cell. .

  Currently, there is great expectation for photovoltaic power generation from the viewpoint of global environmental problems and fossil energy resource depletion problems, and single crystal and polycrystalline silicon photoelectric conversion elements are put into practical use as solar cells. However, this type of solar cell is expensive and has a problem of supply of silicon raw materials, and the practical application of solar cells using materials other than silicon is desired.

  From the above viewpoint, recently, a dye-sensitized solar cell has attracted attention as a solar cell using a material other than silicon. A typical structure of the dye-sensitized solar cell is as shown in FIG.

That is, this battery has a transparent electrode substrate (positive electrode substrate) 1 and a metal electrode substrate (negative electrode substrate) 10.
In the transparent electrode substrate 1, a transparent conductive film 5 (for example, an ITO film) is formed on a transparent substrate 3 such as transparent glass or a transparent resin film, and a vapor deposition film such as platinum or platinum is further formed on the electron-reducing conductive layer. 7 is formed. On the other hand, the metal electrode substrate 10 has a metal substrate 11, and a dye-sensitized semiconductor porous layer 13 is formed on the metal substrate 11. The transparent electrode substrate 1 and the metal electrode substrate 10 have a structure facing each other with the electrolyte layer 20 interposed therebetween, and the peripheral portion between the transparent electrode substrate 1 and the metal electrode substrate 10 is the electrolyte layer 20. Is sealed with a sealing material 30 so as not to leak. That is, the region where the metal electrode substrate 10 and the transparent electrode substrate 1 face each other with the dye-sensitized semiconductor porous layer 13 and the electrolyte layer 20 interposed therebetween is the power generation region X. A sealed region is a sealed region Y.

  In the dye-sensitized solar cell having such a structure, when visible light is irradiated from the transparent electrode substrate 1 side, the dye in the dye-sensitized semiconductor porous layer 11 is excited and transitions from the ground state to the excited state. The dye electrons thus injected are injected into the conduction band in the porous layer 11 and move to the transparent electrode substrate 1 through an external circuit (not shown). The electrons that have moved to the transparent electrode substrate 1 are carried by the ions in the electrolyte layer 20 and return to the pigment. Electric energy is extracted by repeating such a process. The power generation mechanism of such a dye-sensitized solar cell is different from a pn junction photoelectric conversion element, in which light capture and electronic conduction are performed in different places, and is very similar to a plant photoelectric conversion process. Yes.

  In the dye-sensitized solar cell having the above-described structure, the semiconductor porous layer 11 carrying the dye can be directly formed on the low-resistance metal substrate 11, thereby avoiding a decrease in conversion efficiency. Further, there is an advantage that an increase in internal resistance (curvature factor; FF) when the cell is enlarged can be suppressed.

  However, when generating electricity by light irradiation from the positive electrode side as described above, since it is the metal substrate 11, the rectifying action is incomplete, a reverse current is generated, and in order to obtain a sufficiently high conversion efficiency, There is still room for improvement. There is also a problem that the durability is low and the conversion efficiency decreases with time.

In order to improve the above problems, the present applicant has previously proposed a dye sensitization in which a reverse electron prevention layer 15 made of a chemical conversion film is formed on a metal substrate 11 as shown in FIG. A solar cell was proposed (see Patent Document 1).
Further, as means for preventing reverse current, a method of performing surface treatment of an oxide semiconductor layer using an organic solvent solution of titanium isopropoxide modified with acetylacetone has been proposed (Patent Documents 2 and 3). reference).

JP2008-053024 JP2007-242544 JP 2001-273937 A

However, as proposed in Patent Document 1, a reverse electron prevention layer 15 is formed on the metal substrate 11 by chemical conversion treatment, and a semiconductor porous layer 13 sensitized with a dye is formed on the reverse charge prevention layer 15. In the case of forming, the reverse electron prevention layer 15 has high resistance to the electrolyte, so that it is possible to effectively prevent a decrease in conversion efficiency over time, but the reverse current prevention effect is not so high, and thus high change efficiency. Is still inadequate in terms of
In addition, the method proposed in Patent Document 2 improves the conversion efficiency by increasing the actual surface area of the porous layer by firmly bonding oxide fine particles forming the semiconductor porous layer by surface treatment. However, since the viscosity of the organic solvent solution is remarkably low, surface treatment is performed by dipping or spraying. As a result, there is a problem that productivity is remarkably low. Further, the obtained battery has a problem in terms of durability, and the problem that the conversion efficiency decreases with time has not been effectively solved.

  Therefore, the object of the present invention is to produce a reverse electron prevention layer having a high reverse current prevention effect at the same time having high resistance to the electrolyte on the surface of the electrode substrate used in the dye-sensitized solar cell. The object is to provide a coating liquid that can be formed by highly efficient screen printing.

According to the present invention, a coating liquid used for forming a reverse electron blocking layer on the electrode substrate surface, comprising an organic solvent solution containing as a solute a metal compound capable of forming a metal oxide by heat treatment, An organic solvent solution contains a glycol ether as a solute stabilizer and has a viscosity of 10 cP or more at 25 ° C.

In the coating solution of the present invention,
( 1 ) The organic solvent contains at least two kinds of ethyl cellulose and terpineol,
( 2 ) The organic solvent contains ethyl cellulose and terpineol in a weight ratio of ethyl cellulose / terpineol = 0.1 / 99.9 to 20/80,
( 3 ) The metal compound is a metal alkoxide,
( 4 ) containing the metal compound at a concentration of 0.01 to 20% in terms of metal element,
( 5 ) containing the solute stabilizer at a concentration of 0.01 to 20%,
Is preferred.

  The coating liquid of the present invention is used to form a reverse-electricity preventing layer on the surface of a metal substrate, but it has a particularly high viscosity of 10 cP or more at 25 ° C., so it can be applied on a metal substrate by screen printing. It is possible to form a coating film (coating layer) that does not cause any dripping, and therefore, it is possible to form a reverse electron prevention layer with high productivity.

Further, the coating solution, metal compound for forming an oxide that serves as a reverse electron inhibitor, because it is stabilized by a solute stabilizer (grayed recall ether), precipitation of solids in the coating liquid The solution form is stably maintained. As a result, when baking is performed after coating to form a reverse electron prevention layer composed of a thin layer of metal oxide, the generation of defects such as pinholes is effectively suppressed. For this reason, when a semiconductor porous layer is formed thereon, the reverse electron prevention layer effectively functions as a rectifying barrier, and effectively prevents the flow of electrons (reverse electrons) from the metal substrate to the semiconductor porous layer. In addition, the contact between the electrolyte solution from the electrolyte layer and the metal substrate can be effectively prevented, and deterioration (corrosion) of the metal substrate due to the electrolyte can be effectively prevented.

  Thus, according to the coating liquid of the present invention, a reverse current prevention layer that effectively prevents reverse current and effectively prevents corrosion of the metal substrate by the electrolyte can be formed with high productivity by screen printing. The dye-sensitized solar cell provided with such a reverse electron prevention layer exhibits high conversion efficiency, is excellent in durability, and effectively suppresses the decrease in conversion efficiency over time.

<Coating solution>
The coating liquid of the present invention comprises an organic solvent solution of a metal compound, and a solute stabilizer is added to the solution to effectively prevent the precipitation of the metal compound, and thus the solution state is maintained stably. The viscosity at 25 ° C. is adjusted to 10 cP or more, particularly 50 to 2000 cP, so that a coating layer having a uniform thickness can be formed by screen printing.

  The metal compound contained in the coating liquid forms a metal oxide by a heat treatment (firing) described later, and as long as such an oxide can be formed, the metal element is not particularly limited, For example, Ti, Al, Zn, Ni, Fe, Cu or the like may be used. The form of the compound is not particularly limited as long as it can form an oxide by heat treatment and can be dissolved in an organic solvent. In general, it can be easily obtained, and the oxide can be quickly obtained by heat treatment. And is preferably an alkoxide, hydroxide, or chloride because of its high solubility in organic solvents. In addition, when a titanium porous semiconductor porous layer is formed on the reverse electron blocking layer formed using this coating solution, high adhesion is ensured between the reverse electron blocking layer and the semiconductor porous layer. Since it can be used, titanium alkoxide, particularly titanium isopropoxide is preferable, and titanium tetraisopropoxide is most preferable.

As the solute stabilizer is used to prevent the precipitation of the metal compounds, compounds are used which have a high affinity for and a metal compound soluble in themselves an organic solvent, specifically , glycol ethers (cellosolves) is used.

Glycol ether has the following formula:
HOCH ₂ CH ₂ OR
In the formula, R is an alkyl group, an aryl group, or an aralkyl group.
The alkyl group is typically a lower alkyl group having 8 or less carbon atoms such as a methyl group, an ethyl group, an isopropyl group, an n-propyl group, an isobutyl group, an n-butyl group, and an isoamyl group. The aryl group may be exemplified by a phenyl group and the aralkyl group may be exemplified by a benzyl group. Among these, a glycol ether in which R is an alkyl group is preferred, and in particular, butyl cellosolve (R = isobutyl group, n-butyl group) is preferred.

Above glycol ether is soluble in organic solvents, and since easy to form a coordination bond to the metal element, and effectively suppressing the precipitation of the metal compound, excellent properties as a solute stabilizer It seems to show . In addition, since glycol ether is chemically more stable than β-diketone, it exhibits particularly excellent characteristics as a solute stabilizer in the coating solution of the present invention.

  The organic solvent can be used without any particular limitation as long as it can dissolve the above-described metal compound. However, it forms a viscous coating solution particularly suitable for screen printing and is produced by heating. From the standpoint that it can be volatilized without adversely affecting the electrical properties (anti-electrostatic properties) of the oxide, a mixed solvent containing terpineol as a main component, particularly a mixed solvent containing two types of terpineol and ethyl cellulose is preferably used. .

Terpineol (C ₁₀ H ₁₈ O), which is the main component of this organic solvent, is an unsaturated alcohol produced by dehydrating one molecule of water from 1,8-terbin, and three types of α, β and γ are known. Any type can be used, but in general, α-terpineol (Bp: 219 to 221 ° C.) or α-terpineol is the main component, and other types such as β-terpineol are mixed. Mixtures (generally those that are commercially available are mixtures) are preferred.

  That is, the above-mentioned terpineol is a viscous liquid, can easily dissolve the above-mentioned metal compound uniformly, and adversely affects the electrical characteristics of the metal oxide (for example, titanium dioxide) produced by heating. It can be easily volatilized without giving.

  Ethylcellulose, like terpineol, can be easily decomposed and removed by heat treatment without adversely affecting the electrical properties of the metal oxide produced from the metal compound. It has the function of. That is, when a solution of a metal compound is prepared using only terpineol as an organic solvent, the viscosity (25 ° C.) of the coating solution can be 10 cP or more, but it is low viscosity for application by screen printing. This causes inconveniences such as non-uniform application during printing. Therefore, by using ethyl cellulose mixed with terpionel, the coating liquid is adjusted to a viscosity suitable for screen printing (the above-mentioned 50 to 2000 cP) without causing the concentration of the metal compound to be diluted. It is possible to form a coating film having a uniform thickness without any problem. Furthermore, since this ethyl cellulose also has a function as a binder, a metal oxide is produced in a state in which the metal compound is bound via ethyl cellulose at the time of heat treatment (firing) of the coating film described later, For this reason, the use of ethyl cellulose is extremely advantageous in that it forms a good anti-electrostatic layer without pinholes.

  In addition, although ethyl cellulose having various molecular weights is commercially available, from the viewpoint of adjusting the coating liquid to a viscosity particularly suitable for screen printing, toluene is used as a solvent, and a solid ethylcellulose concentration 10% solution is used. What has a viscosity (25 degreeC) in the range of 30-50 cp is suitable.

  From the above viewpoint, the mixed solvent used as the organic solvent in the present invention generally has an ethylcellulose / terpineol (weight ratio) of 0.1 / 99.9 to 20/80, particularly 3 to 97. It should be in range.

  In the coating liquid of the present invention containing each component described above, the content of each component is determined so that the function of each component is effectively exhibited on condition that the viscosity suitable for screen printing as described above is obtained. Is done.

  For example, the concentration of the metal compound in the coating solution is preferably 0.01 to 20%, particularly 0.1 to 5% in terms of metal element. If this concentration is too high, the solid content of the coating solution may become too high, and it may be difficult to form a coating layer having a uniform thickness, and the thickness of the formed reverse electron prevention layer becomes too thick. As a result, the generation of cracks in the layer and the formation of an insulating layer may adversely affect power generation. On the other hand, if the concentration is too low, the thickness of the formed reverse electron prevention layer becomes thin, the function as a rectifying barrier is impaired, and conversion efficiency is lowered.

  Further, the concentration of the solute stabilizer described above is preferably 0.01 to 20%, particularly 1 to 10%. If this concentration is excessively dilute, precipitation of the metal compound is likely to occur, and even if it is used in a larger amount than necessary, no further effect can be expected, and the solubility of the metal compound decreases. This is because there is a risk that it may occur.

  In the coating solution of the present invention, if the amount is small enough not to adversely affect the above-described screen printing suitability and the properties of the formed reverse electron prevention layer, a leveling agent, a surfactant, a thickener, or Other volatile solvents or the like may be added.

<Formation of reverse electron prevention layer>
The above-described coating liquid of the present invention can be applied to the surface of a metal substrate used as an electrode and subjected to heat treatment (firing) to form, for example, the reverse electron prevention layer 15 shown in FIG. That is, by this heat treatment, the organic solvent, etc. is removed by volatilization, thermal decomposition, etc., and an oxide of the metal compound is generated, and the generated metal oxide particles are sintered to prevent dense reverse electrons without pinholes. A layer is obtained.

  As described above, the coating liquid can be applied by screen printing. Of course, if productivity is not taken into consideration, known application means such as spraying, brushing, spin coating, dipping, etc. are used. However, screen printing is applied in terms of efficient and continuous application.

  The heat treatment conditions after coating vary depending on the type of metal compound used, but are generally performed by heating and holding the coating film at a high temperature of 300 to 600 ° C. for 10 to 180 minutes.

  The reverse electron blocking layer formed as described above generally has a thickness in the range of 10 to 500 nm, particularly 50 to 200 nm, and the reverse electron blocking layer having such a thickness is formed. The coating amount of the coating solution is adjusted. That is, if the thickness of the back-prevention preventing layer is excessively large, the current to the metal substrate is hindered due to the formation of an insulating film, and there is a possibility that the battery will not function. Furthermore, the occurrence of defects such as pinholes impairs durability, and when used as a battery, the metal substrate is corroded by the electrolyte from the electrolyte layer, resulting in a decrease in conversion efficiency over time. . Moreover, when the thickness is too thin, the function as a rectification | straightening barrier will be impaired, and there exists a possibility that conversion efficiency may fall by generation | occurrence | production of a reverse current.

<Dye-sensitized solar cell>
The metal substrate on which the reverse electron blocking layer is formed is used as, for example, a negative electrode substrate of a dye-sensitized solar cell having a structure shown in FIG. That is, referring to FIG. 1, a semiconductor porous layer 13 sensitized with a dye is formed on the surface of the metal substrate 11 on which the reverse electron blocking layer 15 is formed as described above. 10 is used as a dye-sensitized solar cell by facing the transparent electrode substrate (positive electrode substrate) 1 with the electrolyte layer 20 in between and sealing the periphery with a sealant 30.

In FIG. 1, the metal substrate 11 for forming the reverse electron prevention layer 15 is not particularly limited as long as it is made of a metal material having a low electrical resistance, but generally, 6 × 10 ⁻⁶ Ω · m. A metal or alloy having the following specific resistance, for example, aluminum, iron (steel), stainless steel, copper, nickel, or the like is used. Further, the thickness of the metal substrate 11 is not particularly limited as long as it has a thickness enough to maintain an appropriate mechanical strength. If productivity is not taken into consideration, the metal substrate 11 may be formed on a resin film or the like, for example, by vapor deposition. Of course, the substrate such as the resin film does not need to be transparent.

  Further, it is possible to form a chemical conversion treatment film disclosed in Japanese Patent Application Laid-Open No. 2008-53165 on the surface of the metal substrate 11, and to form the above-described reverse electron prevention layer 15 on this, Since the formation of such a chemical conversion treatment film causes a further increase in resistance, it is preferable to form the reverse electron prevention layer 15 directly on the surface of the metal substrate 11.

  The dye-sensitized semiconductor porous layer 13 on the reverse electron prevention layer 15 is formed in a portion that becomes the power generation region X, and the periphery thereof becomes a sealing region Y that does not participate in power generation. This dye-sensitized semiconductor porous layer 13 has been conventionally used in dye-sensitized solar cells, and is obtained by adsorbing and supporting a dye on an oxide semiconductor layer.

The oxide semiconductor porous layer for adsorbing and supporting the dye is, for example, an oxide of a metal such as titanium, zirconium, hafnium, strontium, tantalum, chromium, molybdenum, tungsten, or a composite oxide containing these metals, such as SrTiO _3. And a perovskite type oxide such as CaTiO ₃ , and the thickness is usually about 3 to 15 μm.

  Further, the porous layer of the oxide semiconductor needs to be porous in order to carry the dye, and for example, the relative density by the Archimedes method is 50 to 90%, particularly about 50 to 70%. It is preferable that a large surface area can be secured and an effective amount of the dye can be supported.

Such an oxide semiconductor porous layer is, for example, a paste prepared by dispersing fine particles of the above-described oxide semiconductor in an organic solvent or an organic compound having chelate reactivity, or a titanium alkoxide (for example, tetraisopropoxy titanium). It is easily formed by applying a slurry or paste dispersed in an organic solvent together with a binder component such as) on the metal substrate 21 and baking it at a temperature of 600 ° C. or lower for a time to the above-mentioned relative density. be able to. That is, by firing, the TiO ₂ gel formed by the gelation (dehydration condensation) of the binder component joins the semiconductor fine particles and becomes porous.

  The semiconductor fine particles used for forming the slurry or paste as described above should have a particle size in the range of 5 to 500 nm, particularly 5 to 350 nm from the viewpoint of making them porous. Further, as the chelate-reactive organic compound, β-diketone, β-ketoamine, and β-ketoester are representative and can be used without particular limitation as long as it is easily volatile. However, acetylacetone, which is β-diketone, can be used. Is particularly suitable, and is preferably used in an amount of 5 to 35% by weight based on the weight of the semiconductor fine particles. Further, the titanium alkoxide as a binder component is preferably used in an amount of 10 to 60 parts by weight, particularly 20 to 50 parts by weight, per 100 parts by weight of titanium dioxide fine particles. In general, lower alcohols having 4 or less carbon atoms such as methanol, ethanol, isopropanol, n-butanol, sec-butanol, t-butanol and the like are suitable, and these organic compounds can be used without limitation. A solvent may be used independently and can also be used in the form of the mixed solvent which combined 2 or more types. The amount of the organic solvent may be used in such an amount that the slurry or paste exhibits an appropriate coating property. In general, the solid content concentration of the slurry or paste is 5 to 50% by weight, particularly 15 to 40% by weight. It is better to use it in an amount that is in the range. If the amount of solvent is too large, the slurry or paste becomes low-viscosity and it becomes difficult to form a coating layer with a stable thickness due to dripping, etc., and if the amount of solvent is small, the viscosity becomes high-viscosity and workability decreases Because.

  The dye adsorbed on the oxide semiconductor porous layer formed as described above is adsorbed and supported by bringing the dye solution into contact with the porous layer. The contact of the dye solution is usually performed by dipping, and the adsorption treatment time (immersion time) is usually about 30 minutes to 24 hours, and after adsorption, the solvent of the dye solution is removed by drying, The dye-sensitized semiconductor porous layer 13 having the sensitizing dye adsorbed and supported on the surface and inside is formed.

The dye used can function as a sensitizing dye and has a linking group such as a carboxylate group, a cyano group, a phosphate group, an oxime group, a dioxime group, a hydroxyquinoline group, a salicylate group, and an α-keto-enol group. Those known per se are used. For example, a ruthenium complex, an osmium complex, an iron complex, etc. can be used without any limitation. Ruthenium-tris (2,2′-bispyridyl-4,4′-dicarboxylate), ruthenium-cis-diaqua-bis (2,2′-bispyridyl-4,4) in that it has a particularly broad absorption band. Ruthenium-based complexes such as' -dicarboxylate) are preferred. Such a dye solution of a sensitizing dye is prepared using an alcohol-based organic solvent such as ethanol or butanol as a solvent, and the dye concentration is usually about 3 × 10 ^{−4 to} 5 × 10 ⁻⁴ mol / l. It is good to do.

  The transparent electrode substrate 1 disposed opposite to the negative electrode substrate 10 composed of the metal substrate 11, the reverse electron prevention layer 15 and the dye-sensitized semiconductor porous layer 13 as described above has a transparent conductive film 5 on the surface of the transparent substrate 3. And the electron-reducing conductive layer 7 is formed.

  The transparent substrate 3 only needs to have high light transmittance, and is formed of, for example, transparent glass or a transparent resin film. The thickness and size are appropriately determined according to the intended use of the dye-sensitized solar cell to be finally formed.

  Typical examples of the transparent conductive film 5 formed on the transparent substrate 3 include a film made of an indium oxide-tin oxide alloy (ITO film), a film in which tin oxide is doped with fluorine (FTO film), and the like. An ITO film is preferable because of its high electron reducing property and particularly desirable characteristics as a cathode. These are formed on the transparent substrate 3 by vapor deposition, and the thickness is usually about 500 nm to 700 nm.

  The electron reduction conductive layer 7 formed on the transparent conductive film 5 is generally made of a thin platinum layer, and has a function of quickly transferring electrons flowing into the transparent conductive film 5 to the electrolyte layer 20. is there. Such an electron reduction conductive layer 20 is thinly formed by vapor deposition so that the average thickness thereof is about 0.1 to 1.5 nm so as not to impair the light transmittance.

  The negative electrode substrate 10 and the transparent electrode substrate (positive electrode substrate) 1 formed as described above are opposed to each other with the electrolyte layer 20 interposed therebetween, and the power generation region X is formed by the electrolyte layer 20 and the dye-sensitized semiconductor porous layer 13. Will be formed. Such an electrolyte layer 20 is formed of various electrolyte solutions containing cations such as lithium ions and anions such as chlorine ions as in the case of known solar cells. Further, it is preferable that an oxidation-reduction pair capable of reversibly taking an oxidized structure and a reduced structure is present in the electrolyte 20. Examples of such an oxidized-reduced pair include iodine-iodine compounds, bromine- Examples thereof include bromine compounds and quinone-hydroquinone. The electrolyte layer 20 is sealed by the sealing material 30 provided in the sealing region Y located at the periphery of the power generation region X, and liquid leakage from between the electrodes is prevented. In general, the thickness of the electrolyte layer 20 is generally about 10 to 50 μm, although it varies depending on the size of the battery finally formed.

  As the sealing material 30, various heat-sealable thermoplastic resins or thermoplastic elastomers such as low-density polyethylene, high-density polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, or ethylene, Polyolefin resins such as random or block copolymers of α-olefins such as propylene, 1-butene and 4-methyl-1-pentene; ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, ethylene- Ethylene-vinyl compound copolymer resin such as vinyl chloride copolymer; Styrenic resin such as polystyrene, acrylonitrile-styrene copolymer, ABS, α-methylstyrene-styrene copolymer; polyvinyl alcohol, polyvinyl pyrrolidone, polychlorinated Vinyl, polyvinylidene chloride, vinyl chloride Nyl-vinylidene chloride copolymer, vinyl resins such as polyacrylic acid, polymethacrylic acid, polymethyl acrylate, polymethyl methacrylate; nylon 6, nylon 6-6, nylon 6-10, nylon 11, nylon 12, etc. Polyamide resin; Polyester resin such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate; Polycarbonate; Polyphenylene oxide; Cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose; Starch such as oxidized starch, etherified starch, dextrin; and mixtures thereof A resin comprising, for example, is used.

  That is, the sealing material 30 is obtained by molding into a ring shape having a width corresponding to the sealing region Y, for example, by extrusion molding, injection molding, or the like using the above-described thermoplastic resin. 30 is heat-sealed (heat-pressed) in a state of being sandwiched between the negative electrode substrate 10 and the transparent electrode substrate 1 arranged so as to oppose each other, whereby the negative electrode substrate 10 and the transparent electrode substrate 1 are joined. The injection tube is inserted into the sealing material 30, and the electrolyte solution for forming the electrolyte layer 20 is injected into the space between the two electrode substrates through the injection tube, whereby the structure shown in FIG. A dye-sensitized solar cell can be obtained.

  When a transparent resin film or the like is used as the transparent substrate 3, for example, the negative electrode substrate 10 and the transparent electrode substrate 1 are sealed with a sealing agent 30, and then filled with an electrolyte solution from an unsealed opening, Finally, the dye-sensitized solar cell having the structure shown in FIG. 1 can also be produced by completely sealing the opening with the sealant 30.

  In the dye-sensitized solar cell thus formed, as described above, by irradiating visible light from the transparent electrode substrate 1 side, the dye in the dye-sensitized semiconductor porous layer 13 is excited, Transition from the ground state to the excited state, the excited dye electrons are injected into the conduction band in the porous layer 13, and the external circuit (not shown) passes through the metal electrode substrate 10 (metal substrate 11). It moves through to the transparent electrode substrate 1. The electrons that have moved to the transparent electrode substrate 1 are carried by the ions in the electrolyte layer 20 and return to the pigment. By repeating such a process, electric energy is extracted and electric power is generated. That is, in such a solar cell, the reverse electron prevention layer 15 that functions as a rectifying barrier is formed between the surface of the metal substrate 11 (the metal substrate 11 and the dye-sensitized semiconductor porous layer 13) using the coating liquid described above. Therefore, reverse current is effectively prevented and high conversion efficiency can be obtained. The reverse electron prevention layer 15 is a dense layer free from defects such as pinholes and is formed of a metal oxide that is resistant to the electrolyte. Corrosion of the substrate 11 can be effectively prevented. Therefore, extremely high durability is exhibited, and a decrease in conversion efficiency with time can also be effectively prevented.

  Further, in the above-described example, the case where the anti-electrostatic layer formed by the coating liquid is provided on the negative electrode substrate (metal substrate) of the solar cell having the structure shown in FIG. 1 has been described as an example. The layer is not limited to the above example. For example, when a metal substrate is used as the positive electrode substrate and power is generated by light irradiation from the negative electrode side, the coating liquid of the present invention is used on the positive electrode substrate surface. It is of course possible to form a reverse electron prevention layer.

The excellent effects of the present invention will be described in the following experimental examples.
<Experimental example 1>
(Oxide semiconductor layer forming paste)
Two types of commercially available TiO ₂ particles having a spherical particle size of 30 nm and a polyhedral particle size of 15 nm are used as a main agent, terpineol is used as a solvent, an amount of 60% by weight in the paste, ethyl cellulose is used as a binder agent, and the viscosity is 5 to 15 cP. A TiO ₂ paste composed of a low viscosity system, a high viscosity system of 30 to 50 cP, and a weight ratio of low viscosity system / high viscosity system = 60/40 was prepared.

(Reverse electron prevention layer forming paste)
Titanium tetraisopropoxide is the main agent, terpineol and ethylcellulose are mixed in a 2/98 weight ratio as a solvent, and butyl cellosolve is mixed as a stabilizer to a concentration of 3%, and the titanium concentration is 0.5%. The reverse electron blocking layer paste was adjusted so that As a result of measuring the viscosity at 25 ° C. using a B-type viscometer, it was 120 cP.

Next, a commercially available aluminum plate (thickness 0.3 mm) is prepared as a metal substrate, and first, the paste for the reverse electron prevention layer prepared above is applied onto the aluminum plate, and then a TiO ₂ paste is applied thereon. After that, it was baked at 450 ° C. for 30 minutes to form a reverse electron blocking layer and an oxide semiconductor layer. The thickness of each layer was about 200 nm for the reverse electron blocking layer and about 10 μm for the oxide semiconductor layer.
Further, the oxide semiconductor layer was immersed in a dye solution composed of a ruthenium complex dye dispersed in ethanol having a purity of 99.5% for 24 hours, and then dried to obtain a negative electrode structure. The ruthenium complex dye used is represented by the following formula.
[Ru (dcbpy) ₂ (NCS) ₂ ] · 2H ₂ O
On the other hand, a counter electrode (positive electrode) structure composed of an ITO / PEN film deposited with platinum was prepared.

A dye-sensitized solar cell was manufactured by sandwiching an electrolyte solution between the counter electrode structure and the negative electrode structure prepared above. As the electrolyte _solution, used was added 4-tert-butylpyridine LiI / I 2 a (0.5 mol / 0.025 mol) to those dissolved in methoxypropionitrile.
When the conversion efficiency of the obtained battery was measured, it was as follows with a measurement area of 1 cm ² , and high conversion efficiency was obtained.
Conversion efficiency: 4.17%
FF: 0.57
JSC: 10.6
VOC was 0.69, and high conversion efficiency was obtained.

<Experimental example 2>
(Oxide semiconductor layer forming paste)
A paste for forming the oxide semiconductor layer was manufactured in the same manner as in Experimental Example 1.
(Reverse electron prevention layer forming paste)
Mixing terpineol as the main agent with titanium tetraisopropoxide as the solvent and butyl cellosolve as the stabilizer to a concentration of 3%, and adjusting the paste for the reverse electron prevention layer so that the titanium concentration is 0.5% did. As a result of measuring the viscosity at 25 ° C. using a B-type viscometer, it was 5 cP.

Subsequently, each paste was apply | coated on the aluminum plate similarly to Experimental example 1. FIG. In addition, about the paste for reverse electron prevention layers, since the viscosity was low, there was much dripping at the time of coating, and uniform coating was difficult. Thereafter, firing was performed in the same manner as in Experimental Example 1 to form a reverse electron prevention layer and an oxide semiconductor layer. When the film thickness of each layer was measured, the reverse electron prevention layer had a non-uniform film thickness of about 20 to 500 nm, and the oxide semiconductor layer had a thickness of about 10 μm.
Thereafter, a dye-sensitized solar cell was prepared in the same manner as in Experimental Example 1 and the conversion efficiency was measured. The measurement area was 1 cm ² and the results were as follows. It was.
Conversion efficiency: 2.93 to 3.58%
FF: 0.50 to 0.56
JSC: 9.00 to 9.4
VOC: 0.65-0.68

(Experimental example 3)
A paste for forming the oxide semiconductor layer was manufactured in the same manner as in Experimental Example 1.
Next, as in Experimental Example 1, an oxide semiconductor layer paste was applied onto an aluminum plate and baked to form an oxide semiconductor layer. When the film thickness of the oxide semiconductor layer was measured, it was about 10 μm.
Then, to produce a dye-sensitized solar cell in the same manner as in Experimental Example 1 was measured for conversion efficiency, in a measurement area 1 cm ^2, was as follows, and became a low conversion efficiency.
Conversion efficiency: 2.94%
FF: 0.53
JSC: 8.40
VOC: 0.66

The figure which shows schematic structure of the dye-sensitized solar cell which has an electrode substrate in which the reverse electron prevention layer was formed.

Explanation of symbols

1: Transparent electrode substrate 3: Transparent substrate 5: Transparent conductive layer 10: Negative electrode substrate 11: Metal substrate 13: Dye-sensitized semiconductor porous layer 15: Reverse electron blocking layer 20: Electrolyte layer

Claims (6)

A coating liquid used for forming a reverse electron blocking layer on the electrode substrate surface, comprising an organic solvent solution containing a metal compound capable of forming a metal oxide by heat treatment as a solute, and the organic solvent solution is a solute A coating liquid characterized by containing glycol ether as a stabilizer and having a viscosity of 10 cP or more at 25 ° C. The coating liquid according to claim 1, wherein the organic solvent contains at least two kinds of ethyl cellulose and terpineol. The coating liquid according to claim 2 , wherein the organic solvent contains ethyl cellulose and terpineol in a weight ratio of ethyl cellulose / terpineol = 0.1 / 99.9 to 20/80. The coating liquid according to any one of claims 1 to 3 , wherein the metal compound is a metal alkoxide. The coating liquid according to any one of claims 1 to 4 , wherein the metal compound is contained at a concentration of 0.01 to 20% in terms of a metal element. The coating solution according to any one of claims 1 to 5 , which contains the solute stabilizer at a concentration of 0.01 to 20%.

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