JP5617583B2 - Coating composition used for forming a protective film on a metal electrode substrate - Google Patents

Description

  The present invention relates to a coating composition used for forming a protective film on an electrode substrate, particularly a metal electrode substrate in a dye-sensitized solar cell.

  Currently, solar power generation is highly anticipated from the viewpoint of global environmental problems and fossil energy resource depletion problems, and solar cells using single crystal and polycrystalline silicon photoelectric conversion elements have been put into practical use. 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, dye-sensitized solar cells have recently attracted attention as solar cells using photoelectric conversion elements other than silicon. As a representative of this dye-sensitized solar cell, a transparent electrode substrate in which a transparent conductive film such as ITO is provided on the surface of a glass substrate or a transparent plastic substrate, and a metal electrode substrate are sensitized with a dye. The peripheral portion between the metal electrode substrate and the transparent electrode substrate is sealed so that the electrolyte layer does not leak. Sealed with a stopper. That is, the region where the metal electrode substrate and the transparent electrode substrate are opposed to each other with the porous photoelectric conversion layer and the electrolyte layer interposed therebetween is the power generation region, and the region sealed with the sealing material is the power generation region. It is a sealing area unrelated to the above. This porous photoelectric conversion layer is generally provided on a transparent electrode substrate, but can also be provided on a metal electrode substrate (see Patent Document 1).

  In the dye-sensitized solar cell having the above-described structure, when visible light is irradiated from the transparent electrode substrate side, the dye in the dye-sensitized porous layer is excited, transitioned from the ground state to the excited state, and excited. The electrons of the dye are injected into the conduction band in the semiconductor porous layer, and pass through an external circuit from the transparent electrode substrate or metal electrode substrate on which the semiconductor porous layer is formed. Move to transparent electrode substrate. The electrons that have moved to the counter electrode substrate are carried by the ions in the electrolyte layer and return to the dye. 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 structure, particularly when the porous photoelectric conversion layer is provided on the metal substrate, the porous photoelectric conversion layer carrying the dye is directly on the low-resistance metal substrate. Therefore, it is possible to avoid a decrease in conversion efficiency and to suppress an increase in internal resistance (curvature factor; FF) when the cell is enlarged.

  However, when the porous photoelectric conversion layer is provided on the metal substrate and power is generated by light irradiation from the transparent electrode substrate side, the porous photoelectric conversion layer exists on the low-resistance metal substrate, so that the rectifying action is In order to achieve incompleteness, reverse current, and 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.

  As means for improving the above problems, the present applicant formed a reverse electron prevention layer made of a chemical conversion treatment film on a metal substrate, and sensitized with a dye on the reverse electron prevention layer. A method for forming a porous oxide semiconductor layer has been proposed (see Patent Document 2).

  In Patent Document 2, since the chemical conversion treatment film (reverse electron prevention layer) exhibits high resistance to the electrolyte, it is possible to effectively prevent a decrease in conversion efficiency over time. However, the resistance to the electrolyte is further improved. Is required. Further, the reverse current preventing ability of the chemical conversion film is not so high, and therefore further improvement is demanded from the viewpoint of obtaining high change efficiency.

  Patent Document 3 proposes a coating solution for forming a reverse electron prevention layer by the present applicant. That is, this coating solution is composed of an organic solvent solution containing a metal compound capable of forming a metal oxide by heat treatment as a solute. The organic solvent solution contains a solute stabilizer and is 10 cP at 25 ° C. It has the above viscosity, and this is applied to the surface of a metal substrate and dried to form a reverse electron prevention layer serving as a base for a semiconductor porous layer sensitized with a dye. is there. Since the reverse electron prevention layer formed using such a coating liquid is formed from a dense layer of metal oxide, it not only exhibits an excellent rectifying action compared to that formed by chemical conversion treatment, It has good resistance to the electrolyte, and therefore has an advantage that the corrosion of the metal substrate can be effectively prevented and the problem of deterioration in conversion efficiency with time can be effectively avoided.

  However, when the reverse electron prevention layer is formed by the coating liquid as in Patent Document 3, there is a problem that local corrosion (pitting corrosion) occurs on the surface of the underlying metal substrate. Such pitting corrosion expands with time, resulting in a decrease in conversion efficiency. In particular, such pitting corrosion frequently occurs when a reverse electron prevention layer is formed on the surface of a metal substrate having a large surface roughness. Therefore, it is necessary to ensure resistance to the electrolyte and to surely prevent a decrease in conversion efficiency over time, and further improvement is required.

  Further, the present applicant previously includes a titanium oxide, a titanium compound capable of forming an oxide by heat treatment, a dispersant and an organic solvent, wherein the titanium oxide exists as dispersed particles, and the titanium compound exists as a solute. A coating composition was proposed (see Patent Document 4). According to this coating composition, this is applied to the electrode substrate and then heat-treated to thereby form a reverse electron prevention layer formed on the electrode substrate surface, and a porous titanium oxide semiconductor formed on the reverse electron prevention layer The porous photoelectric conversion layer can be formed by one-step coating, and the productivity can be remarkably increased. The electrode obtained from this coating composition has excellent resistance to the electrolyte, and can effectively prevent corrosion of the electrode substrate by the electrolyte even after a long period of time. A patent application has been filed (Japanese Patent Application No. 2009-152837).

JP 2001-273937 A JP2008-053024 JP 2010-20939 A JP2010-262919

  That is, in the electrode obtained from the coating composition disclosed in Patent Document 4, a specific structure in which the titanium dioxide crystal particles forming the porous photoelectric conversion layer bite into the reverse electron prevention layer. As a result, thermal shrinkage of the reverse electron prevention layer during film formation is relaxed, and even when the surface of the electrode substrate is rough, partial breakage of the reverse electron prevention layer is prevented, It is possible to effectively prevent the electrode substrate from being corroded by the electrolyte.

  However, even in the electrode obtained by the coating composition as described above, corrosion of the electrode substrate by the electrolyte, particularly local corrosion (pitting corrosion) has not been able to be stably and reliably prevented. That is, the corrosion prevention by the electrolyte of the electrode substrate depends on the penetration of the titanium dioxide crystal particles in the porous photoelectric conversion layer into the reverse electron prevention layer, and it is extremely difficult to stably maintain the degree of this penetration. For this reason, the corrosion prevention effect of the electrode substrate is extremely unstable.

  Accordingly, an object of the present invention is to form a protective film that is not only excellent in resistance to an electrolyte but also excellent in reverse electron prevention on the surface of an electrode substrate and a metal electrode substrate on which a porous photoelectric conversion layer is formed. It is an object of the present invention to provide a coating composition for forming a protective film.

According to the present invention, a coating composition used to form the protective film of a metal electrode substrate in the dye-sensitized solar cell, the titanium alkoxide, titanate polymer, ethylene glycol monobutyl ether and the organic solvent seen including, There is provided a coating composition, wherein the protective film is formed as a continuous layer of amorphous titanium oxide, and fine crystal particles of titanium dioxide are contained in the continuous layer .

In the coating composition of the present invention,
(1) The titanate polymer is a tetramer of tetrabutyl titanate,
(2) per 100 parts by weight of the titanium alkoxide, 5 to 30 parts by weight of the titanate polymer and 0.1 to 20 parts by weight of the ethylene glycol monobutyl ether;
(3) The titanium alkoxide is titanium isopropoxide,
Is preferred.

  The coating composition for forming a protective film of the present invention forms a protective film by applying it on an electrode substrate and baking it. The protective film has an anti-electron prevention property, an electrolyte, an electrode substrate, Is effectively and stably prevented, and has excellent corrosion prevention characteristics. Therefore, the dye-sensitized solar cell in which the porous photoelectric conversion layer is formed through such a protective film on the electrode substrate surface has extremely good rectification characteristics and high conversion efficiency. Since the corrosion of the electrode substrate is also stably prevented over a long period of time, the decrease in conversion efficiency with time is effectively eliminated. In particular, even when the porous photoelectric conversion layer is formed on the rough surface of the metal electrode, by forming a protective film using the coating composition of the present invention, an excellent reverse electron prevention effect and metal electrode can be obtained. Corrosion prevention effect is exhibited stably over a long period of time.

  That is, the protective film formed using the coating composition of the present invention has a structure in which fine crystalline particles of titanium dioxide are present in a continuous layer of a dense amorphous titanium oxide component containing an alkoxy group. have. In such a structure, the dense amorphous titanium oxide continuous layer has the property that it prevents contact between the electrolyte and the electrode substrate and contributes to corrosion prevention of the electrode substrate. Although it exhibits an electronic prevention function (rectifying action), it has the characteristic that the thermal shrinkage during film formation is extremely small, especially because the fine crystalline particles of titanium dioxide are contained in the amorphous continuous layer. Yes. As a result, breakage of the protective film (pinhole formation) due to heat shrinkage or the like during film formation is effectively prevented, and corrosion of the electrode substrate due to contact between the electrolyte and the electrode substrate is stably exhibited. . For example, even if the surface of the metal electrode substrate is rough, the heat shrinkage during film formation is effectively suppressed, so that the surface of the metal electrode substrate breaks through the protective film and is exposed. It does not occur and corrosion of the metal substrate due to the electrolyte can be prevented stably and reliably over a long period of time.

It is a figure which shows the cross-section of the protective film formed with the coating composition of this invention. It is a schematic sectional drawing which shows schematic structure of the dye-sensitized solar cell which has an electrode substrate in which the protective film shown by FIG. 1 was formed.

<Coating composition>
The coating composition of the present invention contains titanium alkoxide (a), titanate polymer (b), ethylene glycol monobutyl ether (c) and organic solvent (d) as essential components. It is compatible as a solute in the coating composition. Referring to FIG. 1, a protective film 50 formed by applying and baking this composition contains an amorphous continuous layer 51 and a microcrystalline granular material 53 of titanium dioxide, Usually, it is formed on the surface of the metal electrode substrate 60. It can be confirmed that the protective film 50 has such a structure by cross-sectional observation by TEM, XRD (X-ray diffraction), EDX (energy dispersive X-ray spectroscopy), or the like.

(A) titanium alkoxide;
The titanium alkoxide contained in the coating composition is gelled by a heat treatment (firing) described later to form a titanium oxide containing an alkoxy group.
As such a titanium alkoxide, various titanium alkoxides such as titanium methoxide, ethoxide, propoxide, butoxide and the like can be used. In particular, titanium isopropoxide is preferable, and titanium tetraisopropoxide is most preferable. Preferably used.

That is, since the titanium oxide containing an alkoxy group has an alkoxy group derived from titanium alkoxide, the degree of oxidation is low, and a flexible amorphous continuous layer 51 is formed. That is, the titanium oxide forming such an amorphous continuous layer 51 is, for example, the following formula:
TiO ₂ · nTiOR
Where n is a positive number;
R is an alkyl group derived from titanium alkoxide,
And is an amorphous continuous layer containing a titanium oxide component other than titanium dioxide. It can be easily confirmed by XRD that the layer 51 is amorphous.

Moreover, since said titanium oxide contains titanium oxide components other than titanium dioxide, the oxidation degree is lower than titanium dioxide, for example by EDX, following formula;
X = S _Ti / S _O
In the formula, S _Ti represents the energy intensity derived from the Kα ray of titanium,
S _O indicates the energy intensity derived from the oxygen Kα ray.
The Ti / O energy intensity ratio X defined by is considerably lower than that of titanium dioxide.

  For example, a titanate polymer (b), which will be described later, is not used as a titanium component, and a protective film formed of a coating composition containing only titanium alkoxide (consisting only of an amorphous continuous layer 51, and granular crystals of titanium dioxide). In general, the Ti / O energy intensity ratio X is not in the range of 1.20 to 2.39. On the other hand, the Ti / O energy intensity ratio X of the protective film 50 formed by the coating composition of the present invention containing titanium alkoxide and titanate polymer as a titanium component is in the range of about 2.00 to 2.70. The value is lower than the Ti / O energy intensity ratio X (2.40 to 2.80) of titanium dioxide.

  Such an amorphous continuous layer 51 is dense and flexible. Therefore, the protective film 50 having such an amorphous layer 51 has high adhesion to the metal electrode substrate 60, and the metal electrode substrate 60 has a high adhesion. It effectively prevents the electrolyte from coming into contact with the surface, and has an excellent ability to prevent corrosion of the metal electrode substrate 60.

(B) titanate polymer;
The titanate polymer in the coating composition is a component for precipitating microcrystalline titanium dioxide particles 53 having a fine particle size (for example, 30 nm or less) by dehydration condensation polymerization by baking (heat treatment).
As such titanate polymers, polymers of various alkyl titanates are known, but can be stably finely dispersed in an organic solvent, and microcrystalline titanium dioxide particles having the above particle diameter can be easily precipitated. In this respect, tetramer and tetramer of tetrabutyl titanate polymer are preferably used, and tetramer is most preferably used.

  That is, since the coating composition of the present invention contains such a titanate polymer together with the above-described titanium alkoxide, as shown in FIG. The protective film 50 in which 53 is distributed is formed.

The formation of the microcrystalline titanium dioxide particles 53 can be confirmed by cross-sectional observation by TEM or Ti / O energy intensity ratio X by XRD or EDX.
For example, the protective film formed by the coating composition containing only the titanate polymer as the titanium component does not include the amorphous continuous layer 51 described above, and becomes a layer in which only the microcrystalline titanium dioxide particles 53 are connected, The Ti / O energy intensity ratio X is at the same level (2.40 to 2.80) as titanium dioxide.

  The formation of such microcrystalline titanium dioxide particles 53 provides the protective film 50 with a reverse electron prevention property, but at the same time greatly improves the corrosion prevention performance. That is, the titanium dioxide particles 53 are hard and have a small coefficient of thermal expansion. For this reason, thermal contraction due to heating during film formation is effectively suppressed, and pinholes and the like due to thermal contraction are effectively prevented from being generated in the protective film 50. For example, when the surface of the metal electrode substrate 60 on which the protective film 50 as described above is formed is a rough surface, if the thermal contraction of the protective film 50 during film formation is large, the surface of the metal electrode substrate 60 is protected from the protective film 50. In the present invention, since the microcrystalline titanium dioxide particles 53 are formed by blending the titanate polymer, it is possible to effectively avoid such inconvenience.

  In addition, instead of the above-mentioned titanate polymer, it is conceivable to mix titanium dioxide crystal particles themselves into the coating composition from the beginning, but in this case, the titanium dioxide crystal particles are in a continuous state. It cannot be present in the amorphous continuous layer 51, or the continuity of the amorphous continuous layer 51 is impaired due to the presence of titanium dioxide crystal particles. And the object of the present invention cannot be achieved.

  In the present invention, the titanate polymer may be contained in the coating composition in an amount of 5 to 30 parts by weight, particularly 10 to 20 parts by weight per 100 parts by weight of the titanium alkoxide. This is suitable for producing the continuous layer 51 and the titanium dioxide crystal particles 51 in a well-balanced manner. That is, if this amount is too small, a sufficient amount of crystal grains 53 of titanium dioxide are not generated, and therefore the hardness of the protective film 50 is lowered, and heat shrinkage due to heat treatment during film formation is large, and pinholes It becomes easy to generate. On the other hand, if this amount is too large, the particle size of the microcrystalline titanium dioxide particles 53 to be produced becomes excessively large, and it is difficult to form an amorphous and dense continuous layer 51, thereby generating pinholes. As a result, the performance of the protective film 50 is degraded.

(C) ethylene glycol monobutyl ether;
The ethylene glycol monobutyl ether functions as a dispersion stabilizer for stably dispersing the titanate polymer while preventing the titanium alkoxide from precipitating and allowing the titanium alkoxide to exist stably as a solute.
This ether has the following formula:
HOCH ₂ CH ₂ OR
In the formula, R is an isobutyl group or an n-butyl group.
And is also referred to as butyl cellosolve, is chemically stable, is itself soluble in organic solvents, and has a high affinity for titanium alkoxide and titanate polymers.

  Such ethylene glycol monobutyl ether is preferably contained in the coating composition in an amount of 0.1 to 20 parts by weight, particularly 5 to 10 parts by weight per 100 parts by weight of the titanium alkoxide.

(D) an organic solvent;
In the present invention, as the organic solvent, the above-described titanium alkoxide (a) dissolves, and can also be used as a dispersion medium for the titanate polymer (b), and further has an affinity for ethylene glycol monobutyl ether (c). As long as it is high, various types can be used without any particular limitation. A viscous solution particularly suitable for a coating operation such as screen printing can be prepared. From the viewpoint that it can be volatilized without adversely affecting the characteristics, a mixed solvent containing two kinds of lower alcohol having 4 or less carbon atoms, ethyl cellulose and terpineol is preferably used.

  In particular, examples of the lower alcohol include methanol, ethanol, isopropanol, and butanol, which are particularly suitable as a solvent for the titanium alkoxide (a), and in consideration of suitability for high viscosity coating such as screen printing. Is preferably used as a mixed solvent with terpineol and ethyl cellulose.

Terpineol (C ₁₀ H ₁₈ O) is an unsaturated alcohol generated by dehydrating one molecule of water from 1,8-terbin, and three types of α, β and γ are known. A type can also be used, but generally α-terpineol (Bp: 219 to 221 ° C.) or a mixture containing α-terpineol as a main component and other types such as β-terpineol mixed (generally, commercially available) What is being done is a mixture).

  Terpineol is a viscous liquid, but has good affinity with the titanium alkoxide and titanate polymer dissolved and dispersed in the lower alcohol described above. Like the lower alcohol, terpineol is heated to produce titanium dioxide. It can be easily stripped without adversely affecting the electrical properties.

In addition, ethylcellulose, like terpineol, can be easily decomposed and removed by heat treatment without adversely affecting the electrical properties of titanium dioxide produced from titanium alkoxide and titanate polymer. And functions as a binder.
Accordingly, ethyl cellulose is most preferably used in combination with another organic solvent. For example, when a coating composition is prepared using only a lower alcohol or terpineol as the organic solvent, the viscosity of the coating composition becomes extremely low, At this time, sagging or the like is likely to occur, but the combined use of ethyl cellulose can adjust the viscosity of the coating composition to a range suitable for coating.

  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 is generally in the range of ethyl cellulose / terpineol (weight ratio) = 0.1 / 99.9 to 20/80, particularly 3 to 97. Further, it is preferable to use an appropriate amount of lower alcohol so that the viscosity of the coating composition is in a range suitable for coating (for example, 15 to 500 cP at 25 ° C.).

<Preparation of coating composition>
In the coating composition of the present invention containing the above-described components, in order for titanium alkoxide (a) to exist stably as a solute, the dispersion in which titanate polymer (b) was dispersed and titanium alkoxide (a) were dissolved. The solution is preferably prepared separately and then mixed by mixing these dispersions with the solution. If the components are mixed all at once, the titanium alkoxide (a) may be precipitated in an aggregated state. In such a case, it becomes difficult to form a uniform protective film 50. is there.

In this case, the titanate polymer (b) dispersion comprises a titanate polymer (b) and a dispersion stabilizer, ethylene glycol monobutyl ether (c), together with a part of the organic solvent described above, in a predetermined amount ratio. Prepared by mixing and stirring.
A solution of titanium alkoxide (a) is prepared by mixing the remaining organic solvent in a predetermined amount ratio and stirring.
The coating composition of the present invention can be obtained by mixing the thus prepared titanate polymer dispersion and the titanium alkoxide solution.

<Formation of protective film 50>
The protective film 50 shown in FIG. 1 can be formed by applying the coating composition of the present invention to the surface of the metal electrode substrate 60 and performing a heat treatment (firing). That is, the organic solvent is removed by volatilization, thermal decomposition, etc. by this heat treatment, and further, a titanium oxide component is generated by gelation, oxidative decomposition, etc., and a part of the generated titanium oxide component is sintered to pinhole. Thus, a dense titanium oxide-based protective film 50 having the ability to prevent reverse electrons can be obtained.

  The coating liquid can be applied by screen printing. Of course, if productivity is not taken into consideration, publicly known means such as spraying, brushing, spin coating, and dipping can be employed. Screen printing is applied in terms of efficient and continuous application.

  The heat treatment after coating varies depending on the type of titanium compound used, but in the coating composition of the present invention, the coating film may be heated and held at a high temperature of 300 ° C. to 600 ° C. for 10 to 180 minutes.

  The protective film 50 formed as described above generally has a thickness in the range of 5 to 500 nm, particularly 50 to 200 nm, and the coating liquid is formed so that the protective film 50 having such a thickness is formed. The amount of coating is adjusted. That is, if the thickness of the protective film 50 is large, it becomes an insulating film, the function as an electrode is impaired, and there is a possibility that it does not function as a battery. Furthermore, the occurrence of defects such as pinholes impairs durability, and the metal electrode substrate 60 is corroded by the electrolytic solution from the electrolyte layer when used as a battery, resulting in a decrease in conversion efficiency over time. End up. On the other hand, if the thickness is too thin, the function as a rectifying barrier is impaired, and the generation of reverse current may cause a reduction in conversion efficiency.

The above-described protective film 50 can be formed directly on the metal electrode substrate 60, but is composed of the above-described layer composed only of the dense amorphous titanium oxide continuous layer 51 or the microcrystalline titanium dioxide particles 53. By forming the granular layer with an appropriate thickness and forming the protective film 50 thereon, the ability to prevent corrosion of the electrolyte can be further enhanced.
In this case, the layer composed only of the amorphous titanium oxide continuous layer 51 formed under the protective film 50 is formed by a coating composition having a composition obtained by removing the titanate polymer (b) from the coating composition of the present invention. The granular layer formed of the microcrystalline titanium dioxide particles 53 can be formed by a coating composition having a composition obtained by removing the titanium alkoxide (a) from the coating composition of the present invention.
Further, a chemical conversion treatment film (having a reverse electron prevention function) disclosed in JP 2008-53165 A is formed on the surface of the metal electrode substrate 60, and the coating composition of the present invention is formed thereon. It is also possible to form the protective film 50 using

<Electrode and its production>
Referring to FIG. 2, the metal electrode substrate 60 having the protective film 50 formed by the coating composition of the present invention described above is provided with a porous photoelectric conversion layer 13 on the protective film 50, thereby increasing the dye enhancement. Used as the negative electrode 15 of the sensitive solar cell.

The metal electrode substrate 60 is not particularly limited as long as it is formed from a metal material having a low electrical resistance, but in general, a metal or alloy having a specific resistance of 6 × 10 ⁻⁶ Ω · m or less. For example, aluminum, iron (steel), stainless steel, copper, nickel, etc. are used. Further, the thickness of the metal electrode substrate 60 is not particularly limited as long as the metal electrode substrate 60 has a thickness enough to maintain an appropriate mechanical strength. If productivity is not taken into consideration, the metal electrode substrate 60 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.

  As understood from FIG. 2, the porous photoelectric conversion layer 13 is formed in a portion that becomes the power generation region X, and the periphery thereof is a sealed region Y that does not participate in power generation.

This porous photoelectric conversion layer 13 is one in which a dye is supported on a porous layer of an oxide semiconductor.
Examples of the oxide semiconductor include oxides of metals such as titanium, zirconium, hafnium, strontium, tantalum, chromium, molybdenum, and tungsten, or composite oxides containing these metals, such as perovskites such as SrTiO ₃ and CaTiO _3. A type oxide etc. can be illustrated. Among these, titanium dioxide is preferable in that it can be easily obtained and high conversion efficiency can be obtained, and anatase type or brookite type titanium dioxide is particularly preferable.
Moreover, the thickness of the porous photoelectric conversion layer 13 is usually about 3 to 15 μm.

  The oxide semiconductor porous layer as described above preferably has a relative density of, for example, about 50 to 90%, particularly about 50 to 70% by the Archimedes method in order to support the dye, thereby increasing the surface area. Ensure and carry an effective amount of dye.

  In order to form a porous layer of an oxide semiconductor that supports a dye, for example, the above-described oxide semiconductor fine particles are dispersed in an organic solvent or an organic compound having a chelate reactivity to form a paste-like coating composition, Alternatively, a paste-like coating composition is prepared in which fine particles of the oxide semiconductor are dispersed in an organic solvent together with a binder component such as titanium alkoxide (for example, tetraisopropoxy titanium). These coating compositions have the same viscosity as the coating composition of the present invention described above.

For example, a coating composition for forming a porous layer of an oxide semiconductor is applied to the coating layer (layer before baking) of the coating composition of the present invention described above by means such as screen printing, and a predetermined temperature (for example, 600). The porous layer of the oxide semiconductor that supports the dye can be easily formed simultaneously with the protective film 50 by firing at a temperature equal to or lower than 0.degree.
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. Moreover, the protective film 50 mentioned above will be formed simultaneously with the porous formation.

  When forming the protective film 50 using the coating composition of the present invention, the thermal contraction of the protective film 50 is effectively and reliably prevented when the porous layer of the oxide semiconductor is formed as described above. Therefore, the generation of pinholes due to the breakage of the protective film 50 due to heat shrinkage is effectively prevented, and therefore, the excellent resistance to the electrolyte and the ability to prevent back-electrons by the protective film 50 are stably exhibited. It is.

  The loading of the dye in the porous layer of the oxide semiconductor obtained as described above is performed by bringing the dye solution into contact with the porous layer, and the adsorption treatment time (immersion time) is usually from 30 minutes to 30 minutes. It is about 24 hours, and after adsorption, the porous photoelectric conversion layer 13 having the sensitizing dye adsorbed and supported on the surface and inside is obtained by drying and removing the solvent of the dye solution.

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.

By providing the porous photoelectric conversion layer 13 on the protective film 50 on the surface of the metal electrode substrate 60 as described above, the negative electrode 15 is formed.
The porous photoelectric conversion layer 13 is directly formed on the protective film 50. Depending on the case, the layer composed of only the continuous layer 51 of the fine amorphous titanium oxide or the microcrystalline titanium dioxide may be used. A granular layer composed of the particles 53 can be formed with an appropriate thickness, and the porous photoelectric conversion layer 13 can be formed thereon. That is, by interposing the layer as described above between the protective film 50 and the porous photoelectric conversion layer 13, it is possible to further enhance the ability to prevent corrosion of the electrolyte.

  In the negative electrode 15 formed as described above, the counter electrode 1 (transparent electrode) is disposed with the electrolyte layer 20 interposed therebetween, as shown in FIG. The counter electrode 1 has a transparent conductive film 5 and an electron reducing conductive layer 7 formed on the surface of a transparent substrate 3. By arranging the counter electrode 1 so as to face the negative electrode 15 in this manner, A sensitive solar cell is obtained.

  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.

  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 7 is formed thinly 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.

  As described above, the negative electrode 15 and the transparent counter electrode 1 (positive electrode) face each other with the electrolyte layer 20 interposed therebetween, and the power generation region is formed by the electrolyte layer 20 and the porous photoelectric conversion layer 13 sensitized with the dye. X will be formed.

  The electrolyte layer 20 is formed of various electrolyte solutions containing cations such as lithium ions and anions such as chlorine ions as in the known solar cell. 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.

  As shown in FIG. 2, the electrolyte layer 20 is sealed with a sealing material 30 provided in a sealing region Y located at the periphery of the power generation region X, and prevents leakage of liquid from between the electrodes. It will be done. 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, 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 sandwiched between the negative electrode 15 and the counter electrode 1 which are arranged to oppose each other, whereby the negative electrode 15 and the counter electrode 1 are joined, and then the sealing material 30 The dye-sensitized solar cell having the structure shown in FIG. 2 is obtained by inserting an injection tube into the electrode and injecting an electrolyte solution for forming the electrolyte layer 20 into the space between the two electrode substrates through the injection tube. Can be obtained.

  When using a transparent resin film or the like as the transparent substrate 3, for example, three sides of the negative electrode 15 and the counter electrode 1 are sealed with a sealant 30, then filled with an electrolyte solution from an unsealed opening, and finally, The dye-sensitized solar cell having the structure shown in FIG. 2 can also be manufactured by completely sealing the opening with the sealant 30.

  In the dye-sensitized solar cell formed in this way, the dye in the porous photoelectric conversion layer 13 is excited by irradiating visible light from the transparent counter electrode 1 side, and transitions from the ground state to the excited state. Electrons of the excited dye are injected into the conduction band in the porous photoelectric conversion layer 13 and move to the counter electrode 1 through the external circuit (not shown) through the metal electrode substrate 60. The electrons that have moved to the counter electrode 1 are carried by the ions in the electrolyte layer 20 and return to the dye. By repeating such a process, electric energy is extracted and electric power is generated. That is, in such a solar cell, it functions as a reverse electron prevention layer (rectification barrier) between the metal electrode substrate 60 and the porous photoelectric conversion layer 13 using the coating composition of the present invention, and the electrolyte and the metal electrode substrate 60. As a result, the reverse current is effectively prevented and corrosion of the metal electrode substrate 60 is reliably prevented. As a result, high conversion efficiency can be stably obtained. For example, it is possible to effectively prevent a decrease in conversion efficiency over time.

The excellent effects of the present invention will be described in the following experimental examples.
In the following examples, the measurement of the thickness of each layer formed on the aluminum substrate used as the electrode substrate and the measurement of the Ti / O energy intensity ratio X were performed by the following methods.

<Measurement of thickness of amorphous continuous layer, protective film, granular crystal layer and porous photoelectric conversion layer>
The thicknesses of these layers were measured by SEM observation using a scanning electron microscope and TEM observation using an electrolytic emission transmission analysis electron microscope.

<Measurement of Ti / O energy intensity ratio X>
As a processing apparatus, a focused ion processing apparatus (low acceleration FIB / SEM combined apparatus; XINT 200DB manufactured by SIINT) was used, and further, an energy dispersive X-ray spectrometer (γ-TEM manufactured by EDAX) was used as an EDX analysis apparatus.
That is, by using the above focused ion processing apparatus, an ultrathin slice of a layer to be measured is prepared, and then the ultrathin slice is subjected to elemental analysis by an EDX analyzer, thereby obtaining Ti / O energy. The intensity ratio X was measured.

<Example 1>
(Preparation of coating composition)
A titanium alkoxide solution (a paste for forming an amorphous continuous layer) containing titanium isopropoxide as a main component, terpineol and ethyl cellulose as a solvent in a mixed solvent ratio of 2/98 by weight, and butyl cellosolve as a stabilizer in an amount of 20% by weight. ) Was prepared.
Further, a tetrabutyl titanate tetramer as a main agent, a solvent mixture of terpineol and ethyl cellulose in a weight ratio of 2/98 as a solvent, and 20% by weight of butyl cellosolve as a stabilizer are added to form a titanate dispersion (particulate crystal layer formation). Preparation paste) was prepared.
Subsequently, the titanium alkoxide solution and the titanate dispersion were mixed at a weight ratio of 30/70 to prepare a coating composition for a protective film of the present invention.

(Preparation of porous photoelectric conversion 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, ethanol is used in an amount of 70% by weight in the paste, and dispersant is used in an amount of 0.05% in the paste. A TiO ₂ paste containing was prepared.

(Production of electrodes)
Next, a commercially available aluminum plate (thickness 0.3 mm) is prepared as a metal substrate, and on this aluminum plate, a granular crystal layer forming paste (titanate dispersion), a protective film forming coating composition, an amorphous continuous A layer forming paste (titanium alkoxide solution) and a porous photoelectric conversion layer forming paste were applied in this order, and then fired at 450 ° C. for 30 minutes to produce an electrode.

When the cross section of the electrode was observed with a HAADF image by a transmission electron microscope (TEM), granular crystals were present in the granular crystalline titanium oxide layer (granular crystalline layer) and the amorphous continuous layer on the aluminum substrate. It was confirmed that a protective film, an amorphous titanium oxide layer (amorphous continuous layer), and a porous photoelectric conversion layer were formed. The thickness of each layer was about 100 nm, about 50 nm, about 100 nm, and about 10 μm in order from the layer immediately above the aluminum substrate.
The particle diameter of the microcrystalline titanium dioxide particles in the protective film and the granular crystal layer was 15 nm or less.
Furthermore, when the energy intensity ratio of the above-mentioned formula Ti / O was measured for each layer, the average values were 2.53, 2.31, and 1.89 in order from the layer immediately above the aluminum substrate.

Further, the porous photoelectric conversion 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. The ruthenium complex dye used is represented by the following formula.
[Ru (dcbpy) ₂ (NCS) ₂ ] · 2H ₂ O

(Production and evaluation of dye-sensitized solar cell)
On the other hand, a counter electrode (positive electrode) 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 and the negative electrode 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.
The obtained battery was stored in a room temperature environment and checked after 1000 hours. As a result, corrosion was not developed and there was no decrease in conversion efficiency.

<Example 2>
The protective film coating composition was directly applied on the aluminum plate, and the porous photoelectric conversion layer forming paste was applied on the applied layer, and the porous photoelectric conversion layer was formed on the aluminum substrate via the protective film. Except for the above, an electrode was produced in the same manner as in Example 1.

When the cross section of the electrode was observed with a HAADF image by a transmission electron microscope (TEM), the protective film immediately above the aluminum substrate was a titanium oxide layer in which granular crystals were distributed in an amorphous continuous layer, The particle size of the microcrystalline titanium dioxide particles was 15 nm or less.
Moreover, the thickness of this protective film was about 50 nm, and the thickness of the porous photoelectric converting layer on it was about 10 micrometers.
Furthermore, when the Ti / O energy intensity ratio in the protective film was measured, it was 2.33, and in the porous photoelectric conversion layer, it was 2.69.

  Next, a battery was prepared in the same manner as in Example 1, stored in a room temperature environment, and confirmed after 1000 hours. As a result, corrosion was not developed and there was no decrease in conversion efficiency.

<Comparative Example 1>
In Example 1, without using a coating composition for forming a protective film, a granular crystalline titanium oxide layer (granular crystalline layer), an amorphous titanium oxide layer (amorphous continuous layer), and a porous photoelectric conversion layer, An electrode was produced in the same manner as in Example 1 except that the electrodes were formed on the aluminum substrate in this order.

  When the cross section of the electrode was observed with a HAADF image by a transmission electron microscope (TEM), cracks were partially generated in the amorphous titanium oxide layer on the aluminum substrate. This is considered to be due to the influence of internal strain due to thermal shrinkage of the amorphous titanium oxide layer.

50: Protective film 51: Amorphous titanium oxide continuous layer 53: Titanium oxide granular crystal layer 60: Metal electrode substrate

Claims (4)

A coating composition used to form the protective film of a metal electrode substrate in the dye-sensitized solar cell, seen containing titanium alkoxide, titanate polymer, ethylene glycol monobutyl ether and an organic solvent, wherein the protective film is not A coating composition, characterized in that it is formed as a continuous layer of crystalline titanium oxide, and fine crystal particulates of titanium dioxide are contained in the continuous layer .   The coating composition of claim 1 wherein the titanate polymer is a tetrabutyl titanate tetramer.   The coating composition according to claim 1 or 2, wherein the titanate polymer is contained in an amount of 5 to 30 parts by weight and the ethylene glycol monobutyl ether in an amount of 0.1 to 20 parts by weight per 100 parts by weight of the titanium alkoxide. object.   The coating composition according to any one of claims 1 to 3, wherein the titanium alkoxide is titanium isopropoxide.

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