WO2010117062A1 - Electrode used in dye-sensitized solar cell, and coating composition used for producing the electrode - Google Patents

Abstract

Disclosed is an electrode for dye-sensitized solar cells, which comprises a porous photoelectric conversion layer that exhibits excellent reverse electron blocking performance, while having excellent resistance to the electrolyte and stable high conversion efficiency that does not decrease over time. Specifically disclosed is an electrode used in a dye-sensitized solar cell, which is characterized by being composed of an electrode substrate and a photoelectric conversion coating layer that is formed on the electrode substrate. The electrode used in a dye-sensitized solar cell is also characterized in that the photoelectric conversion coating layer is configured of a porous layer region, in which titanium dioxide crystal particles are distributed in the form of layers, and a titanium complex oxide layer region which is positioned closer to the electrode substrate than the porous layer region, with some of the titanium dioxide crystal particles having entered into the titanium complex oxide layer region.

Description

Electrode used for dye-sensitized solar cell and coating composition used for production of the electrode

The present invention relates to an electrode used for a dye-sensitized solar cell and a coating composition used for producing the electrode, and more specifically, an electrode substrate and a photoelectric conversion layer provided on the electrode substrate; And a coating composition used for forming a photoelectric conversion layer on the electrode.

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. 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, FillFFactor; 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).

JP 2001-273937 A JP 2008-053024 A

However, as proposed in Patent Document 2, a reverse electron prevention layer is formed on a metal substrate by chemical conversion treatment, and a semiconductor porous layer sensitized with a dye is formed on the reverse electron prevention layer. Since the reverse electron prevention layer is highly resistant to electrolytes, it can effectively prevent a decrease in conversion efficiency over time, but the reverse current prevention effect is not so high, and thus a high change efficiency is obtained. It is still insufficient.

On the other hand, the present applicant has proposed a coating liquid for forming a reverse electron prevention layer [Japanese Patent Application No. 2008-178341 (Japanese Patent Laid-Open No. 2010-20939)]. 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 described above, 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.

In addition, when forming the reverse electron prevention layer using the coating liquid as described above, after forming the reverse electron prevention layer, coating with a paste coated with a metal oxide is further applied. It is necessary to form a porous oxide semiconductor layer, and in order to form a porous photoelectric conversion layer including a porous oxide semiconductor layer on an electrode metal substrate, the coating must be performed in two stages and produced. There is also a disadvantage that the property is low.

Accordingly, an object of the present invention is a dye-sensitized dye having a photoelectric conversion layer that has excellent reverse electron prevention properties, excellent resistance to electrolytes, and stably exhibits high conversion efficiency without decreasing over time. It is to provide an electrode for a solar cell.
Another object of the present invention is to provide a coating composition capable of forming a photoelectric conversion layer having the above-mentioned characteristics by a single step coating.

As a result of conducting many experiments on the electrodes used in dye-sensitized solar cells and examining their characteristics, the present inventors have particularly found that dispersed particles of semiconductor metal oxide are dispersed in an organic solvent together with a dispersant. In addition, when a metal compound capable of forming an oxide by heat treatment (particularly a metal compound capable of forming the metal oxide) is present as a solute in this organic solvent, it has excellent anti-electrostatic properties, And it discovered that the porous photoelectric converting layer excellent also in the tolerance with respect to electrolyte was formed, and came to complete this invention.

That is, according to the present invention, an electrode used in a dye-sensitized solar cell includes an electrode substrate and a photoelectric conversion coating layer provided on the electrode substrate. It is formed from a porous layer region in which titanium crystal particles are distributed in layers, and a composite oxide titanium layer region located on the electrode substrate side with respect to the porous layer region, and in the composite oxide titanium layer region Provides an electrode characterized in that a part of the crystal grains of the titanium dioxide is bitten.

In the electrode of the present invention,
(1) The complex oxide titanium layer region has the following formula:
TiO ₂ · nTiOR
Where n is a positive number;
R represents an organic group or a metal atom,
Having a molar composition represented by:
(2) The surface of the titanium dioxide crystal particles is coated with composite oxide titanium,
(3) The complex oxide titanium layer region has a thickness of 0.5 to 500 nm,
(4) The pigment is supported on the photoelectric conversion coating layer,
(5) the electrode substrate is a metal substrate;
Further, a dye is supported on the photoelectric conversion layer of this electrode and is used for an electrode of a dye-sensitized solar cell.

According to the present invention, there is also provided a coating composition used for forming a photoelectric conversion coating layer on an electrode substrate, comprising titanium oxide, a titanium compound capable of forming an oxide by heat treatment, a dispersant, and an organic A coating composition comprising a solvent, wherein the titanium oxide is present as dispersed particles and the titanium compound is present as a solute is provided.

In the above coating composition,
(1) The titanium compound is an alkoxide or chloride of titanium,
(2) containing the titanium compound in an amount of 0.01 to 50% by weight per titanium oxide in terms of metal;
(3) The organic solvent is at least one selected from the group consisting of lower alcohols having 4 or less carbon atoms, ethyl cellulose, and terpineol.
Is preferred.

Furthermore, in the above coating composition,
(4) As the dispersing agent, containing a dispersing component for dispersing the titanium oxide and a compatibilizing component for stabilizing the titanium compound as a solute,
(5) the dispersion component is at least one selected from the group consisting of glycol ether, acetic acid, trimethylacetic acid, β-diketone and water, and the compatibilizing component is glycol ether;
(6) The glycol ether is butyl cellosolve or propyl cellosolve,
(7) In terms of metal, the dispersion component is contained in an amount of 0.01 to 50% by weight per titanium oxide, and the compatibilizing component is contained in an amount of 0.01 to 50% by weight per titanium compound. Containing,
(8) Both the dispersion component and the compatibilizing component are glycol ethers,
It can take the form.

The electrode used in the dye-sensitized solar cell of the present invention has a photoelectric conversion coating layer on an electrode substrate, a porous layer region in which titanium dioxide crystal particles are distributed in layers, and a composite oxide titanium layer region The composite oxide titanium layer region is formed on the electrode substrate side with respect to the porous layer. The layer region has a remarkable feature in that a part of the crystal grains of the titanium dioxide bites into the layer region.
An electrode having a photoelectric conversion layer having such a structure not only has an excellent anti-reverse electric characteristic (rectification characteristic) per se, but also has resistance to an electrolyte, as shown in Examples described later. It is also excellent, and corrosion of the electrode substrate due to the electrolyte is effectively prevented even after a long period of time. For example, when it is formed on the surface of a metal substrate having a large surface roughness, pitting corrosion does not occur. Therefore, a decrease in conversion efficiency with time can be effectively prevented, and high conversion efficiency can be stably maintained.

In addition, this electrode can be manufactured by a one-step coating in which a coating composition for forming a photoelectric conversion layer is applied to the surface of a predetermined electrode substrate, for example, a metal substrate, and then heat-treated. But it ’s excellent.

In the coating composition of the present invention used for forming the photoelectric conversion coating layer described above, the titanium oxide present in the form of dispersed particles is a porous titanium oxide layer (that is, the above-described titanium dioxide crystal particles are layered). The titanium compound existing in the solute state is a layer in which the titanium complex oxide is densely distributed by heating (that is, the dense complex oxide titanium layer region). ) And has a function as a binder of titanium oxide particles. Porous layer using this coating composition, which is applied to the surface of a predetermined electrode substrate, for example, a metal substrate, and then heat-treated, so that titanium dioxide crystal particles are distributed in a single stage) A photoelectric conversion coating layer can be formed, which is extremely advantageous in terms of productivity.

It is a figure which shows the cross-section of the electrode for dye-sensitized solar cells of this invention. It is a figure which shows the cross-section of the conventionally well-known dye-sensitized solar cell electrode in which the photoelectric converting layer was formed by the coating in two steps. In the electrode of this invention shown by FIG. 1, it is a figure which expands and shows the interface part of an electrode substrate and this coating layer when the photoelectric conversion coating layer is formed in the rough surface part of the electrode substrate. FIG. 3 is an enlarged view showing an interface portion between the electrode substrate and the photoelectric conversion layer when the photoelectric conversion layer is formed on the rough surface portion of the electrode substrate in the conventionally known electrode shown in FIG. 2. It is a schematic sectional drawing which shows schematic structure of the dye-sensitized solar cell which has an electrode of this invention. 2 is an EDX analysis chart of a porous titanium oxide layer in an electrode produced in Example 1. FIG. 2 is an EDX analysis chart of a low-oxidation titanium layer in an electrode produced in Example 1.

<Electrode structure>
Referring to FIG. 1 showing a cross-sectional structure of an electrode for a dye-sensitized solar cell of the present invention, this electrode is formed on a surface of an electrode substrate 50 such as a metal substrate on a photoelectric conversion coating layer 51 (hereinafter simply referred to as a photoelectric conversion layer). The photoelectric conversion layer 51 includes a dense complex oxide titanium layer region 53 located on the surface side of the electrode substrate 50 and a dioxide oxide formed on the complex oxide titanium layer region. It is comprised from the porous layer area | region 55 which consists of a crystal grain of titanium.

That is, as can be understood from FIG. 1, the upper porous layer region 55 is a porous layered region in which the titanium dioxide crystal particles 55a are connected by sintering, and is mainly composed of titanium dioxide.
On the other hand, the complex oxide titanium layer region 53 has the following formula:
TiO ₂ · nTiOR
Where n is a positive number;
R represents an organic group such as an alkyl group or a metal atom,
It is formed from the complex oxide which has the molar composition shown by this, and it has having an amorphous part containing titanium oxide components other than titanium dioxide. That is, it can be confirmed by XRD or the like that the complex oxide titanium layer region 53 has an amorphous part.

Further, the fact that the upper porous layer region 55 is mainly composed of titanium dioxide and the lower composite oxide titanium layer 53 is a titanium compound different from titanium dioxide is based on the 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,
This can be confirmed by obtaining the Ti / O energy intensity ratio X defined by

That is, in the upper porous layer region 55, the Ti / O energy intensity ratio X is in the range of 2.40 to 2.80. When the Ti / O energy intensity ratio X is determined for high-purity titanium dioxide, the value is about 2.30 to 2.5. Therefore, the porous titanium oxide layer 55 is very close to titanium dioxide. It has an oxidation degree and is found to be mainly composed of titanium dioxide. On the other hand, in the lower complex oxide titanium layered region 53, the Ti / O energy intensity ratio X is in the range of 1.20 to 2.39, which is smaller than the porous titanium oxide layer 55, and therefore has a low oxidation degree. It can be seen that the composite oxide as described above is mainly used.

For example, in the EDX analysis at the central portion of the porous layer region 55 formed in the upper region of the electrode coating layer manufactured in Example 1 described later, the analysis chart is as shown in FIG. . According to this analysis chart, Ti atom peaks appear at the positions of 4.52 keV and 4.93 keV, and oxygen atom peaks appear at the position of 0.55 keV. Therefore, when the Ti / O energy intensity ratio X is calculated from the intensity of each peak, the value is 2.48.
On the other hand, the EDX analysis chart at the center of the composite oxide titanium layer region 53 formed in the lower region of the coating layer is as shown in FIG. 7, and Ti atoms are located at the same positions as in FIG. And when the peak of oxygen atoms is expressed, and calculating the Ti / O energy intensity ratio X in this part from the intensity of each peak, it becomes a value of 1.33, compared with the porous titanium oxide layer 55, The value is quite low. Accordingly, it is confirmed that the upper porous layer region 55 has a high degree of oxidation and is mainly made of titanium dioxide, and the lower layered region 53 is made of the composite oxide titanium mainly containing the composite oxide. can do.

By the way, in the present invention, the photoelectric conversion coating layer 51 composed of the composite oxide titanium layer region 53 containing the amorphous part as described above and the porous layer region 55 is coated in one step, that is, 1 It is formed by drying and heat treatment by applying one kind of coating composition in one step, and in connection with being formed by such a method, the porosity formed by the conventional two-step coating is formed. It has a peculiar structure that is not found in the quality photoelectric conversion layer.

That is, as shown in FIG. 1, in the porous photoelectric conversion layer 51 of the present invention, the titanium dioxide crystal particles 55a forming the upper porous layer region 55 are formed in the lower composite oxide titanium. The layer region 53 has digged in. As can be understood from this, a clear interface is not formed between the layer regions 53 and 55.

For example, the coating composition for forming the composite oxide titanium layer region 53 to be the reverse current prevention layer is applied and dried, and then the coating composition for forming the porous layer region 55 is applied to the composite oxide titanium layer. Even when the photoelectric conversion coating layer 51 is formed on the coating layer for the region 53 by two-step coating in which heat treatment is performed after coating and drying, as shown in FIG. A porous layer region 55 made of titanium dioxide crystal particles 55a is formed on the composite oxide titanium layer region 53 that functions as a reverse current prevention layer. However, as understood from FIG. 2, in this case, the titanium dioxide crystal particles 55 a do not penetrate into the composite oxide titanium layer region 53. A clear interface is formed with the mass layer region 55.

As described above, the structure in which the titanium dioxide crystal particles 55a are bitten into the composite oxide titanium layer 53 is a structure peculiar to the electrode of the present invention in which the porous photoelectric conversion layer 51 is formed by one-step coating. . Moreover, in the electrode of the present invention, such a specific structure exhibits a stable reverse current prevention characteristic (rectification characteristic) and at the same time has extremely high resistance to the electrolyte. For example, even when the surface of the electrode substrate 50 is partially rough, as shown in FIG. 3, the surface of the electrode substrate 50 is covered with a completely dense complex oxide titanium layer region 53. As a result, the contact between the electrolyte and the metal substrate 50 is completely prevented, the electrode substrate 50 is effectively prevented from being corroded by the electrolyte, and even when used for a long period of time, the surface of the electrode substrate 50 is pitting. Therefore, a decrease in conversion efficiency over time is effectively prevented, and high conversion efficiency can be stably maintained.

On the other hand, in the conventionally known electrode in which the photoelectric conversion coating layer 51 is formed on the surface of the electrode substrate 50 by the two-step coating as shown in FIG. 2, the surface of the electrode substrate 50 is particularly rough. In this case, as shown in FIG. 4, a part of the surface of the electrode substrate 50 is exposed through the composite oxide titanium layer region 53, so that the electrolyte directly contacts the electrode substrate 50. Thus, corrosion due to the electrolyte occurs, and for example, pitting corrosion occurs on the surface of the electrode substrate 50 due to long-term use, and conversion efficiency decreases with time.

In the electrode of the present invention, the surface of the electrode substrate 50 is completely covered with the complex oxide titanium layer region 53 as shown in FIG. 3, and the reason why the corrosion of the electrode substrate 50 by the electrolyte is effectively prevented is as follows. Although not clearly clarified, the present inventors presume as follows.

That is, in the electrode of the present invention, since the photoelectric conversion coating layer 51 is formed by one-step coating, an organic solvent for the titanium dioxide crystal particles 55a to form the composite oxide titanium layer region 53 during the heat treatment. It exists in a dispersed state in the solution, and heat treatment is performed in such a state, and the degree of oxidation is low due to gelation from the organic solvent solution in which the titanium dioxide crystal particles 55a are dispersed. Titanium oxide having an / O energy intensity ratio X of 1.20 to 2.39 is produced. For this reason, the composite oxide titanium layer region 53 is formed in a form in which the titanium dioxide crystal particles 55a are eroded. In the heat treatment in such a form, the thermal contraction of the composite oxide titanium layer region 53 is caused. Effectively mitigated. That is, it is considered that the titanium dioxide crystal particles 55a biting into the composite oxide titanium layer region 53 effectively suppress the thermal contraction of the composite oxide titanium layer region 53. Even when the surface is rough, the surface of the electrode substrate 50 does not break through the composite oxide titanium layer region 53, and the entire surface of the electrode substrate 50 is completely covered by the composite oxide titanium layer region 53. It becomes.

For example, in the case where the photoelectric conversion coating layer 51 is formed by the conventional two-stage coating, as understood from FIG. 2, when the final heat treatment is performed, the titanium dioxide crystal particles 55a are converted into the composite oxide titanium layer. The crystal particles 55 a are present on the coating layer for forming the region 53, and the crystal particles 55 a are completely separated from the complex oxide titanium layer region 53. For this reason, due to the heat treatment, the shrinkage balance between the shrinkage of the composite oxide titanium layer region 53 and the porous layer region 55 made of the crystal particles 55a is poor, and the thickness thereof varies greatly. As a result, the electrode having a particularly rough surface When the photoelectric conversion coating layer 51 is formed on the substrate 50, a rough portion of the surface of the electrode substrate 50 breaks through the composite oxide titanium layer region 53 and is exposed.

As described above, the electrode according to the present invention has a unique structure in which the titanium dioxide crystal particles 55a forming the porous layer region 55 bite into the dense complex oxide titanium layer region 53 below. In addition to such a structure, each of the titanium dioxide crystal particles 55a forming the porous layer region 55 contains an amorphous part as shown in FIG. The surface coating with the composite oxide titanium thin film 55b is also a major feature of the photoelectric conversion coating layer 51 (porous layer region 55) formed by one-step coating. That is, the photoelectric conversion coating layer 51 is subjected to heat treatment (gelation) in a state in which the titanium dioxide crystal particles 55a are dispersed in the organic solvent solution for forming the composite oxide titanium layer region 53. A complex oxide titanium layer region 53 is formed. Accordingly, the titanium dioxide crystal particles 55a are sintered in a state where they are covered with low-oxidation titanium having a small Ti / O energy intensity ratio X. As a result, the crystal particles 55a contain an amorphous part. The composite oxide titanium thin film 55b is covered.
In the porous layer region 55 formed by the two-step coating, the composite oxide titanium layer region 53 is generated by gelation in a state separated from the titanium dioxide crystal particles 55a, and can be understood from FIG. Thus, the crystal particles 55a are not covered with the thin film 55b of composite oxide titanium.

Incidentally, the fact that the surface of the titanium dioxide crystal particles 55a as described above is covered with the thin film 55b of the composite oxide titanium containing the amorphous part is that the cross section of this electrode is measured with a transmission electron microscope (TEM). ) By a high angle scattered dark field image (HAADF).

In the photoelectric conversion coating layer 51 in the electrode of the present invention as described above, there is a gap between the composite oxide titanium layer region 53 containing the amorphous portion formed on the surface of the electrode substrate 50 and the porous layer region 55. Since a clear interface is not formed, and the crystal particles 55a bite into the complex oxide titanium layer region 53, it is difficult to accurately measure the thickness of the complex oxide titanium layer region 53. However, if this thickness becomes larger than necessary, the film will crack, and the electrical resistance will increase, causing a deterioration in the function of the battery. If this thickness is thinner than necessary, the characteristics of the composite oxide titanium layer region 53 as a reverse current prevention layer may be insufficient, and cracks may occur due to stress generated when an external load is applied. Function will be reduced. For this reason, generally, as shown in FIG. 1, in the titanium dioxide crystal particles 55a forming the porous titanium oxide layer 55, the particles are in contact with the composite oxide titanium layer region 53. The distance t between the particle A and the electrode substrate 50 is defined as the thickness of the composite oxide titanium layer region 53 with the particle A farthest from the surface of the electrode substrate 50 as a reference. The composite oxide titanium layer region 53 is preferably formed so as to have a thickness of 5 to 500 nm, particularly 30 to 200 nm.
The thickness of the porous layer region 55 made of titanium oxide having a high degree of crystallinity is set to be about 5 to 20 μm as the thickness of the upper portion with reference to the lower part of the particle A. It is suitable.

In addition, the thickness of the composite oxide titanium layer region 53 and the highly crystallized porous layer region 55 as described above can be specifically adjusted by adjusting the composition of the coating composition described later. By adjusting the amount ratio of the titanium dioxide particles dispersed in the titanium compound and the titanium compound dissolved in the coating composition, an appropriate range can be obtained. That is, as the amount of titanium dioxide particles increases, the thickness of the porous layer region 55 described above increases, and as the amount of titanium dioxide particles decreases, the thickness of the composite oxide titanium layer region 53 increases.

Further, in the electrode of the present invention, the electrode substrate 50 on which the photoelectric conversion coating layer 51 having the above-described structure is formed is not particularly limited as long as it is formed from a metal material having low electrical resistance. Specifically, a metal or alloy having a specific resistance of 6 × 10 ⁻⁶ Ω · m or less, such as aluminum, iron (steel), stainless steel, copper, nickel, or the like is used.
Further, the thickness of the electrode substrate 50 is not particularly limited as long as it has a thickness enough to maintain an appropriate mechanical strength. Moreover, if productivity is not considered, the electrode substrate 50 may be formed in the resin film etc. by vapor deposition etc., for example. Of course, the substrate such as the resin film does not need to be transparent.

A chemical conversion treatment film (having a reverse electron prevention function) disclosed in Japanese Patent Application Laid-Open No. 2008-53165 is formed on the surface of the electrode substrate 50 on which the photoelectric conversion coating layer 51 is formed. And it is also possible to form the photoelectric conversion coating layer 51 on this. Further, an electrode substrate using a coating composition as disclosed in JP 2010-20939 A or a coating composition having a composition in which titanium oxide particles are removed from the coating composition of the present invention described later is used. It is also possible to form a back-current prevention layer on the surface of 50 and then form the photoelectric conversion coating layer 51 described above. By providing the photoelectric conversion coating layer 51 on the chemical conversion film and the reverse current prevention layer formed in this way, the reverse current prevention characteristic can be further improved.

In the electrode of the present invention having the above-described structure, the sensitizing dye is supported on the porous layer region 55 located above the photoelectric conversion coating layer 51, and then the electrode (negative electrode) of the dye-sensitized solar cell. Served as use. That is, the porous layer region 55 needs to be porous in order to carry the dye, and for example, the relative density by the Archimedes method is preferably 50 to 90%, particularly preferably about 50 to 70%. Thus, a large surface area can be secured and an effective amount of the dye can be supported.

Further, a porous photoelectric conversion layer can be formed on the photoelectric conversion coating layer 51 by a known means if necessary. For example, using a coating composition having a composition excluding a titanium compound capable of forming an oxide from the coating composition of the present invention, which will be described later, this coating composition is applied onto the photoelectric conversion coating layer 51, and dried and baked. By carrying out, a porous photoelectric converting layer can be formed in an overlapping manner, whereby the surface area can be increased and the amount of the dye supported can be further increased.

<Coating composition>
The electrode of the present invention described above includes titanium dioxide particles (a) and a titanium compound that can form composite oxide titanium (for example, titanium oxide having a Ti / O energy intensity ratio X of 1.20 to 2.39) by heat treatment ( b), a coating composition comprising a dispersing agent (c) and an organic solvent (d), wherein the titanium compound (b) is dissolved in the organic solvent, and this coating composition is applied to the electrode substrate 50. The photoelectric conversion coating layer 51 having the above-described structure is formed on the surface of the electrode substrate 50 by a one-step coating process in which the coating layer is dried and heat-treated.

(A) titanium dioxide particles;
The titanium dioxide particles are present as dispersed particles in the coating composition, are porous sensitized with a dye, and have a porous layer region (oxides) of high-crystallinity titanium oxide having semiconductor characteristics. This is a component for forming (corresponding to a semiconductor layer) 55. That is, since the porous layered region 55 is formed by sintering the particles, the layered region 55 includes the titanium dioxide crystal particles 55a, and thus has a high oxidation degree close to that of titanium dioxide ( For example, the region 55 has a Ti / O energy intensity ratio X of 2.40 to 2.80). As such titanium dioxide, those of anatase type, brookite type and rutile type are known. From the viewpoint of obtaining high conversion efficiency as a porous oxide semiconductor layer, anatase type or brookite type is known. Titanium dioxide is optimal.

Further, the dispersed particle size is not particularly limited, but generally, it is preferable that fine particle size powder is dispersed and adjusted to a particle size of, for example, 500 nm or less. If the dispersed particle size is excessively large, variations in the transmission of light to the formed porous layer are likely to occur, which may make it difficult to exhibit stable characteristics as a solar cell. This particle size can be measured by a laser diffraction scattering method.

The titanium dioxide particles as described above are preferably contained in the coating composition in the range of 5 to 60% by weight, particularly 10 to 40% by weight. When the content of the titanium dioxide particles is small, it becomes difficult to form the porous layer region 55 having a certain thickness, and when the coating composition contains more titanium dioxide particles than necessary, heat treatment is performed. Later, the film tends to crack, and as a result, the electric characteristics may be deteriorated.

(B) a titanium compound;
The titanium compound (b) contained in the coating composition exists as a solute, forms a titanium oxide by heat treatment (firing) described later, functions as a binder of the titanium dioxide particles described above, and reverse electrons. And a prevention layer forming function. 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. Further, from the viewpoint of the function of the titanium dioxide particles as a binder, titanium alkoxide, particularly titanium isopropoxide is preferable, and titanium tetraisopropoxide is most preferable.

That is, the titanium compound (b) forms a titanium oxide by gelation by heat treatment, and at this time, a metal formed by condensation of an alkyl group or an alkoxy group bonded to an oxygen atom and a base metal. Since the alkoxide or the like is incorporated in the titanium oxide, the titanium oxide to be generated has the formula:
TiO ₂ · nTiOR
Where n is a positive number;
R represents an organic group such as an alkyl group or a metal atom,
The composite oxide titanium layer region 53 (for example, Ti / O energy intensity ratio X is 1.20 to 2.39) having such a composition is formed.
The organic group such as alkyl is derived from an organic group such as an alkyl group contained in the titanium compound or an organic group included in the solvent used, and a metal atom is applied by this coating composition. It is considered to be derived from a metal substrate (for example, Al).

In the present invention, the above titanium compound is an amount of 0.01 to 50% by weight, particularly 0.03 to 30% by weight per titanium dioxide particle (amount in terms of metal, and the titanium compound relative to the amount of Ti in the titanium dioxide. It is preferable that it is contained in the coating composition at a ratio of Ti content in the coating composition). That is, if this amount is too small, the thickness of the composite oxide titanium layer region 53 formed under the porous layer region 55 made of high crystallinity titanium shown in FIG. The rectification characteristics are unsatisfactory, or defects such as pinholes are likely to occur, leading to a decrease in conversion efficiency.

(C) a dispersant;
In the coating composition of the present invention, as a dispersant, a dispersion component (hereinafter referred to as a first dispersant) having a dispersion function for stably dispersing the titanium dioxide particles (a) in an organic solvent. And a compatibilizing component (hereinafter referred to as a second dispersant) having a compatibilizing function for stabilizing the solute of the titanium compound (b).

Examples of the first dispersant include glycol ether, acetic acid, trimethylacetic acid, β-diketone, and water, and examples of the second dispersant include glycol ether.

As understood from the above examples, the glycol ether functions as a first dispersant and a second dispersant, and further, without adversely affecting the semiconductor characteristics of the particles by heating. Since it can be easily volatilized, it is the most preferred dispersant in the present invention.

A glycol ether having such a function has the following formula:
HOCH ₂ CH ₂ OR ¹
In the formula, R ¹ 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. Examples of the aryl group include a phenyl group, and examples of the aralkyl group include a benzyl group. Among these, glycol ethers in which R ¹ is an alkyl group are preferable, and in particular, the titanium compound (b) that has an excellent function as a compatibilizing component and prevents the precipitation of the titanium compound (b) as a solute is present. Butyl cellosolve (ethylene glycol monobutyl ether, R ¹ = isobutyl group or n-butyl group) and propyl cellosolve (ethylene glycol monopropyl ether, R) are soluble in organic solvents and have high affinity for titanium compounds. ¹ = propyl group), and butyl cellosolve is most preferable.

In addition to the glycol ether, other dispersants, that is, acetic acid, trimethylacetic acid, β-diketone, and water are used to stabilize the first dispersant (that is, titanium dioxide particles (a) in an organic solvent. The dispersion component is used as a dispersion component having a dispersion function in order to disperse, and since these do not function as a compatibilizing component, they are used in combination with the second dispersant (glycol ether). Any of these may be used depending on the type of the organic solvent used. In any case, the titanium dioxide particles can be dispersed in the organic solvent relatively stably, and the semiconductor of the particles can be heated. It can be easily stripped without adversely affecting the properties.

Examples of the β-diketone in the first dispersant include the following.
Acetylacetone 1,3-Cyclohexadione Methylenebis-1,3-cyclohexadione 2-Benzyl-1,3-cyclohexadione Acetyltetralone Palmitoyltetralone Stearoyltetralone Benzoyltetralone 2-Acetylcyclohexanone 2-Benzoylcyclohexanone 2- Acetyl-1,3-cyclohexanedione Bis (benzoyl) methane Benzoyl-p-chlorobenzoylmethane Bis (4-methylbenzoyl) methane Bis (2-hydroxybenzoyl) methane Benzoylacetone Tribenzoylmethane Diacetylbenzoylmethane Stearoylbenzoylmethane Palmitoylbenzoylmethane Lauroylbenzoylmethane dibenzoylmethane bis (4-chloroben Yl) methane bis (methylene-3,4-dioxybenzoyl) methane benzoylacetylphenylmethane stearoyl (4-methoxybenzoyl) methane butanoylacetone distearoylmethane stearoylacetone bis (cyclohexanoyl) -methane dipivaloylmethane Among the β-diketones exemplified above, acetylacetone is most preferred.

In addition, the water used as the first dispersant is usually used in combination with acetic acid.

In the present invention, the above-mentioned first dispersant is preferably used in an amount of 0.01 to 50% by weight, particularly 0.02 to 20% by weight, in terms of Ti, per titanium dioxide particle (a). .
The second dispersant is preferably used in an amount of 0.01 to 50% by weight, particularly 0.02 to 30% by weight, in terms of Ti, per titanium compound (b).

In addition, when the above-mentioned glycol ether is used in combination as the first dispersant and the second dispersant, the content in the coating composition is the amount as the first dispersant and the second dispersant. The total amount as the amount.

(D) an organic solvent;
In the present invention, the organic solvent can be used as a dispersion medium for the above-described titanium dioxide particles (a), further dissolves the above-described titanium compound (b), and has high affinity with the dispersant (c). If it is, various types can be used without any particular limitation, but a viscous coating solution particularly suitable for screen printing can be formed and can be volatilized by heating without adversely affecting the electrical properties of titanium dioxide. From the viewpoint, at least one selected from the group consisting of lower alcohols having 4 or less carbon atoms, ethyl cellulose, and terpineol is preferable.

In particular, examples of the lower alcohol include methanol, ethanol, isopropanol, and butanol, which are particularly suitable as a dispersion medium for titanium dioxide particles (a) and a solvent for the titanium compound (b), and a screen. When considering the suitability for high-viscosity coating such as printing, it is preferably used as a mixed solvent with terpineol and ethyl cellulose.

Terpineol (C ₁₀ H ₁₈ O) 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. Although types can be used, 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 metal oxide fine particles and metal compound dispersed in the above-mentioned lower alcohol. Similarly to the lower alcohol, terpineol is a metal oxide produced by heating ( For example, it can be easily volatilized without adversely affecting the electrical properties of titanium dioxide).

Furthermore, as with terpineol, ethyl cellulose can be easily decomposed and removed by heat treatment without adversely affecting the electrical properties of the titanium oxide produced from the titanium compound. It has the function of. Accordingly, ethyl cellulose is optimally used in combination with other organic solvents.For example, when only a lower alcohol or terpineol is used as an organic solvent and a titanium compound solution is prepared, the viscosity of the coating composition becomes extremely low, Although dripping or the like tends to occur during coating, the viscosity of the coating composition can be adjusted to a range suitable for coating by using ethyl cellulose in combination.

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. Those having a viscosity (25 ° C.) in the range of 30 to 50 cP are preferred.

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 3/97. In addition, an appropriate amount of lower alcohol is dispersed in the titanium dioxide particles (a) so that the viscosity of the coating composition is in a range suitable for coating (for example, 15 to 500 cP at 25 ° C.). It is good to use as a medium.

<Preparation of coating composition>
The coating composition containing each component described above includes a dispersion in which the titanium dioxide particles (a) are dispersed, and a solution in which the titanium compound (b) is dissolved, in particular, in order to allow the titanium compound (b) to exist stably as a solute. Is preferably prepared by mixing these dispersions and solutions. When the components are mixed all at once, the titanium compound (b) may be precipitated in an aggregated state. In such a case, the high crystallinity formed by sintering the titanium dioxide crystal particles 55a. This is because it becomes difficult to form a dense complex oxide titanium layer region 53 on the base of the porous layer region 55 of titanium oxide.

In preparing the coating composition as described above, the dispersion in which the titanium dioxide particles (a) are dispersed is obtained by using titanium dioxide particles and a first dispersant (glycol ether) in a part of the organic solvent described above, particularly in a lower alcohol. And / or other dispersion components) are mixed in the above-mentioned proportions and stirred. The solution in which the titanium compound (b) is dissolved is mixed with the remaining organic solvent, particularly an ethyl cellulose / terpineol mixed solvent, with a titanium compound and a second dispersant (glycol ether) in a predetermined amount ratio, and stirred. Can be obtained. At this time, it can be heated to an appropriate temperature. The amount of the organic solvent used in these dispersions or solutions is such that the viscosity of the coating composition is suitable for coating when the coating composition is prepared by mixing the two (for example, the viscosity at 25 ° C. The amount may be 10 cP or more, particularly 50 to 2000 cP), and the amount is such that the dissolved titanium does not precipitate.

<Formation of photoelectric conversion coating layer 51>
In the present invention, by using the coating composition described above, the photoelectric conversion coating layer 51 having the above-described structure having the reverse electron prevention property can be formed on the surface of the electrode substrate 50 by one-step coating.

Referring to FIG. 1, this coating composition is applied to the surface of the metal substrate 50 used as the electrode substrate, which will be the power generation region, and then heat-treated (dried and fired) to form the photoelectric conversion coating layer 51. Is done. By this heat treatment, the organic solvent and the like are removed by volatilization, thermal decomposition, etc., and the porous layer region 55 composed of the sintered titanium dioxide crystal particles 55a is densely formed by sintering the titanium dioxide particles and gelling the titanium compound. The composite oxide titanium layer region 53 is formed. Since the gelation of the titanium compound is performed in the form of incorporating the titanium dioxide particles, the titanium dioxide crystal particles 55a are converted into the composite oxide titanium layer region 53. Further, the titanium dioxide crystal particles 55a have a structure in which the titanium dioxide crystal particles 55a are coated with a composite oxide titanium having an amorphous part, for example, a composite oxide titanium having a Ti / O energy intensity ratio of 1.20 to 2.39. It is.

The coating composition can be applied by known application means such as screen printing, spray spraying, brush coating, spin coating, dipping, etc., but screen printing is effective in that it can be applied efficiently and continuously. Is preferred.

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

The coating amount of the coating composition is usually such that the thickness of the lower composite oxide titanium layer region 53 is in the above-described range (0.5 to 500 nm, particularly 30 to 200 nm), and the porous layer region 55 on the upper layer. The thickness is set to be about 5 to 20 μm.

The photoelectric conversion coating layer 51 (specifically, the porous layer region 55) obtained as described above adsorbs and supports a dye according to a conventional method, and the photoelectric conversion coating layer 51 sensitized with such a dye. The surface of the metal substrate 50 is used as an electrode substrate of a solar cell as an electrode (negative electrode substrate).

In the case where the photoelectric conversion coating layer 51 is formed on the reverse current prevention layer or the chemical conversion treatment layer, for example, power generation of the metal substrate 50 is performed in order to prevent the occurrence of defects due to positioning errors during manufacturing. It is preferable to form a reverse current prevention layer and a chemical conversion treatment layer not only on the surface to be the region but also on the surface to be the sealing region.

The dye adsorbed on the photoelectric conversion coating layer 51 is adsorbed and supported by bringing the dye solution into contact with the porous layer region 55. 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. After adsorption, the solvent of the dye solution is removed by drying. A sensitizing dye is adsorbed and supported on the surface and inside of the porous layer region 55 described above.

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.

<Dye-sensitized solar cell>
The electrode having on the surface the photoelectric conversion coating layer 51 having the porous layer region 55 sensitized with the dye as described above is used as, for example, a negative electrode substrate of a dye-sensitized solar cell having a structure shown in FIG.

Referring to FIG. 5, in the solar cell having this structure, a porous photoelectric conversion layer 13 sensitized with a dye is formed on the surface of metal substrate 11, and this is used as negative electrode substrate 10 to form electrolyte layer 20. The transparent electrode substrate (positive electrode substrate) 1 is sandwiched between and has a structure in which the periphery thereof is sealed with a sealant 30. The negative electrode substrate 10 is formed by using the coating composition described above. This is an electrode of the present invention having a structure in which the photoelectric conversion coating layer 51 formed by one-stage coating is formed on the surface of the electrode substrate 50. That is, the photoelectric conversion coating layer 13 includes a porous titanium oxide layer region 13a on which a dye is mainly adsorbed and supported, and a dense complex oxide titanium layer formed on the surface side of the metal substrate (electrode substrate) 11. It consists of a region 13b.

As understood from FIG. 5, the photoelectric conversion coating 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.

The transparent electrode substrate 1 disposed opposite to the negative electrode substrate 10 (electrode of the present invention) comprising the metal substrate 11 and the photoelectric conversion coating layer 13 sensitized with the dye as described above is transparent on the surface of the transparent substrate 3. The conductive film 5 and the electron reducing conductive layer 7 are 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) and a film in which tin oxide is doped with fluorine (FTO film). 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 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.

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 photoelectric conversion coating layer 13 (particularly, sensitized with the electrolyte layer 20 and the dye). The power generation region X is formed by the porous layer region 13a) of titanium oxide. 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, and examples of such an oxidation-reduction 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.

Examples of the sealing material 30 include 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, chloride Vinyl resins such as vinyl-vinylidene chloride copolymer, 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. By heat sealing (thermocompression bonding) in a state where the material 30 is sandwiched between the negative electrode substrate 10 and the transparent electrode substrate 1 arranged to face each other, the negative electrode substrate 10 and the transparent electrode substrate 1 are joined. Next, an injection tube is inserted into the sealing material 30, and an 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. The 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. 5 can also be manufactured by completely sealing the opening with the sealant 30.

In the dye-sensitized solar cell thus formed, the dye carried on the photoelectric conversion coating layer 13 (titanium oxide porous layer region 13a) is irradiated with visible light from the transparent electrode substrate 1 side. Excited and transitioned from the ground state to the excited state, the excited electrons of the dye are injected into the conduction band in the photoelectric conversion layer 13, and the external circuit (not shown) is passed through the metal electrode substrate 10 (metal substrate 11). 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 composite oxide titanium layer region 13b that functions as a rectifying barrier is formed in the region facing the metal substrate 11 in the photoelectric conversion layer 13, so that reverse current is effectively prevented and high conversion is achieved. Efficiency can be obtained.

Further, the photoelectric conversion coating layer 13 having the two-layer structure as described above is formed by one-step coating. That is, the dense composite oxide titanium layer region 13b existing on the surface of the metal substrate 11 and the titanium oxide porous layer region 13a formed thereon are integrally formed by one-step coating, so that the porous layer region 13a is formed. Defects such as pinholes due to the heat treatment at the time do not occur in the composite oxide titanium layer region 13b. Therefore, even if the surface of the metal substrate 11 is a rough surface having a large surface roughness, in the power generation region X, the surface is completely covered with the complex oxide titanium layer 13b. The surface is not exposed and does not directly contact the porous oxide semiconductor layer 13a. In addition, the composite oxide titanium layer region 13b is formed of a metal oxide having resistance to the electrolyte. Therefore, corrosion of the metal substrate 11 by the electrolyte solution from the electrolyte layer 20 can be surely prevented, and this dye-sensitized solar cell exhibits extremely high durability and effectively prevents a decrease in conversion efficiency over time. ing.

Furthermore, in the above solar cell, since the photoelectric conversion coating layer 13 composed of the composite oxide titanium layer region 13b and the porous layer region 13a of titanium oxide can be formed by one-step coating, its productivity is extremely high. .

In the above example, the case where the photoelectric conversion coating layer formed by the coating composition is formed on the surface of the metal substrate has been described as an example. However, such a photoelectric conversion coating layer is limited to the above example. However, it is of course possible to form it on the surface of the transparent electrode substrate, for example.

The excellent effects of the present invention will be described in the following experimental examples.
In the following examples, the thickness of each layer in the porous photoelectric conversion layer and the measurement of the Ti / O energy intensity ratio X were performed by the following methods.

<Measurement of the thickness of the porous layer region of titanium oxide and the composite oxide titanium layer region>
The thickness of the porous layer region of titanium oxide and the composite oxide titanium layer region was measured by SEM observation with a scanning electron microscope and TEM observation with an electrolytic emission transmission analysis electron microscope.

<Measurement of Ti / O energy intensity ratio X>
To measure the Ti / O energy intensity ratio of the porous layer region and the composite titanium oxide layer region, first, ultrathin sections were obtained using a focused ion processing device (device name: Xvision 200DB manufactured by SIINT, a low acceleration FIB / SEM composite device). After that, the ultrathin section was measured by performing elemental analysis with EDX (device name: γ-TEM manufactured by EDAX, an energy dispersive X-ray spectroscopic analyzer).

<Example 1>
(Paste preparation for porous layer region formation)
Two types of commercially available TiO ₂ particles having a spherical particle size of 30 nm and an irregular shape (polyhedral shape) of 15 nm are mainly used, ethanol is used as a solvent in an amount of 70% by weight, and butyl cellosolve is used as a dispersant. A TiO ₂ paste (first paste) containing in an amount of 05% by weight was prepared.

(Preparation of composite oxide titanium layer region forming paste)
A mixed solvent of terpineol and ethyl cellulose in a weight ratio of 2/98 is used as a solvent, and titanium tetraisopropoxide (main agent) and butyl cellosolve as a dispersing agent (stabilizing component) are mixed with this mixed solvent, and the composite oxide titanium. A layer region forming paste (second paste) was prepared (butyl cellosolve concentration: 3% by weight, titanium concentration: 0.5% by weight).

(Preparation of coating composition for forming photoelectric conversion coating layer)
The first paste and the second paste were mixed while being stirred at a weight ratio of 1: 1 to prepare a coating composition for forming a photoelectric conversion coating layer.

(Production of electrodes)
Next, a commercially available aluminum plate (thickness: 0.3 mm) is prepared as a metal substrate, and the coating composition prepared above is applied onto the aluminum plate, and then baked at 450 ° C. for 30 minutes to produce a photoelectric conversion. A coating layer was prepared.

When the cross section of the electrode was observed with a HAADF image by a transmission electron microscope (TEM), a porous layer region in which titanium dioxide crystal particles were distributed in layers was formed in the upper region in the photoelectric conversion coating layer. The dense composite titanium oxide layer region is formed in the lower part thereof, and the titanium dioxide crystal particles in the porous layer region bite into the lower composite oxide titanium layer region and It was confirmed that the surface of the titanium dioxide crystal particles was coated with a composite oxide titanium containing an amorphous part.

Further, EDX analysis was performed on the upper porous layer region and the lower composite oxide titanium layer region, and the analysis charts at the center of each region are shown in FIGS. 6 and 7. From this analysis chart, the average value of the Ti / O energy intensity ratio X in the upper porous layer region is 2.45, and the Ti / O energy intensity ratio X in the lower composite oxide titanium layer region is 1.82. there were.
The lower complex oxide titanium layer region had a thickness of about 150 nm, and the upper porous layer region had a thickness of about 10 μm.

Further, the photoelectric conversion coating 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, a solution obtained by dissolving LiI / I ₂ (0.5 mol / 0.025 mol) in methoxypropionitrile and adding 4-tert-butylpyridine was used.
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>
An electrode and a dye-sensitized solar cell were prepared under the same conditions as in Example 1 except that acetic acid was used as a dispersant for the paste for forming the porous layer region.
When the cross section of the electrode was observed with TEM, it was observed that the same cross section as in Example 1 was formed. The results of EDX analysis and battery evaluation are shown in Table 1.

<Example 3>
An electrode and a dye-sensitized solar cell were prepared under the same conditions as in Example 1 except that trimethylacetic acid was used as a dispersant for the paste for forming the porous layer region.
When the cross section of the electrode was observed with TEM, it was observed that the same cross section as in Example 1 was formed. The results of EDX analysis and battery evaluation are shown in Table 1.

<Example 4>
The electrode and dye-sensitized sun were used under the same conditions as in Example 1 except that a mixture of acetic acid and distilled water (acetic acid / distilled water = 50/50 wt%) was used as a dispersant for the paste for forming the porous layer region. A battery was created.
When the cross section of the electrode was observed with TEM, it was observed that the same cross section as in Example 1 was formed. The results of EDX analysis and battery evaluation are shown in Table 1.

<Example 5>
An electrode and a dye-sensitized solar cell were prepared under the same conditions as in Example 1 except that acetylacetone was used as a dispersant for the paste for forming the porous layer region.
When the cross section of the electrode was observed with TEM, it was observed that the same cross section as in Example 1 was formed. The results of EDX analysis and battery evaluation are shown in Table 1.

<Example 6>
As a dispersant for the paste for forming the porous layer region, a mixture of acetic acid and distilled water (acetic acid / distilled water = 50/50 wt%), 2 for the composite oxide titanium layer region forming paste, terpineol and ethyl cellulose as the solvent. / 98 weight ratio mixed solvent, and mixed with propyl cellosolve as titanium tetraisopropoxide (main agent) and dispersant (stabilizing component), and mixed oxide titanium layer region forming paste An electrode and a dye-sensitized solar cell were prepared under the same conditions as in Example 1 except that (second paste) was prepared (propyl cellosolve concentration: 3% by weight, titanium concentration: 0.5% by weight). .
When the cross section of the electrode was observed with TEM, it was observed that the same cross section as in Example 1 was formed. The results of EDX analysis and battery evaluation are shown in Table 1.

<Example 7>
As a dispersant for the paste for forming the porous layer region, as a mixture of acetic acid and distilled water (acetic acid / distilled water = 50/50 wt%), as a dispersant (stabilizing component) for the paste for forming the composite oxide titanium layer region An electrode and a dye-sensitized solar cell were prepared under the same conditions as in Example 1 except that the concentration of butyl cellosolve was 0.01% by weight.
When the cross section of the electrode was observed with TEM, it was observed that the same cross section as in Example 1 was formed. The results of EDX analysis and battery evaluation are shown in Table 1.

<Example 8>
As a dispersant for the paste for forming the porous layer region, as a mixture of acetic acid and distilled water (acetic acid / distilled water = 50/50 wt%), as a dispersant (stabilizing component) for the paste for forming the composite oxide titanium layer region An electrode and a dye-sensitized solar cell were prepared under the same conditions as in Example 1 except that the concentration of butyl cellosolve was 20% by weight.
When the cross section of the electrode was observed with TEM, it was observed that the same cross section as in Example 1 was formed. The results of EDX analysis and battery evaluation are shown in Table 1.

<Example 9>
As a dispersant for the paste for forming the porous layer region, as a mixture of acetic acid and distilled water (acetic acid / distilled water = 50/50 wt%), as a dispersant (stabilizing component) for the paste for forming the composite oxide titanium layer region An electrode and a dye-sensitized solar cell were prepared under the same conditions as in Example 1 except that the concentration of butyl cellosolve was 50% by weight.
When the cross section of the electrode was observed with TEM, it was observed that the same cross section as in Example 1 was formed. The results of EDX analysis and battery evaluation are shown in Table 1.

<Comparative Example 1>
Using the composite oxide titanium layer region forming paste (second paste) prepared in Example 2, this paste was applied on the same aluminum plate as in Example 2, dried at 120 ° C., and then On top of this, the paste for forming a porous region (first paste) prepared in Example 2 was applied and dried at 120 ° C. At this time, the thickness of the coating layer of the lower composite oxide titanium layer was about 150 nm, and the thickness of the coating layer of the porous titanium oxide layer was about 10 μm.

Subsequently, the coating layer laminated | stacked as mentioned above was baked for 30 minutes at 450 degreeC, and the complex oxide titanium layer and the porous titanium oxide layer were formed.
When the thickness of each layer thus formed was measured, the thickness of the upper porous titanium oxide layer was approximately the same as about 10 μm, but the lower composite oxide titanium layer was non-uniform, about 20 to 500 nm. It was a thick film. From this, it can be seen that the lower composite oxide titanium layer is largely thermally contracted.

Further, the Ti / O energy intensity ratio X of each layer was the same as that in Example 2, but the biting of the titanium dioxide crystal particles into the composite oxide titanium layer was not observed, and further, on the surface of the titanium dioxide crystal particles. No titanium oxide coating was observed.

Further, a battery was produced in the same manner as in Example 2, stored in a room temperature environment, and confirmed after 24 hours. As a result, corrosion occurred and the battery was hardly functioning.
The corrosion form is pitting corrosion, which is considered to be due to the presence of exposed portions of the aluminum surface.

50: Electrode substrate 51: Porous photoelectric conversion layer 53: Composite oxide titanium layer 55: Porous titanium oxide layer 55a: Crystal particles of titanium dioxide 55b: Composite oxide titanium coating layer

Claims (15)

1. An electrode used in a dye-sensitized solar cell, comprising an electrode substrate and a photoelectric conversion coating layer provided on the electrode substrate, wherein the photoelectric conversion coating layer has a distribution of titanium dioxide crystal particles in layers. And a composite oxide titanium layer region positioned on the electrode substrate side with respect to the porous layer region, and the titanium oxide crystal particles are formed in the composite oxide titanium layer region. An electrode characterized by part of the bite.
2. The complex oxide titanium layer region has the following formula:
   TiO ₂ · nTiOR
   Where n is a positive number;
   R represents an organic group or a metal atom,
   The electrode according to claim 1, having a molar composition represented by:
3. The electrode according to claim 1, wherein the surface of the titanium dioxide crystal particles is coated with a composite oxide titanium.
4. The electrode according to claim 1, wherein the complex oxide titanium layer region has a thickness of 0.5 to 500 nm.
5. The electrode according to claim 1, wherein a dye is supported on the photoelectric conversion coating layer.
6. The electrode according to claim 1, wherein the electrode substrate is a metal substrate.
7. A coating composition used for forming a photoelectric conversion coating layer on an electrode substrate, comprising titanium oxide, a titanium compound capable of forming an oxide by heat treatment, a dispersant and an organic solvent, the titanium oxide Exists as dispersed particles, and the titanium compound is present as a solute.
8. The coating composition according to claim 7, wherein the titanium compound is an alkoxide or chloride of titanium.
9. The coating composition according to claim 7, wherein the titanium compound is contained in an amount of 0.01 to 50 wt% per titanium oxide in terms of metal.
10. The coating composition according to claim 7, wherein the organic solvent is at least one selected from the group consisting of lower alcohols having 4 or less carbon atoms, ethyl cellulose, and terpineol.
11. The coating composition according to claim 7, comprising a dispersing component for dispersing the titanium oxide and a compatibilizing component for solute stabilization of the titanium compound as the dispersant.
12. The coating composition according to claim 11, wherein the dispersion component is at least one selected from the group consisting of glycol ether, acetic acid, trimethylacetic acid, β-diketone, and water, and the compatibilizing component is glycol ether.
13. The coating composition according to claim 12, wherein the glycol ether is butyl cellosolve or propyl cellosolve.
14. In terms of metal, the dispersion component is contained in an amount of 0.01 to 50% by weight per titanium oxide, and the compatibilizing component is contained in an amount of 0.01 to 50% by weight per titanium compound. The coating composition according to claim 11.
15. The coating composition according to claim 12, wherein both the dispersion component and the compatibilizing component are glycol ethers.

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