JP5736721B2 - Semiconductor electrode substrate and electrode used in dye-sensitized solar cell - Google Patents

Description

  The present invention relates to a substrate for a semiconductor electrode and an electrode used in a dye-sensitized solar cell, and more specifically, an electrode comprising an electrode substrate and a porous photoelectric conversion layer provided on the electrode substrate. About.

  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; 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.

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

  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 (Japanese Patent Application No. 2009-94694). 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).

  That is, the electrode obtained from the above coating composition has 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 alleviated, and even when the surface of the electrode substrate is rough, partial breakage of the reverse electron prevention layer is prevented, and corrosion of the electrode substrate by the electrolyte is prevented. Can be effectively prevented.

  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 provide an electrode for a dye-sensitized solar cell that is excellent in reverse electron prevention, excellent in resistance to electrolytes, and stably exhibits high conversion efficiency without decreasing over time. An object of the present invention is to provide a semiconductor electrode substrate used for formation.
Another object of the present invention is to provide an electrode for a dye-sensitized solar cell formed by using the semiconductor electrode substrate.

According to the present invention, in a substrate for a semiconductor electrode used in a dye-sensitized solar cell having an electrolyte solution, in which a titanium oxide-based protective layer is formed on a conductive substrate,
The titanium oxide-based protective layer includes an amorphous continuous layer of an amorphous titanium oxide containing an alkoxy group, and a granular crystal layer in which microcrystalline titanium dioxide particles having a particle size of 30 nm or less are connected,
Between the amorphous continuous layer and the granular crystal layer, an interface layer in which the amorphous titanium oxide and the microcrystalline titanium dioxide particles coexist is formed ,
A semiconductor electrode substrate is provided in which the granular crystal layer is located on the conductive substrate side, and the amorphous continuous layer is located above the granular crystal layer via the interface layer .

Furthermore, according to the present invention, the semiconductor electrode substrate, and a porous photoelectric conversion layer formed on the titanium oxide-based protective layer of the semiconductor electrode substrate , electrode for dye-sensitized solar cell having an electrolyte solution is provided.

  In the semiconductor electrode substrate of the present invention, a titanium oxide-based protective layer is formed on a conductive substrate, and this titanium oxide-based protective layer is formed of an amorphous continuous layer of amorphous titanium oxide and a fine layer. In particular, in the present invention, an amorphous material is provided that exhibits excellent resistance to the electrolyte and reverse electron prevention characteristics. It has a novel feature in that an interfacial layer in which amorphous titanium oxide and microcrystalline titanium dioxide particles coexist is formed between the solid continuous layer and the granular crystal layer. That is, since such an interface layer is formed, the resistance to the electrolyte is stably and reliably improved, and therefore, by forming a porous photoelectric conversion layer on the titanium oxide-based protective layer, It is possible to obtain a dye-sensitized solar cell electrode in which a decrease in conversion efficiency due to corrosion of the electrode substrate is stably prevented.

  The above interface layer is a layer in which microcrystalline titanium dioxide particles are contained in a continuous layer of amorphous titanium oxide, so that it is extremely dense and has a characteristic that thermal shrinkage during film formation is extremely small. Have. As a result, breakage of the titanium oxide-based protective layer (pinhole formation) due to thermal shrinkage during film formation is effectively prevented, and corrosion of the electrode substrate due to contact between the electrolyte and the electrode substrate is effectively prevented. The In addition, the interface layer exists in a layered form with a constant thickness, and does not have an unstable form such that crystal grains bite into the amorphous continuous layer. Therefore, such an interface layer can stably and reliably prevent the corrosion of the electrode substrate, and using such a semiconductor electrode substrate, a dye that stably exhibits high conversion efficiency without decreasing over time. An electrode for a sensitized solar cell can be formed.

It is a figure which shows the cross-section of the board | substrate for semiconductor electrodes of this invention. It is a schematic sectional drawing which shows the schematic structure of the electrode formed using the board | substrate for semiconductor electrodes shown by FIG. 1, and the dye-sensitized solar cell provided with this electrode.

<Electrode substrate structure>
In FIGS. 1A and 1B showing the cross-sectional structure of the semiconductor electrode substrate of the present invention, a titanium oxide-based protective layer 51 is formed on the surface of the conductive substrate 50 as a whole. . The titanium oxide-based protective layer 51 includes an amorphous continuous layer 51a made of amorphous titanium oxide and a granular crystal layer 51b, and an interface layer 51c is formed between these layers 51a and 51b. Has been.

The conductive substrate 50 on which the titanium oxide-based protective layer 51 is formed is not particularly limited as long as it is formed from a low electrical resistance metal material, but generally 6 × 10 ^−6. A metal or alloy having a specific resistance of Ω · m or less, such as aluminum, iron (steel), stainless steel, copper, nickel, or the like is used. Further, the thickness of the substrate 50 is not particularly limited as long as it has a thickness that can maintain an appropriate mechanical strength. Furthermore, if productivity is not considered, the conductive substrate 50 may be formed on the surface of 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.

  Incidentally, 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 conductive substrate 50 on which the titanium oxide-based protective layer 51 is formed. It is also possible to form a titanium oxide-based protective layer 51 to be described later.

  In the titanium oxide-based protective layer 51, the positional relationship between the amorphous continuous layer 51a and the granular crystal layer 51b is not particularly limited. For example, in FIG. 1A, the granular crystal layer 51b is the conductive substrate 50. The amorphous continuous layer 51a is located above the granular crystal layer 51b with the interface layer 51c interposed therebetween. In FIG. 1B, on the contrary, the amorphous continuous layer 51a is positioned on the conductive substrate 50 side, and the granular crystal layer 51b is formed on the amorphous continuous layer 51a via the interface layer 51c. Located on the upper side.

The amorphous continuous layer 51a is a layer formed from an amorphous titanium oxide containing an alkoxy group. Specifically, the amorphous continuous layer 51a is obtained by gelling titanium alkoxide, and is derived from the titanium alkoxide. Since an alkoxy group (for example, methoxy, ethoxy, propoxy, butoxy, etc.) is present, the amorphous layer has a low degree of oxidation and is flexible.
That is, the titanium oxide forming the amorphous continuous layer 51a has the following formula:
TiO ₂ · nTiOR
Where n is a positive number;
R is an alkyl group,
And is amorphous including a titanium oxide component other than titanium dioxide. It can be confirmed by XRD (X-ray diffraction) or the like that the layer 51a is amorphous.
Further, the degree of oxidation of the amorphous continuous layer 51a is determined by 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,
The Ti / O energy intensity ratio X defined by the above can be confirmed, and this Ti / O energy intensity ratio X is in the range of 1.20 to 2.39, which is considerably higher than that of titanium dioxide. The value is low.
The amorphous continuous layer 51a can be confirmed to be a dense layer by observing the cross section with a transmission microscope (TEM).

As confirmed from the cross-sectional observation by TEM, the above-described amorphous continuous layer 51a is a dense layer, and therefore effectively prevents the contact between the electrolyte and the surface of the conductive substrate 50 and the conductive substrate 50. Having a rectifying action (that is, a reverse electron preventing action) for suppressing the flow of electrons from the surface of the substrate to the porous photoelectric conversion layer (not shown in FIG. 1) formed on the titanium oxide-based protective layer 51 It is.
In general, the thickness of the amorphous continuous layer 51a is preferably in the range of 5 to 150 nm. If this thickness is excessively large, the electrical resistance of the titanium oxide-based protective layer 51 is remarkably increased, and the characteristics as the electrode substrate are impaired. If the thickness is too thin, the resistance to the electrolyte and This is because the ability to prevent reverse electrons is impaired.

  On the other hand, the granular crystal layer 51b is a layer in which microcrystalline titanium dioxide particles having a particle diameter of 30 nm or less are connected. X can be confirmed. For example, since the granular crystal layer 51b is made of titanium dioxide, the Ti / O energy intensity ratio X is in the range of 2.40 to 2.80.

That is, the granular crystal layer 51b is coarser than the amorphous continuous layer 51a, but is considerably harder and higher in hardness than the amorphous continuous layer 51a, and its thermal expansion coefficient is also small. As a result, heat shrinkage during film formation is extremely small, and it has a function of effectively preventing the generation of pinholes due to heat shrinkage.
In order to sufficiently exhibit the above heat shrinkage preventing ability without damaging the resistance to the electrolyte of the titanium oxide-based protective layer 51 and the ability to prevent reverse electrons, the thickness of the granular crystal layer 51b is generally: It is preferably in the range of 5 to 300 nm.

  Thus, by forming the titanium oxide-based protective layer 51 with the amorphous continuous layer 51a and the granular crystal layer 51b as described above, it is possible to obtain excellent resistance to the electrolyte and reverse electron prevention. However, in the present invention, in addition to the amorphous continuous layer 51a and the granular crystal layer 51b, an interface layer 51c is provided between the layers 51a and 51b.

The interface layer 51c is a layer in which the amorphous titanium oxide containing an alkoxy group and microcrystalline titanium dioxide particles coexist. That is, in this layer, the hard particles of microcrystalline titanium dioxide are tightly incorporated in the flexible continuous layer of amorphous titanium oxide, which ensures the ability of the microcrystalline titanium dioxide particles to suppress thermal shrinkage. For example, it is possible to effectively suppress thermal shrinkage during the formation of the amorphous continuous layer 51a adjacent to the interface layer 51c, and to reliably prevent the breakage and the generation of pinholes.
In the case where such an interface layer 51c is not formed, the microcrystalline titanium dioxide particles of the granular crystal layer 51b are only in contact with the amorphous continuous layer 51a, and a part of the particles is partially non-exposed. Even if it bites into the crystalline continuous layer 51a, it hardly bites into the continuous layer 51a. Therefore, the heat shrinkage preventing ability cannot be exhibited stably and reliably, and film breakage and pinholes often occur during film formation. In particular, when the surface of the conductive substrate 50 is a rough surface, the occurrence of pinholes and the like becomes significant during film formation.

  In the present invention, the presence of the interface layer 51c can also be confirmed by cross-sectional observation by TEM or Ti / O energy intensity ratio X by EDX. For example, since the interface layer 51c is a mixture of amorphous titanium oxide and microcrystalline titanium dioxide particles, the degree of oxidation is lower than that of the granular crystal layer 51b and higher than that of the amorphous continuous layer 51a. The Ti / O energy intensity ratio X is an intermediate value between the layers 51b and 51a.

In such an interface layer 51c, amorphous titanium oxide and microcrystalline titanium dioxide particles should coexist in an appropriate balance so that the above-described heat shrinkage preventing ability can be sufficiently exerted. The Ti / O energy intensity ratio X is preferably in the range of 2.00 to 2.70, particularly in the range of 2.10 to 2.55.
Further, from the viewpoint of stably and reliably exhibiting the heat shrinkage preventing ability of the interface layer 51c, it is preferable that the thickness of the interface layer 51c is 5 nm or more, particularly in the range of 5 to 200 nm.

  Thus, in the semiconductor electrode substrate of the present invention, the titanium oxide-based protective layer 51 on the conductive substrate 50 is formed by the amorphous continuous layer 51a, the granular crystal layer 51b, and the interface layer 51c. It is possible to reliably prevent the occurrence of film breakage and pinholes during the film formation, and thus it is possible to stably exhibit the resistance to the electrolyte and the ability to prevent reverse electrons.

<Coating composition for forming a titanium oxide-based protective layer>
The titanium oxide-based protective layer 51 having the above-described structure includes a coating composition for forming the amorphous continuous layer 51a, a coating composition for forming the granular crystal layer 51b, and an interface layer 51c. The coating compositions are formed by sequentially applying and drying these coating compositions according to the layer structure, and finally baking them all at once. The baking temperature at this time is usually about 300 to 550 ° C.
Each of the above coating compositions is applied by means such as spin coating, die coating, and screen printing, but is generally applied by screen printing in that it can be easily applied to a large area.

1. A coating composition for forming the amorphous continuous layer 51a;
This coating composition is disclosed in, for example, Japanese Patent Application Laid-Open No. 2010-20939, and an organic solvent solution containing a titanium alkoxide capable of forming a titanium oxide by heat treatment as a solute is used.

  In the above coating composition, various titanium alkoxides such as titanium methoxide, ethoxide, propoxide, butoxide can be used as the titanium alkoxide, but titanium isopropoxide is particularly preferable, and titanium tetraisopropoxy is used. Is most preferably used.

  The organic solvent can be used without particular limitation as long as it can dissolve titanium alkoxide, but a solution having a viscosity suitable for a coating operation such as screen printing can be prepared and easily volatilized. From the viewpoint of being possible, a mixed solution containing terpineol and a main component, particularly, a mixed solvent containing two kinds of terpineol and ethyl cellulose is preferably used.

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

  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. 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. In addition, an appropriate amount of lower alcohol (methanol, ethanol, propanol, etc.) should be added 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 can also be added.

  Furthermore, it is preferable to add a solute stabilizer for allowing the titanium alkoxide to exist stably as a solute (that is, to prevent precipitation of titanium alkoxide) in the coating composition. As such a solute stabilizer, a compound which is itself soluble in an organic solvent and has a high affinity for a metal compound is used. For example, glycol ether (cellosolve) and β-diketone are preferably used. The

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

  Examples of the β-diketone include 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, dibe Zoylmethane, bis (4-chlorobenzoyl) methane, bis (methylene-3,4-dioxybenzoyl) methane, benzoylacetylphenylmethane, stearoyl (4-methoxybenzoyl) methane, butanoylacetone, distearoylmethane, stearoylacetone, Examples thereof include bis (cyclohexanoyl) -methane and dipivaloylmethane, and among these, acetylacetone is preferred.

  Such a solute stabilizer is preferably used in the range of 0.02 to 30 parts by weight per 100 parts by weight of the titanium alkoxide.

2. A coating composition for forming the granular crystal layer 51b;
As a coating composition for forming this layer, a dispersion in which a titanate polymer is dispersed in an organic solvent is used.

  The titanate polymer is a component for precipitating microcrystalline titanium dioxide particles having a particle size of 30 nm or less by dehydration condensation polymerization by 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 view of this, polymers of tetrabutyl titanate, particularly tetramers and demers, are preferably used.

  Further, as the organic solvent for dispersing the titanate polymer, terpineol and ethyl cellulose similar to those used in the coating composition described above can be used, and in particular, a viscosity suitable for a coating operation is ensured. From the viewpoint of being capable of being mixed, a mixed solvent containing terpineol and ethyl cellulose is suitable, and a lower alcohol can also be mixed in order to ensure a predetermined viscosity as in the case described above.

  The titanate polymer content in such a coating composition depends on the type of polymer or organic solvent so that the viscosity of the coating composition is suitable for coating operations (15 to 500 cP at 25 ° C.). An appropriate range is set.

In such a coating composition, it is preferable to use a dispersion stabilizer in order to stably disperse the titanate polymer. As such a dispersion stabilizer, glycol ether, particularly ethylene glycol monobutyl ether (butyl cellosolve) is used. Are preferably used. The amount of the dispersion stabilizer used is generally in the range of 5 to 50 parts by weight, particularly 10 to 30 parts by weight per 100 parts by weight of titanate polymer.
Furthermore, this coating composition may contain titanium alkoxide (particularly, tetratitanium isopropoxide) as a binder component, if necessary. However, if the blending amount of the binder component is large, the dispersion stability of the titanate polymer is impaired, and precipitation of microcrystalline titanium dioxide particles becomes difficult. Therefore, the blending amount should be limited to a small amount, for example Should be in the range of 70 parts by weight or less, especially 50 parts by weight or less per 100 parts by weight of titanate polymer.

3. A coating composition for forming the interface layer 51c;
Such a coating composition has a composition obtained by blending the above-described coating composition for forming the amorphous continuous layer 51a and the coating composition for forming the granular crystal layer 51b. Specifically, A titanium alkoxide for precipitating amorphous titanium oxide and a titanate polymer for precipitating microcrystalline titanium dioxide particles having a particle size of 30 nm or less, and a solute stabilizer or titanate polymer for titanium alkoxide These components are dissolved or dispersed in the organic solvent described above.
Suitable titanium alkoxides and titanate polymers, solute stabilizers, dispersion stabilizers, and organic solvents are also as described above, and their contents and addition amounts are also as described above.

<Electrode and its production>
Referring to FIG. 2, the semiconductor electrode substrate of the present invention described above (denoted by 10 in FIG. 2) is provided with a dye-sensitized layer by providing a porous photoelectric conversion layer 13 on the titanium oxide-based protective layer 51. Used as the negative electrode 15 of the sensitive solar cell.

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 viscosities as various coating compositions used for forming the titanium oxide-based protective layer 51 described above.
That is, this coating composition is applied to the coating layer (the layer before baking) of the above-described coating composition for the titanium oxide-based protective layer 51 by means such as screen printing, and a predetermined temperature (for example, 600 ° C. or less). Thus, it can be easily formed by firing for a time to obtain the above-described relative density. 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. In addition, the titanium oxide-based protective layer 51 described above is formed at the same time as the porous structure.

  That is, when forming a porous layer of an oxide semiconductor as described above, in the present invention, the thermal contraction of the titanium oxide-based protective layer 51 is effectively and reliably prevented. The breakage of the physical protective layer 51 and the generation of pinholes are effectively prevented, so that the excellent resistance to the electrolyte and the ability to prevent back electrons by the protective layer 51 are stably exhibited.

  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 titanium oxide-based protective layer 51 of the semiconductor electrode substrate 10 as described above, the negative electrode 15 is formed.

  As shown in FIG. 2, the counter electrode 1 (transparent electrode) is disposed on the negative electrode 15 with the electrolyte layer 20 interposed therebetween. 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 conductive substrate 50. 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 conductive substrate 50 and the porous photoelectric conversion layer 13 using the various coating compositions described above, and the electrolyte and the conductive substrate. Since the titanium oxide-based protective layer 51 that prevents contact with the substrate 50 is formed, reverse current is effectively prevented and corrosion of the conductive substrate 50 is reliably prevented. As a result, high conversion efficiency is stabilized. For example, a decrease in conversion efficiency over time can be effectively prevented.

The excellent effects of the present invention will be described in the following experimental examples. Example 2 is a reference example.
In the following examples, the thickness of each layer formed on the conductive substrate (aluminum substrate) and the Ti / O energy intensity ratio X were measured by the following method.

<Measurement of thickness of amorphous continuous layer, interface layer, 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>
To measure the Ti / O energy intensity ratio of the porous photoelectric conversion layer and the titanium oxide layer, first create an ultrathin slice using a focused ion processing device (device name: low-acceleration FIB / SEM composite device SIINT XVision 200DB). Then, the ultrathin section was measured by performing elemental analysis with EDX (device name: γ-TEM manufactured by EDAX, an energy dispersive X-ray spectrometer).

<Example 1>
(Preparation of paste for forming amorphous continuous layer)
A paste for forming an amorphous continuous layer was prepared by adding titanium isopropoxide as a main agent, terpineol and ethylcellulose as a solvent in a mixed solvent ratio of 2/98 by weight, and 20% by weight of butyl cellosolve as a stabilizer.

(Preparation of paste for forming granular crystal layer)
A paste for forming a granular crystal layer was prepared by adding tetrabutyl titanate tetramer as a main agent, terpineol and ethylcellulose as a solvent in a mixed solvent ratio of 2/98 by weight, and 20% by weight of butyl cellosolve as a stabilizer.

(Preparation of paste for interface layer formation)
The amorphous continuous layer forming paste and the granular crystal layer forming paste were mixed at a ratio of 30/70% by weight to prepare an interface layer forming paste.

(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 the coating composition prepared above is prepared on this aluminum plate by using a granular crystal layer forming paste, an interface layer forming paste, an amorphous material. A continuous layer forming paste and a porous photoelectric conversion layer forming paste were applied in this order, and then fired at 450 ° C. for 30 minutes to prepare an electrode.

The cross section of the electrode was observed with a HAADF image by a transmission electron microscope (TEM). As a result, a granular crystalline titanium oxide layer (granular crystalline layer) was formed immediately above the aluminum substrate, and a titanium oxide layer in which granular crystals and amorphous were mixed. It was confirmed that an (interface layer), 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 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>
Each layer-forming paste prepared in Example 1 is formed on the same aluminum plate as in Example 1 by using an amorphous continuous layer forming paste, an interface layer forming paste, a granular crystal layer forming paste, and a porous photoelectric conversion. The layers were applied in the order of the layer forming paste, and then baked at 450 ° C. for 30 minutes to produce an electrode.

The cross section of the electrode was observed by a HAADF image by a transmission electron microscope (TEM). As a result, an amorphous titanium oxide layer, a titanium oxide layer in which granular crystals and amorphous were mixed, and granular crystal oxidation were formed immediately above the aluminum substrate. It was confirmed that a titanium layer and a porous photoelectric conversion layer were formed, and the particle size of the microcrystalline titanium dioxide particles in the granular crystal layer was 15 nm or less.
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.
Furthermore, when the energy intensity ratio of the above-described formula Ti / O was measured for each layer, the average value was 1.94, 2.33, 2.69 in order from the layer immediately above the aluminum substrate.

  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>
Each layer forming paste prepared in Example 1 was placed on the same aluminum plate as in Example 1 in the order of an amorphous continuous layer forming paste, a granular crystal layer forming paste, and a porous photoelectric conversion layer forming paste. Then, it was baked 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), an amorphous titanium oxide layer, a granular crystalline titanium oxide layer, and a porous photoelectric conversion layer were formed immediately above the aluminum substrate. It was confirmed that there were some cracks in the titanium oxide layer and portions where cracks were mixed. This is considered to be due to the influence of internal strain due to thermal shrinkage of the amorphous titanium oxide layer.

<Comparative Example 2>
Each layer forming paste prepared in Example 1 was placed on the same aluminum plate as in Example 1 in the order of a granular crystal layer forming paste, an amorphous continuous layer forming paste, and a porous photoelectric conversion layer forming paste. Then, it was baked at 450 ° C. for 30 minutes to produce an electrode.

  When the cross section of the electrode is observed with a HAADF image by a transmission electron microscope (TEM), a granular crystalline titanium oxide layer, an amorphous titanium oxide layer, and a porous photoelectric conversion layer are formed immediately above the aluminum substrate. It was confirmed that there were some cracks in the titanium oxide layer and portions where cracks were mixed. This is considered to be due to the influence of internal strain due to thermal shrinkage of the amorphous titanium oxide layer.

50: Conductive substrate 51: Titanium oxide protective layer 51a: Amorphous continuous layer 51b: Granular crystal layer 51c: Interface layer

Claims (2)

In a substrate for a semiconductor electrode used in a dye-sensitized solar cell having an electrolyte solution, in which a titanium oxide-based protective layer is formed on a conductive substrate,
The titanium oxide-based protective layer includes an amorphous continuous layer of an amorphous titanium oxide containing an alkoxy group, and a granular crystal layer in which microcrystalline titanium dioxide particles having a particle size of 30 nm or less are connected,
Between the amorphous continuous layer and the granular crystal layer, an interface layer in which the amorphous titanium oxide and the microcrystalline titanium dioxide particles coexist is formed ,
The substrate for semiconductor electrodes, wherein the granular crystal layer is located on the conductive substrate side, and the amorphous continuous layer is located above the granular crystal layer via the interface layer . An electrolyte solution comprising the semiconductor electrode substrate according to claim 1 and a porous photoelectric conversion layer formed on the titanium oxide-based protective layer of the semiconductor electrode substrate. electrode for dye-sensitized solar cell having a.

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