JP2012119189A - Photoelectrode and dye-sensitized solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectrode excellent in utilization efficiency of incident light, and a dye-sensitized solar cell provided with the same.SOLUTION: A photoelectrode 1 is configured such that: a transparent electrode 10, a photoelectric conversion layer 13, and a light reflecting layer 14 are laminated in this order; the photoelectric conversion layer 13 is formed of a porous semiconductor on which a sensitizing dye is supported; and the light reflecting layer 14 is formed of a porous material on which the sensitizing dye is not supported. A dye-sensitized solar cell is configured to include the photoelectrode 1.

Description

  The present invention relates to a photoelectrode and a dye-sensitized solar cell including the photoelectrode.

  A generally well-known dye-sensitized solar cell is a so-called Gretzell type (see Non-Patent Document 1). That is, using a transparent substrate having a transparent conductive layer on the surface, a porous film (porous semiconductor layer) made of a semiconductor such as titanium oxide is provided on the conductive layer, and a porous material having a large specific surface area. By making a photoelectric conversion layer by supporting a sensitizing dye on a semiconductor layer, a photoelectrode with an increased amount of sensitizing dye can be used. By using such a photoelectrode, many excited electrons can be extracted. It has become.

  However, in this dye-sensitized solar cell, electric power is generated only when incident light passes through the porous semiconductor layer carrying the sensitizing dye. FIG. 3A schematically shows the behavior of incident light at the photoelectrode of the dye-sensitized solar cell at this time. As shown here, incident light incident from the substrate 91 side of the photoelectrode 9A is absorbed by the sensitizing dye in the photoelectric conversion layer 93 and contributes to power generation by releasing photoexcited electrons into the porous semiconductor layer. To do. Here, reference numeral 92 denotes a conductive layer. However, only a small part of incident light is absorbed by the sensitizing dye and contributes to power generation, and most of the incident light is transmitted through the photoelectric conversion layer 93. Therefore, the utilization efficiency of light energy in the photoelectrode 9A is extremely high. Low. Therefore, in order to improve the power generation efficiency of the dye-sensitized solar cell, improvement in the utilization efficiency of incident light is strongly demanded.

  From this point of view, various investigations have been made on a method of laminating a plurality of porous semiconductor layers on a base material and causing the semiconductor layer disposed far from the base material to function as a light reflecting layer that reflects or scatters incident light. Has been. Specifically, a method of laminating three or more porous semiconductor layers, and increasing the average particle diameter of the semiconductor particles constituting these semiconductor layers to a smaller value closer to the base material and a larger one farther from the base material (Patent Literature) 1), and a technique (see Patent Document 2) for increasing the average particle diameter of semiconductor particles as the distance from the substrate increases. In any method, the porous semiconductor layer having the larger average particle diameter of the semiconductor particles is caused to function as a light reflecting layer.

  However, in the methods described in these patent documents, the material of the light reflecting layer is the same as the material of the porous semiconductor layer constituting the photoelectric conversion layer, and a sensitizing dye is carried on the porous semiconductor layer (dyed). When the photoelectric conversion layer is used, there is a problem that a large amount of sensitizing dye is supported (dyed) in the light reflection layer. FIG. 3B schematically shows the behavior of incident light at the photoelectrode of the dye-sensitized solar cell at this time. FIG. 3B shows a case where the porous semiconductor layer has two layers, but the same applies to the case where the porous semiconductor layer has three or more layers. As shown here, a part of incident light incident from the substrate 91 side of the photoelectrode 9B is absorbed by the sensitizing dye in the photoelectric conversion layer 93 (the porous semiconductor layer has a small average particle diameter of the semiconductor particles). Contributes to power generation. A part of the transmitted light transmitted through the photoelectric conversion layer 93 further passes through the light reflecting layer 94, and the remaining part is the light reflecting layer 94 (the porous semiconductor layer has a large average particle diameter of the semiconductor particles). The light is reflected and reenters the photoelectric conversion layer 93 to contribute to power generation. However, since a large amount of sensitizing dye is carried on the light reflecting layer 94, most of the transmitted light that has not passed through the light reflecting layer 94 is absorbed by the sensitizing dye, and the photoelectric conversion layer 93. Only a small part of the reflected light re-enters. Therefore, the desired effect of improving the utilization efficiency of incident light of the photoelectrode cannot be obtained.

  On the other hand, a hydrophobic organic compound that is not a sensitizing dye is adsorbed on the surface of a semiconductor particle having a large average particle diameter to form a light reflecting layer, and when the porous semiconductor layer is dyed, In addition to semiconductor particles, a binder containing a silica polymer in which at least some of the surface functional groups are substituted with an alkyl group is added to the paste used when forming the light reflecting layer (see Patent Document 3). And the technique (refer patent document 4) which suppresses the dyeing | staining in a light reflection layer by providing hydrophobicity is disclosed. In any of these methods, the forming material of the porous semiconductor layer, which is a light reflecting layer, is chemically modified to impart hydrophobicity, and attempts to inhibit the loading of the dye in the dyeing process.

JP 2003-142170 A JP 2002-352868 A JP 2002-0775474 A JP 2009-016304 A

Nature, 353, 737, 1991

  However, in the methods described in Patent Documents 3 and 4, when the forming material of the porous semiconductor layer is heated to about 500 ° C. in the firing step for forming the porous semiconductor layer, many of the chemically modified sites are formed. As a result, the dyeing in the light reflecting layer is not sufficiently suppressed, and as shown in FIG. 3B, the utilization efficiency of incident light of the photoelectrode cannot be sufficiently improved. there were.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the dye-sensitized solar cell provided with the photoelectrode excellent in the utilization efficiency of incident light, and this photoelectrode.

To solve the above problem,
The present invention is a photoelectrode in which a transparent electrode, a photoelectric conversion layer, and a light reflection layer are laminated in this order, the photoelectric conversion layer is made of a porous semiconductor carrying a sensitizing dye, and the light reflection layer is A photoelectrode comprising a porous body on which a sensitizing dye is not supported is provided.
In the photoelectrode of the present invention, the porous body in the light reflecting layer is preferably formed from a metal chalcogenide compound.
The present invention also provides a dye-sensitized solar cell comprising the photoelectrode of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the dye-sensitized solar cell provided with the photoelectrode excellent in the utilization efficiency of incident light, and this photoelectrode can be provided.

It is a schematic sectional drawing which illustrates the photoelectrode of this invention. It is a schematic sectional drawing for demonstrating the manufacturing method of the photoelectrode shown in FIG. It is a schematic diagram for demonstrating the behavior of the incident light in a photoelectrode, (a) The photoelectrode which is not provided with the light reflection layer, (b) The photoelectrode provided with the light reflection layer by which the sensitizing dye was carry | supported, ( c) A schematic view of the photoelectrode of the present invention. It is a graph which shows the light reflectivity of the light reflection layer in Experimental example 1 and 2.

<Photoelectrode>
The photoelectrode of the present invention is a photoelectrode in which a transparent electrode, a photoelectric conversion layer, and a light reflection layer are laminated in this order, and the photoelectric conversion layer is made of a porous semiconductor carrying a sensitizing dye, and the light The reflective layer is characterized by comprising a porous body on which no sensitizing dye is supported.
Since the light reflecting layer does not carry a sensitizing dye, the light reflecting layer is excellent in incident light reflectivity and scattering ability, and the photoelectrode is extremely excellent in incident light utilization efficiency.
Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic cross-sectional view illustrating a photoelectrode of the present invention.
In the photoelectrode 1 shown here, a conductive layer 12 is provided on the surface of a base material 11, and a photoelectric conversion layer 13 and a light reflection layer 14 are laminated on the conductive layer 12 in this order, and is roughly configured. The base material 11 and the conductive layer 12 constitute an electrode (transparent electrode) 10.

  The base material 11 should just be what can permeate | transmit visible light (transparent base material), and it is preferable that the material is glass or a plastics. In particular, in order to increase the photoelectric conversion efficiency, the visible light transmittance is preferably as high as possible, preferably 70% or more, more preferably 75% or more, further preferably 80% or more, 85% The above is particularly preferable. In the present invention, visible light preferably means light having a wavelength of 360 to 830 nm. The visible light transmittance can be measured by, for example, a transmittance photometer with an integrating sphere.

The glass is not particularly limited, and examples thereof include soda lime glass, quartz glass, borosilicate glass, Vycor glass, alkali-free glass, blue plate glass, and white plate glass.
The plastic is not particularly limited, and examples thereof include polyacryl, polycarbonate, polyester, polyimide, polystyrene, polyvinyl chloride, and polyamide. Among these, polyester, especially polyethylene terephthalate (PET), is produced and used in large quantities as a transparent heat-resistant film.
From the viewpoint of producing a thin, light and flexible dye-sensitized solar cell, the substrate 11 is preferably a PET film.

The conductive layer 12 only needs to transmit at least visible light (transparent conductive layer), and examples of the material thereof include metal oxides and conductive polymers.
Examples of the metal oxide include indium oxide / tin oxide (ITO), fluorine-doped tin oxide (FTO), zinc oxide, tin oxide, antimony-doped tin oxide (ATO), indium oxide / zinc oxide (IZO), gallium oxide / Examples include zinc oxide (GZO) and titanium oxide. Among these, ITO with high conductivity and FTO excellent in heat resistance and weather resistance are particularly preferable.
The conductive layer 12 may be either a single layer or a plurality of layers. In the case of a plurality of layers, all the layers may be the same or different, and some layers may be different.

The photoelectric conversion layer 13 is composed of a porous semiconductor layer on which a sensitizing dye is supported.
As a preferable forming material of the porous semiconductor layer, titanium oxide (TiO ₂ ) can be exemplified.
Examples of the shape of the material for forming the porous semiconductor layer include particles, needles, plates, fibers, and the like.
The thickness of the porous semiconductor layer is preferably 1 to 30 μm, and more preferably 3 to 20 μm. By being more than a lower limit, light can be utilized more fully and the photoelectric conversion efficiency in a dye-sensitized solar cell further improves. Moreover, since the light can be used more effectively by being below the upper limit value, the diffusion resistance of the oxidation / reduction reaction species is reduced, and the resistance of the electrode itself is reduced, so that the photoelectric conversion efficiency in the dye-sensitized solar cell is further increased. improves.

  The said sensitizing dye is not specifically limited, What is used with the normal dye-sensitized solar cell may be used. Specifically, cis-di (thiocyanato) -bis (2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium (II), cis-di (thiocyanato) -bis (2,2′-bipyridyl- 4,4′-dicarboxylic acid) ruthenium (II) bis-tetrabutylammonium salt (hereinafter abbreviated as N719), tri (thiocyanato)-(4,4 ′, 4 ′ ′-tricarboxy-2,2 ′) : Ruthenium-based dyes such as 6 ', 2' '-terpyridine) ruthenium tris-tetrabutylammonium salt (black dye). In addition, coumarin dyes, polyene dyes, cyanine dyes, hemicyanine dyes, thiophene dyes, indoline dyes, xanthene dyes, carbazole dyes, perylene dyes, porphyrin dyes, phthalocyanine dyes, merocyanine dyes, Examples include various organic dyes such as catechol dyes and squarylium dyes. Furthermore, the donor-acceptor composite dye etc. which combined these dyes can be illustrated.

  The said pigment | dye carry | supported by the porous semiconductor layer may be only 1 type, and 2 or more types may be sufficient as it. In the case of two or more kinds, the combination and ratio may be appropriately selected according to the purpose.

The light reflecting layer 14 is made of a porous body that does not carry a sensitizing dye.
The material of the porous body in the light reflecting layer 14 may be a semiconductor or may not be a semiconductor. And when it is a semiconductor, the same material as the said porous semiconductor layer may be sufficient.
The light reflection layer 14 is preferably as the light reflectance (visible light reflectance) is high, and is preferably white, white, or having a metallic luster. Examples of the material for forming the porous body include a compound preferably containing a metal element and a chalcogen, and more preferably a compound consisting of a metal element and a chalcogen. Here, “chalcogen” is a generic name for Group 16 elements, and examples thereof include oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po). More preferable examples of the material for the porous body include metal chalcogenide compounds such as titanium oxide, zirconium oxide, and barium sulfate.

Examples of the shape of the material for forming the porous body in the light reflecting layer 14 include a particle shape, a needle shape, a plate shape, and a fiber shape.
Moreover, it is preferable that the forming material of the porous body is larger in size than the forming material of the porous semiconductor layer in the photoelectric conversion layer 13. For example, when the material for forming the porous body and the porous semiconductor layer are both in the form of particles, the material for forming the porous body has a larger average particle diameter than the material for forming the porous semiconductor layer. It is preferable. By doing so, the light reflectance is further improved. The size of the forming material is preferably selected in consideration of the wavelength of incident light and the light absorption characteristics of the sensitizing dye. For example, since it is known that particles having a particle diameter of about half the wavelength of light reflect this light efficiently, for example, a specific sensitizing dye (for example, N719) is used. Etc.), and when it is desired to improve the light reflectance in a wavelength region where the photosensitivity of the dye is low (for example, 700 to 800 nm), preferably the average particle size, more preferably the particle size, It is preferable to set the value to a half of the range (for example, 350 to 400 nm).
Through the above steps, the photoelectrode 1 is obtained.

  The thickness of the light reflecting layer is preferably 0.1 to 10 μm, and more preferably 2 to 6 μm. By being more than a lower limit, a light reflectance improves further and the photoelectric conversion efficiency in a dye-sensitized solar cell further improves. Moreover, the thickness of a photoelectrode can be made thin because it is below an upper limit.

  The light reflectance of the light reflecting layer is preferably 40% or more with respect to visible light. In particular, it is preferably 60% or more and more preferably 70% or more with respect to light having a wavelength of 450 to 780 nm.

  The photoelectrode 1 is very excellent in the utilization efficiency of incident light by the above configuration. About the behavior of the incident light in the photoelectrode 1, a schematic diagram is shown in FIG. As shown here, a part of incident light incident from the substrate 11 side of the photoelectrode 1 is absorbed by the sensitizing dye in the photoelectric conversion layer 13 and contributes to power generation. The transmitted light that has passed through the photoelectric conversion layer 13 partially passes through the light reflection layer 14 but does not pass through the light reflection layer 14 because no sensitizing dye is supported on the light reflection layer 14. Most of the transmitted light is reflected and reenters the photoelectric conversion layer 13 to contribute to power generation. Thus, since the ratio of the transmitted light that reenters the photoelectric conversion layer 13 is high, the utilization efficiency of the incident light is extremely high.

The photoelectrode 1 can be manufactured by the following method, for example. FIG. 2 is a schematic cross-sectional view for explaining the manufacturing method of the photoelectrode 1.
First, as shown in FIG. 2A, a base material 11 having a conductive layer 12 on the surface is used, and a porous semiconductor layer 13 a is laminated on the conductive layer 12.
The porous semiconductor layer 13a may be laminated by a known method, for example, a method using a paste containing a material for forming the porous semiconductor layer 13a, an aerosol deposition method (hereinafter abbreviated as AD method), or the like. Can be stacked.

The method of laminating using a paste will be described below by taking as an example the case of forming a porous titanium oxide layer as the porous semiconductor layer 13a, but also when using a material other than titanium oxide as the forming material, It can laminate | stack by the same method.
The porous titanium oxide layer can be formed, for example, by applying a titanium oxide-containing paste on a base material and subjecting it to a heat treatment (firing). The method for applying the paste is not particularly limited, and examples thereof include known methods such as a screen printing method, a spin coating method, a squeegee method, a doctor blade method, and an air spray method.

  As a preferable thing of the said titanium oxide containing paste, what mix | blended titanium oxide, organic binder resin, and the solvent can be illustrated. Furthermore, if necessary, heat extinguishing resin particles for forming voids in the porous titanium oxide layer and various additives may be blended.

A porous titanium oxide layer can carry | support a pigment | dye efficiently, so that a surface area is large. Therefore, the larger the surface area of titanium oxide as the forming material, the better.
In order to increase the surface area of titanium oxide, the primary particle diameter (volume average particle diameter) of titanium oxide is preferably as small as possible. Therefore, the primary particle diameter of the titanium oxide particles is preferably 3 to 500 nm, and more preferably 3 to 200 nm. Moreover, it is preferable that content of what a primary particle diameter is 3-500 nm in a titanium oxide particle is 60 mass% or more. By being 3 nm or more, the interaction at the particle interface becomes small, and the dispersion of the particles becomes easy. Moreover, the synthesis | combination of a titanium oxide particle becomes easy and can be obtained cheaply. On the other hand, when the thickness is 500 nm or less, the surface area of the titanium oxide particles is further increased. However, for example, with only titanium oxide particles having a primary particle diameter of 3 to 5 nm, the particles may be closely bonded to each other, and the surface area of the porous titanium oxide layer may not be sufficiently increased. Therefore, for example, only those having a primary particle diameter of 5 to 50 nm may be used, or two kinds having different primary particle diameters such as a combination of those having a primary particle diameter of 3 to 50 nm and those having a primary particle diameter of 50 to 500 nm are used. The above may be used in combination.

  The crystal form of titanium oxide may be any of anatase type, rutile type and brookite type. When used for the production of a dye-sensitized solar cell, for example, by using an anatase type, the reaction activity can be made higher than that of a rutile type, and the electron injection from the dye becomes more efficient. Further, since the rutile type has a high refractive index, the rutile type can further enhance the light scattering effect and the light confinement effect, and can further increase the light utilization efficiency in the porous titanium oxide layer.

  The shape of titanium oxide is not particularly limited, and examples thereof include a spherical shape or a similar shape thereof, a regular octahedral shape or a similar shape thereof, a star shape or a similar shape thereof, a needle shape, a plate shape, and a fiber shape. Among these, a spherical or regular octahedral shape having a similar shape is easily available. Moreover, the light scattering effect and the electron transfer efficiency can be further enhanced by using a fibrous form such as a long fiber form.

  It is preferable that the compounding quantity of the titanium oxide in the said paste is 5-40 mass%, and it is more preferable that it is 10-30 mass%. By being more than a lower limit, a paste can be apply | coated with moderate film thickness, and also it becomes unnecessary to add organic binder resin etc. excessively for viscosity adjustment. Moreover, by being below the upper limit, the viscosity of the paste becomes better, the application of the paste becomes easier, and the thickness of the paste after application does not become too thick. In particular, when the amount of titanium oxide is 10 to 30% by mass, the overall concentration can be adjusted more easily, and a porous titanium oxide layer having an appropriate thickness can be easily formed.

  The organic binder resin is dissolved in a solvent to adjust the viscosity of the titanium oxide-containing paste. Further, the dispersion state of the titanium oxide and the heat extinguishing resin particles is stabilized.

  The organic binder resin preferably has the ability to disappear during the heat treatment of the titanium oxide-containing paste, like the heat extinguishing resin particles. Moreover, the thing which disperses titanium oxide satisfactorily and is easily dissolved in a polar solvent is preferable.

  The organic binder resin is not particularly limited, and is modified with polyvinyl alcohol acetal such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, polyethylene glycol, polyvinyl alcohol, polyvinyl butyral, gelatin, polyacrylic acid, polyacrylamide And dextrin. Among these, as a raw material of a paste for forming a titanium oxide electrode of a dye-sensitized solar cell, ethyl cellulose can be exemplified as a particularly preferable one from the viewpoint of actual use and availability. Examples of commercially available ethyl cellulose include “Etocel (registered trademark) (manufactured by Dow Chemical Company, USA)”.

  The grade of ethyl cellulose is represented, for example, by the viscosity when dissolved in a mixed solvent of toluene: ethanol = 80: 20 at a concentration of 5%. When using ethyl cellulose, the grade is appropriately selected depending on the size or blending amount of titanium oxide, the particle size or blending amount of the heat extinguishing resin particles, the type of solvent, the presence or absence of blending of a surfactant, and the like. For example, ethyl cellulose having a viscosity of preferably 7 to 100 cP, more preferably 10 to 45 cP is used.

  The said organic binder resin may be used individually by 1 type, and may use 2 or more types together. When using 2 or more types together, the combination and ratio may be appropriately selected according to the purpose.

  The blending amount of the organic binder resin in the paste is preferably 3 to 30% by mass. By being above the lower limit, the dispersion stability of the paste is further improved. Moreover, the viscosity of a paste does not become high too much and it can apply | coat a paste to a base material more easily because it is below an upper limit.

  Although the solvent mix | blended with the said paste is not specifically limited, What has moderate polarity, a boiling point, and vapor pressure is preferable.

The polarity of the solvent affects the dispersibility of titanium oxide. And since an oxygen atom exists in the surface of titanium oxide, from the viewpoint of polarity, the solvent is preferably an alcohol or an amide having a hydroxyl group capable of forming a hydrogen bond.
The solvent is preferably a solvent having a certain boiling point and a low saturated vapor pressure so that the concentration change of each component during storage of the paste is suppressed.
Further, the solvent preferably has a boiling point not higher than the baking temperature (for example, 500 ° C.) of the paste and does not form a residue by decomposition or the like before volatilization so as to volatilize during baking.

Specific examples of the solvent include alcohols, amides, sulfoxides, amines, ethers, esters, natural alcohols, water and the like.
Examples of the alcohols include butyl alcohol, benzyl alcohol, and butyl carbitol.
Examples of the amides include dimethylformamide, dimethylacetamide, n-methyl-2-pyrrolidone and the like.
Examples of the sulfoxides include dimethyl sulfoxide.
Among the ethers, examples of the cyclic ethers include dioxane, and examples of the glycol ethers include ethyl cellosolve and methyl cellosolve.
Examples of the esters include dibutyl phthalate.
Examples of the natural alcohols include terpineol.
Among these, terpineol can be exemplified as a particularly preferable one from the past use record. Terpineol is commercially available, is inexpensive, and is readily available in large quantities.

  The said solvent may be used individually by 1 type, and may use 2 or more types together. When using 2 or more types together, the combination and ratio may be appropriately selected according to the purpose.

  Examples of the material of the heat extinguishing resin particles include synthetic resins such as polystyrene and acrylic resin that can be surely lost when the titanium oxide-containing paste layer formed on the substrate is heated.

  The average particle size of the heat extinguishing resin particles is preferably 10 nm to 1 μm. By being more than the lower limit, the void portion in the titanium oxide layer becomes larger, which is more advantageous from the viewpoints of providing a reaction field by contact with the electrolyte solution and improving light utilization efficiency by light scattering, for example. Moreover, by being below an upper limit, a space | gap part does not become large too much and the surface area of a porous titanium oxide layer becomes still larger. As a result, the amount of the dye supported on the porous titanium oxide layer is further increased, and the power generation efficiency in the dye-sensitized solar cell is further improved. Furthermore, since the void portion does not become too large, the strength of the titanium oxide electrode itself can be further improved. The lower limit value of the average particle diameter of the heat extinguishing resin particles is more preferably 20 nm, and further preferably 30 nm. The upper limit is more preferably 500 nm, and more preferably 300 nm.

  The heat extinguishing resin particles may be used singly or in combination of two or more. When using 2 or more types together, the combination and ratio may be appropriately selected according to the purpose.

  The amount of the heat extinguishing resin particles in the paste is preferably 3 to 60% by mass, and more preferably 10 to 40% by mass. By being more than a lower limit, a void can be appropriately formed in the porous titanium oxide layer, and the surface area of the porous titanium oxide layer can be further increased. Moreover, by being below an upper limit, the density of the porous titanium oxide layer after baking becomes higher, the electrical conductivity as an electrode improves, and the intensity | strength of a porous titanium oxide layer improves further. In particular, when the blending amount is 10 to 40% by mass, the blending effect of the heat extinguishing resin particles is remarkably high, the porous titanium oxide layer has a more preferable porous structure, and the dye conversion is further enhanced in photoelectric conversion efficiency. A solar cell can be provided.

  Examples of the additive include a dispersant such as a surfactant, a dispersion stabilizer, an antifoaming agent, an antioxidant, a colorant, and a viscosity modifier.

The paste preferably contains a dispersant for stabilization.
A strong ionic dispersant such as a salt is highly likely to cause a change in performance due to adhesion of an alkali metal or the like to titanium oxide. Therefore, as the dispersant, a non-alkali metal dispersant is preferable, and both nonionic and ionic are preferable.

The dispersant is not particularly limited, and propylene glycol fatty acid esters, glycerin fatty acid esters, polyglycerin fatty acid esters, polyoxyethylene glycerin fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene Examples include sorbite fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene alkyl ether phosphoric acids, polyoxyethylene alkyl ether carboxylic acids, polyethylene glycol fatty acid esters and the like.
The dispersant may be appropriately selected according to the types and concentrations of the titanium oxide particles, the heat extinguishing resin particles and the additives, and polyoxyethylene alkyl ether carboxylic acids are preferred because of particularly high dispersibility.

  The order of addition of the blending components when preparing the paste is not particularly limited. For example, what is necessary is just to adjust suitably so that a titanium oxide and a heat extinction resin particle may be in a favorable dispersion state. Moreover, a paste can be prepared using a well-known disperser, for example.

The temperature during the heat treatment (firing) of the paste is preferably 200 to 500 ° C, and more preferably 300 to 500 ° C.
Moreover, it is preferable that it is 10 minutes-10 hours, and, as for the time of the heat processing (baking) of the said paste, it is more preferable that it is 30 minutes-3 hours.

So far, the method using the paste has been described, but the porous semiconductor layer 13a can also be laminated by the AD method.
In the AD method, fine particles are accelerated to subsonic to supersonic speed by a carrier gas such as helium or argon, and sprayed onto the base material at high speed to join the fine particles and the base material or the fine particles to each other on the base material. This is a technique for forming a thin film.
At least a part of the fine particles colliding with the surface of the base material bites into the surface of the base material and is not easily peeled off. Furthermore, by continuing the spraying, another fine particle collides with the fine particle that has sunk on the surface of the base material, and a new surface is formed on the surface of each fine particle due to the collision between the fine particles. Join. In the collision between the fine particles, a temperature rise that causes the fine particles to melt hardly occurs. Therefore, a grain boundary layer made of vitreous substantially does not exist at the interface where the fine particles are joined. And by continuing spraying of microparticles | fine-particles, many microparticles | fine-particles join gradually to the base-material surface, and a porous thin film is formed. Since the formed thin film has sufficient strength, baking by baking is unnecessary.

As the AD method, for example, the ultrafine particle beam deposition method disclosed in “International Publication No. WO01 / 27348A1 Pamphlet” and the brittle material ultrafine particle low temperature molding method of “Patent No. 32655481” can be applied.
When the AD method is applied, the same material as the method using the paste can be used as the material for forming the porous semiconductor layer 13a.
Through the steps so far, the porous semiconductor layer 13a can be formed.

Next, as shown in FIG. 2B, a sensitizing dye is supported on the porous semiconductor layer 13 a (the porous semiconductor layer 13 a is dyed) to obtain a photoelectric conversion layer 13. The loading of the sensitizing dye is performed, for example, by adsorption.
The sensitizing dye can be supported, for example, by bringing a solution containing the sensitizing dye (hereinafter abbreviated as “dye solution”) into contact with the porous semiconductor layer 13a.
The method for bringing the dye solution into contact is not particularly limited, and examples thereof include each method for bringing a liquid into contact with a substrate, such as a coating method, a dropping method, a printing method, and a dipping method. Can be arbitrarily selected.

The solvent component in the dye solution may be appropriately selected according to the kind of the dye used, and examples thereof include alcohols, nitriles, ethers, esters, ketones, hydrocarbons, halogenated hydrocarbons, and the like. it can.
The alcohols may be linear, branched or cyclic, and may be monohydric alcohols or polyhydric alcohols, such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl. Examples include -1-propanol (isobutanol), 2-butanol, 2-methyl-2-propanol (tert-butanol), and ethylene glycol. Examples of the nitriles include acetonitrile and propionitrile.
The ethers may be linear, branched or cyclic, and examples thereof include dimethyl ether, diethyl ether, ethyl methyl ether, and tetrahydrofuran.
Examples of the esters include ethyl acetate, propyl acetate, butyl acetate and the like.
Examples of the ketones include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone.
The hydrocarbons may be linear, branched or cyclic, and may be any of aliphatic hydrocarbons and aromatic hydrocarbons, such as pentane, hexane, heptane, octane, cyclohexane, toluene, xylene, etc. Can be illustrated.
Examples of the halogenated hydrocarbons include methylene chloride and chloroform.

  The said solvent is so preferable that a water content is low, and what was dehydrated using a desiccant etc. is preferable. By reducing the water content, inhibition of pigment loading is further suppressed, and the pigment can be loaded in a better state.

  The said solvent may be used individually by 1 type, and may use 2 or more types together. When using 2 or more types together, the combination and ratio may be appropriately selected according to the purpose.

  The dye concentration of the dye solution is not particularly limited, but is usually preferably 0.05 to 1 mM, more preferably 0.1 to 0.5 mM. In the present specification, the unit “M” representing concentration refers to “mol / L”.

  The contact of the dye solution is preferably performed in a dry atmosphere, and more preferably in an inert gas atmosphere such as nitrogen gas, helium gas, or argon gas. Here, the “dry atmosphere” means that the moisture content in the gas is reduced so as not to hinder the effects of the present invention. In this way, by suppressing the mixing of moisture into the porous semiconductor layer 13a or the dye solution at the time of contact, the inhibition of dye support is further suppressed, and the dye can be supported in a better state.

After the contact with the dye solution, the porous semiconductor layer 13a may be washed with a solvent such as alcohol or dried as necessary.
Through the steps up to here, the photoelectric conversion layer 13 can be formed.

Next, as illustrated in FIG. 2C, the light reflecting layer 14 is stacked on the photoelectric conversion layer 13.
In order to suppress the deterioration of the sensitizing dye supported on the porous semiconductor layer 13a, the light reflecting layer 14 is preferably formed by a method that does not require a heating process at a high temperature. The method using is more preferable.

In the AD method, an aerosol in which an appropriate amount of a carrier gas such as nitrogen gas, oxygen gas, air, helium gas, and argon gas is mixed with a porous material is prepared, and the photoelectric conversion layer 13 is held in a vacuum processing chamber. The light reflecting layer 14 can be formed in a room temperature environment by causing the aerosol to collide at high speed against the base material 10 provided with. Here, “normal temperature” means a temperature that is not extremely high with respect to room temperature, and is a temperature that is sufficiently lower than the temperature of several hundred degrees C. required in the baking process of the prior art. Refers to a temperature below ℃.
The primary particle diameter of the material for forming the porous body is preferably 100 to 500 nm.
The carrier gas is preferably an inert gas such as nitrogen or argon.
The pressure in the decompression chamber is preferably 1 kPa or less.
The aerosol collision speed is preferably 10 to 400 m / sec.

  As a method of using a sol of a forming material, a sol is prepared with a low-boiling solvent such as an alcohol-based medium such as ethanol, a nitrile-based solvent such as acetonitrile or the like, and applied to the forming material of the light reflecting layer 14. An example is a method in which the solvent is removed by drying under low temperature or low pressure conditions, more preferably under low temperature and low pressure conditions. Further, by applying pressure treatment to the coating layer after drying, the light reflecting layer 14 in which the forming materials, the forming material, and the photoelectric conversion layer 13 are pressure-bonded and peeling from the photoelectric conversion layer 13 is further suppressed. Can be formed.

The method for applying the sol may be the same as the method for applying the paste when the porous semiconductor layer 13a is laminated, but the air spray method is preferable.
The drying temperature is preferably room temperature (25 ° C.) to 100 ° C., and the pressure is preferably 3 to 50 kPa. Moreover, it is preferable that the pressure applied at the time of a pressurization process is 10-200 Mpa.

  In the production method described above, a sensitizing dye is supported on the porous semiconductor layer, a photoelectric conversion layer is formed in advance, and a light reflection layer is formed on the photoelectric conversion layer. Therefore, in the point that the light reflecting layer does not have an opportunity to come into contact with the sensitizing dye at the time of dyeing, after forming the porous semiconductor layer and the light reflecting layer, the porous semiconductor layer carries the sensitizing dye, and the photoelectric conversion layer This is completely different from the conventional method of manufacturing a photoelectrode, in which is formed. And since the light reflection layer is formed after the photoelectric conversion layer is formed, the light reflection layer 14 is highly suppressed in carrying the sensitizing dye. This photoelectrode is completely different from the photoelectrode, and the utilization efficiency of incident light is extremely excellent.

<Dye-sensitized solar cell>
The dye-sensitized solar cell of the present invention includes the above-described photoelectrode of the present invention. And it can be set as the structure similar to the conventional dye-sensitized solar cell except having provided this photoelectrode. For example, a counter electrode provided with a conductive layer such as platinum (Pt) on the surface of a transparent substrate is prepared, and the electrodes are arranged to face each other at a predetermined interval. What is necessary is just to fill electrolyte.
The dye-sensitized solar cell of the present invention is extremely excellent in power generation performance because the photoelectrode is extremely excellent in utilization efficiency of incident light.

  Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the following examples.

<Manufacture of photoelectrodes>
[Example 1]
(Production of a photoelectrode having a light reflection layer formed by the AD method)
The photoelectrode having the structure shown in FIG. 1 was manufactured by the following method.
Using a glass substrate provided with FTO as a transparent conductive layer on the surface, a titanium oxide paste (Ti-Nanoxide T / SP, manufactured by Solaronix) was applied on the transparent conductive layer by a screen printing method, and nitrogen was applied. A porous titanium oxide layer was formed by heating and baking at 500 ° C. for 30 minutes in an atmospheric pressure atmosphere to obtain an electrode substrate. The thickness of the porous titanium oxide layer was 10 μm.
Next, an N719 solution in which N719 was dissolved in a mixed solvent of acetonitrile / tert-butanol (1/1, volume ratio) to a concentration of 0.5 mM was prepared. And the electrode base material was immersed in this N719 solution for 24 hours at room temperature in nitrogen gas atmosphere. Thereafter, the electrode substrate was taken out from the N719 solution, washed with dehydrated acetonitrile to remove excess N719, and further dried in a dry atmosphere, whereby N719 was supported (adsorbed) on the porous titanium oxide layer. A photoelectric conversion layer was formed.
Next, a porous titanium oxide layer was formed on the photoelectric conversion layer by an AD method using anatase-type titanium oxide (primary particle diameter 400 nm) to obtain a light reflecting layer. The AD method was performed under the conditions of argon as a carrier gas, temperature: room temperature (25 ° C.), pressure: 0.5 kPa, and aerosol collision speed: 200 m / sec. The thickness of the porous titanium oxide layer as the light reflecting layer was 5 μm.
As a result, a photoelectrode in which no sensitizing dye was supported on the light reflecting layer was obtained.

[Example 2]
(Manufacture of a photoelectrode having a light reflecting layer formed using a sol of a forming material)
In the same manner as in Example 1, N719 was supported on the porous titanium oxide layer of the electrode substrate to form a photoelectric conversion layer.
Next, a dispersion sol having a titanium oxide concentration of 30% is prepared using anatase-type titanium oxide (primary particle diameter 400 nm) and ethanol, and this is applied onto the photoelectric conversion layer by an air spray method. Drying was performed under low temperature and low pressure conditions of 50 ° C. and pressure: 10 kPa. Furthermore, the coated layer after drying was pressurized at 100 MPa with a press machine to form a porous titanium oxide layer, which was used as a light reflecting layer. The thickness of the porous titanium oxide layer as the light reflecting layer was 5 μm.
As a result, a photoelectrode in which no sensitizing dye was supported on the light reflecting layer was obtained.

<Comparison of light reflectance in light reflecting layer>
[Experimental Example 1]
(Preparation of a sample with a light reflecting layer on which no sensitizing dye is supported and measurement of light reflectance)
A porous titanium oxide layer having a thickness of 4 μm was formed on a glass substrate having a thickness of 1 mm by the AD method under the same conditions as in Example 1, and Sample 1 was obtained.
Subsequently, the light reflectance (integral reflectance) of the sample 1 was measured with a spectrophotometer with an integrating sphere (U-4100 manufactured by Hitachi High-Technologies Corporation). The measurement results are shown in FIG.

[Experiment 2]
(Preparation of sample with light reflecting layer carrying sensitizing dye and measurement of light reflectance)
A porous titanium oxide layer is formed by AD method on a glass substrate having a thickness of 1 mm under the same conditions as in Example 1, and N719 is supported on the porous titanium oxide layer by the same method as in Example 1. Sample 2 was obtained.
Next, the light reflectance (integral reflectance) of Sample 2 was measured by the same method as in Experimental Example 1. The measurement results are shown in FIG.

When the absorbance of N719 is measured, it has a maximum value in the vicinity of a wavelength of 530 nm. Therefore, the light reflectance at a wavelength of 530 nm was compared.
From FIG. 4, at a wavelength of 530 nm, the sample 1 had a light reflectance of 81.4%. In sample 1, there is no light absorption by the sensitizing dye, and light absorption of titanium oxide at a wavelength of 530 nm is negligible. Therefore, the non-reflectance of the light of sample 1, that is, the light transmitted through sample 1 and in sample 1 The total value of the ratio of light trapped in the light was 18.6% (= (100-81.4)%). Since the ratio of the confined light is very small with respect to the ratio of the transmitted light, the non-reflectance of light is hereinafter referred to as “light transmittance” for convenience. On the other hand, sample 2 is considered to have the same light transmittance as sample 1, and the light reflectance at the wavelength is 26.0%. Therefore, the light absorption rate of sample 2 by the sensitizing dye is 55. Calculated to be 4% (= (100-18.6-26.0)%). These results are shown in Table 1.

  As described above, it was confirmed that the light reflectance was drastically improved by not supporting the sensitizing dye in the light reflection layer. That is, when a photoelectrode is used, the same improvement in light reflectivity is expected, so that the photoelectrode of the present invention can be said to have very high utilization efficiency of incident light.

  The present invention can be used for the production of a dye-sensitized solar cell.

  DESCRIPTION OF SYMBOLS 1 ... Photoelectrode, 10 ... Electrode (transparent electrode), 11 ... Base material (transparent base material), 12 ... Conductive layer (transparent conductive layer), 13 ... Photoelectric conversion layer, 13a ... Porous semiconductor layer, 14 ... Light reflecting layer

Claims (3)

A transparent electrode, a photoelectric conversion layer, and a light reflection layer are laminated in this order,
The photoelectric conversion layer is made of a porous semiconductor carrying a sensitizing dye,
The light reflecting layer is made of a porous body that does not carry a sensitizing dye.   The photoelectrode according to claim 1, wherein the porous body in the light reflecting layer is formed of a metal chalcogenide compound.   A dye-sensitized solar cell comprising the photoelectrode according to claim 1.

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