JP2013196852A - Method for manufacturing photoelectrode, photoelectrode, and dye-sensitized solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a photoelectrode, which improves productivity of a photoelectrode, and to provide a photoelectrode obtained by the manufacturing method and a dye-sensitized solar cell provided with the photoelectrode.SOLUTION: The method for manufacturing a photoelectrode is characterized in that: (1) oxide semiconductor particles on which a sensitizing dye is previously adsorbed are deposited on a conductor; (2) the particles are blown to the conductor at a high speed to form a thin film constituted of the particles on the conductor; (3) a plurality of types of the particles on which different sensitizing dyes are adsorbed are laminated on the conductor so that a layer is divided by types of the sensitizing dyes to have a multilayer structure having two or more layers; and (4) a plurality of types of the particles on which sensitizing dyes different in absorption peak wavelength in a visible light region are adsorbed are laminated on the conductor so that a layer is divided by types of the sensitizing dyes to have a multilayer structure having two or more layers.

Description

  The present invention relates to a photoelectrode manufacturing method, a photoelectrode, and a dye-sensitized solar cell.

In recent years, various measures for reducing carbon dioxide emissions have been studied worldwide to prevent global warming. In particular, in power generation, in addition to conventional large-scale centralized power generation such as thermal power, nuclear power, and hydroelectric power generation, it is possible to deal with local disasters through distributed power generation using renewable energy (natural energy) such as solar energy, wind power, and geothermal power. Efforts are being made to reduce total carbon dioxide emissions.
In particular, solar cells have already been put into practical use, mainly in silicon, and are generally mounted on the roofs of stores and houses. However, silicon-based solar cells have a problem of high cost and low cost merit for users. For further spread, solar cells that are inexpensive and can be easily manufactured and are highly efficient are desired.
One technique corresponding to this is an organic solar cell. Of these, dye-sensitized solar cells with particularly high efficiency are attracting attention. The dye-sensitized solar cell was reported by Gretzell et al. Of the Swiss Federal Institute of Technology in Lausanne in 1991, and is considered a promising candidate for the next-generation solar cell because of its relatively simple manufacturing method, inexpensive raw materials, and high efficiency. Non-patent document 1 describes a general schematic structure of a dye-sensitized solar cell and the principle of power generation.

Nature, 353, 737, 1991

In general, a photoelectrode of a dye-sensitized solar cell is formed by forming a porous film made of an oxide semiconductor such as titanium oxide on a base material, and then immersing the porous film in the dye solution together with the base material. This requires a dye adsorption step for adsorbing the dye to the porous film.
However, in order to adsorb a sufficient amount of the dye to the porous film, a long immersion time of several tens of minutes to several tens of hours is required. When the photoelectrode of the dye-sensitized solar cell is to be continuously produced in the form of an apparatus such as a roll-to-roll, for example, there is a problem that the dye adsorption step becomes a rate-limiting step of production and it is difficult to perform continuous production. The above problem may be solved in the future if a device for long-time immersion treatment is developed in some way in the process of continuous production, but the device with such special devices has an occupied area. It is expected that there will be problems such as being excessive and the price of the device becoming enormous. Also, if photoelectrodes are produced in a single-wafer type rather than a continuous production method, it is possible to perform a long-time immersion treatment for each single wafer, but the productivity (manufacturing speed) is greatly impaired. .

  The present invention has been made in view of the above circumstances, and is a photoelectrode production method with improved photoelectrode productivity, a photoelectrode obtained by the production method, and a dye sensitization provided with the photoelectrode. The issue is to provide solar cells.

The method for producing a photoelectrode according to claim 1 of the present invention is characterized in that oxide semiconductor particles on which a sensitizing dye is adsorbed in advance are formed on a conductor.
According to a second aspect of the present invention, there is provided a method for producing a photoelectrode according to the first aspect, wherein the particles are sprayed onto the conductor at a high speed to form a thin film composed of the particles on the conductor. It is characterized by.
The method for producing a photoelectrode according to claim 3 of the present invention is the method for producing a photoelectrode according to claim 1 or 2, wherein a plurality of types of the particles having different sensitizing dyes adsorbed on the conductor are used. Each layer is divided into two or more layers to form a multilayer structure.
In the method for producing a photoelectrode according to claim 4 of the present invention, in any one of claims 1 to 3, sensitizing dyes having different absorption peak wavelengths in the visible light region are adsorbed on the conductor. A plurality of types of the particles are laminated so as to have a multilayer structure of two or more layers by dividing the layer for each type of the sensitizing dye.
The method for producing a photoelectrode according to claim 5 of the present invention is the method for producing a photoelectrode according to any one of claims 1 to 4, wherein the first particles having the first sensitizing dye adsorbed on the conductor, A second particle adsorbed with two sensitizing dyes is laminated, and the absorption peak wavelength in the visible light region of the first sensitizing dye and the second sensitizing dye is different by 10 nm or more.
The method for producing a photoelectrode according to claim 6 of the present invention uses the transparent conductive layer formed on a plastic transparent substrate as the conductor in any one of claims 1 to 5. It is characterized by.
The photoelectrode according to claim 7 of the present invention includes an oxide semiconductor layer having a multilayer structure, and a sensitizing dye having a different absorption peak wavelength in the visible light region is adsorbed for each layer constituting the multilayer structure. It is characterized by being.
The dye-sensitized solar cell according to claim 8 of the present invention includes the photoelectrode obtained by the manufacturing method according to any one of claims 1 to 6 or the photoelectrode according to claim 7. It is characterized by being.

  In the present specification and claims, “membrane” and “layer” are not distinguished unless otherwise specified. Usually, both “film” and “layer” mean “a form having a two-dimensional (planar) extension and a relatively thin thickness”.

  According to the method for producing a photoelectrode of the present invention, it is possible to prepare in advance a particle on which a sensitizing dye is adsorbed in advance as a material for the photoelectrode. If the particles are stocked, the photoelectrodes can be completed simply by depositing the particles on the substrate in accordance with the demand for the photoelectrodes, and therefore can be shipped quickly. That is, according to the method for producing a photoelectrode of the present invention, a photoelectrode can be completed only by performing film formation, which is a conventional production rate-determining method for adsorbing a sensitizing dye later. Therefore, productivity (production speed) is excellent.

  Some types of sensitizing dyes require a long time for adsorption to the particles. In the conventional method, such a sensitizing dye has been difficult to adopt because it extremely reduces the production rate even if it has excellent light absorption. However, according to the production method of the present invention, a sensitizing dye that requires a long time to be adsorbed can be used without any problem. This is because the dye adsorption process does not need to be performed from the start of film formation to the completion of the photoelectrode.

  Furthermore, according to the method for producing a photoelectrode of the present invention, the oxide semiconductor layer in which the dye is uniformly adsorbed is suppressed by suppressing variation in the amount of dye adsorbed and unevenness in the oxide semiconductor layer composed of the particles. Thus, a photoelectrode with excellent performance can be manufactured with high yield. In the conventional method, a dye adsorption treatment is performed in which a dye solution is brought into contact with the oxide semiconductor layer after film formation. However, in this conventional method, a difference in site in the oxide semiconductor layer (for example, Due to the difference in the production lot of the surface portion and the inner back portion) and the photoelectrode, there is a disadvantage that the adsorptivity variation or unevenness of the dye occurs, and the performance of the photoelectrode varies.

  The photoelectrode of the present invention has a multilayer structure composed of a plurality of layers in which a plurality of types of sensitizing dyes having different absorption peak wavelengths in the visible light region are adsorbed on different layers, so that the photoelectrode can absorb the light. The absorption spectrum can be broadened. For this reason, the photoelectric conversion efficiency of the dye-sensitized solar cell (photoelectric conversion element) provided with the said photoelectrode can be improved.

It is an example of schematic structure of the film-forming apparatus which can be used for manufacture of the photoelectrode which concerns on this invention. It is the schematic diagram which showed the cross section of the multilayer structure in an example of the photoelectrode which concerns on this invention. It is an example of the IV characteristic of the dye-sensitized solar cell provided with the photoelectrode which concerns on this invention.

Hereinafter, embodiments of the photoelectrode production method, photoelectrode, and dye-sensitized solar cell of the present invention will be described. Each embodiment is an example of the present invention, and the present invention is not limited to each embodiment.
In the present specification and claims, “film” and “layer” are not distinguished unless otherwise specified. Usually, both “film” and “layer” mean “a form having a two-dimensional (planar) extension and a relatively thin thickness”.

<Method for producing photoelectrode>
The method for producing a photoelectrode according to the present invention is a method in which particles made of an oxide semiconductor in which a sensitizing dye is adsorbed in advance are formed on a conductor.

[conductor]
The conductor is not particularly limited as long as it is a member electrically connected to the oxide semiconductor. The shape, size, and material of the conductor are not particularly limited, and for example, a conductive layer or a metal plate formed on a substrate can be applied. Usually, since it is preferable that a photoelectrode has the transmittance | permeability of visible light, it is preferable that the said conductor is a transparent conductive layer formed on the transparent base material.

As the transparent conductive layer, a transparent conductive layer used in a conventionally known dye-sensitized solar cell is applicable, and for example, a thin film composed of a metal oxide or a conductive polymer can be used.
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 / Zinc oxide (GZO), titanium oxide, etc. are mentioned. Among these, ITO with low specific resistance and high electrical conductivity and FTO excellent in heat resistance and weather resistance are particularly preferable.
The transparent conductive layer may be either a single layer or a plurality of layers. In the case of a plurality of layers, all the layers may be made of the same material, or some of the layers may be made of different materials. Also good.

[Base material]
The substrate has a surface on which a transparent or non-transparent conductive layer formed thereon can be formed, and a shape capable of supporting an oxide semiconductor layer formed on the conductive layer And a substrate having a size is preferable, and a transparent substrate having visible light permeability is more preferable.
A suitable material constituting the transparent substrate is plastic or glass. From the viewpoint of increasing the photoelectric conversion efficiency, the material preferably has a higher visible light transmittance, and preferably has a transmittance of 85% or more, for example. Normally, “visible light” 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.

  As said glass, what has the transmittance | permeability of visible light is preferable, and soda lime glass, quartz glass, borosilicate glass, Vycor glass, alkali free glass, blue plate glass, white plate glass, etc. are mentioned.

As said plastic, what has the transmittance | permeability of visible light is preferable, for example, polyacryl, a polycarbonate, polyester, a polyimide, a polystyrene, a polyvinyl chloride, polyamide etc. are mentioned. Among these, polyester, particularly polyethylene terephthalate (PET), is produced and used in large quantities as a transparent heat-resistant film.
From the viewpoint of producing a thin and light flexible dye-sensitized solar cell, the substrate is preferably a plastic transparent substrate, and more preferably a PET film.

[particle]
The particles made of the oxide semiconductor are not particularly limited as long as they can adsorb the sensitizing dye and can be formed on the conductor, and are used in conventionally known dye-sensitized solar cells. Oxide semiconductor particles can be used. Examples of the oxide semiconductor include titanium oxide (TiO ₂ ), zinc oxide (ZnO), and strontium titanate (SrTiO ₃ ). By using these oxide semiconductors, the loading rate and electrical conductivity of the dye can be increased. As said oxide semiconductor, the titanium oxide which is excellent in the electrical conductivity at the time of forming a porous film is preferable.

  The shape of the particle is not particularly limited as long as it can be formed on the conductor, and examples thereof include a spherical shape, a substantially spherical shape, a polyhedral shape, a needle shape, a plate shape, and a fiber shape. Among these, from the viewpoint of increasing the form stability and structural strength of the formed thin film, it is preferably spherical, substantially spherical or polyhedral. Further, when a porous film is formed, if the particles have a sphere or a shape close to a sphere, it is easy to control the porosity of the porous film (sometimes referred to as porosity or porosity). It becomes.

The primary particle diameter of the particles may vary in a suitable range depending on the method of forming the particles on the conductor, but is usually preferably 1 nm to 500 μm, more preferably 1 nm to 250 μm, and more preferably 5 nm to 100 μm is more preferable, and 10 nm to 10 μm is particularly preferable. In addition, as a method for obtaining the primary particle diameter of the particles, for example, a method of determining the peak value of the volume average diameter distribution obtained by measurement with a laser diffraction particle size distribution measuring apparatus or the long diameters of a plurality of particles by SEM observation The method of measuring and averaging is mentioned. The primary particle diameter of the particles is preferably measured by the SEM observation.
The primary particle size of the particles used in the method for producing a photoelectrode of the present invention may be one type of particles having a uniform primary particle size, or a mixture of two or more types of particles having different primary particle sizes. May be used.

[Method of adsorbing sensitizing dye to particles]
The method for adsorbing the sensitizing dye to the particles is not particularly limited as long as the particles can maintain the state in which the particles carry the sensitizing dye. In the conventional method for producing a photoelectrode, a dye is adsorbed by immersing a porous film made of an oxide semiconductor formed on a substrate in a dye solution in which a sensitizing dye is dissolved in a solvent. Has been done. In the present invention, a method of adsorbing the sensitizing dye to the particles can be applied by immersing the particles in the same dye solution as before or by spraying or dropping the dye solution onto the particles.

  The solvent is appropriately selected according to the type of sensitizing dye to be used, and examples thereof include alcohols, nitriles, ethers, esters, ketones, hydrocarbons, and halogenated hydrocarbons.

  The alcohols may be linear, branched or cyclic in the chemical structure, and may be any of monohydric alcohols and polyhydric alcohols such as methanol, ethanol, 1-propanol, 2-propanol, Examples include 1-butanol, 2-methyl-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 in the chemical structure, and examples thereof include dimethyl ether, diethyl ether, ethyl methyl ether, and tetrahydrofuran. Examples of the esters include ethyl acetate, propyl acetate, and butyl acetate. Examples of the ketones include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. The hydrocarbons may be linear, branched, or cyclic in the chemical structure, and may be any of aliphatic hydrocarbons and aromatic hydrocarbons, such as pentane, hexane, heptane, octane. , Cyclohexane, toluene, xylene and the like. 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 the loading of the sensitizing dye is further suppressed, and the sensitizing dye can be carried 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 are suitably selected according to the objective.

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

  The dye solution is preferably handled 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 dye solution, the inhibition of the loading of the sensitizing dye is further suppressed, and the sensitizing dye can be carried in a better state.

After adsorbing (supporting) a sensitizing dye on the particles using the dye solution, the particles may be lightly washed with excess solvent using a solvent such as alcohol.
In addition, it is preferable to dry the said particle | grains which adsorb | sucked the sensitizing dye previously before using for a film-forming process. For example, when the film is formed by the AD method described later, it may be difficult to form the film by spraying particles with the solvent attached at a high speed.

[Sensitizing dye]
The sensitizing dye is not particularly limited as long as it is a dye that can be physically or chemically adsorbed on the particles, and a sensitizing dye used in a conventionally known dye-sensitized solar cell may be used. it can. Examples of the sensitizing dye include ruthenium-based dyes containing ruthenium generally called N3, N719 (red dye) or N749 (black dye), or coumarin-based, polyene-based, cyanine-based, hemicyanine-based, thiophene-based, indoline-based, xanthene-based dyes. And various organic dyes such as carbazole, perylene, porphyrin, phthalocyanine, merocyanine, catechol, and squarylium. Furthermore, donor-acceptor composite dyes obtained by combining these dyes can be used.

As the sensitizing dye used in the present invention, those having a carboxy group in the chemical structure are preferable. Since the particles are made of an oxide semiconductor, the carboxy group can exert an anchoring effect on the particles, and the adsorptivity between the sensitizing dye and the particles is increased, so that the sensitizing dye is separated from the particles. Desorption can be suppressed.
In the present invention, one sensitizing dye may be used alone, or two or more sensitizing dyes may be used in combination.

As a preferred example of the sensitizing dye, MK-2 (2-Cyano-3- [5 '''-(9-ethyl-9H-carbazol-3-yl)-represented by the following chemical formula (1): 3 ', 3'',3''', 4-tetra-n-hexyl- [2,2 ', 5', 2 '', 5 '', 2 ''']-quarter thiophenyl-5-yl] acrylic acid).
MK-2 is a donor-acceptor type organic dye molecule having a carbazole skeleton, a plurality of hexylthiophene skeletons, and a cyanoacrylic acid group. It is known that the carbazole skeleton serves as an electron donating site and the cyanoacrylic acid group functions as an electron withdrawing site. In addition, the alkyl group (hexyl group) bonded to the hexylthiophene skeleton has an effect of suppressing the formation of aggregates due to intermolecular π-π stacking, thereby improving the efficiency of electron injection from the dye to the titanium oxide electrode. be able to. Moreover, the carboxy group has an anchor effect, and the adsorption power of MK-2 to the particles is enhanced. Thereby, it can further suppress that MK-2 detaches | leaves from the said particle | grain at the time of film-forming.

[Film formation method]
As a method of forming the particles having the sensitizing dye adsorbed thereon on the conductor, an aerosol deposition method (AD method) in which the particles are sprayed onto the conductor at high speed using a carrier gas, Examples of suitable methods include an electrostatic fine particle coating method in which the particles are accelerated by electrostatic force and collided with the conductor to form a film, or a cold spray method. According to these methods, a porous film or non-porous dense film (hereinafter sometimes referred to as a dense film) formed by bonding the particles to each other is formed without firing the particles. can do. Since the baking treatment is unnecessary, there is no possibility that the sensitizing dye previously adsorbed on the particles is thermally decomposed or damaged. In addition, the specific method of AD method, electrostatic fine particle coating method, and cold spray method may be the same as the conventional well-known method. However, in the present invention, it is important that a sensitizing dye is previously adsorbed to the particles before film formation. Details of the film forming method using the AD method will be described later.

  As another film forming method, an organic solvent sol is prepared by dispersing the particles adsorbed with a sensitizing dye in an organic solvent in which the sensitizing dye is difficult to dissolve, and the organic solvent sol is placed on the conductor. An example is a method of forming a porous film or a dense film by applying a predetermined thickness, further drying, and then pressurizing the dried product to bind the particles together. Also in the film forming method using the organic solvent sol, since the baking treatment is unnecessary, there is no possibility that the sensitizing dye previously adsorbed on the particles is thermally decomposed or damaged. Details of the film forming method using the organic solvent sol will be described later.

  As another film forming method, a paste prepared by mixing the particles adsorbed with a sensitizing dye with a resin binder or the like is prepared, and the paste is applied on the conductor with a predetermined thickness. A method of performing firing for bonding or binding can be exemplified. In order to reduce the thermal decomposition of the sensitizing dye in this firing, firing is preferably performed at as low a temperature as possible, for example, firing at about 150 ° C. is preferable. The specific method for preparing and baking the paste may be the same as a conventionally known method. However, in the present invention, it is important to preliminarily adsorb the sensitizing dye to the particles constituting the paste before film formation.

  In the method for producing a photoelectrode of the present invention, among the above-described film forming methods, a porous film (hereinafter simply referred to as “porous film”) composed of an oxide semiconductor layer by an AD method or a method using an organic solvent sol. Alternatively, it may be referred to as a “porous layer”). By using the AD method or the organic solvent sol method, a porous film excellent in conductivity, light absorption, light utilization efficiency (light scattering in the porous film), electrolyte diffusibility and structural strength can be easily formed. can do.

[AD method]
In the AD method, the particles (hereinafter sometimes simply referred to as “fine particles”) are accelerated to a subsonic to supersonic speed by a carrier gas such as helium or argon, and the fine particles are sprayed onto the substrate at a high speed. In this technique, fine particles and a base material, or fine particles are joined to form a fine particle on the base material (a thin film made of fine particles is formed).
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. Further, by continuing the spraying, another fine particle collides with the fine particle that has sunk on the surface of the base material, and the collision of the fine particles forms a new surface on the surface of each fine particle. Join each other. 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. By continuing the spraying of the fine particles, a large number of fine particles are gradually joined to the surface of the base material to form a porous film or a dense film. Since the formed thin film has sufficient strength, baking by baking is usually unnecessary.

Known AD methods include, for example, the ultrafine particle beam deposition method disclosed in “International Publication No. WO01 / 27348A1” and the brittle material ultrafine particle low temperature molding method disclosed in “Patent No. 32655481”. It is done.
In these known AD methods, it is important to preliminarily apply an internal strain to the fine particles to determine whether or not cracks will occur by pre-processing the fine particles to be sprayed with a ball mill or the like. By adding this internal strain, the sprayed fine particles can be easily deformed when colliding with the base material or the already deposited fine particles, and as a result, a non-porous dense film can be formed. It is said.

  In the present invention, when a non-porous dense film is formed on the conductor, the above-described known method and apparatus can be applied without departing from the spirit of the present invention.

  In the present invention, when a porous film is formed on the conductor, the above-described known methods and apparatuses can be applied without departing from the spirit of the present invention. At this time, a porous film more suitable for the photoelectrode can be formed by appropriately adjusting the spraying speed and the particle diameter among the film forming conditions of the known method. In this case, the size of the void formed between the fine particles is not particularly limited. It is preferable that the voids form a sponge-like porous structure inside the porous membrane. In the dye-sensitized solar cell, an electrolyte or an electrolytic solution containing an electrolyte diffuses into the porous film through the voids formed in the photoelectrode, and electrons are donated to the sensitizing dye supported on the fine particles.

  In the case of forming a dense film, it is preferable to perform a pretreatment in which internal strain is applied to the particles in advance before spraying the fine particles, but this pretreatment is not necessary in the case of forming a porous film. For example, rutile-type titanium oxide particles have an appropriate strength, so that the structure is easily maintained without being crushed during film formation, and voids (pores) are formed between joined fine particles. A porous film having a large specific surface area can be formed.

The thickness of the porous film constituting the photoelectrode is preferably 1 μm to 30 μm, and more preferably 10 μm to 20 μm.
When the thickness of the porous film is not less than the lower limit of the above range, the probability that the sensitizing dye supported on the fine particles absorbs light energy can be further increased, and the photoelectric conversion efficiency in the dye-sensitized solar cell is further increased. It can be improved. On the other hand, when the thickness of the porous film is less than or equal to the upper limit of the above range, the diffusion resistance of the oxidation / reduction reactive species (electrolyte) becomes small, and the series resistance component inside the battery becomes small. The photoelectric conversion efficiency in the battery is further improved.

The larger the specific surface area of the porous film constituting the photoelectrode, that is, the surface area per unit weight (cm ² / g), the better the contact efficiency between the sensitizing dye supported on the particle surface and the electrolyte component, and the photoelectric conversion efficiency Can be improved. In order to increase the specific surface area of the porous membrane, the primary particle diameter (volume average particle diameter) of the particles is preferably as small as possible. For example, when titanium oxide particles are used as the particles, the primary particle diameter is 1 nm to 200 nm. Preferably, the thickness is 1 nm to 100 nm, more preferably 5 nm to 50 nm, and particularly preferably 10 nm to 30 nm.
If the primary particle diameter of the fine particles is not less than the lower limit of the above range, the pores of the porous film will be more suitable for diffusion of the electrolyte, and if it is not more than the upper limit of the above range, the specific surface area of the porous film will be sufficient. The sensitizing dye can be sufficiently supported by increasing the size.

  When the film is formed by the AD method, only titanium oxide particles having a primary particle diameter of, for example, 10 to 100 nm may be used. However, depending on the spraying conditions, the particles are closely bonded to each other in the formed porous film. The specific surface area of the film may not be sufficiently large. Therefore, as a method of forming a porous film having a sufficient specific surface area more easily, for example, particles having a primary particle size of 10 nm to 100 nm (small particle) and particles having a particle size of 0.2 μm to 10 μm (large particle) In combination, that is, a method using two or more kinds of particles having different primary particle diameters.

  When two or more kinds of particles having different primary particle diameters are used in combination, it is preferable to mix each particle in advance before film formation. When mixing each particle, it is preferable to use a dry blender. Examples of the blender include known methods such as a container rotation type, a stirring blade type, and an air type. Moreover, you may use the dry mixing by a mortar, an automatic mortar, etc., without using a blender.

  When titanium oxide particles are used as the particles, the crystal form of titanium oxide may be any of anatase type, rutile type and brookite type. A porous film made of anatase-type titanium oxide has higher reaction activity than a porous film made of rutile-type titanium oxide, and electron injection from the sensitizing dye becomes more efficient. On the other hand, since rutile type titanium oxide has a high refractive index, the light scattering effect and light utilization efficiency in the porous film can be further enhanced by forming the porous film with rutile type titanium oxide.

  The shape of the titanium oxide particles is not particularly limited, and examples thereof include a spherical shape or a similar shape thereof, an 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 may be further improved by using a fibrous form such as a long fiber form.

  The method for supporting the sensitizing dye on the titanium oxide particles is not particularly limited, and the method of bringing the titanium oxide particles into contact with the dye solution described above can be applied.

[Film deposition system]
An example of a film forming apparatus applicable to the formation of a porous film by the AD method is illustrated in FIG. The film forming chamber 1 of the film forming apparatus 10 is provided with a stage 13 for placing the base material 3 on which a transparent conductive layer as a conductor is formed. The stage 13 is movable in the horizontal direction with the base material 3 disposed. Further, a vacuum pump 12 is connected to the film forming chamber 1, and the inside of the film forming chamber 1 is set to a negative pressure as necessary. A nozzle 2 having a rectangular opening is disposed in the film forming chamber 1. The opening of the nozzle 2 is disposed so as to face the substrate 3 on the stage 13. A gas cylinder 5 is connected to the nozzle 2 via a transport pipe 6. A mass flow controller 7, an aerosol generator 8, a crusher 9, and a classifier 11 are provided in the transport pipe 6 in order from the gas cylinder 5 side. Depending on the type of fine particles and sensitizing dye, the sensitizing dye may be detached from the fine particles by rubbing the fine particles in the crusher 9 and the classifier 11. When the degree of desorption becomes severe, the crusher 9 and the classifier 11 need not be used.

  In the film forming apparatus 10, helium, which is a carrier gas, is supplied from the gas cylinder 5 to the carrier pipe 6, and the flow rate of the helium is adjusted by the mass flow controller 7. The aerosol generator 8 is loaded with fine particles on which a sensitizing dye has been adsorbed in advance, and the fine particles are dispersed in helium flowing through the conveying tube 6, and the fine particles are conveyed to the crusher 9 and the classifier 11. The fine particles 4 are ejected from the nozzle 2 onto the transparent conductive layer formed on the substrate 3 at a subsonic to supersonic ejection speed. At this time, the inside of the film forming chamber 1 is evacuated by the pump 12 so that the film can be formed in a helium atmosphere used as a carrier gas.

The speed of the fine particles accelerated by the carrier gas varies depending on the kind, size, combination, etc. of the fine particles, but it cannot be said unconditionally. For example, when spraying rutile titanium oxide particles of about 10 nm to 30 nm, the spraying speed is as follows: 10-1000 m / s is preferable, 10-500 m / s is more preferable, and 10-200 m / s is further more preferable. After determining the conductor and fine particles to be used, it is preferable to examine the correlation between the spraying speed and the state of the porous film to be formed.
The upper limit of the preferred range of the spraying speed is that when the fine particles collide with the conductor or the previously deposited fine particles, the porous film is maintained while maintaining the particle diameter at the time of spraying without being excessively crushed. It is preferable to consider so that it can form.
It is preferable to examine the lower limit value of the preferable range of the spraying speed so that the fine particles can be reliably bonded to the conductor or the fine particles deposited in advance to form a sufficiently strong porous film.

  Film formation by the AD method is preferably performed at a temperature sufficiently lower than the melting point of the fine particles to be used, for example, in an atmosphere of 200 ° C. or lower. Moreover, it is preferable that the said temperature is below melting | fusing point of the base material to be used. When the substrate is made of plastic, the temperature is preferably less than the Vicat softening temperature.

[Deposition method using organic solvent sol]
In the method for producing a photoelectrode of the present invention, a method of forming a film by incorporating the particles having a sensitizing dye adsorbed in advance into an organic solvent sol can be applied.

  The organic solvent sol is a sol-like fluid in which the particles are dispersed in an organic solvent. At this time, since the sensitizing dye is adsorbed to the particles in advance, the organic solvent is a kind of organic solvent that does not desorb the sensitizing dye from the particles, that is, an organic solvent having low solubility of the sensitizing dye. It is preferable that At this time, as the organic solvent, one organic solvent may be used alone, or two or more organic solvents may be used in combination.

  As the film forming method, the prepared organic solvent sol is applied onto the conductor and dried to obtain a dried product obtained by evaporating the organic solvent, and further, the dried product is pressed under pressure. A method of joining or binding the particles contained in the dried product to form a porous film or a dense film is preferable. It is possible to adjust the porosity of the porous membrane by adjusting the pressure of the pressure press. The pressure may be appropriately adjusted according to the size of the particles and the type of material. For example, when titanium oxide particles (primary particle diameter of about 10 nm to 500 nm) are used as the particles, the pressure is adjusted to 10 MPa to 200 MPa. The method of doing can be illustrated.

  The method for applying the organic solvent sol is not particularly limited as long as it is a method that can be applied in a desired shape (for example, in a thin film shape) or a film thickness. Screen printing method, spin coating method, squeegee method, doctor blade method, air spray A known method such as a method can be applied.

  The blending amount of the particles in the organic solvent sol is preferably 5 to 60% by mass, and more preferably 20 to 40% by mass. When the blending amount of the particles is not less than the lower limit of the above range, the organic solvent sol can be applied with an appropriate film thickness. On the other hand, when the blending amount of the particles is not more than the upper limit of the above range, the viscosity of the organic solvent sol can be suppressed from being excessively increased and can be easily applied.

[Formation of multilayer structure]
The layer structure used when depositing the particles on the conductor may be a single layer or a multilayer structure. Hereinafter, a case where a multilayer structure is formed will be described. However, in the case of a single layer structure, only the first layer of the multilayer structure may be formed.

The photoelectrode 20 illustrated in FIG. 2 has a multilayer structure in which a glass plate as a base material 26, a transparent conductive layer as a conductor 25 formed on one surface 26a of the base material 26, and a conductor 25 are sequentially laminated. The first porous layer 21, the second porous layer 22, the third porous layer 23, and the fourth porous layer 24 are provided.
Although the example of the photoelectrode 20 has a four-layer structure, the number of layers to be stacked is not particularly limited, and can be appropriately adjusted according to the purpose of forming a multilayer structure, for example, a 2 to 10 layer structure.

  As a film forming method for forming a porous film having a multilayer structure like the photoelectrode 20, the AD method is particularly preferable. A multilayer structure can be easily formed by preparing the particles constituting each layer and sequentially spraying and laminating the particles on the conductor 25 by the AD method. On the other hand, the film formation method using a paste in which particles are mixed with a binder resin or a solvent is complicated because it is necessary to perform paste application and firing or drying for each layer. In addition, by repeating the firing, the first layer is subjected to a plurality of firing treatments, so that the sensitizing dye previously adsorbed on the particles constituting the first layer may be thermally decomposed. .

  Various characteristics can be imparted to the porous film having a multilayer structure by changing the kind of particles constituting each layer or the kind and concentration of the sensitizing dye adsorbed in advance on the particles constituting each layer for each layer. .

  For example, a plurality of types of the particles on which different sensitizing dyes are adsorbed are stacked on the conductor so as to form a multilayer structure of two or more layers by dividing the layer for each type of the sensitizing dye. It is done. Since the porous film having a multilayer structure laminated in this way has different chemical structures and absorption spectrum characteristics depending on the type of the sensitizing dye, the spectrum of the light absorbed by the photoelectrode provided with the porous film The range becomes wider, and as a result, the photoelectric conversion efficiency by the photoelectrode can be improved. In order to sufficiently exhibit this effect, the sensitizing dyes disposed in the respective layers are preferably used in combinations having different absorption peak wavelengths in the visible light region.

  When different types of sensitizing dyes are arranged for each layer, it is preferable to consider the absorption peak wavelength in the visible light region (360 nm to 830 nm) of each sensitizing dye. For example, the absorption peak wavelength of N719 is around 540 nm, and the absorption peak wavelength of N749 is around 600 nm. Thus, sensitizing dyes often have different absorption peak wavelengths and absorption spectra in the visible light wavelength range.

  When two or more sensitizing dyes having different absorption spectra are arranged in each layer, the absorption peak wavelengths of the sensitizing dyes are preferably different from each other by 5 nm or more, more preferably 10 nm or more, and more preferably 30 nm or more. Is more preferable, and it is particularly preferable that the difference be 50 nm or more. By using a combination of two or more sensitizing dyes whose absorption peak wavelengths are different from the above lower limit values or more, the multilayer structure can exhibit a broad absorption spectrum as a whole, and the light energy incident on the photoelectrode can be further reduced. It can absorb a lot and improve the photoelectric conversion efficiency. The upper limit of the difference in absorption peak wavelength of each sensitizing dye is not particularly limited.

<Photoelectrode>
As an embodiment of the photoelectrode having the multilayer structure, the photoelectrode 20 shown in FIG. 2 can be exemplified. The photoelectrode 20 according to the present invention includes the oxide semiconductor layer having the multilayer structure, and a sensitizing dye having a different absorption peak wavelength in the visible light region is adsorbed to each layer constituting the multilayer structure. . In the photoelectrode 20, the first porous layer 21 is formed with titanium oxide particles adsorbing N3 (absorption peak: around 500 nm), and the second multi-layer is formed with titanium oxide particles adsorbing N719 (absorption peak: around 540 nm). The porous layer 22 is formed, the third porous layer 23 is formed with titanium oxide particles adsorbing N749 (absorption peak: around 600 nm), and finally the titanium oxide particles not adsorbing the dye are first. The structure provided with the porous film of the 4 layer structure which formed the four porous layer 24 into a film can be illustrated. Thus, when it is the structure by which the sensitizing dye which has a different absorption spectrum for each layer is arrange | positioned, the incident light of a wide wavelength range can be absorbed and a photoelectric conversion efficiency can be improved more. In this specific example, since the fourth porous layer 24 is a white layer that does not adsorb a dye, it can mainly function as a layer that reflects or scatters light. That is, after a part of light incident from the base material 26 and the conductor 25 side passes through the first porous layer 21 to the third porous layer 23 and reaches the fourth porous layer 24, It is reflected or scattered by the fourth porous layer 24 and returned to the first porous 21 to the third porous 23 side again. When the returned light is absorbed by the sensitizing dyes of the first porous layer 21 to the third porous layer 23, the absorption rate of incident light, that is, the light utilization rate can be increased.

<Dye-sensitized solar cell>
The dye-sensitized solar cell of the present invention includes the above-described photoelectrode of the present invention. The configuration other than the photoelectrode can be the same as that of a conventionally known dye-sensitized solar cell. For example, a counter electrode (counter electrode) in which a conductive layer such as platinum is provided on the surface of a substrate is prepared, the photoelectrodes of the present invention are arranged facing each other at a predetermined interval, and electrolysis is performed between these electrodes. The structure filled with the liquid is mentioned.
The dye-sensitized solar cell of the present invention is excellent in photoelectric conversion efficiency because the photoelectrode is extremely excellent in utilization efficiency of incident light.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.

<Example 1>
[Adsorption of sensitizing dye]
Commercially available MK-2 was dissolved in toluene (concentration of 0. 0) by mixing 95: 5 mixed particles of TiO ₂ large particles (primary particle size: about 2 µm) and small particles (primary particle size: about 30 nm). 5M), the dye was adsorbed to the TiO ₂ particles by immersing in the dye solution prepared at 5 M) and holding at 30 ° C. for 24 hours. After the dye adsorption, the dye solution in which the particles were immersed was held under reduced pressure to volatilize and remove toluene as a solvent, and MK-2 was adsorbed in advance to the mixed particles before film formation.

[Porous membrane formation by AD method]
Using a glass substrate with ITO, which is a transparent conductive layer, on the surface, the mixed particles are sprayed onto the transparent conductive layer by the AD method to form a porous film (porous titanium oxide layer) with a film thickness of 5 μm. Thus, a photoelectrode was obtained. The formed porous film was sufficiently loaded with the dye.
Film formation by the AD method was performed under the following conditions.
・ Atmosphere in the deposition chamber: normal temperature (25 ° C.), vacuum (20 Pa)
-Carrier gas: oxygen gas (1 L / min)
-Shape of opening of spray nozzle: rectangle of 10 mm x 0.5 mm-Spray speed of mixed particles (100 m / s)

[Preparation of dye-sensitized solar cell]
A photoelectrode composed of a porous film carrying a dye and a glass substrate was lightly washed with alcohol, and then a 30 μm thick silicon rubber spacer was placed around the thin film, and an electrolytic solution (Iodolyte 50, manufactured by Solaronics) was poured. Subsequently, a counter electrode made of glass with platinum coating was placed over the glass so as not to enter air, and the photoelectrode and the counter electrode were sandwiched with a double clip and pressed to obtain a simple cell of a dye-sensitized solar cell. The effective area was 4 mm square.

[Evaluation of photoelectric conversion efficiency]
Using a solar simulator (AM1.5, 100 mW / cm ² ) equipped with an IV characteristic measurement device, the photoelectric conversion efficiency of the prepared simple cell was evaluated. At this time, the output current value was measured while scanning the DC voltage at 40 mV / sec to obtain IV characteristics (current-voltage characteristics). Based on this, an open circuit voltage (Voc), a short circuit current density (Jsc), a fill factor (FF), and a photoelectric conversion efficiency (PCE) were calculated. The results are shown in Table 1 and FIG.

  As described above, a fully functional dye-sensitized solar cell could be produced by the method for producing a photoelectrode of the present invention. In addition, since the dye is preliminarily adsorbed to the titanium oxide particles before the porous film is formed, compared to the case where the dye is adsorbed after the film formation, from the start of film formation to the completion of the photoelectrode and the dye-sensitized solar cell. The time required is much faster. Therefore, it is clear that according to the method for producing a photoelectrode of the present invention, the productivity (production speed) of the photoelectrode can be increased.

DESCRIPTION OF SYMBOLS 1 ... Film-forming chamber, 2 ... Nozzle, 3 ... Base material, 4 ... Fine particle by which sensitizing dye was previously adsorbed, 5 ... Gas cylinder, 6 ... Transport pipe, 7 ... Mass flow controller, 8 ... Aerosol generator, 9 ... Crusher, 10 ... film forming apparatus, 11 ... classifier, 12 ... pump, 13 ... stage, 20 ... photoelectrode, 21 ... first porous layer, 22 ... second porous layer, 23 ... third Porous layer, 24 ... fourth porous layer, 25 ... conductor, 26 ... substrate, 26a ... one surface.

Claims (8)

A method for producing a photoelectrode, comprising depositing oxide semiconductor particles having a sensitizing dye adsorbed thereon on a conductor. The method for producing a photoelectrode according to claim 1, wherein the particles are sprayed onto the conductor at a high speed to form a thin film composed of the particles on the conductor. A plurality of types of the particles having different sensitizing dyes adsorbed thereon are laminated on the conductor so as to form a multilayer structure of two or more layers by dividing the layer for each type of the sensitizing dye. The manufacturing method of the photoelectrode of Claim 1 or 2. A plurality of types of the particles in which sensitizing dyes having different absorption peak wavelengths in the visible light region are adsorbed on the conductor are divided into layers for each type of the sensitizing dye so as to have a multilayer structure of two or more layers. The method for producing a photoelectrode according to any one of claims 1 to 3, wherein the photoelectrode is laminated.   On the conductor, first particles adsorbed with a first sensitizing dye and second particles adsorbed with a second sensitizing dye are laminated, and the first sensitizing dye and the second sensitizing dye are laminated. The method for producing a photoelectrode according to any one of claims 1 to 4, wherein an absorption peak wavelength of the sensitizing dye in the visible light region is different by 10 nm or more. The method for producing a photoelectrode according to any one of claims 1 to 5, wherein a transparent conductive layer formed on a plastic transparent substrate is used as the conductor. A photoelectrode comprising an oxide semiconductor layer having a multilayer structure, wherein a sensitizing dye having a different absorption peak wavelength in the visible light region is adsorbed in each layer constituting the multilayer structure. A dye-sensitized solar cell, comprising the photoelectrode obtained by the production method according to any one of claims 1 to 6 or the photoelectrode according to claim 7.

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