JP4576544B2 - Film-type dye-sensitized photocell - Google Patents

Description

  The present invention relates to a film type dye-sensitized photovoltaic cell having a structure in which a dye-sensitized semiconductor layer not containing a binder material is supported on a transparent film electrode and capable of generating power with high efficiency by irradiation with visible light.

  Recently, it can be manufactured at low cost and can be formed as a wet type instead of the conventional solid junction solar cell using a silicon pn junction or a compound semiconductor heterojunction as a photovoltaic layer. Dye-sensitized solar cells that make use of chemical reactions are attracting attention.

  The basic technique of this dye-sensitized solar cell is disclosed in Non-Patent Document 1 and Patent Document 1. This dye-sensitized solar cell has responded to visible light up to 800 nm and has already achieved an energy conversion efficiency of 10% or more, but it has an energy conversion of 15% or more that surpasses that of amorphous silicon solar cells. Energetic research continues to achieve efficiency.

  On the other hand, research on dye-sensitized solar cells that are colorful and excellent in transparency, especially on film-type dye-sensitized solar cells, has been conducted as having characteristics different from silicon solar cells. A low-temperature film-forming method of a semiconductor porous film using electrophoresis for use in manufacturing a film-type solar cell has been proposed (see Non-Patent Document 2 and Patent Document 2). In addition, a so-called pressing method in which a dispersion of semiconductor fine particles is coated on an electrode support and formed into a film by applying pressure has been proposed as a film forming method without using a binder (see Patent Document 3).

  In these methods, the semiconductor porous film can be formed at a low temperature of 150 ° C. or less, which is within the heat resistance range of the plastic electrode, and the roll type production method used in the printing field can be applied, so the cost is low. Although there is an advantage that a solar cell can be manufactured, a solar cell using an electrode obtained thereby has a disadvantage that it has an energy efficiency of about 1 to 3% and is lower than a glass electrode manufactured by a conventional firing method. There is.

  This is because the conventional firing method forms a film at a high temperature of 450 ° C. or higher, so that impurities derived from the raw material are completely removed. However, the press method and other low-temperature film forming methods completely remove these impurities. This is because impurities (mostly organic substances) present in the dispersion solvent of semiconductor particles and organic substances added in a small amount as a binder for film formation are mixed in the porous semiconductor film as an insulating substance. Therefore, in the low-temperature film formation, the polymer and organic impurities used as binder materials are reduced to below a certain level to form a high-purity dye-sensitized semiconductor film, which is a lightweight, large-area film type solar cell There is a strong demand in this field to produce.

US Pat. No. 4,927,721 (Claims and others) JP 2002-100416 A (Claims and others) Special Table 00/72373 A1 (Claims and others) “Nature”, 353, 1991, p737-740. "Chemistry letter", 2002, p1250

  The present invention was made in order to provide a flexible film type dye-sensitized photovoltaic cell having a high-purity porous semiconductor film formed by low-temperature film formation, thereby having high energy conversion efficiency and excellent mechanical stability. It is.

  The present inventors have conducted various studies on a photovoltaic cell using a dye-sensitized porous semiconductor layer formed by low-temperature film formation in order to improve its energy conversion efficiency. As a result, the surface resistance of a plastic support has been reduced. The object can be achieved by lowering the density and making the dye-sensitized porous semiconductor particle layer substantially composed only of a semiconductor, an inorganic oxide, and a dye, and controlling the porosity within a specific range. Based on this finding, the inventors have made the present invention.

  That is, the present invention uses a transparent conductive plastic support carrying a dye-sensitized porous semiconductor particle layer as one electrode, and a counter electrode or an additional support through an ion conductive electrolyte. In a film type photovoltaic cell having a structure in which a separator layer for preventing a short circuit is laminated between an ionic conductive electrolyte, the transparent conductive plastic support has a conductive lead wire for collecting current in a plane, and a surface resistance 3 Ω / □ or less, and the dye-sensitized porous semiconductor particle layer is formed on the porous semiconductor particle layer formed at 200 ° C. or less by the binder-free coating method, with ultraviolet irradiation, ozonolysis treatment, The dye sensitization is formed by performing any one or more of plasma treatment, corona discharge treatment, and heat treatment at 200 ° C. or lower. In the porous semiconductor particle layer thus formed, the mass of the solid content excluding the semiconductor, the inorganic oxide, and the pigment is less than 1% with respect to the total mass of the particle layer, and the porosity is 50% or more and 85% or less. The present invention provides a mechanically flexible film-type photovoltaic cell.

  Thus, in the photovoltaic cell of the present invention, a dye-sensitized semiconductor thin film obtained by adsorbing a dye to a porous semiconductor fine particle layer is used as a photoelectrode, and an ion conductive layer and optionally a separator and a counter electrode are laminated thereon. This is a mechanically flexible dye-sensitized photocell composed of a multilayer body.

  Thus, in a photoelectrochemical cell using a dye-sensitized semiconductor layer as a photoelectrode, the sensitizing dye on the semiconductor injects electrons or holes into the semiconductor under photoexcitation to control the direction of the sensitized photocurrent. Produce.

  In the case of a dye-sensitized n-type semiconductor, which is a typical example, the photoelectrode becomes a photoanode, and an anode-sensitized photocurrent is generated by electron injection from the dye. The dye injects excited electrons into the conduction band of the n-type semiconductor, and the conduction band electrons move from the surface of the semiconductor to the bulk and reach the conductive support carrying the semiconductor, that is, the plastic support in the present invention.

  The dye molecule after electron injection becomes an oxidant radical deficient in electrons, but is electronically reduced by an electron donor in the electrolytic solution in contact with the dye, that is, a reducing agent, and is quickly regenerated. The electrons received by the conductive support are transferred to the counter electrode through the external circuit. At this time, current and electromotive force are generated in the external circuit under light excitation. The maximum value of the product of these current and electromotive force is measured as the maximum output power of the photovoltaic cell.

Next, the present invention will be described in more detail with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view showing the structure of an example of a film type photovoltaic cell of the present invention. Here, the cell comprises a photoelectrode film support 1, a photoelectrode transparent conductive layer 2, an undercoat layer 7, a dye-sensitized porous semiconductor layer 3, an ion conductive electrolyte layer 4, a separator 6, a counter conductive layer 5, The counter electrode film support 8 is laminated in this order, and the dye-sensitized semiconductor layer 3 includes a dye and semiconductor fine particles sensitized thereby, and the ion conductive electrolyte layer 4 penetrating into the gaps between the semiconductor fine particles. It consists of.

  The ion conductive electrolyte layer 4 penetrating into the voids is composed of the same components as the material used for the ion conductive electrolyte layer 4. A conductive support is constituted by a layer composed of the transparent conductive layer 2 and the support 1, and the conductive layer 5 and the support 8. In such a photovoltaic cell, when the main purpose is power generation by sunlight, this is referred to as a dye-sensitized solar cell.

  In the present invention, the transparent conductive plastic support carrying the porous semiconductor layer is composed of a conductive layer and a plastic film substrate carrying the conductive layer. As the conductive layer, a metal such as platinum, gold, silver, copper, aluminum, or indium, or a conductive metal oxide such as carbon or indium-tin composite oxide or tin oxide is used. Of these, conductive metal oxides are preferable in terms of optical transparency, and indium-tin composite oxides are particularly preferable.

  The conductive layer used for the transparent conductive plastic support in the present invention is required to have a low surface resistance, and the surface resistance value is 3Ω / □ or less, preferably 1Ω / □ or less. Auxiliary leads for collecting current can be arranged on the conductive layer by patterning or the like.

  Such auxiliary leads are usually formed of a low-resistance metal material such as copper, silver, aluminum, platinum, gold, titanium, or nickel. In the transparent conductive layer in which the auxiliary lead is patterned, the resistance value of the surface including the auxiliary lead is controlled to 3Ω / □ or less, preferably 1Ω / □ or less. Such an auxiliary lead pattern is preferably formed on a transparent substrate by vapor deposition, sputtering, or the like, and further provided with a transparent conductive layer made of tin oxide or ITO film.

In a transparent conductive plastic support carrying a dye-sensitized porous semiconductor particle layer, when the conductive lead wire for current collection is patterned in the surface, the resistance of the support surface including the lead wire Is 1 Ω / □ or less, and the area of the conductive plastic support forming the continuous structure is preferably 30 cm ² or more. The area of the continuous conductive plastic support is more preferably 60 cm ² or more, and most preferably a large area of 100 cm ² or more.

  The thickness of the transparent conductive plastic support is preferably 100 μm or more and 300 μm or less including the support and the porous semiconductor particle layer carried by the support from the point that the electrode has flexibility and mechanical stability. It is particularly preferable that the thickness is 130 μm or more and 250 μm or less. The thickness of the plastic support alone is preferably from 80 μm to 280 μm, particularly preferably from 100 μm to 220 μm.

  The transmittance of the transparent conductive plastic support is preferably 60% or more, particularly preferably 70% or more at a wavelength of 500 nm. Since the portion where the current collecting auxiliary lead is disposed on the support becomes opaque, the transparent aperture ratio of the photovoltaic cell is reduced, so that the ratio of the auxiliary lead to the light receiving area is within 10%. In particular, it is preferably within 5%.

  As the plastic material for the transparent conductive plastic support, a material which is not colored and has high transparency, high heat resistance, excellent chemical resistance and gas barrier properties, and low cost is preferably selected. From this viewpoint, preferable plastic materials include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), syndiotactic polystyrene (SPS), polyphenylene sulfide (PPS), polycarbonate (PC), polyarylate (PAr), polysulfone ( PSF), polyester sulfone (PES), polyetherimide (PEI), transparent polyimide (PI) and the like are used. Particularly preferred in terms of cost are polyethylene terephthalate (PET) and polyethylene naphthalate (PEN).

  The porous semiconductor layer of the present invention comprises a so-called mesoporous semiconductor film in which nano-sized pores are formed in a network. As a semiconductor material for forming the semiconductor film, a metal oxide and a metal chalcogenide can be used.

  The metal elements of these oxides and chalcogenides include titanium, tin, zinc, iron, tungsten, zirconium, strontium, indium, cerium, vanadium, niobium, tantalum, cadmium, zinc, lead, antimony, bismuth, cadmium, lead, etc. Can be mentioned.

  Preferred examples of the metal compound having a perovskite structure include strontium titanate, calcium titanate, sodium titanate, barium titanate, and potassium niobate.

Other preferable semiconductor materials include n-type inorganic semiconductors such as TiO ₂ , TiSrO ₃ , ZnO, Nb ₂ O ₃ , SnO ₂ , WO ₃ , Si, CdS, CdSe, V ₂ O ₅ , ZnS, ZnSe, There are SnSe, KTaO ₃ , FeS ₂ , PbS, etc. Among these, more preferred semiconductors are TiO ₂ , ZnO, SnO ₂ , WO ₃ , Nb ₂ O ₃ , and particularly preferred are titanium oxide and zinc oxide. , One or more semiconductors selected from tin oxide and composites thereof. The particle diameter of these semiconductor particles is selected so that the average particle diameter of primary particles is 2 nm to 50 nm, preferably 2 nm to 30 nm.

  In the photovoltaic cell of the present invention, the porous semiconductor particle layer made of the above semiconductor particles is sensitized by the dye, and thus has the dye as an adsorbed molecule on the surface of the porous film. In the present invention, the dye-sensitized porous semiconductor film is characterized in that the purity of the semiconductor film does not contain a binder and is extremely high.

  In other words, the dye-sensitized porous semiconductor film is substantially composed only of a semiconductor, an inorganic oxide, and a dye, and a solid component other than these is a component constituting the porous film or a component mixed with the porous film. Is not contained inside the porous membrane.

The fact that the porous semiconductor particle layer is substantially composed only of a semiconductor, an inorganic oxide, and a dye is that the semiconductor, the inorganic oxide, and the dye are main components necessary for the formation of the particle layer. Means that the total mass of is substantially equal to the total solid mass of the particle layer.
Examples of solids other than the semiconductor, inorganic oxide, and pigment that may be mixed in the particle layer include polymer resins and carbon materials.

  In the preferred form of the porous semiconductor particle layer in the present invention, the proportion of the solid content excluding the semiconductor, the inorganic oxide, and the dye is less than 3% of the total mass of the particle layer. The porosity shown by the volume fraction occupied by the pores is 50% or more and 85% or less. The porosity is particularly preferably 65% or more and 85% or less. Further, the ratio of the solid content excluding the semiconductor, the inorganic oxide, and the pigment to the total mass of the porous semiconductor particle layer is particularly preferably less than 1%.

  The inorganic oxide is not particularly limited, and includes metals, alkali metals, transition metals, rare earth oxides, lanthanoids, and nonmetallic oxides such as Si, P, and Se. Examples of the metal include Al, Ge, Sn, In, Sb, Tl, Pb, and Bi. Examples of the alkali metal include Li, Mg, Ca, Sr, and Ba. Examples of the transition metal include Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Pd, Ag, W, Os, Ir, Pt, and Au. .

  In the present invention, the ratio of the semiconductor and the inorganic oxide to the total mass of the porous semiconductor particle layer can be measured, for example, by the following method. That is, the porous particle layer is detached from the plastic support, and as a substance other than the particle layer constituent component contained in the porous particle layer, a liquid component or a solid component derived from a constituent component such as an electrolytic solution is used. The solvent is used to wash away only the particle layer, and the particle layer is dried and the total solid content is weighed.

  The particle layer is thoroughly washed with a polar organic solvent such as alcohol and acetonitrile and a nonpolar organic solvent such as toluene and chloroform to remove the organic substance, and then the particle layer is heated at 400 ° C. or higher in an oxygen atmosphere or in air. Heat for more than an hour. The value obtained by measuring the mass of the residue after heating and dividing the dry mass of the residue by the total solid mass is the target solid content ratio.

  In the present invention, the ratio of the dye to the total mass of the porous semiconductor particle layer can be measured, for example, by the following method. That is, after the particle layer is detached from the plastic support and the total mass is weighed, the particle layer is sufficiently washed with an organic solvent effective for elution of the pigment such as water, methanol, and acetonitrile, and the pigment is removed from the particle layer. Detach and wash the particle layer to such an extent that the color of the dye hardly remains. After removing the solvent from the washing solution containing the dye by evaporation, the dry mass of the remaining dye is weighed. A value obtained by dividing the dry mass of the pigment by the total solid mass is the ratio of the target pigment.

  Further, the total of the ratio of the semiconductor and inorganic oxide and the dye thus obtained is reduced from 1 as the ratio of the solid content excluding the semiconductor, the inorganic oxide and the dye to the total mass of the particle layer. Desired. What is contained as solid content except a semiconductor, an inorganic oxide, and a pigment | dye includes a polymeric resin, a carbon material, etc., for example.

  The porous semiconductor layer of the film battery of the present invention preferably has a characteristic structure containing a network of cracks connected in a mesh pattern on the surface. A crack is a crack generated in a continuous porous semiconductor film spread two-dimensionally. This crack is caused by an inorganic structure having the same physical properties (crystallinity, composition) or different physical properties as the continuous semiconductor film. Buried. Such a structure imparts moderate flexibility to the porous membrane and prevents the porous membrane from peeling from the flexible plastic support.

  The network of cracks may be regular or random. The substance filling the cracks may be crystalline or amorphous. The average length of the crack gap is in the range of 0.1 to 50 μm, preferably in the range of 2 to 20 μm. The crack gap may or may not be sensitized by dye adsorption.

  The porous semiconductor particle layer may contain two or more kinds of fine particles having different particle size distributions. In this case, the average size of the small particles is preferably 20 nm or less. Large particles having an average particle size exceeding 200 nm can be added to the ultrafine particles at a rate of 5 to 30% in order to increase light absorption.

  The method for producing the above-mentioned nano-sized semiconductor fine particles can be carried out by using a known method. For example, the sol-gel method described in “Science of Sol-Gel Method”, Agne Jofusha (1998) It can be prepared by a method of producing an oxide by hydrolyzing a metal chloride in an oxyhydrogen salt or a so-called gas phase synthesis method in which a metal compound is thermally decomposed at a high temperature in a gas phase to form ultrafine particles. it can.

  The transparent conductive plastic electrode carrying the dye-sensitized porous semiconductor film of the present invention forms a semiconductor film at a low temperature within the range of the heat resistance of the plastic, for example, 200 ° C. or less, preferably 150 ° C. or less. It is manufactured with the technique of low temperature film formation. Such low-temperature film formation is already known, and is produced by coating these known methods, for example, a press method, a hydrothermal decomposition method, an electrophoretic electrodeposition method, and a particle dispersion without using a binder material such as a polymer. The binder-free coating method can be used.

  Among these methods, as shown in the present invention, the basic film forming methods preferable for achieving the conditions for suppressing the solid content as an impurity to be extremely low are hydrothermal decomposition method, electrophoretic electrodeposition method and binder-free coating. Is the law. Of these, the binder-free coating method is the most advantageous because of the simplicity of the manufacturing process.

  In order to reduce the solid content of impurities to 1% or less as shown in the present invention, in addition to these film forming methods, as a means for decomposing and removing film forming raw materials and precursor compound residues, semiconductors It is effective to add ultraviolet irradiation, ozonolysis treatment, plasma treatment, corona discharge treatment, microwave irradiation treatment, heat treatment, etc. to the film as post-treatment.

  Next, as a dye molecule used for sensitization of a porous semiconductor, known sensitizing materials that have been used for dye-sensitized semiconductors are widely used. Examples of such dyes include organic dyes such as cyanine, merocyanine, oxonol, xanthene, squarylium, polymethine, coumarin, riboflavin, and perylene, Ru complexes, metal phthalocyanine derivatives, metal porphyrin derivatives, There are complex dyes such as chlorophyll derivatives. In addition, synthetic dyes and natural dyes described in “Functional Materials”, June 2003, pages 5 to 18 and “Journal of Chemical Physics” (J. Chem. Phys.), B.C. An organic dye mainly composed of coumarin described in Vol. 107, page 597 (2003) can also be used.

As the ion conductive electrolyte layer in the present invention, an aqueous electrolyte, an organic solvent electrolyte, an ionic liquid electrolyte (molten salt electrolyte) or the like can be used. As an oxidation-reduction agent contained in these electrolyte solutions, a combination of I ₂ and iodide (as iodide, metal iodide such as LiI, NaI, KI, etc., tetraalkylammonium iodide, pyridinium iodide, imidazolium iodide) Electrolyte containing iodine salt of quaternary ammonium compound such as id, etc., Br ₂ and bromide combination (as bromide metal bromide such as LiBr, NaBr, KBr, etc., or quaternary ammonium such as tetraalkylammonium bromide, pyridinium bromide) Compound bromine salts), metal complexes such as ferrocyanate-ferricyanate and ferrocene-ferricinium ions, sulfur compounds such as sodium polysulfide and alkylthiol-alkyldisulfides, viologen dyes, Hide Rhoquinone-quinone and the like can be used. Among these, an electrolyte in which an iodine salt of a quaternary ammonium compound such as I ₂ and LiI, pyridinium iodide, imidazolium iodide or the like is combined is preferable in terms of providing high performance as a photovoltaic cell.

  Examples of the solvent for the organic solvent electrolyte include carbonate compounds such as ethylene carbonate and propylene carbonate, alcohols such as ethyl alcohol, ethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, polyethylene glycol monoalkyl ether, and polypropylene glycol monoalkyl ether. Polyhydric alcohols such as ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, glycerin, ethers such as dioxane, ethylene glycol dialkyl ether, propylene glycol dialkyl ether, polyethylene glycol dialkyl ether, polypropylene glycol dialkyl ether, γ- Butyrolactone, α-methyl-γ Lactones such as butyrolactone, β-methyl-γ-butyrolactone, γ-valerolactone, 3-methyl-γ-valerolactone, nitrile compounds such as acetonitrile, methoxyacetonitrile, propionitrile, benzonitrile, dimethyl sulfoxide, sulfolane, etc. Heterocyclic compounds such as proton polar substances and 3-methyl-2-oxazolidinone are used. These may be used alone or in combination of two or more.

  As the ionic liquid electrolyte, a molten salt electrolyte is most preferable from the viewpoint of non-volatility and nonflammability. The molten salt electrolyte is preferably a room temperature molten salt that becomes liquid near room temperature, such as alkyl imidazolium salts such as dimethylimidazolium, methylpropylimidazolium, methylbutylimidazolium, and methylhexylimidazolium. The iodide etc. can be mentioned.

  In addition, known pyridinium salts, imidazolium salts, triazolium salts, and the like can be used as the electrolyte. The molten salt is described in Japanese Patent Application Laid-Open No. 2002-190323, Japanese Patent Application Laid-Open No. 2001-199961, Japanese Patent Application Laid-Open No. 2001-196105, etc. as having a low viscosity and providing high performance when used in a dye-sensitized photovoltaic cell. It is also possible to use known molten salts.

  Further, the ionic liquid electrolyte in the present invention is gelled or solidified by adding a polymer such as polyacrylonitrile or polyvinylidene fluoride or an oil gelling agent to the polymer or by causing a crosslinking reaction of the polymer therein. Can also be used.

  Further, as a method of gelling by adding an oil gelling agent, a method using a compound having an amide structure in the molecular structure is preferable, and an example of gelling an electrolytic solution (JP-A-11-185863), a molten salt electrolyte In the present invention, any of these known methods can be arbitrarily selected and used in the present invention (Japanese Patent Laid-Open No. 2000-58140).

  A solid material such as an n-type semiconductor or a p-type semiconductor can be mixed and used for the ion conductive electrolyte layer of the film type photovoltaic cell of the present invention. Moreover, these solid materials can be inserted between the dye-sensitized porous semiconductor film electrode and the counter electrode to form a short-circuit preventing layer.

Further, as the charge transport material, a hole transport material can be used in combination with the ion conductive electrolyte layer. In this case, a p-type inorganic compound semiconductor is preferable. A compound semiconductor containing monovalent copper is preferable as the p-type inorganic compound semiconductor. Examples of such a semiconductor include CuI, CuSCN, CuInSe ₂ , Cu (In, Ga) Se ₂ , CuGaSe ₂ , Cu ₂ O, CuS, and the like _{CuGaS 2, CuInS 2, CuAlSe 2} . Among these, CuI and CuSCN are preferable, and CuI is particularly preferable. As other p-type inorganic compound semiconductors, GaP, NiO, CoO, FeO, Bi ₂ O ₃ , MoO ₂ , Cr ₂ O _{3 and the} like can be used.

  If desired, the multilayer film type photovoltaic cell of the present invention can include a separator layer for preventing short circuit. This separator layer is inserted between the dye-sensitized porous semiconductor film electrode and the counter electrode, and aims to prevent physical contact between both electrodes, which are flexible electrodes.

  The material forming the separator layer is an electrically insulating material, and the shape thereof may be any of a film shape, a particle shape, and a shape integrated with the electrolyte layer, but a film-type separator is used. It is preferable. When used in the form of a film, the film is made of a porous film that permeates the electrolytic solution, for example, an organic material such as a resin film, a nonwoven fabric, or paper. Such a porous film may be a hydrophilic film formed by hydrophilizing the surface.

  The thickness of this film needs to be 80 μm or less, preferably 5 to 50 μm, and more preferably 5 to 25 μm. It is necessary to use a film having a porosity of 50 to 85%.

  Various inorganic materials and organic materials can be used as the particles. As the inorganic material, silica, alumina, fluorine resin and the like are preferable, and as the organic material, beads such as nylon, polystyrene, polyethylene, polypropylene, polyester and polyimide are preferable.

  The average particle size of these particles is preferably 10 to 50 μm, and more preferably 15 to 30 μm. When the separator is integrated with the electrolyte, for example, an electrolytic solution gelled with a polymer or the like, an electrolytic solution whose viscosity is increased by crosslinking the electrolytic solution by a crosslinking reaction of a compound in the electrolytic solution, and the like are used. These so-called quasi-solidified electrolytes are also included in a broad sense.

  As the counter electrode of the film type photovoltaic cell of the present invention, a conductive film electrode is used in the same manner as the dye-sensitized porous semiconductor film electrode. The support for the counter electrode is preferably a plastic film, and a plastic support similar to the preferred support described in the dye-sensitized porous semiconductor film electrode is used. The counter electrode may be optically transparent or opaque depending on the application, and the counter electrode needs to be transparent when it is intended to produce a transparent photovoltaic cell.

  For the conductive layer of the counter electrode, metals such as platinum, gold, silver, copper, aluminum, magnesium, indium, carbon or conductive metal oxide, indium-tin composite oxide (ITO), fluorine-doped tin oxide (FTO), etc. The conductive metal oxide can be used as a conductive material. Among these, platinum, ITO, and FTO are preferable in terms of excellent corrosion resistance.

  Similar to the dye-sensitized porous semiconductor film electrode, an auxiliary lead wire for collecting current can be provided on the surface of the conductive layer. The range of the preferred surface resistance of the counter electrode including the counter electrode provided with such an auxiliary lead wire is 3Ω / □ or less, preferably 1Ω / □ or less. The surface of the counter electrode is preferably coated with a material that is chemically stable with respect to contact with the electrolytic solution, and in particular one or more selected from carbon materials, conductive polymers, platinum, tin oxide, and zinc oxide. It is preferable to be coated with the material.

  The most preferable counter electrode is a conductive plastic film having a surface resistance value of 1Ω / □ or less, and the surface of the counter electrode in contact with the ion conductive layer is selected from a carbon material, a conductive polymer, platinum, tin oxide, and zinc oxide. Cover with one or more materials.

  The film type photovoltaic cell of the present invention may be transparent or opaque depending on the application. When a transparent battery is used, it is necessary to use a transparent electrode for the counter electrode. When it is opaque, an opaque electrode is used as the counter electrode. In the production of a battery having high energy conversion efficiency and high light absorption rate, the counter electrode is preferably made of an opaque film.

  In the case of producing a battery having light transmission properties at the same time as a relatively high photovoltaic power generation function, a film-type photovoltaic cell exhibiting a maximum light transmittance in a wavelength range of 400 to 800 nm is 10% or more. Preferably exhibits transparency to visible light. More preferably, the light transmittance is at most 40% in the wavelength range of 400 nm to 800 nm.

  The film type photovoltaic cell of the present invention can have a colorful appearance in order to add aesthetic design depending on the application. In this case, in the transparent conductive plastic support carrying the dye-sensitized porous semiconductor film, the surface of the dye-sensitized porous semiconductor film is dye-sensitized with two or more different colors. Is preferred.

  The surface of the dye-sensitized porous semiconductor film is preferably dye-sensitized with different colors over three or more colors. In particular, for the purpose of colorful printing, it is preferable that sensitization is performed by including three colors of yellow, magenta and cyan as color elements.

  In addition to the above basic layer configuration, the film type photovoltaic cell of the present invention can be further provided with various layers as desired. For example, a dense semiconductor thin film layer can be provided as an undercoat layer between the conductive plastic support and the porous semiconductor layer.

A metal oxide is preferable as the undercoat layer, and examples thereof include TiO ₂ , SnO ₂ , Fe ₂ O ₃ , WO ₃ , ZnO, and Nb ₂ O ₅ . The undercoat layer is, for example, Electrochim. In addition to the spray pyrolysis method described in Acta 40, 643-352 (1995), it can be applied by sputtering or the like.

  The preferred thickness of the undercoat layer is 5 to 100 nm. In addition, a functional layer such as a protective layer, an antireflection layer, or a gas barrier layer is provided on the outer surface of one or both of the porous semiconductor electrode and the counter electrode acting as a photoelectrode, between the conductive layer and the substrate, or in the middle of the substrate. May be. These functional layers can be formed by a coating method, a vapor deposition method, a bonding method, or the like depending on the material.

  The total thickness of the film type photovoltaic cell of the present invention is 150 μm or more and 500 μm or less, preferably 250 μm or more and 450 μm or less for the purpose of ensuring mechanical flexibility and performance stability.

  According to the present invention, a large-area flexible film-type dye-sensitized photocell excellent in energy conversion efficiency and mechanical stability can be obtained.

  Next, the best mode for carrying out the present invention will be described as examples.

(1) Preparation of Conductive Plastic Electrode As a transparent conductive plastic film, polyethylene naphthalate (PEN) having a film thickness of 125 μm and a surface resistance of 10Ω / □ supporting ITO as a conductive film was used. In order to reduce the surface resistance of this conductive film, a silver dispersed paste is applied to a silver current collecting auxiliary lead wire having a line width of 60 to 180 μm and a thickness of 20 μm on the ITO film in parallel with a gap of 10 mm. Patterning. On these silver patterns, a polyester resin was applied as a protective film with a width of 250 μm to completely protect the silver wire. By changing the line width of silver, the surface resistance of the obtained patterned conductive ITO-PEN film was changed from 0.5 to 7Ω / □.

(2) Preparation of thin film (a) Preparation of thin film by binder- free coating method Washed rutile and anatase mixed crystalline titanium dioxide nanoparticles (average particle size 20 nm) made by Showa Denko using ultrapure water and isopropyl alcohol. After that, 30 g was stirred and dispersed in 100 ml of a 9: 1 mixed solvent of tert-butyl alcohol (purity 99.5% or more) and acetonitrile (purity 99.5% or more), and titanium dioxide having a particle diameter of 5 nm was dispersed in this dispersion. Add 10% by weight of acidic sol (concentration: 8% by weight) in which particles are dispersed in a mixed solvent of water and ethyl alcohol, and mix the resulting dispersion evenly using a mixing conditioner of both rotation and revolution. A viscous paste was prepared. This titania paste was applied to the ITO surface of the ITO-PET film by a doctor blade method and dried at 40 ° C. for 20 minutes to form a porous particle layer.

Next, in order to increase the purity of the particle layer, the particle layer was exposed to UV light from a 100 W low-pressure mercury lamp ultraviolet light source at 120 ° C. for 10 minutes to perform a cleaning process. Thus, a porous semiconductor film electrode having an average thickness of 10 μm was produced.
As a comparative experiment, a polyethylene glycol (PEG) having an average molecular weight of 20,000 as a solid content other than semiconductor particles was added to the dispersion obtained by performing the film washing without performing the particle cleaning step and the UV light treatment. An ITO-PET film carrying a low-purity porous film coated with a small amount of the above powder and dried by heating was also produced.

(B) Thin Film Preparation by Electrophoretic Electrodeposition The crystalline titanium dioxide nanoparticles used above were prepared in a 1: 9 ratio of acetonitrile (purity 99.5% or higher) and tert-butyl alcohol (purity 99.5% or higher). The mixture was dispersed in a mixed solvent at an addition amount of 0.030 g / ml and treated with ultrasonic waves for 3 minutes. This dispersion was injected into a gap (distance 0.4 mm) in which the ITO-PEN film substrate electrode and the conductive tin oxide glass electrode were faced in parallel, and the conductive tin oxide glass electrode was used as the counter electrode to the ITO-PEN film substrate electrode. Electrophoretic deposition was performed by applying a DC voltage of 30 V for 45 seconds. By this method, an electrodeposited film of porous titanium dioxide having an average thickness of 6 μm was formed on the film electrode.

  By the same method, a second electrophoretic electrodeposition was performed on this electrodeposition film to produce a porous semiconductor film electrode having an average thickness of 9 μm. This porous electrodeposition film is impregnated with an acidic sol solution (concentration: 6% by mass) containing titanium hydroxide, which is a precursor of titanium dioxide, and is subjected to heat treatment on a 120 ° C. hot plate for 20 minutes. went.

Next, in order to increase the purity of the particle layer, UV light / ozone treatment using a 13 W low-pressure mercury lamp and an ozone generator was performed on the particle layer at 120 ° C. for 20 minutes. Thus, a porous semiconductor film electrode having an average thickness of 10 μm was produced.
As a comparative experiment, a film electrode was also prepared in which film formation was performed without performing the particle cleaning step and the UV light / ozone treatment.

  The surface of the titanium dioxide layer of the porous semiconductor formed on the film by the above method was observed with a digital microscope. As a result, the method (a) depends on the concentration of the titanium dioxide particle dispersion used for coating, and the method (b) depends on the voltage conditions for electrophoretic electrodeposition and the concentration of the electrophoretic dispersion. Thus, it was recognized that cracks having a gap size of 1 to 50 μm were generated on the surface of the porous semiconductor layer. The cracks were two-dimensionally connected in a mesh shape and showed the characteristic of spreading over the entire film surface. This crack does not occur depending on the conditions of film formation, and the distribution changes from individual generation to a structure connected in a mesh shape as the size changes.

(3) Preparation of dye-sensitized film electrode A Ru complex dye having optical absorption at a wavelength of 400 to 800 nm was dissolved in a mixed solvent of acetonitrile: t-butanol (1: 1) at a concentration of 3 × 10 ⁻⁴ mol / liter. The porous semiconductor film electrode substrate was immersed in the dye solution and allowed to stand at 40 ° C. for 30 minutes with stirring to complete the dye adsorption, thereby preparing a dye-sensitized ITO-PEN film electrode.

(4) Preparation of counter electrode As a transparent conductive plastic film, polyethylene terephthalate (PET) having a film thickness of 188 μm and a surface resistance of 12 Ω / □ supporting ITO as a conductive film was used. In order to reduce the surface resistance of the conductive film, a silver dispersion paste is applied to form an ITO film-like auxiliary lead wire for collecting current with a line width of 200 μm and a thickness of 20 μm in parallel lines with a gap of 4 mm. Patterned. On these silver patterns, a polyester resin was applied as a protective film with a width of 200 μm to completely protect the silver wire. The resulting patterned conductive ITO-PET film had an aperture ratio of 95% and a light transmittance including the pattern portion of 76%. The surface resistance of this counter electrode was 0.9Ω / □.

  Further, an opaque counter electrode was also prepared with respect to the transparent counter electrode. A platinum thin film having a thickness of 90 nm was supported on the ITO-PET film by vacuum low-temperature sputtering. The counter electrode was opaque and the surface resistance was 0.5Ω / □.

(5) Preparation of separator As a separator film for preventing short circuit, a porous film made of polyethylene nonwoven fabric with a porosity of 60% and a thickness of 10 μm was used. The surface of this film was used with a 13 W low-pressure mercury lamp and an ozone generator. Hydrophilic treatment was performed by UV / ozone treatment.

(6) Production of flexible film type photovoltaic cell The semiconductor layer adsorbed with the dye was scraped off from the ITO-PEN film to form a rectangular light receiving layer having a light receiving area of 40 cm ² (5 cm × 8 cm). A transparent silver patterned ITO-PET film or an opaque platinum-deposited ITO-PET film as a counter electrode is superimposed on this electrode by inserting the above separator film, and the capillary effect is inserted in the gap where the separator film is inserted. The electrolyte was injected at 50 ° C. As an electrolytic solution, a room temperature molten salt having a composition of methyl butyl imidazolium iodide, methyl ethyl imidazolium tetrafluoroborate, tert-butyl pyridine and iodine in a mass ratio of 6: 4: 1: 0.2 was used. An epoxy thermal effect type sealing material was injected into the edge portion of the sandwich type film battery thus produced, and a curing treatment was performed at 110 ° C. for 20 minutes. The film-type photovoltaic cell of the business card size thus assembled has a thickness of 380 μm and a weight of 2.2 g.

(7) Photoelectric conversion characteristics of film-type photovoltaic cell AM1.5 simulated sunlight with an incident light intensity of 100 mW / cm ² is applied to the above-mentioned film-type photovoltaic cell using a solar simulator for a 500 W xenon lamp. Irradiated from the dye-sensitized semiconductor film electrode side. The battery was fixed in close contact with the stage of the thermostat, and the temperature of the element during irradiation was controlled at 30 ° C. Using a current-voltage measuring device (Keutley source meter 2400 type), the DC voltage applied to the device is scanned at a constant speed of 10 mV / second, and the photocurrent output from the device is measured, thereby providing a photocurrent-voltage characteristic. Was measured. Table 1 shows the photocurrent density (Jsc), open circuit electromotive force (Voc), and energy conversion efficiency (η) of the above-described various elements together with the contents of the cell components.

(8) Peeling resistance of semiconductor film by bending of film A fatigue test is performed by mechanically bending the film type photovoltaic cell assembled as described above to a curvature of 0.1 to 0.5 cm ⁻¹ , and after bending, the film type photovoltaic cell The state of peeling of the dye-sensitized porous semiconductor layer was visually determined.

From the results in Table 1, the following is clear.
1) The energy conversion efficiency is remarkably increased by lowering the surface resistance of the conductive film of the dye-sensitized electrode, and a high efficiency of 4% or more can be obtained at 3Ω / □ or less. This effect was derived from an increase in the fill factor (FF) in the photocurrent-voltage characteristics (cell numbers 1 to 5).

2) In a film battery without a separator film, performance does not appear due to a failure such as a short circuit or the efficiency is remarkably reduced (cell numbers 6 to 10). This is a problem peculiar to a film type battery having flexibility. Further, it has been found that the semiconductor layer tends to be peeled off due to bending of the battery.

3) It was found that a battery having no crack network in the semiconductor film had a problem in mechanical stability because the semiconductor film was broken by mechanical bending and peeled off from the film (cell numbers 11 and 12).

4) Even when an electrode having a sufficiently low surface resistance is used, if the solid content other than the semiconductor, inorganic oxide, and pigment in the porous semiconductor film increases, the energy conversion efficiency decreases. In particular, the decrease is remarkable in the system of 1% or more, and the drop in efficiency becomes more remarkable in the system of 3% or more (cell numbers 13 to 16). That is, high battery performance can be obtained by using a porous membrane having high semiconductor purity.

5) When the porosity of the porous semiconductor particle layer decreases, the efficiency decreases, and the peelability due to mechanical bending tends to increase. The latter is due to the fact that the particle layer becomes hard and the flexibility is lowered. The decrease in efficiency is thought to be due to a decrease in the effective surface area of the semiconductor layer due to a decrease in porosity (cell numbers 17 to 20).

6) The above is the result for the opaque battery, but the same tendency was found for the transparent batteries (cell numbers 21 to 28). In the transparent battery, the efficiency decreases monotonously due to the increase in transmittance, but this does not mean a basic decrease in performance, but merely reflects the decrease in light absorption. For the user, the efficiency is reduced, but the advantage is that light transmittance is obtained as an added value.

Instead of the Ru complex dye used in Example 1, a squarylium cyanine derivative (adsorbent absorption peak, 660 nm) as a blue dye, eosin Y (adsorbent absorption peak, 540 nm) as a red dye, and coumarin 343 as a yellow dye. A porous titanium dioxide layer (area 60 cm ² ) formed by the binder-free coating method using the absorption peak of the adsorbent (440 nm) was dye-sensitized.

  At this time, the resin felt impregnated with the dye solution is pressed against the surface of the titanium dioxide layer at 40 ° C. for 10 minutes, so that different colors in three colors of blue, red, and yellow are obtained at different locations in the plane. Dye sensitization was performed to produce a colorful dye sensitized film electrode. This film electrode was assembled into a film-type photovoltaic cell with the same configuration as the cell 5 in Table 1 of Example 1. This colorful photovoltaic cell was also excellent in resistance to peeling due to bending and gave an energy conversion efficiency of 3.1%.

As described above, the film-type photovoltaic cell and the film-type solar cell having the constituent conditions disclosed in the present invention provide high energy conversion efficiency while having an area of 30 cm ² or more, excellent flexibility, and resistance to peeling of the semiconductor film. It was shown to be a highly stable and mechanically stable photovoltaic cell.

  According to the present invention, there is provided a dye-sensitized mechanically flexible film-type photovoltaic cell that is excellent in the efficiency of solar energy conversion, low in cost, excellent in environmental circulation, and has a low environmental load. Thus, it is possible to provide a robot that can drive energy conversion by photosynthesis by an artificial plant imitation system and can be used for education of environmental circulation systems based on environmental sensing and green chemistry.

It is sectional drawing which shows the structure of one example of the film type photovoltaic cell of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoelectrode film support 2 Transparent conductive layer 3 Dye sensitized porous semiconductor layer 4 Ion conductive electrolyte layer 5 Counter electrode conductive layer 6 Separator layer 7 Undercoat layer 8 Counter electrode film support

Claims (15)

In a film-type photovoltaic cell having a structure in which a transparent conductive plastic support carrying a dye-sensitized porous semiconductor particle layer is used as one electrode and a counter electrode is laminated on the support through an ionic conductive electrolyte, the transparent conductive plastic support is provided with a conductive lead for current collection in the plane, which has a surface resistance 3 [Omega] / □ or less, the porous semiconductor particle layer is the color Motozo sense, the binder-free coating method 200 The porous semiconductor particle layer formed at a temperature of ℃ or lower is subjected to one or more of ultraviolet irradiation, ozonolysis treatment, plasma treatment, corona discharge treatment, and heat treatment at 200 ℃ or lower. In the porous semiconductor particle layer formed and sensitized with the dye, the mass of the solid content excluding the semiconductor, the inorganic oxide, and the dye is based on the total mass of the particle layer. With less than%, mechanically flexible film photovoltaic cell porosity is equal to or less than 85% 50%. A transparent conductive plastic support carrying a dye-sensitized porous semiconductor particle layer is used as one electrode, and the counter electrode is short-circuited between the support and the ion conductive electrolyte via the ion conductive electrolyte. In a film type photovoltaic cell having a structure in which a separator layer for prevention is laminated, the transparent conductive plastic support is provided with a conductive lead wire for current collection in the surface and has a surface resistance of 3Ω / □ or less, The porous semiconductor particle layer obtained by forming the dye-sensitized porous semiconductor particle layer at 200 ° C. or less by the binder-free coating method is irradiated with ultraviolet rays, ozone decomposition treatment, plasma treatment, corona discharge treatment, and 200 ° C. In the porous semiconductor particle layer formed by performing any one or two or more of the following heat treatments and sensitizing the dye, Solids mass excluding inorganic oxide and dye, with less than 1% relative to the total weight of the particle layer, mechanically flexible porosity is equal to or less than 85% 50% Film type photovoltaic cell.   The film type photovoltaic cell according to claim 1 or 2, wherein the transparent conductive plastic support has a surface resistance of 1 Ω / □ or less. Film photovoltaic cell according to claim 1, wherein the dye-sensitized porous semiconductor particle layer is a structure having a crack network coupled in a network form on the surface. The film type photovoltaic cell according to any one of claims 2 to 4 , wherein the separator layer is made of a porous resin having a thickness of 80 µm or less. The film type photovoltaic cell according to claim 5, wherein the separator layer is hydrophilized. In the transparent conductive plastic support having thereon a dye-sensitized porous semiconductor particle layer, the area of conductive plastic support to form a the conductive support successive claims 1 to 6 is 30 cm ² or more The film type photovoltaic cell according to any one of the above. The film type photovoltaic cell according to any one of claims 1 to 7 , wherein the porous semiconductor particles are one or more kinds of semiconductors selected from titanium oxide, zinc oxide, tin oxide and a composite thereof. The film type photovoltaic cell according to any one of claims 1 to 8 , wherein the ionic electrolyte is mainly composed of a room temperature molten salt. The film type photovoltaic cell according to claim 9, wherein the room temperature molten salt comprises an alkylimidazolium compound. The counter electrode is a conductive plastic film having a surface resistance of 1Ω / □ or less, and the surface of the counter electrode in contact with the charge transport layer is made of one or more materials selected from carbon materials, conductive polymers, platinum, tin oxide, and zinc oxide. The film type photovoltaic cell according to any one of claims 1 to 10 , which is coated. Transparent conductive plastic support having thereon a dye-sensitized porous semiconductor particle layer, the film-type photovoltaic cell according to any of claims 1 to 11 is a transparent film selected from polyethylene terephthalate and polyethylene naphthalate . 13. The film type photovoltaic cell according to claim 12 , wherein the plastic support constituting the conductive plastic film of the counter electrode is a transparent film selected from polyethylene terephthalate and polyethylene naphthalate. The transparent film type photovoltaic cell according to any one of claims 1 to 13 , wherein the maximum light transmittance in a wavelength range of 400 to 800 nm is 10% or more. The opaque film type photovoltaic cell according to claim 14 , wherein the transmittance of the transparent conductive plastic support is 60% or more at a wavelength of 500 nm.

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