JP2007109500A - Dye-sensitized solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dye-sensitized solar cell using a metal oxide film increasing porosity, achieving high surface area and enhancing electron conductivity by using a vacuum deposition method excellent in productivity, and clean and safe. <P>SOLUTION: The dye-sensitized solar cell is formed by laminating a conductive film layer, a dye molecule adsorbed anatase type titanium oxide layer, an electrolyte or a hole transport material layer, and a counter electrode in order on at least a substrate. The anatase type titanium oxide layer has a columnar structure and intensity ratio of peaks originating in (101) planes and (004) planes of the anatase type observed by X-ray diffraction is in a range of 1:1.5 to 1:3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a dye-sensitized solar cell comprising a conductive film layer on a substrate, an anatase-type titanium oxide layer adsorbed with dye molecules, an electrolyte or hole transport material layer, and a counter electrode.

  In general, single-crystal silicon solar cells, amorphous silicon solar cells, compound semiconductor solar cells, and the like are known as solar cells, but it has been difficult to suppress manufacturing costs and raw material costs, which has hindered the spread of solar cells. Under such circumstances, it is known that a dye-sensitized solar cell using an electrode formed by supporting a dye on the surface of a semiconductor layer has characteristics of low cost and high conversion efficiency (Patent Document 1, Patent) Reference 2).

  A generally known dye-sensitized solar cell is composed of a conductive film layer on a substrate, a metal oxide layer on which a dye molecule is adsorbed, an electrolyte or hole transport material layer, and a counter electrode. The light that enters the cell and reaches the inside of the cell is absorbed by the dye, and the excited dye instantly injects electrons into the adsorbed metal oxide through chemical bonds, and the ionized dye is an electrolyte or hole. Electricity is generated by receiving electrons from the transport material.

  Metal oxides are usually porous and have succeeded in increasing the amount of dye adsorbed by increasing the surface area per unit area, and high power generation efficiency is obtained. The porous metal oxide is usually produced by hydrothermal synthesis of titanium alkoxide or the like to produce a titanium oxide fine particle-dispersed sol of about 10-50 nm, coated on a transparent conductive film, and then baked to produce 10 to 20 μm. It is manufactured with a film thickness of about.

  However, when using a laminate of fine particles as described above, interfacial resistance between the fine particles acts, and the electronic conductivity of the metal oxide tends to be deteriorated. Interfacial resistance must be reduced by refiring, which has problems with safety, productivity, and economy.

In order to solve this problem, a method for producing titanium oxide having a columnar structure by using a CVD method, a vacuum deposition method or a sol-gel method has been provided in recent years, which is a safe, highly productive and economical method. It is expected to obtain a large surface area and at the same time improve the electron conductivity (see Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3).
Japanese Patent No. 2664194 Japanese Patent No. 2101079 Chemical Vapor Deposition 1998, Vol. 4, no. 3, p. 109 Chemistry of Materials 1998, Vol. 10, p. 2419 Solar Energy Materials & Solar Cells 2005, Vol. 85, p. 321

  However, the titanium oxide having a columnar structure that has been used so far has a small crystallite diameter constituting a polycrystal, so that the crystal planes are disordered so that electron conduction is hindered and sufficient conductivity is achieved. Sex was not obtained.

  Therefore, the present invention is excellent in productivity, and by using a clean and safe vacuum film formation method, the dye sensitization using a metal oxide film that achieves high porosity, high surface area, and high electron conductivity is achieved. Provide solar cells.

  The invention according to claim 1 is a dye-sensitized solar cell in which a conductive film layer, an anatase-type titanium oxide layer adsorbed with a dye molecule, an electrolyte or hole transport material layer, and a counter electrode are sequentially laminated on at least a substrate. The anatase type titanium oxide layer has a columnar structure, and the intensity ratio of peaks derived from the anatase type (101) plane and (004) plane observed by X-ray diffraction is 1: 1.5 to 1: It is a dye-sensitized solar cell characterized by being between 3.

  A second aspect of the present invention is the dye-sensitized solar cell according to the first aspect, wherein the anatase-type titanium oxide has a pore diameter peak between 10 and 100%.

The invention according to claim 3 is the dye-sensitized solar cell according to any one of claims 1 and 2, wherein the density of the anatase-type titanium oxide is 0.5 to 3.0 g / cm ^3. .

  The invention according to claim 4 is characterized in that the crystallite diameter of the (101) plane and the (004) plane of the anatase-type titanium oxide is 13 to 40 nm. It is a solar cell.

  In the present invention, since titanium oxide is columnarized using a reactive vapor deposition method, productivity, economy, and safety are high, and high electronic conductivity is achieved. In a dye-sensitized solar cell having such a titanium oxide layer, high photoelectric conversion efficiency can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 shows an example of a cross-sectional structure of the dye-sensitized solar cell of the present invention. FIG. 2 shows an example of the X-ray diffraction spectrum of the metal oxide film in the dye-sensitized solar cell of the present invention. FIG. 3 shows an example of the pore size distribution of the metal oxide film in the dye-sensitized solar cell of the present invention.

  Examples of the base material 1 that can be used in the present invention include polymethyl methacrylate, polycarbonate, polystyrene, polyethylene sulfide, polyethersulfone, polyolefin, polyethylene terephthalate, polyethylene naphthalate, triacetylcellulose, polyimide and other plastic films, or glass. Can be used.

  Light may enter from either the top or bottom of the dye-sensitized solar cell 10 shown in FIG. 1, and at least the base material 1 on the incident light side needs to be transparent. The materials are not limited to those listed above. Such a substrate may have a surface modified by corona treatment, plasma treatment, chemical treatment, or the like, if necessary.

  As the transparent conductive layer 2 in the present invention, indium oxide (ITO) doped with tin, tin oxide doped with fluorine, indium, etc., zinc oxide doped with aluminum, gallium, etc., and other visible light region absorption A transparent conductor having a small amount and high conductivity is preferable.

  The transparent conductive layer 2 can be formed by vacuum deposition processes such as vacuum deposition, reactive deposition, ion beam assisted deposition, sputtering, ion plating, plasma CVD, etc. A film forming method may be used.

  As long as at least one of the upper and lower transparent conductive layers 2 is transparent, an opaque conductor may be used for the remaining one.

  As the metal oxide layer 3 in the present invention, when an anatase-type titanium oxide polycrystal is used and the X-ray diffraction spectrum of the titanium oxide thin film is observed, the peak intensity ratio between the (101) plane and the (004) plane of the anatase phase is It is characterized by being between 1: 1.5 and 1: 3. When Cu-Kα1 is used for the measurement X-ray, the peak of the (101) plane is observed around 2θ = 2.25 °, and the (004) plane is observed around 2θ = 37.80 °. When the peak intensity ratio falls within this range, the crystal planes are arranged in order, so that good electron conduction characteristics can be obtained, and sufficient conductivity can be obtained.

The formation method of the metal oxide layer 3 is as follows. The metal oxide film is formed by a reactive vapor deposition method using metal titanium or titanium oxide as a vapor deposition source and evaporating the vapor deposition source by an electron beam or a plasma gun while introducing oxygen gas in a vacuum. The film forming pressure is in the range of 1 × 10 ⁻² Pa to 1 Pa. During film formation, assistance may be performed with a plasma, an ion gun, a radical gun, or the like. The substrate temperature can be arbitrarily selected between −50 ° C. and 600 ° C., but it is more preferably 300 ° C. or lower in order to keep the porosity high. Further, when a flexible base material such as a plastic film is used as the base material, higher productivity can be obtained by forming a film by a roll-to-roll method.

  The metal oxide layer 3 obtained as described above is generally converted to an anatase polycrystalline phase by firing at 300 ° C. to 600 ° C., more preferably 400 ° C. to 500 ° C. The firing is performed in the air, and the obtained metal oxide can be surface-treated by any method such as plasma treatment, corona treatment, UV treatment, chemical treatment, and the like. Further, post-processing can be performed using any means such as pressure treatment using a compressor, laser annealing, or the like.

The crystallite diameters of the (101) plane and (004) plane of the metal oxide layer 3 are obtained from the Scherrer equation from the X-ray diffraction spectrum, and are preferably 13 to 40 nm. The Scherrer equation is expressed as D = 0.9λ / βcos θ using the peak position 2θ [°] and the peak half-value width β [radian]. At this time, the crystallite diameter is D [Å], and the measured X-ray wavelength is λ [Å]. Cu-Kα1 is used for the measurement X-ray, and the X-ray wavelength at this time is 1.54056Å. Here, when the crystallite diameter is larger than the conventional 5 to 12 nm, the electron conductivity in the metal oxide layer is increased, and the photoelectric conversion efficiency is improved.

The width, column interval, film thickness and specific surface area of the columnar body of the metal oxide layer having a columnar structure used in the present invention can be arbitrarily selected, but carrier conductivity, light transmission, light scattering, electrolyte In view of the optimization of the interface area, the columnar body width is preferably 20 nm to 10 μm, the interval is 10 μm or less, the specific surface area is 10 m ² / g to 100 m ² / g, and the film thickness is more preferably 15 μm or less.

  In the present invention, particularly when the pore size distribution of the metal oxide layer is measured, the peak of the pore size is preferably between 10 and 100%, more preferably between 20 and 80%. The pore size distribution was measured by measuring the adsorption isotherm curve using nitrogen gas at a liquid nitrogen temperature of -196 ° C., and using the pore size distribution obtained using the BJH method from the obtained adsorption isotherm curve. The pore diameter peak in the present invention is the highest peak in the pore diameter distribution obtained by the BJH method. For example, in the pore diameter distribution graph shown in FIG. The surface area can be optimized by optimizing the pore diameter peak.

Furthermore, in this invention, it is preferable that the density of a metal oxide layer is 0.5-3.0 g / cm < ³ >. This value is due to the optimization of the surface area. The density of the metal oxide layer in the present invention can be obtained by measuring the volume and weight of the laminated metal oxide.

  The metal oxide layer 3 may be formed obliquely with respect to the normal line of the substrate. Further, the metal oxide layer may be discontinuous on the transparent conductive layer 2 as shown in FIG. 4, but when used as a dye-sensitized solar cell, it is continuously formed as shown in FIG. This is more preferable because the contact between the transparent conductive layer 2 and the electrolyte can be avoided.

  Examples of the dye 4 in the present invention include ruthenium and osmium trispyridine-based and bispyridine-based transition metal complexes, or organic dyes such as phthalocyanine, porphyrin, cyanidin dye, coumarin dye, merocyanine dye, and rhodamine dye. These dyes preferably have a large extinction coefficient and are stable against repeated redox. The dye is preferably chemically adsorbed on the metal oxide semiconductor and has a functional group such as a carboxyl group, a sulfonic acid group, a phosphoric acid group, an amide group, an amino group, a carbonyl group, or a phosphine group. preferable.

  Any method can be used to adsorb the dye 4 to the titanium oxide. After adjusting the dye to an appropriate concentration by dissolving it in an appropriate solvent, the polycrystallized titanium oxide is immersed in the dye solution. Is generally used. Since the amount of adsorbed dye greatly affects the performance of the dye-sensitized solar cell, it is necessary to select an optimal adsorption method by adjusting the concentration, solvent, immersion time, temperature and the like.

  As the electrolyte or hole transporting material layer 5 in the present invention, iodide, bromide, quinone complex, TCNQ complex, dicyanoquinone diimine complex, etc. containing iodine with respect to a polar solvent such as acetonitrile or propylene carbonate as a solvent. A solution containing a redox system in which is dissolved can be used. In order to avoid the possibility of liquid leakage, it is more preferable to use a solid charge transport layer containing a gel electrolyte and a p-type semiconductor.

  Specific examples of materials that can be used for the solid charge transport layer include aromatic amine compounds such as triphenylamine, diphenylamine, and phenylenediamine, condensed polycyclic hydrocarbons such as naphthalene and anthracene, azo compounds such as azobenzene, and stilbene. Compounds having a structure in which aromatic rings such as ethylene bonds or acetylene bonds are connected, heteroaromatic compounds substituted with amino groups, porphyrins, phthalocyanines, quinones, tetracyanoquinodimethanes, dicyanoquinone diimines , Tetracyanoethylene, viologens, dithiol metal complexes and the like. Other materials that can be used for the solid charge transport layer include CuI, AgI, TiI, and other metal iodides, CuBr, CuSCN, polypyrrole, polythiophene, polyaniline, and PEDOT / PSS. Further, an iodide, a quinone complex, or the like may be included in a polymer gel such as polyalkylene ether. These materials can be used in any combination as required.

  As a method for forming the electrolyte or hole transport material layer 5 in the present invention, microgravure coating, dip coating, screen coating, spin coating, or the like can be used. In the case of using a solid electrolyte or p-type semiconductor, after forming a solution using an arbitrary solvent, coating is performed using the above method, and the substrate is heated to an arbitrary temperature to evaporate the solvent. .

  As the conductive catalyst layer 6 in the present invention, any conductive material can be used, and examples thereof include metals such as platinum, gold, silver, and copper, or carbon. In forming these, a vacuum film forming method similar to that of the transparent conductive layer 2 or a method of wet coating a paste made of fine particles of these materials can be used.

  Hereinafter, the present invention will be specifically described based on examples.

The dye-sensitized solar cell 10 having the layer configuration of FIG. 1 was produced as follows. Glass (Corning 7059, 1.0 mm thickness) was used as the substrate 1, and indium tin oxide (ITO) was formed thereon as the transparent conductive layer 2 by vacuum sputtering. On the obtained transparent conductive base material, 9 μm of titanium oxide was formed as the metal oxide layer 3 by a reactive vacuum deposition method in which oxygen gas was introduced. The film formation pressure at this time was 2.5 × 10 ⁻¹ Pa. Furthermore, the obtained laminate was baked at 450 ° C. for 30 minutes in the air using an electric furnace. When the cross-sectional image of the obtained laminated body was observed by SEM, the titanium oxide layer had a columnar structure. When the X-ray diffraction spectrum of the obtained laminate was measured, a spectrum showing anatase-type TiO ₂ polycrystal was observed, and the peak showing the (101) plane showed (004) plane at 2θ = 25.24 °. A peak was observed at 2θ = 37.79 °, and the peak intensity ratio was 1: 2.1. The half widths of the peaks indicating the (101) plane and the (004) plane were 0.431 ° and 0.641 °, respectively, and the crystallite diameters were 18.9 nm and 13.1 nm, respectively, according to the Scherrer equation. When 30 sheets of the obtained laminate were cut into strips having a width of 5 mm were used, and the adsorption isotherm of nitrogen gas at the liquid nitrogen temperature was measured, the pore diameter peak was 55.6 mm. The density was 2.19 g / cm ³ . The obtained laminate was immersed in a 2.5 × 10 ⁻⁴ M ethanol solution of bis (4,4′-dicarboxy-2,2′-bipyridyl) dithiocyanate ruthenium (dye 4) to obtain the dye. After being supported on the metal oxide layer 3, ethanol washing and drying were performed. The following operations were performed under a dry argon atmosphere. An electrolyte made of 0.4 M TPAI (tetrapropylammonium iodide), 0.05 M I ₂ , 0.05 M tert-butylpyridine, 3-methoxypropionitrile was prepared as the electrolyte layer 5, and the metal oxide layer 3 was It was dripped. Further, a laminate composed of the base material 1 and the transparent conductive layer 2 formed in the same manner as described above is prepared as a counter electrode, and platinum formed by vapor deposition is formed thereon as the conductive catalyst layer 6 so as to oppose the laminate. After preparing an electrode and fixing the conductive catalyst layer 6 and the electrolyte layer 5 so as to overlap each other, a side surface was sealed with a UV curable acrylic resin to prepare a dye-sensitized solar cell.

The current-voltage characteristics of the dye-sensitized solar cell obtained above were measured. M.M. When using pseudo sunlight of 1.5, 100 mW / cm ² , the short-circuit current J _SC = 17 mA / cm ² , the open circuit voltage V _OC = 0.80 V, the fill factor FF = 0.71, and the photoelectric conversion efficiency is η = It was 9.7%.

It is sectional drawing which shows an example of the dye-sensitized solar cell in this invention. It is a spectrum figure which shows an example of the X-ray-diffraction spectrum of the titanium oxide layer in this invention. It is a graph which shows an example of the hole diameter distribution of the titanium oxide layer in this invention. It is sectional drawing which shows an example of the columnar structure titanium oxide layer in this invention. It is sectional drawing which shows an example of the columnar structure titanium oxide layer in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base material 2 Transparent conductive layer 3 Metal oxide layer 4 Dye 5 Electrolyte or hole transport material layer

Claims (4)

  In the dye-sensitized solar cell in which a conductive film layer, an anatase-type titanium oxide layer on which a dye molecule is adsorbed, an electrolyte or hole transport material layer, and a counter electrode are sequentially laminated on at least a substrate, the anatase-type titanium oxide layer Has a columnar structure, and the intensity ratio of peaks derived from the (101) plane and (004) plane of anatase type observed by X-ray diffraction is between 1: 1.5 and 1: 3. Dye-sensitized solar cell characterized.   2. The dye-sensitized solar cell according to claim 1, wherein the pore diameter of the anatase-type titanium oxide is between 10 and 100%. ^3. The dye-sensitized solar cell according to claim 1, wherein the anatase-type titanium oxide has a density of 0.5 to 3.0 g / cm ³ .   4. The dye-sensitized solar cell according to claim 1, wherein a crystallite diameter of the (101) plane and the (004) plane of the anatase-type titanium oxide is within a range of 13 to 40 nm.

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