JP4423735B2 - Photoelectric conversion element - Google Patents

Description

【００７１】
実施例１と比較例１の色素増感半導体層の膜厚はほぼ同じであるにもかかわらず、色素担持量は実施例１の方が２．６倍多い。すなわち、酸化チタン粒子内部に細孔があるため、増感色素の担持量が多くなったことを示し、その結果、短絡光電流も色素担持量の増大に応じた増加を示した。
【００７２】
実施例２
脱水エタノールに１０wt％のＰｌｕｒｏｎｉｃ Ｐ−１２３（ＢＡＳＦ社製）を溶解させた。次に、四塩化チタン０．０１ｍｏｌをこの脱水エタノール溶液に添加し、激しく１時間攪拌し、酸化チタンのゾル溶液を調製した。この酸化チタンのゾル溶液５０ｍｌに厚さ１ｍｍの導電性ガラス基板（Ｆ−ＳｎＯ₂，１０Ω／ｓｑ，旭硝子製）を浸漬後、５ｍｍ／ｍｉｎの速さで導電ガラスを引き上げた。続いて、４０℃に設定したオーブンに入れて、脱水エタノールを飛ばした後、４５０℃で３０分間焼成した。この浸漬−焼成を繰り返して得られた酸化チタンの膜厚は２．３μｍであった。得られた酸化チタン薄膜の表面をＳＥＭで観察した結果、粒径が約１５ｎｍの酸化チタン粒子からなることを確認した。また、Ｘ線回折の結果から得られた酸化チタンはアナターゼ型であり、さらに、ＴＥＭ観察と窒素ガスの吸着-脱離等温曲線から酸化チタン粒子の内部に６ｎｍの細孔が生成されていることを確認した。
【００７３】
上記の多孔質酸化チタン薄膜が堆積した導電ガラスを［Ru(4,4'-ジカルボキシル-2,2'-ビピリジン)₂(NCS)₂］で表される増感色素溶液中に浸漬し８０℃で還流を行いながら色素吸着処理を行った。このようにして得た半導体電極を実施例１と同様な方法で光電変換素子を組み立てた。前記と同様な方法で半導体電極に担持された増感色素の担持量、および組み立てた光電変換素子の光短絡電流を測定した。半導体電極に担持された増感色素の担持量は０．０３８μｍｏｌ／ｃｍ²、光電変換素子の光短絡電流は６．４ｍＡ／ｃｍ²であった。
【００７４】
実施例３
脱水エタノールに１０wt％のＰｌｕｒｏｎｉｃ Ｐ−１２３（ＢＡＳＦ社製）を溶解させた。次に、チタンテトライソプロポキシド０．０５ｍｏｌをこの脱水エタノール溶液に添加し、激しく１時間攪拌し、酸化チタンのゾル溶液を調製した。実施例２と同様に、この酸化チタンのゾル溶液５０ｍｌに厚さ１ｍｍの導電性ガラス基板（Ｆ−ＳｎＯ₂，１０Ω／ｓｑ，旭硝子製）を浸漬後、５ｍｍ／ｍｉｎの速さで導電ガラスを引き上げた。続いて、８０℃に設定したオーブンに入れて、１時間放置後、４５０℃で３０分間焼成した。この浸漬−焼成を繰り返して得られた酸化チタンの膜厚は１．６μｍであった。得られた酸化チタン薄膜の表面をＳＥＭで観察した結果、粒径が約２０ｎｍの酸化チタン粒子からなることを確認した。また、Ｘ線回折の結果から得られた酸化チタンはアナターゼ型であり、さらに、ＴＥＭ観察と窒素ガスの吸着-脱離等温曲線から酸化チタン粒子の内部に８ｎｍの細孔が生成されていることを確認した。
【００７５】
上記の多孔質酸化チタン薄膜が堆積した導電ガラスを［Ru(4,4'-ジカルボキシル-2,2'-ビピリジン)₂(NCS)₂］で表される増感色素溶液中に浸漬し８０℃で還流を行いながら色素吸着処理を行った。このようにして得た半導体電極を実施例１と同様な方法で光電変換素子を組み立てた。前記と同様な方法で半導体電極に担持された増感色素の担持量、および組み立てた光電変換素子の光短絡電流を測定した。半導体電極に担持された増感色素の担持量は０．０２５μｍｏｌ／ｃｍ²、光電変換素子の光短絡電流は５．３ｍＡ／ｃｍ²であった。
【００７６】
【発明の効果】
以上説明したように、本発明によれば、半導体粒子内部に細孔を生成し、半導体粒子の外表面だけでなく、粒子の細孔内部にも増感色素を担持させることにより、色素増感半導体層全体の増感色素担持量が増大され、その結果、非常に高い光電流出力を示す光電変換素子を得ることができる。
【図面の簡単な説明】
【図１】本発明の光電変換素子の一例の概要断面図である。
【図２】図１に示された光電変換素子の部分拡大概要断面図である。
【符号の説明】
１ 本発明の光電変換素子
３，１１ 基板
５ 電極
７ 色素増感半導体層
９ 対電極
１３ 電解質層
１５ 半導体粒子
１７ 増感色素
１９ 細孔[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photoelectric conversion element. More specifically, the present invention relates to a photoelectric conversion element capable of realizing a high photocurrent output by increasing the amount of sensitizing dye supported.
[0002]
[Prior art]
Solar cells are highly expected as clean energy sources, and pn junction solar cells have already been put into practical use. On the other hand, photochemical cells that take out electrical energy by utilizing a chemical reaction in a photoexcited state have been developed by many researchers. However, when it comes to practical use, it is far more than the already proven pn junction solar cells. There wasn't.
[0003]
Among conventional photochemical cells, a type utilizing a redox reaction comprising a sensitizer and an electron acceptor is known. For example, there is a system in which a thionine dye and iron (II) ion are combined. In addition, since the discovery of the Honda-Fujishima effect, photochemical cells utilizing photocharge separation of metals and their oxides are also known.
[0004]
When the semiconductor is in contact with a metal, Schottky bonding can be performed depending on the work function of the metal and the semiconductor, but similar bonding can also be performed when the semiconductor and the solution are in contact. For example, Fe in solution²⁺/ Fe³⁺, Fe (CN)₆ ^Four-/ Fe (CN)₆ ^3-, I^-/ I₂, Br^-/ Br²When a redox system such as hydroquinone / quinone is included, when an n-type semiconductor is immersed in a solution, electrons near the surface of the semiconductor move to the oxidizing agent in the solution and reach an equilibrium state. As a result, the vicinity of the semiconductor surface is positively charged and a potential gradient is generated. As a result, a gradient also occurs in the conduction band and valence band of the semiconductor.
[0005]
When the surface of the semiconductor electrode immersed in the redox solution is irradiated with light, light having energy higher than the band gap of the semiconductor is absorbed, generating electrons in the conduction band and holes in the valence band near the surface. Electrons excited in the conduction band are transferred to the inside of the semiconductor by the above-described potential gradient existing near the surface of the semiconductor, while holes generated in the valence band take electrons from the reductant in the redox solution.
[0006]
When a metal electrode is immersed in an oxidation-reduction solution to form a circuit between the metal electrode and the semiconductor, the reductant from which electrons have been taken by holes diffuses in the solution, receives electrons from the metal electrode, and is reduced again. By repeating this cycle, the semiconductor electrode functions as a negative electrode and the metal electrode functions as a positive electrode, respectively, and power can be supplied to the outside. Therefore, the photovoltaic power is the difference between the redox level of the redox solution and the Fermi level in the semiconductor.
[0007]
In order to increase the photovoltaic power, (1) use a redox solution having a low redox level, that is, a strong oxidizing power, and (2) between the redox level and the Fermi level in the semiconductor. It is possible to create a large difference, that is, to use a semiconductor with a large band gap.
[0008]
However, if the oxidizing power of the redox solution is too great, an oxide film is formed on the surface of the semiconductor itself, and the photocurrent stops within a short time. As for the band gap, a semiconductor having a band gap of 3.0 eV or less, further 2.0 eV or less generally has a problem of being easily dissolved in a solution due to a current flowing during photoelectric conversion. For example, n-Si forms an inactive oxide film on the surface by light irradiation in water, and n-GaAs and n-CdS dissolve oxidatively.
[0009]
In order to solve these problems, attempts have been made to cover a semiconductor with a protective film, and p-type conductive polymers such as polypyrrole, polyaniline, and polythiophene having hole transport properties are used for the semiconductor protective film. Ingenuity has been proposed. However, there was a problem with durability, and it was stable only for a few days at most.
[0010]
In order to solve the problem of photodissolution, use of a semiconductor having a band gap of 3 eV or more can be considered, but it is too large to efficiently absorb sunlight having an intensity peak in the vicinity of 2.5 eV. Therefore, only the ultraviolet part of sunlight can be absorbed, the visible region occupying the majority is not absorbed at all, and the photoelectric conversion efficiency becomes extremely low.
[0011]
In order to achieve both effective use of the visible light region and light stability of semiconductors with a large band gap, a dye-sensitized solar in which a sensitizing dye that absorbs visible light on the longer wavelength side, which is smaller than the semiconductor band gap, is supported on the semiconductor. Batteries are known. The difference from a conventional wet solar cell using a semiconductor is a photocharge separation process in which electrons are excited by irradiating light to the dye and the excited electrons move from the dye to the semiconductor.
[0012]
Dye-sensitized solar cells are often viewed in connection with photosynthesis. At first, chlorophyll was considered as a pigment as in the case of photosynthesis, but unlike natural chlorophyll, which is constantly replaced with new chlorophyll, there is a problem in terms of stability with pigments used in solar cells. The photoelectric conversion efficiency was less than 0.5%. It is very difficult to construct a solar cell by simulating the process of natural photosynthesis as it is.
[0013]
In this way, dye-sensitized solar cells are designed to absorb long-wavelength visible light based on hints from photosynthesis. However, since the electron conduction mechanism is actually complicated, the increase in loss is a problem. It became. In a solid solar cell, the absorption efficiency can be increased by increasing the thickness of the light absorbing layer. However, for dye-sensitized solar cells, only the monolayer on the surface can inject electrons into the semiconductor electrode. Therefore, it is desirable that the dye on the semiconductor surface be a monomolecular layer in order to eliminate useless light absorption.
[0014]
Moreover, in order for the electrons in the excited dye to be efficiently injected into the semiconductor, it is preferably chemically bonded to the semiconductor surface. For example, regarding titanium oxide, it is important that the dye has a carboxyl group in order to chemically bond to the semiconductor surface.
[0015]
In this regard, the Fujihira group has made significant improvements. They say that the carboxyl group of Rhodamine B is SnO₂It was reported in the journal Nature in 1977 that the photocurrent has become more than 10 times that of the conventional adsorption method due to ester bonding with hydroxyl groups on the surface. This is due to the fact that the ester bond is closer to the surface of the semiconductor than the conventional amide bond, in which the π orbit where the electrons that absorbed the energy of light in the dye exist.
[0016]
However, even if electrons can be effectively injected into the semiconductor, electrons in the conduction band may recombine with the ground level of the dye or may recombine with the redox material. Because of such problems, the photoelectric conversion efficiency remained low despite the above-described improvements in electron injection.
[0017]
As described above, a major problem with conventional dye-sensitized solar cells is that only sensitizing dyes supported on a semiconductor surface as a single layer can inject electrons into the semiconductor. That is, single crystals and polycrystalline semiconductors that have been often used for semiconductor electrodes until now have a smooth surface and no pores inside, and the effective area on which the sensitizing dye is carried is equal to the electrode area. Is less loaded.
[0018]
Therefore, when such an electrode is used, the monomolecular sensitizing dye supported on the electrode can absorb only 1% or less of the incident light even at the maximum absorption wavelength, and the light utilization efficiency becomes extremely poor. Attempts have been made to make the sensitizing dye multilayer in order to increase the light collecting ability, but generally a sufficient effect has not been obtained.
[0019]
Gretzell et al., As a means for solving such problems, made the titanium oxide electrode porous, loaded a sensitizing dye, and significantly increased the internal area (for example, Japanese Patent No. 2664196). This titanium oxide porous film is produced by the sol-gel method, and the porosity of the film is about 50%, and a nanoporous structure having a very high internal surface area is formed. For example, at a film thickness of 8 μm, the roughness factor (ratio of the actual area inside the porous to the substrate area) reaches about 720. When this surface is calculated geometrically, the concentration of the sensitizing dye is 1.2 × 10^-7mol / cm²In fact, about 98% of the incident light is absorbed at the maximum absorption wavelength.
[0020]
This new dye-sensitized solar cell, also called the Gretzel cell, has a dramatic increase in the amount of sensitizing dye supported by the porous titanium oxide mentioned above, and absorbs sunlight efficiently and the rate of electron injection into the semiconductor. The development of a sensitizing dye that is significantly faster is a major feature.
[0021]
Have developed a bis (bipyridyl) Ru (II) complex for dye-sensitized solar cells. The Ru complex has the structure of the general formula cis-X2 bis (2,2'-bipyridyl-4,4'-dicarboxylate) Ru (II). X is Cl-, CN-, SCN-. These have been systematically studied for fluorescence, visible light absorption, electrochemical and photoredox behavior. Among these, cis- (diisocyanate) -bis (2,2′-bipyridyl-4,4′-dicarboxylate) Ru (II) has remarkably superior performance as a solar absorber and a dye sensitizer. It was shown to have.
[0022]
The visible light absorption of this dye sensitizer is a charge transfer transition from metal to ligand. In addition, the carboxyl group of the ligand is directly coordinated to the Ti ion on the surface, forming an intimate electronic contact between the dye sensitizer and titanium oxide. Due to this electronic contact, electron injection from the dye sensitizer into the conduction band of titanium oxide occurs at a very fast rate of 1 picosecond or less, and the conduction band of titanium oxide by the oxidized dye sensitizer in the opposite direction. The recapture of electrons injected into the nuclei is said to occur on the order of microseconds. This speed difference creates the directionality of photoexcited electrons, which is why charge separation is performed with extremely high efficiency. This is a difference from a pn junction solar cell that performs charge separation by the potential gradient of the pn junction surface, and is an essential feature of the Gretzel cell.
[0023]
The structure of the Gretzel cell is a sandwich type cell in which an electrolyte solution containing a redox pair is enclosed between two conductive glass substrates coated with a fluorine-doped tin oxide transparent conductive film. One of the glass substrates is obtained by laminating a porous film composed of colloidal titanium oxide ultrafine particles on a transparent conductive film, and further adsorbing a sensitizing dye to form a working electrode. The other is a counter electrode obtained by coating a small amount of platinum on a transparent conductive film. A spacer is sandwiched between two glass substrates, and an electrolyte solution is injected into a very small gap between them using a capillary phenomenon. The electrolyte solution uses a mixed solvent of ethylene carbonate and acetonitrile and solutes tetra-n-propylammonium iodide and iodine.^-/ I^3-The redox couple of The platinum coated on the counter electrode is the redox pair I^3-I^-Has a catalytic action of cathodic reduction.
[0024]
The principle of operation of a grettzel cell is basically the same as a wet solar cell using a conventional semiconductor. However, the reason why the photocharge separation response is uniformly and efficiently performed in any part of the porous electrode such as a Gretzel cell is mainly because the electrolyte layer is liquid. That is, simply immersing the dye-carrying porous electrode in the solution allows the solution to uniformly diffuse into the porous and form an ideal electrochemical interface.
[0025]
However, the fact that the hole transport layer is a liquid layer is not preferable from the viewpoint of the stability of the solar cell. In fact, in many cases, leakage of the electrolyte solution causes deterioration of other battery components even when the battery is manufactured. It is known to occur in advance and reduce the performance of the solar cell. In order to put the Gretzel cell into practical use, it is necessary to make a detailed study of each element constituting the Gretzel cell, as exemplified by the electrolyte.
[0026]
A major feature of the Gretzel cell is that it uses ultrafine titanium oxide to increase the surface area in order to dramatically increase the amount of sensitizing dye supported. Therefore, if the surface area of titanium oxide is made larger, it is naturally expected that the amount of sensitizing dye carried increases and the resulting photocurrent becomes larger. In the past, in order to increase the surface area, the surface of the titanium oxide thin film was roughened (for example, see JP-A-10-112337), or a polymer was added to the titanium oxide thin film to create pores. (See Miki et al., Solar / Wind Energy Lectures 1998, 147-150).
[0027]
However, since the former method employs a method of anodizing titanium metal, the titanium oxide thin film is not porous, and as a result, the photocurrent is smaller than a thin film made of ultrafine titanium oxide. In addition, the latter method has a feature that the pores can be controlled, but the pore diameter is too large, leading to a decrease in the amount of dye supported. Thus, in the prior art, nothing superior to a thin film using titanium oxide ultrafine particles has been invented.
[0028]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a photoelectric conversion element capable of increasing the amount of a sensitizing dye carried by disposing a semiconductor layer having a large surface area and, as a result, obtaining a large photocurrent output.
[0029]
[Means for Solving the Problems]
  The subject is disposed at least between an electrode having a semiconductor layer deposited on one surface, a counter electrode facing the semiconductor layer of the electrode, and the semiconductor layer and the counter electrode of the electrode. In the photoelectric conversion element having an electrolyte layer, the semiconductor particles forming the semiconductor layer have pores, and the semiconductor particles carry a sensitizing dye on the outer surface and in the pores. Particle size is 10nm ~30In addition, the inner diameter of the pores is in the range of 3 nm to 10 nm, and the loading of the sensitizing dye on the semiconductor particles is 10^-8-10^-6mol / cm²It is solved by the photoelectric conversion element which is the range.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
As a means for increasing the surface area of titanium oxide, it is conceivable to reduce the primary particle diameter of titanium oxide of ultrafine particles. The inventors of the present invention made a porous titanium oxide thin film using ultrafine titanium oxide having a small primary particle size and measured the amount of the dye supported. Although it increased, it was found that the photocurrent obtained hardly increased or decreased compared with the increase. Furthermore, the cause of this is that the porous membrane using ultrafine titanium oxide with a small primary particle diameter has an increased surface area compared with that with a large primary particle diameter, but the pore diameter in the porous film has decreased. I found out. That is, if the pore diameter in the porous membrane is reduced, it becomes difficult to transfer the redox material in the electrolyte solution.
[0031]
Therefore, the present inventors have proposed a porous oxidation that increases the photocurrent as the amount of dye supported increases, if the surface area can be increased without reducing the pore size in the porous membrane. As a result of continual research, thinking that a titanium thin film could be produced, conventional porous titanium oxide was produced by producing a porous thin film consisting of titanium oxide particles of appropriate primary particle diameter with pores inside. It was discovered that the amount of dye supported was larger than that of the thin film, and a photocurrent corresponding to the amount of dye supported was obtained, and the present invention was completed.
[0032]
The difference between the photoelectric conversion element of the present invention and the Gretzel cell is that the semiconductor particles forming the semiconductor layer in the photoelectric conversion element of the present invention have pores therein and carry a sensitizing dye in the pores. Is what you can do. The Gretzel cell is obtained by making a semiconductor film porous only with semiconductor particles, and the semiconductor particles themselves do not have pores inside and remain solid. Therefore, the amount of the sensitizing dye supported by the photoelectric conversion element of the present invention is significantly larger than the amount of the sensitizing dye supported by the conventional Gretzel cell. For this reason, the photocurrent output of the photoelectric conversion element of the present invention is much higher than the photocurrent output of the conventional Gretzel cell.
[0033]
Hereinafter, an example of the photoelectric conversion element of the present invention will be specifically described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an example of the photoelectric conversion element of the present invention. As shown in the drawing, the photoelectric conversion element 1 of the present invention has an electrode 5 formed on one surface of a substrate 3. A dye-sensitized semiconductor layer 7 is formed on one surface of the electrode 5. Further, a counter electrode 9 is present opposite to the dye-sensitized semiconductor layer 7. The counter electrode 9 is formed on one surface of another substrate 11. An electrolyte layer 13 exists between the dye-sensitized semiconductor layer 7 and the counter electrode 9.
[0034]
As the substrates 3 and 11, glass or plastic can be used. Since plastic is flexible, it is suitable for applications that require flexibility. Since the board | substrate 3 functions as a light-incidence side board | substrate, it is preferable that it is transparent. On the other hand, the substrate 11 may be transparent or opaque, but it is preferable that the substrate 11 be transparent because light can be incident from the substrates on both sides.
[0035]
The electrode 5 formed on one surface of the substrate 3 is a metal itself, or has a conductive agent layer on glass or plastic. Preferred conductive agents include metals (for example, platinum, gold, silver, copper, aluminum, rhodium, indium, etc.), carbon, or conductive metal oxides (indium-tin composite oxide, fluorine-doped tin oxide, etc.). Can be mentioned.
[0036]
The electrode 5 is better as the surface resistance is lower. The range of the surface resistance is preferably 50Ω / □ or less, more preferably 30Ω / □ or less. The lower limit is not particularly limited, but is usually 0.1Ω / □.
[0037]
The electrode 5 is better as the light transmittance is higher. A preferable light transmittance is 50% or more, and more preferably 80%. The electrode 5 preferably has a conductive agent layer on glass or plastic. The film thickness of the electrode 5 is preferably 0.1 to 10 μm. When the film thickness of the electrode 5 is less than 0.1 μm, it becomes difficult to form an electrode film having a uniform film thickness. On the other hand, when the film thickness exceeds 10 μm, the light transmittance is lowered, and sufficient light is not incident on the dye-sensitized semiconductor layer 7. When the transparent electrode 5 is used, light is preferably incident from the electrode 5 on the side on which the dye-sensitized semiconductor layer 7 is applied.
[0038]
The counter electrode 9 functions as a positive electrode of the photoelectric conversion element 1 and has the same meaning as the electrode 5 on the side on which the dye-sensitized semiconductor layer 7 is deposited. As the counter electrode 9 of the photoelectric conversion element 1 in the present invention, a material having a catalytic action for giving electrons to a reductant of the electrolyte is preferable in order to efficiently act as the positive electrode of the photoelectric conversion element 1. Examples of such materials include metals (eg, platinum, gold, silver, copper, aluminum, rhodium, indium, etc.), graphite, or conductive metal oxides (indium-tin composite oxide, fluorine-doped tin oxide, etc. ) Etc. Of these, platinum and graphite are particularly preferred. The substrate 11 on the side on which the counter electrode 9 is provided can also have a transparent conductive film (not shown) on the surface to which the counter electrode 9 is attached. For example, the transparent conductive film can be formed from the same material as the electrode 5. In this case, the counter electrode 9 is also preferably transparent.
[0039]
FIG. 2 is a partially enlarged schematic cross-sectional view of the dye-sensitized semiconductor layer 7 deposited on the substrate 3 side of the photoelectric conversion element 1 shown in FIG. As shown in the figure, the dye-sensitized semiconductor layer 7 is composed of semiconductor particles 15 and a sensitizing dye 17 carried on the particles. The sensitizing dye 17 is supported not only on the outer surface of the semiconductor particle 15 but also inside the pores 19 formed in the particle. By carrying the sensitizing dye 17 on the semiconductor particles 15, a photoelectric conversion element having high photoelectric conversion efficiency can be obtained.
[0040]
The film thickness of the dye-sensitized semiconductor layer 7 is preferably in the range of 0.1 μm to 100 μm. When the film thickness of the dye-sensitized semiconductor layer 7 is less than 0.1 μm, a sufficient photoelectric conversion effect may not be obtained. On the other hand, when the film thickness is more than 100 μm, it is not preferable because inconveniences such as remarkable deterioration of the transmittance for visible light and near infrared light occur. A more preferable range of the film thickness of the semiconductor layer 7 is 1 μm to 50 μm, a particularly preferable range is 5 μm to 30 μm, and a most preferable range is 10 μm to 20 μm.
[0041]
  The particle size of the semiconductor particles 15 is 10 nm to30It is in the range of nm. If the particle diameter of the semiconductor particles 15 is smaller than 10 nm, the pore diameter of the dye-sensitized semiconductor layer 7 becomes small, and it becomes difficult to move the redox substance in the electrolyte solution, and the obtained photocurrent is reduced. It is. From this viewpoint, the pore diameter of the dye-sensitized semiconductor layer 7 is preferably 10 nm or more. When the particle diameter of the semiconductor particles 15 is smaller than 10 nm, the pore diameter of the dye-sensitized semiconductor layer 7 is less than 10 nm. . The particle size of the semiconductor particles 15 is30If it is larger than nm, the surface area of the semiconductor layer 7 is not so large, so that a sufficient amount of sensitizing dye cannot be obtained, and as a result, the obtained photocurrent is not as expected.
[0042]
  The inner diameter of the pores 19 formed inside the semiconductor particles 15 is,Within the range of 3 nm to 10 nmRu. When the inner diameter of the pore 19 is smaller than 3 nm, it becomes difficult to carry the sensitizing dye inside the pore. On the other hand, when the inner diameter of the pores 19 is larger than 10 nm, pores of 10 nm or more can be sufficiently formed in the dye-sensitized semiconductor layer 7 even if conventional semiconductor particles without pores are used. The meaning of providing The shape of the pores 19 is indefinite, and there are through-holes and recessed holes. Accordingly, the pores having a shape and an internal volume sufficient to accommodate the sensitizing dye can satisfy the requirements of the present invention.
[0043]
The measurement of the inner diameter of the pores 19 inside the semiconductor particles 15 and the pore diameter of the dye-sensitized semiconductor layer 7 can be obtained from the measurement results of adsorption-desorption isotherm curves of nitrogen gas and krypton gas. For example, the pore diameter can be determined from the pore distribution curve obtained by measurement with ASAP2010 (manufactured by Micromeritics).
[0044]
The semiconductor particles 15 having the pores 19 can be generated using a known method comprising preparing from a sol solution of a semiconductor material to which a poly (alkylene oxide) block copolymer is added. The sol solution of a semiconductor material can hydrolyze a metal salt, hydrolyze a metal alkoxide obtained by reaction of an alcohol with a metal salt or a metal, or hydrolyze a metal salt dissolved in a metal alkoxide. It is prepared by a known method consisting of: For example, titanium alkoxides include tetraisopropyl titanate, tetrabutyl titanate, butyl titanate dimer, tetrakis (2-ethylhexyloxy) titanium, tetrastearyl titanate, triethanolamine titanate, diisopropoxy bis (acetylacetonato) titanium, titanium Examples include ethyl acetoacetate, titanium isopropoxyoctylene glycolate, and titanium lactate.
[0045]
The poly (alkylene oxide) block copolymer added to the sol solution of the semiconductor material is preferably one in which ethylene oxide is added to polypropylene glycol. In particular, ABA type and AB type block copolymers capable of forming pores with three-dimensional regularity are preferable. Examples thereof include Pluronic series manufactured by BASF and New Pole PE series manufactured by Sanyo Chemical Industries.
[0046]
The solvent for the sol solution of the semiconductor material may be any solvent that is compatible with the metal salt or metal alkoxide, and can be used alone or in a mixture without limitation. For example, there are ethanol, 1-propanol, 2-propanol, N-hexane, benzene, toluene, xylene, trichrene, propylene dichloride and the like. In particular, a non-aqueous solvent is preferable in order to suppress a rapid hydrolysis reaction.
[0047]
By baking the semiconductor particles obtained by hydrolyzing the sol solution of the above semiconductor material, the poly (alkylene oxide) block copolymer can be removed to obtain semiconductor particles having pores. The range of the firing temperature is preferably 400 ° C to 600 ° C. If it is lower than 400 ° C., the polymer may not be burned completely. When the temperature is higher than 600 ° C., sintering of the semiconductor particles proceeds, causing a problem that the pores are blocked.
[0048]
The thus-obtained semiconductor particle slurry liquid having the pores thus obtained is applied by a known method (for example, a coating method using a doctor blade or a bar coater, a spray method, a dip coating method, a screen printing method, a spin coating method, etc. ), The porous dye-sensitized semiconductor layer 7 can be formed by applying to the surface of the substrate 3 having the electrode 5 and then heating and sintering at a temperature in the range of 400 ° C. to 600 ° C.
[0049]
Semiconductor materials include Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, Cr oxides, SrTiO_Three, CaTiO_ThreePerovskite such as CdS, ZnS, In₂S_Three, PbS, Mo₂S, WS₂, Sb₂S_Three, Bi₂S_ThreeZnCdS₂, Cu₂S sulfide, CdSe, In₂Se_Three, WSe₂, HgS, PbSe, CdTe metal chalcogenides, other GaAs, Si, Se, Cd₂P_Three, Zn₂P_Three, InP, AgBr, PbI₂, HgI₂, BiI_ThreeIs preferred. Alternatively, a composite containing at least one selected from the semiconductors, for example, CdS / TiO₂, CdS / AgI, Ag₂S / AgI, CdS / ZnO, CdS / HgS, CdS / PbS, ZnO / ZnS, ZnO / ZnSe, CdS / HgS, CdS_x/ CdSe_1-x, CdS_x/ Te_1-x, CdSe_x/ Te_1-xZnS / CdSe, ZnSe / CdSe, CdS / ZnS, TiO₂/ Cd_ThreeP₂, CdS / CdSeCd_yZn_1-yS and CdS / HgS / CdS are preferred.
[0050]
As the sensitizing dye 17 to be carried on the semiconductor particles 15, any dye that is commonly used in conventional dye-sensitized photoelectric conversion elements can be used. Such dyes are known to those skilled in the art. Such dyes are, for example, RuL₂(H₂O)₂Ruthenium-cis-diaqua-bipyridyl complexes or ruthenium-tris (RuL_Three), Ruthenium-bis (RuL₂), Osnium-Tris (OsL_Three), Osmium-bis (OsL₂) Type transition metal complex, zinc-tetra (4-carboxyphenyl) porphyrin, iron-hexocyanide complex, phthalocyanine, and the like. Organic dyes include 9-phenylxanthene dyes, coumarin dyes, acridine dyes, triphenylmethane dyes, tetraphenylmethane dyes, quinone dyes, azo dyes, indigo dyes, cyanine dyes, merocyanine dyes Examples thereof include dyes and xanthene dyes. Of these, ruthenium-bis (RuL₂) Derivatives are preferred.
[0051]
As shown in FIG. 2, the method for supporting the sensitizing dye 17 on the semiconductor particles 15 having the pores 19 is, for example, a substrate 3 with an electrode in which a semiconductor particle layer is deposited in a solution in which a sensitizing dye is dissolved. The method of immersing is mentioned. Any solvent can be used as the solvent for the solution as long as it can dissolve the sensitizing dye, such as water, alcohol, toluene, and dimethylformamide. Further, as the dipping method, heating and refluxing or applying ultrasonic waves can be performed when the electrode-attached substrate 3 on which the semiconductor particle layer is applied is dipped in the sensitizing dye solution for a certain period of time. In order to remove the sensitizing dye remaining on the dye-sensitized semiconductor layer 7 without being supported after the dye is supported on the semiconductor particles 15, it may be washed with alcohol or heated to reflux. Further, it is preferable to dissolve t-butylpyridine in alcohol so that there is no portion of the semiconductor particles 15 on which the sensitizing dye 17 is not supported. When t-butylpyridine is present in the alcohol, the semiconductor particle surface and the electrolyte can be separated by the sensitizing dye and t-butylpyridine at the semiconductor particle / electrolyte interface, and the leakage current can be suppressed. The characteristics of the photoelectric conversion element can be remarkably improved.
[0052]
The amount of the sensitizing dye 17 supported on the semiconductor particles 15 is 10^-8-10^-6mol / cm²In the range of 0.1 to 9.0 × 10 in particular.^-7mol / cm²Is preferred. The carrying amount of the sensitizing dye 17 is 10^-8mol / cm²If it is less than 1, the effect of improving the photoelectric conversion efficiency becomes insufficient. On the other hand, the loading amount of the sensitizing dye 17 is 10^-6mol / cm²If it is too high, the effect of improving the photoelectric conversion efficiency is saturated and only uneconomical.
[0053]
The electrolyte used in the electrolyte layer 13 in the photoelectric conversion element 1 of the present invention is not particularly limited as long as a pair of redox constituents composed of an oxidant and a reductant are contained in the solvent. And redox constituents having the same charge in the reductant are preferred. In this specification, the redox-system constituent substance means a pair of substances that are present reversibly in the form of an oxidant and a reductant in an oxidation-reduction reaction. Such redox constituents are known to those skilled in the art. Examples of the redox component that can be used in the present invention include chlorine compound-chlorine, iodine compound-iodine, bromine compound-bromine, thallium ion (III) -thallium ion (I), mercury ion (II) -mercury ion (I ), Ruthenium ion (III) -ruthenium ion (II), copper ion (II) -copper ion (I), iron ion (III) -iron ion (II), vanadium ion (III) -vanadium ion (II), Manganate ion-permanganate ion, ferricyanide-ferrocyanide, quinone-hydroquinone, fumaric acid-succinic acid and the like can be mentioned. Needless to say, other redox constituents can also be used. Among them, iodine compound-iodine is preferable. Examples of the iodine compound include metal iodides such as lithium iodide and potassium iodide, quaternary ammonium iodide compounds such as tetraalkylammonium iodide and pyridinium iodide, and dimethylpropyl iodide. Particularly preferred are diimidazolium iodide compounds such as imidazolium.
[0054]
The solvent used for dissolving the electrolyte is preferably a compound that dissolves the redox constituent and has excellent ion conductivity. As the solvent, any of an aqueous solvent and an organic solvent can be used, but an organic solvent is preferable in order to make the redox constituent material more stable. For example, carbonate compounds such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, ester compounds such as methyl acetate, methyl propionate, gamma-butyrolactone, diethyl ether, 1,2-dimethoxyethane, 1, Ether compounds such as 3-dioxosilane, tetrahydrofuran and 2-methyl-tetrahydrafuran, heterocyclic compounds such as 3-methyl-2-oxazodilinone and 2-methylpyrrolidone, nitrile compounds such as acetonitrile, methoxyacetonitrile and propionitrile, sulfolane And aprotic polar compounds such as didimethyl sulfoxide and dimethylformamide. These can be used alone or in combination of two or more. Of these, carbonate compounds such as ethylene carbonate and propylene carbonate, heterocyclic compounds such as 3-methyl-2-oxazozirinone and 2-methylpyrrolidone, and nitrile compounds such as acetonitrile, methoxyacetonitrile and propionitrile are particularly preferable.
[0055]
As the electrolyte layer 13, any of liquid, solid, or gel electrolyte can be used. In particular, a liquid electrolyte is preferable for improving the photoelectric conversion efficiency. Further, by filling the liquid electrolyte in a porous support (not shown), it is possible to completely prevent the electrolyte solution from leaking.
[0056]
As the porous support that can be used for such purposes, for example, a filtration filter (membrane filter), or a separator or a nonwoven fabric used for a primary battery or a secondary battery can be preferably used. In particular, when there is a void penetrating in the normal direction with respect to the porous support surface, high photoelectric conversion efficiency can be obtained because the porous support itself has little effect of inhibiting the movement of the redox couple.
[0057]
The material of the filtration filter used as the porous support is preferably made of glass fibers, polyolefins such as polypropylene and polyethylene, polyesters such as polyethylene terephthalate, and the like.
[0058]
The material of the separator or non-woven fabric used as the porous support includes polyolefins such as polypropylene and polyethylene, polyesters such as polyethylene terephthalate, polyamides, polyferylene sulfide, and vinylon (a copolymer of vinyl chloride and vinyl acetate). ), Polyimide, vinylon (acetalized polyvinyl alcohol) and the like are preferable. These separators or nonwoven fabrics can be used alone or in combination with two or more separators or nonwoven fabrics. Here, the “composite nonwoven fabric” means a blend stretch-type nonwoven fabric obtained by blending and spinning / stretching the above two kinds of materials, or one of the two kinds of materials as a core and the other covering the periphery thereof. The core-sheath structure type non-woven fabric is obtained by heat-sealing a composite fiber (conjugate fiber). For example, a heat fusion type nonwoven fabric using a high melting point polypropylene as a core component and a low melting point polyethylene as a sheath component is well known.
[0059]
  The thickness of the porous support is the semiconductor layer7And counter electrode9And is defined by the surface spacing. However, in general, the thickness of the porous support is preferably 1 mm or less. When the thickness of the porous support is more than 1 mm, the electrolyte layer13The moving distance of the oxidation-reduction pair becomes longer, the electron transfer reaction mediated by the oxidation-reduction pair becomes rate-limiting, and the photoelectric conversion efficiency decreases.
[0060]
  Semiconductor layer7And counter electrode9Eliminating the space between the electrolyte layer and the electrolyte layer where the holding mechanism by the porous support does not work13This eliminates the portion, which in turn leads to prevention of liquid leakage and improved reliability. However, the semiconductor layer7And counter electrode9The assembly process to eliminate the space withInThe semiconductor layer is strongly pressed against each other7And counter electrode9May be mechanically destroyed, which may cause a decrease in photoelectric conversion efficiency. Therefore, the semiconductor layer7And counter electrode9At least 1 μm or more between the semiconductor layer and the semiconductor layer7And counter electrode9It is preferable to prevent mechanical destruction. Therefore, the semiconductor layer7And counter electrode9The thickness of the porous support provided between and 1 is preferably 1 μm or more.
[0061]
  Semiconductor layer of the present invention7And counter electrode9Electrolyte layer between13The porous support used to constitute the semiconductor layer7And counter electrode9In addition to preventing the movement of the redox pair of the electrolyte filled between the two, the electrolyte must be kept from leaking. Therefore, the porous support of the present invention is necessary and sufficient to hold the electrolytic solution so as not to hinder the movement of the redox couple of the electrolytic solution necessary for the formation of the photoelectric conversion element and to prevent liquid leakage. Must have porosity.
[0062]
  For this reason, the electrolyte layer in the photoelectric conversion element 1 of the present invention13In the case of using a porous support for constituting the porous support, it is preferable to use a porous material having a porosity (porosity) in the range of 30% to 80%. When a porous support having a porosity of less than 30% is used, the effect of the porous support to hinder the movement of the redox couple is increased, and the electron transfer reaction mediated by the redox pair becomes rate-limiting, resulting in photoelectric conversion efficiency. Becomes lower. On the other hand, when a porous support having a porosity of more than 80% is used, the pore size is increased, the electrolyte solution holding ability by capillary action is lowered, and a sufficient liquid leakage suppressing effect cannot be obtained.
[0063]
【Example】
Next, the present invention will be described more specifically with reference to examples. However, this invention is not limited only to those Examples.
[0064]
Example 1
10% by weight of New Pole PE-108 (manufactured by Sanyo Chemical Industries) was dissolved in dehydrated ethanol. Next, 0.01 mol of titanium tetrachloride was added to this dehydrated ethanol solution and stirred vigorously for 1 hour to prepare a sol solution of titanium oxide. 10 g of the titanium oxide sol solution was transferred to a petri dish, placed in an oven set at 40 ° C., and allowed to stand until dehydrated ethanol was completely eliminated. The titanium oxide gel remaining in the petri dish was baked at 400 ° C. for 4 hours to completely remove New Pole PE-108. As a result of observing the obtained titanium oxide powder by SEM, the particle size was about 30 nm. Moreover, the titanium oxide obtained from the result of X-ray diffraction was anatase type. Furthermore, it was confirmed from the TEM observation and nitrogen gas adsorption-desorption isothermal curves that 8 nm pores were formed inside the titanium oxide particles.
[0065]
The above-mentioned titanium oxide particles are dispersed at a concentration of about 1 wt% in 20 ml of a mixed solution of water and acetylacetone (volume mixing ratio = 20/1) containing 0.2 ml of Nonipol 100 (manufactured by Sanyo Chemical Industry Co., Ltd.). Prepared. Next, this slurry liquid was added to a 1 mm thick conductive glass substrate (F-SnO).₂, 10Ω / sq, manufactured by Asahi Glass Co., Ltd.) and dried, and the resulting dried product was baked in air at 500 ° C. for 30 minutes to form a porous titanium oxide film. Next, the conductive glass provided with the porous titanium oxide thin film is [Ru (4,4′-dicarboxyl-2,2′-bipyridine)₂(NCS)₂In the sensitizing dye solution represented by the formula, the dye adsorption treatment was performed while refluxing at 80 ° C.
[0066]
The semiconductor electrode obtained as described above and its counter electrode were brought into contact with an electrolyte solution to constitute a photoelectric conversion element. In this case, as the counter electrode, conductive glass in which platinum was deposited with a thickness of 20 nm was used. The distance between both electrodes was 0.1 mm. As the electrolyte solution, a mixed solution (volume mixing ratio = 80/20) of ethylene carbonate and acetonitrile containing tetrapropylammonium iodide (0.5 M) and iodine (0.04 M) was used.
[0067]
Table 1 below shows the amount of the sensitizing dye carried on the semiconductor electrode obtained as described above and the short-circuit current of the assembled photoelectric conversion element. The amount of the sensitizing dye carried was measured by immersing the semiconductor electrode carrying the sensitizing dye in an alkaline ethanol solution to elute the sensitizing dye, and then calculating the change in absorbance of the ethanol solution. Moreover, the optical short circuit current of the photoelectric conversion element was calculated | required from the current-voltage characteristic at the time of light irradiation.
[0068]
Comparative Example 1
Titanium oxide particles (Nippon Aerosil Co., Ltd., P25, average particle diameter 20 nm) in 20 ml of a mixture of water and acetylacetone (0.2 ml) containing 0.2 ml of Nonipol 100 (Sanyo Kasei Kogyo Co., Ltd.) A slurry liquid was prepared by dispersing at a concentration of about 1 wt%. Next, this slurry liquid is made into a 1 mm thick conductive glass substrate (Asahi Glass, F-SnO₂, 10Ω / sq) and dried, and the obtained dried product was baked in the air at 500 ° C. for 30 minutes to form a porous titanium oxide film. Next, together with the substrate provided with this porous titanium oxide film, [Ru (4,4′-dicarboxyl-2,2′-bipyridine)₂(NCS)₂The dye adsorption treatment was carried out while refluxing at 80 ° C. A photoelectric conversion element was assembled in the same manner as in Example 1 using the semiconductor electrode thus obtained.
[0069]
In each of the photoelectric conversion elements obtained in Example 1 and Comparative Example 1, the amount of the sensitizing dye supported on the semiconductor electrode and the optical short-circuit current of the assembled photoelectric conversion element were measured. The amount of the sensitizing dye carried was measured by immersing the semiconductor electrode carrying the sensitizing dye in an alkaline ethanol solution to elute the sensitizing dye, and then calculating the change in absorbance of the ethanol solution. Moreover, the optical short circuit current of the photoelectric conversion element was calculated | required from the current-voltage characteristic at the time of light irradiation. The measurement results are shown in Table 1 below.
[0070]
[Table 1]

[0071]
Although the film thicknesses of the dye-sensitized semiconductor layers of Example 1 and Comparative Example 1 are substantially the same, the amount of dye supported is 2.6 times greater in Example 1. That is, since there were pores inside the titanium oxide particles, it was shown that the carrying amount of the sensitizing dye was increased, and as a result, the short-circuit photocurrent also increased with the increase in the carrying amount of the dye.
[0072]
Example 2
10 wt% Pluronic P-123 (BASF) was dissolved in dehydrated ethanol. Next, 0.01 mol of titanium tetrachloride was added to this dehydrated ethanol solution and stirred vigorously for 1 hour to prepare a sol solution of titanium oxide. A conductive glass substrate (F-SnO) having a thickness of 1 mm was added to 50 ml of this sol solution of titanium oxide.₂, 10Ω / sq, manufactured by Asahi Glass), the conductive glass was pulled up at a speed of 5 mm / min. Then, after putting in the oven set to 40 degreeC, dehydrated ethanol was skipped, it baked at 450 degreeC for 30 minutes. The film thickness of titanium oxide obtained by repeating this immersion-firing was 2.3 μm. As a result of observing the surface of the obtained titanium oxide thin film with SEM, it was confirmed that the titanium oxide thin film was composed of titanium oxide particles having a particle size of about 15 nm. Moreover, the titanium oxide obtained from the result of X-ray diffraction is anatase type, and further, 6 nm pores are generated inside the titanium oxide particles from TEM observation and nitrogen gas adsorption-desorption isotherm curve. It was confirmed.
[0073]
Conductive glass deposited with the above porous titanium oxide thin film [Ru (4,4'-dicarboxyl-2,2'-bipyridine)₂(NCS)₂In the sensitizing dye solution represented by the formula, the dye adsorption treatment was performed while refluxing at 80 ° C. A photoelectric conversion element was assembled from the semiconductor electrode thus obtained in the same manner as in Example 1. The amount of the sensitizing dye supported on the semiconductor electrode and the short-circuit current of the assembled photoelectric conversion element were measured by the same method as described above. The amount of the sensitizing dye supported on the semiconductor electrode is 0.038 μmol / cm.²The photoelectric short-circuit current of the photoelectric conversion element is 6.4 mA / cm.²Met.
[0074]
Example 3
10 wt% Pluronic P-123 (BASF) was dissolved in dehydrated ethanol. Next, 0.05 mol of titanium tetraisopropoxide was added to this dehydrated ethanol solution and stirred vigorously for 1 hour to prepare a sol solution of titanium oxide. As in Example 2, a conductive glass substrate (F-SnO) having a thickness of 1 mm was added to 50 ml of the sol solution of titanium oxide.₂, 10Ω / sq, manufactured by Asahi Glass), the conductive glass was pulled up at a speed of 5 mm / min. Subsequently, it was placed in an oven set at 80 ° C., left for 1 hour, and baked at 450 ° C. for 30 minutes. The film thickness of titanium oxide obtained by repeating this immersion-firing was 1.6 μm. As a result of observing the surface of the obtained titanium oxide thin film with SEM, it was confirmed that the surface was made of titanium oxide particles having a particle size of about 20 nm. Moreover, the titanium oxide obtained from the result of X-ray diffraction is anatase type, and furthermore, 8 nm pores are generated inside the titanium oxide particles from TEM observation and nitrogen gas adsorption-desorption isotherm curve. It was confirmed.
[0075]
Conductive glass deposited with the above porous titanium oxide thin film [Ru (4,4'-dicarboxyl-2,2'-bipyridine)₂(NCS)₂In the sensitizing dye solution represented by the formula, the dye adsorption treatment was performed while refluxing at 80 ° C. A photoelectric conversion element was assembled from the semiconductor electrode thus obtained in the same manner as in Example 1. The amount of the sensitizing dye supported on the semiconductor electrode and the short-circuit current of the assembled photoelectric conversion element were measured by the same method as described above. The amount of the sensitizing dye supported on the semiconductor electrode is 0.025 μmol / cm.²The photoelectric short-circuit current of the photoelectric conversion element is 5.3 mA / cm.²Met.
[0076]
【The invention's effect】
As described above, according to the present invention, the dye sensitization is performed by generating pores inside the semiconductor particles and supporting the sensitizing dye not only on the outer surface of the semiconductor particles but also inside the pores of the particles. The amount of the sensitizing dye carried by the entire semiconductor layer is increased. As a result, a photoelectric conversion element that exhibits a very high photocurrent output can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an example of a photoelectric conversion element of the present invention.
2 is a partially enlarged schematic cross-sectional view of the photoelectric conversion element shown in FIG.
[Explanation of symbols]
1 Photoelectric conversion element of the present invention
3,11 substrate
5 electrodes
7 Dye-sensitized semiconductor layer
9 Counter electrode
13 Electrolyte layer
15 Semiconductor particles
17 Sensitizing dye
19 pores

Claims (8)

An electrode having a semiconductor layer deposited on at least one surface thereof, a counter electrode facing the semiconductor layer of the electrode, and an electrolyte layer disposed between the semiconductor layer and the counter electrode of the electrode In the photoelectric conversion element,
The semiconductor particles forming the semiconductor layer have pores, the semiconductor particles carry a sensitizing dye on the outer surface thereof and in the pores,
The particle size of the semiconductor particles is in the range of 10 nm to 30 nm, the inner diameter of the pores is in the range of 3 nm to 10 nm, and the loading amount of the sensitizing dye on the semiconductor particles is 10 ⁻⁸ to 10 ^−. It is the range of ⁶ mol / cm < ² >, The photoelectric conversion element characterized by the above-mentioned.   The film thickness of the said semiconductor layer exists in the range of 0.1 micrometer-100 micrometers, The photoelectric conversion element of Claim 1 characterized by the above-mentioned.   The photoelectric conversion element according to claim 1, wherein the electrolyte layer includes a porous support impregnated with an electrolyte solution. The photoelectric conversion element according to claim 3 , wherein the porosity of the porous support is in the range of 30% to 80%. The photoelectric conversion element according to claim 3 , wherein the porous support has a thickness in the range of 1 μm to 1 mm. The photoelectric conversion device according to claim 3-5 wherein the porous support is characterized in that it consists of a filtration filter, separator or nonwoven fabric. The photoelectric conversion element according to claim 6 , wherein the filtration filter is made of a material selected from the group consisting of glass fibers, polyolefins, and polyesters. The separator or nonwoven fabric is at least selected from the group consisting of polyolefins, polyesters, polyamides, polyferylene sulfide, vinylon (a copolymer of vinyl chloride and vinyl acetate), polyimide, and vinylon (acetalized polyvinyl alcohol). The photoelectric conversion element according to claim 6 , wherein the photoelectric conversion element is formed of one kind of material.

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