JP2005293863A - Solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell using diamond-like carbon as a counter electrode material that is the counter electrode material replacing platinum, has catalyst operation for appropriately reducing an electrolyte, and cannot be corroded by the electrolyte. <P>SOLUTION: The diamond-like carbon is used as a material having a catalyst function as a cathode used for the counter electrode of a dye sensitized solar cell, thus providing an inexpensive dye sensitized solar cell having high corrosion resistance and chemical resistance properties. And when giving conductivity to the diamond-like carbon by nitrogen doping, a pattern is formed by a conductive section and an insulating section, thus forming the solar cell only at a desired portion, or forming a plurality of solar cells at one base. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a dye-sensitized solar cell using a metal oxide semiconductor having a dye attached to the surface.

  Solar cells are used in various fields and products as a clean energy source. At present, silicon crystal systems and silicon amorphous systems are mainly used as solar cells, but solar cells having various mechanisms have been proposed and studied.

  In recent years, dye-sensitized solar cells have attracted attention. A dye-sensitized solar cell generally has a metal oxide semiconductor layer such as titanium oxide formed on a conductive thin film such as ITO or FTO on a substrate made of glass or resin, and absorbs light energy on the semiconductor surface. A dye for donating electrons to the semiconductor is adsorbed to form a working electrode, and a counter electrode is provided for the working electrode. Furthermore, an electrolyte layer is provided between the electrodes, and electrons can be exchanged to form a battery.

  Dye-sensitized solar cells can be made of resin as the base material, and since a thin layer is formed on the surface of the solar cell, the shape can be freely determined, or bending can be performed after the battery is formed. There is an advantage that the degree of freedom of the shape is very high and the weight can be reduced.

Also, the materials used are relatively inexpensive, and silicon-based solar cells also require enormous energy for silicon purification in the manufacturing process, but such processes are not necessary for dye-sensitized solar cells, and the manufacturing cost Is also relatively small and therefore excellent in cost.

In addition, dye-sensitized solar cells have a feature that the amount of power generation is less reduced even at low illuminance, such as during cloudy weather or indoor use, compared to silicon-based solar cells. There is also an advantage without worry.

On the other hand, research using diamond-like carbon as a field emission device has recently become active. Diamond-like carbon is a substance with an amorphous structure of a carbon skeleton, and is called because it has high hardness and is very similar to diamond in friction characteristics, corrosion resistance, and electrical characteristics. By doping the diamond-like carbon with nitrogen atoms, conductivity can be imparted to the diamond-like carbon that was originally an insulator.
Japanese Patent Laid-Open No. 1-220380

  In the past, dye-sensitized solar cells have generally used platinum as a counter electrode, which has been a factor in increasing costs. The counter electrode serves as a part of the battery that reduces the electrolyte by using the electrons taken out from the electrolyte by the working electrode and returned around the external circuit. At this time, the catalyst for reducing the electrolyte is platinum, and at the same time, it plays a role of a barrier so that the counter electrode and its substrate are not eroded by the electrolyte.

  In other words, the necessary requirements for the counter electrode material are catalysis as a cathode that can assist in the reduction of the electrolyte, and that it is not eroded by the electrolyte. To date, useful materials that have been replaced with platinum have been proposed as counter electrode materials. However, there was no substitute for platinum.

  Therefore, the present invention has been made in view of the above problems, and is a counter electrode material that replaces platinum, and has a catalytic action that can satisfactorily reduce the electrolyte and is not eroded by the electrolyte. We intend to provide solar cells using diamond-like carbon.

  In order to achieve the above object, the present invention is configured as follows. That is, a working electrode having a metal oxide semiconductor having a dye that can be excited to donate electrons to a semiconductor when it is irradiated with light and attached to the surface, and a counter electrode with respect to the working electrode are interposed through an electrolyte layer. A dye-sensitized solar cell laminated oppositely, wherein the counter electrode is provided with diamond-like carbon as a substance having a catalytic function as a cathode that assists reduction of the electrolyte It is.

  In a dye-sensitized solar cell, a metal oxide semiconductor such as titanium oxide is provided on a translucent conductive thin film, and a dye capable of absorbing light on the surface of the metal oxide semiconductor and supplying electrons to the semiconductor is provided. A working electrode is attached, a counter electrode is provided for the working electrode, and an electrolyte material containing an electrolyte for transferring electrons between the electrodes is filled.

  When the dye-sensitized solar cell is irradiated with light, the dye adhering to the surface of the metal oxide semiconductor is excited, electrons generated by this excitation move to the metal oxide semiconductor, and the electrons further enter the conductive film. It travels through an external circuit and is sent to the light emitter and charging device. Then, the electrons return to the counter electrode side, reduce the electrolyte with the counter electrode, and return to the solar cell system. On the other hand, the dye having transferred electrons to the semiconductor is in an oxidized state, but is reduced from the electrolyte solution to obtain electrons, and returns to the original state.

  Diamond-like carbon may be used as a substance having a catalytic function as a cathode that helps reduce the electrolyte of the counter electrode of the dye-sensitized solar cell.

  Diamond-like carbon is a substance with an amorphous structure of a carbon skeleton, and is called because it has high hardness and very similar to diamond in friction characteristics, corrosion resistance, and electrical characteristics. In other words, diamond-like carbon is a material made of carbon that has high corrosion resistance, chemical resistance, and sealing properties, and also has a catalytic function as a cathode, and is suitable as a counter electrode material for dye-sensitized solar cells. I can say that.

  However, diamond-like carbon is an insulator as it is. The diamond-like carbon is doped with nitrogen using plasma CVD or the like, and thus has conductivity and can be used as a counter electrode material for a dye-sensitized solar cell.

  The diamond-like carbon may be provided with conductivity, and a diamond-like carbon film may be formed on the substrate as it is to form an electrode, or a diamond-like carbon film may be formed on any conductive film.

  Conventionally, since this diamond-like carbon is an insulator, after forming a diamond-like carbon film on the surface of the substrate on which the counter electrode is to be formed, nitrogen doping is carried out only at necessary places to form the counter electrode in a desired shape or It can also be patterned to size. If this technique is used, a plurality of counter electrodes can be formed on one substrate.

  According to the present invention, by using diamond-like carbon as a material having a catalytic function as a cathode used for a counter electrode of a dye-sensitized solar cell, the dye sensitization is inexpensive and has high corrosion resistance and chemical resistance. A solar cell of the type can be provided.

  In addition, when imparting conductivity to diamond-like carbon, by forming a pattern, a solar cell can be formed only at a desired portion, or a plurality of solar cells can be formed on one substrate.

  Embodiments according to the present invention will be specifically described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of the implementation of the dye-sensitized solar cell of the present invention. The working electrode 2 includes a working electrode side substrate 20, a transparent conductive film 21, and a metal oxide semiconductor layer 22 stacked in this order. The counter electrode 1 includes a counter electrode substrate 10, a conductive film 11, and diamond as a counter electrode material. Like carbons 12 are sequentially laminated, and the working electrode 2 and the counter electrode 1 are laminated to face each other with the electrolyte layer 3 interposed therebetween.

  The counter electrode 1 is formed by forming a conductive film 11 on a counter electrode substrate 10 and further providing a diamond-like carbon film 12 on the conductive film. As the conductive film, a transparent conductive film such as ITO or FTO, a metal thin film, or the like can be used. The film thickness of the diamond-like carbon film is preferably about 0.1 to 5 μm, and conductivity can be imparted to the film by doping the diamond-like carbon film with nitrogen by plasma CVD or the like.

  At this time, the conductive film of the counter electrode can be omitted. In this case, electricity may be extracted from the diamond-like carbon film using the conductive diamond-like carbon film itself as a conductive film. Moreover, when forming diamond-like carbon on a base material or a conductive film, an intermediate layer can be provided to improve adhesion and conductivity.

  The working electrode 2 is formed by providing a transparent conductive film 21 on the surface of a translucent working electrode substrate 20 and further providing a metal oxide semiconductor layer 22 thereon. The surface of the metal oxide semiconductor is attached with a dye that can be excited and donate electrons to the semiconductor when irradiated with light.

  When light is irradiated onto the metal oxide semiconductor layer 22 having a dye attached to the surface, the dye absorbs the light energy and is excited to generate electrons. The electrons move to the metal oxide semiconductor and are sent to an external circuit through the conductive film 21. The electrons that have passed through the external circuit return to the counter electrode 1, and the electrons are returned to the solar cell system by reducing the electrolyte at the diamond-like carbon film 22 that is the counter electrode. In this way, a series of electric circuits is completed. On the other hand, the dye having the electrons transferred to the semiconductor is in an oxidized state, but receives the electrons from the electrolyte layer and is reduced to return to the original state.

  The substrate material for the electrode is not particularly limited, and for example, polycarbonate resin, tempered glass, acrylic resin, PET resin, PEN resin, and the like are preferably used. As the light-transmitting conductive film, an ITO film, an FTO film, or the like can be used. If light-transmitting property is not required, a metal thin film or the like can also be used.

  Examples of the metal oxide semiconductor used include titanium oxide, zinc oxide, tin oxide, tungsten oxide, zirconium oxide, hafnium oxide, strontium oxide, indium oxide, yttrium oxide, lanthanum oxide, vanadium oxide, niobium oxide, tantalum oxide, and oxide. Chromium, molybdenum oxide, iron oxide, nickel oxide, silver oxide, etc., strontium titanate, calcium titanate, etc., and mixtures thereof can be used. In consideration of chemical stability, cost, and electromotive force of power generation, titanium oxide Is preferably used.

  At this time, the crystal system of titanium oxide is not particularly limited, but it is preferable to include anatase type titanium oxide having high activity. Further, a mixture of a rutile type and an anatase type may be used. The titanium oxide on the conductive thin film is preferably laminated with fine particles. By doing so, the surface area becomes large, the area irradiated with light is wide, and the exchange of electrons with the electrolyte is also suitable. To be done. At this time, the titanium oxide is preferably fine particles of about several tens nm to several hundreds nm. Further, two or more kinds of particles having different particle diameters may be mixed, and incident light can be suitably scattered to absorb light efficiently. Further, even when a tubular nanotube type titanium oxide having a diameter of several nanometers to several tens of nanometers is used instead of fine particles, the efficiency can be increased because the surface area is large.

  A dye is adsorbed on the surface of the metal oxide semiconductor. Various dyes have been proposed for dye-sensitized solar cells and can be used. For example, ruthenium complex system, cobalt complex system in metal complex system, cyanine system, merocyanine system, phthalocyanine system, coumarin system, riboflavin system, xanthene system, triphenylmethane system, etc. are well known, These can be used. In particular, ruthenium complexes are preferable for metal complex systems, and merocyanine systems are preferable for organic systems.

  Various electrolytes have been proposed for dye-sensitized solar cells, and these can be used. As a general one, lithium iodide, iodine, and DMPImI which is an imidazolium salt of a room temperature molten salt are used as an electrolyte, and these are dissolved in a solvent of methoxyacetonitrile, and 4-tert-butylpyridine for voltage adjustment as an additive. Is used as an electrolyte material. In addition, ethylene carbonate or the like may be blended as a solvent, and MPrImI or MBuImI may be used as a room temperature molten salt. Further, MEImBF4- may be added as a diluent.

  Moreover, when a polymerizing agent is added to the above electrolyte material to cause gelation, accidents such as leakage of the electrolyte material from the solar cell can be prevented in advance. Moreover, CuI which is a solid electrolyte material can also be used as an electrolyte material.

  Next, FIG. 2 shows a schematic view of a solar cell having a conductive portion and an insulating portion patterned by partially doping the diamond-like carbon film on the counter electrode with nitrogen, as viewed from above. As described above, by providing the diamond-like carbon film with a conductive portion and an insulating portion, a plurality of solar battery units can be easily formed in one solar battery cell. By freely connecting the solar cell units electrically in series or in parallel, a solar cell having a desired voltage or current can be obtained.

It is a schematic diagram of the cross section which shows an example of implementation of the solar cell of this invention. It is a schematic diagram which shows an example of implementation of the solar cell of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Counter electrode 10 Counter electrode base material 11 Conductive film 12 Diamond-like carbon film 2 Working electrode 20 Working electrode base material 21 Transparent conductive film 22 Metal oxide semiconductor layer 3 Electrolyte layer A Conductive part B Insulating part

Claims (1)

A working electrode having a metal oxide semiconductor with a dye that can be excited to donate electrons to the semiconductor when light is applied to the surface and a counter electrode to the working electrode are opposed to each other with an electrolyte layer interposed therebetween. And the counter electrode is provided with diamond-like carbon as a material having a catalytic function as a cathode that assists in reducing the electrolyte. .

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