Solar cell

The present invention relates to a dye-sensitized solar cell using a metal oxide semiconductor in which a dye is adhered to a surface.

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

In recent years, dye-sensitized solar cells have been attracting attention as one of them. Dye-sensitized solar cells generally have a metal oxide semiconductor layer such as titanium oxide provided on a conductive thin film such as ITO or FTO on a base material made of glass or resin to absorb light energy on the semiconductor surface. A dye that donates electrons to a semiconductor is adsorbed to form an working electrode, and a counter electrode is provided for this working electrode. Furthermore, an electrolyte layer is provided between the electrodes to enable the transfer of electrons, which is used as a battery.

The base material of a dye-sensitized solar cell can be a resin, and a thin layer is formed on the surface of the dye-sensitized solar cell to form a solar cell. There is an advantage that the degree of freedom for the shape is very high and the weight can be reduced.

In addition, the materials used are relatively inexpensive, and silicon-based solar cells require enormous energy to purify silicon in the manufacturing process, but dye-sensitized solar cells do not require such a process and the manufacturing cost. Because it is relatively small, it is also excellent in terms of cost.

In addition, dye-sensitized solar cells have the advantage that the amount of power generation does not decrease much even in low light such as in cloudy weather or when used indoors, compared to silicon-based solar cells. There is also an advantage that you do not have to worry about.

On the other hand, research on using diamond-like carbon as a field emission device has become active in recent years. Diamond-like carbon is a substance having an amorphous structure with a carbon skeleton, and is so called because it has high hardness and is very similar to diamond in friction characteristics, corrosion resistance, and electrical characteristics. By doping this diamond-like carbon with a nitrogen atom, it is possible to impart conductivity to the diamond-like carbon, which was originally an insulator.<patcit num="1"><text>Japanese Patent Application Laid-Open No. 1-220380</text></patcit>

<p> Until now, dye-sensitized solar cells have generally used platinum for the counter electrode, which is one of the factors that increase the cost. The counter electrode plays a part of a battery that reduces the electrolyte by utilizing 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 also acts as a barrier so that the counter electrode and its base material are not eroded by the electrolyte.</p><p> That is, the necessary requirements for the counter electrode material are catalytic action as a cathode that can assist the reduction of the electrolyte and not being eroded by the electrolyte, and useful materials that can replace platinum have been proposed as counter electrode materials. However, there was no substitute for platinum.</p><p> Therefore, the present invention has been made in view of the above-mentioned problems, and is a counter electrode material that replaces platinum, and is a counter electrode material that has a catalytic action capable of satisfactorily reducing the electrolyte and is not eroded by the electrolyte. The purpose of the present invention is to provide a solar cell using diamond-like carbon.</p>

<p> In order to achieve the above object, the present invention has the following configuration. That is, an working electrode having a metal oxide semiconductor having a dye attached to the surface of the semiconductor, which is excited when irradiated with light and can donate electrons to the semiconductor, and a counter electrode with respect to the working electrode are formed via an electrolyte layer. A dye-sensitized solar cell laminated so as to face each other, wherein the counter electrode is provided with diamond-like carbon as a substance having a catalytic function as a cathode that assists reduction of an electrolyte. Is.</p><p> Dye-sensitized solar cells are provided with a metal oxide semiconductor such as titanium oxide on a translucent conductive thin film, and a dye capable of absorbing light on the surface of the metal oxide semiconductor to give electrons to the semiconductor. It is attached to form an working electrode, a counter electrode to the working electrode is provided, and an electrolyte material containing an electrolyte for exchanging electrons is filled between the electrodes.</p><p> When the dye-sensitized solar cell is irradiated with light, the dye adhering to the surface of the metal oxide semiconductor is excited, the electrons generated by this excitation move to the metal oxide semiconductor, and the electrons further transfer to the conductive film. It travels and is sent to the illuminant and charging device through an external circuit. Then, the electrons return to the counter electrode side, reduce the electrolyte at the counter electrode, and return to the inside of the solar cell system. On the other hand, the dye in which electrons have moved to the semiconductor is in an oxidized state, but is reduced from the electrolyte solution to receive electrons and returns to the original state.</p><p> 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 this dye-sensitized solar cell.</p><p> Diamond-like carbon is a substance having an amorphous structure with a carbon skeleton, and is so called because it has high hardness and is very similar to diamond in friction characteristics, corrosion resistance, and electrical characteristics. That is, diamond-like carbon is a material made of carbon having high corrosion resistance, chemical resistance, and airtightness, 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.</p><p> However, diamond-like carbon is an insulator as it is. By performing nitrogen doping on this diamond-like carbon using plasma CVD or the like, it has conductivity and can be used as a counter electrode material for a dye-sensitized solar cell.</p><p> This diamond-like carbon may be provided with conductivity and a diamond-like carbon film may be formed on the base material as it is to serve as an electrode, or a diamond-like carbon film may be formed on some conductive film.</p><p> Further, since this diamond-like carbon is conventionally an insulator, a diamond-like carbon film is formed on the surface of the substrate on which the counter electrode is formed, and then nitrogen doping is performed only at necessary locations to form the counter electrode in a desired shape. It can also be patterned to size. Using this technique, it is possible to form a plurality of counter electrodes on one substrate.</p>

<p> 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, it is inexpensive and has high corrosion resistance and chemical resistance. A type of solar cell can be provided.</p><p> Further, by forming a pattern when imparting conductivity to diamond-like carbon, it is possible to form a solar cell only in a desired portion, or to form a plurality of solar cells on one base material.</p>

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 implementation of the dye-sensitized solar cell of the present invention. The working electrode 2 is formed by laminating a working electrode side base material 20, a transparent conductive film 21, and a metal oxide semiconductor layer 22 in this order, and the counter electrode 1 is a counter electrode base material 10, a conductive film 11, and diamond as a counter electrode material. The like carbon 12 is formed by being laminated in order, and the working electrode 2 and the counter electrode 1 are laminated so as to face each other via the electrolyte layer 3.

The counter electrode 1 is formed by forming a conductive film 11 on a counter electrode base material 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 the film can be imparted with conductivity by performing nitrogen doping on the diamond-like carbon film by plasma CVD or the like.

At this time, the conductive film of the counter electrode may be omitted. In this case, the conductive diamond-like carbon film itself may be used as a conductive film to extract electricity from the diamond-like carbon film. Further, 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 the translucent working electrode base material 20 and further providing a metal oxide semiconductor layer 22 on the transparent conductive film 21. A dye that can be excited to donate electrons to the semiconductor when irradiated with light is attached to the surface of the metal oxide semiconductor.

When light is applied to the metal oxide semiconductor layer 22 having the dye adhered to the surface, the dye absorbs the light energy and excites it to generate electrons. These electrons move to the metal oxide semiconductor and are sent to the external circuit through the conductive film 21. The electrons that have passed through the external circuit return to the counter electrode 1, and the diamond-like carbon film 22 that is the counter electrode reduces the electrolyte so that the electrons return to the solar cell system. In this way, a series of electric circuits is completed. On the other hand, the dye in which electrons have moved to the semiconductor is in an oxidized state, but receives electrons from the electrolyte layer and is reduced to return to the original state.

The base material of 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. Further, as the translucent conductive film, an ITO film, an FTO film, or the like can be used, and if translucency is not required, a metal thin film or the like can also be used.

The metal oxide semiconductors used are, for example, 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 oxidation. Chromium, molybdenum oxide, iron oxide, nickel oxide, silver oxide, etc., strontium titanate, calcium titanate, etc., and mixtures thereof can be used, and titanium oxide is considered in consideration of chemical stability, cost, and electromotive force of power generation. 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 rutile type and anatase type may be used. Titanium oxide on the conductive thin film is preferably laminated with fine particles, and by doing so, the surface area is large, the area irradiated with light is large, and the transfer of electrons to and from the electrolyte is also suitable. It is done in. At this time, titanium oxide is preferably fine particles having a size of several tens of nm to several hundreds of nm. Further, two or more kinds of particles having different particle sizes may be mixed, and the incident light can be suitably scattered and the light can be absorbed efficiently. Further, even if a tubular nanotube-type titanium oxide having a diameter of several nm to several tens of nm is used instead of fine particles, the surface area is large and the efficiency can be improved.

A dye is adsorbed on the surface of the above metal oxide semiconductor. As the dye to be adsorbed, various dyes have been proposed for dye-sensitized solar cells, and they can be used. For example, ruthenium complex type and cobalt complex type for metal complex type, cyanine type, merocyanine type, phthalocyanine type, coumarin type, riboflavin type, xanthene type, triphenylmethane type and the like are well known as organic dyes. These can be used, and in particular, a ruthenium complex is preferable for a metal complex type, and a merocyanine type is preferable for an organic type.

In addition, various electrolytes have been proposed for dye-sensitized solar cells, and these can be used. Generally, 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 is used as an additive. Is used as an electrolyte material. In addition, ethylene carbonate or the like may be blended as the solvent, and MPrImI, MBuImI or the like may be used as the room temperature molten salt. Further, MEImBF4- may be further added as a diluent.

Further, if a polymerizing agent is added to the above-mentioned electrolyte material to gel it, accidents such as liquid leakage of the electrolyte material from the solar cell can be prevented. Further, CuI, which is a solid electrolyte material, can also be used as the electrolyte material.

Next, FIG. 2 shows a schematic view of a solar cell cell in which a conductive portion and an insulating portion are patterned by partially nitrogen doping the diamond-like carbon film on the counter electrode, as viewed from above. By providing the diamond-like carbon film with a conductive portion and an insulating portion in this way, it is possible to easily form a plurality of solar cell units in one solar cell. By freely connecting the solar cell units electrically in series or in parallel, it is possible to obtain a solar cell having a desired voltage and current.

<figref num="1">It is the schematic of the cross section which shows an example of the implementation of the solar cell of this invention.</figref><figref num="2">It is a schematic diagram which shows an example of the implementation of the solar cell of this invention.</figref>

Code description

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