Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
2001-02-23
2002-05-28
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
C136S257000, C136S258000, C136S251000, C257S053000, C257S434000, C257S433000, C257S432000
Reexamination Certificate
active
06395973
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a photovoltaic device having a transparent conductive films disposed on a surface of a transparent substrate to which light is applied, a photoelectric conversion active layer of amorphous silicon disposed on the transparent conductive film, and a metallic electrode film disposed on the photoelectric conversion active layer.
BACKGROUND ART
In recent years, there have been a growing demand for energies, particularly an electric energy. New power plants for thermal electric power generation which consumes petroleum and coal are not easy to construct in view of the exhaustion of raw fuels in the future, and new power plants for nuclear electric power generation which consumes uranium or the like are not easy to construct either in view of environmental problems at issue today.
It has been studied by governments to make up for a power shortage with new energies including electric power generation based on solar energy. In Japan where available land is limited, it has been mainly planned to generate electric power from solar energy with solar cells that are mounted on house roofs and walls. Solar cells for generating electric power have been made of crystalline silicon or polycrystalline silicon so far. Mass-production of such solar cells poses a problem in that silicon as a raw material will suffer a shortage. For this reason, research efforts are being directed to amorphous silicon solar cells which consume less raw material of silicon than crystalline silicon solar cells or polycrystalline silicon solar cells.
Heretofore, many amorphous silicon solar cells have been used as power supplies for calculators and watches. Since solar cells for these devices may be of a small area, reflected interference color irregularities (hereinafter referred to as “reflected color irregularities”) caused due to a thickness distribution of thin films (hereinafter referred to as “film thickness irregularities”) of solar cells has not posed a significant problem.
However, solar cells mounted on house roofs and walls take up a large area. Since those solar cells still suffer aesthetic problems such as reflected color irregularities, they need to be improved to make themselves more commercially attractive. Presently available large-area amorphous silicon solar cells are not highly commercially attractive because of the problem of reflected color irregularities that are caused by film thickness irregularities of a transparent conductive film made of tin oxide, for example, which is a component thereof.
If a transparent conductive film made of tin oxide, for example, has no film thickness irregularities, then no problem of reflected color irregularities arises in principle. According to the actual industrial production practice, however, it is difficult to produce transparent conductive films free of film thickness irregularities inexpensively in view of film thickness irregularities. Reflected colors of present large-area amorphous silicon solar cells are only in a range from red to reddish purple, and hence a choice of colors for such solar cells is limited.
Known processes of manufacturing amorphous silicon solar cells with a controlled reflected color tone include a process of growing a transparent conductive film and then etching it to a desired thickness as disclosed in Japanese laid-open patent publication No. 58-74087 and a process of forming a wedge-shaped thin film of irregular thickness on the reverse side of a substrate as disclosed in Japanese laid-open patent publication No. 60-142576. According to a process of controlling a reflected color tone of a glass substrate with a transparent conductive film formed thereon, as disclosed in Japanese patent publication No. 3-72586, a layer of high refractive index is formed on a substrate, and a layer of lower refractive index than the layer of high refractive index is formed thereon, producing a two-layer film, which is formed beneath an infrared-reflective transparent semiconductor that is a transparent conductive film.
The process of growing a transparent conductive film and then etching it to a desired thickness as disclosed in Japanese laid-open patent publication No. 58-74087 does not indicate specific details of the control of an etched amount. The process not only makes it difficult to control the film thickness, but also suffers poor productivity as the thin film once grown is etched.
The process of forming a wedge-shaped thin film of irregular thickness on the reverse side of a substrate as disclosed in Japanese laid-open patent publication No. 60-142576 uses a rainbow-color pattern. Therefore, if produced solar cells are used on house roofs, then they pose an aesthetic problem, and also suffer difficulty in forming a wedge-shaped thin film of irregular thickness and a reduction in productivity.
Japanese patent publication No. 3-72586 discloses nothing as to a reflected color tone produced if an amorphous silicon film is formed on a transparent conductive film and then a metallic film such as of aluminum is formed on the amorphous silicon film. Therefore, it is difficult to infer what a reflected color tone would be like with such a structure, and a desired color tone may not necessarily be obtained.
A photovoltaic device according to the present invention solves the above deficiencies of the prior art, and suffers less reflected color irregularities when used on house roofs and walls, exhibits a reflected color including at least one of a neutral color and a greenish color, thus making highly aesthetic house roofs and walls on which the photovoltaic device is mounted, and can be produced with excellent productivity.
DISCLOSURE OF INVENTION
The present invention has been made in order to solve the above problems. An invention described in claim
1
is a photovoltaic device comprising a transparent conductive film, a semiconductor thin film, and a metallic electrode film successively deposited on one surface of a transparent substrate, characterized in that the thickness distribution of the transparent conductive film is in a range of ±10% of a central film thickness, a transparent thin film comprising at least one layer is deposited between the transparent substrate and the transparent conductive film, and a* and b* of a reflected color from the transparent substrate to which light is applied may vary within a range of ±5 of a* and b*.
According to an invention described in claim
2
, in the invention described in claim
1
, the transparent thin film has a refractive index ranging from 1.45 to 1.8 and a thickness ranging from 20 to 80 nm.
According to an invention described in claim
3
, in the invention described in claim
2
, the transparent thin film is primarily made of silicon oxide or aluminum oxide.
According to an invention described in claim
4
, in the invention described in claim
1
, the transparent thin film comprises a first layer and a second layer, the first layer thin film positioned closer to the transparent substrate has a refractive index ranging from 1.8 to 2.5 and a thickness ranging from 10 to 50 nm, and the second layer thin film deposited on the first layer thin film has a refractive index ranging from 1.45 to 1.8 and a thickness ranging from 10 to 50 nm.
According to an invention described in claim
5
, in the invention described in claim
4
, the first layer thin film is primarily made of tin oxide or titanium oxide, and the second layer thin film is primarily made of silicon oxide or aluminum oxide.
According to an invention described in claim
6
, in the invention described in any one of claims
1
through
5
, the transparent conductive film has a thickness smaller than 800 nm.
According to an invention described in claim
7
, in the invention described in claim
1
, the transparent conductive film has a thickness ranging from 800 to 1500 nm.
An invention described in claim
8
is a photovoltaic device comprising a transparent conductive film, a semiconductor thin film, and a metallic electrode film successively deposited on one surface of a trans
Fujisawa Akira
Hirata Masahiro
Norimatsu Hodaka
Diamond Alan
Merchant & Gould P.C.
Nippon Sheet Glass Co. Ltd.
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