Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
2001-01-12
2002-10-29
Christianson, Keith (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C136S258000
Reexamination Certificate
active
06472248
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microcrystalline series photovoltaic element having a high photoelectric conversion efficiency and which enables one to produce a high performance semiconductor device, representatively such as a high performance solar cells a high performance photosensor, or the like, where particularly said solar cell stably exhibits solar cell characteristics without being deteriorated even when continuously used outdoors over a long period of time. The present invention also relates a process for producing said photovoltaic element. The present invention further relates to a building material in which said photovoltaic element is used and a sunlight power generation apparatus in which said photovoltaic element is used.
2. Related Background Art
Various photovoltaic elements have been using not only as independent power sources of electrical equipments but also as alternate energy sources of daily power supply systems. However, for the photovoltaic elements used as alternate energy sources of daily power supply systems, they are still unsatisfactory particularly in terms of their cost per a unit quantity of generated power. In this connection, various studies have been conducting in order to develop improved photovoltaic elements. For instance, particularly with respect to the materials which play the most important role in photoelectric conversion, technical research and development of crystalline type photovoltaic elements, thin film type photovoltaic elements, and the like have been carrying out. The crystalline type photovoltaic element is meant a photovoltaic element having a photoelectric conversion member comprising a single crystalline silicon semiconductor material or a polycrystalline silicon semiconductor material. The thin film type photovoltaic element is meant a photovoltaic element having a photoelectric conversion member comprising an amorphous silicon-containing semiconductor material such as an amorphous silicon semiconductor material and an amorphous silicon-germanium semiconductor material; a microcrystalline silicon-containing semiconductor material such as a microcrystalline silicon semiconductor material and a microcrystalline silicon-germanium semiconductor material; an amorphous or microcrystalline silicon carbide semiconductor material; or a compound semiconductor material. For such microcrystalline silicon-containing semiconductor material, although various studies have been made, its reduction to practical use has not progressed as in the case of the crystalline or amorphous semiconductor materials.
Now, attention has been focused on a report by J. Meier et als., stating that a photovoltaic element (a solar cell) in which a microcrystalline silicon (&mgr;c-Si) semiconductor material is used exhibits a good photoelectric conversion efficiency and is free of light-induced degradation [see, J. Meier et als.,
Mat. Res. Soc. Symp. Proc.,
vol 420. pp. 3-14, 1996 (hereinafter referred to as “document 1”)]. In document 1, there are described that said photovoltaic element (solar cell) was prepared by a high frequency plasma CVD process wherein glow discharge is caused in an atmosphere composed of silane gas diluted with a large amount of hydrogen gas (H
2
) by supplying a VHF (very high frequency) power with a frequency of 70 MHz therein and that the photovoltaic element is structured to have a p-i-n junction where the i-type semiconductor layer comprises a &mgr;c-Si semiconductor material. Document 1 describes that the photovoltaic element afforded a photoelectric conversion efficiency of 7.7%, and no light-induced degradation was observed for the photovoltaic element Document 1 also describes that a stacked type photovoltaic element (solar cell) prepared by stacking a &mgr;c-Si semiconductor material and another &mgr;c-Si semiconductor material was found to have an initial photoelectric conversion efficiency of 13.1% and a relative light-induced degradation of 12.4%.
Besides, in K. Yamamoto et als.,
Jpn. J. Appl. Phys.
vol. 33 (1994), pp. L1751-L1754, Part 2, No. 12B, Dec. 15, 1994 (hereinafter referred to as “document 2”), there is described a photovoltaic element (a solar cell) having a polycrystalline layer formed by subjecting a heavily boron-doped a-Si (amorphous silicon) p-type layer to excimer laser annealing and a pillar-like &mgr;c-Si structure formed by way of plasma CVD on said polycrystalline layer.
However, the photovoltaic elements disclosed in documents 1 and 2 have such disadvantages as will be mentioned below.
Particularly, with reference to the description of document 1, it is understood that no light-induced degradation is observed for the microcrystalline photovoltaic elements disclosed therein. However, for the photovoltaic element for which no light-induced degradation was observed, it is understood that the &mgr;c-Si active layer is of a thickness of 3.6 &mgr;m which is relatively thick and that the short-circuit current of the photovoltaic element is 25.4 mA/cm
2
and the photoelectric conversion efficiency thereof is 7.7% which is undesirably small. And it is also understood that in the formation of the &mgr;c-Si active layer with such large thickness of 3.6 &mgr;m, since the deposition rate is 1.2 Å/sec which is slow, it takes about 8 hours in order to complete the formation thereof. In addition, for the stacked type microcrystalline photovoltaic element disclosed in document 1, although the initial photoelectric conversion efficiency thereof is 13.1% which is satisfactory, the photovoltaic element unavoidably suffers light-induced degradation upon repeated use where the initial photoelectric conversion efficiency is eventually deteriorated. And it obviously takes a long time for the preparation of the stacked type microcrystalline photovoltaic element.
With reference to the description of document 2, it is understood that the &mgr;c-Si active layer of the photovoltaic element is of a thickness of 2 &mgr;m, the short-circuit current of the photovoltaic element is 14.3 mA/cm
2
, and the photoelectric conversion efficiency thereof is 2.5% which is extremely small.
Separately, four persons of the group who reported document 2 jointly have developed the technique disclosed in document 2 and reported a thin film polycrystalline photovoltaic element (solar cell) formed by way of plasma CVD in which the active layer has a thickness of 3.5 &mgr;m and which has a short-circuit current of 26.12 mA/cm
2
and a photoelectric conversion efficiency of 9.8% (see, Kenji Yamamoto et als., 14
th European Photovoltaic Solar Energy Conference,
Barcelona. Spain, Jun. 30-Jul. 4, 1997, pp. 1018-1021). However, the photovoltaic element reported is still insufficient particularly in terms of the photoelectric conversion efficiency and the productivity.
Independently, it is known that a silicon thin film exhibiting crystalline properties may be grown from liquid phase by way of a casting method or the like. However, this method is disadvantageous in that high temperature treatment is required and that the method is not satisfactory particularly in terms of the productivity and production cost.
Besides, Japanese Unexamined Patent publication No. 109638/1993 discloses a method of forming a polycrystalline silicon film by subjecting an amorphous silicon film to a heat treatment so as to cause solid phase epitxaxy. Particularly, this publication describes a method in that a doped amorphous silicon film doped with P and a non-doped amorphous silicon film are sequentially formed on a substrate by means of a plasma CVD method, followed by subjecting to a heat treatment at about 600° C. for several tens hours, where the doped amorphous silicon film is polycrystallized to have a grain size of more than several microns (&mgr;m) and along with this, the non-doped amorphous silicon film is also polycrystallized to have a grain size of more than several microns (&mgr;m), whereby a polycrystalline film is obtained. Japanese Unexamined Patent publication No. 136062/1993 disc
Higashikawa Makoto
Kariya Toshimitsu
Kondo Takaharu
Matsuda Koichi
Sano Masafumi
Christianson Keith
Fitzpatrick ,Cella, Harper & Scinto
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