Recent Advances in a-Si Solar Cell Technology in Japan
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RECENT ADVANCES IN A-SI SOLAR CELL TECHNOLOGY IN JAPAN Y. KUWANO Research Center, SANYO Electric Co., Ltd. 1-18-13 Hashiridani, Hirakata City, Osaka,
Japan
ABSTRACT
Recent advances in a-Si solar cells in Japan are reviewed. Improvements in single-junction and multi-junction solar cells are described in three main points, namely, fabrication methods, materials, and cell structures. Recently, a conversion efficiency of 11.7% was obtained for a single-junction structure. For an a-Si/poly-Si stacked structure and an a-Si/(CdS/CdTe) 4 terminal structure, conversion efficiencies of more than 13% were achieved. Then recent advances in the prevention of the light induced degradation of a-Si solar cells is mentioned. Several methods which can improve the a-Si solar cell stability are described. Finally, the present status of the industrialization of a-Si solar cells and some of the latest applications are described together with their propects.
1. INTRODUCTION
Since 1976 when Carlson and Wronski invented the amorphous silicon (a-Si) solar cell, it has become a focus of attention as a low-cost solar cell (1)(2). Especially in Japan, intensive research efforts have been concentrated on a-Si solar cell technologies with the aid of the accelerative promotion of the Sunshine Project (Table I). A number of technological breakthroughs led to rapid improvement in conversion efficiency (Fig. 1). Most recently, a conversion efficiency of 11.7% was obtained for a single-junction structure and more than 13% was achieved for an a-Si/poly-Si stacked structure and an a-Si/(CdS/CdTe) 4 terminal structure. a-Si solar cells are presently commercialized in consumer electronics and small-scale, stand-alone systems, which account for about 70% (4.7 MWp in 1984) of all solar cell production in Japan. In this paper, recent advances in a-Si solar cell technologies for single-junction structures and multi-bandgap structures in Japan are reported. Improvements in the prevention of light induced degradation are also mentioned and the present status of a-Si solar cell applications is described. Finally, future prospects for a-Si solar cell technology are discussed.
2.
ADVANCES IN SINGLE-JUNCTION A-SI SOLAR CELLS
The conversion efficiency of the single-junction a-Si solar cell has been improved to be 11.7% (1cm 2) and 9.72% (100cm 2) (3). Various investigations for improving the conversion efficiency are
Mat- Res. Soc- Symp. Proc. Vo. 70. 1•986 Materials Research Society
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Table I History of a-Si solar cells in Japan
20
a>b (llamakawa) o>1 .0 1979Integrated type a-Si solar cell (Kuwano) 1980Consecutive, separated reaction chamber method (Kuwano) C 1 FUJI) Mass-production of a-Si solar cell (SANYO,
1981p-type a-SiC (Hamakawa) 2kW powergenerating system (SANYO) 1982a-Si solar cell fabricated bySitHl(Hayashi) 1983Battery charger powered bya-Si solar cell put onthe market (SANYO) 1984a-Si solar cell fabricated with full photo-CVD method (Kompgai} Conversion efficiency ofmorethan ll
(SANYO, FUJI)
Small area ./ cell .. *
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