High Quality a-Si Films and Superlattice Structure p-Layer a-Si Solar Cells
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HIGH QUALITY a-Si FILMS AND SUPERLATTICE STRUCTURE p-LAYER a-Si SOLAR CELLS SHOICHI NAKANO, KANEO WATANABE,
SHINYA TSUDA, HISAKI TARUI, TSUYOSHI TAKAHAMA, HISAO HAKU, MASATO NISHIKUNI, YOSHIHIRO HISHIKAWA, AND YUKINORI KUWANO
Research Center, SANYO Electric Co., Ltd. 1-18-13, Hashiridani, Hirakata City, Osaka,
Japan
ABSTRACT As a new preparation method for high-quality a-Si films, we have A low developed the super chamber, a separated UHV reaction chamber system. impurity concentration and excellent film properties were obtained by the A conversion efficiency of 11.7% was obtained for an a-Si super chamber. solar cell using a high-quality i-layer deposited by the super chamber, and a p-layer fabricated by a photo-CVD method. As a new material, amorphous superlattice structure films were fabricated by the photo-CVD method for the first time. Quantization effects and low damage to the interfaces were observed. Superlattice structure p-layer a-Si solar cells were fabricated for the first time, and a conversion efficiency of 10.5% was obtained. 1. INTRODUCTION Amorphous silicon (a-Si) is recently gathering much attention as a suitable material for electronic devices, such as solar cells, photosensors, and thin film transistors. As for the a-Si solar cell, the conversion efficiency has been improved to a level of more than 11% (1). In order to use it as a power source, however, further improvement in the conversion efficiency is required. For this purpose, we have developed a new fabrication method and new materials to improve film properties. In this paper, we first report on the separated ultra-high vacuum reaction chamber method, called the super chamber, as a new fabrication method. The effect on the reduction of impurities is mentioned, and the solar cell characteristics are described. Next, as a new material, the a-Si superlattice structure film, which was fabricated by the photo-CVD method for the first time, is reported, and the characteristics of the superlattice structure p-layer a-Si solar cell are discussed. 2.
HIGH-QUALITY a-Si FILMS AND HIGH-EFFICIENCY CELLS FABRICATED BY THE SUPER CHAMBER
In amount of the charge length,
a-Si films fabricated by conventional systems, there is a large of impurities, and these affect film properties, such as the extent Staebler-Wronski effect, the space density, the carrier diffusion and so on
(2).
To prevent
these
_
__
impurities, we have developed the separated UHV reaction chamber system, and we call it the super chamber. A block diagram of the super chamber is shown in Fig. 1. Reaction gas is supplied by a low-leakage and high-purity gas system, and is exhausted by a UHV
pumping system. -9A background pressure on the order of 10 Torr is obtained, which is two to three orders lower than that of conventional chambers.
Mat. Re,. Soc. Symp. Proc. Vol. 70. c 1986 Material, Research Society
Substrate
a•
andhi-pity
UHea Vreawtiom V chbamer
UHV ping system
iS Fig.1 Block diagram of the superchamber (separated UHV reaction chamber)
512
Impurity concentrati
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