Approaches for stable multi-junction a-Si solar cells

Improvements in the stabilized efficiency of single-junction and multi-junction a-Si solar cells are studied. It has been found that the stabilized efficiency can be improved by suppressing the oxygen and nitrogen content in the i-layer. The defect density and conversion efficiency are strongly correlated with the content of hydrogen having an SiH/sub 2/ configuration rather than with the total hydrogen content in a-Si i-layers. A practical estimation method, which considers the variation of the I-V characteristics of each component cell, is also developed in order to optimize multi-junction cells. The world's highest stabilized efficiency of 8.8% for a single-junction a-Si solar cell and 10.6% for an a-Si/a-SiGe double-junction solar cell are achieved for 1 cm/sup 2/ cells.