Improvement for high-efficiency, stable multi-junction cells

The world's highest conversion efficiency of 12.0% was obtained for a 100 cm/sup 2/ single-junction a-Si solar cell submodule, by combining a high-quality i-layer, a high-quality buffer layer treated by hydrogen plasma, and other successful techniques. For further improvement in the conversion efficiency and long-term stability, high-quality a-SiGe:H was studied for use on the bottom cell of the multijunction solar cell. The authors' research, focusing on film composition, revealed that the optical gap (E/sub opt3/) of a-SiGe:H could be expressed by E/sub opt3/=1.3C/sub H-/ 0.6C/sub Ge/+1.4(eV), where C/sub H/ is H content and C/sub Ge/ is Ge content. Moreover, film qualities were found to be dependent on C/sub H/ and C/sub Ge/ even at the same E/sub opt3/. These results led to high-efficiency and stable a-Si/a-Si/a-SiGe multijunction solar cells.<
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