Design considerations for stable amorphous silicon and silicon-germanium solar cells

The effects of degradation of the electronic properties of a-Si:H and a-(Si,Ge):H alloys on light soaking on the device physics of the a-Si and a-(Si,Ge) cells are examined. It is shown that both the decrease in mobility-lifetime products and the decrease in electric field in the middle of the device contribute to the rapid decrease in fill factor. To the authors propose using a novel graded bandgap scheme, where the grading in the bandgap is in the middle of the device. The feasibility of fabricating such devices is examined.<
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