Amorphous silicon-based solar cells exhibit a significant decline in their efficiency during their first few hundred hours of illumination; however, the degradation of multiple layer solar cells and of nanocrystalline silicon cells is much lower. The
single-junction cell loses about 30 % of its initial efficiency after about 1000 hours; the triple-junction module loses about 15 % of its initial efficiency (see Fig. 41.2).
All amorphous silicon-based solar cells exhibit such degradation with light, which is called the Staebler-Wronski effect (Staebler and Wronski 1977a, 1977b). The effect anneals out nearly completely within a few minutes at temperatures of about 160 0 C, and anneals substantially in outdoor deployment at summer operating temperatures of 60 0 C.
The Staebler-Wronski effect contributes to noticeable seasonal variations in the conversion efficiency of a-Si:H as observed for modules in the field in Switzerland (since during the winter season the daytime temperature was insufficient for annealing), but there was no discernible, permanent degradation of this module over the three-year extent of this test; one study over ten years does suggest degradation of about 0.7 % per year (Gregg et al. 2005), which is comparable to the long-term degradation of c-Si cells.
