We find that the volume fraction of amorphous component in hydrogenated nanocrystalline silicon intrinsic layers is not necessarily the determining factor for the light-induced metastability of n-i-p solar cells. Small grains and/or intermediate range order may play an important role in improving the stability. The distribution of nanocrystallites along the growth direction is also important. Based on the findings, we have optimized the hydrogen dilution profiling for controlling the structural evolution and have reduced the light-induced degradation of solar cells. As a result, we have achieved initial and stable active-area efficiencies of 14.1% and 13.2%, respectively, using an a-Si:Hc-Si:Hc-Si:H triple-junction structure.
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