Surface photovoltage measurement of light instability of amorphous silicon films

Abstract
The effect of prolonged light exposure on photovoltaic quality of glow discharge amorphous silicon films has been studied by the surface photovoltage technique. Two principal results have been observed. (i) The minority-carrier diffusion length degrades but stabilizes at 0.25–0.3 μm. (ii) The space-charge width collapses at open circuit voltage under as little as 0.0001 sun bias illumination. The combination of these two effects suggests that it is gross changes in the built-in electric fields that most seriously degrade the fill factor in amorphous silicon solar cells, rather than changes in μτ.