Effects of Structural Properties of νc-Si:H Absorber Layers on Solar Cell Performance

Abstract

ABSTRACTThin film microcrystalline silicon solar cells with absorber layers of various structural composition have been prepared. The highest conversion efficiency is observed at preparation conditions close to the transition to the amorphous growth regime, i.e. crystalline volume fraction is high but not at its maximum. The optimized material consists of crystalline “fibers” with small diameter which extend through the whole absorber layer. On further approach to the transition regime a set in of amorphous growth can be observed, resulting in decreasing solar cell performance. Surprisingly, material prepared under conditions favoring highly crystalline growth exhibits a less efficient carrier extraction if applied to the solar cell. We discuss increasing bulk recombination as possible cause for this observation. The maximum conversion efficiency obtained was 8.7 % for a 1 νm single junction solar cell. Using our optimized deposition conditions with simultaneously higher discharge powers the deposition rate can be increased up to 4.6 Å/s at the high efficiency of 8.3 %.