Staebler-Wronski Defects: Creation Efficiency, Stability, and Effect on a-Si:H Solar Cell Degradation

The creation efficiency of Staebler-Wronski (SW) defects, their thermal stability, and their effect on degradation of a-Si:H solar cells is discussed with emphasis on hydrogen bonding configurations. In device-quality a-Si:H films prepared by different methods, creation efficiency of SW defects is remarkably similar. The increased stability against SW degradation in hydrogen-diluted material is mainly due to low thermal stability of SW defects. The SW defect creation is, however, reduced in films with lower hydrogen content prepared by annealing to elevated temperatures. While defect thermal stability strongly affects electron mobility-lifetime product in a-Si:H films, it has little effect on extent of the degradation in cells. This suggests that carrier capture coefficient into defects are governed by their charge state. Thermal stability of SW defects is likely governed by numerous, pre-existing, paired hydrogen configurations nearby the defects that serve as an annealing source for the defects, as suggested by tritiated a-Si:H experiments.