The Influence of Minority Carrier Density on Degradation and Regeneration Kinetics in Multicrystalline Silicon Wafers

The rate at which silicon solar cells and wafers degrade and regenerate when subjected to light and elevated temperatures (LeTID) is known to depend on the minority carrier concentration. In this article, we utilize spatial differences in the rate of degradation and regeneration in multicrystalline silicon wafers to estimate the dependence of these rates on minority carrier concentration. We apply the relation obtained from spatial investigations in a model describing temporal LeTID defect evolution. With the updated model in which the evolving minority charge carrier density during degradation and regeneration is considered, we obtain a drastically improved fit between measured and modeled data. The activation energy for the regeneration process determined from our proposed model (0.56±0.12eV at 1 sun) is lower than most values reported in the literature but correspond perfectly to the activation energy reported by Graf et al. by whom evolving carrier injection is accounted for experimentally. Hence, our results underpin the importance of taking the evolution of charge carrier injection into account in the evaluation of LeTID kinetics. Finally, we use our updated model to obtain spatial maps of degradation and regeneration parameters. Clear correlations are shown between LeTID kinetics parameters and local processing conditions.