Reducing light and elevated temperature induced degradation (LeTID) is important for the industrial success of PERC (passivated emitter and rear cell) solar cells fabricated on high-performance multicrystalline silicon (multi-Si) wafers. Although there has been a lot of progress in understanding the degradation kinetics, the defect(s) responsible for LeTID in multi-Si wafers at elevated temperatures (≈80 °C, 1 Sun) has yet to be identified. In this study, the authors look at the possibility of using phosphorus diffusion gettering (PDG) for reducing LeTID in multi-Si wafers and solar cells. By measuring light induced defect concentrations in multi-Si wafers before and after LeTID, the authors observe that PDG can substantially reduce the average defect concentration. Trace element analysis using inductively coupled plasma mass spectrometry reveals that multi-Si wafers from the edge of the ingot contain a high concentration of Cu, Ni and Ti in grains that degrade more than neighboring grains. To explore PDG for reducing LeTID in multi-Si PERC solar cells, the authors fabricate cells with two different emitter profiles. Etching back a heavily diffused emitter to obtain a high sheet resistance is observed to improve the LeTID performance of the solar cells, an effect that is very likely related to a reduced impurity concentration within the wafer.
