On the impact of dark annealing and room temperature illumination on p-type multicrystalline silicon wafers

Abstract

In the past few years, carrier-induced degradation (CID) in p-type multicrystalline silicon (mc-Si) has been receiving significant attention. Recently, it has been reported that this material is also susceptible to degradation under dark anneal at moderate temperatures. In the first part of this study, we investigate the impact of the dark anneal temperature on mc-Si wafers. We identify both degradation and regeneration of the effective lifetime, where higher temperatures lead to faster rates and lower degradation extent. A fitting model is developed to describe the kinetics of these processes, where the degradation and regeneration process are assumed to happen simultaneously. An Arrhenius analysis of the degradation and regeneration rates, extracted from the proposed model, determines activation energies of 1.08 ± 0.05 eV for the degradation process and 1.11 ± 0.04 eV for the regeneration one. An improvement of the minority carrier effective lifetime of up to 40% is observed after a long dark anneal process. This improvement is associated with enhancement of both the bulk and surface passivation. Temperature- and injection-dependent lifetime spectroscopy measurements indicate that the recombination parameters of the associated defect causing the degradation in the dark are similar to those determined for the CID-related defect; therefore, it seems both defects have a similar nature.In the second part of the study, the effect of the illumination intensity at room temperature on the degradation/regeneration is studied. Surprisingly, an improvement in the effective lifetime is found, followed by a very slow degradation. The proposed model is found to be suitable to fit these measurements. The extracted rates suggest that the observed behavior is due to a regeneration that is much faster than the degradation.The reported findings provide new insights into CID in p-type mc-Si that will help improve understanding and assist in developing mitigation solutions.