Suppression of LeTID in p-type multi-crystalline PERC silicon solar cells by biased annealing process

P-type multi-crystalline PERC silicon solar cells are susceptible to strong light and elevated temperature-induced degradation (LeTID). Various approaches, such as illuminated annealing and modified thermal processes, have been investigated to suppress LeTID. An undesirable side effect of these processes is an increased contact resistance at the front screen printed fingers, and therefore a lower fill factor. Previous work has indicated that this may be caused by the transport and accumulation of hydrogen at the contacts and that this behaviour can be limited by applying a reverse bias across the cell during a dark anneal. In this paper, we have conducted a similar biased annealing process to investigate the effect of different cooling conditions on PERC cell performance, and developed a biased annealing treatment that not only improves the efficiency but also maintains the stability during the light soak test. Preliminary results of transferring this process into 6-inch PERC cells using a full-scale industrial tool are also presented.