Recovery of LeTID by low intensity illumination: Reaction kinetics, completeness and threshold temperature

Light (and elevated Temperature) Induced Degradation (LeTID) can seriously limit the efficiency of mc-Si PERC solar cells if no countermeasures are taken. Within this paper, the subsequent regeneration reaction, also induced by light at elevated temperatures, is investigated systematically in the low intensity regime (up to 4 suns) as a possible countermeasure. As might be expectable, degradation and regeneration reaction are found to speed up with increasing treatment temperature; however, completeness of regeneration is also found to be noticeably reduced at high temperatures (up to 380°C). This enforces the introduction of reverse reactions and gives rise to a 3-state reaction model for LeTID explaining the observed threshold temperature above which LeTID elimination does not work anymore. Furthermore, it is found that a treatment at high temperatures not only fails to eliminate LeTID, but also slows down the regeneration in a later low temperature treatment.