Eliminating light- and elevated temperature-induced degradation in P-type PERC solar cells by a two-step thermal process

Light- and elevated temperature-induced degradation (LeTID) can have a severe impact on the carrier lifetime of silicon substrates used in solar cell production and thus remains a crucial challenge for manufacturers. In this work, we introduce a two-step annealing process to mitigate LeTID in multi-crystalline silicon (mc-Si) passivated emitter and rear cell (PERC) solar cells. We demonstrate that the first annealing step (450 degrees C) with a slow belt speed (0.5 m/min) plays a primary role in mitigating LeTID in the cells, but also results in an increase in contact resistance. The application of a second annealing step at a similar temperature (400-500 degrees C) with a faster belt speed (1.4 m/min) recovers the contact resistance whilst maintaining the stability of the cell. Applying this approach to the p-type mc-Si PERC solar cells resulted in a reduction of efficiency loss during light soaking from similar to 6%(rel) (control) to similar to 1%(rel) (treated sample). This finding is significant for p-type mc-Si solar cell manufacturers, as the process can be applied to finished cells using a standard belt firing furnace to stabilise cell efficiency for long term operation in the field.