Investigating the different degradation behavior of multicrystalline silicon PERC and Al-BSF solar cells

Abstract

Commercial passivated emitter and rear cell (PERC) devices are critically hindered by a thus-far unidentified degradation mechanism called light- and elevated temperature-induced degradation (LeTID). In contrast to PERC devices, aluminum back-surface field (Al-BSF) devices are markedly more resistant to the same degradation mechanism. In this work, we employ device simulations to elucidate the differences between Al-BSF and PERC degradation behavior and thus accelerate the search for the root cause of LeTID. We find that a difference in defect activation under degradation conditions is a more likely explanation than enhanced sensitivity to bulk lifetime for PERC compared to Al-BSF devices. By employing device simulation for the two architectures under high illumination intensity, we identify a narrow parameter space for the LeTID defect precursor. When combined with experimental observations, this may yield important new information about LeTID defect formation.