Light-induced degradation and regeneration of multicrystalline silicon Al-BSF and PERC solar cells

Light-induced degradation (LID) is a well-known problem faced by p-type Czochralski (Cz) monocrystalline silicon (mono-Si) wafer solar cells. In mono-Si material, the physical mechanism has been traced to the formation of recombination active boron-oxygen (B-O) complexes, which can be permanently deactivated through a regeneration process. In recent years, LID has also been identified to be a significant problem for multicrystalline silicon (multi-Si) wafer solar cells, but the exact physical mechanism is still unknown. In this work, we study the effect of LID in two different solar cell structures, aluminium back-surface-field (Al-BSF) and aluminium local back-surface-field (Al-LBSF or PERC (passivated emitter and rear cell)) multi-Si solar cells. The large-area (156 mm x 156 mm) multi-Si solar cells are light soaked under constant 1-sun illumination at elevated temperatures of 90 degrees C. Our study shows that, in general, PERC multi-Si solar cells degrade faster and to a greater extent than Al-BSF multi-Si solar cells. The total degradation and regeneration can occur within similar to 320 hours for PERC cells and within similar to 200 hours for Al-BSF cells, which is much faster than the timescales previously reported for PERC cells. An important finding of this work is that Al-BSF solar cells can also achieve almost complete regeneration, which has not been reported before. The maximum degradation in Al-BSF cells is shown to reduce from 2% (relative) to an average of 1.5% (relative) with heavier phosphorus diffusion. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim