Degradation and regeneration in mc‐Si after different gettering steps

• Published in: Progress in photovoltaics 2017-07, Vol.25 (7), p.545-552
• Main Authors: Zuschlag, Annika, Skorka, Daniel, Hahn, Giso
• Format: Article
• Language: English
• Subjects: Boron; Carrier lifetime; Contamination; Current carriers; Defects; Degradation; Gallium; Gettering; High temperature; Illumination; Impurities; LeTID; multicrystalline; Passivity; Photovoltaic cells; Regeneration; silicon; Solar cells; Stellar mass; Sun
• ISSN: 1062-7995; 1099-159X
• DOI: 10.1002/pip.2832

Light and elevated temperature induced degradation (LeTID) affects significantly the performance of multicrystalline (mc) Si passivated emitter and rear cell (PERC) solar cells, and underlying mechanisms of LeTID are still unknown. In this work LeTID and following regeneration of an industrial mc‐Si PERC solar cell is compared to differently processed minority charge carrier lifetime samples under illumination (1 sun) and elevated temperature (75 °C). LeTID on cell level reveals the same kinetics compared to lifetime samples. Varying the processing sequence has a significant effect on LeTID of lifetime samples. Ungettered samples with fired SiNx:H surface passivation show a very strong LeTID and regeneration effect, with degradation kinetics being similar for all wafer areas irrespective of initial material quality. In contrast, regeneration sets in earlier in good quality areas. Differently gettered samples with lower contamination level than ungettered samples are less sensitive to LeTID, while overall degradation and regeneration behavior is strongly influenced by applied gettering sequences. Al‐gettered samples show a more pronounced degradation effect than P‐gettered samples, leading to the assumption that P‐gettering is more effective in the reduction of LeTID sensitive defects. If the gettering step is less effective, in lifetime samples after degradation a beginning regeneration effect could be observed. A model is presented, describing LeTID in boron as well as gallium doped mc‐Si being based on impurities that can be gettered and redistributed during high temperature steps. Using this experimental approach helps to clarify the underlying mechanisms of LeTID and leads to a better understanding of degradation and regeneration mechanisms in mc Si. Copyright © 2016 John Wiley & Sons, Ltd Light and elevated temperature induced degradation affects significantly the performance of multicrystalline silicon PERC solar cells, and the underlying mechanisms are still unknown. We show that all areas are affected, but effective gettering steps influence significantly the degree of degradation, with P‐gettering being more effective than Al‐gettering. A model is presented describing the degradation based on getterable and redistributable impurities.