The impact of surface polarisation on the degradation of tunnel oxide passivating contacts in silicon solar cells

Tunnelling oxide passivating contact (TOPCon) silicon solar cells have risen to the mainstream in photovoltaic energy deployment worldwide. Enhancing the reliability and longevity of TOPCon solar modules will ensure the continuous growth of solar power on a multi-terawatt scale. This work investigates the mechanisms involved in surface-related degradation (SRD) in TOPCon passivating schemes, specifically focusing on two aspects. Firstly, TOPCon contacts can exhibit firing-induced instabilities that correlate with increased recombination from degradation in surface passivation. Secondly, we explored the influence of surface polarisation, induced by corona charging, on SRD by subjecting samples to various light soaking and annealing conditions. The results demonstrate that the presence of an electric field at the surface accelerates SRD, particularly under positive corona charge conditions. Effective lifetimes on symmetrical TOPCon specimens were significantly reduced and correlated to surface passivation degradation under positive polarisation. The degradation observed supports previous findings where charged hydrogen ions, which respond readily to electric fields, play a critical role in the observed degradation. This study contributes to the body of evidence aimed at understanding hydrogen kinetics at the SiOx/c-Si interface, providing valuable insights into the mechanisms driving SRD in TOPCon solar cells, with implications for enhancing the stability and performance of silicon solar panels.