TOPCon Solar Cell Degradation via Pinhole Nucleation

Reducing recombination at the interfaces is crucial to further improve the performance of silicon solar cells. One of the most promising cell designs, TOPCon cells suppress surface recombination by forming an ultra-thin SiOx passivating layer on the c-Si wafer. Efficient carrier extraction through the oxide layer via exponentially suppressed quantum tunneling is achieved by making the SiOx layer ultra-thin, ~1.5 nm. However, experiments indicate that at such extreme thinness, Si-rich pinholes start to pierce the SiOx layers that can act as regions of enhanced recombination. In this paper we demonstrate that over time the non-stoichiometric SiOx layer phase separates into Si-rich regions piercing a SiO2 layer. We believe that this is a probable mechanism of pinhole formation. We also report early indications that adding hydrogen increases this pinhole formation tendency.