Insights into nitrogen-incorporated nano silicon oxide on the passivation performance of p-type tunneling oxide passivating contact structures

Although n-type tunneling oxide passivating contact (TOPCon) solar cells dominate the mainstream crystalline silicon (c-Si) technologies in the photovoltaic market, p-type TOPCon solar cells also hold great potential to advance TOPCon technology and may achieve efficiencies comparable to heterojunction solar cells in the future due to their unique passivation method. In this study, we investigate a method for introducing nitrogen (N) atoms into the SiOx layer using N2O/NH3 mixture gas, aiming to reduce B diffusion and activation at the SiOx/poly-Si interface and within the c-Si substrate. Our findings indicate that while incorporating N atoms into SiOx layers prepared with the N2O/NH3 gas mixture significantly suppresses B diffusion within the c-Si substrate and reduces B activation at both the SiOx/poly-Si interface and within the c-Si substrate, the passivation performance of p-type TOPCon with N-doped SiOx remains relatively low. In contrast, p-type TOPCon with SiOx prepared using pure N2O demonstrates significantly higher passivation, achieving an implied open-circuit voltage (iVoc) of 723 mV and a low single-sided recombination current density (J0,s) of 9.6 fA/cm2. This disparity is attributed to the presence of N in SiOx, which leads to a thinner SiOx layer, reduced Si4+ content, and increased surface defects, thereby counteracting the beneficial effects of N doping. This study provides comprehensive insights into the impact of N-doped SiOx on the passivation performance of p-type TOPCon, along with the underlying mechanisms, providing valuable insights for enhancing p-type TOPCon passivation.