Boron-Doped Polysilicon Passivating Contacts Achieving a Single-Sided J0 of 4.0 fA/cm2 Through a Two-Step Oxidation Process

Tunnel oxide passivating contacts with boron-doped polysilicon (i.e., p-type TOPCon) hold substantial potential for application in the devices with higher efficiency, that is, back-junction (BJ) or all-back-contact (BC) solar cells. However, achieving excellent passivation for p-type TOPCon remains a challenge. In this study, we propose a two-step oxidation (TSO) method using low-temperature oxidated silicon oxide (SiO_x) with a post-nitrous oxide/hydrogen plasma (N₂O/H₂) treatment to prepare high-quality ultrathin SiO_x and achieve highly passivated p-type TOPCon. Through optimization of plasma treatment pressure and annealing conditions, we achieve excellent passivation and contact properties of double-sided p-type TOPCon, with an implied open-circuit voltage (iV_oc) of 740 mV, marking the highest publicly reported value for p-type TOPCon. Additionally, we achieve a single-sided saturation recombination current density (J_0,s) of 4.0 fA/cm² and a contact resistivity of 22 mΩ cm². Semi-finished back-junction solar cell incorporating TSO-SiO_x exhibits excellent passivation performance with an iV_oc of 744 mV, demonstrating the feasibility of device applications. The two-step oxidation method proposed in this work enhances the passivation performance of p-type TOPCon, offering a technique with significant potential for industrial applications in preparing high-quality p-type TOPCon.