Boron‐Doped Polysilicon Passivating Contacts Achieving a Single‐Sided J 0 of 4.0 fA/cm 2 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 (N 2 O/H 2 ) 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/cm 2 and a contact resistivity of 22 mΩ cm 2 . 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.