Enhanced Passivation of Boron‐Doped Polysilicon Passivated Contacts With a Single‐Sided J ₀ of 2.8 fA/cm ² by Dual‐Layer Silicon Oxide Structure

ABSTRACT Boron (B)‐induced interface defects remain a key bottleneck that limits the passivation quality of p‐type tunnel oxide passivating contacts (TOPCon), thereby constraining the efficiency of back‐contact TOPCon (TBC) solar cells. Here, we introduce a dual‐layer silicon oxide (SiO _x ) design that forms a SiO _x /p ⁺ poly‐Si/SiO _x /p ⁺⁺ poly‐Si passivation structure. The additional SiO _x layer effectively mitigates interlayer stress, preventing blistering during high‐temperature annealing, and increases interfacial hydrogen concentration to suppress defect states. Through systematic optimization of the preparation and annealing conditions of the outer SiO _x layer, the p‐type TOPCon structures achieve outstanding passivation on n‐type wafers, with a single‐sided recombination current density ( J _0,s ) of 2.8 fA/cm ² and an implied open‐circuit voltage ( iV _oc ) of 741 mV. This represents one of the best results reported to date, surpassing the current industrial records. Compared with the previous single‐layer SiO _x designs, this configuration delivers a substantial improvement of passivation while simultaneously enabling a reduced poly‐Si thickness. Numerical simulations further demonstrate a 0.18% absolute efficiency gain in TBC cells with the dual‐layer structure compared to single‐layer configuration. This work demonstrates that a dual‐layer SiO _x architecture effectively lowers interface defect density and enhances p‐type TOPCon passivation, underscoring its significant potential for industrial application in high‐efficiency TBC cells.