Optimization of high-efficiency hole-selective passivating contacts in p-type TOPCon solar cells approaching 26%: a comparative performance study

High-efficiency hole-selective passivating contacts are crucial for achieving high performance in solar cells via full-area charge extraction. In this study, we numerically simulated the hole-selective passivating contact using Al₂O₃ with MoO_x, NiO_x, WO_x, or CuO_x and applied it to the rear of a p-type tunnel oxide passivated contact (TOPCon) solar cell. Our investigation revealed that the ultrathin layer of Al₂O₃ with a 10⁻⁷ cm⁻² pinhole density serving as a tunneling layer, played a vital role in enhancing the hole selectivity of the simulated structures. We have optimized the best device structure with NiO_x as the back surface layer in the TOPCon solar cell. We have identified a thickness for the of 4 nm NiO_x layer, with a trap density to 10¹⁴ cm⁻³. The optimal thickness for the tunneling layer Al₂O₃ was found to be approximately 0.3 nm. We have obtained the highest efficiency of 25.89% in the p-type TOPCon device with NiO_x as the high efficiency hole selectivity, marking the highest performance among all oxide-based p-type TOPCon solar cells in our analysis. This study underscores the significant potential of the hole-selective passivating material Al₂O₃/NiO_x/Ag in full-area charge carriers selective layer for solar cells.