Self-Assembled Superacid Monolayers on c-Si Provide Exceptional Surface Passivation and Low Contact Resistivity

Minimizing surface recombination is crucial for enhancing silicon solar cell passivation. Conventional dielectric materials require vacuum deposition and high-temperature annealing, increasing complexity and cost. This study explores Nonafluorobutane sulfonic acid (C₄HF₉O₃S), a superacid, as a passivation layer for silicon solar cells. Unlike traditional dielectrics, it eliminates the need for vacuum processing or high-temperature annealing while offering excellent passivation. Results show that the superacid forms a self-assembled monolayer on silicon, improving passivation and enabling efficient charge extraction. N-type silicon coated with the superacid achieves an effective lifetime exceeding 8.5 ms, and when combined with Al, it forms an interface with a contact resistivity as low as 5.75 mΩ.cm². Characterization and density functional theory (DFT) calculations confirm both chemical and field-effect passivation mechanisms, validating the monolayer's superior performance. When integrated into a full solar cell, the Nona layer enhances device performance, yielding a 3.05% absolute efficiency gain compared to the reference cell without Nona. This study introduces a cost-effective alternative to conventional dielectrics, simplifying processing while reducing production costs and CO₂ emissions, paving the way for sustainable, high-efficiency silicon solar cells.