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 (C 4 HF 9 O 3 S), 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.cm 2 . 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 CO 2 emissions, paving the way for sustainable, high‐efficiency silicon solar cells.