Achieving over 20% efficiency in HTL-free carbon-electrode perovskite solar cells via multifunctional surface engineering

is employed as a post-treatment additive for perovskite films in HTM-free carbon-electrode perovskite solar cells (C-PSCs) to achieve multiple functions, including passivating surface defects, optimizing interfacial energy levels, and enhancing the moisture resistance. Consequently, the optimized device achieves a highest power conversion efficiency (PCE) of 20.26%, one of the best efficiencies reported for C-PSCs.