Radical Molecular Network‐Buffer Minimizes Photovoltage Loss in FAPbI₃ Perovskite Solar Cells

Abstract Formamidinium lead iodide (FAPbI₃) perovskite solar cells (PSCs) hold immense potential for high‐efficiency photovoltaics, but maximizing their open‐circuit voltage ( V OC ) remains challenging. Targeting the inherently stable {111} c ‐dominant facets is a promising approach for enhancing stability, but their formation typically suffers from high defect densities and disordered growth. This study introduces a novel approach using an in situ polymerizable radical molecule, ATEMPO, as an additive to address these issues. ATEMPO preferentially interacts with the {111} c perovskite facets, guiding their growth and forming a “radical molecular network‐buffer” upon polymerization. The network effectively mitigates lattice strain, suppresses defect formation, enhances charge transport via redox‐mediated hopping, and provides a hydrophobic barrier, significantly improving moisture resistance. This strategy yields high‐quality, {111} c ‐oriented FAPbI₃ films, leading to a champion PCE of 25.28% with a remarkably high V OC of 1.203 V, corresponding to an energy loss ( E loss ) of only 0.297 eV, among the highest V OC reported for FAPbI₃‐based PSCs. Furthermore, a mini‐module fabricate with an active area of 12.5 cm 2 achieve a high PCE of 21.39%. the work paves the way for developing high‐performance, stable PSCs with minimized photovoltage loss. Furthermore, it offers a promising strategy to enhance device longevity and address environmental concerns.