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

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 cm² 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.