Optimizing Crystallization, Defects, and Toughness with an Amphiphilic Molecule for High‐Performance Rigid and Flexible Perovskite Solar Cells

Abstract Although flexible perovskite solar cells (FPSCs) hold broad application prospects, their suboptimal power conversion efficiency (PCE) and stability that stemming from insufficient crystallinity and poor mechanical robustness, remain the primary challenges impeding commercialization. Herein, a judiciously selected amphiphilic molecule, 1‐[3,5‐bis(trifluoromethyl)phenyl]biguanide hydrochloride (BtFBG·HCl), is integrated into the perovskite precursor for crystallization regulation, defect passivation, and interface toughening simultaneously. The BtFBG·HCl molecules form intermediate phases with perovskite components to retard crystallization kinetics, while simultaneously passivating diverse defects through their electro‐positivity and ‐negativity groups, thereby yielding high‐quality crystals with suppressed non‐radiative recombination. Moreover, the extruded BtFBG·HCl acts as a robust interfacial bridge between SnO 2 and the perovskite layer, performing dual functions of interface toughening and structural stabilization of the device. Ultimately, the optimized rigid and flexible devices achieve excellent PCEs of 25.61 and 24.29%, accompanied by greatly improved operational stability and mechanical durability, with retaining over 90% of their initial PCEs for 1330 h maximum power point tracking in N 2 , 1000 h storage in 45 ± 5% relative humidity, 1200 h aging under continuous heating stress, and 5000 continuous bending cycles, respectively. This work may provide a new avenue for advancing efficient, stable, and durable FPSCs in the future.