In Situ Polymerization Controlled Growth of Perovskite via Benzoic Acid Crosslinking Agent for Highly Efficient and Mechanically Robust Flexible Perovskite Solar Cell.

The controlled growth of perovskite on flexible substrates is essential for achieving highly efficient and stable flexible perovskite solar cells (FPSCs). Herein, a novel strategy of 4-hydroxybenzoic acid (4-HBA) is developed to regulate the crystallization dynamics of perovskite. In situ cross-linking network of 4-HBA provided an excellent formwork for high-quality perovskite growth by controlling excessive nucleation and prolonging crystallization. Grain boundary defects, residual stress, and Young's modulus of the perovskite film are greatly decreased. The dynamic hydrogen bonds between free hydroxyl groups and carboxyl groups/halogen enhanced the self-healing ability of perovskite film. The electrostatic interaction between the benzene ring of 4-HBA and uncoordinated Pb²⁺, coupled with π-π stacking of 4-HBA, enhanced the conductivity of perovskite film. As a result, the optimal power conversion efficiency (PCE) of rigid perovskite solar cells (PSCs) and FPSCs reached 24.76% and 22.73%, respectively. The FPSCs retained 91% of initial efficiency after 10 000 bending cycles at 5 mm radius. The FPSCs after 4000 bends at 2 mm radius, regained 89% original PCE with 60℃ heating. The unencapsulated FPSCs retained 83% original PCE after 1000 h of Air Mass 1.5 Global illumination. This work offered an efficient strategy for high-efficiency and robust FPSCs.