Constructing Synergistic Interactions Between Multi‐Hydroxyl Molecules and Perovskite to Alleviate Mechanical‐Thermal Mismatch for Achieving High‐Performance Flexible Solar Cells

Abstract Due to the presence of residual tensile strain, as well as the inherent brittleness and film quality of the perovskite, flexible perovskite solar cells (f‐PSCs) face ongoing challenges in stability. To address these issues, this study introduces a multi‐hydroxyl regulated stress management strategy for f‐PSCs. Three hydroxyl‐substituted phenylacetic acids (p‐hydroxyphenylacetic acid, 3,4‐dihydroxyphenylacetic acid, and 2‐(3,4,5‐trihydroxyphenyl)acetic acid) are incorporated into the perovskite films to investigate the significance of their interaction modes with perovskite in regulating f‐PSC performance. These multi‐hydroxyl molecules, through their progressively enhanced synergistic interactions with the perovskite, effectively promote greater energy dissipation during stress deformation, reducing the Young's modulus of the perovskite by 11.1% and decreasing the thermal expansion coefficient of perovskite film by 38.5%, thereby improving the mechanical strength of the f‐PSCs. Additionally, the multi‐hydroxyl molecules regulate the excess PbI 2 during the fabrication process of perovskite, enhancing the film quality and optimizing the energy level alignment. As a result, the inverted f‐PSCs achieved a champion power conversion efficiency (PCE) of 25.01%. These devices demonstrated excellent mechanical and thermal stability, retaining 90% of their original PCE after 3000 bending cycles, and maintaining 83% of their initial PCE after continuous heating at 85 °C for 1000 h.