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

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 PbI2 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.