Cation and Octahedral Synergistic Regulation for Stable FAPbI Perovskite Solar Cells.

Formamidinium lead iodide (FAPbI) perovskite, one of the most promising light-absorbing materials, faces substantial stability issues, including FA organic component volatilization and undesirable phase transition between corner-sharing and face-sharing [PbI] octahedra. Especially, the asymmetric hydrogen bonding, arising from oriented and irregularly spinning FA cation, accelerates these transformations, compromising both the efficiency and long-term stability of FAPbI PSCs. Herein, a robust strategy is reported to stabilize FAPbI perovskite by using tricyclohexylphosphine trifluoromethanesulfonate (CyPHSOCF ) to strengthen hydrogen bonds within FA and alleviate octahedral deformation. The hydrogen-bonding capacity of CyPH effectively constrains and stabilizes orientated FA through strong hydrogen bonds (F─H, N─H), while the strong electronegative SOCF ion modifies [PbI] octahedral deformation by diversified covalent bonds (Pb─F, Pb─O) and releases the internal stress of the lattice. As such, the resulting FAPbI demonstrates mitigated organic volatilization and suppressed phase transition, significantly enhancing phase stability under thermal/humidity stress conditions. Moreover, because of co-regulated FA cation and octahedral lattice, FAPbI perovskite exhibits improved carrier dynamics and better matched energy-level alignment with carrier transport layers. The optimized FAPbI-based PSCs deliver an impressive efficiency of 25.93% and exhibit exceptional stability, retaining 97% of initial efficiency after over 1500 h maximum power point tracking.