Polarize the Solvent to Regulate the Intermediate Phase and Dynamic Crystallization of Perovskite Films

Perovskite solar cells (PSCs) have demonstrated substantial potential due to their superior optoelectronic performance, but rapid and often poorly controlled crystallization during dynamic solution processing frequently leads to defective crystal growth and compromised film quality. Herein, we introduce a strategy utilizing polar polymers to intricately regulate solvent polarity and evaporation kinetics, thereby modulating the dynamics of perovskite crystallization. Particularly, the strongly polarized, high-population fluorinated groups in poly(pentafluorostyrene) strongly interact with solvent molecules in the precursor solution, stabilizing the solvent-containing intermediate phase and controlling the exfoliation of solvent molecules during perovskite crystallization. Direct imaging by scanning transmission electron microscopy reveals the structure of the intermediate phase, and in situ optical studies demonstrate that the regulated crystallization suppresses defect formation and improves film quality. Consequently, inverted PSCs fabricated via this new solvent engineering strategy achieve an efficiency of 26.4% and retain 92% after 1000 h of continuous illumination, underscoring the effectiveness of this strategy of polarizing the solvent.