Phase-Pure 2D/3D Tin-Based Perovskite Films for Solar Cells

Metastable quasi-2D perovskite films exhibit decreased light absorption capacity and degraded charge transfer kinetics, undergoing irreversible changes in composition and structure under external stresses. Developing high-quality phase-pure 2D/3D perovskite films is significant but challenging for perovskite photovoltaics. Herein, 4,4-difluoropiperidine (DFPD⁺) cations with a high positive charge density at the cationic terminal are introduced to tightly couple with Sn–I components to construct phase-pure DFPD₂SnI₄/FASnI₃ 2D/3D perovskite films via a one-pot solution process. The good lattice matching between DFPD₂SnI₄ and FASnI₃ perovskites and the preferential formation of the DFPD₂SnI₄ precursor effectively regulate film crystallization and boost the oriented growth of FASnI₃ (h00) planes. Moreover, the robust DFPD₂SnI₄ perovskites with hydrogen bonds in organic spacers are distributed along grain boundaries to stabilize the edge lattice of FASnI₃ grains, inhibit defect generation, and improve environmental stability. The optimized devices deliver an optimal power conversion efficiency of 13.34% and exhibit enhanced storage and operation stability.