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.