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 DFPD 2 SnI 4 /FASnI 3 2D/3D perovskite films via a one-pot solution process. The good lattice matching between DFPD 2 SnI 4 and FASnI 3 perovskites and the preferential formation of the DFPD 2 SnI 4 precursor effectively regulate film crystallization and boost the oriented growth of FASnI 3 (h00) planes. Moreover, the robust DFPD 2 SnI 4 perovskites with hydrogen bonds in organic spacers are distributed along grain boundaries to stabilize the edge lattice of FASnI 3 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.