Polyethylene Glycol Polymer Scaffold Induced Intermolecular Interactions for Crystallization Regulation and Defect Passivation in FASnI3 Films

Tin (Sn)-based perovskites as promising alternatives of Pb analogues have attracted increased attention for their ideal optical bandgap, low toxicity, and high carrier mobility but are still subject to an uncontrollable crystallization process and Sn(II)-induced serious defects and thus poor photovoltaic performance and unsatisfactory stability. Herein, we propose a strategy to construct a fluid flexible polymer scaffold by introducing an eco-friendly polyethylene glycol (PEG) polymer with plenty of ether bond groups (C–O–C) in an FASnI3 precursor to regulate the nucleation and growth of perovskite grains and fabricate uniform and full coverage perovskite films with lower defect density. We demonstrate that the hydrogen-bond interactions between FA+ and C–O–C and Lewis acid–base complexation between uncoordinated Sn and C–O–C groups can effectively regulate film crystallization behavior, improve perovskite film coverage, and reduce defect state density. Importantly, PEG as a fluid flexible polymer scaffold during the annealing process can cross-link the adjacent perovskite grains and relieve the stress between grains. With this method, we obtain high-quality PEG-modified FASnI3 perovskite films with lager grain size, higher coverage without pinholes, lower trap state density, and higher carrier lifetime. The optimized device achieves an optimal PCE of 7.53% under reverse scan and the unencapsulated device maintains more than 90% of the initial PCE after aging for 720 h in a N2 glovebox.