Crystallization Kinetics Modulation of FASnI3 Films with Pre-nucleation Clusters for Efficient Lead-free Perovskite Solar Cells.

Tin halide perovskites are rising as promising materials for lead-free perovskite solar cells (PSCs). However, the crystallization rate of tin halide perovskites is much faster than the lead-based analogs, leading to more rampant trap states and much lower power conversion efficiencies. Here, we disclose a key finding to modulate the crystallization kinetics of FASnI 3 (FA: formamidinium) through a non-classical nucleation mechanism based on pre-nucleation clusters (PNCs). By introducing piperazine dihydriodide to tune the colloidal chemistry of the FASnI 3 perovskite precursor solution, stable clusters could be readily formed in the solution before nucleation. These pre-nucleation clusters act as intermediate phase and thus can reduce the energy barrier for the perovskite nucleation. The precursor solution enriched with such intermediate PNCs could be readily converted to a high-quality perovskite film with a much lower defect density. This PNCs-based method has led to a conspicuous photovoltaic performance improvement for FASnI 3 -based PSCs, delivering an impressive efficiency of 11.39% plus improved stability.