Crystallization Kinetics Modulation of FASnI 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 lower efficiency. Here, we disclose a key finding to modulate the crystallization kinetics of FASnI through a non-classical nucleation mechanism based on pre-nucleation clusters (PNCs). By introducing piperazine dihydriodide to tune the colloidal chemistry of the FASnI 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, resulting in a high-quality perovskite film with lower defect density. This PNCs-based method has led to a conspicuous photovoltaic performance improvement for FASnI -based PSCs, delivering an impressive efficiency of 11.39 % plus improved stability.