Piperazine Suppresses Self-Doping in CsSnI₃ Perovskite Solar Cells

Tin-based halide perovskite materials are promising candidates for lead-free halide perovskite solar cells. However, they suffer from poor device reproducibility and limited overall power conversion efficiencies due to their tendency to become semimetallic from p-type defect states. Herein, we demonstrate an effective approach to address this issue via the addition of piperazine to the precursor solution of tin-based halide perovskite films, to suppress the undesirable p-doping of CsSnI 3 films. Piperazine is found to significantly reduce the conductivity of CsSnI 3 films, improve the film coverage, and at the same time suppress the crystallization of excess SnI 2 . Consequently, short-circuit behaviors are eliminated, with significantly improved CsSnI 3 solar-cell performance. Moreover, the effects of incorporating SnCl 2 and SnF 2 into the CsSnI 3 devices were investigated in conjunction with addition of piperazine to achieve CsSnI 3 devices with a maximum power conversion efficiency of 3.83%.