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 CsSnI3 films. Piperazine is found to significantly reduce the conductivity of CsSnI3 films, improve the film coverage, and at the same time suppress the crystallization of excess SnI2. Consequently, short-circuit behaviors are eliminated, with significantly improved CsSnI3 solar-cell performance. Moreover, the effects of incorporating SnCl2 and SnF2 into the CsSnI3 devices were investigated in conjunction with addition of piperazine to achieve CsSnI3 devices with a maximum power conversion efficiency of 3.83%.