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Lead (Pb)‐free tin (Sn)‐based perovskite solar cells (PSCs) have been recognized as one of the solutions to the toxicity of Pb and drawn considerable attention. However, Sn 4+ caused by oxidation or incomplete reduction during synthesis severely deteriorates the device performance. Herein, the authors firstly reveal that the addition of Sn powder into the FASnI 3 (FANH 2 CHNH 2 + ) precursor solution prepared from SnI 2 with 99% purity leads to great improvement of the device performance with a maximum power conversion efficiency (PCE) of 6.75%, which is, to the best of their knowledge, the highest efficiency among those of the FASnI 3 ‐based PSCs with SnF 2 as the only additive, comparable to and even higher than the device fabricated from SnI 2 with a high purity of 99.999%.
Gu et al. (2018) studied this question.