Improving Performance of Lead-Free Formamidinium Tin Triiodide Perovskite Solar Cells by Tin Source Purification

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, Sn4+ 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 SnI2 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 SnF2 as the only additive, comparable to and even higher than the device fabricated from SnI2 with a high purity of 99.999%.