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Tin (Sn)-based perovskites are very promising for the fabrication of low-toxicity lead-free perovskite solar cells (PSCs), but they suffer from easy oxidation of Sn2+ to Sn4+ which leads to poor performance. Herein, we report a facile solution method for the purification of SnI2 in Sn-based PSCs by toluene washing. We found that toluene can dissolve undesired SnI4 and retain the SnI2 source, which enabled us to fabricate efficient Sn-based PSCs with much-reduced harmful Sn4+ impurities. The as-prepared formamidinium tin iodide perovskite films have markedly improved film morphology, enhanced crystalline quality, increased carrier lifetime, etc. Ultimately, the best-performing solar cell obtained using toluene-purified SnI2 precursors delivers a promising power conversion efficiency of 10.70% and the efficiency even increases to 11.06% after nearly one month of storage in an N2 atmosphere. This work paves a facile way for overcoming the complicated purification of SnI2 for efficient Sn-based PSCs. [ABSTRACT FROM AUTHOR]