Indium Iodide Additive Realizing Efficient Mixed Sn─Pb Perovskite Solar Cells

Abstract Low‐bandgap mixed tin (Sn)‐lead (Pb) perovskite solar cells promise efficiency beyond the pure‐Pb ones. However, the difference in the interaction rate of SnI 2 and PbI 2 with organic salts causes spatial distribution heterogeneity of Sn 2+ and Pb 2+ in mixed Sn─Pb perovskite layers. This causes a Sn‐rich surface, which can trigger more severe Sn 2+ oxidation and nonradiative recombination. A strategy, of introducing indium ion (In 3+ ) into the perovskite precursor solution to compete with Sn 2+ when reacting with organic salts is developed. Therefore, the nucleation and crystallization of perovskite films are well‐controlled, leading to improved film quality with a more balanced Sn/Pb ratio on the film surface. Additionally, In 3+ has a lower reduction potential compared to Sn 2+ which can generate an extra energy barrier for Sn 2+ oxidation. The improved film quality and reduced surface oxidation result in accelerated electron transfer and reduced carrier recombination rate. The modified devices achieve a power conversion efficiency (PCE) of 23.34%, representing one of the highest PCEs in mixed Sn─Pb solar cells made with PCBM.