Reducing Energy Disorder for Efficient and Stable Sn−Pb Alloyed Perovskite Solar Cells.

Abstract Sn−Pb alloyed perovskites have drawn considerable attention because of their appropriate band gap for both single‐junction and multi‐junction tandem photovoltaics, but the easy‐formation of energy disorder still limits their practical applications. Here, we report that the combination of 1‐bromo‐4‐(methylsulfinyl) benzene (BBMS) and SnF 2 greatly reduced the Urbach energy of perovskite films, and largely restrained the oxidation of Sn 2+ . With the help of density functional theory calculations, we clarified the interactions between BBMS and perovskite were responsible for the improvements. As a result, a high efficiency of >22 % was obtained for the Sn−Pb alloy‐based solar cells treated by BBMS and SnF 2 . More importantly, the BBMS‐treated devices demonstrated outstanding stability, retaining 98 % of its original efficiency after heating at 60 °C for 2660 h under N 2 .