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

An organic small molecule, 1-bromo-4-(methylsulfinyl)benzene (BBMS), was utilized to reduce the energy disorder of a Sn-Pb alloyed perovskite film via hydrogen bonding and coordination bonding interactions, and the resultant BBMS-treated device showed a high efficiency of over 22 % as well as outstanding long-term stability.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 SnF2 greatly reduced the Urbach energy of perovskite films, and largely restrained the oxidation of Sn2+ . 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 SnF2 . More importantly, the BBMS-treated devices demonstrated outstanding stability, retaining 98 % of its original efficiency after heating at 60 °C for 2660 h under N2 .