Regulating Energy Disorder For Efficiengt And Stable Sn-Pb Alloyed Perovskite Solar Cells

Single-junction Sn-Pb alloyed perovskite solar cells developed rapidly,and their power conversion efficiency（PCE）has reached 23.3%.Sn-Pb alloyed perovskite exhibits low exciton binding energy and high charge carrier mobility,more importantly,the bandgap can be flexibly tuned by changing the ratio of Sn and Pb.Sn-Pb alloyed perovskite has attracted much attention due to their suitable band gaps for single-and multi-junction tandem cells,but the easy formation of energy disorder due to the unconstrained oxidation of Sn²⁺and poor film quality still limits their photovoltaic performance and practical applications.Although several tactics have been exploited to enhance Sn-Pb alloyed perovskite films crystallization and restrain the oxidation of Sn²⁺to Sn⁴⁺,the devices performance and long-term stability are still worse than the Pb-based perovskite solar cells.Therefore,it remains a major challenge to achieve efficient and stable Sn-Pb alloyed PSCs.In this paper,1-bromo-4-（methylsulfinyl）benzene（BBMS）,as an addition,was introduced into the precursor solution containing Sn F₂ to prepare perovskite films and assemble complete devices,the optimal additive amount of BBMS was 0.5 mg/ml,which determined by the photovoltaic performance parameters of the devices.Subsequently,the perovskite films containing Sn F₂,0.5 mg/ml BBMS and Sn F₂ were noted as the control group and experimental group,respectively.From the perspective of energy disorder,a series of characterizations of perovskite films and devices have been performed.The results showed that BBMS and Sn F₂ greatly reduced the Urbach energy of perovskite films,largely restrained the oxidation of Sn²⁺and improved crystal quality.With the help of density functional theory calculations,we elucidated that hydrogen bonding and coordination bonding between BBMS and perovskite was responsible for the improved devices performance and stability.Benefiting from the reduced energy disorder,the carrier dynamics of the perovskite films was significantly optimized.Ultimately,a high efficiency of>22%was obtained for the Sn-Pb alloy-based solar cells treated by BBMS and Sn F₂.What’s more,the BBMS treated devices showed outstanding thermal stability,retaining 98%of its original efficiency after heating at 60℃for 2660 h under N₂.