Well‐Defined Fullerene Bisadducts Enable High‐Performance Tin‐Based Perovskite Solar Cells

Abstract Tin‐based perovskite solar cells (TPSCs) are attracting intense research interest due to their excellent optoelectric properties and eco‐friendly features. To further improve the device performance, developing new fullerene derivatives as electron transporter layers (ETLs) is highly demanded. Four well‐defined regioisomers (trans‐2, trans‐3, trans‐4, and e) of diethylmalonate‐C 60 bisadduct (DCBA) are isolated and well characterized. The well‐defined molecular structure enables us to investigate the real structure‐dependent effects on photovoltaic performance. It is found that the chemical structures of the regioisomers not only affect their energy levels, but also lead to significant differences in their molecular packings and interfacial contacts. As a result, the devices with trans‐2, trans‐3, trans‐4, and e as ETLs yield efficiencies of 11.69%, 14.58%, 12.59%, and 10.55%, respectively, which are higher than that of the as‐prepared DCBA‐based (10.28%) device. Notably, the trans‐3‐based device also demonstrates a certified efficiency of 14.30%, representing one of the best‐performing TPSCs.