Effects of Organic Cations on Carrier Transport at the Interface between Perovskites and Electron Transport Layers in (FA,MA)SnI3 Solar Cells

Charge extraction at carrier transport layers adjacent to perovskites is crucial for the optimization of perovskite solar cells. In particular, Sn-perovskites with no lead elements are known to struggle from charge extraction. Here, we report the effects of organic ligands such as FA and MA (FA = HC­(NH2)2 +; MA = CH3NH3 +) on charge separation at the interface between electron transport layers and perovskites. TiO2 mesoporous covering the tin-perovskites show significant changes in the electronic structure and built-in potentials according to the ratio of FA to MA. Through a local probe with potential and current mapping, charge transport has been intensively examined. The best cell in this study is obtained as 5.37% at FA/MA = 3:1 with only iodine at the halide sites. Even though the value itself is not comparable with lead halides, it could pave a new direction to improve lead-free perovskite solar cells.