Bi-Linkable Reductive Cation as Molecular Glue for One Year Stable Sn-Based Perovskite Solar Cells

Tin (Sn)-based perovskites as the most promising alternative for Pb analogues have been extensively investigated due to their eco-friendly nature, suitable bandgap, and theoretically superior optoelectronic properties. However, Sn-based perovskite solar cells (PSCs) still suffer from poor stability due to the presence of large amount of defect trap-states in the perovskite film including uncoordinated Sn2+ and dangling organic bond at the grain boundaries (GBs). Herein, we introduced a bilinkable reductive cation, formamide (FM) with both formyl group and amine group, into formamidinium tin triiodide (FASnI3) to serve as molecular glue for enhancing the performance and stability of its PSCs. FM is found to interact simultaneously with uncoordinated Sn2+ and dangling FA in FASnI3, which glues the precursors and enlarges the colloidal size in precursor solution, leading to enlarged grain size, preferred orientation, reduced defect density, and improved stability of the prepared film. As a result, PSCs device based on 10% FMI achieves a 40% enhanced PCE from 5.51% to 7.71% with prominent enhanced stability, which retains its 90% initial PCE after stored in N2 for one year without encapsulation. This work provides insights into improving the stability of Sn-based perovskite film, which could promote the development of long-term stable Sn-based PSCs.