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 N₂for 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.