1-Dodecyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide Interface Design  for Stable and Effective Perovskite Solar Cells

Power conversion efficiency (PCE) is limited by the high density of defects and poor energy level alignment of the SnO 2 /perovskite (PVK) buried interface in perovskite solar cells (PSCs). Herein, a synergistic molecular interface engineering strategy is designed by using an ionic liquid, 1-dodecyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide salt (DMIMTFSI) to modify this critical interface. The strong electron-withdrawing TFSI − anion induces a downward shift of the conduction band of SnO 2 , thereby optimizing energy level alignment and facilitating electron extraction. Meanwhile, the DMIM + cation passivates interfacial defects through robust chemical interactions with Pb 2+ and I − ions. Furthermore, the long alkyl chain of DMIMTFSI templates the formation of an ordered porous PbI 2 morphology, which improves the crystallinity of the overlying PVK film. The DMIMTFSI modification reduces the trap-state density by 31.86%, prolongs the carrier lifetime by 39.42%, and increases the built-in potential from 0.95 to 1.02 V. Therefore, the DMIMTFSI-modified device achieves a PCE of 24.14%, significantly outperforming the pristine device of 22.34%. The unencapsulated modified device retained 87% of its initial PCE after being stored for 1000 h under ambient conditions, demonstrating excellent environmental stability. This work provides a viable multifunctional interface engineering pathway toward high-performance and stable PSCs. Graphical The insertion of the ionic liquid of 1-dodecyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (DMIMTFSI) into the interface of perovskite/tin oxide significantly improves the power conversion efficiency of perovskite solar cells from 22.34% to 24.14%. This is due to the synergistic effect of defect passivation, energy level modulation, and crystal growth promotion of DMIMTFSI.