Ionic‐Liquid‐Assisted Fabrication of High‐Performance Methylammonium‐Free Perovskite Solar Cells via Smoothed‐Interface Engineering

A judicious modification of the buried interface can enhance the quality of perovskite films and reduce non‐radiative recombination losses, particularly in methylammonium (MA)‐free perovskite solar cells (PSCs). In this study, the ionic‐liquid 1,3‐dimethylimidazolium methanesulfonate (DMIMMeSO4) is employed, characterized by its high ionic conductivity and excellent thermal stability, to regulate the perovskite/SnO2 interface. The nitrogen component in DMIMMeSO4 can interact with Sn4+ through Lewis acid–base interactions, effectively passivating defects associated with tin and suppressing the formation of oxygen vacancies, leading to reduced non‐radiative recombination of charge carriers. In addition, [MeSO4]− can also form coordination bonds with PbI2, creating a better perovskite film with smoothed interface. Moreover, DMIMMeSO4 also optimize the energy‐level alignment, thereby reducing the charge‐transfer barrier and enhancing charge‐extraction efficiency. As a result, power conversion efficiency of 23.91% is achieved by MA‐free PSCs modified with DMIMMeSO4. Furthermore, after 1000 h of ambient air storage, devices that are not encapsulated maintaine over 90% efficiency. In all of these results, it is clearly indicated that interface modulation based on ionic‐liquid‐assisted smoothed‐interface engineering is an effective approach for obtaining high‐performance PSCs.