Synergistic Defect Passivation by the Treatment of Ionic Liquids for Efficient and Stable Perovskite Solar Cells

The quality of perovskite films plays a crucial role in the performance of perovskite solar cells (Pero‐SCs) in terms of power conversion efficiency (PCE) and stability. Herein, an ionic liquid, tetra ‐butylammonium trifluoromethanesulfonate (denoted TBASF), is used to treat perovskite films. The tetra‐butylammonium cation (TBA + ) can bind the unreacted PbI 2 and form a low‐dimensional material on the surface of the perovskite. This membrane improves the water resistance of the perovskite film. Meanwhile, trifluoromethanesulfonate anion (SF − ) can passivate the uncoordinated Pb 2+ and stabilize I − on the perovskite surface, which is beneficial to the stability of the devices. After the treatment, the Pero‐SCs achieve a champion PCE of 22.80% and excellent stability in highly humid conditions.