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 PbI2 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 Pb2+ 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.