Importance and Advancement of Modification Engineering in Perovskite Solar Cells

Perovskite solar cells (PSCs) have achieved excellent power conversion efficiencies comparable to those of silicon‐based cells. However, there are still many deficiencies in device stability, performance reproducibility, and hysteresis effect. Some surface modifiers and additives have been introduced in the last few years. Among them, organic ionic materials have attracted much attention due to their advantages of wide selection, strong electronic interaction, and good solubility. In this review, various ionic materials utilized in PSCs during recent several years are summarized. Their mechanisms to improve the device performance are thoroughly discussed, including the defect passivation on the surfaces and grain boundaries, improvement of energy‐level alignment, modification of surface morphology, modulation of crystal structure, stabilization of perovskite phase, suppression of ion migration, protection against moisture, and formation of low‐dimensional perovskite species. Finally, an outlook on the future research trends is proposed.