Enhancing the Photovoltaic Performance and Moisture Stability of Perovskite Solar Cells Via Polyfluoroalkylated Imidazolium Additives.

Although the power conversion efficiency of perovskite solar cells has reached 25.5%, their long-term stability is still a barrier to commercialization. In this work, 1-methyl-3-(3',3',4',4',4'-pentafluorobutyl)imidazolium tetrafluoroborate (MFIM-2) ionic liquid and another two analogues were used as additives to study their interaction mechanism with the FAPbI3 perovskite layer. The results reveal that MFIM-2 suppressed the formation of PbI2 crystals during crystallization, enlarged the grain size, and reduced the defect density, which led to an increased photovoltage of 1.12 V and efficiency of 19.4%. Furthermore, the moisture stability of the solar cell devices was also improved. Devices with MFIM-2 retained above 83% of the original value after 35 days in an atmosphere with about 25% relative humidity, and the perovskite film with MFIM-2 showed no phase transition in a 10 month aging process. These results demonstrate that the additive strategy of the polyfluoroalkylated imidazolium salt is a promising way for simultaneously extending the lifetime and improving the device performance of the perovskite solar cells.