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'-pentafluorobutypimidazolium tetrafluoroborate (MFIM-2) ionic liquid and another two analogues were used as additives to study their interaction mechanism with the FAPbI(3) 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.

Automated summary

The study utilized MFIM-2 ionic liquid and two other analogues as additives to investigate their interaction mechanism with the FAPbI(3) perovskite layer. The results demonstrated that MFIM-2 effectively suppressed PbI2 crystal formation, increased grain size, reduced defect density, and improved photovoltage and efficiency, along with enhancing the devices' moisture stability. The additive strategy of polyfluoroalkylated imidazolium salt shows promise in extending the lifetime and enhancing the device performance of perovskite solar cells simultaneously.