Solvent engineering of LiTFSI towards high-efficiency planar perovskite solar cells

The performance and stability of perovskite solar cell (PSC) are inseparable from the quality of perovskite film, and the solvent engineering is being seemed as an effective strategy to enhance the properties of perovskite. Acetonitrile (ACN) is often used as a solvent to dissolve bis(trifluoromethane)sulfonimide lithium salt (LiTFSI), but ACN can corrode the perovskite film, which hinders the promotion of PSC efficiency and durability. Herein, a solvent engineering approach is implemented to search for suitable alternatives for ACN to abate the degradation of the perovskite films. The results demonstrate that isopropanol (IPA) with smaller polarity can effectively dissolve LiTFSI and slow down the degradation of the perovskite layer compared with ACN, which can result in the reduction of defects as well as the nonradiative recombination. Consequently, the devices using LiTFSI/IPA as additive achieve superior power conversion efficiencies (PCEs) with relatively less hysteresis effects and get a champion PCE of 19.43%, while the device using LiTFSI/ACN gets an inferior PCE of 17.12%.