The Chemistry of the Passivation Mechanism of Perovskite Films with Ionic Liquids

Passivation of perovskite films by ionic liquids (ILs)improves the performance (efficiency and stability) of perovskitesolar cells (PSCs). However, the role of ILs in the passivation ofperovskitefilms is not fully understood. Here, we report thereactions of commonly used ILs with the components ofperovskites. The reaction of ILs with perovskite precursors (PbI2and methylammonium iodide or formamidinium iodide) in a 1:1:1molar ratio affords one-dimensional (1D) salts composed of the ILcation interspersed along infinite 1D polymeric [PbI3]-nchains. If the IL is applied in excess, the resulting crystal is composed of sixcations surrounding a discrete [Pb3I12]6-cluster. All the isolated salts were unambiguously characterized by single-crystal X-ray diffraction analysis, which also reveals extensive hydrogen-bonding interactions