Improved efficiency of methylammonium-free perovskite thin film solar cells by fluorinated ammonium iodide treatment

Abstract Volatile, CH3NH3+-free, [CH(NH2)2]0.9Cs0.1PbI3 organic-inorganic perovskite thin films were treated with fluorinated ammonium iodide {4-fluoro-phenethylammonium iodide (4F-PEAI)} solution and thin two-dimensional (4F-PEA)2PbI4 films were formed on the surface, resulting in a significant improvement in photoluminescence intensity. When applied to low-temperature-processed PSCs with planar structure, untreated PSCs exhibited PCEs of 18.6% and 17.0% during reverse and forward scanning, respectively. The PSCs treated with 4F-PEAI showed improved open-circuit voltage, fill factor, and PCEs of 20.6% and 18.5% during reverse and forward scanning, respectively.