Functionalized imidazolium iodide salts (ionic liquids) modified with -CH2-CH=CH2, -CH2C equivalent to CH, or -CH2C equivalent to N groups are applied as dopants in the synthesis of CH3NH3PbI3-type perovskites together with a fumigation step. Notably, a solar cell device prepared from the perovskite film doped with the salt containing the -CH2-CH=CH2 side-chain has a power conversion efficiency of 19.21%, which is the highest efficiency reported for perovskite solar cells involving a fumigation step. However, doping with the imidazolium salts with the -CH2C equivalent to CH and -CH2C equivalent to N groups result in perovskite layers that lead to solar cell devices with similar or lower power conversion efficiencies than the dopant-free cell.