A Strategy to Produce High Efficiency, High Stability Perovskite Solar Cells Using Functionalized Ionic Liquid‐Dopants

Functionalized imidazolium iodide salts (ionic liquids) modified with CH 2 CHCH 2 , CH 2 CCH, or CH 2 CN groups are applied as dopants in the synthesis of CH 3 NH 3 PbI 3 ‐type perovskites together with a fumigation step. Notably, a solar cell device prepared from the perovskite film doped with the salt containing the CH 2 CHCH 2 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 CH 2 CCH and CH 2 CN groups result in perovskite layers that lead to solar cell devices with similar or lower power conversion efficiencies than the dopant‐free cell.