Protic ionic liquid assisted solution processing of lead halide perovskites with water, alcohols and acetonitrile

A major obstacle and persisting challenge towards safe and sustainable industrial scale processing and commercialization of perovskite based (opto) electronic devices including solar cells lies in the essential need of strongly coordinating toxic solvents such as N, N-dimethylformamide (DMF) in the preparation of perovskite precursor inks. In this work, we present novel ink systems for perovskite precursors composed of protic ionic liquids (PILs) based on methylammonium cation and carboxylate anion and their binary blends with water, alcohols and acetonitrile for solution processing of CH3NH3PbX3 (X = I, Br). Among the investigated ink-systems, new PIL methylammonium propionate and its blends were identified as the most promising candidates in terms of chemical stability and compatibility for single- and two-step solution processing of the perovskite materials. Multi-cation mixed halide perovskites solar cells prepared with PIL/acetonitrile solvent system showed power conversion efficiency in excess of 15%.