Ionic liquid-assisted green solution approach for high-performance Cu2ZnSn(S,Se)4 thin film solar cells

In this research, a facile and environmentally friendly solution approach is developed to deposit Cu2ZnSn(S,Se)(4) thin films by addition of n-butylammonium butyrate ionic liquid. n-Butylammonium butyrate plays a critical role in solution deposition of Cu2ZnSnS4 precursor thin film. We find that liquid n-butylammonium butyrate can dissolve a number of metal oxides, including Cu2O, ZnO, and SnO as well as various metal chlorides, metal nitrates and metal acetates. Smell-free Cu2ZnSnS4 precursor solution is synthesized by dissolving Cu2O, ZnO, SnCl2 and thiourea in an ethanol solution of n-butylammonium butyrate. Thermally degradable n-butylammonium butyrate can be completely removed by a low-temperature sintering process, forming high quality Cu2ZnSnS4 nanoparticle thin film. A power conversion efficiency of 8.79% is obtained by this facile and green solution approach.