Efficient Cu 2 ZnSnS 4 solar cells spray coated from a hydro-alcoholic colloid synthesized by instantaneous reaction

Efficient copper zinc tin sulphide (Cu 2 ZnSnS 4 ) thin film photovoltaic devices were fabricated with a new, fast, and simple preparation method using environmentally friendly solvents. Our process is based upon a versatile and instantaneous synthesis of a Cu–Zn–Sn–S colloid. Dispersing this colloid in a mixture of water (90%) and ethanol (10%), spraying it, and annealing sequentially the samples in two different gases allowed us to grow large grain, crystalline layers of promising photovoltaic quality. We measured cell efficiencies up to 5.0% under simulated AM1.5G (cell area 0.25 cm 2 ). To the best of our knowledge, this is the highest reported efficiency reached with Cu 2 ZnSnS 4 using a spray deposition technique with innocuous solvents.