Synthesis of the Cu2ZnSn(S,Se)4 alloys with tunable phase structure and composition via a novel non-toxic solution method

A new facile solution-based method to fabricate Cu2ZnSn(S,Se)4 (CZTSSe) alloys is presented without involving toxic solvent and post-growth selenization. Influences from the source concentration in the precursor solution and the annealing conditions on the product composition and phase transition are thoroughly examined. Experimental results show that the Se content can be adjusted over a wide composition region, which leads to highly controllable band-gap tailoring of CZTSSe absorbers. Furthermore, a wurtzite-derived phase structure is found readily to form even under such moderate synthesis conditions, and shows dependences on the chemical composition and the annealing temperature. The findings provide more freedom in the modification of CZTSSe material properties based on this novel phase structure.