Mild solvothermal synthesis of Cu2ZnSn(SxSe1−x)4 nanocrystals with tunable phase structure and composition

Cu2ZnSn(SxSe1−x)4 (CZTSSe) nanocrystals (NCs) are synthesized via a one-pot solvothermal method under the mild reaction condition. By varying the S/Se ratio in the solution, the chalcogen composition of CZTSSe NCs can be well controlled over the whole range, leading to a tunable bandgap from 1.11 to 1.49 eV. Furthermore, it reveals that the S/Se ratio of anionic precursors has a dramatic effect on the phase structure of CZTSSe NCs. When the S/(S + Se) ratio (x) is higher than 0.5, wurtzite (WZ)-derived structure is the dominant phase; on the contrary, the zinc blende (ZB)-derived structure overwhelms the former as x gradually reduces from 0.5 to 0. Our findings thus suggest a novel and facile method to obtain CZTSSe NCs with metastable WZ phase, which is distinguished from previously reported routes based on carefully choosing organic solvents and/or capping ligands. In addition, the obtained CZTSSe NCs are readily dispersed in low boiling point and low toxicity solvent to form homogeneous and stable NCs ink. The photocurrent response measurement on the CZTSSe NCs films demonstrates its potential as a low-cost, high-reproducibility and high-yield NC preparing approach towards efficient CZTSSe solar cells.