Insight into the crystal phase and shape evolution from monoclinic Cu_1.94S to wurtzite Cu₂ZnSnS₄ nanocrystals

Phase pure wurtzite Cu₂ZnSnS₄ (CZTS) nanocrystals have been prepared by using monoclinic Cu_1.94S nanoplates as starting materials via a hot-injection method. The rapid injection of Zn-thiols resulted in the symmetrical growth of CZTS onto both sides of Cu_1.94S nanoplates, yielding sandwich-like CZTS-Cu_1.94S heterostructures, which finally converted into CZTS nanocrystals. Interestingly, with 50% excess Sn precursor in the initial reaction system, the morphology of CZTS can retain the shape of nanoplates with increased thickness. The morphology and crystal phase evolution processes have been further investigated to understand the formation mechanism. These findings are meaningful for the controllable synthesis of copper chalcogenide nanocrystals as well as their photoelectrical applications.