Effect of Fe content on Cu₂Fe_xZn_1−xSnS₄ single crystals fabricated by flux growth method

High quality micron-sized Cu₂Fe_xZn_1−xSnS₄ single crystals have been successfully fabricated by flux growth method using CuS, FeS, ZnS and SnS as the raw materials and CsCl as the fluxing agent. The effects of Fe contents on the morphology, structure and optical properties of Cu₂Fe_xZn_1−xSnS₄ single crystals were investigated. X-ray diffraction and Raman analyses reveal that the kesterite and stannite phases coexist in the Cu₂Fe_xZn_1−xSnS₄ crystals, and peak splittings of (2 0 4) and (3 1 2) are observed for the sample with x  =  0.2. The optical absorption spectra reveal that the optical bandgap of the single crystal samples has little dependence on the Fe content due to the coexistence of the kesterite and stannite phases. The bandgap of the Cu₂Fe_xZn_1−xSnS₄ single crystal generally locates between 1.672 and 1.716 eV. Though the bandgap is not ideal as the absorber for single-junction solar cells according to the S–Q limit, it is an ideal material for the top cell in tandem solar cells and solar-driven water splitting. (paper)