Synthesis and characterization of Cu ₂ CoSnS ₄ thin films prepared via radio-frequency (RF) magnetron sputtering

Cu ₂ CoSnS ₄ (CCTS) thin films, for the first time, were successfully fabricated by RF magnetron sputtering with two different metal precursor stacking sequences followed by sulfurization treatment under kinds of temperatures. Structure, morphology, composition, chemical valence states and optical properties of the as-grown films were discussed by X-ray diffraction (XRD), Raman spectroscopy (Raman), Scanning electron microscopy (SEM), Energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible-near-infrared spectrophotometer (UV–vis–NIR spectrophotometer) respectively. XRD and Raman analysis indicated that the as-obtained Cu ₂ CoSnS ₄ thin films possess a stannite structure and the crystallinity was improved accompanying the incremental sulfurization temperature under both two depositing orders. The growth mechanism of CCTS films during vulcanization process was also discussed. XRD, Raman spectroscopy and SEM analysis showed that the precursors deposited in Cu/Co/Sn sequence had the best crystallinity after 600 °C sulfurization annealing. Under this preparation condition, XPS analysis showed that the chemical states of the four main elements in the film were Cu (I), Co (II), Sn (IV) and sulfide ions,and it exhibited the direct band gap of 1.58 eV by UV–vis–NIR absorption spectra, which is close to the ideal values for photovoltaic utilization.