Substitution effects on physical and chemical properties of Cu2Fe1-xCoxSnS4 thin films synthesized by the sol-gel technique

The impact of iron and cobalt substitution on the structural, morphological and optical properties of the copper iron cobalt tin sulfide Cu2Fe1-xCoxSnS4 thin films was studied. Employing the simple and easy sol-gel spin-coating technique on soda-lime glass substrates without sulfurization phase, Cu2Fe1-xCoxSnS4 (x = 0, 50 and 100%) compound was formed with the (112) preferential orientation for all thin films in the tetragonal stannite structure at space-group I42 m. By performing X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy, Energy Dispersive analysis and UV–Vis–NIR spectrophotometry, the physical and chemical properties were examined. The substitution was observed to provide a slight variation of the lattice parameters. The crystallite size was found to vary between 14 and 32 nm and decreased by increasing the cobalt content. The Raman spectra confirm the result of the XRD via the appearance of two peaks located at 321 and 284 cm−1, corresponding to the A1 vibration mode. The morphological analysis showed homogenous film surfaces. Optical characterizations showed that all thin films exhibit a band-gap energy, estimated between 1.1 and 1.53 eV, with an absorption coefficient greater than 104 cm−1. The possible use of thin films as an absorber for solar cells, with an adjustable optical band gap is proven.