Improving the grain size of Cu ₂ ZnSnS ₄ thin films by annealing thermally evaporated Cu–ZnS–Sn–S precursors

In this study, Cu ₂ ZnSnS ₄ (CZTS) thin films were grown on Mo-coated glass substrates by thermal evaporation of the precursor layers followed by annealing in a graphite box. The effect of annealing on the grain growth and morphology of the CZTS thin films was investigated at two different temperatures and S ₂ partial pressures. X-ray diffraction and Raman spectroscopy analyses confirmed the formation of CZTS films with a kesterite structure with (112) preferred orientation. The grain growth was significantly enhanced by annealing the stacks at 550∘C for 30 min at a S ₂ partial pressure of 1.2×104Pa. The grain size was found to be in the range of 1.0-2.0μm. The same grain size was obtained by carrying out the annealing at 580∘C and a S ₂ partial pressure of 1.96×104Pa just for 10 min. This grain size was much larger than the grain size of CZTS films obtained from annealing the stacks in two-zone tubular furnaces.