Cu₂ZnSnS₄ solar cell has been fabricated with a non-toxic buffer layer and Al doped ZnO transparent conducting layer. A detailed material study on each layer of the solar cell has been carried out independently. The precursor films prepared by spin coating were sulphurized at different temperatures to optimize the conditions to obtain phase pure CZTS films. X-ray diffraction, Raman spectroscopy and rietveld refinement studies confirmed the phase purity of the film sulphurized at 500 °C. The optimum CZTS properties like band gap of 1.45 eV, high absorption coefficient ~2 × 10⁵ cm⁻¹ and dense surface morphology were obtained for films sulphurized at 500 °C. Carrier concentration, mobility and resistivity of these films were ~1 × 10¹⁹ cm⁻³, 0.23 cm² V⁻¹ s⁻¹ and 2.7 Ωcm, respectively. The efficiency measurements of the cells with device structure SLG/Mo/CZTS/ZnS/AZO/Ag were carried out using absorber films with three different thicknesses. The optimized CZTS absorber layer with thickness of ~1.8 µm exhibited solar cell conversion efficiency of 3.02% for an active area of 0.21 cm² with open-circuit voltage of 0.38 V, short-circuit current density of 17.19 mA/cm² and fill factor of 46%.