Investigation of the impact of sulfur on the properties of CZTS nanomaterials for enhanced supercapacitor performance

Cu₂ZnSnS₄ (CZTS) has been synthesised using ethylene glycol as a solvent by the solvothermal method. Preliminary characterisation, like X-ray diffraction, Raman spectroscopy, and FTIR, confirmed the tetragonal structure of CZTS with kesterite phase. In the synthesis, a series of samples with different concentrations of sulfur were produced, accompanied by an in-depth analysis of structural parameters such as crystallite size and strain, utilising both the Scherrer equation and the Williamson-Hall method. Utilisation of field emission scanning electron microscopy in conjunction with energy dispersive X-ray (EDX) has enabled the observation of the evolution of spherical morphology and the decrease in agglomeration as the concentration of sulphur was elevated. The peaks observed in EDX and XPS confirmed the presence of elements and their atomic percentages within the synthesised samples. The Tauc plot was employed to determine the optical band gap; it first increases from 1.60 eV to 1.66 eV and then decreases to 1.56 eV. Additionally, electrochemical investigations were conducted utilising CV, GCD, and EIS experiments. A comparative analysis was conducted for samples with the highest (CZTS8) and lowest (CZTS5) sulphur concentrations. Specific capacitance measurements of 481 F g^-1 and 316 F g^-1 were obtained for CZTS8 and CZTS5, respectively. CZTS8 demonstrates an impressive 88% capacitance retention over 2600 cycles, and the extension of the linear portion of the EIS graph indicates that both samples exhibit commendable capacitive behaviour.