Parametric Optimization and Characterization of Chemically Bath Deposited Nanocrystalline CdS Thin Films via Response Surface Methodology

In this paper, CdS (cadmium sulfide) thin films (TFs) were successfully synthesized using the chemical bath deposition (CBD) technique. The effects of synthesis pH and temperature on the structural, morphological, compositional, and optical properties of the CdS thin films were systematically investigated. The deposited CdS TFs were characterized using Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX), elemental mapping, and UV–Vis spectroscopy. Surface morphology and topographical features were further examined by AFM analysis. The characterization results revealed that the optimum CdS TF was obtained at a synthesis pH of 10 and a temperature of 80 °C. Although the optical band gap of bulk CdS at room temperature is approximately 2.42 eV, the synthesized TFs exhibited band gap energies ranging from 2.63 to 2.76 eV, depending on the synthesis conditions. This increase in band gap is attributed to variations in crystallite size and microstructure resulting from changes in pH and synthesis temperature. Overall, the findings demonstrate that both synthesis temperature and pH have a significant influence on the particle size, optical properties, and microstructure of CdS TFs. Initially, three-dimensional response surface plots of the FT-IR, XRD, and UV-Vis results obtained from CdS TFs prepared by the CBD method under various temperature and pH conditions were successfully generated using response surface modeling (RSM). Furthermore, the adequacy and statistical significance of the developed model were evaluated via Analysis of Variance (ANOVA).