Synthesis, Characterization and Study of the Optical and Solid-State Properties of Cadmium Sulfide Thin Films Deposited by Spray Pyrolysis for Optoelectronic Device Applications

Cadmium sulfide (CdS) thin films were synthesized using the spray pyrolysis technique and deposited on glass substrates at controlled temperatures of 303 K, 333 K, and 363 K to investigate their optical and solid-state properties for optoelectronic device applications. Precursor solutions of cadmium nitrate tetrahydrate and thiourea were prepared in aqueous media, homogenized, and atomized onto pre-cleaned, preheated substrates, forming films through thermal decomposition. Thereafter, Optical characterization was done using UV-Vis spectrophotometry. Absorbance spectra revealed maximum absorption in the UV- visible region (280-500 nm), with the 333 K film exhibiting the highest absorbance (2.01), indicating enhanced light-harvesting capability. Refractive index analysis showed temperature dependent n - shaped dispersion profiles, with peak values of 1.625 (303 K), 2.52 (333 K), and 2.125 (363 K), reflecting variations in film compactness and electronic structure. Tauc plot analysis confirmed direct allowed electronic transitions, yielding band gap energies of 3.87 eV (303 K), 2.30 eV (333 K), and 2.41 eV (363 K). Films deposited at 333 - 363 K displayed band gap values consistent with literature and suitable for visible-light optoelectronic applications, whereas the wider band gap at 303 K suggests limited crystallinity or quantum confinement effects. The result of this study has demonstrated that substrate temperature significantly enhances the optical performance of CdS thin films prepared by spray pyrolysis, with the 333-363 K range offering the best properties for devices such as solar cells, photodetectors, and optical sensors.