Thiourea-controlled synthesis of CdS thin films: a study on crystallinity and optical behavior

Cadmium sulfide (CdS) thin films were synthesized on glass substrates using the chemical bath deposition (CBD) technique to investigate the effects of varying thiourea concentrations on their structural and optical properties. X-ray diffraction (XRD) analysis confirmed a cubic zinc blende structure, with decreasing crystallinity and grain sizes, which reduced from 55.67 nm to 11.34 nm, as thiourea concentration increased. The micro strain and dislocation density showed an increasing trend, with micro strain rising from to and dislocation density increasing from lines/m² to lines/m², indicating a deterioration in crystalline quality and increased lattice imperfections at higher thiourea concentrations. These structural changes influenced film morphology, reducing grain connectivity and increasing surface disorder. Optical analyses revealed a blue shift in the transmission spectra, higher transmittance, and a band gap widening from 1.80 eV to 1.96 eV, with Urbach energy rising from 0.2 eV to 0.5 eV. The refractive index has been found to decrease with increasing thiourea content. These findings demonstrate that thiourea concentration significantly affects both the structural integrity and optical properties of CdS thin films, highlighting their potential for tailored optoelectronic applications.