Study of Effect of Cadmium Source on the Structural, Morphological, Vibrational, and Optical Properties of CdS Window Layers

Abstract

Cadmium sulfide (CdS) thin films hold significant potential for photovoltaic and optoelectronic applications. However, attaining remarkable physicochemical properties remains an important aim. In the present paper, we report this aim by studying the influence of cadmium sources Cd(CH3COO)2, CdSO4, and Cd(NO3)2, rarely reported in the literature, on these properties. CdS films were synthesized on glass substrates, at 75°C, via chemical bath deposition. XRD analysis of prepared films indicates that the dominant structure of CdS thin films was hexagonal with a (002) preferential orientation in all samples. The lowest thickness (864 nm), highest crystallite size (95.88 nm), lowest deformation (1.04 × 10‒4) and lowest density of dislocations (1.08 × 10‒4 lines × nm–2) were found using Cd(CH3COO)2. Raman spectra showed that the greatest asymmetry of the peak located at 306.42 cm‒1 corresponding to the fundamental vibrational mode (1LO) and attributed to the Cd‒S chemical bonding, was observed for CdS films prepared from CdSO4 and Cd(NO3)2. This result meant that the defects concentration was higher using these two sources than using Cd(CH3COO)2. Furthermore, the optical results of CdS film prepared from Cd(CH3COO)2 exhibited the largest band gap (2.42 eV), lowest Urbach energy (133.21 meV), and highest transmittance (85%) in the visible wavelengths range (300‒800 nm). The extinction coefficient and refractive index were also affected by the cadmium source. Our findings demonstrated that Cd(CH3COO)2 is the best cadmium source compared to CdSO4 and Cd(NO3)2 to enhance the physicochemical properties of CdS film and make it perfectly suitable for use as a window layer for photovoltaic cells and optoelectronic devices.