The effect of growth technique on the characteristic properties of CdS layers for solar cell applications

Abstract

The effects of two different growth methods including electrodeposition (ED) (two-electrode configuration) and chemical bath deposition (CBD) on the characteristic properties of CdS thin-films were explored and reported. The electrodeposited CdS (ED-CdS) layers were grown on glass/fluorine-doped tin oxide (FTO) substrates using acidic and aqueous solution containing 0.3 M of thiourea (SC(NH2)2) and 0.2 M of cadmium chloride hydrate (CdCl2.xH2O). The chemical bath deposited CdS (CBD-CdS) layers were also grown on glass/FTO substrates using alkaline and aqueous solution containing 4 × 10–3 M of cadmium acetate dihydrate (Cd(CH3CO2)2.2H2O), 20 × 10–3 M of thiourea (TU) and 6 × 10–2 M ammonium acetate (NH4C2H3O2). The deposited CdS thin-films were characterised using X-ray diffraction (XRD), UV–Visible spectrophotometer (UV–Vis), scanning electron microscopy (SEM), and photoelectrochemical (PEC) cell measurement to study their structural, optical, morphological, and electrical properties, respectively. The structural study shows the polycrystalline nature of the ED-CdS and CBD-CdS thin-films with stable hexagonal phase after heat treatment. The preferred orientation for both ED-CdS and CBD-CdS layers was along (002) hexagonal plane. The average crystallite size of CdS thin-films grown by both deposition methods were in the range ~ (11–38) nm and ~ (22–53) nm before and after heat treatment, respectively. Optical studies reveal the direct bandgap value of 2.42 eV for the heat-treated ED-CdS and CBD-CdS layers which correspond to the bulk bandgap of CdS (hexagonal phase). Morphological studies depict the average grain sizes in the range ~ (90–260) nm for the CdS thin-films. The PEC cell measurements show that the CdS layers grown by both ED and CBD methods were n-type in electrical conduction before and after heat treatment. No visible precipitations of elemental S or CdS particles were observed in the deposition electrolyte of ED-CdS showing a stable bath using TU precursor during the growth. The solar cells fabricated using CBD-CdS showed better performance as compared to the devices fabricated using ED-CdS due to the uniform coverage of FTO surface and better fill factor (FF).