Sulfur to Cadmium Ratio-Dependent Studies on Properties of Solution-Processed CdS Nanocrystals

One of the most used metal chalcogenide semiconductor materials in the fabrication of photovoltaic devices is cadmium sulfide (CdS), due to its wide band gap, high carrier mobility, and proper energy levels. In this study, a solution-based method is introduced for the synthesis of CdS nanocrystals (NCs) at room temperature with different sulfur to cadmium ratios in wet synthesis media. The effect of the sulfur to cadmium ratio (S:Cd) in the synthesis media on the morphological, structural, and optical properties of CdS NCs has been investigated. FTIR analysis showed that Cd–S bonds formed in the room temperature synthesis process. It was found that, by reducing the S:Cd ratio, the band gap of the synthesized CdS NCs increases. Furthermore, XRD data revealed that the crystal structure of the synthesized CdS is more cubic at lower sulfur concentrations and hexagonal at higher concentrations. Moreover, it was found that the S:Cd ratio has an important effect on the stability of colloidal suspensions of CdS NCs. The CdS NCs synthesized with the highest sulfur to cadmium ratio (S:Cd = 8:1) in the synthesis media formed the most stable colloidal suspension of CdS NCs in dimethylformamide.