Effect of stirring rate of electrolyte on properties of electrodeposited CdS layers

Abstract

CdS is the most matching window material available for the CdTe absorber layer of CdS/CdTe solar cells and electrodeposition is a promising technique adaptable for fabrication of thin films of CdS owing to its simplicity, low cost, scalability and manufacturability. The quality of electrodeposited thin film semiconductor layers depends significantly on the electrodeposition potential, concentrations of precursor salts, pH, temperature and the rate of stirring of the electrolyte. In this study, the attention was focused on the effect of “stirring rate of electrolyte” since it has not been studied in detail in the past, despite of its strong relation to the rate of mass transport towards the working electrode where the thin film semiconductors are electrodeposited. This study was carried out via electrodepositing of CdS thin layers on fluorine doped tin oxide conducting glass working electrodes at different rates of stirring of the electrolyte while keeping the rest of the electrodeposition parameters unchanged at a previously identified set of values. The morphological, electrical and optical properties of the CdS layers grown at different stirring rates were used to determine the effect of stirring rate on the quality of CdS layers. The study revealed that, a stirring rate in the range of 60–125 rpm which produced orderly flows in the electrolyte around the working electrode (1 × 3 cm²) placed at the center of a 100 ml electrolytic bath with a distance of 2 cm apart between the graphite counter electrode and the conducting glass electrode could produce good quality CdS layers when electrodeposition was carried out at a cathodic deposition potential of 660 mV with respect to the saturated calomel electrode. The concentrations of CdCl₂ and Na₂S₂O₃ in the bath used were 0.10 and 0.01 M respectively. The temperature and pH of it were 60 °C and 1.80 respectively.