A study on CdCl₂ activation of CBD-CdS films

Cadmium sulfide (CdS) thin films were deposited using chemical bath deposition (CBD) technique on fluorine-doped tin oxide glass substrates. Cadmium sulfate, thiourea, and ammonium hydroxide were used as Cd source, S source, and the complexing agent, respectively in the reaction bath. The post-deposition CdCl₂ activation of chemical bath deposited CdS (CBD-CdS) thin films was done by dip coating in a saturated CdCl₂ bath. X-ray diffractograms show the growth of large CdS grains with better crystalline quality over the recrystallization process due to CdCl₂ treatment. The development of large clusters was determined to be due to coalescence of smaller clusters. The photoelectrochemical (PEC) cell (CdS/Na₂S₂O₃/Pt) parameters, such as V_OC and I_SC for CdCl₂ activated CBD-CdS thin films were found to be higher compared to untreated CBD-CdS thin films. The improved effective surface area of the film and higher carrier concentration due to grain boundary passivation could be the reason for higher V_OC and I_SC values found in CdCl₂-treated CdS films. Additionally, all the CdCl₂-treated CdS films showed an increase in the optical transmittance spectra and bandgap compared to untreated CdS films. Relative energy band edge position of the grown CdS films was found to be adjustable with the CdCl₂ treatment time. The best photoactivity was found for the CdS films which were dip-coated for 10 min in CdCl₂ solution.