Effects of cadmium salts on the structure, morphology and optical properties of acidic chemical bath deposited CdS thin films

CdS thin films were deposited from different cadmium salts by using acidic chemical bath deposition (CBD) process. Quality characterizations were performed using different methods such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL). The crystal quality of CdS thin films was improved after CdCl2 thermal annealing at 380 °C. A compact structure of CdS thin films can be obtained by using CdCl2 in comparison with the other cadmium salts. Although a Cd/S molar ratio of ∼1 was used in our experiments, strong PL signals confirmed the high quality of CdS thin films.

Research highlights▶ N-type semiconducting CdS thin films have been widely used as a window layer in the solar cells. CdS thin films prepared by chemical bath deposition (CBD) have been used in CdTe and CIGS based solar cells. Among existing techniques, CBD was simple and inexpensive to deposit CdS thin films for mass production. Typically, the CBD process for CdS films is carried out in an alkaline aqueous solution comprised of thiourea and ammonia. Recently, CBD process in acidic solutions has been developed and used for the optimization of CdS thin films. However, the effects of the variables for the acidic CBD, especially, the dependence on cadmium salts, have not been investigated systematically. In this paper, we studied the growth process, structure, morphology and optical properties of CdS thin films deposited using different cadmium salts, which is helpful for the optimization of growth condition for high quality CdS thin films used in solar cells. Acidic CBD-CdS thin films were prepared by using different cadmium salts. A post-annealing process at 380 °C was used to improve crystal quality. The CdS-Ci thin films have the highest deposition rate than other films obtained by different solution, which is due to an easier releasing rate for Cd(CH3COO)2 than the CdCl2 and CdSO4 solutions. CdS-Cli thin films have a relatively larger band gaps and better qualities. Strong PL spectra at room temperature confirm the good quality of the CdS thin films.