Modification in the Chemical Bath Deposition Apparatus, Growth and Characterization of CdS Semiconducting Thin Films for Photovoltaic Applications

摘要

In this paper, growth and characterisation of CdS thin films by Chemical Bath Deposition (CBD) technique using the reaction between CdCl_2, (NH_2)_2CS and NH_3 in an aqueous solution has been reported. The parameters actively involved in the process of deposition have been identified. A commonly available CBD system has been successfully modified to obtain the precious control over the pH of the solution at 90 °C during the deposition and studies have been made to understand the fundamental parameters like concentration of the solution, pH and temperature of the solution involved in the chemical bath deposition of CdS. It is confirmed that the pH of the solution plays a vital role in the quality of the CBD-CdS films. Structural, optical and electrical properties have been analysed for as-deposited and annealed films. XRD studies on CBD-CdS reveal that the change in cadmium ion concentration in the bath results in the change in crystallisation from cubic phase with (111) predominant orientation to a hexagonal phase with (002) predominant orientation. The structural changes due to varying cadmium ion concentration in the bath affects the optical and electrical properties. Optimum electrical resistivity, band gap and refractive index value are observed for the annealed films deposited from 0.8 M Cadmium ion concentration. The films are suitable for solar cell fabrication. Further on, annealing the samples at 350 °C in H_2 for 30 min resulted in an increased diffracted intensity as well as shifts of the peak towards lower scattering angles due to enlarged CdS unit cell. This brought about an increase in the lattice parameters and narrowing in the band gap values. The results are compared with the analyses of previous work.