Preparation and characterization of Cd1−x Zn x S buffer layers for thin film solar cells

Abstract

Cd1−x Zn x S (x = 0, 0.1, 0.2, 0.3, 1.0) thin films have been grown successfully on soda-lime glass substrates by chemical bath deposition technique as a very promising buffer layer material for optoelectronic device applications. The composition, structural properties, surface morphology, and optical properties of Cd1−x Zn x S thin films were characterized by energy dispersive analysis of X-ray technique (EDAX), X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis spectrophotometer techniques, respectively. The annealed films were observed to possess the deficient sulfur composition. The results of XRD show that the Cd1−x Zn x S (x = 0.1) thin film annealed at 450 °C forms hexagonal (wurtzite) structure with lattice parameters a = 0.408814 nm, c = 0.666059 nm, and its average grain size is 24.9902 nm. The diffraction peaks become strong with the increasing annealing temperatures. The surface of Cd1−x Zn x S (x = 0.1) thin film annealed at 450 °C is uninterrupted and homogenous as compared to other temperatures. From optical properties, it is observed that the presence of small amount of Zn results in marked changes in the optical band gap of CdS. The band gaps of the Cd1−x Zn x S thin films vary from 2.42 to 3.51 eV as composition varies from x = 0.0 to 1.0. The optical studies in figs reveal that Cd1−x Zn x S thin film annealed at 450 °C shows a high transmittance as a direct-gap semiconductor. The calculated band gap (E g) of the film is about 2.56 eV annealed at 450 °C. This is in close agreement with the reported value (2.49 eV) of Cd0.9Zn0.1S film. Compared to the E g value (2.42 eV) of CdS, the increased E g value is due to the entrance of the element of zinc.