Structural and optical properties of Cu:CdS thin films on soft polymer substrate

Abstract

The structural and optical properties of copper doped cadmium sulfide (Cu:CdS) thin films on flexible polyethylene terepthalate substrates have been presented. The hexagonal crystallite structure of as-deposited thin films was characterized by the X-ray diffraction technique. X-ray photoelectron spectroscopy has been used to study the chemical binding energy and compositional analysis of the deposited thin films. The surface morphology of the deposited thin films has been analysed by an atomic force microscope image. The optical and photoluminescence properties of deposited films have been studied by UV–Vis–NIR spectrophotometer and fluorimeter respectively. A linear shrinkage of lattice parameters has been observed in the CdS thin films with Cu doping because of the smaller ionic radius of Cu than that of Cd. The optical band gap energy of CdS thin films decreased initially with Cu doping due to s, p–d exchange interactions and then increased due to the reduction in crystallite size. The photoluminescence property of the Cu:CdS thin films has been studied at room temperature (30 °C). Photoluminescence spectra showed two emission peaks around 545 nm and 580 nm, respectively, the exact positions of which are dependent on the Cu at% in the thin films. The former is due to the band-band transition of CdS, and the second is due to sulphur vacancy.