Effect of precursors on the microstructural, optical, electrical and electrochromic properties of WO₃ nanocrystalline thin films

Spray-deposited tungsten oxide (WO₃) nanocrystalline thin films were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and atomic force microscopy in order to study the precursor induced changes in their structural and morphological properties. The crystallite size and the root mean square surface roughness have been found to be minimum for the WO₃ thin films prepared using ammonium tungstate. The optical and spectral studies of the films were carried out using UV–visible spectroscopy and photoluminescence spectroscopy. Electrical transport properties of the films were studied by measuring the film resistivity as a function of temperature. Electrochromic studies of the WO₃ films were carried out from cyclic voltammetry, chronocoulometry and chronoamperometry measurements. The films grown using ammonium tungstate exhibit high electrochromic reversibility (~91 %) and large charge storage capacity. The cyclic voltammograms of the films do not change even after 50 scan cycles, confirming the electrochromic stability in the WO₃ films. Overall, the film prepared using ammonium tungstate may be a suitable candidate for electrochromic devices.