Electrochromic characteristics of pulsed spray pyrolyzed polycrystalline WO3 thin films

The structural, optical, and electrochromic properties of polycrystalline tungsten oxide films have been investigated using various characterization techniques. X-ray diffraction analysis confirmed the polycrystalline monoclinic structure of the films with preferable (002) orientation and an average crystallite size of 50 nm. X-ray photoelectron spectroscopy analysis has revealed symmetric W 4f peaks and only the W6+ state to be present in the as-deposited and bleached thin films. By inserting hydrogen ions and electrons into the films, the W 4f peaks become broader and there is an extra peak of the W5+ state. Atomic force microscopy and scanning electron microscopy show a rough surface with fibrous-reticulated morphology. The cyclic-voltammetry data show the diffusion-control mechanism of hydrogen ion and electron insertion in the film. These polycrystalline films with fibrous-reticulated structure show a good electrochromic performance. This improved electrochromic performance is explained on the basis of improved interfacial charge-transfer kinetics of the H+ ions into the films. Such porous and fibrous-reticulated morphology polycrystalline WO3 thin films have potential application in improving the performance of electrochromic smart devices.