Electrochromic Devices Based on Porous Tungsten Oxide Thin Films

Abstract

Recent developments in the synthesis of transition metal oxides in the form of porous thin films have opened up opportunities in the construction of electrochromic devices with enhanced properties. In this paper, synthesis, characterization and electrochromic applications of porous WO3thin films with different nanocrystalline phases, such as hexagonal, monoclinic, and orthorhombic, are presented. Asymmetric electrochromic devices have been constructed based on these porous WO3thin films. XRD measurements of the intercalation/deintercalation of Li+into/from the WO3layer of the device as a function of applied coloration/bleaching voltages show systematic changes in the lattice parameters associated with structural phase transitions in LixWO3. Micro-Raman studies show systematic crystalline phase changes in the spectra of WO3layers during Li+ion intercalation and deintercalation, which agree with the XRD data. These devices exhibit interesting optical modulation (up to ~70%) due to intercalation/deintercalation of Li ions into/from the WO3layer of the devices as a function of applied coloration/bleaching voltages. The obtained optical modulation of the electrochromic devices indicates that, they are suitable for applications in electrochromic smart windows.