Electrochromic Properties of PEG-Modified Tungsten Oxide Thin Films

To improve the electrochromic properties of WO 3 thin films, polyethylene glycol (PEG)-modified WO 3 films via Sol-Gel method were prepared on indium-tin oxide (ITO) glass using dipping-coating technique with post annealing treatment in air.Crystal structures and morphologies of the as-prepared films were investigated by means of X-ray diffraction (XRD) and scanning electron microscope (SEM).Optical properties and cyclic voltage-current characteristic of the films were experimentally studied.Compared with the corresponding neat WO 3 films, the PEG-modified WO 3 films exhibit superior electrochromic properties, which possesses longer lifetime after 5000 cycles without obvious degradation, as well as higher optical modulation up to 71% at the wavelength of 633 nm.The results suggest that PEG addition in conjunction with post annealing treatment may change the micro-structure of WO 3 films to increase the electrochromic properties, due to the enhancement of ion diffusion capacity in the electrochromic material, as evident from the formation of the porous structure with an average pore diameter of 9 nm.As cycling stability is very crucial for practical applications of electrochromic materials, particularly for smart windows, this research provides a promising low-cost wet-chemical route to high performance WO 3 -based electrochromic devices.