Hydrothermally Synthesized Nanostructured WO3 Thin Films for Electrochromic Devices

Abstract

The greatest alternative to conventional windows and curtains is an electrochromic smart device with adjustable optical properties. Transition metal oxide plays a major role in electrochromic devices (ECDs). A simple hydrothermal method was developed to fabricate WO3 thin films on Fluorine-doped Tin Oxide (FTO) glass substrates. Sodium Tungstate Dihydrate (Na2WO4.2H2O) and Sodium Nitrate (NaNO3) were used as the starting materials for the preparation of WO3 thin films under different hydrothermal reaction time. The structural, chemical and morphological characterization of the thin films were conducted using different techniques including X-Ray Diffraction (XRD), UVVis absorption, Electrochemical Impedance Spectroscopy (EIS) and Scanning Electron Microscopy (SEM). According to the results, the particle size of the thin films was ranging from a few microns to hundreds of nanometers. XRD results showed that the WO3 was in monoclinic phase and the average crystallite size was 56.55 nm. The band gap value of the prepared WO3 was measured and it was 2.9 eV. The electrochromic performance of the WO3 thin films was characterized by LiCl in Propylene Carbonate (PC) and Ethylene Carbonate (EC) as the electrolyte. ECD with the configuration of WO3/Gel electrolyte (LiCl in PC+EC+ poly ethylene oxide (PEO))/FTO was prepared and a color change between dark blue and colorless was observed when an electric field of 3.5 V was applied across the device. A relatively high optical modulation of 12.2% at 675 nm was observed.