Tungsten and Titanium Oxide Thin Films Obtained by the Sol-Gel Process as Electrodes in Electrochromic Devices

Abstract

In this work, WO3 and TiO2 thin films have been obtained by the sol-gel spin coating method. The as-deposited samples were annealed at different annealing temperatures in the range between 100°C and 500°C. Micro-Raman spectroscopy confirmed that WO3 thin films annealed at 100°C and 300°C are amorphous while the crystallization process occurred at 500°C as established by the typical Raman modes of γ-WO3. Amorphous thin films of TiO2 have been obtained using annealing at 100°C and 300°C. The crystalline phase of the anatase-TiO2 has been obtained after the thermal treatment conducted at 500°C. The electrochromic devices were characterized by cyclic voltammetry and UV–Vis–NIR spectroscopy and it has been shown that the best configurations of the electrochromic devices studied in this work can be obtained by using the WO3 thin films amorphous, which means annealed at 100°C and 300°C, and TiO2 thin films crystalline, that is annealed at 500°C. The higher coloration efficiency values in the visible region (λ = 550 nm) and in the near-infrared region (λ = 1020 nm) support the idea that such devices could be used in order to control the light flux but also heat flux. It means that such electrochromic devices can be usefully employed as smart windows promoting energy and economic savings.