Post-annealing effect on the structural and optical properties of tungsten trioxide thin films prepared by thermal evaporation

In this work, WO3 thin film was synthesized in a single step with a thickness of 200 nm on a quartz substrates at room temperature, in a base pressure of about 10- 5 mbar by the physical thermal evaporation. Consequently, the fabricated layers underwent annealing for a duration of 1 h at three different temperatures of 200, 400, and 500 degrees C within an argon environment. UV-Vis spectroscopy and photoluminescence spectroscopy characterize the desired thin films. Additional X-ray diffractometery was also conducted to identify the crystalline structures of the produced films. The results of XRD measurements showed that the calcined films have orthorhombic structure and directional prevalent (001). Optical band gap of all the films was determined from the UV-Vis obtained spectra. Duo to the annealing process, WO3 band gap decreased from 3.25eV to 2.6 eV. Different optical and structural behaviors with increased annealing temperatures also confirmed a transition was observed from monoclinic to orthorhombic phase in synthesized WO3 films by this process. Also, an examination conducted to show how annealing treatment has impacts on the Cyclic voltammetry (CV) of the prepared films. We found that the annealed WO3 film has more intercalated charges, causes it more suitable for electrochromic applications.