Influence of substrate temperature on growth and Electrochromic properties of WO3 thin films

WO3 thin films are prepared by electron beam evaporation (EBE) technique under the base pressure of 2 × 10-5 mbar at various substrate temperature (Ts) ranging from room temperature (RT) to 450 °C. The deposited films were characterized systematically to analyse the influence of substrate temperature on structural, morphological, compositional, vibrational, electrical, optical and electrochromic properties. The EDS data of deposited films confirm the presence of tungsten (W) and Oxygen (O) elements. XRD spectra reveal that films deposited at Ts < 250 °C are found to be amorphous and turns to crystalline as the substrate temperature raised to 450 °C. The morphological studies reveal that, beyond 250 °C of substrate temperature the material structure slowly changes to well crystallined structure with grain size about 70-80 nm. W = O and O-W-O bonds were present in the films which were confirmed by Raman spectra. The optical data represents the indirect allowed transitions and the band gap values are observed to be decreased from 3.24 to 2.93 eV with rise of substrate temperature from RT to 450 °C. It is also found that the RT electrical conductivity is increased with increase of Ts. Finally it is found that the coloration efficiency (CE) of the films deposited at RT is 30.63 cm2/C at the wavelength of 550 nm.