Effect of Substrate Temperature on the Structural and Electrochromic Properties of Mo Doped WO<sub>3</sub> Thin Films

Abstract

Thin films of Mo (1.3 at.%) doped WO3 films were deposited on glass and ITO coated glass substrates held at substrate temperatures in the range 473 673 K by RF magnetron sputtering technique. The effect of substrate temperature on the structural and morphological, and electrochromic properties of the deposited films were investigated by X-ray diffraction, scanning electron microscope, Raman spectroscope and with electrochemical cell. X-ray diffraction profiles showed that the films formed at substrate temperature of 473 K consisted of weak (020) reflection related to the orthorhombic phase of WO3 in the amorphous matrix. The films formed at substrate temperatures 473 K were of polycrystalline in nature. The crystallite size of the films increased from 12 to 43 nm with increase of substrate temperature from 473 to 673 K. The scanning electron microscope images of the films formed at 473 K showed the leaf like structure with grain size of 1.2 μm. When substrate temperature increased to 573 K the size of the grains enhanced to 2.4 μm. Raman spectra of the films confirmed the presence of characteristic vibration modes of W = O, W - O - W and O - W - O. The optical band gap of the films increased with increase of substrate temperature. The electrochromic property, that is the color efficiency increased from 42.5 to 50.5 cm2/C with the increase of substrate temperature from 473 to 673 K respectively. The structural and electrochromic properties of the Mo doped WO3 films will be correlated with the substrate temperature maintained during growth of the films.