Structural analysis of pure and LiCF3SO3-doped amorphous WO3 electrochromic films and discussion on coloration kinetics

Structural differences between pure and LiCF3SO3-doped amorphous WO3 thin films were studied by Raman spectroscopy and X-ray photoelectron spectroscopy analysis. Based on our interpretation of reports in the literature on Raman spectra of WO3 thin films, we found that the LiCF3SO3-doped amorphous WO3 film presented greater amounts of oxygen vacancies, W+4 valence state and W+6=O surface vibration modes. These structural differences served as the basis to make inferences about the dissimilarities also found in the kinetic coloration observed during the electroinsertion reaction, focusing particularly on the dynamics of Li+ insertion into the two different structures.