Electrochromism in tungsten oxide thin films prepared by chemical bath deposition

Tungsten oxide (WO3) thin films were prepared by a simple, economical, chemical bath deposition method onto fluorine doped tin oxide (FTO) coated glass substrates. The electrochemical properties of the films were characterized by cyclic voltammetry. The obtained films exhibited electrochromism, changing color from initially colorless to deep blue, and back to colorless. Visible transmittance spectra of (WO3) films were recorded in-situ in their both, bleached and colored states. From those spectra, absorption coefficient ( a ) and the optical energy gaps were evaluated. The dependence of the optical density on the charge density was examined and the coloration efficiency ( h ) was calculated to be 22.11 cm2 C-1. The response times of the coloring and bleaching to an abrupt potential change from -2.5 V to +2.5 V and reverse, were found to be 9.3 and 1.2 s respectively. The maximum light intensity modulation ability of the films, when the AM1.5 spectrum is taken as an input, was calculated to be about 50 %.