Electrocoloration curve analysis in WO3 thin films

An analytical expression for electrochromic coloration of WO3 amorphous thin films is proposed based on a semiclassical equation for harmonic oscillator and in the Smakulaʹs formula. The coloration efficiency (η) as a function of the photon energy (hv) of the light-beam chosen to determine the change in the optical density with the amount of injected electrical charge into the film, was deduced in the range 0.5–3.0 eV (400–2500 nm). Given the oscillator strength constant value and the refraction index as a function of hν, η can be determined, with good approximation, for any value of the photon energy in the range 0.5–3.0 eV. The usefulness of the method is demonstrated on data obtained from the literature.