Optical measurements and modeling of an all solid state inorganic thin film electrochromic system

Abstract

Single layer optical measurements have been carried on for multilayer physical vapor deposited thin film electrochromic system. The measurements have has been performed for tungsten oxide (active electrochromic material) and vanadium pentoxide (counter electrode material) thin films and for indium tin oxide (transparent electric conductor material) thin film. The electrolyte layer was assumed dispersion free with rear refractive index n = 1.5 and imaginary part k = 0. The optical parameters, n and k, for each layer were measured in the visible and near infrared spectral regions. They have been calculated by the spectrophotometrically measured reflectance and transmittance and by the physical thickness measured using a stylus profilometer. The final five layer electrochromic system has been modelled in the colored state using a multilayer thin film calculation program. The complete electrochromic device has been spectrophotometrically described and comparison with the calculated results indicate that the single layer technique is not appropriate to describe, optically, the electrochromic coating. The optical model allows the design optimization of electrochromic systems for switchable energy saving glazings.