High near-infrared reflectivity modulation with polycrystalline electrochromic WO3 films

Abstract

A near-infrared reflectivity exceeding 60% at 2.5-μm wavelength has been observed for a polycrystalline, rf sputter-deposited electrochromic (EC) WO3 film in a deeply colored state. This reflectivity is considerably higher than that previously reported for a thermally evaporated EC-WO3 film that was crystallized by a post-deposition thermal anneal. The shapes of the x-ray spectra of the two films are also different. The results of ellipsometry measurements of the optical constants provide convincing evidence for the validity of a free-electron Drude model to explain the reflectivity modulation observed in polycrystalline EC-WO3.