Near-infrared reflectance modulation with electrochromic crystalline WO3 films deposited on ambient temperature glass substrates by an oxygen ion-assisted technique

Abstract

Electrochromic, crystalline WO3 films have been deposited on glass substrates at ambient temperature by an oxygen-ion-assisted technique using oxygen ion energies ≥300 eV and oxygen ion to vapor molecule (WO3) ratios, γ≥2.5. After lithiation, the resulting LixWO3 films exhibited >50% reflectivity in the near infrared, and the reflectivity dispersion was fit by a Drude free-electron model, yielding the Drude parameters: plasma energy, Ep=3.3 eV; and the loss (damping) parameter, EΓ=1.0 eV. (The bound electron permittivity, εb, was fixed at 4.0.) These values are comparable to those obtained with WO3 films rf sputter deposited onto substrates at temperatures >420 °C. During the ion-assisted deposition the substrate temperature reached approximately 90 °C, caused primarily by radiation from the WO3 evaporant source. This indicates that economical low-temperature substrates, such as plastics, could be used. These results suggest that practical electrochromic smart windows for energy-efficient buildings might be produced using ion-assisted deposition techniques.