Electrochromic Nb-doped WO3 films: Effects of post annealing

The Nb-doped WO3 films were deposited by e-beam co-evaporation method using ceramic WO3 targets and metal Nb slugs. The films were analyzed by glancing incident angle X-ray diffraction (GIAXRD), UV/visible spectrophotometer, electrochemical cyclic voltammetry, X-ray photoelectron spectroscopy (XPS). The as-prepared film is brown and amorphous in structure. The film has low transmission in optical visible region. The XPS results indicate that the as-deposited film is non-stoichiometric. By applying a negative potential, the as-deposited film does not show obvious electrochromic effect. However, the electrochromic properties of Nb-doped WO3 films are improved by post annealing treatment at 350, 400, and 450 degrees C in oxygen atmosphere. The Nb-doped WO3 films transform into crystalline structure and become transparent after post annealing treatment. The energy band gap, optical modulation, and color efficiency increase with annealing temperature. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.