Electrochromic materials from the visible to the infrared region:: an example WO3

Herein, the example of the most typical electrochromic material, namely WO3, is used to illustrate the potential of electrochromic materials for controlling infrared reflectance and hence, emissivity. Playing with various growth parameters, contrast in reflectance between the inserted H xWO3 and deinserted WO3 states as high as 73% in mid-wavelength band (MW, 3-5 mu m) was achieved for 320 nm WO3 films. The latter electrochromic materials were radio frequency sputtered on Au substrate at ambient temperature in 6 Pa of chamber pressure. In comparison, for long wavelength band (LW, 8-12 mu m), the contrast in reflectance did not exceed 30%. The origins of the various electrochromic behaviours are correlated to the film structure, morphology and composition, indicating better properties for porous, nonstoichiometric films.