Visible and Near-Infrared Electrochromic Smart Windows with Amorphous WO_3−x and Cu-Doped NiO Operating in Three Modes

Abstract

Electrochromic windows are promising devices for efficiently controlling transmission of light and heat through windows in order to suppress energy consumption of buildings. In particular, versatile electrochromic windows operating in the bright, cool, and dark modes attract attention. In the present work, we synthesized amorphous oxygen-deficient WO_3−x nanoparticles and Cu-doped NiO nanoparticles by simple and convenient methods and assembled an electrochromic cell by using the nanoparticles. In the bright mode at +1.0 V, the cell transmitted ∼90 % visible light at 500 nm and ∼80 % near infrared (NIR) light at 1000 nm, whereas the transmittance was suppressed to 10–20 % in both of the visible and NIR ranges in the dark mode at −3.0 V. In the cool mode at −2.5 V, the cell showed a marked contrast in the optical transmittance: ∼90 % in the visible and ∼20 % in the NIR range. The oxygen deficiency of the WO_3−x cathode and/or the Cu doping of the NiO anode led to the high visible-NIR transmittance contrast in the cool mode, in addition to excellent cyclability at least for 12000 cycles and improved coloration efficiencies in the visible and NIR ranges.