Achieving neutral-tinted and energy-efficient electrochromic device enabled by sputtered tungsten-niobium-oxygen film for smart windows

WO 3 based electrochromic device (ECD) is becoming the mostly-used one for smart windows, however, in WO 3 tinted state, the intrinsically deep blue and strong infrared (IR) light absorption, resulting in a habitant discomfortableness and also an enhanced thermal gain from the heated device surface, severely restrict its diversified applications. Herein, we firstly conduct a kind of columnarly-grown and amorphous WO 3 film with high concentration of niobium doping (Nb/(Nb+W) = 54.1 at.%). This film is fabricated via sputtering a home-made ceramic target, and subsequently improved by a rapid thermal annealing (RTA) process. Comparing with the conventional WO 3 , the newly-established system owns not only basic EC properties comprising large light modulation range, fast response, and long-term electrochemically cyclic stability, but also a neutral-tinted color ( a * = −1.5, b * = 1.0) as well as a relatively lower IR absorption (63.7 %) in tinted state. These outstanding performances enable the assembled ECD with neutral color ( a * = 0.6, b * = −2.7) and a higher energy efficiency in cutting down the interior space air temperature about 4.3 °C in its fully-tinted state, underscoring the potential of the tungsten-niobium-oxygen for commercially viable ECDs.