The influence of sol–gel processing on the electrochromic properties of mesoporous WO3 films produced by ultrasonic spray deposition

• Mesoporous WO3 thin films were prepared using scalable ultrasonic spray deposition employing sol–gel chemistry with a triblock copolymer templating agent.
• State-of-the-art electrochromic performance was achieved with respect to coloration efficiency (>50 cm2/C), modulation (>75%), switching times (~6 s).
• The materials chemistry of the sol–gel process is evaluated by dynamic UV–vis spectroscopy.
• The material properties of the resulting mesoporous tungsten oxide are extensively characterized by FTIR, Raman, TEM, SAD and correlated to electrochromic performance.

High performance mesoporous tungsten oxide films were deposited by ultrasonic spray deposition using templated sol–gel chemistry. The dynamics of both sol preparation and hydrolysis were investigated by UV–vis spectroscopy. A stable sol was formed after 12 h, while optimum electrochromic performance was obtained for 12 h of hydrolysis. Electrochromic performance is strongly correlated to the annealing conditions, with optimized films displaying coloration efficiency >50 cm2/C and switching times <10 s. FTIR spectroscopy revealed that WO3 produced under optimized conditions were free of hydroxyl and carbonate impurities. Performance scaled with the specific surface area and nanoscale morphology. The WO3 films display good long term cycling durability up to 2500 cycles, which was attributed to the high degree of film crystallinity.

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