Flexible foils with electrochromic coatings: science, technology and applications

This paper covers a number of aspects of a novel flexible electrochromic foil capable of varying its optical transmittance. The foil includes thin films of tungsten oxide and nickel oxide and an intervening polymer electrolyte serving as lamination material. Concerning scientific aspects, we discuss the prevalent defects in amorphous tungsten oxide and how they lead to a consistent picture of the optical properties of tungsten oxide films as a function of non-stoichiometry and ion intercalation. We also present a refined model for the coloration/bleaching due to proton extraction/insertion in surface sheaths of nano-crystallites of nickel oxide. We then turn to aspects of technology and treat ways to enhance the bleached-state transmittance by mixing the nickel oxide with another oxide having a wide band gap, pre-assembly charge insertion/extraction by facile gas treatments of the films and practical device manufacturing. The final part covers some applications with emphasis on architectural “smart windows” capable of achieving improved indoor comfort together with significant energy savings due to lowered demands for space cooling. We also touch upon applications concerning eyewear.