<title>Flexible electrochromic foils: science, technology, and application</title>

Abstract

We discuss 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 laminated together by a polymer electrolyte. Starting with <i>scientific</i> issues, we discuss the dominating defects in amorphous tungsten oxide and how they may yield a consistent picture of the optical properties of tungsten oxide films versus nonstoichiometry and ion intercalation. We also present a detailed model for the coloration/bleaching due to proton extraction/insertion in thin surface sheaths of nanocrystallites of nickel oxide. Next we consider aspects of <i>technology</i> and treat options to enhance the bleached-state transmittance by mixing the nickel oxide with another oxide having a wide band gap. We also cover pre-assembly charge insertion/extraction by facile gas treatments of the films as well as practical device manufacturing. The final part of the paper deals with a number of <i>applications</i>, with emphasis on architectural "smart windows" which can improve indoor comfort at the same time as they accomplish significant energy savings due to lowered requirements for air cooling. Applications concerning electrochromics-based eyewear are introduced; these may be approaching market introduction.