title: Eliminating degradation and uncovering ion-trapping dynamics in electrochromic WO3 thin films.
abstract: There is keen interest in the use of amorphous WO3 thin films as cathodic electrodes in transmittance-modulating electrochromic devices. However, these films suffer from ion-trapping-induced degradation of optical modulation and reversibility on extended Li(+)-ion exchange. Here, we demonstrate that ion-trapping-induced degradation, which is commonly believed to be irreversible, can be successfully eliminated by constant-current-driven de-trapping; that is, WO3 films can be rejuvenated and regain their initial highly reversible electrochromic performance. Pronounced ion trapping occurs when x exceeds ∼0.65 in LixWO3 during ion insertion. We find two main kinds of Li(+)-ion-trapping site (intermediate and deep) in WO3, where the intermediate ones are most prevalent. Li(+) ions can be completely removed from intermediate traps but are irreversibly bound in deep traps. Our results provide a general framework for developing and designing superior electrochromic materials and devices.
authors.affiliation: Department of Engineering Sciences, The Ångström Laboratory, Uppsala University, PO Box 534 SE-75121 Uppsala, Sweden.
authors.forename: Rui-Tao
authors.initials: RT
authors.lastname: Wen
authors.affiliation: Department of Engineering Sciences, The Ångström Laboratory, Uppsala University, PO Box 534 SE-75121 Uppsala, Sweden.
authors.forename: Claes G
authors.initials: CG
authors.lastname: Granqvist
authors.affiliation: Department of Engineering Sciences, The Ångström Laboratory, Uppsala University, PO Box 534 SE-75121 Uppsala, Sweden.
authors.forename: Gunnar A
authors.initials: GA
authors.lastname: Niklasson