Electrochromic device

Abstract

An improvement of electrochromic devices incorporating a perfluorosulfonic acid polymer ion conducting layer interposed between a working electrode and a counter electrode. The improvement relates to the composition of the perfluorosulfonic acid polymer of the ion conducting layer. In the present invention the composition of the perfluorosulfonate polymer layer is a polymer comprising a substantially fluorinated backbone which has recurring pendant groups attached thereto represented by the formula --O--(CFR'.sub.f).sub.b --(CFR.sub.f).sub.a --SO.sub.3 --, where a=0-3, b=0-3, a+b=at least 1, and R.sub.f and R'.sub.f are independently selected from the group consisting of a halogen and a substantially fluorinated alkyl group having one or more carbon atoms. One example of such a polymer is the copolymer of tetrafluoroethylene and 1,1,2,2-tetrafluoro-2-((trifluoroethenyl)oxy)ethane sulfonic acid having an equivalent weight of about 800. The primary benefit of the present invention is that the electrochromic device darkens sufficiently to be useful when the device is operated at high temperature such as can be encountered in an automobile electrochromic sun roof on a sunny day in a hot climate.