Electrochromic smart windows

Abstract

A solid state electrochromic smart window has the configuration glass/TC/EC/IC/IS/TC/glass, where TC is a transparent conductor, EC is an electrochromic coating, IC is an H+ or Li+ ion conductor and IS is an H+ or Li+ ion storage layer. Application of a small voltage at the TC electrodes changes optical transmission of the device in a persistent reversible manner. Porous and slightly crystallized sol-gel coatings of TiO2-CeO2 composition have the required properties for ion storage counter electrodes. Layers 150 nm thick have 80% optical transmission in the visible range, do not color after H+ and Li+ insertion and show good electro-chemical stability. These layers have been used as H+ or Li+ ion storage electrodes, where EC was WO3. The protonic IC was a cellulose polyacetate polymer and the lithium IC was PEO-LiN(SO2CF3). Electro-chemical and optical performances of the cells are reported. © 1992 Elsevier Science