Ultrafast Electrochromic Windows Based on Redox-Chromophore Modified Nanostructured Semiconducting and Conducting Films

Abstract

Described is the construction of an ultrafast electrochromic window. One electrode of this window is based on a transparent nanostructured TiO 2 (anatase) film (4.0 μm thick) supported on conducting glass (F-doped tin oxide, 10 Ω cm -2, 0.5 μm thick) and modified by chemisorption of a monolayer of the redox chromophore bis(2-phosphonoethyl)-4,4‘-bipyridinium dichloride. The other electrode is based on a transparent nanostructured SnO 2 film (3.0 μm thick) supported on conducting glass (F-doped tin oxide, 10 Ω cm -2, 0.5 μm thick) and modified by chemisorption of a monolayer of the redox chromophore [β-(10-phenothiazyl)propoxy]phosphonic acid. The electrolyte used is LiClO 4 (0.2 mol dm -3 ) in γ-butyrolactone. The excellent performance of a 2.5 cm × 2.5 cm window over 10 000 electrochromic test cycles switching times (coloring and bleaching) of less than 250 ms, coloration efficiency of 270 cm 2 C -1, steady-state currents (colored and bleached) of less than 6 μA cm -2, and memory of greater than 600 s (time required for low end transmittance to increase by 5%) suggest a practical technology.