Fast Switching Electrochromic Devices Containing Optimized BEMA/PEGMA Gel Polymer Electrolytes

An optimized thermoset gel polymer electrolyte based on Bisphenol A ethoxylate dimethacrylate and Poly(ethylene glycol) methyl ether methacrylate (BEMA/PEGMA) was prepared by facile photo-induced free radical polymerisation technique and tested for the first time in electrochromic devices (ECD) combining WO3 sputtered on ITO as cathodes and V2O5 electrodeposited on ITO as anodes. The behaviour of the prepared ECD was investigated electrochemically and electro-optically. The ECD transmission spectrum was monitored in the visible and near-infrared region by varying applied potential. A switching time of ca. 2？s for Li+ insertion (coloring) and of ca. 1？s for Li+ de-insertion (bleaching) were found. UV-VIS spectroelectrochemical measurements evidenced a considerable contrast between bleached and colored state along with a good stability over repeated cycles. The reported electrochromic devices showed a considerable enhancement of switching time with respect to the previously reported polymeric ECD indicating that they are good candidates for the implementation of intelligent windows and smart displays. 1. Introduction Recently electrochromic (EC) materials have attracted considerable attention due to their potential application in several types of optical devices including intelligent windows and smart displays. They can change colour in a persistent and reversible way by potential-promoted ion insertion/de-insertion mechanism. Generally, this colour response is induced by the application of a low-dc potential [1]. The mounting interest in the use of these materials on electrochromic devices (ECD) is mainly due to the high visibility and high reflective contrast ratio compared to other displays, for example, LCD without backlighting. EC materials are generally inorganic oxides that can be divided between those changing colour under ions insertion (cathode) and those changing colour during ions de-insertion (anode). Many transition metal (W, Ir, Mn, Co) oxides have been studied for their electrochromic behaviour and stability with respect to the organic ones [1]. One of the first candidates studied for such application was tungsten oxide (WO3) [2–4]. In particular, the surfactant assisted electrochemical synthesis of WO3 [5] is one of the most promising methods for the production of nanostructured powders suitable for inks formulations. The counter electrode, in general, is considered the limiting factor in the EC device [6]. Vanadium oxide (V2O5) is a good candidate for EC devices as it is a lithium battery cathode material, which shows different colours