Contrast Enhancement in Polymeric Electrochromic Devices Encompassing Room Temperatu re Ionic Liquids

We report the preparation and spectro - electrochemical characterization of electrochromic devices (ECD) combining inkjet - printed WO 3 as cathode and electro - deposited V 2 O 5 as anode. ECD were prepared for the first time with an optimized formulation of gel polymer electrolyte based on Bisphenol A ethoxylate dimethacrylate and Poly(ethylene glycol) methyl ether methacrylate (BEMA/PEGMA) encompassing the Room Temperature Ionic Liquid (RTIL, 1 - Ethyl - 3 - methylimidazolium bis(trifluoromethylsulfonyl)imide) as solvent. The UV - VIS spectrum of ECD was recorded at different potentials during Li + insertion and de - insertion; additionally the Percent Trasmittance (T%) of ECD vs. time was investigated during repeated bleaching and coloring cycles allowing thus the esti mation of switching times and device stability. Due to the lower ionic conductivity and the apparent superior solvent permeability within WO 3 active layer, RTIL containing ECD showed slower switching times, but higher contrast with respect to the similar o nes with EC/DEC as solvent. These results indicate that the ECD containing environment - friendly RTIL electrolytes are suitable for applications requiring high contrast, high safety and moderately fast switching times.