Truly solid state electrochromic devices constructed from polymeric ionic liquids as solid electrolytes and electrodes formulated by vapor phase polymerization of 3,4-ethylenedioxythiophene

Abstract

Using polymeric ionic liquids, namely poly[1-(2-(2-(2-(methacryloyloxy)ethoxy)ethoxy)ethyl)-3-methylimidazolium]bis(trifluoromethylsulfonyl)imide or tetracyanoborate, and poly(3,4-ethylenedioxythiophene) (PEDOT) as an ion conductor and electrodes, respectively, the all-polymer-based thin-film symmetrical electrochromic devices (ECDs) have been constructed and tested. The proposed architecture serves as a prove of concept that polymeric ionic liquids (PILs) can be themselves used as solid electrolytes thus avoiding any electrolyte leakage since the ionic liquid species are grafted on the polymer backbone. Three different methods for the synthesis of PEDOT electrode films, including two new approaches consisted in vapor phase polymerization of 3,4-ethylenedioxythiophene (EDOT) in the presence of ionic monomer and poly(ethylene glycol)(di)methacrylates, have been investigated. Two oxidants, Fe[(CF3SO2)2N]3 and Fe[(CN)4B]3, bearing the same anions as PILs were prepared for the first time and utilized in the vapor phase polymerization of EDOT. It was found that the more compact structure and the highest conductivity are achieved for PEDOT electrodes prepared by vapor phase polymerization of EDOT in the presence of ionic monomer and poly(ethylene glycol)(di)methacrylates, followed by radical polymerization of the latters. The simplicity of ECDs assembly, their fast switching times (3–5 s), high coloration efficiency (up to 430 cm2/C), satisfactory optical contrast (up to 28.5%), absence of any liquids and good performance in air and in vacuum were found among the advantages of the proposed technology.