Enhanced Electrochromic Switching and Electrochemical Stability of Conducting Polymer on the Ionic Liquid Functionalized ITO Electrode

Conducting polymers (CPs) based electrochromic materials have drawn wide interests owing to multicolor display property, high coloration efficiency, good processibility and high optical contrast. However, the relatively slow response speed and poor long-term stability have severely limited their applications. Therefore, to improve the response speed and long-term stability via various methodsis is one of the key to expand the practical applications of the CPs-based electrochromic devices. Ionic liquids are good for electrochemical synthesis and applications as a promising medium due to their wide electrochemical windows, good electrical conductivity and solvent transport properties.^1-2 Therefore, ionic liquids has been introduced to improve the EC performance of conducting polymers. In this paper,  conducting polymer poly(4,4',4"-tris[4-(2-bithienyl) phenyl]amine) (PTBTPA) incorporated with 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF₄) was successfully prepared via electrochemical polymerization on the [BMIM]BF₄ functionalized ITO substrate. The PTBTPA–[BMIM]BF₄ film presents reversible multicolor changes from orange, olive green to dark gray. The electrochromic measurement exhibits the switching speed of conducting polymer is significantly enhanced by incorporating with ionic liquid than that of the pure PTBTPA film. Electrochemical impedance spectra demonstrates the PTBTPA–[BMIM]BF₄ film possesses much lower charge transfer resistance and faster charge transfer speed. In addition, the PTBTPA–[BMIM]BF₄ film presents better electrochemical stability in the ionic liquid.