Effect of counter anion on the uniformity, morphology and electrochromic properties of electrodeposited poly(3,4-ethylenedioxythiophene) film

Poly (3,4-ethylenedioxythiophene) (PEDOT) films were successfully deposited on fluorine-doped tin oxide (FTO) glass, through a facile electropolymerization process in aqueous solutions containing Cl−, p-toluenesulfonate ion (TsO−), NO3− or ClO4−. The influences of the counter anion in the electrolyte on the uniformity, morphology and electrochromic properties of the obtained PEDOT films were investigated. Scanning electron microscopy (SEM) was employed to characterize the morphology of the as-deposited films. Electrochemical measurements and ultraviolet–visible (UV–Vis) transmittance spectra were applied to investigate the electrochromic properties of PEDOT films, and the compositions of the films were studied by X-ray photoelectron spectroscopy (XPS). It has been demonstrated that the anion in the electrolyte during the electropolymerization process directly influences the uniformity, morphology and electrochromic performance of PEDOT films. The films prepared in Cl− possess a microstructure with poor uniformity, and present a unique bright blue/brown transition during the oxidation/reduction cycles, while that prepared in TsO−, NO3− and ClO4− consist of hierarchical submicroflowers, nanonetworks and submicroparticles, respectively, and all of them show sky blue/purple transition. The electrochromism process of PEDOT films are accompanied by insertion and extraction of ClO4−. Additionally, the maximum contrast, switching time and cycle life of the films are found to be varied with the counter anion.