The electrochemistry and ion transport properties of PEDOT in different solvents have been investigated. Conductivity enhancement has been observed in dimethyl sulfoxide (DMSO) and ethylene glycol (EG). This is attributed to the transformation of polymer chains from compact to linear structure induced by such high dipole moment solvent treatment (DMSO or EG). The results of electrochemical quartz crystal microbalance (EQCM) indicate that the solvent plays an important role in redox process. The poly(3,4-ethylenedioxythiophene) (PEDOT) reveals a better reversibility of ionic transfer in DMSO compared with that measured in acetonitrile (ACN). A solution and thin film system electrochromic device (ECD) based on 4-phenothiazin-10-yl-anisole (APS) solution and a PEDOT thin film was assembled and studied. The device demonstrates the color change from colorless (0 V) to deep blue violet (1.6 V). A maximum transmittance window 65% was obtained at 520 nm with the operating potentials between 0 and 1.6 V in DMSO electrolytes. Coloration efficiency of the ECD has been found to be 410 cm(2)/C. No pre-darkening or pre-bleaching of the electrodes is required for assembly of such ECD. (C) 2014 Elsevier B.V. All rights reserved.