Major effect of electropolymerization solvent on morphology and electrochromic properties of PEDOT films

Although significant efforts were devoted to improving the properties of conductive polymers, the effects of solvent and supporting electrolytes on the morphology and electrochromic features of electropolymerized materials have been scantly investigated. In this work, the effects of the polymerization conditions, such as the solvents and supporting electrolytes, on the morphological structure and electrochromic properties of PEDOT films were systematically studied. Surprisingly, we find a very significant solvent effect and a small supporting electrolyte effect. We show that morphological properties also strongly correlate with electrochromic properties. Films prepared in propylene carbonate have a smoother structure than those prepared in acetonitrile and this leads to superior electrochromic properties, such as an exceptionally high contrast ratio (71%), transparency in the doped state (80%), and coloration efficiency (193 cm²/C) for the films prepared in propylene carbonate. Significant differences between propylene carbonate and acetonitrile were explained by different solubilities of EDOT oligomers produced during initial stages of electropolymerization in these solvents.