TUNING THE BANDGAP FOR POLYMERIC SMART WINDOWS AND DISPLAYS

Abstract The band gap, and thus the optical properties, of polythiophene can be turned for use in electrochromic applications by attaching substituents to the monomers before polymerization. Electron donating substituents lower the bandgap, while steric interaction of side groups on adjacent thiophene rings forces the conjugated backbone to twist and increases the band gap. By choosing the right combination, a polymer with specific optical properties can be designed. Properties of interest for electrochromic applications, like oxidation potential, ionic conductivity and thermal stability, can also be improved by substitution. Poly(ethylene-dioxythiophene) (PEDOT) has shown to have interesting optical properties, increased ionic conductivity and a high thermal stability.