Conductive polymers as electrochromic material in solid state electrochromic devices

Abstract

By combining a processable electronically conductive polymer [poly(3-octylthiophene) (P3OT), polypyrrole (PPy)], a solid polymer electrolyte [(PEO)₈LiClO₄], and a metal oxide (V₂O₅), a solid state electrochromic device is constructed. The polymer films are fabricated by spin coating from solution (P3OT) and template polymerization (PPy). The metal oxide is electrochemically doped with Li⁺ and the electrodes are mounted in a sandwich structure with a thin film of polymer electrolyte in between. As the applied cell potential is changed, the optical absorption of the cell is changed. Owing to the difference in columbic capacity between the different materials, the optical changes of the cell are due to optical changes of the polymer only. This means that, instead of having to adapt often contradictory optical changes in two electrochromic materials for the desired application, one can use a polymer with a proper optical signature, letting the band gap determine the electro-optical behavior of the cell.