A novel all-organic electrochromic device (ECD) is presented. By electrodepositing poly (3-methylthiophene) (PMeT) in boron fluoride ethyl ether (BFEE), a strong Lewis acid, a good-quality PMeT film was obtained. On the basis of studies of PMeT, it can be regarded as a pseudo-anodic coloring material for ECDs. On the other hand, poly(3,4-ethylenedioxy-thiophene) (PEDOT) is an ideal cathodic coloring electrochromic material known for its high optical contrast, long-term stability, and high coloration efficiency. By combining these two thiophene derivatives, the application potential of this device was determined. The color of the ECD switches between deep blue at -1.4V (PEDOT vs. PMeT) and light red at 0.6V. The device exhibits stable electrochromic performance, with a maximum optical attenuation (Delta T-max) at 655 nm reaching 46% (from 9% to 55%), and achieves a high coloration efficiency of 336 cm(2)/C. After 100 repeated cycles, the cell still retained at 91.3% of its Delta T-max at 655 nm. (c) 2005 Elsevier B.V. All rights reserved.