Electrochemical copolymerization of 4,4'-di(N-carbazoyl)biphenyl (CBP) with 2,2'-bithiophene (BT) is carried out in acetonitrile (ACN)/dichloromethane (DCM) (1:1, by volume) solution containing sodium perchlorate (NaClO(4)) as a supporting electrolyte. Characterizations of the resulting copolymer P(CBP-co-BT) are performed by cyclic voltammetry (CV), UV-vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and thermogravimetry (TG). The P(CBP-co-BT) film has distinct electrochromic properties and exhibits four different colors (orange yellow, blue, yellowish green and greenish blue) under various potentials. Maximum contrast (AT%) and response time of the copolymer film are measured as 51.6% and 0.94 s at 667 nm. An electrochromic device (ECD) based on P(CBP-co-BT) and poly(3,4-ethylenedioxythiophene) (PEDOT) is constructed and characterized. The optical contrast (Delta T%) at 700 nm is found to be 28.6% and the response time is measured as 0.47 s. The coloration efficiency (CE) of the device is calculated to be 234 cm(2) C(-1) at 700 nm. An ECD also has good optical memories and redox stability. (C) 2011 Elsevier B.V. All rights reserved.