Electrochromic films of a methylcarbazole derivative: optimization of polymerization and optical contrast

The effect of the polymerization potential and time on the electrochemical and optical responses of electrogenerated films of poly-3,6-bis(2-(3,4-ethylenedioxy)thienyl)-N-methylcarbazole] (PBEDOT-NMCz) was studied. Every electrogenerated film was characterized according to the charge consumed during polymerization, its redox charge density (calculated by integration of a control voltammogram), the efficiency of the polymerization process (defined as the charge consumed during electropolymerization to create one redox site), and its optical contrast. Within the studied polymerization potential range, 0.75 to 2 V, the charge consumed during polymerization increased with the potential, while the efficiency of the polymerization process decreased. The redox site production rate reached a maximum at 1.25 V. The optical contrast of the obtained films remained the same when polymerizing in the range between 0.75 and 1.25 V. Polymerization at more anodic potentials resulted in films of lower electrochromic quality (defined as the maximum contrast achievable). The optimal conditions for electropolymerization in terms of optimum energy consumption and the best electrochromic quality of the films were established.