Fabrication of nanostructured polythiophene derivative films and their applications in large-size electrochromic devices

Conducting polymers (CPs) are commonly explored in electrochromic devices (ECDs) because of their designable compound structure, rich color, fast switching speed, flexibility and high coloration efficiency. However, the preparation of large-size nanostructured electrochromic polymer (ECP) films is still a great challenge. Herein, we present a facile and efficient strategy to construct neat large-size nanostructured ECP films without molecular design. Polyterthiophene (PTTh), poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(2,2 '-bithiophene) (PBTh) are selected as the model polymers due to their good EC behaviors. The PTTh hollow microspheres, PEDOT and PBTh nanoparticles (NPs) were prepared by in situ chemical oxidative polymerization without templates, and then were made into stable dispersions, which were processed into films by spray-coating method. The obtained films were further assembled into the ECDs. We investigated the structure, morphology and electrochemical properties of PTTh, PEDOT and PBTh films, and EC performance of corresponding ECDs. The results indicate that the uniform and loose PTTh film possesses 3D porous structure composed of many hollow microspheres, while the PEDOT and PBTh films consist of many NPs. These films exhibit good electrochemical performance. The ECD based on PEDOT film achieves an optical contrast of 29%, coloration efficiency of 217 cm2/C, and its coloration time and bleaching time are 3.48 and 0.09 s, respectively. This study suggests that in situ chemical oxidative polymerization preparation of ECP microspheres or NPs might be a facile strategy for fabricating neat large-size ECP films, and its preparation process is easily conducted, showing great potential applications in conducting polymer-based ECDs.