Synthesis and electrochromic properties of poly(3-hexyl-thiophene) in a room temperature ionic liquid and its application to an electrochromic device

Electrochemical polymerization in a room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆), was used to prepare electrochromic poly(3-hexylthiophene) (PHexT). Characterization of the resulting polymer was performed by cyclic voltammetry and scanning electron microscopy analyses. Spectroelectrochemistry and electrochromic properties were also characterized using various experimental techniques in the same pure ionic liquid. The thin film of PHexT was orange red in its fully reduced state. After oxidization of the undoped polymer, the film underwent a reversible change to the blue form. The PHexT film exhibited high chromatic contrast (40%), comparative switching time (2.5 s) and great electrochromic efficiency (230 cm²/C). A PHexT-based electrochromic device was constructed and its electrochromic properties were also investigated in this paper.