Ion diffusion and electrochromic performance of poly(4,4′,4″-tris[4-(2-bithienyl)phenyl]amine) based on ionic liquid as electrolyte

Ionic liquids 1-butyl-3-methyl-imidazolium tetrafluoroborate ([BMIM]BF 4 ), 1-butyl-3-methylimidazoliumhexafluorophosphate ([BMIM]PF 6 ) and conventional medium tetrabutylammonium perchlorate (TBAP) were utilized as electrolyte for the preparation of poly(4,4′,4′'-tris[4-(2-bithienyl)phenyl]amine) (PTBTPA) films and assembling of EC devices. FTIR spectra and EDX pattern demonstrate an effective doping of the anion into the PTBTPA film at the oxidation state. SEM images investigate the thickness of the polymer films and the morphologies of crimped structure at the oxidation state. The ion diffusion distance (the thickness of polymer film) plays a more critical role for the EC switching speed. According to the electrochemical impedance spectra, the improved ionic conductivity with ionic liquid [BMIM]BF 4 as the electrolyte promote ions more easily dope into the polymer film which leads to the higher optical contrast. In addition, the size of doping anion during the redox process has essential influence on the electrochemical stability.