Electrochemical synthesis of poly(3,4-ethylenedioxythiophene) nanotubes towards fast window-type electrochromic devices

A structure comprising nanotubes on a transparent substrate is a key to fabricating fast window-type electrochromic devices. We describe the fabrication of a thin porous anodic aluminium oxide (AAO) structure as a template and poly(3,4-ethylenedioxythiophene) (PEDOT) nanotubes. The AAO template with small pore diameters (about 70 nm) is prepared by sputtering and subsequently anodizing a thin layer of aluminium on an indium-doped tin oxide/glass substrate. The PEDOT nanotubes are electrochemically synthesized on flat electrodes in the AAO nanopores. This requires a low monomer concentration and a high applied potential, mainly because of the increased monomer flux into the pores of the thin template due to the steeper concentration gradient. Fast colour changes (50 and 70 ms response times for oxidation and reduction, respectively) are achieved using partially-filled PEDOT nanotubes in a window-type electrochromic device.