Controllable vapor phase polymerization of PEDOT films using imidazole as an inhibitor and their electrical and electrochromic properties

PEDOT films were fabricated by vapor-phase polymerization (VPP) with different inhibitor contents in oxidant-containing solutions, and were characterized by X-ray diffraction, Raman spectroscopy, UV/vis transmittance spectra, atomic force microscopy, electrical conductivity and electrochromic measurements. The imidazole which serves as an inhibitor plays key roles on the polymerization reaction, and varying its content results in drastically different properties of the PEDOT films. In the imidazole/Fe(III) p -toluenesulfonate (Im/Fe) weight ratio range of 0∼0.25, the rate of polymerization can be significantly slowed down by increasing the Im/Fe ratio. The optimum Im/Fe ratio of 0.1 and polymerization time of 3 h results in PEDOT films with the highest conductivity on glass substrate (626 S/cm). Higher doping level is found in PEDOT films fabricated with the Im/Fe ratio above 0.1, causing low conductivity due to their loose morphology. The electrochromic properties of the films can be enhanced by prolonging the polymerization time to 3 h. It is found that the transmittance difference at 550 nm is above 10 % in PEDOT films fabricated with 3 h of polymerization. An electrochromic device is assembled and its coloring time is less than 3 s.