Temperature dependent conductivity of vapor-phase polymerized PEDOT films

• The conductivity of VPP PEDOT films is critically dependent on temperature.
• Synchrotron GAXRD shows [1 0 0] inter-chain stacking determines film conductivity.
• Temperature has a significant effect on VPP film growth rate.

The structure and properties of PEDOT films prepared under different vapor-phase polymerization (VPP) temperatures were characterized by grazing angle X-ray diffraction, Raman spectroscopy, UV/vis absorption, atomic force microscopy, scanning electron microscopy and electrical conductivity measurements. The VPP temperature plays key roles on the polymerization reaction rate and the mobility of the polymer chains as well as the volatilization of the reactant and product, which result in drastically different properties of the VPP PEDOT films. In the range of 33–57 °C, the lattice structure and the morphology of the films can be significantly affected by the VPP temperature. The optimum temperature (46 ± 1 °C) resulted in PEDOT film with the highest conductivity on glass substrate (622 S/cm), which is ascribed to highly ordered crystal structure and smooth morphology. After polymerization, the topography, efficiency of current transport and crystal structure of the PEDOT film in response to temperature were in situ monitored by means of conductive AFM and grazing XRD. For PEDOT films with a high level of conjugation, the film conductivity is mainly determined by the crystal structure of the film. The lamella inter-chain stacking order in [1 0 0] direction deeply influences the film conductivity, while the π–π stacking order in [0 1 0] direction has no apparent relation with the film conductivity. The film with highly ordered structure in [1 0 0] direction tends to have good film conductivity.