Parameters affecting the quality of vapour phase polymerised (VPP) PEDOT and their influence on electrochromic device performance were investigated. Specifically, the role of water during synthesis was examined and a polymerisation mechanism proposed. Paradoxically, water vapour is essential for PEDOT polymerisation, however, too high a loading leads to crystallite formation in the oxidant layer, rendering the oxidant inactive. Changes in water vapour affect the doping level of the polymer, presumably due to poor conjugation along the polymer's backbone during synthesis. The addition of a surfactant, PPG-ran-PEG, was studied using XPS. The surfactant inhibited oxidant crystal growth and slowed the rate of PEDOT polymerisation, reducing film defects and improving PEDOT conductivity. Controlling and optimising the levels of water vapour and surfactant during synthesis resulted in reproducible, high conductivity, high optical switch, PEDOT films. Finally, complementary dual-polymer electrochromic devices utilising (pre- and post-process-enhanced) VPP PEDOT and PMAS (control) were fabricated and changes in switching transmission evaluated.

Vapor phase polymerization (VPP) is at the forefront for synthesizing high conductivity poly(3,4-ethylenedioxythiophene) (PEDOT) as an alternative to indium tin oxide (ITO). Little attention, however, has been directed to the oxidant layer used in the polymerization process. In this study the observation of an oxidant layer (oxidant + PEG–PPG–PEG) possessing liquid-like properties during the vacuum synthesis of PEDOT is reported. This is in contrast to the other oxidant layer variants studied which are observed as solid (pristine oxidant) or gel-like (oxidant + pyridine). Tailoring of the liquid-like properties leads to confluent PEDOT films with a conductivity of 2500 S cm⁻¹, placing this PEDOT within the conductivity range of commercially available ITO. Building on the liquid-like observation, XPS and ToF-SIMS experiments reveal that PEDOT growth is via a bottom-up mechanism with transportation of new oxidant up to the forming PEDOT layer.