The reduced pressure synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) with sheet-like morphology has been achieved with the introduction of an amphiphilic triblock copolymer into the oxidant thin film. Addition of the copolymer not only results in an oxidant thin film which remains liquid-like under reduced pressure but also induces structured growth during film formation. PEDOT films were polymerized using the vacuum vapor phase polymerization (VPP) technique, in which we show that maintaining a liquid-like state for the oxidant is essential. The resulting conductivity is equivalent to commercially available indium tin oxide (ITO) with concomitant optical transmission values. PEDOT films can be produced with a variety of thicknesses across a range of substrate materials from plastics to metals to ceramics, with sheet resistances down to 45 Ω/□ (ca. 3400 S•cm −1 ), and transparency in the visible spectrum of >80% at 65 nm thickness. This compares favorably to ITO and its currently touted replacements.

Vapor phase polymerization (VPP) is at the forefront for synthesizing high conductivity poly(3,4ethylenedioxythiophene) (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 À1 , 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.

The synthesis of high conductivity poly(3,4‐ethylenedioxythiophene) (PEDOT) films using vacuum vapour phase polymerisation is reported. Water vapour is introduced into the chamber and results suggest that it acts as a proton scavenger during polymerisation. Process optimisation leads to PEDOT films that have high conductivity and a blue‐black appearance. Poor quality films have lower conductivity and a characteristic greenish colour. UV‐vis‐NIR spectra show that poor PEDOT films are characterised by higher absorption in the UV‐vis region and an absorption plateau in the NIR region, which suggests an increased level of disrupted conjugation along the polymer backbone or higher oligomer content. Conversely, high quality PEDOT is characterised by an extended NIR absorption tail and lower absorption in the UV‐vis region.magnified image

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.