Ozone-Based Oxidative Chemical Vapor Deposition Yields Overoxidized PEDOT

Oxidative chemical vapor deposition (oCVD) is an attractive synthetic route to polymer coatings, offering such advantages as precise control over deposition at the nanoscale and elimination of the need to solubilize monomers in a solution. We investigate oCVD as a path to generate poly(3,4-ethylene dioxythiophene) (PEDOT) but using ozone (O3) gas as the oxidant rather than the more common conventional liquid or solid oxidants. The chemical structure of the resulting polymer films is shown to be an overoxidized form of PEDOT (O-PEDOT) comprising short-chain PEDOT as well as overoxidized ketone and sulfone structures formed by oxidation of the thiophene ring, even as the oxyethylene chain of PEDOT remains intact. This disruption of conjugation and formation of short-chain oligomers results in the film being electronically insulating, exhibiting a conductivity of 4.7 × 10–11 S cm–1. In such forms, the O-PEDOT film presents itself as an attractive dielectric polymer for advanced energy applications due to its conformality in 3D porous structures, low surface roughness (∼0.5 nm), and pinhole-free nature for films as thin as 15 nm. We also present the oCVD reaction of pyrrole-O3, in which similar overoxidation occurs, although this time oxidation does not occur at the heteroatom. This work widens the scope of materials that can be synthesized using oCVD, introducing a path for coating thin, pinhole-free dielectrics on planar and complex substrates.