Structural Control of Charge Storage Capacity to Achieve 100% Doping in Vapor Phase-Polymerized PEDOT/Tosylate.

Vapor phase polymerization (VPP) is used to fabricate a series of tosylate-doped poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes on carbon paper. The series of VPP PEDOT/tosylate coatings has varying levels of crystallinity and electrical conductivity because of the use (or not) of nonionic triblock copolymers in the oxidant solution during synthesis. As a result, the impact of the structure on charge storage capacity is investigated using tetra-n-butylammonium hexafluorophosphate (0.1 M in acetonitrile). The ability to insert anions, and hence store charge, of the VPP PEDOT/tosylate is inversely related to its electrical conductivity. In the case of no nonionic triblock copolymer employed, the VPP PEDOT/tosylate achieves electrochemical doping levels of 1.0 charge per monomer or greater (≥100% doping level). Such high doping levels are demonstrated to be plausible by molecular dynamics simulations and density functional theory calculations. Experiments show that this high doping level is attainable when the PEDOT structure is weakly crystalline with (relatively) large crystallite domains.

Influence of Postsynthesis Heat Treatment on Vapor-Phase-Polymerized Conductive Polymers.

The effect of thermal treatment on the structure and electrical/optical properties of vapor phase-polymerized poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:Tos) and polypyrrole:tosylate (PPy:Tos) polymer films was investigated. Thermal treatment was applied postpolymerization but prior to washing the embedded oxidant layer out of the polymer film. Structural and chemical changes arising from the treatment were studied in the context of their conductive and electrochromic behavior. Spectroscopic analysis indicated a rise in the doping levels of both conductive polymers when exposed to thermal treatment. Additionally, an increase in the film thickness was recorded after the oxidant and other unbound species were removed from the polymer layer using an ethanol rinse. As such, a strong indication that polymerization continued even in the absence of (external) monomer vapor was present. This film thickness increase was most pronounced for PPy:Tos but also present in the PEDOT:Tos film. Heat-treated films exhibited enhanced cohesion, making them more robust and therefore increasing the viability for the material to be used in the optoelectronics area. This robustness, due to additional (cross-linking) oligomer growth, came at the expense of lower conductivity relative to their untreated counterparts.