Effect of organic solvent treatments on oCVD-deposited PEDOT thin films

Thiophene-based polymers, notably poly(3,4-ethylenedioxythiophene) (PEDOT) and its composite with poly(styrenesulfonate) (PEDOT:PSS), are attractive targets for thermoelectric research because of their high ZT values and ease of thin-film synthesis, but traditional solution-phase routes limit both chemical control and applicable form factors. Oxidative chemical vapor deposition (oCVD) is an alternative technique capable of producing highly conductive PEDOT films without the use of PSS, yet the thermoelectric properties of PEDOT produced through oCVD have not been as thoroughly investigated. Here, we report an enhancement in thermoelectric properties of oCVD-grown PEDOT films with V2O5 inclusions through treatment in polar aprotic, high-dielectric organic solvents (DMSO, EG, and DMF). In solution-phase deposited films, the performance enhancements from post-deposition treatments in such solvents are often attributed to depletion or segregation of the insulating PSS phase, but the similar enhancements in our PSS-free films show that other effects on the physicochemical nature of the PEDOT must also be present. Our observations provide key insights into routes to optimize vapor-phase deposited PEDOT as well as the potentially misunderstood effects of organic solvents on PEDOT in general.