Electron spin resonance and electrical transport in films of poly (3,4-ethylenedioxythiophene) doped with poly(styrenesulphonate)

We report electron spin resonance (ESR) and electrical transport measurements in pristine poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulphonate) (PEDOT:PSS) films and ethylene glycol (EG)-treated PEDOT:PSS films. Based on the assumption that ESR from PEDOT:PSS is mainly due to hole polarons, we estimated the polaron mobility in the PEDOT:PSS films as μ p ≈ 0.1 - 1 cm² V^-1 s^-1. We also estimated that bipolaron mobilities are in the range of approximately 10-100 cm² V^-1 s^-1, assuming that the initial hole density is unaffected by bipolaron formation. We measured transient currents following application of voltage bias in several films, which had the features of space-charge limited currents despite being measured with coplanar electrodes. The relative nominal mobilities obtained for hole polarons in PEDOT:PSS and for bipolarons in EG-PEDOT:PSS were not inconsistent with the results obtained from the ESR and conductivity measurements. However, although the inferred mobility was voltage-independent for untreated samples with hole polarons, the inferred mobility increased steeply with the applied voltage, consistent with exp (V) behavior, for EG-treated samples.