Correlating Charge Transport with Intrinsic Energetic Disorder, Paracrystallinity and Carrier-Dopant Distance in Doped Conjugated Polymers

High-performing organic electronics rely on organic materials with efficient charge transport. Recent advances in understanding the effects of dopants in polymers pushed the field towards a deeper understanding of dopant-induced energetic disorder. Yet, the interaction between intrinsic energetic disorder, caused by polymer morphology, and extrinsic energetic disorder, caused by Coulomb interactions with dopant ions, has not been fully established. Here we investigate the role of repeat unit connectivity and long-range order of thiophene-based polymers on dopant-induced energetic disorder. The charge transport properties were obtained by measuring Seebeck coefficient and electrical conductivity using a vapor doping-de-doping procedure. The thin film structures were studied using UV-Vis spectroscopy, X-ray scattering, and atomic force microscopy. A phonon-assisted hopping model was used to simulate charge transport and fit to experimental data. This experimental-computational study shows that polymers with shorter polaron-counterion distances lead to increased extrinsic dopant-induced disorder due to additional Coulomb interactions. Our work shows a need for an integrated molecular design that requires both low intrinsic disorder and extrinsic dopant-induced energetic disorder for efficient charge transport.