Microstructure and heteroatom dictate the doping mechanism and thermoelectric properties of poly(alkyl-chalcogenophenes)

Heteroatom substitution can favorably alter electronic transport in conductive polymers to improve their thermoelectric performance. This study reports the spectroscopic, structural, and properties of poly(3–(3?,7?-dimethyloctyl) chalcogenophenes) or P3RX doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), where heteroatom [X = thiophene (T), selenophene (Se), tellurophene (Te)], doping methodology, extent are systematically varied. Spectroscopic measurements reveal that while all appreciably doped, mechanism is inherently different. Poly(3-hexylthiophene) (P3HT, used as a control) poly(3–(3?,7?-dimethyloctyl)tellurophene) (P3RTe) primarily via integer charge transfer (ICT), whereas poly(3–(3?,7?-dimethyloctyl)selenophene) (P3RSe) poly(3–(3?,7?-dimethyloctyl)thiophene) (P3RT) complex (CTC) mechanisms. Despite these differences, saturate roughly same number F4TCNQ counterions (1 dopant per 4 6 heterocycles), reinforcing idea varies mechanism. Grazing incidence wide-angle x-ray scattering provide insight into structural driving forces behind different mechanisms—P3RT P3RSe have similar microstructures which intercalates between ?-stacked backbones resulting CTC (localized carriers), P3HT P3RTe alkyl side chain region, giving rise ICT (delocalized carriers). These spectroscopic observations shed light on why obtain electrical conductivities ca. 3 S/cm, P3RT <10?3 S/cm under thin film processing conditions. Ultimately, this work quantifies effects heteroatom, microstructural ordering, doping, mechanism, thereby providing rational guidance for designing future polymer-dopant systems.