Systematic investigation of charge transport and thermoelectric properties in semicrystalline polymers: electrochemical doping effects on doping level and temperature dependence using one sample

Abstract We developed a system to measure the temperature dependence of the Seebeck coefficient ( S ), electrical conductivity, and magnetoconductivity of conducting polymers with controlled doping levels, using an electrolyte-gated transistor structure on a single sample. In the semicrystalline polymer poly[2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT), S reflects hopping-like transport in the low-doped state, while metallic behavior dominates in the highly-doped state. At low temperatures in the highly-doped regime, S deviates from metallic behavior, showing an unusual trend attributed to the coexistence of localized and delocalized transport processes. Magnetoconductance measurements down to 80 mK confirm this coexistence, highlighting the interplay between two-dimensional weak localization and variable-range hopping. These findings reveal the complexity of transport mechanisms in conducting polymers and provide essential insights for optimizing thermoelectric and electronic devices through careful control of doping and transport properties.