Distinctive Doping Behavior of Conjugated Polymers With Pendant-Side Conjugation for Enhanced Thermoelectric Properties

Abstract

Organic thermoelectric (OTE) materials are continuously evolving through the development of novel conjugated polymers and corresponding doping methods. FeCl3 doping is the most commonly used method because of its affordability and strong oxidizing power. However, at high dopant concentrations, FeCl3 interferes with the molecular ordering and negatively impacts on the morphology, which causes a substantial decline in performance. To address this issue, in this study, new OTE polymers with π-conjugation along the pendant side are developed. This unique polymeric structure enables pendant doping with FeCl3 by forming a strong binding complex at the conjugated side chains, where an abundant free volume exists. Consequently, the intermolecular ordering of the OTE polymer is well preserved even under high dopant concentration, thereby enabling a high power factor exceeding 10 µW m−1 K−2 consistently across a wide range of high dopant concentrations (16–32 mM) for the first time. This distinctive doping behavior on the pendant side will provide a new opportunity to develop high-performance OTE polymers.