A lamellar-ordered poly[bi(3,4-ethylenedioxythiophene)-alt-thienyl] for efficient tuning of thermopower without degenerated conductivity

Abstract

Modulating the structural order of conjugated polymers has emerged as a significant approach to enhance the organic thermoelectric performance. Among these materials, poly(3,4-ethylenedioxythiophene) is considered a promising candidate due to its high conductivity. However, its low thermopower remains a major obstacle to further improve its performance as an organic thermoelectric material. To address this issue, a series of thiophene derivatives with high rigidity and containing dioxyethylene groups were synthesized, and polymer films were prepared through a simple and mild in-situ polymerization method. The polymer molecule containing a thiophene block, named poly[bi(3,4-ethylenedioxy)-alt-thienyl] , exhibits significant self-rigidification due to non-covalent interactions between oxygen and sulfur atoms, resulting in highly ordered assembly. By adding thiophene and thieno[3,2-b]thiophene structures to the intermediate precursor bi(3,4-ethylenedioxy), the 3,4-ethylenedioxy content in the polymer molecule is altered, leading to an almost four-fold increase in the thermopower of the thin film polymer and achieving a maximum thermopower of around 26 μV·K-1. Although poly[bi(3,4-ethylenedioxy)-alt-thienyl] shows a significant increase in thermopower compared to poly[bi(3,4-ethylenedioxy)], the thin film conductivity exhibits a nearly imperceptible decreasing trend due to its highly ordered microstructure. This work highlights the potential to control the aggregation state of polymer molecules and achieve an approximate decoupling between the conductivity and thermopower of thermoelectric materials by rationally designing polymer molecules.