Elucidating the Role of Polymer–Dopant Interaction in the Electrical Properties of Polymers with Non-Conjugated Spacers

Abstract

Chemical doping of conductive polymers has been an important strategy to optimize the electronic properties of thermoelectric materials. The precise control of doping is essential but limited by the understanding of polymer−dopant interactions, which usually impair the doping efficiency and induce an imbalance of electrical conductivity (σ) and the Seebeck coefficient (S). In this work, flexible nonconjugated spacers, an alkyl group (Alkyl) and a 1,3-diethylurea group (TUT), are intentionally introduced into the main chain of a series of random copolymers. Interestingly, the formation of hydrogen bonds between TUT and the dopant, tetrafluorotetracyanoquinodimethane (F4TCNQ), can lock the dopants and allows PTUT x -g 3 2T 1−x higher carrier concentrations than PAlkyl x -g 3 2T 1−x , while lower carrier mobilities are observed in PTUT x -g 3 2T 1−x . As a result, PAlkyl 0.3 -g 3 2T 0.7 obtains a higher Seebeck coefficient of 91 μV K −1 compared with PTUT 0.3 -g 3 2T 0.7 (55 μV K −1 ), although they show the same electrical conductivity. In addition, it is observed that the electrical conductivity of PTUT 0.3 -g 3 2T 0.7 can be increased by 3× at 200% strain due to the existence of flexible nonconjugated spacers. The above results demonstrate that the design of polymer−dopant interaction via "locking groups" would be an efficient way to control the electrical properties of conductive polymers and achieve the decoupling of S and σ.