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

Chemical doping of conductive polymers\nhas been an important strategy\nto optimize the electronic properties of thermoelectric materials.\nThe precise control of doping is essential but limited by the understanding\nof polymer–dopant interactions, which usually impair the doping\nefficiency and induce an imbalance of electrical conductivity (σ)\nand the Seebeck coefficient (<i>S</i>). In this work, flexible\nnonconjugated spacers, an alkyl group (Alkyl) and a 1,3-diethylurea\ngroup (TUT), are intentionally introduced into the main chain of a\nseries of random copolymers. Interestingly, the formation of hydrogen\nbonds between TUT and the dopant, tetrafluorotetracyanoquinodimethane\n(F4TCNQ), can lock the dopants and allows PTUT<sub><i>x</i></sub>-g<sub>3</sub>2T<sub>1–<i>x</i></sub> higher\ncarrier concentrations than PAlkyl<sub><i>x</i></sub>-g<sub>3</sub>2T<sub>1–<i>x</i></sub>, while lower carrier\nmobilities are observed in PTUT<sub><i>x</i></sub>-g<sub>3</sub>2T<sub>1–<i>x</i></sub>. As a result, PAlkyl<sub>0.3</sub>-g<sub>3</sub>2T<sub>0.7</sub> obtains a higher Seebeck\ncoefficient of 91 μV K<sup>–1</sup> compared with PTUT<sub>0.3</sub>-g<sub>3</sub>2T<sub>0.7</sub> (55 μV K<sup>–1</sup>), although they show the same electrical conductivity. In addition,\nit is observed that the electrical conductivity of PTUT<sub>0.3</sub>-g<sub>3</sub>2T<sub>0.7</sub> can be increased by 3× at 200%\nstrain due to the existence of flexible nonconjugated spacers. The\nabove results demonstrate that the design of polymer–dopant\ninteraction via “locking groups” would be an efficient\nway to control the electrical properties of conductive polymers and\nachieve the decoupling of <i>S</i> and σ.