Improving Thermoelectric Performance of n‐Doped Semiconductive Polymer by Lowering the Electrostatic Potential of Dopant Counterions

Abstract n‐Doping plays a pivotal role in controlling charge carrier density and charge transport characteristics for thermoelectric polymers to achieve required performance. A fundamental challenge, however, arises from the strong Coulombic binding between dopant counterions (cations) and polymer polarons formed during doping, which significantly limits charge carrier generation and polaron delocalization. Molecular strategies on modulating the counterion‐polaron distance to weaken Coulombic interactions are thereof essential to overcome this limitation. Theoretical considerations suggest that rationally reducing the electrostatic potential (ESP) of n‐dopant counterions could promote their spatial separation from the polymer backbone, thereby mitigating Coulombic interactions. To address this, a series of julolidine functionalized benzimidazole n‐dopants bearing 0, 1, and 2 methoxy groups with tunable ESPs, compared with prototypical N‐DMBI, are organized by integrating requisite compatibility and electronic properties. Experimental and theoretical calculation results reveal that the implementation of these dopants on the model n‐type polymer ThDPP‐CNBtz successfully regulates the Coulombic interactions between counterions and polymer polarons. Notably, the thermoelectric performance exhibits a systematic enhancement with decreasing dopant counterion surface potentials.