Achieving Ultrahigh n-Type Thermoelectric Power Factor in an Intrinsically Large Transport-Fermi Energy Gap Conjugated Polymer.

Abstract

The conductivity of organic thermoelectric materials has seen significant improvements in the past few years, but often at the expense of the Seebeck coefficient. Consequently, the thermoelectric performance, especially for n-type materials, remains considerably lower than that of their inorganic counterparts. Herein, a high-performance n-type thermoelectric polymer, P(TDPP-BT-LEG) is reported, with an unexpectedly high Seebeck coefficient and ultrahigh power factor, driven by its intrinsically large energy gap between the Fermi and transport energy levels and high charge carrier mobility. Notably, it is shown that strong electrostatic interactions induced by the ethylene glycol side chains facilitate charge transfer between the dopants and the polymer. This enables effective doping of polymers with high LUMO levels. Furthermore, efficient charge transport, arising from favorable molecular packing, allows the polymer to maintain high electrical conductivity even at low charge carrier concentrations. Ultimately, this polymer achieves a record-high n-type power factor of 397 µW m^-1 K^-2, with a high Seebeck coefficient of -420 µV K^‒1. This study highlights the potential of enhancing the Seebeck coefficient through precise energy level tuning and molecular design, fundamentally advancing the rational design of high-performance organic thermoelectric materials.