Revealing unipolar thermoelectric performance in bipolar polymer

<p indent="0mm">Conjugated polymers are attracting increased attention as thermoelectric (TE) materials for energy harvesting applications in low-temperature regimes. However, in many doped ambipolar polymers, the simultaneous transport of both holes and electrons under temperature gradients leads to an offset in thermopower (<italic>S</italic>), which suppresses TE performance and complicates intrinsic understanding of bipolar TE conversion. Herein, we quantitatively investigate the p-n polarity transition in FeCl₃-doped bipolar PDPP4T films by measuring the magneto-thermoelectric Nernst effect, combined with Hall and Seebeck effect analyses. Notably, behind the <italic>S =</italic> 0 point, we observe a significant thermopower offset originating from the balancing contributions of electrons and holes. This countervailing thermopower value is extracted to reach 400 μV K⁻¹, which could ideally produce an estimated maximum unipolar ZT of 0.24 at <sc>175 K,</sc> due to rising polaron states and reduced carrier concentration. Our findings reveal the extraordinary hidden unipolar TE performance achievable in doped bipolar polymer towards ultra-low-temperatures thermoelectric.