Abnormal Seebeck effect in doped polymer and two-band transport model*

Employing Boltzmann transport equation coupled with Density-Functional Theory and non-equilibrium molecular dynamics simulation, we developed a combined scheme of calculating the thermoelectric property for polymeric materials. In the case of PEDOT doped with PSS, theory can give optimal carrier density for the power factor. It is found that the ideal crystalline polymer leads to a tiny thermoelectric figure of merit because of the extremely high thermal conductity. Thus, engineering of disordered structure at nanoscale is essential.
We find that the formation of polaron band upon doping is essential to understand the "abnormal Seebecj effect", namely, for the potassium doped nickel-coordinated polymer, the Seebeck coefficient first increases with temperature and then suddenly drops. We proposed a two-band transport model to explain such exotic behavior.