Interfacial Density-of-States Engineering Enables Transport Mechanism Transition in P3HT/Nitrogen-Doped Graphene Thermoelectric Composites

The achievable power factor of organic thermoelectric materials is constrained by thermoelectric transport mechanism coupled between the Seebeck coefficient (S) and electrical conductivity (σ). Here, we construct a nitrogen-doped graphene (NG)/poly(3-hexylthiophene) (P3HT) composite system, in which the thermoelectric transport mechanism can be continuously tuned through interfacial density-of-states (DOS) engineering between NG and P3HT. A direct interplay between polymer ordering, interfacial electronic structure, and carrier energy distribution was investigated. It is revealed that high P3HT concentration induces a Pisarenko-dominated regime with increased σ and suppressed thermopower; meanwhile, moderate thermal annealing generates NG-induced interfacial potential barriers, enabling energy-selective carrier transport that simultaneously enhances S and σ. Furthermore, excessive annealing time or temperature introduces DOS scattering associated with backbone disorder, leading to deteriorated transport performance. These results provide direct spectroscopic evidence for a transition from σ-controlled to energy-filtering-dominated transport in organic thermoelectric composites for decoupling thermoelectric parameters through interfacial electronic structure engineering.