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

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.