Unexpectedly High Cross-plane Thermoelectric Performance in Layered Carbon Nitrides
Organic thermoelectric (TE) materials create a brand new perspective to search for high-efficiency TE materials, due to their small thermal conductivity. The overlap of pz orbitals, commonly existing in organic π-stacking semiconductors, can potentially result in high electronic mobility comparable to inorganic electronics. Here we propose a strategy to utilize the overlap of pz orbitals to increase the TE efficiency of layered polymeric carbon nitride (PCN). Through first-principles calculations and classical molecular dynamics simulations, we find that A-A stacked PCN has unexpectedly high cross-plane ZT up to 0.52 at 300 K, which can contribute to n-type TE groups. The high ZT originates from its one-dimensional charge transport and small thermal conductivity. The thermal contribution of the overlap of pz orbitals is investigated, which noticeably enhances the thermal transport when compared with the thermal conductivity without considering the overlap effect. For a better understanding of its TE advantages, we find that the low-dimensional charge transport results from strong pz-overlap interactions and the in-plane electronic confinement, by comparing π-stacking carbon nitride derivatives and graphite. This study can provide a guidance to search for high cross-plane TE performance in layered materials.