Significantly enhanced thermoelectric performance of Van der Waals interface coupling molecular junction with nitrogen-doped graphene nanoribbon electrodes

Abstract

Rational design of model structure and effective strategy to overcome inherent mismatch between molecular orbital energy and Fermi level (FL) of electrodes are the key prerequisites to fully rationalize and optimize thermoelectric properties for a single molecular junction. A bis-phenylethynyl-anthrancene (BIS-molecule) with conjugated structure is contacted with armchair/zigzag graphene nanoribbon (AGNR/ZGNR) electrodes by van der Waals (vdW) interface coupling. The optimized distance between molecular and two leads is associated with interface stacking mode. Weak-coupling structure greatly suppresses phonon transport behavior due to interface resistance. Thermal conductance (κtol) has been greatly increased at FL with N-doping based on two different mechanisms. Mass matching effect plays a dominate role for κtol increase in N-doped AGNR_BIS_AGNR, meanwhile sharp and degenerated DOS is main contribution to κtol in N-doped ZGNR_BIS_ZGNR. Nitrogen-doping can adjust Fermi level of electrodes into molecular resonance region, resulting in the enhancement of electronic coupling between central molecular and leads, which is come from obvious charge transfer from graphene nanoribbon to BIS-molecule. Moreover, an excellent thermoelectric figure-of-merit (ZT) of 14.1/3.5 has been obtained near FL for nitrogen-doped molecular junction.