Theoretical study of vertical van der Walls metal-porphyrin and metal free-porphyrin junctions

Abstract

This paper provides a theoretical study of the thermoelectric properties of a vertical graphene/porphyrins/graphene architecture. It presents the details of calculating the conductance of metal-porphyrins, which is found to be enhanced by manipulating the metal central atom of the organic 125 porphyrin framework over the family and The results demonstrate that even when there is no direct inter-molecular coupling, indirect inter-molecular interactions mediated by the graphene electrodes produce quantum interference effects in the electronic structure of the molecular junction. These junctions are all observed to be HOMO-dominated, meaning that their Seebeck exhibit the same sign and similar behavior. The resulting single-molecule thermopowers range from almost +50 μV/K for both - and -porphyrin to +77 μV/K and +85 μV/K for - and -porphyrin, respectively. For these geometries, the effect of the metal complex with porphyrin on the conductance of the junctions can be seen. An extra resonance appeared in the HOMO-LOMO gap, and it can be disappeared or be shifted closer to Fermi energy to create a new path for the electron transmission. It only depends on the type of metal coordinating at the porphyrin center. Introducing such a new technique for designing high conductance and thermopower opens a door for high thermoelectric performance materials.