Enhanced thermoelectric properties in anthracene molecular device with graphene electrodes: the role of phononic thermal conductance

Density functional theory (DFT) and the non-equilibrium Green’s function (NEGF) formalism in the linear response regime were employed to investigate the impact of doping on the electronic and phononic transport properties in an anthracene molecule attached to two metallic zigzag graphene nanoribbons (ZGNRs). Boron (B) and nitrogen (N) atoms were used for doping and co-doping (NB) of carbon atoms located at the edge of the anthracene molecule. Our results show that B doping enhances the electronic transport in comparison with the other dopants which is due to its ability to increase the binding energy of the system. The chemical doping of the anthracene molecule mainly impacts on the thermopower which results in a significantly enhanced electronic contribution of the figure of merit. On the contrary, considering the effect of phononic thermal conductance suppresses the figure of merit. However, by taking into account the effect of both electron and phonon contributions to the thermal conductance, we find that the thermoelectric efficiency can be improved by B doping. The potential role of the phononic thermal conductance in shaping the thermoelectric properties of molecular junctions has been ignored in numerous studies, however, our findings demonstrate its importance for a realistic and accurate estimation of the thermoelectric figure of merit.