ABSTRACT
Thermoelectric properties of hybrid systems composed of graphene nanoribbons (GNRs) coupled to rectangular rings or functionalized with aromatic carbon molecules are theoretically addressed here. Graphene-based nanostructures are designed with the purpose of enhancing thermopower responses compared to the thermal performance of pristine GNRs. The electronic transport is calculated using standard tight binding models and the Landauer transport formalism. We found that both semiconducting and metallic armchair nanoribbons coupled to rings exhibit a pronounced enhancement of the thermoelectric responses with comparable intensities, due to Fano antiresonance and Breit-Wigner-like resonances in the electronic transport. As expected, details of the ring geometry and ribbons are important in determining the precise chemical potential values for optimal performance. Different configurations of attached aromatic molecules (single and double molecules) at the graphene nanoribbon edges are addressed. Our findings show that the presence of a molecule induces a gap formation in the metallic pristine GNRs, and a pronounced peak of the Seebeck coefficient is revealed for low chemical potential values, independent of the molecule length. Other features on the Seebeck spectra are found to depend on the electronic nature of the GNRs and on the molecule length and distribution. We have shown that by playing with them, it is possible to design better thermoelectric devices based on GNRs.