Theoretical study on thermoelectric properties of kinked graphene nanoribbons

A ballistic transport model based on electron and phonon band structures has been implemented to evaluate the thermoelectric properties of kinked AA/ZZ-graphene nanoribbons (GNRs) connected by two armchair GNRs or zigzag GNR segments with an angle of 120^∘{}, as well as hybridized structures connected by different edge segments and angles. Compared to straight GNRs with the same width, the thermoelectric properties of kinked AA-GNRs and ZZ-GNRs are enhanced due to increases in the figure of merit (ZT) and power factor and the reduction in lattice thermal conductance. For kinked AA-GNRs, ZTₘₐₓ (the first peak of ZT) is almost twice that of straight AGNRs, while for ZZ-GNRs, ZTₘₐₓ is greatly improved from that of straight ZGNRs, which is around zero. Furthermore, because of the comparable ZTₘₐₓ values of both kinked AA-GNRs and ZZ-GNRs, it is indicated that kinked structures reduce the edge sensitivity on thermoelectric properties of GNRs. Finally, the effects of the kinked width and arm length as well as shape influence of the various hybridized kinked GNRs are also investigated. In general, the structures with smaller width have better performance, and ZTₘₐₓ is larger for the structures with two ZGNR segments but smaller for the structures with only one ZGNR segment. It is due to this fact that two ZGNR segments connected by 120^∘{} can open up a bandgap, whereas one ZGNR segment alone still preserves metallic behavior and degrades the performance for the whole hybridized kinked structure.