High thermoelectric figure of merit in rhombic porous carbon nitride nanoribbons

By performing extensive density functional theory calculations combined with non-equilibrium Green's function technique, we predict the rhombic porous carbon nitride nanoribbon (rPCNNR) and the vertical rPCNNR junction exhibiting high thermoelectric figure of merit (ZT) values of 0.57 and 2.1 at room temperature respectively. Theoretical results reveal that the ZT value of rPCNNR is significantly larger than that of armchair graphene nanoribbon with the almost same width (similar to 0.035) due to the large Seebeck coefficients and the significantly decreased thermal conductance of rPCNNR, where the phonon states are blocked by the built-in porous structure and rhombic edge in rPCNNR. The ZT value is further enhanced to be 2.1 in the vertical rPCNNR junction, which is achieved by the synergy effect between the dramatically suppressed thermal conductance in in-plane direction due to the weak van der Waals interaction between two rPCNNRs, the almost unchanged Seebeck coefficients, and the good electron conductivity provided by the strong overlapping of delocalized VB- and CB-derived states in the scattering region. These presented findings highlight rPCNNR as a promising candidate in building flexible devices with high thermoelectric performance.