Interfacial design and thermoelectric properties of C₃N₄-C₂₀ molecular junctions based on quantum interference

Abstract Quantum interference effect serves as a critical strategy for addressing incorrect energy level alignment between frontier molecular orbitals and electrodes in molecular junctions. Weak-coupling structures offer an effective approach to suppress phonon thermal conductance. The thermoelectric properties of pure C 3 N 4 nanoribbon devices and C 3 N 4 -C 20 molecular junctions are systematically investigated based on density functional theory (DFT) combined with non-equilibrium Green’s function (NEGF) formalism. The results show that pure C 3 N 4 nanoribbon devices have superior charge transport capabilities and excellent Seebeck coefficients. A remarkable thermoelectric figure of merit ( ZT = 0.98) is achieved near 0.09 eV. The pronounced scattering effect induced by embedding a C 20 molecule in the center of the C 3 N 4 nanoribbon significantly suppresses phonon transport. A maximum ZT value of 1.68 is observed at 0.987 eV. The electron mobility of C 3 N 4 -C 20 -par is effectively increased due to quantum interference effect which greatly improves the alignment between the C 20 molecule’s frontier orbital energy level and C 3 N 4 electrodes. The C 3 N 4 -C 20 -van der Waals (vdW) molecular junction allows very few phonons to pass through the C 20 molecule from the left electrode to the right electrode. As a result, the C 3 N 4 -C 20 -vdW junction achieves an excellent ZT value of 3.82 near the Femi level.