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

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 C₃N₄ nanoribbon devices and C₃N₄-C₂₀ 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 C₃N₄ 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 C₂₀ molecule in the center of the C₃N₄ nanoribbon significantly suppresses phonon transport. A maximum ZT value of 1.68 is observed at 0.987 eV. The electron mobility of C₃N₄-C₂₀-par is effectively increased due to quantum interference effect which greatly improves the alignment between the C₂₀ molecule’s frontier orbital energy level and C₃N₄ electrodes. The C₃N₄-C₂₀-van der Waals (vdW) molecular junction allows very few phonons to pass through the C₂₀ molecule from the left electrode to the right electrode. As a result, the C₃N₄-C₂₀-vdW junction achieves an excellent ZT value of 3.82 near the Femi level.