关键词: quantum interference effect, C$_{3}$N$_{4}$-C$_{20}$ molecular junctions, thermoelectric properties, first-principles theory

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.

Key words: quantum interference effect, C$_{3}$N$_{4}$-C$_{20}$ molecular junctions, thermoelectric properties, first-principles theory