Thermoelectric property regulation of dimer-triangulene molecular junctions based on oxygen edge-modification engineering

Abstract

Oxygen edge modification is an effective strategy to regulate the thermal/electrical transport properties of molecular junctions due to such modification with unique lone-pair electron structure. In this work, the thermoelectric properties of dimer-triangulene molecular junctions with/without oxygen edge modification were investigated using density functional theory (DFT) combined with a non-equilibrium Green's function (NEGF) approach. Results indicated that TRI–TRI(4O) exhibits a higher molecular frontier orbital energy gap than TRI–TRI with four oxygen atoms substituting four hydrogen atoms for edge saturation. It is manifested that a strong Coulomb repulsive force is induced due to the enhancement of electronic localization, which results in an increase in the energy gap. Furthermore, due to the significant increase in momentum overlap near the Fermi level, the molecular frontier energy gap of TRI–TRI(20O) obviously decreased with complete oxidation of edges. In the case of back-to-back connected molecular junctions, both the molecular energy gap and the phonon thermal conductance decreased sequentially with the increase in the number of oxygen atoms (TRITRI > TRITRI(4O) > TRITRI(16O)). Phonon thermal conductances of TRI–TRI(20O) and TRITRI(16O) decreased primarily due to the lone-pair electrons of oxygen atoms enhancing the anharmonicity of the edge-state. The conductances of TRI–TRI(20O) and TRITRI(4O) increased obviously compared with TRI–TRI, which originated from a constructive quantum interference (CQI) near the Fermi level. As a result, TRI–TRI(2O) achieved an ideal ZT value (1.28) near the Fermi level. This work provides important theoretical guidance for the thermoelectric application of dimer-triangulene molecular junctions.