Harnessing Chemical Bonding Principle to Modulate Carrier Transport and Thermoelectric Performance in Pentagonal HgSe2 Monolayer

Abstract Two-dimensional pentagonal materials have attracted significant attention in thermoelectrics due to their unique geometric symmetry and intrinsic anisotropy. However, breaking the strong coupling between electron and phonon transport at the atomic scale to achieve synergistic optimization remains a critical challenge in this field. Here, based on first-principles calculations combined with Boltzmann transport theory and the self-consistent phonon method, we systematically investigate the electronic properties, lattice dynamics, and thermoelectric properties of pentagonal MSe2 (M = Pt, Mg, Hg) monolayers. By contrasting PtSe2, dominated by strong covalent bonding, and MgSe2, governed by ionic bonding, we elucidate how HgSe2 achieves a favorable balance between electrical and thermal transport through its distinctive chemical bond characteristics. Our findings reveal that HgSe2 constructs an ideal “phonon glass-electron crystal” model via weak chemical bonding between the constituted heavy atoms. On one hand, the weak bonding feature caused by size and mass fluctuations induces strong lattice anharmonicity, significantly suppresses phonon group velocities, and enhances multiphonon scattering, resulting in an ultralow room-temperature lattice thermal conductivity of 0.66 W/mK. On the other hand, the weak Hg–Se and covalent Se–Se bonds optimize the band structure, achieving an excellent power factor via high hole mobility and a large Seebeck coefficient. Benefiting from these special transport characteristics, the p-type HgSe2 monolayer exhibits a remarkable thermoelectric figure of merit of 2.44 at 500 K, substantially surpassing analogous systems. This work uncovers the competitive regulatory mechanism of constituent element attributes and cation electronic configurations on carrier transport and lattice anharmonicity, providing important theoretical guidance for the design of next-generation high-efficiency low-dimensional thermoelectric materials through chemical bond engineering.