High Thermoelectric Performance and Low Lattice Thermal Conductivity in 2D Topological Insulators MBiH (M = Ga, In): A First-Principles Study

Thermoelectric materials have drawn significant attention due to their potential for energy harvesting and waste heat utilization. Recently, two-dimensional (2D) materials have become promising candidates for thermoelectric applications due to their unique electronic and thermal properties. The camelback-shaped band structures of 2D topological insulators (TIs), coupled with the low-frequency lattice vibrations of heavy elements, synergistically enhance the Seebeck coefficient while suppressing the lattice thermal conductivity. These combined effects make 2D TIs highly promising candidates for thermoelectric applications. Herein, we studied the electronic and thermal properties of 2D topological insulator MBiH (M = Ga, In) based on first-principles calculations and Boltzmann transport theory. The result demonstrates that the extremely low lattice thermal conductivities of 0.080 W/mK for GaBiH and 0.101 W/mK for InBiH at 700 K can be attributed to strong phonon anharmonicity and short relaxation times. Consequently, the maximum thermoelectric figure of merit (ZT) for GaBiH and InBiH reaches 3.95 and 2.87, respectively, significantly surpassing those of 2D nontopological insulator materials containing heavy elements. These findings indicate that MBiH (M = Ga, In) monolayers are promising candidates for thermoelectric applications.