Understanding phonon transport properties on Janus XSSe (X = Hf, Pb, Pt) monolayers via density functional theory

Janus monolayers have emerged as promising candidates for thermoelectric applications due to their unique structural and electronic properties. This study investigates the phonon thermal transport of Janus XSSe (X = Hf, Pb, Pt) monolayers using density functional theory (DFT) and Boltzmann Transport Theory (BTT). Our calculations reveal exceptionally low lattice thermal conductivities of 0.80, 1.43, and 11.0 W/mK for HfSSe, PbSSe, and PtSSe, respectively, at 300 K. The transverse acoustic (TA) phonon mode dominates the thermal transport, contributing 42.49%, 46.37%, and 46.82% to the total lattice thermal conductivity in these materials. Significant anharmonicity, characterized by low phonon lifetimes and reduced group velocities, further suppresses the lattice thermal conductivity. Additionally, we report indirect bandgaps of 1.49 eV, 0.64 eV, and 2.25 eV for HfSSe, PbSSe, and PtSSe, respectively. These findings highlight the potential of Janus XSSe monolayers for thermoelectric applications and provide insights into their phonon transport mechanisms.