Two-Dimensional β‑PdX2 (X=S, Se, and Te) Monolayers with Promising Potential for Thermoelectric Applications

Transition metal dichalcogenides have attracted extensive research attention due to their unique electronic, topological, and optical properties. Based on first-principles methods and Boltzmann transport theory, the thermoelectric performance of β-PdX2 (X = S, Se, and Te) monolayers was comprehensively studied in this work. It is worth noting that the structural anisotropy of β-PdX2 monolayers leads to obvious anisotropy of thermoelectric coefficients along the x and y directions. By investigating the thermal transport up to four-phonon scattering, it was found that the strong higher-order phonon scattering plays a decisive role in ultra-low lattice thermal conductivity of β-PdX2 monolayers. A low lattice thermal conductivity of 3.4 (1.0) W m–1 K–1 is predicted for β-PdTe2 at 300 K along the x (y) direction. In addition, due to the suitable band gap and high carrier mobility, the highest power factor of 25.7 mW m–1 K–2 is obtained in n-type β-PdX2 monolayers, which is superior to many other two-dimensional thermoelectric materials. Finally, a maximum ZT of 5.2 is achieved for the n-type β-PdS2 monolayer along the y direction at 600 K. Meanwhile, the maximum p-type ZT also reaches 3.3 along the y direction at 600 K in the β-PdSe2 monolayer. Our results demonstrate that β-PdX2 monolayers are promising candidates for two-dimensional thermoelectric materials with excellent conversion performance.