Thermoelectric Efficiency of Two-Dimensional Pentagonal-PdSe₂ at High Temperatures and the Role of Strain

Two-dimensional penta-PdSe2 is a recently discovered material exhibiting air stability, superior field effect mobility, low-symmetry lattice, and an ultrahigh thermoelectric power factor (PF). These profitable characteristics are preferential for thermoelectric applications. In particular, the thermoelectric figure of merit (ZT) has been theoretically reported to be around 1.1 at room temperature (300 K) as predicted by the simplified constant relaxation time approximation. Nonetheless, the exhaustive heat-to-electricity conversion efficiency at higher temperatures and the influences of external stimuli (e.g., strain) remains unexplored. Based on the ab initio density functional theory and Boltzmann transport theory considering the vital scattering mechanisms (e.g., electron–phonon coupling), this work elucidates the thermoelectric functionality of penta-PdSe2 operating at mid-to-high temperatures. The findings reveal that PdSe2 is a promising high-temperature thermoelectric material because of its maximized ZT of 0.84, 0.42, and 0.09 at 900, 600, and 300 K upon p-type doping, respectively. These ultrahigh numbers are physically attributed to the mutual suppression of lattice thermal conductivity and the relatively insignificant fading of PF at high temperatures. Moreover, we unravel the impacts of strain on the thermoelectric properties. The crystal stability of PdSe2 is intrinsically prone to compressive strain, whereas it can endure immense tensile strain. The presence of biaxial tensile strain at minor 2.0% drastically reduces the ZT value by more than 50% compared to the original strain-free PdSe2.