Thermoelectric properties of two-dimensional Janus penta-PdXY (XY = SeTe, SSe, or STe) monolayers: Electron–phonon averaged approximation studies

Accurate evaluation of the thermoelectric (TE) figure of merit (ZT) using theoretical methods is essential for developing efficient TE materials for practical applications. Previous work based on the deformation potential (DP) theory predicts that the Janus penta-PdSeTe monolayer exhibits excellent TE performance, where the room-temperature ZT values could approach 1.3. However, in this study, we demonstrate that the DP theory substantially overestimates the electron lifetime, thereby obviously overestimating the TE conversion efficiency of the Janus penta-PdXY (XY = SeTe, SSe, or STe) monolayers. Using a more advanced electron–phonon averaged approximation, we reveal that there exist strong electron–phonon interactions in the Janus penta-PdXY monolayers, causing pivotal suppression of the electron lifetime. Based on this more accurate electron lifetime, the room-temperature ZT value obtained for Janus penta-PdSeTe is merely 0.07, notably lower than that predicted in previous studies. Its homologous derivatives also exhibit relatively low TE conversion efficiencies, with ZT values of 0.06 and 0.13 for penta-PdSSe and penta-PdSTe monolayers, respectively. These values are close to the experimental measurements obtained for PdSe2, a similar sample, verifying the reliability of our calculations. This study deepens the understanding of the thermal and TE transport properties of low-dimensional penta-type Pd-based materials and could provide useful guidance for future theoretical research on TE materials.