Ultra-high carrier mobility and ultra-low lattice thermal conductivity in PdSSe monolayers with fully Stone–Wales defects

The Stone–Wales (SW) defects have a critical impact on the physical properties of the carbon-based materials with pentagonal and hexagonal rings, which also emerge in other pentagon-based materials with the Cairo tessellation. However, scarce attention has been paid to SW defect engineering in two-dimensional (2D) pentagonal materials. In the present letter, we propose four unreported 2D PdSSe monolayers (designated as SW1–SW4) by introducing SW defects into the penta-PdSSe monolayer. The electronic structure, optical, electrical transport, and thermal transport properties of these SW defect structures have been systematically investigated based on first-principles calculations. SW1–SW4 retain the square-planar coordination as presented in the pristine penta-PdSSe, exhibiting excellent dynamical, thermal, and mechanical stability. Particularly, SW1 and SW2 exhibit direct bandgaps, which are more favorable for electronic transitions. The suitable band alignments meet the requirement of photocatalytic water splitting. Furthermore, the defect structures show high visible-light absorption coefficients (∼105 cm−1) and ultra-high carrier mobility (∼103 cm2V−1s−1). More excitingly, these defect structures display ultra-low anisotropic lattice thermal conductivities (lower than 2 Wm−1K−1 at room temperature). The suitable bandgap values, appropriate band edge positions, good optical absorption performances, and ultra-high carrier mobility concomitant with ultra-low lattice thermal conductivity render these PdSSe monolayers with SW defect structures as promising semiconductor materials for potential applications in nanoelectronics, optoelectronics, solar cell, photocatalyst, and thermoelectric energy conversions.