Improving thermoelectric performance of asymmetrical Janus 1T-SnSSe monolayer by the synergistic effect of band convergence and crystal lattice softening under strain engineering

Abstract

Recently, the 1T-SnSSe monolayer has attracted increasing attention in the thermoelectric community on account of its low-cost and environmental friendliness. In this paper, the thermoelectric properties of asymmetrical 1T-SnSSe monolayer under strain engineering are comprehensively evaluated using density functional theory (DFT) and semiclassical Boltzmann transport theory calculations. The analysis of mechanical stability, phonon spectrum, and ab initio molecular dynamics (AIMD) simulations demonstrates that the strained 1T-SnSSe monolayers are mechanically, dynamically, and thermally stable. The improvement of the Seebeck coefficient for the strained 1T-SnSSe monolayers mainly originates from the band convergence. Meanwhile, the thermal transport properties of the strained 1T-SnSSe monolayers are suppressed by crystal lattice softening. As a result, the optimal ZT of ∼1.75 and ∼1.56 @ 900 K for the p-type and n-type 1T-SnSSe monolayers are obtained at the biaxial tensile strain of 6% with the optimal carrier concentrations of ∼1 × 1014 and ∼2 × 1013 cm−2. Our present work not only provides a fundamental understanding of electronic and thermal transport properties of the strained 1T-SnSSe monolayers, but also sheds some light on the theoretical exploration of low-dimensional nanomaterials for thermoelectric applications.