Stacking pattern induced high ZTs in monolayer SnSSe and bilayer SnXY (X/Y = S, Se) materials with strong anharmonic phonon scattering

Abstract

Two-dimensional (2D) Sn-based Janus materials have attracted enormous attention on account of the inexpensive, earth-abundant, and eco-friendly merits. Whereas, few works give explicit analysis about the underlying mechanism of stacking pattern from monolayer (ML) to bilayer (BL) configuration on the thermoelectric properties of Sn-based Janus materials. In our present work, the elastic modulus, phonon dispersion and ab initio molecular dynamics (AIMD) simulations are performed, which firstly verifies the mechanical, dynamic and thermal stabilities of ML SnSSe and BL SnXY (X/Y = S, Se) materials. Notably, the lowest lattice thermal conductivity (κl∼1.85 W/m K@300 K) is observed in BL SnSe2. Consequently, the optimal values of figure-of-merit (ZT) are observed for n-type (∼4.57@900 K) or p-type (∼3.71@900 K) BL SnSe2. Additionally, the optimal ZT can be improved from ML to BL configuration because of the weaker phonon transport caused by structure engineering, as evidenced by the maximal ZTs of n-type and p-type ML SnSSe (∼1.11 and ∼1.20@900 K) and BL SeSnS/SSnSe (∼2.55 and ∼1.71@900 K). Our present work not only provides deep insight into electronic and phonon transport properties in ML SnSSe and BL SnXY, but also paves the way for the theoretical investigation of high thermoelectric performance for Sn-based Janus materials.