Effect of superlattice period length on thermoelectric performance: A case study of monolayer CrS2, CrSe2, and CrS2/CrSe2 lateral superlattice

Abstract

Two-dimensional (2D) lateral superlattice is a promising route to tailor thermoelectric properties, yet the impact of superlattice period length on the modulation of phonon and electronic transport remains insufficiently characterized. Using a monolayer CrS2/CrSe2 superlattice as a model system, we combine density-functional theory with a machine-learning potential to quantify the period-dependent thermoelectric properties. Due to the reduced phonon group velocities and shortened phonon lifetimes, our calculation results reveal that the room-temperature lattice thermal conductivity (κp) of short-period superlattice (SS) and long-period superlattice (LS) structures along the modulation direction is reduced by 71.3% and 82.9%, respectively, compared with that of the pristine CrS2. Moreover, the interface-induced charge redistribution in LS disrupts electronic transport continuity, suppressing electrical conductivity (σ). By contrast, SS retains more extended charge states while maintaining σ with reduced κp. As a result, the ZT value of SS (∼0.39) is higher than that of LS (∼0.21) at 600 K, despite LS having a lower κp. This work emphasizes the importance of co-optimizing phonon and electronic transport in superlattice structures by tuning the superlattice period, providing engineering strategies for designing 2D superlattice thermoelectric materials.