Transport and Thermoelectric Properties of SnX (X = S or Se) Bilayers and Heterostructures

Vertically stacked two-dimensional materials based on weak interactions have received significant attention because of possibilities of effective modulation of their electronic, transport, and optoelectronic performance. In this work, we systematically investigate the interlayer coupling effect in bilayer SnS, SnSe, and SnS/SnSe heterostructures, from the geometries to the electronic evolutions and thermoelectric properties, based on first-principles calculations and Boltzmann transport theory. The SnS/SnSe heterostructure shows a band structure more similar to that of the SnSe component and modulated charge transfer for the inner sublayer, as compared to the intrinsic bilayers. Furthermore, from monolayer to bilayer SnS and SnSe systems and the SnS/SnSe heterojunction, we discover different layer-dependent behaviors and coupling-modulation effects, which are prominent in the design of two-dimensional thermoelectric devices. The optimal power factor of SnS/SnSe superior to those of all other structures is found for the p-type doping along the armchair direction, within the carrier concentration range of 1019∼5 × 1020 cm–3 because of its small effective mass, moderate electron–phonon scattering, and enhanced elastic modulus. These findings indicate that heterointerlayer coupling could be a promising strategy for high-performance thermoelectric materials, beyond the size control.