Origins of Minimized Lattice Thermal Conductivity and Enhanced Thermoelectric Performance in WS2/WSe2 Lateral Superlattice

We report a configuration strategy for improving the thermoelectric (TE) performance of two-dimensional transition metal dichalcogenide WS2 based on the experimentally prepared WS2/WSe2 lateral superlattice (LS) crystal. On the basis of density function theory combined with a Boltzmann transport equation, we show that the TE figure of merit zT of monolayer WS2 is remarkably enhanced when forming into a WS2/WSe2 LS crystal. This is primarily ascribed to the almost halved lattice thermal conductivity due to the enhanced anharmonic processes. Electronic transport properties parallel (xx) and perpendicular (yy) to the superlattice period are highly symmetric for both p- and n-doped LS owing to the nearly isotropic lifetime of charger carriers. The spin-orbital effect causes a significant split of conduction band and leads to three-fold degenerate sub-bands and high density of states (DOS), which offers opportunity to obtain a high n-type Seebeck coefficient (S). Interestingly, the separated degenerate subbands and upper conduction band in monolayer WS2 form a remarkable stair-like DOS, yielding a higher S. The hole carriers with much higher mobility than electrons reveal the high p-type power factor, and the potential to be good p-type TE materials with optimal zT exceeds 1 at 400 K in WS2/WSe2 LS.