Enhancing thermoelectric performance in Janus MoTeS through periodic structural alternations and van der Waals contact

Atomic-scale structural engineering provides a promising approach to enhance the thermoelectric performance of low-dimensional materials. The two-dimensional Janus MoTeS, with its inherent out-of-plane asymmetry, enables direct modulation of thermoelectric transport properties through tailored periodic S–Te atomic arrangements. Herein, three Janus MoTeS configurations with periodic S–Te atom alternation are constructed in order to realize highly efficient thermoelectric properties by first-principles calculations based on density functional theory. The Seebeck coefficient is enhanced and the phonon thermal conductance is suppressed when the alternation frequency of the structure in the transport direction increases, yielding a figure of merit (ZT) of 1.58 at 300 K in the high-frequency alternating (HFA) structure. Further, the phonon thermal conductance decreases greatly when the HFA monolayer device is extended into a van der Waals heterojunction, resulting in a high ZT of 1.80 at 300 K, which rises to 3.49 at 500 K. These findings highlight the potential of atomic-level alternation engineering for optimizing thermoelectric performance in Janus 2D materials.