Enhanced Thermoelectric Performance by Carrier Optimization in Layered SnSe2 with Low Thermal Conductivity

Abstract

The intrinsically suppressed thermal transport arising from weak interlayer interactions in layered SnSe2 is largely offset by its inherently inadequate electrical conduction, thereby impeding the realization of high thermoelectric performance. Here, a peak thermoelectric ZT of ∼1.4 is realized at 723 K in a SnSe2 polycrystal via optimization of charge carrier density. The ambient-temperature electron concentration, initially approximately 1.0 × 1019 cm–3, is raised to 5.2 × 1019 cm–3, leading to substantially boosted charge conduction and the power factor over a wide thermal span. Simultaneously, the total heat conduction stays at a modest level of merely ∼0.6–0.8 W m–1 K–1 under high-temperature conditions. First-principles computations reveal that soft interlayer acoustic vibrational modes together with pronounced lattice anharmonicity, rooted in weak van der Waals interactions between the layers, constitute the microscopic reason for the suppressed thermal transport. The intrinsically soft lattice, combined with substitution-induced local disorder, allows electrical transport to be optimized while retaining low thermal conductivity. These findings establish layered SnSe2 as a promising n-type thermoelectric and highlight carrier optimization within a soft lattice as an effective strategy for high-efficiency thermoelectric conversion.