Enhanced thermoelectric figure-of-merit of MoS2/α-MoO3 nanosheets via tuning of sulphur vacancies

Abstract

• Increased electrical conductivity of ~97% via zero-barrier charge injection. • Enhanced Seebeck of 553 μV K −1 due to the modified band level by hole injection. • Reduced thermal conductivity to ~44% by all-scale hierarchical phonon scattering. • Achieved high zT = 1.18 for optimized MoS 2 /MoO 3 interface via simple chemical route. As a consequence of high thermoelectric (TE) properties, low cost, and environmental friendliness, molybdenum disulphide (MoS 2 ) has emerged as the material of choice for TE generator for room temperature to mid temperature (800 K) applications. The compound has high figure-of-merit (zT) value due to the combination of anharmonicity, valley degeneracy and ultralow thermal conductivity (at low-dimension). In this work, MoS 2 /MoO 3 hierarchical structures are prepared by hydrothermal method and it exhibits improved TE performance. The enhanced phonon scattering is observed in thin layered nanosheets and improved electrical conductivity by zero-barrier charge injection at MoS 2 /MoO 3 interface. While MoO 3 supports in optimizing the electrical transport properties, low-dimension layered MoS 2 nanosheets and interfaces of MoS 2 /MoO 3 results in phonon scattering. High resolution transmission electron microscopy (HRTEM) indicates enriched interface of nanocrystals and nanosheets. This results in ~97% increased electrical conductivity compared to the pristine MoS 2 at 600 K while retaining ~44% reduction in thermal conductivity at 550 K. More importantly, the phonon scattering and carrier optimization have been tailored strategically, and a relatively high power factor (PF) of 411.43 µW m −1 K −2 at 600 K with a significantly lowered thermal conductivity of 0.16 W m −1 K −1 at 550 K have been achieved. The maximum zT of 1.18 at 600 K is achieved for hierarchical MoS 2 nanosheets/MoO 3 nanocrystal’s optimized effective interface.