Enhanced Thermoelectric Performance in WSSe–MgO vdW Heterostructures: Insights from Electronic and Phonon Transport Properties

We investigate the structural, electronic, and phonon transport properties of WSSe–MgO van der Waals (vdW) heterostructures using density functional theory and Boltzmann transport calculations. Two stacking models, distinguished by the orientation of S and Se atoms, are considered, with stacking (a) in both models exhibiting the highest stability, as confirmed by binding energy calculations and ab initio molecular dynamics simulations. Electronic structure calculations show an indirect band gap of 1.613 eV for Model-II and a direct band gap of 2.01 eV for Model-I. Carrier mobility and relaxation times calculated via deformation potential theory highlight high electron mobility, supporting favorable thermoelectric (TE) behavior. Phonon dispersion indicates dynamic stability and low-frequency soft optical modes, which, combined with strong anharmonicity of the flexural acoustic (ZA) phonons, result in significantly reduced lattice thermal conductivity (κl ≈ 11.67 W/m·K (12.96) at 700 K) for both models. Mode-resolved Grüneisen parameters, phonon lifetimes, and scattering rates demonstrate that low-frequency ZA phonons dominate thermal transport suppression, enhancing the figure of merit (ZT). Therefore, the WSSe–MgO vdW heterostructure exhibits remarkable TE performance, with ZT reaching 2.53 (2.3) for p-type (n-type) doping at 700 K for both models. The average ZT of 1.5 (1.3) suggests a maximum energy conversion efficiency of around 16.64% (15.63%). These results underscore the promise of WSSe–MgO heterostructures as efficient TE materials, combining low lattice thermal conductivity with favorable electronic transport, and highlight their potential for energy conversion, making them a promising candidate for future energy systems and TE devices.