Effects of a second phase with different bandgaps on the thermoelectric performance of polycrystalline SnSe materials

SnSe is a promising thermoelectric (TE) material that has attracted increasing attention in recent years. Nano-engineering provides a straightforward and practical approach to enhancing the TE transport performance and mechanical strength of materials. This study reported a strategy that can effectively enhance the figure of merit (ZT) to 1.65 with an endotaxially nanostructured 0.5% telluride sample. This high performance resulted from a closely coupled phonon-blocking/electron-transmitting system enabled by embedding endotaxially nanostructured second phases. The valence band alignment between the matrix SnSe and the embedded second-phase metal telluride (ATe, A = Pb, Ge, Ga, and Zn) controlled the hole transport by embedding a suitable forbidden band. Surprisingly, the nanostructured GaTe second phase, with a broader energy gap compared to SnSe, played a dual role by tuning the carrier concentration and mobility, which increased the electrical transport properties to 710 μW cm⁻¹ K⁻², and enhancing phonon scattering, which decreased the lattice thermal conductivity to ∼0.2 W m⁻¹ K⁻¹ at 823 K. Finally, a peak ZT of ∼1.65 at 823 K and high mechanical properties were obtained. These values were better than those of most reported polycrystalline SnSe materials and provided a favorable reference for subsequent modifications. The results showcased the potential of the SnSe-based nanocomposites fabricated in this study for cost-effective TE applications.