Nanocrystal-based thermoelectric SnTe-NaSbSe2 alloys with strengthened band convergence and reduced thermal conductivity

Abstract

Ternary I-V-VI2 colloidal NaSbSe2 nanocrystals are herein used to improve the performance of lead-free SnTe thermoelectric materials. We showcase a versatile bottom-up engineering approach to produce nanocrystal-based SnTe-NaSbSe2 alloys from the rapid hot press of colloidal nanocrystal building blocks. The incorporation of NaSbSe2 nanocrystals significantly enhances the Seebeck coefficient of SnTe. The band convergence and simultaneous increasing band gap of SnTe-NaSbSe2 alloys are certified by the first-principles density functional theory calculations. Besides, defect engineering generated by the incorporation of NaSbSe2 nanocrystals such as Sn vacancies, substitution point defects, dense dislocations, and strains generated by the NaSbSe2 nanoparticles incorporation result in a dramatic reduction of the lattice thermal conductivity below the amorphous limit of pure SnTe, down to 0.38 W m−1 K−1. As a consequence, power factors enhance up to 1.77 mW m−1 K−2, which is ∼193 % higher than that of the pristine SnTe, and thermoelectric figures of merit up to 1.15 at 823 K for (SnTe)0.85(NaSbSe2)0.15 are achieved.