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

• SnTe-NaSbSe 2 alloys based on colloid synthesis are detailed for the first time. • The Seebeck coefficient are significantly optimized at the same time. • κ L of 0.38 W m−1 K−1 below the amorphous limit of Debye–Cahill is achieved. • The ZT reaches up to 1.15 at 823 K for (SnTe) 0.85 (NaSbSe 2) 0.15. Ternary I-V-VI 2 colloidal NaSbSe 2 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-NaSbSe 2 alloys from the rapid hot press of colloidal nanocrystal building blocks. The incorporation of NaSbSe 2 nanocrystals significantly enhances the Seebeck coefficient of SnTe. The band convergence and simultaneous increasing band gap of SnTe-NaSbSe 2 alloys are certified by the first-principles density functional theory calculations. Besides, defect engineering generated by the incorporation of NaSbSe 2 nanocrystals such as Sn vacancies, substitution point defects, dense dislocations, and strains generated by the NaSbSe 2 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 (NaSbSe 2) 0.15 are achieved. [ABSTRACT FROM AUTHOR]