Band and microstructure engineering toward high thermoelectric performance in SnTe

Abstract

SnTe-based compounds have long been considered competitive for thermoelectric power generation. However, their intrinsically high hole concentration due to Sn vacancies and inferior band structure featuring a large energy offset in two valence bands at the band edges largely limits their electrical performance. Meanwhile, the relatively high lattice thermal conductivity of SnTe compared to other IV–VI-based thermoelectrics makes their overall thermoelectric performance enhancement challenging. In this study, we prove that spontaneous optimization in both the carrier concentration and band structure of SnTe can be achieved by alloying a small amount of AgBiS₂, thereby yielding a high power factor of 2.25 mW m⁻¹ K⁻². It is further elucidated through first-principles calculations that AgBiS₂ is a proper choice for band structure engineering compared with other dopants and alloying substances. Moreover, plenty of nano-precipitates and grain boundaries were observed in the SnTe matrix, which led to a reduction in lattice thermal conductivity to an amorphous limit of 0.3 W m⁻¹ K⁻¹, finally resulting in a peak zT of 1.6 at 903 K. This value exceeds most of the values reported for SnTe-based compounds.