Band and microstructure engineering toward high thermoelectric performance in SnTe

Abstract

SnTe based compounds have long been considered to be competitive in thermoelectric power generation. However, its intrinsically high hole concentration due to Sn vacancies and inferior band structure featured by large energy offset in two valence bands at band edges largely limit the electrical performance. Meanwhile, the relatively high lattice thermal conductivity of SnTe compared to other IV-VI based thermoelectrics makes the overall thermoelectric performance promotion challenging. In this study, we prove the spontaneous optimization in both carrier concentration and band structure can be realized in SnTe by a small amount of AgBiS₂ alloying, giving rise to a high power factor of 2.25 mW m^–1 K^–2. It is further elaborated that AgBiS₂ is a proper choice for band structure engineering by comparing to others dopants and alloying substances that facilitate band convergence through first-principles calculations. Moreover, the substitution of Ge on Sn sites generates plenty of nano-precipitates and grain boundaries in SnTe matrix, which leads to the reduction of lattice thermal conductivity to amorphous limit of 0.3 W/m K, finally resulting in a peak zT of 1.6 at 903 K and exceeding most of the values reported in SnTe-based compounds.