Optimized Mn and Bi co-doping in SnTe based thermoelectric material: A case of band engineering and density of states tuning

Tin telluride (SnTe) overwhelmingly continues to be studied owing to its promising thermoelectric properties, tunable electronic structure, and its potential as an alternate to toxic lead telluride (PbTe) based materials. In this research, we engineer the electronic properties of SnTe by co-doping Mn and Bi below their individual solubility limit. The First principles density functional theory studies reveal that both Bi and Mn introduce resonance states, thereby increasing the density of states near the Fermi level leading to enhanced Seebeck coefficient. This unique combination of using two resonant dopants to introduce flatter bands is effective in achieving higher performance at lower temperatures manifesting into a large Seebeck value of ∼91 μV/K at room temperature in the present case. Both elements optimally co-doped results in a very high power factor value of ∼24.3 μW/cmK² at 773 K when compared to other high performance SnTe based materials. A zT of ∼0.93 at 773 K is achieved by tuning the proportion of the co-dopants Mn and Bi in SnTe. The hardness value of pristine SnTe was also seen to increase after doping. As a result, synergistic optimized doping proves to be a suitable means for obtaining thermoelectric materials of superior characteristics without the need for heavy doping.