Enhanced Thermoelectric Performance Achieved in SnTe via the Synergy of Valence Band Regulation and Fermi Level Modulation

SnTe is deemed a promising mid-temperature thermoelectric material for low toxicity, low cost, and decent performance. Sole doping/alloying on Sn sites was reported to result in either modified band alignment or reduced lattice thermal conductivity, thus contributing to an enhanced overall thermoelectric figure of merit. However, this strategy alone is always unable to take full use of the material's advantage, especially considering that it simultaneously pushes the hole concentration off the optimal range. In this work, we adopted a two-step approach to optimize the thermoelectric performance of SnTe in order to overcome the limitation. First, Mn was alloyed into Sn sites to increase the density of state effective mass of SnTe by regulating the valence bands; the Fermi level was further regulated by iodine doping, guided by a refined two-band model. Additionally, the lattice thermal conductivity was also suppressed by the microstructure optimizing via Mn doping and additional phonon scattering at ITe mass/strain fluctuation. As a result, a high ZT of 1.4 at 873 K was achieved for Sn0.91Mn0.09Te0.99I0.01. This study provides a way to refine the single doping stratagem used in other thermoelectric materials.