Enabling High Quality Factor and Enhanced Thermoelectric Performance in BiBr-Doped SnMnTe via Band Convergence and Band Sharpening.

Lead-free SnTe-based materials are expected to replace PbTe and have gained much attention from the thermoelectric community. In this work, a maximum of ∼1.31 at 873 K is attained in SnTe via promoting a high quality factor resulting from Mn alloying and BiBr doping. The results show that Mn alloying in SnTe converges the L band and the ∑ band in valence bands to supply enhanced valley degeneracy and the density of states effective mass, giving rise to a high power factor of ∼21.67 μW cm K at 723 K in SnMnTe. In addition, the subsequent BiBr doping can sharpen the top of the valence band to coordinate the contradiction between the band effective mass and the carrier mobility, thus enhancing the carrier mobility while maintaining a relatively large density of states effective mass. Consequently, a maximum power factor of 23.85 μW cm K at 873 K is achieved in SnMnTe-0.8 atom % BiBr. In addition to band sharpening, BiBr doping can also effectively suppress the bipolar effect at elevated temperatures and reduce the lattice thermal conductivity by strengthening the point defect phonon scattering. Benefitting from doping BiBr in SnMnTe optimizes the carrier mobility and suppresses the lattice thermal conductivity, resulting in a dramatically enhanced quality factor. Accordingly, an average of ∼0.62 in the temperature range of 300-873 K is obtained in SnMnTe-0.8 atom % BiBr, ∼250% increase compared with that in SnTe.