Enabling High Quality Factor and Enhanced Thermoelectric Performance in BiBr₃-Doped Sn_0.93Mn_0.1Te via Band...

Lead-free SnTe-based materials are expected to replace PbTe and have gained much attention from the thermoelectric community. In this work, a maximum ZT of ∼1.31 at 873 K is attained in SnTe via promoting a high quality factor resulting from Mn alloying and BiBr₃ 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^-1 K^-2 at 723 K in Sn_0.93Mn_0.1Te. In addition, the subsequent BiBr₃ 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^-1 K^-2 at 873 K is achieved in Sn_0.93Mn_0.1Te-0.8 atom % BiBr₃. In addition to band sharpening, BiBr₃ 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 BiBr₃ in Sn_0.93Mn_0.1Te optimizes the carrier mobility and suppresses the lattice thermal conductivity, resulting in a dramatically enhanced quality factor. Accordingly, an average ZT of ∼0.62 in the temperature range of 300-873 K is obtained in Sn_0.93Mn_0.1Te-0.8 atom % BiBr₃, ∼250% increase compared with that in Sn_1.03Te.