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 Sn0.93Mn0.1Te. 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 Sn0.93Mn0.1Te-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 Sn0.93Mn0.1Te 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 Sn0.93Mn0.1Te-0.8 atom % BiBr3, ∼250% increase compared with that in Sn1.03Te.