  As one of the most important n-type thermoelectric (TE) materials, Bi2Te3 has
been studied for decades, with efforts to enhance the thermoelectric
performance based on element doping, band engineering, etc. In this study, we
report a novel bulk-insulating topological material system as a replacement for
n-type Bi2Te3 materials: V doped Bi1.08Sn0.02Sb0.9Te2S (V:BSSTS) . The V:BSSTS
is a bulk insulator with robust metallic topological surface states.
Furthermore, the bulk band gap can be tuned by the doping level of V, which is
verified by magnetotransport measurements. Large linear magnetoresistance is
observed in all samples. Excellent thermoelectric performance is obtained in
the V:BSSTS samples, e.g., the highest figure of merit ZT of ~ 0.8 is achieved
in the 2% V doped sample (denoted as V0.02) at 550 K. The high thermoelectric
performance of V:BSSTS can be attributed to two synergistic effects: (1) the
low conductive secondary phases Sb2S3, and V2S3 are believed to be important
scattering centers for phonons, leading to lower lattice thermal conductivity;
and (2) the electrical conductivity is increased due to the high-mobility
topological surface states at the boundaries. In addition, by replacing one
third of costly tellurium with abundant, low-cost, and less-toxic sulfur
element, the newly produced BSSTS material is inexpensive but still has
comparable TE performance to the traditional Bi2Te3-based materials, which
offers a cheaper plan for the electronics and thermoelectric industries. Our
results demonstrate that topological materials with unique band structures can
provide a new platform in the search for new high performance TE materials.
