High thermoelectric performance of few-quintuple Sb₂Te₃ nanofilms

Antimony telluride (Sb₂Te₃) has a very low ZT value at room temperature, even though the alloys of Bi₂Te₃ and Sb₂Te₃ are the most widely used thermoelectric materials. Taking advantage of nano-structures and topological insulators (TIs), we report that high ZT values of larger than 2 can be achieved in one quintuple-layer (QL, ZT ≥ 2.1) and 4 QLs (ZT ≥ 2.2) of Sb₂Te₃ at room temperature, while the ZT value for bulk is around 0.5. For 1 QL, Seebeck coefficient has been greatly enhanced due to the increase in the number of band extrema by virtue of the twelvefold valley degeneracy from surface states. For 4 QLs, the high ZT value is attributed to the much longer surface relaxation time associated with the robust nature of the topological surface states. Moreover, the ZT values and the TI character of few-quintuple Sb₂Te₃ nanofilms demonstrate thickness(layer)-dependent behaviors. Our results offer significant clues for future applications and investigations of Sb₂Te₃-related quintuple layers as promising p-type thermoelectric materials and quasi-2D topological insulators for nanoelectronics.