Enhanced cryogenic thermoelectric cooling of Bi0.5Sb1.5Te3 by carrier optimization

Abstract As the best‐performing materials for thermoelectric cooling, Bi 2 Te 3 ‐based alloys have long attracted attention to optimizing the room‐temperature performance of Bi 2 Te 3 for both power generation and refrigeration applications. This focus leads to less emphasis and fewer reports on the cooling capability below room temperature. Given that the optimal carrier concentration ( n opt ) for maximizing the cooling power is highly temperature dependent, roughly following the relationship n opt ∝ T 3/2 , lowering the carrier concentration is essential to improve the cooling capability at cryogenic temperatures. Taking p‐type Bi 0.5 Sb 1.5 Te 3 as an example, careful control of doping in this work enables a reduction in carrier concentration to 1.7 × 10 19 cm −3 from its optimum at 300 K of 3.4 × 10 19 cm −3 . This work successfully shifts the temperature at which the thermoelectric figure of merit ( zT ) peaks down to 315 K, with an average zT as high as 0.8 from 180 to 300 K. Further pairing with commercial n‐type Bi 2 Te 3 ‐alloys, the cooling device realizes a temperature drop as large as 68 K from 300 K and 24 K from 180 K, demonstrating the extended cooling capability of thermoelectric coolers at cryogenic temperatures. image