High-performance double-stage Mg₃Bi₂-based thermoelectric cooler

Thermoelectric coolers (TEC) play a critical role in establishing substantial temperature differences required for cooling photoelectric detectors. While single-stage devices suffice for moderate cooling, multi-stage TECs are indispensable when pursuing cryogenic cooling below 200 K. The existing multi-stage TECs, however, remain constrained by their exclusive dependence on Bi₂Te₃-based alloys. Recently, the n-type Mg₃Bi₂-based material with high thermoelectric performance around room temperature has been discovered. Herein, we report the design of the double-stage TEC with 7 pairs of thermoelectric legs in the upper stage and 17 pairs of legs in the bottom stage, utilizing the n-type Mg3.1Sb0.497Bi1.5Te0.003 in combination with p-type (Bi, Sb)₂Te₃. An assembly process that enables precise integration of thermoelectric legs with ceramic substrates through a one-step reflow soldering has been developed. When operating at a hot-side temperature of 350 K, the double-stage TEC achieves a maximum cooling temperature difference of ~103.2 K. The cooling performance of this double-stage TEC is comparable to that of the device based on commercial Bi₂Te₃ alloys. Our results demonstrate that n-type Mg₃Bi₂-based materials are highly promising for thermoelectric cooling applications.