Elevating thermoelectric performance in the sub-ambient temperature range for electronic refrigeration

Solid-state thermoelectric coolers, which enable direct heat pumping by utilizing electricity, play an essential role in electronic refrigeration. Given that these devices usually cool down to the sub-ambient temperature range, their performance is critically dependent on the material properties at temperatures below 300 K. Consequently, enhancing the thermoelectric properties of materials at sub-ambient temperature is of paramount importance for advancing cooling technology. Herein, a single-crystalline Mg₃Bi₂-based material has been prepared and exhibits high electron mobility. As a result, thermoelectric figure-of-merit values of ∼1.05 at 300 K and ∼0.87 at 250 K (along the <i>ab</i> plane) have been achieved, which are superior to commercial n-type Bi₂(Te, Se)₃. Thermoelectric coolers (single- and double-stage devices) based on the n-type single-crystalline Mg₃Bi_1.497Sb_0.5Te_0.003 and p-type (Bi, Sb)₂Te₃ have been fabricated. The double-stage cooler demonstrates a remarkable maximum cooling temperature difference of ∼106.8 K at the hot-side temperature of 350 K, surpassing the performance of commercial Bi₂Te₃-based devices. Notably, the Mg₃Bi₂-based double-stage device exhibits exceptional cyclic stability, maintaining its cooling performance without any observable degradation after approximately 2,000 cycles between the input currents of 1 and 3 A. These findings show that single-crystalline Mg₃Bi₂ alloys hold great promise for thermoelectric cooling applications.