Thermoelectric cooling goes cooler

Thermoelectric cooling (TEC) is a solid-state technology that utilizes electricity to pump heat from one side of a material or device to the other.It leverages the dual role of charge carriers, which transport charge and heat, enabling heat redistribution under external electric and/or magnetic fields.This technology offers advantages including miniaturization, solid-state operation, vibration-free performance, and long-term reliability, making it particularly beneficial in applications where conventional compressor-based cooling is less suitable.Currently, TEC has been mainly employed in near-room-temperature scenarios, including but not limited to refrigerators, precise temperature control in optical modules, and polymerase chain reaction detectors.In recent years, there has been a growing demand for solid-state cooling technologies capable of operating at lower temperatures.For instance, cooling infrared detectors to temperatures below 150 K is crucial to minimize noise and improve sensitivity [1].This brings new challenges for TEC to achieve enhanced cooling capabilities-operating at lower temperature ranges while delivering superior performance.The currently commonly used TEC technology mainly relies on the Peltier effect, a phenomenon discovered by French physicist Jean Charles Athanase Peltier in 1834.In the Peltier effect, the direction of the electric current corresponds either parallel or antiparallel to the thermal gradient (Figure 1a), depending on the type of charge carriers.Typically, a TEC module consists of alternating N-type and P-type thermoelectric materials arranged in a -shape series configuration (Figure 1b).When electric power is applied, electrons in the N-type leg and holes in the P-type leg move directionally, generating a cooling effect on one side and a heating effect on another.Materials that have been commonly employed for Peltier cooling include Bi-Sb, Bi 2 Te 3 , and Mg 3 Bi 2-x Sb x [2].Due to the limitations on the z value and the reduction in T, the thermoelectric (TE) figure of merit (zT) of these materials generally decreases with decreasing temperature.However, it is noteworthy that Bi-Sb exhibits an optimal operating temperature range below room temperature, with its zT peaking between 120-200 K, reaching approximately 0.6 [2,3].By further introducing a magnetic field to enhance the Seebeck coefficient while reducing electronic thermal conductivity, the zT value of Bi-Sb alloys at low temperatures can be further improved.A maximum zT value exceeding 1.5 in the temperature range of