Thermoelectric module for low temperature applications

The possibility of a prototype thermoelectric cooling device for operation near liquid nitrogen temperatures has been explored. In these devices, the figure of merit involves a combination of the properties of the two branches of the module. Here, we investigate the fabrication of a module with a new low temperature material, CsBi₄Te₆ (p-type), and the best known low temperature n-type materials Bi₈₅Sb₁₅. Transport measurements for each of these materials show high performance at low temperatures. Known values for the figure of merit Z_max of CsBi₄Te₆ 3.5 × 10^-3 K^-1 at 225K and for Bi₈₅Sb₁₅ is 6.5 × 10^-3; K^-1 at 77K. At 100K these values drop to 2.0 × 10^-3 K^-1 for CsBi₄Te₆ and 6.0 × 10^-3 K^-1 for Bi₈₅Sb₁₅. Theoretical simulations based on these data show a cooling of ΔT = 12K at 100K, which is almost three times the efficiency of a Bi₂Te₃ module at that temperature. We present transport measurements of elements used in the fabrication of a low temperature thermoelectric module and properties of the resulting module.