Development of a High-Efficiency Cascaded Thermoelectric Module

This paper describes progress toward the development of a cascaded thermoelectric module capable of an efficiency of 10 percent. The integration of the module with an isotope heat source to provide a long-life high-efficiency space power system is discussed. The basic concept chosen to meet the efficiency objective consists of SiGe elements metallurgically bonded to an interstage plate which in turn serves as the hot plate for a PbTe stage. The PbTe stage uses segmented elements contained in a gas-filled hermetically sealed enclosure. The fabrication techniques developed to minimize extraneous temperature drops between the two stages and attain a mechanically stable module are described. The design leads to an efficiency in excess of 10 percent with the module operated between 1840 and 400°F. Performance testing of a 20-watt module is discussed and the results compared to the design values.