A performance comparison of SiGe and skutterudite based segmented thermoelectric devices

Abstract

For the past 25 years, unicouples made of Silicon Germanium alloys (Si0.8Ge0.2 and Si0.63Ge0.38) have been used in the majority of the spacecraft powered by Radioisotope Thermoelectric Generators (RTGs) to explore various planets of the solar system as well as the sun. These unicouples operate typically at hot and cold side temperatures of 1175–1273 K and 573 K, respectively, converting the heat produced in the General Purpose Heat Source (GPHS) modules to electricity at efficiencies <7%. Recently, Segmented Thermoelectric Unicouples (STUs) made of n-type Bi2Te3 and CoSb3-based alloys and p-type Bi2Te3 and CeFe4Sb12-based alloys have been developed and tested successfully with a demonstrated efficiency to date of ∼10% and the potential for achieving 14–15% when operated at hot and cold side temperatures of 973 K and 300 K, respectively. This paper compares the performance of SiGe unicouples and skutterudite STUs, at same hot side temperature of 973 K and cold side temperatures of 300, 573, and 673 K, and the same total length and cross sectional dimensions of the p-leg. The area of the n-leg and the lengths of the segments of various materials in the STUs are determined based on maximizing either the electrical power density or the conversion efficiency. Results showed that replacing SiGe with skutterudite STUs in future radioisotope power systems (or even in conjunction with a space nuclear reactor and space probes), could increase the thermal to electric conversion efficiency at a heat source temperature of 973 K by ∼40% to 198% for Tc=673 K and 300 K, respectively. This would reduce by more than half the mass of the 238PuO2 fuel needed and the radiator’s surface area for rejecting the waste heat.