Development of integrated two-stage thermoelectric generators for large temperature difference

Multi-stage thermoelectric (TE) modules can withstand a large temperature difference and can be used to obtain a high conversion efficiency. In this study, two-stage PbTe/Bi2Te3 TE modules were developed with an enhanced efficiency through a comprehensive study of device structure design, module fabrication, and performance evaluation. PbTe-based AgPbmSbTem+2 (abbreviated as LAST) is a typically high ZT material, while the corresponding TE module was rarely reported so far. How to utilize LAST to fabricate high efficiency TE modules therefore remains a central problem. Finite element simulation indicates that the temperature stability of the two-stage module for LAST is better than that of two-segmented module. Compared to Cu, Ni, and Ni-Fe alloys, Co-Fe alloy is an effective metallization layer for PbTe due to its low contact resistance and thin diffusion layer. By sintering a slice of Cu on TE legs, pure tinfoil can be used as a common welding method for mid-temperature TE modules. A maximum efficiency (eta(max)) of 9.5% was achieved in the range of 303 to 923 K in an optimized PbTe/Bi2Te3 based two-stage module, which was almost twice that of a commercial TE module.