Excessively Doped PbTe with Ge-Induced Nanostructures Enables High-Efficiency Thermoelectric Modules

The application of thermoelectrics in waste heat recovery requires high conversion efficiency, which is best achieved through the combination of progressive performance-enhancing strategies. In this study, we combined engineered doping, nanostructuring, and module fabrication in PbTe-based thermoelectrics to generate high-ZT materials along with high-efficiency modules. The use of excess Na (4%) as a p-type dopant greatly enhanced the thermoelectric power factor by generating extra charge carriers at high temperature. The addition of minute amounts of Ge (≤1%) generated nanoprecipitates, which greatly reduced the lattice thermal conductivity. An optimal ZT of ∼1.9 at ∼805 K was achieved for Pb_0.953Na_0.040Ge_0.007Te as a p-type leg, which was combined with PbTe_0.9964I_0.0036 as an n-type leg to fabricate thermoelectric modules. An exceptionally high efficiency of ∼12% for a temperature difference of 590 K was obtained in a cascade Bi₂Te₃/nanostructured PbTe module with eight p-n pairs. Thermoelectric technology enables the direct conversion of waste heat to electricity and therefore is a sustainable solution to the global energy crises. Many advancements in thermoelectric material development have been made in the past decade, leading to high thermoelectric figure of merit (ZT). Nanostructuring is one such successful approach. However, these advanced materials have not yet been fully explored for module development, leaving a big gap between materials and module development. In this work, we not only develop high-ZT (∼1.9) PbTe thermoelectric material using Ge-induced nanostructuring but also demonstrate their use in cascade-type module fabrication, exhibiting a record efficiency of ∼12% for a temperature gradient of 590 K. These results exhibit the potential of nanostructured materials in thermoelectric application setting, paving the path for obtaining exceptionally high-efficiency modules. To grow the thermoelectric market, the module development must be at par with the advancements in the materials development. In this work, we successfully bridge the two by developing high-ZT (∼1.9) PbTe-based thermoelectric material and using this material in thermoelectric module development, leading to a record high efficiency of ∼12%. The ZT was enhanced through nanostructuring and engineered doping. The high-efficiency module will pave the way for many new opportunities for thermoelectric power generation in commercial applications.