Germanium Chalcogenide Thermoelectrics: Electronic Structure Modulation and Low Lattice Thermal Conductivity

Abstract

Thermoelectric materials can convert untapped heat to electricity and are expected to have an important role in future energy utilization. IV–VI metal chalcogenides are the most promising candidates for mid-temperature thermoelectric power generation. Among them, PbTe and their alloys have been proven to be the superior thermoelectric materials. Unfortunately, the toxicity of lead (Pb) prevents the application of lead chalcogenides and demands the search for lead-free high-performance solids. This perspective discusses the recent progress of thermoelectric property studies on germanium chalcogenides (GeTe, GeSe, and GeS) for mid-temperature power generation. Here, we have discussed the crystal structure, chemical bonding, and phonon dispersion of germanium chalcogenides to understand the underlying lattice dynamics and low lattice thermal conductivity from a chemistry perspective. We have also discussed the uniqueness of the electronic structure of GeTe and GeSe, which plays an important role in tailoring thermoelectric properties. Additionally, the implications of the recent state-of-art strategies such as resonant level formation, valence band convergence, slight symmetry breaking of the crystal and electronic structures, point defect, and nanostructure induced phonon scattering on the high thermoelectric performance of the germanium chalcogenides are discussed in detail. In conclusion, we highlight some of the innovative ideas for discovery and designing of new thermoelectric compositions. Finally, we point out the major challenges and opportunities in this field. All the strategies discussed in this perspective not only make germanium chalcogenides as a promising candidate for future thermoelectric applications but also serve as a guide to enhance the thermoelectric performance of other materials.