From an environmental perspective, lead-free SnTe would be preferable for solid-state waste heat recovery if its thermoelectric figure-of-merit could be brought close to that of the lead-containing chalcogenides. In this work, we studied the thermoelectric properties of nanostructured SnTe with different dopants, and found indium-doped SnTe showed extraordinarily large Seebeck coefficients that cannot be explained properly by the conventional two-valence band model. We attributed this enhancement of Seebeck coefficients to resonant levels created by the indium impurities inside the valence band, supported by the first-principles simulations. This, together with the lower thermal conductivity resulting from the decreased grain size by ball milling and hot pressing, improved both the peak and average nondimensional figure-of-merit ( ZT ) significantly. A peak ZT of ∼1.1 was obtained in 0.25 atom % In-doped SnTe at about 873 K.

Improving ionic thermoelectrics: Using ions as charge carriers in thermoelectric devices usually requires using either thermal diffusion or redox reactions at two electrodes with different temperatures. Han et al. leveraged both of these strategies to develop a gelatin-based ionic thermoelectric device that uses alkali salts and an iron-based redox couple to generate a large thermopower. This device is capable of generating useful amounts of energy from body heat. Science , this issue p. 1091

Thermoelectric power generation represents a class of energy conversion technology, which has been used in power supply of aeronautic and astronautic exploring missions, now showing notable advantages to harvest the widely distributed waste heat and convert the abundant solar energy into electricity at lower cost than Si-based photovoltaic technology. Thermoelectric dimensionless figure of merit (ZT) plays a key role in the conversion efficiency from thermal to electrical energy. Most state-of-the-art thermoelectric materials are characterized with various nanostructures from fine grains, dispersed particles, nano-inclusions to atomic defects, and therefore are referenced as nanocomposite. Recently, remarkable advances have been achieved in various material systems through the introduction of different nanostructures to tune the transport of phonons and electrons. In this review, we firstly clarify some fundamental tradeoffs dictating the ZT value through the relationship ZT=(S²σ/κ)T. We also pay special attentions to the recent advances in some selected materials, including half-Heuslers, PbTe, CoSb₃, Bi₂Te₃, etc. Finally, we provide an outlook of new directions in this filed, especially a proposal on a new concept of ordered nanocomposite. Graphical abstract This paper reviews the recent advances in thermoelectric nanocomposite materials including half-Heuslers, skutterudites, PbTe, PbSe, PbS, AgSbTe₂, and Bi₂Te₃-based materials, with a special attention given to the fundamental tradeoffs dictating the ZT values. A large reduction in lattice thermal conductivity has been demonstrated in these materials due to the presence of nanostructures, leading to higher ZTs. To further improve the ZT, a new concept of ordered nanocompositeis proposed. Highlights ► Thermoelectric power generation represents a class of clean energy conversion technology. ► Some fundamental tradeoffs limit the ZT value through the relationship ZT=(S²σ/κ)T. ► The concept of nanocomposite increases the ZT value of the state-of-the-art materials. ► A new concept of ordered nanocomposite is proposed.Solid-State Solar-Thermal Energy Conversion Center (DE-SC0001299)Solid-State Solar-Thermal Energy Conversion Center (DE-FG02-09ER46577