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1. Amphoteric Indium Enables Carrier Engineering to Enhance the Power Factor and Thermoelectric Performance in n ‐Type Ag n Pb 100 In n Te 100+2 n (LIST)

   https://doi.org/10.1002/aenm.201900414  

   Xiao, Yu ; Wu, Haijun ; Wang, Dongyang ; Niu, Changlei ; Pei, Yanling ; Zhang, Yang ; Spanopoulos, Ioannis ; Witting, Ian Thomas ; Li, Xin ; Pennycook, Stephen J. ; et al ( March 2019 , Advanced Energy Materials)

   The Ag and In co‐doped PbTe, Ag_nPb₁₀₀In_nTe_100+2n(LIST), exhibitsn‐type behavior and features unique inherent electronic levels that induce self‐tuning carrier density. Results show that In is amphoteric in the LIST, forming both In³⁺and In¹⁺centers. Through unique interplay of valence fluctuations in the In centers and conduction band filling, the electron carrier density can be increased from ≈3.1 × 10¹⁸cm⁻³at 323 K to ≈2.4 × 10¹⁹cm⁻³at 820 K, leading to large power factors peaking at ≈16.0 µWcm⁻¹K⁻²at 873 K. The lone pair of electrons from In⁺can be thermally continuously promoted into the conduction band forming In³⁺, consistent with the amphoteric character of In. Moreover, with rising temperature, the Fermi level shifts into the conduction band, which enlarges the optical band gap based on the Moss–Burstein effect, and reduces bipolar diffusion and thermal conductivity. Adding extra Ag in LIST improves the electrical transport properties and meanwhile lowers the lattice thermal conductivity to ≈0.40 Wm⁻¹K⁻¹. The addition of Ag creates spindle‐shaped Ag₂Te nanoprecipitates and atomic‐scale interstitials that scatter a broader set of phonons. As a result, a maximumZTvalue ≈1.5 at 873 K is achieved in Ag₆Pb₁₀₀InTe₁₀₂(LIST).

    

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2. High Thermoelectric Performance in Supersaturated Solid Solutions and Nanostructured n‐Type PbTe–GeTe

   https://doi.org/10.1002/adfm.201801617  

   Luo, Zhong‐Zhen ; Zhang, Xiaomi ; Hua, Xia ; Tan, Gangjian ; Bailey, Trevor P. ; Xu, Jianwei ; Uher, Ctirad ; Wolverton, Chris ; Dravid, Vinayak P. ; Yan, Qingyu ; et al ( June 2018 , Advanced Functional Materials)

   Sb‐doped and GeTe‐alloyed n‐type thermoelectric materials that show an excellent figure of meritZTin the intermediate temperature range (400–800 K) are reported. The synergistic effect of favorable changes to the band structure resulting in high Seebeck coefficient and enhanced phonon scattering by point defects and nanoscale precipitates resulting in reduction of thermal conductivity are demonstrated. The samples can be tuned as single‐phase solid solution (SS) or two‐phase system with nanoscale precipitates (Nano) based on the annealing processes. The GeTe alloying results in band structure modification by widening the bandgap and increasing the density‐of‐states effective mass of PbTe, resulting in significantly enhanced Seebeck coefficients. The nanoscale precipitates can improve the power factor in the low temperature range and further reduce the lattice thermal conductivity (κ_lat). Specifically, the Seebeck coefficient of Pb_0.988Sb_0.012Te–13%GeTe–Nano approaches −280 µV K⁻¹at 673 K with a low κ_latof 0.56 W m⁻¹K⁻¹at 573 K. Consequently, a peakZTvalue of 1.38 is achieved at 623 K. Moreover, a high averageZT_avgvalue of ≈1.04 is obtained in the temperature range from 300 to 773 K for n‐type Pb_0.988Sb_0.012Te–13%GeTe–Nano.

    

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3. Flexible Thermoelectric Devices of Ultrahigh Power Factor by Scalable Printing and Interface Engineering

   https://doi.org/10.1002/adfm.201905796  

   Varghese, Tony ; Dun, Chaochao ; Kempf, Nicholas ; Saeidi‐Javash, Mortaza ; Karthik, Chinnathambi ; Richardson, Joseph ; Hollar, Courtney ; Estrada, David ; Zhang, Yanliang ( November 2019 , Advanced Functional Materials)

   Printing is a versatile method to transform semiconducting nanoparticle inks into functional and flexible devices. In particular, thermoelectric nanoparticles are attractive building blocks to fabricate flexible devices for energy harvesting and cooling applications. However, the performance of printed devices are plagued by poor interfacial connections between nanoparticles and resulting low carrier mobility. While many rigid bulk materials have shown a thermoelectric figure of meritZTgreater than unity, it is an exacting challenge to develop flexible materials withZTnear unity. Here, a scalable screen‐printing method to fabricate high‐performance and flexible thermoelectric devices is reported. A tellurium‐based nanosolder approach is employed to bridge the interfaces between the BiSbTe particles during the postprinting sintering process. The printed BiSbTe flexible films demonstrate an ultrahigh room‐temperature power factor of 3 mW m⁻¹K⁻²andZTabout 1, significantly higher than the best reported values for flexible films. A fully printed thermoelectric generator produces a high power density of 18.8 mW cm⁻²achievable with a small temperature gradient of 80 °C. This screen‐printing method, which directly transforms thermoelectric nanoparticles into high‐performance and flexible devices, presents a significant leap to make thermoelectrics a commercially viable technology for a broad range of energy harvesting and cooling applications.

    

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4. Doping and Anisotropy–Dependent Electronic Transport in Chalcogenide Perovskite CaZrSe 3 for High Thermoelectric Efficiency

   https://doi.org/10.1002/adts.201900060  

   Osei‐Agyemang, Eric ; Enninful Adu, Challen ; Balasubramanian, Ganesh ( July 2019 , Advanced Theory and Simulations)

   The potential of an environmentally friendly and emerging chalcogenide perovskite CaZrSe₃for thermoelectric applications is examined. The orthorhombic phase of CaZrSe₃has an optimum band gap (1.35–1.40 eV) for single‐junction photovoltaic applications. The predictions reveal that CaZrSe₃possesses an absorption coefficient of ≈4 × 10⁵cm⁻¹at photon energies of 2.5 eV with an early onset of optical absorption (≈0.2 eV) well below the optimum band gap. Seebeck coefficient,S, is inversely proportional to the carrier mobility as the calculated average effective mass for electrons is higher than for holes;p‐type doping enhances the electrical conductivity, σ. The electronic thermal conductivityκ_eremains low at all temperatures. The upper limit of the thermoelectric figure of merit (ZT_e) attains ≈1.0 when doped at specific chemical potentials, while a high Seebeck coefficient contributes to the ZT_e = 1.95 at 50 K forp‐type doping with 10¹⁸cm⁻³carrier concentration, demonstrating high thermoelectric efficiency.

    

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5. Discovery of multivalley Fermi surface responsible for the high thermoelectric performance in Yb 14 MnSb 11 and Yb 14 MgSb 11

   https://doi.org/10.1126/sciadv.abe9439  

   Perez, Christopher J. ; Wood, Maxwell ; Ricci, Francesco ; Yu, Guodong ; Vo, Trinh ; Bux, Sabah K. ; Hautier, Geoffroy ; Rignanese, Gian-Marco ; Snyder, G. Jeffrey ; Kauzlarich, Susan M. ( January 2021 , Science Advances)

   null (Ed.)

   The Zintl phases, Yb 14 M Sb 11 ( M = Mn, Mg, Al, Zn), are now some of the highest thermoelectric efficiency p-type materials with stability above 873 K. Yb 14 MnSb 11 gained prominence as the first p-type thermoelectric material to double the efficiency of SiGe alloy, the heritage material in radioisotope thermoelectric generators used to power NASA’s deep space exploration. This study investigates the solid solution of Yb 14 Mg 1− x Al x Sb 11 (0 ≤ x ≤ 1), which enables a full mapping of the metal-to-semiconductor transition. Using a combined theoretical and experimental approach, we show that a second, high valley degeneracy ( N v = 8) band is responsible for the groundbreaking performance of Yb 14 M Sb 11 . This multiband understanding of the properties provides insight into other thermoelectric systems (La 3− x Te 4 , SnTe, Ag 9 AlSe 6 , and Eu 9 CdSb 9 ), and the model predicts that an increase in carrier concentration can lead to zT > 1.5 in Yb 14 M Sb 11 systems. 

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