The binary compound of GeTe emerging as a potential medium-temperature thermoelectric material has drawn a great deal of attention. Here, we achieve ultralow lattice thermal conductivity and high thermoelectric performance in In and a heavy content of Cu codoped GeTe thermoelectrics. In dopants improve the density of state near the surface of Femi of GeTe by introducing resonant levels, producing a sharp increase of the Seebeck coefficient. In and Cu codoping not only optimizes carrier concentration but also substantially increases carrier mobility to a high value of 87 cm 2 V −1 s −1 due to the diminution of Ge vacancies. The enhanced Seebeck coefficient coupled with dramatically enhanced carrier mobility results in significant enhancement of PF in Ge 1.04−x−y In x Cu y Te series. Moreover, we introduce Cu 2 Te nanocrystals' secondary phase into GeTe by alloying a heavy content of Cu. Cu 2 Te nanocrystals and a high density of dislocations cause strong phonon scattering, significantly diminishing lattice thermal conductivity. The lattice thermal conductivity reduced as low as 0.31 W m −1 K −1 at 823 K, which is not only lower than the amorphous limit of GeTe but also competitive with those of thermoelectric materials with strong lattice anharmonicity or complex crystal structures. Consequently, a high ZT of 2.0 was achieved for Ge 0.9 In 0.015 Cu 0.125 Te by decoupling electron and phonon transport of GeTe. This work highlights the importance of phonon engineering in advancing high-performance GeTe thermoelectrics.

SnTe is an emerging Pb‐free thermoelectric compound that has drawn significant attention for clean energy conversion. Chemical doping is routinely used to tailor its charge carrier concentration and electronic band structures. However, the efficacy of dopants is often limited by their small solubility. For example, only 0.5% Ag can be incorporated into the SnTe matrix. Yet, significantly more Ag (>7%) can be dissolved if SnTe is alloyed with AgSbTe2. This large enhancement of solubility can be understood from a chemical bonding perspective. Both SnTe and AgSbTe2 employ metavalent bonding as identified by an unusual bond‐rupture in atom probe tomography. Density functional theory calculations show that upon Ag doping the energy offset of the upmost two valence bands decreases significantly. This induces band alignment in SnTe, which results in an enhanced power factor over a broad temperature range. Moreover, the increased concentration of point defects and associated lattice strain lead to strong phonon scattering and softening, contributing to an extremely low κL of 0.30 Wm−1K−1. These synergistic effects contribute to a peak ZT of 1.8 at 873 K and a record‐high average ZT of ≈1.0 between 400 and 873 K in Sn0.87Mn0.08Sb0.08Te–5%AgSbTe2 alloy.

SnTe is an attractive candidate for applications as a p-type thermoelectric semiconductor. The pristine SnTe compound exhibits poor thermoelectric performance at high temperatures because of its high hole concentration, small band gap, and large energy difference between the light and heavy bands (ΔE(L – Σ)). To overcome these problems, we investigate band structure changes upon the addition of trivalent dopants based on the tight-binding (TB) model and density functional theory (DFT) calculations. We find that tuning the relative on-site energies of the cation and anion s and p orbitals is a potential route for engineering band convergence. Codoping with Ge in addition to trivalent substitutions further enhances thermoelectric performance. We find that a low concentration of the isovalent Ge as well as As, which also acts as a donor (Sn0.952Ge0.016As0.016Te), induces band convergence (ΔE(L – Σ) = 0.12 eV) and enlarges the band gap (0.20 eV). This band convergence results in a remarkable increase of the peak power factor, while the increased band gap energy suppresses detrimental bipolar effects. We find that the theoretical and experimental results are in good agreement here, and the high power factor (high weighted mobility) can be attributed to the increased band convergence. Our work can efficiently screen the promising trivalent substitutions in SnTe-based materials codoped with Ge and find promising candidates for improved thermoelectric performance.

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SnSe is considered as one of the most intriguing new thermoelectric materials. Polycrystalline SnSe offers a wide range of thermoelectric applications for its facile synthesis processing and machinability. Here, we...