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A recent discovery of high-performance Mg3Sb2 has ignited tremendous research activities in searching for novel Zintl-phase compounds as promising thermoelectric materials. Herein, a series of planar Zintl-phase XCuSb (X = Ca, Sr, Ba) thermoelectric materials are developed by vacuum induction melting. All these compounds exhibit high carrier mobilities and intrinsic low lattice thermal conductivities (below 1 W·m−1·K−1 at 1010 K), resulting in peak p-type zT values of 0.14, 0.30, and 0.48 for CaCuSb, SrCuSb, and BaCuSb, respectively. By using BaCuSb as a prototypical example, the origins of low lattice thermal conductivity are attributed to the strong interlayer vibrational anharmonicity of Cu—Sb honeycomb sublattice. Moreover, the first-principles calculations reveal that n-type BaCuSb can achieve superior thermoelectric performance with the peak zT beyond 1.1 because of larger conducting band degeneracy. This work sheds light on the high-temperature thermoelectric potential of planar Zintl compounds, thereby stimulating intense interest in the investigation of this unexplored material family for higher zT values.

the dimensionless figure of merit zT = PF•T/κ = α 2 σT/(κ e + κ L ), where α, σ, T, κ e , and κ L are the Seebeck coefficient, electrical conductivity, absolute temperature, and electronic and lattice contributions to the total thermal conductivity, respectively. [3] PF denotes the TE power factor that characterizes electrical transport performance. In practice, the average power factor (PF avg ) is directly proportional to the output power density of TE devices. [4] Therefore, for practical application, a higher PF avg is more desirable for achieving a large output power. In principle, PF and PF avg are both determined by electronic band structure and optimal carrier concentration. [5][6][7] Several strategies have been proposed to enhance both PF and PF avg . For example, Pei et al. [8] showed that a high peak PF can be achieved in PbTe by increasing the band degeneracy; Zhu et al. [9] demonstrated that FeNb 1−x Ti x Sb reaches high PF via reducing band effective mass, which results in high carrier mobility. In recent years, it has been elucidated that grain boundaries also play an important role in carrier scattering for certain TE compounds. For instance, Zhao et al. [10,11] revealed that both p and n-type SnSe single crystals that are free of grain boundaries exhibit high PFs; Snyder et al. [12,13] discovered that PF of Mg 3 Sb 2 -based Thermoelectric materials are typically highly degenerate semiconductors, which require high carrier concentration. However, the efficiency of conventional doping by replacing host atoms with alien ones is restricted by solubility limit, and, more unfavorably, such a doping method is likely to cause strong charge-carrier scattering at ambient temperature, leading to deteriorated electrical performance. Here, an unconventional doping strategy is proposed, where a small trace of alien atoms is used to stabilize cation vacancies in Cu 3 SbSe 4 by compositing with CuAlSe 2 , in which the cation vacancies rather than the alien atoms provide a high density of holes. Consequently, the hole concentration enlarges by six times but the carrier mobility is well maintained. As a result, a record-high average power factor of 19 µW cm −1 K −2 in the temperature range of 300-723 K is attained. Finally, with further reduced lattice thermal conductivity, a peak zT value of 1.4 and a record-high average zT value of 0.72 are achieved within the diamond-like compounds. This new doping strategy not only can be applied for boosting the average power factor for thermoelectrics, but more generally can be used to maintain carrier mobility for a variety of semiconductors that need high carrier concentration.

Cu2SnS3 (CTS), a typical ternary copper-based sulfide, is considered as a potential p-type thermoelectric (TE) material with the advantages of environmental friendliness and low cost, but its performance is limited by the high lattice thermal conductivity and electrical resistivity. Herein, we have successfully synthesized undoped and In-doped CTS nanoparticles with a pure tetragonal phase by the colloidal method. More interestingly, plenty of twin boundaries appear in all the samples sintered from the synthesized nanoparticles independent of composition. The twin boundaries can effectively reduce the lattice thermal conductivity, while the tetragonal phase is beneficial to meliorate the electrical performance of CTS. Consequently, the highest zT reaches 0.36 at 700 K for Cu2Sn0.85In0.15S3, which is enhanced by 17 times compared to that of the pristine CTS with mainly the monoclinic phase. The tunable phase and microstructure via the colloidal method provide useful guidance to promote the performance of eco-friendly TE sulfides.

Quasi‐2D semiconductors have garnered immense research interest for next‐generation electronics and thermoelectrics due to their unique structural, mechanical, and transport properties. However, most quasi‐2D semiconductors experimentally synthesized so far have relatively low carrier mobility, preventing the achievement of exceptional power output. To break through this obstacle, a route is proposed based on the crystal symmetry arguments to facilitate the charge transport of quasi‐2D semiconductors, in which the horizontal mirror symmetry is found to vanish the electron–phonon coupling strength mediated by phonons with purely out‐of‐plane vibrational vectors. This is demonstrated in ZrBeSi‐type quasi‐2D systems, where the representative sample Ba1.01AgSb shows a high room‐temperature hole mobility of 344 cm2 V−1 S−1, a record value among quasi‐2D polycrystalline thermoelectrics. Accompanied by intrinsically low thermal conductivity, an excellent p‐type zT of ≈1.3 is reached at 1012 K, which is the highest value in ZrBeSi‐type compounds. This work uncovers the relation between electron–phonon coupling and crystal symmetry in quasi‐2D systems, which broadens the horizon to develop high mobility semiconductors for electronic and energy conversion applications.