Polycrystalline SnSe materials with ZT values comparable to those of SnSe crystals are greatly desired due to facile processing, machinability, and scale-up application. Here manipulating interatomic force by harnessing lattice strains was proposed for achieving significantly reduced lattice thermal conductivity in polycrystalline SnSe. Large static lattice strain created by lattice dislocations and stacking faults causes an effective shortening in phonon relaxation time, resulting in ultralow lattice thermal conductivity. A combination of band convergence and resonance levels induced by Ga incorporation contribute to a sharp increase of Seebeck coefficient and power factor. These lead to a high thermoelectric performance ZT ∼ 2.2, which is a record high ZT reported so far for solution-processed SnSe polycrystals. Besides the high peak ZT, a high average ZT of 0.72 and outstanding thermoelectric conversion efficiency of 12.4% were achieved by adopting nontoxic element doping, highlighting great potential for power generation application at intermediate temperatures. Engineering lattice strain to achieve ultralow lattice thermal conductivity with the aid of band convergence and resonance levels provides a great opportunity for designing prospective thermoelectrics.

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As an ecofriendly thermoelectric material with intrinsic low thermal conductivity, ternary diamond-like Cu2SnSe3 (CSS) has attracted much attention. Nevertheless, its figure of merit, ZT, is limited by its small thermopower (S) and power factor (PF). Here, we show that an increase in thermopower by 63% and a carrier-mobility rise of 81% at 300 K can be simultaneously achieved through 5% substitution of Fe for Sn due to both enhancement of electronic density of states and degeneracy of multiple valence band maxima, which lead to high PF = 10.3 μW·cm–1·K–2 at 823 K for Fe-doped CSS (CSFS). Besides, an ultrahigh PF of 14.8 μW·cm–1·K–2 (at 773 K) and 45% reduction of lattice thermal conductivity (at 823 K) are realized for CSFS-based composites with 0.125 wt % of MgO nanoinclusions, owing to further enhancement of S via energy-dependent scattering and strong phonon scattering by the embedded nanoparticles. Consequently, a maximum ZT = 1 at 823 K is reached for the CSFS/f MgO composite samples with f = 0.125 wt %, which is around 2.5 times larger than that of the CSS compound.

Here, we report a remarkable high-average figure of merit (ZT) of 0.73 with the peak ZT of 1.9 in bulk polycrystalline tin selenide (SnSe), generating a high energy conversion efficiency of ∼12.5%. The remarkable high thermoelectric performance results from the enhanced electrical transport properties and reduced lattice thermal conductivity through Schottky vacancies and endotaxial nanostructuring. High angle annular dark field scanning transmission electron microscopy identified amounts of Schottky vacancies and endotaxial PbSe nanoprecipitates present in the SnSe matrix. Schottky vacancies and endotaxial PbSe nanostructures contribute to low lattice thermal conductivity by establishing strong phonon scattering centers. Consequently, an extreme low lattice thermal conductivity of 0.23 W m −1 K −1 was achieved at 873 K. Schottky vacancies lead to the increase in carrier concentration, contributing to the enhancement of electrical conductivity and power factor (PF). The maximum PF reached 7.5 μW cm −1 K −2 at 873 K. In addition to the high peak ZT, a high average ZT and outstanding thermoelectric conversion efficiency were realized, which ensured its huge potential in practical application. This work provides a new strategy for enhancing thermoelectric performance and designing prospective highperformance thermoelectric materials.

As an environmentally friendly thermoelectric material with its constituents being free of Pb/Te, tetrahedrite Cu12Sb4S13 absorbs much research interest. However, its low thermoelectric performance inhibits its applications. Here, we show that through dual substitution of Se for S and Zn for Cu in the compound, both the electrical conductivity and the thermopower are enhanced, leading to the elevation of the power factor as high as ∼33% (at 723 K). Analyses indicate that the substitution of Se for S gives rise to changes in stoichiometry of Cu12Sb4S13 through precipitation of impurity phase Cu3SbS4, which causes variations of S vacancies and hole concentrations, while Zn2+ substitution for Cu1+ introduces donors, both of which tune and optimize the carrier concentration. Besides, the lattice thermal conductivity of dual substituted samples is reduced by as low as ∼30% (at 723 K) due to intensified phonon scattering of the impurities (Se and Zn). As a result, a large figure of merit ZT = 0.9 (at 723 K) is achieved in Cu12−yZnySb4S12.8Se0.2 samples with y = 0.025 and 0.05, which is ∼41% higher than that of pristine tetrahedrite Cu12Sb4S13, indicating that dual substitution is an effective approach to improving its thermoelectric performance.