Lattice Strain Leads to High Thermoelectric Performance in Polycrystalline SnSe.

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.

Improved Figure of Merit of Cu2SnSe3 via Band Structure Modification and Energy-Dependent Carrier Scattering.

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.

Thermoelectric performance of nanostructured In/Pb codoped SnTe with band convergence and resonant level prepared via a green and facile hydrothermal method.

SnTe is considered as a promising alternative to the conventional high-performance thermoelectric material PbTe, which inspired the thermoelectric community for a while. Here, we design a green, facile and low-energy-intensity hydrothermal route without involving any toxic or unstable chemicals to fabricate SnTe-based thermoelectric materials. Ultralow lattice thermal conductivity and enhanced thermoelectric performance are achieved via the combination of band engineering and nanostructuring. Enhanced Seebeck coefficient and power factor are induced by converging the band structure and creating resonant levels due to Pb and In doping. More importantly, due to the reduced grain sizes, nanoparticles, and dual-atom point defect scattering, ultralow lattice thermal conductivity was obtained in the bulk samples fabricated by the hydrothermal route. Benefiting from the enhanced power factor and significantly reduced thermal conductivity, the peak ZT is enhanced to ∼0.7 in In/Pb codoped SnTe, a 60% improvement over pure SnTe.