Boosting the thermoelectric performance of p-type heavily Cu-doped polycrystalline SnSe via inducing intensive crystal imperfections and defect phonon scattering.

In this study, we, for the first time, report a high Cu solubility of 11.8% in single crystal SnSe microbelts synthesized via a facile solvothermal route. The pellets sintered from these heavily Cu-doped microbelts show a high power factor of 5.57 µW cm-1 K-2 and low thermal conductivity of 0.32 W m-1 K-1 at 823 K, contributing to a high peak ZT of ∼1.41. Through a combination of detailed structural and chemical characterizations, we found that with increasing the Cu doping level, the morphology of the synthesized Sn1-x Cu x Se (x is from 0 to 0.118) transfers from rectangular microplate to microbelt. The high electrical transport performance comes from the obtained Cu+ doped state, and the intensive crystal imperfections such as dislocations, lattice distortions, and strains, play key roles in keeping low thermal conductivity. This study fills in the gaps of the existing knowledge concerning the doping mechanisms of Cu in SnSe systems, and provides a new strategy to achieve high thermoelectric performance in SnSe-based thermoelectric materials.

Polycrystalline SnSe with Extraordinary Thermoelectric Property via Nanoporous Design.

Nanoporous materials possess low thermal conductivities derived from effective phonon scatterings at grain boundaries and interfaces. Thus nanoporous thermoelectric materials have full potential to improve their thermoelectric performance. Here we report a high ZT of 1.7 ± 0.2 at 823 K in p-type nanoporous polycrystalline SnSe fabricated via a facile solvothermal route. We successfully induce indium selenides (InSe y) nanoprecipitates in the as-synthesized SnSe matrix of single-crystal microplates, and the nanopores are achieved via the decompositions of these nanoprecipitates during the sintering process. Through detailed structural and chemical characterizations, it is found that the extralow thermal conductivity of 0.24 W m-1 K-1 caused by the effective phonon blocking and scattering at induced nanopores, interfaces, and grain boundaries and the high power factor of 5.06 µW cm-1 K-2 are derived from a well-tuned hole carrier concentration of 1.34 × 1019 cm-3 via inducing high Sn vacancies by self-doping, contributing to high ZTs. This study fills the gap of achieving nanoporous SnSe and provides an avenue in achieving high-performance thermoelectric properties of materials.

High Thermoelectric Performance in Sintered Octahedron-Shaped Sn(CdIn) xTe1+2 x Microcrystals.

In this study, we fabricate In/Cd codoped octahedron-shape Sn(CdIn) xTe1+2 x microcrystals with a promising thermoelectric performance by using a facile solvothermal method. The high hole-carrier concentration of pristine SnTe is significantly reduced through effective In/Cd codoping, which increases the Seebeck coefficient in a wide temperature range. Moreover, codoped In/Cd not only modifies the band structure by creating the resonance energy level at the valence band and converging light hole and heavy hole valence bands of SnTe but also provides In/Cd-rich nanoprecipitates in the matrix, leading to a high power factor of ∼26.76 µW cm-1 K-2 at 773 K in the sintered SnIn0.03Cd0.03Te1.06. Compared with the bulk counterparts, a much lower lattice thermal conductivity is achieved over a wide temperature range because of strong phonon scattering by point defects, nanoprecipitates, lattice distortion, and grain boundaries in the sintered SnIn xCd xTe1+2 x ( x = 3 and 4%) samples. Consequently, a high ZT of ∼1.12 is obtained at 773 K in the p-type SnIn0.03Cd0.03Te1.06, suggesting that nanoprecipitate-included Cd/In codoped octahedron-shaped Sn(CdIn) xTe1+2 x microcrystals are a convincing candidate for medium-temperature thermoelectric applications.