Realization of High Thermoelectric Performance in Polycrystalline Tin Selenide through Schottky Vacancies and Endotaxial Nanostructuring

Abstract

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.

The Importance of Surface Adsorbates in Solution‐Processed Thermoelectric Materials: The Case of SnSe

“…[16][17][18] Alternatively, surfactants can be exchanged with volatile compounds [19] or even inorganic species [20] that can further tune material properties. [12,18,21] Conversely, the presence of surface adsorbates is usually neglected in the case of the so-called surfactant-free methods, [4,[22][23][24][25][26][27][28][29][30][31][32][33][34] the most widely used to produce thermoelectric powders in solution. The vast majority of reports dealing with surfactant-free synthesis do not perform any surface treatments since the particles are considered "naked".…”

Lattice Strain Leads to High Thermoelectric Performance in Polycrystalline SnSe

“…Ag-doped (SnSe) 1– x (SnS) x polycrystals showed impressive low thermal conductivity as well as a high peak ZT of 1.67 due to nanoscale point defect scattering . Although polycrystalline SnSe has been promoted through the above-mentioned strategies, the majority of existing high- ZT polycrystalline SnSe involves less eco-friendly elements, either Pb ,,, or Cd. , Furthermore, these materials still show relatively low average ZT values. To fully realize their potential, thermoelectric materials must work over the entire, several-hundred Kelvin operating range .…”

“…Electronically, Pisarenko plots demonstrate the negative correlation between carrier concentration and thermopower . The optimization of carrier concentrations leads to a significantly reduced Seebeck coefficient of the doped polycrystalline SnSe system, which greatly limits the ability for further optimizing electrical transport properties and ZT value . Furthermore, polycrystalline SnSe still shows low average ZT values due to a low PF at relatively low temperature.…”

“…13 The optimization of carrier concentrations leads to a significantly reduced Seebeck coefficient of the doped polycrystalline SnSe system, which greatly limits the ability for further optimizing electrical transport properties and ZT value. 46 Furthermore, polycrystalline SnSe still shows low average ZT values due to a low PF at relatively low temperature. Creating resonant levels inside the valence band can improve the Seebeck coefficient and PF over the low temperature range.…”

Bottom-Up Engineering Strategies for High-Performance Thermoelectric Materials

“…For semiconductor thermoelectric materials, the introduction of small quantities of impurity (element doping) during the bottom-up preparation can not only tailor the carrier concentration and/or mobility to optimize the σ, but also induce point defects (vacancies or self-interstitials) and adjust the microstructures (e.g., phase separation, formation of nanoscaled precipitates or ultra-fine grains) to reduce the κ L [211][212][213][214][215][216][217][218][219][220]. Although the carrier concentration in a material can be modulated using defect-engineering, or stoichiometry control during synthesis, reaching the optimized carrier concentration (typically 10 19 cm −3 ) often require additional extrinsic doping.…”