High Thermoelectric Performance in Polycrystalline SnSe Via Dual‐Doping with Ag/Na and Nanostructuring With Ag₈SnSe₆

Abstract

Single crystalline SnSe is one of the most intriguing new thermoelectric materials but the thermoelectric performance of polycrystalline SnSe seems to lag significantly compared to that of a single crystal. Here an effective strategy for enhancing the thermoelectric performance of p‐type polycrystalline SnSe by Ag/Na dual‐doping and Ag8SnSe6 (STSe) nanoprecipitates is reported. The Ag/Na dual‐doping leads to a two orders of magnitude increase in carrier concentration and a convergence of valence bands (VBM1 and VBM5), which in turn results in sharp enhancement of electrical conductivities and high Seebeck coefficients in the Ag/Na dual‐doped samples. Additionally, the SnSe matrix becomes nanostructured with dispersed nanoprecipitates of the compound Ag8SnSe6, which further strengthens the scattering of phonons. Specifically, ≈20% reduction in the already ultralow lattice thermal conductivity is realized for the Sn0.99Na0.01Se–STSe sample at 773 K compared to the thermal conductivity of pure SnSe. Consequently, a peak thermoelectric figure of merit ZT of 1.33 at 773 K with a high average ZT (ZTave) value of 0.91 (423–823 K) is achieved for the Sn0.99Na0.01Se–STSe sample.

Boosted carrier mobility and enhanced thermoelectric properties of polycrystalline Na0.03Sn0.97Se by liquid-phase hot deformation

“…Since the PFs were limited at a higher temperature, such a peak ZT was not very competitive compared with those inrevious reports. 19,20,36,44 However, compared with the results of normal LPS or HD methods, a higher averaged ZT value (ZT ave ) was achieved using the LPHD technique as summarized in Fig. 6b.…”

“…The excellent TE performance could be realized by increasing the power factor (PF = a 2 s) or compressing the thermal conductivity as much as possible. [6][7][8] Usually, several strategies such as resonant doping, 9,10 band convergence [11][12][13] and carrier concentration optimization 14,15 can effectively increase the power factor, while the lattice thermal conductivity k l can be reduced by the all-scale hierarchical structuring [16][17][18][19] and dense defects [20][21][22][23] as phonon scattering centers.…”

Enhancing power factor of SnSe sheet with grain boundary by doping germanium or silicon

“…However, the high cost of synthesizing SnSe single crystal and its poor mechanical properties impede the practical applications of this material. Therefore, many studies have been carried out for studying the thermoelectric performance of 3D polycrystalline SnSe [3][4][5][6][7][8][9] and 2D SnSe 10 . It has been found that the ZT value of polycrystalline SnSe is dramatically reduced as compared to that of single-crystal SnSe because of the existence of grain boundaries (GBs) in polycrystalline structures, which can reduce the electrical conductivity.…”

“…To improve the performance, chemical doping has been used. Previous studies have shown that alkali elements [3][4][5] , halogens 6,7 , and Ag 8,9 are the promising dopants for increasing the ZT value of 3D polycrystalline SnSe. For instance, the ZT value of K-doped polycrystalline SnSe is 1.1 at 773 K 5 , which is more than twice the original value of pure polycrystalline SnSe (0.5) at 823 K 12 , but still much less than that (2.6-2.8) of its single crystal counterpart.…”

All-scale Architecturing of Microstructure in Chalcogenide Thermoelectric Materials

“…The introduction of nano-size precipitate significantly depresses the lattice thermal conductivity. As a result, an enhanced ZT of ~1.3 is obtained [3].…”