Pressure-induced enhancement of thermoelectric power factor in pristine and hole-doped SnSe crystals

• Published in: RSC advances 2019-08, Vol.9 (46), p.26831-26837
• Main Authors: Su, Na, Qin, B. C, Zhu, K. J, Liu, Z. Y, Shahi, P, Sun, J. P, Wang, B. S, Sui, Y, Shi, Y. G, Zhao, L. D, Cheng, J.-G
• Format: Article
• Language: English
• Subjects: Band structure of solids; Chemistry; Cylinders; Electrical resistivity; Optimization; Phosphorus; Power factor; Pressure; Seebeck effect; Thermoelectricity; Valence band
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/c9ra05134a

We evaluate the influence of pressure on the thermoelectric power factors PF ≡ S 2 σ of pristine and Na-doped SnSe crystals by measuring their electrical conductivity σ ( T ) and Seebeck coefficient S ( T ) up to ∼22 kbar with a self-clamped piston-cylinder cell. For both cases, σ ( T ) is enhanced while S ( T ) reduced with increasing pressure as expected, but their imbalanced variations lead to a monotonic enhancement of PF under pressure. For pristine SnSe, σ (290 K) increases by ∼4 times from ∼10.1 to 38 S cm −1 , while S (290 K) decreases by only ∼12% from 474 to 415 μV K −1 , leading to about three-fold enhancement of PF from 2.24 to 6.61 μW cm −1 K −2 , which is very close to the optimal value of SnSe above the structural transition at ∼800 K at ambient pressure. In comparison, the PF of Na-doped SnSe at 290 K is enhanced moderately by ∼30% up to 20 kbar. In contrast, the PF of isostructural black phosphorus with a simple band structure was found to decrease under pressure. The comparison with black phosphorus indicates that the multi-valley valence band structure of SnSe is beneficial for the enhancement of PF by retaining a large Seebeck coefficient under pressure. Our results also provide experimental confirmation on the previous theoretical prediction that high pressure can be used to optimize the thermoelectric efficiency of SnSe. The thermoelectric power factor of SnSe is enhanced by three times under a hydrostatic pressure of 22.5 kbar.