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Ultrahigh average ZT realized in p-type SnSe crystalline thermoelectrics through producing extrinsic vacancies.

Crystalline SnSe has been revealed as an efficient thermoelectric candidate with outstanding performance. Herein, record-high performance can be realized in p-type SnSe crystals through simply introducing small amount of SnSe2, as a kind of extrinsic defect dopant. This excellent performance mainly arises from the largely enhanced power factor by increasing the hole carrier concentration from ~ 4.0 × 1019 to ~ 6.55 × 1019 cm-3, which was surprisingly promoted by introducing extrinsic SnSe2 even though pristine SnSe2 is n-type conductor. The optimized carrier concentration promotes Fermi level deeper and activates more valence bands, leading to an extremely-high power factor ~ 54 μWcm-1K-2 at 300 K through enlarging band effective mass and Seebeck coefficient. Along with the greatly decreased thermal conductivity due to phonon scattering by Sn vacancies and SnSe2 microdomains, maximum ZT values ~ 0.9 to 2.2 at 300 - 773 K and record-high average ZT > 1.7 are achieved in Na doped SnSe crystals with 2% extrinsic SnSe2. This work provides a new strategy for optimizing thermoelectric performance through introducing defect dopants, which might be well implemented in other thermoelectric systems.