Effect of vacancy on thermoelectric properties of polycrystalline SnSe

Recently reported unprecedented ZT value of ∼ 2.6 at 915 K for single crystalline SnSe makes this compound as promising candidate for thermoelectric application. The enhancement of thermoelectric conversion efficiency of the polycrystalline form of SnSe is equally essential for commercialization and mass scale production. Herein, we report the effect of cation vacancies on the thermoelectric properties of pure and substituted (5% of Sb and In) compositions. Phase pure compositions with nano-sheet-like stacked morphology have been studied for its crystal structure, electrical conduction, Seebeck coefficient and thermal conduction. Presence of vacancies and localized states confirmed from Urbach energy and shows significant influence on resistivity and Seebeck coefficient. Anisotropy in the crystal structure and presence of defects (point and vacancies) are found to be the major contributors for reduction in the thermal conductivity by 41% and 64% for Sb and In substituted compositions, respectively.