Influence of vacancy defects on the thermoelectric performance of SnSe sheet

Abstract

Native defects are present in materials under various growth conditions. A fundamental understanding of the effect and nature of these defects in the lattice is crucial to optimize its thermoelectric performance. In this paper, we investigate the influence of the vacancy defects on the thermoelectric performance of the SnSe sheet. The results indicate that the process of vacancy formation is endothermic in nature. The calculated electronic structure shows that the band gap in case of sheet containing one Se vacancy decreases whereas the band gap in case of sheet containing a pair of Sn & Se vacancies increases with respect to the pristine sheet. However, in case of the sheet containing one Sn vacancy, the formation of a lone pair state near the valance band maximum results in the disappearance of band gap in the sheet. The calculated relaxation time of charge carriers shows higher values for the pristine sheet as compared to the sheet containing vacancies. The transport calculations show that the introduction of vacancies in the lattice deteriorates the thermoelectric performance of the sheet. • Systematic investigations of influence of vacancies on the thermoelectric properties has been performed. • Introduction of vacancies in the sheet results in dangling states formation in the gap region between VBM and CBM. • The bandgap for sheet containing Se vacancy decreases whereas bandgap for sheet containing a pair of Se & Sn vacancies increases w.r.t. pristine sheet. • In case of Sn vacancy, the bandgap of the sheet is disappeared due to formation of dangling states. • The transport coefficients of the sheet are deteriorated with the introduction of vacancies in the sheet.