Sn vacancy engineering for enhancing the thermoelectric performance of two-dimensional SnS

Abstract

The carrier type and concentration of a semiconductor are intimately associated with the kind and density of point defects possessed within itself. And two-dimensional SnS intrinsically exhibits a p-type semiconductor behavior, which is correlated with Sn vacancies. Here, we present tuning the hole concentration of SnS in a wide range of 10¹⁶–10¹⁹ cm⁻³ through a cationic lattice site vacancy engineering strategy, by simply changing the molar ratio of raw materials, i.e., SnCl₂versus Na₂S·9H₂O. The thermoelectric properties of these Sn vacancy engineered SnS samples were investigated. Combining the significantly improved power factor due to the increased hole concentration with an intrinsically low lattice thermal conductivity arising from lattice anharmonicity, a respectable zT value up to 0.8 at 873 K could be achieved in polycrystalline SnS. This work demonstrates that low-cost and easily fabricated SnS is a promising candidate for thermoelectric application, despite it usually being considered as a low-asymmetrical crystal with a relatively large band gap (∼1.1 eV).