Thermoelectric Properties of Pure SnSe Single Crystal Prepared by a Vapor Deposition Method

As a promising eco-friendly high-performance thermoelectric material, SnSe single crystal has attracted much attention during the past several years. In this work, SnSe single crystal is prepared through a novel vapor deposition method in which polycrystalline SnSe is volatilized on a hot side (800–850 °C) and single-crystalline SnSe spontaneously nucleates on the cold side (500–650 °C) based on the inside wall of a quartz ampoule. This crystal growth technique is beneficial for obtaining high-purity SnSe crystal as some metal ions, such as Li⁺, Na⁺, and K⁺, in the quartz ampoule will be restricted from diffusing into the material. SnSe single crystal along the a-axis is measured to experience a Pnma–Cmcm phase transition around 800 K where power factor (PF) exhibits the highest value of 6.2 µW cm⁻¹ K⁻² and total thermal conductivity k_tot shows the lowest value of 0.48 W m⁻¹ K⁻¹. Accordingly, SnSe single crystal reaches a maximum ZT = 0.98 near phase transition temperature. These results not only provide an effective approach for pure SnSe single crystal fabrication, but also reveal the intrinsic electronic and phononic transport properties of thermoelectric SnSe.