Thickness-dependent thermoelectric transporting properties of few-layered SnSe

•The thickness-dependent thermoelectric transporting is studied for few-layered SnSe with thickness from 1 L to 4 L.•The relaxation time and the carrier mobility are derived by extensive calculations using EPW.•As the thickness increases, the carrier mobility increases while the thermal conductivity decreases.•The thermoelectric performance is significantly enhanced as the thickness increases from 1 L to 4 L.•Bulk SnSe of n-type has larger figure of merit along the out-of-plane direction than the in-plane directions.