Rare earth element Ce enables high thermoelectric performance in n-type SnSe polycrystals

SnSe exhibits excellent thermoelectric performance in both n- and p-type single crystals, but its n-type polycrystals are restricted because of the lower electrical conductivity. Here, we dually introduced rare earth element Ce and PbTe to optimize the thermoelectric properties of n-type SnSe polycrystals. It is demonstrated that Ce is an effective cationic dopant to convert SnSe from p- to n-type conductor, and an enhanced peak zT value of ∼0.9 at 823 K was obtained in Sn_0.97Ce_0.03Se due to the improved power factor. Furthermore, PbTe alloying not only reduced the band gap to increase the carrier concentration, but also enhanced the density-of-states effective mass, and hence further increased the power factor in the whole measured temperature range. Meanwhile, the lattice thermal conductivity was significantly reduced owing to the enhanced phonon scattering by the mass and strain fluctuations. As a result, the peak zT value was increased to ∼1.3 for Sn_0.9Pb_0.07Ce_0.03Se_0.93Te_0.07 together with a high average zT value of ∼0.52 in the temperature range of 300 to 823 K.