Multipoint Defect Synergy Realizing the Excellent Thermoelectric Performance of n-Type Polycrystalline SnSe via Re Doping

SnSe has attracted much attention due to the excellent thermoelectric (TE) properties of both p- and n-type single crystals. However, the TE performance of polycrystalline SnSe is still low, especially in n-type materials, because SnSe is an intrinsic p-type semiconductor. In this work, a three-step doping process is employed on polycrystalline SnSe to make it n-type and enhance its TE properties. It is found that the Sn0.97Re0.03Se0.93Cl0.02 sample achieves a peak ZT value of approximate to 1.5 at 798 K, which is the highest ZT reported, to date, in n-type polycrystalline SnSe. This is attributed to the synergistic effects of a series of point defects: V-Se(..), Cl-Se(.),V-Sn(,,),Re(Sn)x, Re-0. In those defects, the V-Se.. compensates for the intrinsic Sn vacancies in SnSe, the Cl-Se. acts as a donor, the V-Sn(,), acts as an acceptor, all of which contribute to optimizing the carrier concentration. Rhenium (Re) doping surprisingly plays dual-roles, in that it both significantly enhances the electrical transport properties and largely reduces the thermal conductivity by introducing the point defects, Re(Sn)x, Re-0. The method paves the way for obtaining high-performance TE properties in SnSe crystals using multipoint-defect synergy via a step-by-step multielement doping methodology.