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 ≈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: VSe.., ClSe.,VSn,,,ReSn×, Re 0. In those defects, the VSe.. compensates for the intrinsic Sn vacancies in SnSe, the ClSe. acts as a donor, the VSn,, 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, ReSn×, 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. In this work, point defect engineering is employed for changing the carrier species, enhancing the electrical transport properties, and reducing the thermal conductivity of the SnSe polycrystal. An n‐type Sn0.97Re0.03Se0.93Cl0.02 bulk sample achieves a peak ZT of 1.5 at 798 K, the highest value recorded for an n‐type SnSe polycrystalline sample.