Realizing high thermoelectric performance in n-type SnSe polycrystals via (Pb, Br) co-doping and multi-nanoprecipitates synergy

Both p- and n-type SnSe single crystals have been reported to possess high thermoelectric performances, thus highlighting the possibility for commercialization. Polycrystalline SnSe that has better mechanical properties however possesses inferior thermoelectric properties compared to single crystal SnSe. In this work, n-type polycrystalline SnSe_0.95 + x wt% PbBr₂ (x = 0, 0.5, 1, and 1.5) samples were synthesized by combining mechanical alloying and spark plasma sintering technology. The effects of PbBr₂ doping on thermoelectric performance of SnSe were studied in detail. The results show that the carrier concentration was dramatically increased from 2.51 × 10¹⁷ cm⁻³ in pure SnSe_0.95 to 1.79 × 10¹⁹ cm⁻³ in SnSe_0.95 + 1.5 wt% PbBr₂, further resulting in an enhanced electrical conductivity. Multi-nanoprecipitates are present in the samples, including SnO, SnPb and SnBr_xO_y, which possibly affect the Seebeck coefficient and the lattice thermal conductivity. A peak ZT value of 1.1 was obtained at 773 K for the SnSe_0.95 + 1.0 wt% PbBr₂ sample. This work highlights that PbBr₂ is an effective dopant to improve the TE performance of n-type polycrystalline SnSe.