Enhanced thermoelectric properties of n-type sulfide compound Bi2SeS2 by Cl doping

Sulfides composed of an eco-friendly and low-cost composition have received widespread attention as a substitute for traditional thermoelectric materials. However, n-type sulfides with high performance are rare compared with p-type ones. This work revealed that Bi ₂SeS ₂ with n-type conductivity characteristics is a potential thermoelectric material, whose ZT value reaches ∼ 0.70 at 773 K for the Cl doped sample Bi ₂Se _0.98S ₂Cl _0.02. Cl serving as a carrier donor can increase the electrical conductivity by optimizing the carrier concentration. Coupled with a moderate Seebeck coefficient in the range of 100–200 μV/K, a high power factor of ∼6.46 μWcm ⁻¹K ⁻² at 773 K was achieved. In addition, the lattice thermal conductivity reduces because of the formation of precipitates, as well as the induced mass and stress fluctuations due to the doping of heterogeneous Cl element, which effectively suppress the increase in total thermal conductivity. The combination of optimized power factor and low thermal conductivity leads to a final high ZT value, which is relatively higher than or comparable to most other reported n-type sulfide thermoelectric material.