Despite the significant advances in bulk thermoelectric systems,the most leading thermoelectric material,such as Bi2Te3,PbTe,and SiGe mainly consist of expensive elements such as Te and Ge,or toxic elements such as Pb.Due to the non-toxic,inexpensive,and ultrahigh abundance of sulfur(S),sulfur-based thermoelectric materials have drawn some attentions and their ZT values larger than unit have recently been achieved,especially in the p-type.Historically,the thermoelectric performance of n-type lead-free S-based materials is not more than 0.7 at 773 K,which needs to be improved so to pair up with the p-type to make modules more efficient.In this paper,we reported two kinds of thermoelectric materials,including Bi2S3 and CoSbS.For Bi2S3 thermoelectric materials,the high electrical resistivity leads to a low ZT value.In this work,incorporating small amounts of CuBr2 into Bi2S3 system prepared by melting and spark plasma sintering can remarkably enhance the thermoelectric performance.Cu intercalation and Br substitution at sulfur sites contribute to a sharp decrease of electrical resistivity.Simultaneously,the strong point defects caused by Br alloying and formed Cu nanoparticles noticeably suppress the thermal conductivity.Collectively,the maximum ZT of 0.72 at 773K is obtained for the 0.5mol%CuBr2 doped sample parallel to the press direction,which is the highest ZT value ever reported for Bi2S3 system,even comparable to the PbS-based thermoelectric materials.The mechanism on the effect of Cu nanoparticles on the lattice thermal conductivity of Bi2S3 is also clarified.The effect of Ni doping on both electron and phonon transport properties of nanostructured CoSbS was investigated in this study.We found a more than 2 times increase on figure-of-merit(ZT).The noticeable enhancement is mainly attributed to the optimized carrier concentration,high effective mass and strong electron-phonon scattering upon Ni doping.A ZT of 0.5 was achieved at 873 K together with a power factor of 20 μW cm-1 K-2 for the Ni doped CoSbS samples.The reduced lattice thermal conductivity via the strong electron-phonon scattering for Ni doped CoSbS samples is confirmed by the quantitative calculation of the various phonon scattering mechanisms according to the Callaway model.