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Tin sulfide (SnS), a typical IV–VI compound with low-cost, abundant-earth and eco-friendly elements, has aroused widespread attentions in the thermoelectric community due to its similar electron and phonon structures with SnSe. However, undoped SnS possesses the features of low carrier concentration and inferior band structures, which produces indecent thermoelectric performance. In this work, we successfully resolved these shortcomings of SnS through stepwise Na doping and Se alloying. Firstly, the carrier concentration of SnS was increased and optimized through Na doping, which leads to an enhancement both in electrical conductivity and Seebeck coefficients through activating multiple valance bands. Secondly, the electronic band structure of SnS was modified through Se alloying, both narrowing band gap and flatting valence band shape contribute excellent electrical transport properties, resulting in maximum power factor ∼6.0 μWcm−1K−2. After synergistically optimizing interdependent thermoelectric parameters through Na doping and Se alloying, a record high ZT of 0.70 at 873 K was obtained in polycrystalline SnS. Our work indicates that SnS is one of very promising earth-abundant thermoelectric materials for power generation in mediate-temperature range. • Power factor of p -type SnS was improved from 2.5 μWcm−1K−2 to 4.8 μWcm−1K−2 at 923 K through Na doping. • Power factor of p -type SnS was improved from 4.8 μWcm−1K−2 to 6.0 μWcm−1K−2 at 873 K through Se alloying. • ZT max of p -type SnS is distinctly enhanced from 0.25 to 0.70 at 873 K after Na doping and Se alloying. [ABSTRACT FROM AUTHOR]

As an earth abundant material, PbS, has been paid extensive attention in the thermoelectric community. The high lattice thermal conductivity of PbS indicates there is room left to further improve thermoelectric performance of PbS. In this system we aimed to reduce the lattice thermal conductivity through nanostructuring grain sizes, which was processed by mechanical alloying followed by spark plasma sintering. We found that the lattice thermal conductivity can be reduced from ∼1.5 W m −1 K −1 at 723 K for PbS ingot to as low as ∼0.50 W m −1 K −1 for the PbS with nano-scale grain sizes, as a result, a ZT value of 0.80 at 723 K was achieved for 1.0% PbCl 2 doped PbS with the second phases of Bi 2 S 3 (Sb 2 S 3 , SrS, CaS). These results indicate that PbS is a robust alternative of PbTe and PbSe for medium temperature thermoelectric applications. [ABSTRACT FROM AUTHOR]