Enhanced thermoelectric performance of polycrystalline SnSe by doping with the heavy rare earth element Yb

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As an environmentally friendly thermoelectric material, SnSe has attracted great attention because of its excellent performance in its single-crystal form. On the other hand, the better mechanical property and lower manufacturing cost of its polycrystalline counterpart with the better mechanical property and lower manufacturing cost can serve as a better candidate for widespread applications. Previous reports on p-type polycrystalline SnSe mainly focus on optimizing the carrier concentration by doping alkali metals or decreasing the lattice thermal conductivity by nanostructuring. Here, we report the effect of Yb doping on the thermoelectric properties of polycrystalline SnSe prepared by solvothermal synthesis. Through introducing Yb, the p-type carrier concentration is increased and the density of states at valence band maximum is distorted, which is revealed by DFT calculation, leading to an increase of the effective mass. Thus, the power factor has been markedly enhanced to 0.78 mW m−1 K−2 at 823 K (about 1.6 times that of undoped SnSe). Moreover, Yb doping in SnSe decreases the lattice thermal conductivity by intensifying the phonon scattering. As a result, a high zT of 1.1 at 823 K in Sn0.98Yb0.02Se is achieved along the in-plane direction. This work provides a new way for improving the thermoelectric properties of SnSe by modifying its valence band structure.