Achieving high Figure of Merit in p-type polycrystalline Sn0.98Se via self-doping and anisotropy-strengthening

In this study, we report a record peak Figure of Merit (ZT) of 1.36 ± 0.12 in polycrystalline Sn0.98Se macro-sized plates, fabricated via a facile solvothermal method. The obtained exceptional thermoelectric performance comes from their high power factor of 6.95 μWcm−1K−2 and ultra-low thermal conductivity of 0.42 Wm−1K−1 at 823 K. Through our Hall measurements, we found the high carrier concentration of 1.5 × 1019 cm−3 derived from the self-doping, which contributes to a high electrical conductivity and a moderate Seebeck coefficient. Moreover, detailed structural characterizations reveal a strong preferred orientation in our sintered Sn0.98Se pellets. The phonon scattering sources such as grain boundaries, synergistically coupled with the anharmonicity boding of Sn0.98Se crystals with a high density of 98.5%, result in an intrinsic ultra-low thermal conductivity. This study provides a new perspective to achieve high thermoelectric performance in polycrystalline SnSe materials.