Enhanced Thermoelectric Performance in Li Doped SnS via Carrier Concentration Optimization

Tin sulfide (SnS) has attracted increasing attentions due to its similar band structure and crystal structure to tin selenide (SnSe). The layered structure and strong anharmonicity of these materials result in an ultralow lattice thermal conductivity, which is advantageous for the thermoelectric performance. Further enhancement in thermoelectric properties is expected to improve the carrier concentration and power factor by band structure optimization. In this work, lithium (Li) is proved to be an efficient dopant for SnS and the carrier concentration is increased to 1.3 × 1018 cm-3 at room temperature for Sn0.98Li0.02S. Calculations show that Li doping flattens the edge of the valence band and increases the number of carrier pockets in SnS, which collectively enhance the electronic transport properties. Moreover, the phonon scattering was enhanced by the nano-precipitates and increased boundaries in Sn1-xLixS, resulting in 40% reduction in thermal conductivity at room temperature. Combined with the enhanced power factor (∼3 μW cm-1 K-2 at 848 K) and low thermal conductivity (0.36 W m-1 K-1 at 848 K), the maximum ZT of 0.66 is achieved in Sn1-xLixS bulk samples at 848 K.