Improving the thermoelectric performance of the SnS monolayer by Na doping: A theoretical study

Aiming at exploring new thermoelectric (TE) materials of high performance, we theoretically calculate the TE transport properties including the Seebeck coefficient, electrical conductance, thermal conductance, power factor, and figure of merit $ZT$ of the SnS monolayer. Different from the heavy-metal doping, the economical and environment-friendly Na doping is adopted to improve the $ZT$ of the monolayer SnS. It is shown that the Na doping can increase the maximum $ZT$ along the armchair and zigzag directions, respectively, and the highest $ZT$ peak is moved to the proximity of chemical potential $\mu =0\mathrm{eV}$, which indicates that the corresponding TE device can work at a low bias voltage. As the temperature increases from 300 K to 800 K, the maximum $ZT$ of the pristine SnS monolayer is increased from 0.89 to 2.26 (from 1.33 to 2.89) along the armchair (zigzag) direction, and the maximum $ZT$ of the Na-doped one is increased from 1.24 to 2.45 (from 1.44 to 2.86) along the armchair (zigzag) direction. This implies that the Na-doped SnS monolayer can be utilized to design promising TE devices working in a broad temperature scope and at a lower bias voltage.