Role of lone pair electrons in n-type thermoelectric properties of tin oxides **

Oxide materials have shown promising thermoelectric applications due to their availability, tunability, and thermal stability. Among oxide materials, the layered tin oxides (SnO) attract raising attention in the electronic and optoelectronic field owing to their lone pair electrons. We have investigated the thermoelectric properties of layered SnO structures through first-principle calculations. SnO exhibits superior n-type thermoelectric properties and the metallicity of SnO becomes stronger with the number of layers increasing. The lone pair electrons around Sn atoms are the key factor to n-type properties and they will get bonded and anti-bonded in the case of interlayer interaction. Monolayer SnO exhibits the best thermoelectric performances and the average n-type ZT value of monolayer SnO can achieve 0.90 at 500-700 K. Our results demonstrate that layered SnO will be the potential n-type two-dimensional oxide thermoelectric material.