Realizing High Thermoelectric Performance in Polycrystalline SnSe via Silver Doping and Germanium Alloying

It has been reported that SnSe crystals possess outstanding thermoelectric property, while polycrystals are inferior on account of the poor electrical transport properties. Therefore, we try to improve the disadvantage of polycrystalline SnSe via synergistic Ag doping and Ge alloying. First, the carrier concentration of SnSe is enhanced by Ag doping, resulting in a maximum carrier concentration ∼1.0 × 10¹⁹ cm^-3. Second, the Seebeck coefficient is increased by Ge alloying through enlarging the band effective mass and narrowing the band gap, resulting in a highest power factor of ∼10.0 μW cm^-1 K^-2 at 793 K. In addition, Ge alloying contributes greatly to reducing the lattice thermal conductivity through scattering phonons induced by the point defects. Above all, a maximum ZT value of ∼1.5 at 793 K is obtained for the Sn_0.975Ag_0.01Ge_0.015Se sample with the simultaneously optimized thermoelectric transport parameters.