Effect of Ag, Sb and Se co-doping on the thermoelectric performance of SnS

As an inexpensive and non-toxic binary layered compound, SnS shows great potential in thermoelectric applications. In this work, we performed a systematical study on how minute co-doping of Ag, Sb and Se in a mole ratio of 1 : 1 : 2 (namely AgSbSe2) affects thermoelectric transport properties of p-type SnS. It is found that AgSbSe2 has a high solid solution limit (at least 4 mol %) in the matrix, and the band gap of SnS gets reduced upon Ag, Sb and Se co-doping. The strong anharmonic chemical bonding and reinforced point defect scattering synergistically contribute to a low thermal conductivity of similar to 0.88 W m(-1) K-1 at room temperature for the sample Sn0.92Ag0.04Sb0.04S0.92Se0.08. An abnormal decrease of hole concentration in the co-doped SnS is established, which is attributed to the generation of more Sn4+ ions in the lattice. Fine tuning of Ag/Sb ratio might populate more charge carriers and yield higher thermoelectric performance.