A combined experimental and modelling approach for the evaluation of the thermoelectric properties of Ag-doped SnS

We report for the first time a systematic, combined computational and experimental study of the impact of Ag doping on the thermoelectric properties of SnS and introduce a fitting procedure to determine parameters that cannot easily be determined experimentally. Pristine and Ag-doped SnS ceramics were prepared by spark plasma sintering (SPS) at 853 K, serving as a reference for theoretical investigation. Ag doping was experimentally found to enhance the power factor and reduced thermal conductivity, improving the maximum thermoelectric figure of merit zT from 0.06 in pristine SnS to 0.22 in 2.78 at% Ag-doped SnS at 800 K. First-principles calculations were employed to establish the effects of Ag doping on the electronic structure, lattice dynamics and thermal conductivity. Electronic-structure calculations show that the holes created by Ag move the Fermi level into the valence band, resulting in a higher valley degeneracy, while lattice-dynamics modelling shows that disruption of the regular bonding network caused by Ag doping results in a substantial drop in the phonon group velocities and lattice thermal conductivity. A fitting procedure was used to determine the temperature-dependent carrier concentration and relaxation time by combining transport calculations with experimental measurements, providing insight into how the sample morphology and doping affect charge transport. This combined experimental and modelling approach provides unprecedented understanding of the effects of Ag doping on the thermoelectric performance of SnS, giving valuable insight into ongoing work on this and related chalcogenide thermoelectrics.