Enhanced thermoelectric performance of Pb doped Cu₂SnSe₃ synthesized employing spark plasma sintering

We report an enhancement in the thermoelectric performance of Cu₂SnSe₃ alloy on Pb doping, owing to a sharp increase in its power factor. The powder XRD pattern of all samples of Cu₂Sn_1−xPb_xSe₃ (0≤x≤0.03), prepared using solid state reaction, exhibited a cubic structure with a space group of F4̅3m. The results show that temperature dependent electrical resistivity, ρ(T) increases with increasing temperature thereby demonstrating that the samples display heavily doped semiconducting nature, which could be satisfactorily described by small polaron hopping model in the whole temperature range of measurement for all the samples. Both the resistivity and the Seebeck coefficient are reduced with 2 vol% Pb doping. The thermal conductivity of all the samples reduces with increasing temperature. Despite a decrease in Seebeck coefficient the power factor shows an increase on Pb doping, owing to a sharp surge in the electrical conductivity which results in an enhanced ZT_max ~0.64 at 700 K for an optimized composition of Cu₂Sn_0.98Pb_0.02Se₃, which is nearly twice the value of the corresponding undoped counterpart.