The effect of multisubstitution on the thermoelectric properties of chalcogenide-based Cu2.1Zn0.9Sn1−xInxSe4 (0 ≤ x ≤ 0.1)



Quinary chalcogenide compounds Cu2.1Zn0.9Sn1−xInxSe4 (0 ≤ x ≤ 0.1) were prepared by melting (1170 K) followed by annealing (773 K) for 172 h. Powder X-ray diffraction (XRD) data accompanied by electron probe microanalysis (EPMA) and Raman spectra of all the samples confirmed the formation of a tetragonal kesterite structure with Cu2FeSnS4-type. The thermoelectric properties of all the samples were measured as a function of temperature in the range of 300–780 K. The electrical resistivity of all the samples exhibits metallic-like behavior. The positive values of the Seebeck coefficient and the Hall coefficient reveal that holes are the majority charge carriers. The codoping of copper and indium leads to a significant increase of the electrical resistivity and the Seebeck coefficient as a function of temperature above 650 K. The thermal conductivity of all the samples decreases with increasing temperature. Lattice thermal conductivity is not significantly modified as the doping content may infer negligible mass fluctuation scattering for copper/zinc and indium/tin substitution. Even though, the power factors (S2/ρ) of indium-doped samples Cu2.1Zn0.9Sn1−xInxSe4 (x = 0.05, 0.075) are almost the same, the maximum zT = 0.45 at 773 K was obtained for Cu2.1Zn0.9Sn0.925In0.075Se4 due to its smaller value of thermal conductivity.