Enhanced Power Factor and Figure of Merit of CuZnSnSe-Based Thermoelectric Composites by Ag Alloying

The quaternary chalcogenide composites CuZnSnAgSe (0 ≤ ≤ 0.075) have been successfully synthesized by high-temperature melting and annealing followed by hot-pressing. The phase structure of the bulk sample has been analyzed by powder X-ray diffraction and Rietveld refinement combined with Raman spectroscopy to confirm CuZnSnSe as the main phase with ZnSe and CuZn secondary phases. The thermoelectric properties of all specimens have been investigated in the temperature range of 300-700 K. The replacement of Sn by Ag significantly enhances the electrical transport properties by providing extra charge carriers. The tremendous reduction in electrical resistivity enhances the power factor, and a maximum power factor of 804 μW K m is achieved at 673 K for the specimen with 5% Ag content. Furthermore, increased point defects increase phonon scattering, resulting in reduced thermal conductivity. The combined effect of improved power factor and suppressed thermal conductivity provides a good boost to the dimensionless figure of merit. The maximum figure of merit of = 0.25 has been achieved at 673 K for CuZnSnAgSe, which is 2.5 times the value of the parent sample.