Enhanced Power Factor and Figure of Merit of Cu₂ZnSnSe₄-Based Thermoelectric Composites by Ag Alloying

Abstract

The quaternary chalcogenide composites Cu 2 ZnSn 1−x Ag x Se 4 (0 ≤ x ≤ 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 Cu 2 ZnSnSe 4 as the main phase with ZnSe and Cu 5 Zn 8 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 −2 m −1 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 zT = 0.25 has been achieved at 673 K for Cu 2 ZnSn 0.95 Ag 0.05 Se 4 , which is 2.5 times the value of the parent sample.

Effect of annealing temperature on microstructure and thermoelectric transport properties of Cu2.1Zn0.9SnSe4 alloys

“…The electrical resistivity of 600 °C sample exhibits semi-metallic behavior in the first half and metallic behavior in the second half as the values of electrical resistivity decrease with increasing temperature up to 473 K and then increase sharply with the rising temperature which probably be resulted from ionized impurity scattering; meanwhile the values of electrical resistivity of other samples show slight increase with the increasing temperature exhibiting degenerate semiconducting behavior [25]. Temperature dependence of electrical resistivity of 600 °C sample is different from other samples but is consistent with previous reports [8,9,19]. Furthermore, the electrical resistivity of the samples decreases with the increasing annealing temperature.…”

“…The Lorentz fit of Raman spectroscopy, shown in Fig. 2, depicts the major peak located at 181 cm -1 which is allocated to CZTSe main phase [4,19] and ZnSe secondary phase peaks located at 205 cm -1 at 252 cm -1 [20]. Furthermore, the presence of CuSe secondary phase present in XRD results is not detected in Raman Spectra, as a strong peak located at around 262 cm -1 associated with CuSe is not present in our Raman spectra [21][22][23], which may be due to the low concentration of CuSe phase.…”

Towards Low Cost and Sustainable Thin Film Thermoelectric Devices Based on Quaternary Chalcogenides

“…[55] A few studies on the TE performance of kesterites in bulk form revealed improved properties when cation disorder is introduced, [56][57][58][59] and with Cu-doping, [60][61][62] especially for the selenide compound. [61,[63][64][65][66] In particular, they have been deemed promising materials for their exceptional TE performance over cost ratio, [60] thus making them particularly interesting for sustainable and low cost generation. Surprisingly, it emerges a substantial scarcity of TE investigation for the thin film configuration of these materials, [67,68] despite the vast knowledge acquired in their fabrication and PV characterization.…”

Superior thermoelectric properties of ternary chalcogenides CsAg5Q3 (Q = Te, Se) predicted using first-principles calculations

“…This can be achieved by tailoring new TEMs using various strategies such as band engineering, 8,9 nanostructuring, 10–12 and alloying or substituting. 13–18…”