Effect of energy filtering on Cu₂NiSnS₄/CuO composites for thermoelectric applications

Earth-adequate quaternary chalcogenides like Cu₂NiSnS₄ with more complex crystal structures can become non-toxic and cost-effective thermoelectric (TE) materials. TE materials, by employing the energy filtering effect through appropriate energy bandgap, have enhanced their TE efficiency. The composition of CuO in Cu₂NiSnS₄ matrix has enhanced the Seebeck coefficient (S) and declined the thermal conductivity (κ) simultaneously, due to the decrement of carrier concentration (n), by increasing the wt% of CuO in the composites. The highest power factor of 270.88 μW m⁻¹ K⁻² at 573 K is recorded for 30 wt% composites. The 30 wt% composite material thermal conductivity exhibited a low value of 0.442 W m⁻¹ K⁻¹ through stronger phonon scattering at the interface boundaries formed between the Cu₂NiSnS₄ matrix and CuO compositions. A maximum zT of 0.35 for the Cu₂NiSnS₄/30 wt% CuO composite was obtained, 75% larger than that of the Cu₂NiSnS₄ matrix at 573 K. This strategy of introducing metal oxides into the metal sulphide matrix for obtaining efficient TE performance could be extended to other eco-friendly quaternary chalcogenides.