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Microwave synthesis of Copper Zinc Tin Sulphide (CZTS) sphere like particles has been demonstrated. The structural and morphological properties of CZTS particles are characterized by XRD, SEM and Raman spectroscopy and subsequently thermoelectric properties are investigated. XRD results of prepared powder sample matches well with tetragonal crystal structure of CZTS bulk. No other impurity phase has been detected from the XRD analysis. Raman spectrum further confirms the formation of single phase CZTS with characteristics peak for CZTS at 334.1 cm-1. SEM studies reveal that the CZTS particles are spherical in shape with uniform sizes of ∼ 250-350 nm. Hot pressed CZTS system shows a power factor ∼21 µW/mK2 and ZT∼ 0.024 at 623 K. Significant enhancement in the Figure of merit for CZTS system is observed in comparison to reported nanostructures of the same system may be due to increased electrical conductivity.

Earth-abundant quaternary chalcogenide semiconductors with complex structures, such as copper zinc tin sulphide (Cu 2 ZnSnS 4 ; CZTS), have the potential to become economic and non-toxic thermoelectric materials. However, the inferior power factor of CZTS, due to its insignificant electrical conductivity, negates the advantage of inherent small thermal conductivity. In the present report, the thermoelectric properties of CZTS composites integrated with graphene nanosheets (GNs) CZTS/x (x = 0.25, 0.5, 0.75 or 1 wt% GNs) were synergistically optimized. The inclusion of GNs (⩽0.75 wt%) simultaneously enhanced the carrier transport (electrical conductivity σ) by providing conductive pathways as well as suppressed lattice thermal conductivity (κ L ) due to the enhanced grain barriers in addition to interface scattering. This synergistic optimization enhanced the figure of merit, ZT, of CZTS/GN nanocomposites to its highest value (∼0.5) at 623 K for the addition of 0.75 wt% GNs, which is nearly a seven-fold enhancement over the pristine sample. The novel strategy of fabricating CZTS/GN nanocomposites by utilizing GNs is an alternative way to obtain the highest thermoelectric performance (ZT ∼ 0.5) in CZTS, and can be extended to other environmentally friendly quaternary chalcogenides.

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