Environmentally friendly p-type CTS-based thin-film thermoelectric generator

Abstract

Cu-based sulphides are promising materials for environmentally friendly Te-free thermoelectric generators (TEGs). Cu2SnS3 (CTS) stands out for its electronic properties, stemming from its conductive Cu–S networks, especially in fully disordered cubic structural form. While wet chemical techniques are the most utilized for CTS synthesis, they introduce organic contaminants that reduce electronic connectivity between grains, limiting their performance as in-plane thin-film TEGs. We present a new method to improve the electronic properties of CTS thin films for thermoelectric applications involving three-step dry route synthesis of ball milling, thermal evaporation, and sulfurization of Cu2–Sn metallic precursors. Via this method, charge carrier concentration increased significantly, as estimated by Hall effect analysis, which was attributed to the Cu-poor stoichiometry, also confirmed via energy-dispersive X-ray spectroscopy (EDXS). Microstructural analysis by scanning electron microscopy (SEM) revealed micrometre-sized grains composed of even smaller crystalline domains, which X-ray diffraction (XRD) showed to be ~ 50 nm in diameter. When compared with literature results, our procedure leads to a fourfold enhancement in the thermoelectric power factor ($$PF={S}^{2} \sigma$$ P F = S 2 σ ), determined through the Seebeck coefficient measurements ($$S$$ S ) and electronic conductivity (σ) estimated by the van der Pauw technique. The CTS TEG has a power volume density of 2.3 μW K−1 cm−3, measured by a custom current–voltage–power (I–V–P) setup with varying load resistance. Results present a 100% increase in performance compared to ink-based techniques and were reproducible across three different batches. This strategy, improving the density of the CTS thin films, offers a new way to enhance Cu-based thin-film TEGs.