A molecular precursor route to quaternary chalcogenide CFTS (Cu₂FeSnS₄) powders as potential solar absorber materials

In the present work we report on the synthesis of tetragonal stannite Cu₂FeSnS₄ powders using a solvent free melt method using a mixture of Cu, Fe, and Sn(ii)/Sn(iv) O-ethylxanthates heated at different temperatures. The as-synthesized powders were characterized by powder X-ray diffraction (p-XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-Vis absorption spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy, which confirm the successful synthesis of stannite CFTS. Optical measurements show that Cu₂FeSnS₄ powders have visible light absorption onsets in the far red with direct band gap energies in the range 1.32-1.39 eV which are suitable for acting as efficient absorber layers in solar cells. Electronic characterisation of these materials deposited as thin films by spin coating show that they are p type semiconductors with respectable carrier mobilities of ca. 60 cm² V^-1 s^-1 with carrier densities on the order of 10¹⁴ cm^-1.