Fabrication of High Quality Bornite and Chalcopyrite Thin Films by Aerosol Assisted Chemical Vapour Deposition

Recently, several transition metal chalcogenide materials with favourable optical and electrical properties suitable for sustainable solar-based energy generation have been identified. In this work, thin films of two promising ternary sulphides (bornite and chalcopyrite) in the Cu-Fe-S system were successfully synthesised as thin films from utilising iron(III) tris-N,N-diethyldithiocarbamate and copper(II) bis-N,N-diethyldithiocarbamate molecular precursors in aerosol-assisted chemical vapour deposition at 450 C for an hour. The deposited thin films were studied by powder X-ray diffraction and the resulting patterns indexed to orthorhombic and tetragonal copper iron sulfide (bornite, Cu5FeS4 and chalcopyrite, CuFeS2). The morphology of the films at the microscale was explored by scanning electron microscopy revealing a polycrystalline thin film, with elemental ratios (i.e., Cu:Fe:S) of the two materials corresponding to that expected for bornite (≈5:1:4) and chalcopyrite (≈1:1:2), consistent with the X-ray structural characterisation. Characterisation of the electrical transport properties of these high-quality thin films by the four-point probe method was performed. The results revealed resistivity of 1.8 × 10-4 Ω-m for bornite and 1.6 × 10-2 Ω-m for chalcopyrite, which is consistent with previously reported values for the bulk materials. Estimation of optical energy band gap from Tauc plots of the ultraviolet visible spectroscopy data was taken for bornite and chalcopyrite giving direct band gap energies of at 1.28 eV and 0.97 / 1.62 eV respectively, demonstrating their potential utility as either solar absorbing thin films or for photocatalysts for water splitting.