Chalcogenisation of Cu-Sb metallic precursors into Cu3Sb(SexS1-x)3

Cu₃SbS₃ is a novel chalcogenide semiconductor with p-type conductivity and an energy bandgap of 1.84 eV. By incorporating selenium into this material to form Cu₃Sb(Se_xS_1−x)₃ where x=Se/(Se+S), the energy bandgap can be altered to be in the range 1.38–1.84 eV for 0<x<0.49. The energy bandgap can hence be adjusted to be near the optimum for making the absorber layer for use in single and multi-junction photovoltaic solar cell devices. In this paper these materials were prepared using a two-stage process that involved magnetron sputtering of the Cu–Sb precursor layers followed by conversion to Cu₃SbS₃ by annealing in the presence of elemental sulphur and to Cu₃Sb(S_xSe_1−x)₃ by annealing in the presence of a mixture of sulphur and selenium. The films synthesised were characterised using scanning electron microscopy, energy dispersive x-ray analysis, x-ray diffraction, secondary ion mass spectroscopy and photo-electrochemical measurements. When the Cu₃SbS₃ was formed on glass substrates it had a cubic crystal structure whereas when it was formed on Mo-coated glass it had the monoclinic crystal structure. Likewise the layers of Cu₃Sb(S,Se)₃ formed on Mo-coated glass also had the monoclinic crystal structure. Spectral response curves were recorded over the spectral range 400–1400 nm for semiconductor—electrolyte junctions. Photovoltaic solar cell devices were made using p-type Cu₃Sb(S_xSe_1−x)₃ as the absorber layer and n-type CdS as the buffer layer. The photovoltaic effect was observed in these devices.