As the demand for photovoltaics rapidly increases, there is a pressing need for the identification of new visible light absorbing materials for thin-film solar cells that offer similar performance to the current technologies based on CdTe and Cu(In,Ga)Se 2 . Metal sulphides are the ideal candidate materials, but their band gaps are usually too large to absorb significant fractions of visible light. However, by combining Cu + (low binding energy d 10 band) and Sb 3+ /Bi 3+ (low binding energy s 2 band), the ternary sulphides CuSbS 2 and CuBiS 2 are formed, which have been gathering recent interest for solar cell applications. Using a hybrid density functional theory approach, we calculate the structural and electronic properties of these two materials. Our results highlight the stereochemical activity of the Sb and Bi lone pair electrons, and predict that the formation of hole carriers will occur in the Cu d 10 band and hence will involve oxidation of Cu(I).

Thin films of Cu 3 BiS 3 have been produced by conversion of stacked and co electroplated BiCu metal precursors in the presence of elemental sulfur vapour. The roles of sulfurization temperature and heating rate in achieving singlephase good quality layers have been explored. The potential loss of Bi during the treatments has been investigated, and no appreciable compositional difference was found between films sulfurized at 550 °C for up to 16 hours. The structural, morphological and photoelectrochemical properties of the layers were investigated in order to evaluate the potentials of the compound for application in thin film photovoltaics.