Cu(In,Ga)Se-2-based solar cells buffered with indium sulfide grown by numerous techniques have reached efficiencies comparable to those achieved by standard devices buffered with (CBD)CdS. The present paper firstly recalls some of the properties of the indium sulfide single crystal and Points Out the disagreements concerning the thin films properties inventoried in the literature. Secondly, the influence of the presence of some "foreign elements" within file indium sulfide on its properties is presented. It is shown that these "foreign elements", even at low concentration levels, are possibly at the origin or the thin films properties deviations compared to the single crystal. The impact of these contaminants on the solar cells performance is finally discussed.