The solar cell, which consists of a CuInS2 thin film prepared by sulfurization of a metallic precursor deposited either on a Pt sheet or a Mo-coated soda lime glass substrate, exhibited an efficiency of 10.5% at air mass 1.5 without antireflection coating. When the latter is used as a substrate, an initially more Cu-rich film was often torn off from the substrate. The film＇s adhesion to it was significantly improved by introducing a very thin Ga layer between the Mo surface and a stacked Cu/In precursor layer. A heterojunction solar cell of the comparable efficiency was obtained using this adherent thin film.