A method for chemically cleaning and passivating a chalcogenide layer is provided, wherein the method comprises bringing the chalcogenide layer into contact with an ammonium sulfide containing ambient, such as an ammonium sulfide liquid solution or an ammonium sulfide containing vapor. Further, a method for fabricating photovoltaic cells with a chalcogenide absorber layer is provided, wherein the method comprises: providing a chalcogenide semiconductor layer on a substrate; bringing the chalcogenide semiconductor layer into contact with an ammonium sulfide containing ambient, thereby removing impurities and passivating the chalcogenide semiconductor layer; and afterwards providing a buffer layer on the chalcogenide semiconductor layer.