A method for forming a thin film photovoltaic device. The method includes providing a transparent substrate comprising a surface region, forming a first electrode layer overlying the surface region, forming a copper layer overlying the first electrode layer and forming an indium layer overlying the copper layer to form a multi-layered structure. The multi-layered structure is subjected to a thermal treatment process in an environment containing a sulfur bearing species to forming a copper indium disulfide material. The copper indium disulfide material comprising a copper-to-indium atomic ratio ranging from about 1.2:1 to about 2:1 and a thickness of substantially copper sulfide material having a copper sulfide surface region. The thickness of the copper sulfide material is selectively removed to expose a surface region having a copper poor surface comprising a copper to indium atomic ratio of less than about 0.95:1. The method subjects the copper poor surface to a sodium species to convert the copper poor surface from an n-type semiconductor characteristic to a p-type semiconductor characteristic. A window layer is formed overlying the copper indium disulfide material.