A method for forming a thin film photovoltaic device. The method includes providing a transparent substrate comprising a surface region. A first electrode layer is formed overlying the surface region. A copper layer is formed overlying the first electrode layer and an indium layer is formed overlying the copper layer to form a multi-layered structure. The method subject at least the multi-layered structure to a thermal treatment process in an environment containing a sulfur bearing species to form a bulk copper indium disulfide material. The bulk copper indium disulfide material includes one or more portions of copper indium disulfide material characterized by a copper-to-indium atomic ratio of less than about 0.95:1 and 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 and one or more portions of the bulk copper indium disulfide material to copper species to convert the copper poor surface from an n-type characteristic to a p-type characteristic and to convert any of the one or more portions of the bulk copper indium disulfide material having the copper-to-indium atomic ratio of less than about 0.95:1 from a p-type characteristic to an n-type characteristic. A window layer is formed overlying the copper indium disulfide material.