Sodium species surface treatment of thin film photovoltaic cell and manufacturing method

A method for forming a thin film photovoltaic device, the method comprising:

• 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;
• forming an indium layer overlying the copper layer to form a multi-layered structure;
• subjecting at least the multi-layered structure to a thermal treatment process in an environment containing a sulfur bearing species;
• forming a copper indium disulfide material from at least the thermal treatment process of the multi-layered structure, 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, wherein the formed copper indium disulfide is mixed with a copper indium aluminum disulfide or copper indium gallium disulfide;
• removing the thickness of the copper sulfide material to expose a surface region having a copper poor surface comprising a copper to indium atomic ratio of less than about 0.95:1;
• subjecting 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;
• subjecting the copper poor surface to a treatment process during a time period associated with the subjecting of the copper poor surface with the sodium species;
• and
• forming a window layer overlying the copper indium disulfide material.