Bulk sodium species 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 bulk copper indium disulfide material from at least the treatment process of the multi-layered structure, the bulk copper indium disulfide material comprising 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 the bulk copper indium disulfide material having a surface region characterized by a copper poor surface comprising a copper to indium atomic ratio of less than about 0.95:1;
• subjecting the copper poor surface and one or more portions of the bulk copper indium disulfide material to sodium 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;
• and
• forming a window layer overlying the copper indium disulfide material;
• and
• whereupon the subjecting of the copper poor surface and the one or more portions of the bulk copper indium disulfide material is performed during at least a thermal treatment process for a time period.