NOVELTY - Method (M1) for forming thin film photovoltaic device, comprises: e.g. (a) providing a transparent substrate (110) comprising surface region; (b) forming first electrode layer overlying surface region; (c) forming copper layer (130) overlying first electrode layer; (d) forming indium layer (140) overlying copper layer to form multi-layered structure (150); (e) subjecting the multi-layered structure to thermal treatment process in environment containing sulfur bearing species; and (f) forming bulk copper indium disulfide material from the treatment process of multi-layered structure.    USE - The method is useful for forming a thin film photovoltaic device (claimed), which is useful in solar cells.    ADVANTAGE - The method utilizes: environmental friendly materials that are commercially available and relatively less toxic than other thin-film photovoltaic materials; and prevents any formation of the metal disulfide layer, thus providing high efficiency photovoltaic device, which is free from a parasitic junction on an absorber layer based upon the copper poor chalcopyrite material.    DETAILED DESCRIPTION - Method (M1) for forming a thin film photovoltaic device, comprises: (a) providing a transparent substrate (110) comprising a surface region; (b) forming a first electrode layer overlying the surface region; (c) forming a copper layer (130) overlying the first electrode layer; (d) forming an indium layer (140) overlying the copper layer to form a multi-layered structure (150); (e) subjecting at least the multi-layered structure to a thermal treatment process in an environment containing a sulfur bearing species; (f) forming a bulk copper indium disulfide material from at least the treatment process of the multi-layered structure, where the bulk copper indium disulfide material comprises at least one portion of copper indium disulfide material having a copper-to-indium atomic ratio of less than 0.95:1, and a surface region having a copper poor surface comprising a copper to indium atomic ratio of less than 0.95:1; (g) subjecting the copper poor surface and the portion 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 portion of the bulk copper indium disulfide material from an n-type characteristic to an p-type characteristic; and (h) forming a window layer overlying the copper indium disulfide material, where the subjecting of the copper poor surface and the portions of the bulk copper indium disulfide material is performed during at least a thermal treatment process for a time period. INDEPENDENT CLAIMS are also included for    (1) method (M2) for forming a thin film photovoltaic device, comprising: the steps (a) and (b) as above per se; forming a copper indium material by at least sputtering a target comprising an indium copper material; subjecting the copper indium material to thermal treatment process in an environment containing a sulfur bearing species; forming a copper poor indium disulfide material from at least the thermal treatment process of the copper poor indium material, where the copper indium disulfide material comprises an atomic ratio of copper:indium of less than 0.95:1; compensating the copper poor copper indium disulfide material using a copper species to change from an n-type characteristic to a p-type characteristic; and forming a window layer overlying the copper indium disulfide material; and    (2) forming a thin film photovoltaic device, comprising: the steps (a) and (b) as above per se; forming a chalcopyrite material overlying the electrode layer, where the chalcopyrite material comprises a copper poor copper indium disulfide region, and the copper poor copper indium disulfide region has an atomic ratio of copper:indium of less than or equal to 0.99; compensating the copper poor copper indium disulfide region using a copper species to change in characteristic from an n-type to a p-type; forming a window layer overlying the chalcopyrite material; and forming a second electrode layer overlying the window layer.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic illustration of the method and structure for forming thin film photovoltaic device.    Substrate (110)    Electrode layer (120)    Copper layer (130)    Indium layer (140)    Multilayered structure (150)