NOVELTY - The method involves forming a bulk copper indium disulfide material/thin film (220) from a multi-layered structure. A copper poor surface and portions of the bulk copper indium disulfide material/thin film are subjected to chloride species i.e. chloride ions. The copper poor surface is converted from n-type characteristic to p-type characteristic. The portions of the bulk copper indium disulfide material/thin film are converted from the n-type characteristic to the p-type characteristic. A window layer overlying the bulk copper indium disulfide material/thin film is formed.    USE - Method for forming a thin film photovoltaic device i.e. thin film photovoltaic cell, for a high efficiency photovoltaic application i.e. solar cell application. Can also be used for forming semiconducting thin films and multilayers comprising iron sulfide, cadmium sulfide, zinc selenide and metal oxides such as zinc oxide, iron oxide and copper oxide.    ADVANTAGE - The method enables forming a conductive layer overlying a portion of a surface region of the window layer, where the conductive layer is transparent conductive oxide (TCO) and functions as the window layer, thus maximizing fill factor and conversion efficiency of the photovoltaic device and eliminating a separate window layer. The method enables maintaining an interface region between an electrode layer and the copper indium disulfide material/thin film free from a metal disulfide layer having different semiconductor characteristics from the copper indium disulfide material/thin film, thus preventing any formation of the metal disulfide layer.    DETAILED DESCRIPTION - The subjecting of the chloride species is provided by a process e.g. spin coating, spraying, spray pyrolysis, pyrolysis, dipping, deposition, sputtering and electrolysis. An INDEPENDENT CLAIM is also included for a thin film photovoltaic device comprising a substrate.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a structure for forming a thin film photovoltaic device.    Substrate (110)    Electrode layer (120)    Thermal treatment process (200)    Sulfur bearing species (210)    Bulk copper indium disulfide material/thin film (220)    Cap layer (221)    Surface region (225)