NOVELTY - Method (I) for producing a film of compound material, comprises: providing a substrate (310); depositing a film on substrate, where the deposited film has a first chemical composition comprising at least one first chemical element and at least one second chemical element; and inducing at least one residual chemical reaction in deposited film using a source containing at least one second chemical element to increase content of the second chemical element in deposited film so that deposited film has a second chemical composition.    USE - The method is useful in producing a thin film, which is useful for producing thin film solar cell (claimed).    ADVANTAGE - The method: utilizes the step of inducing residual chemical reaction that enables more flexible control of the film's morphology, promotes polycrystalline grain growth and grain fusing, removes pinholes and improves inter grain electrical transport; and improves the adhesion between the absorber layer and the first contact layer by substantially reducing the amount of chemical reactions required in the film after deposition.    DETAILED DESCRIPTION - Method (I) for producing a film of compound material, comprises: providing a substrate; depositing a film on the substrate, where the deposited film has a first chemical composition comprising at least one first and second chemical elements; and inducing at least one residual chemical reaction in the deposited film using a source containing at least one second chemical element to increase the content of the second chemical element in the deposited film so that the deposited film has a second chemical composition, where the content of the second element in the second chemical composition is larger than the content of the second element in the first chemical composition. INDEPENDENT CLAIMS are also included for:    (1) a thin film formed by the method (I);    (2) a method (II) for producing a thin-film solar cell, comprising: depositing a first contact layer (320) on a substrate (310), producing an absorber layer (340) over the first contact layer, and depositing a window layer (330) and a second contact layer (350) over the absorber layer, where the absorber layer is produced by the method (I); and    (3) the thin film solar cell formed by the method (II).    DESCRIPTION OF DRAWING(S) - The figure shows a superstrate configuration of the thin film solar cell.    Substrate (310)    First contact layer (320)    Window layer (330)    Absorber layer (340)    Second contact layer (350)