NOVELTY - The method of forming a solar cell absorber layer on a base, comprises depositing a metallic precursor layer on the base, reacting the metallic precursor layer with selenium, thus forming a compound layer, removing a surface slice of the compound layer thus forming a modified compound film, and depositing a transparent conductive layer over the modified compound film to fabricate a solar cell. The metallic precursor layer comprises a Group IB material, which is indium, or copper and silver, and a Group IIIA gradable material, which is gallium and aluminum.    USE - The method is useful for forming solar cell absorber layer on a base for fabricating thin film solar cells.    ADVANTAGE - The method is capable of economically depositing solar-cell-quality absorber materials on large area substrates with high-throughput.    DETAILED DESCRIPTION - The method of forming a solar cell absorber layer on a base, comprises depositing a metallic precursor layer on the base, reacting the metallic precursor layer with selenium, thus forming a compound layer, removing a surface slice of the compound layer thus forming a modified compound film, and depositing a transparent conductive layer over the modified compound film to fabricate a solar cell. The metallic precursor layer comprises a Group IB material, which is indium, or copper and silver, and a Group IIIA gradable material, which is gallium and aluminum. The compound layer has a graded composition of Group IIIA gradable material such that a molar ratio of Group IIIA gradable material/(Group IIIA gradable material+indium) on an exposed surface of the compound layer is less than 0.1. The modified compound film is formed with Group IBIIIA VIA material, such that the molar ratio of Group IIIA gradable material/(Group IIIA gradable material+indium) on a newly exposed surface of the modified Group IBIIIA VIA compound film is 0.15-0.3. The removing step is carried out by dry etching, wet etching, mechanical polishing, chemical mechanical polishing, electro-polishing and electrochemical mechanical polishing. The reacting step comprises depositing a layer of selenium over the metallic precursor layer forming a stack and raising the temperature of the stack to 400-600 degrees C. A cadmium sulfide layer is deposited on the modified compound film before the deposition of the transparent conductive layer. INDEPENDENT CLAIMS are included for:    (1) a method of forming solar cell absorbers on a surface of a base;    (2) a method of modifying the composition of a top surface of a solar cell absorber compound film formed on a surface of a continuous flexible base; and    (3) a system for modifying the composition of solar cell absorber compound films formed on a surface of a continuous flexible base.    DESCRIPTION OF DRAWING(S) - The diagram shows a process flow chart for forming a solar cell absorber layer on a base.