NOVELTY - Forming a light absorption layer, comprises: wet coating a controlling precursor on a base precursor, where the band gap of the controlling precursor is larger than that of the base precursor, and the controlling precursor is a Group I-III-VI compound including copper-indium-gallium-aluminum-selenium-sulfide compound (I); and performing a heating process so as to make the base precursor and the controlling precursor form the light absorption layer.    USE - The method is useful for forming a light absorption layer, which is useful in a solar cell structure (claimed).    ADVANTAGE - The method provides the light absorption layer, which avoids the residue of metal oxide, and is uniformly distributed, thus increasing the photoelectric conversion efficiency of the solar cell structure; and utilizes the controlling precursor in which its thickness can be easily controlled, and has thermal stability higher than that of the metal precursor, so that the composition of the light absorption formed after the heating process can be easily controlled.    DETAILED DESCRIPTION - Forming a light absorption layer, comprises: wet coating a controlling precursor on a base precursor, where the band gap of the controlling precursor is larger than that of the base precursor, and the controlling precursor is a Group I-III-VI compound including copper-indium-gallium-aluminum-selenium-sulfide compound of formula (Cua(In1-b-c Gab Alc) (Se1-d Sd)2); and performing a heating process so as to make the base precursor and the controlling precursor form the light absorption layer.    a = greater than 0;    b-d = 0-1; and    b+c = greater than 0 and less than or equal to 1.    An INDEPENDENT CLAIM is also included for a solar cell structure (100), comprising: a substrate (110); a metal layer (120) disposed on the substrate; the light absorption layer (130) disposed on the metal layer; a buffer layer (140) disposed on the light absorption layer; a window layer disposed on the buffer layer; a conductive layer disposed on the window layer; and many conducting wires disposed on the conductive layer.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic illustration of the solar cell structure.    Solar cell structure (100)    Substrate (110)    Metal layer (120)    Light absorption layer (130)    Buffer layer (140)