NOVELTY - The method involves forming an aluminum layer (11) and a P-type polycrystalline silicon-germanium layer (13) on a P-type monocrystalline silicon substrate (10) in sequence. The substrate is annealed, where the aluminum layer and the germanium layer are annealed at 400-650 degree Celsius. An aluminum-induced crystallization process in which germanium atoms of the germanium layer and silicon atoms of the substrate simultaneously pass through the aluminum layer, is undertaken, where the germanium layer is converted into the silicon-germanium layer between the substrate and the aluminum layer.    USE - Method for fabricating a P-type polycrystalline silicon-germanium structure for a solar cell that is utilized for converting light energy into electric energy.    ADVANTAGE - The method utilizes an aluminum-induced crystallization process to convert the amorphous germanium layer into the P-type polycrystalline silicon-germanium layer so as to achieve simple, reliable and low-cost fabrication of the polycrystalline silicon-germanium structure. The aluminum layer is formed on bottom of the solar cell through the aluminum-induced crystallization process so as to eliminate need for fabricating additional bottom electrodes, thus reducing fabrication cost of the solar cell. The P-type monocrystalline silicon substrate, a N-type amorphous silicon-germanium layer and the P-type polycrystalline silicon-germanium layer respectively extract energies of visible light, light having shorter wavelengths and light having longer wavelengths so as to fabricate the solar cell that can use energy of light distributed in wide range of a spectrum and has high photoelectric conversion efficiency.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of a solar cell containing a P-type polycrystalline silicon-germanium layer.    P-type monocrystalline silicon substrate (10)    Aluminum layer (11)    P-type polycrystalline silicon-germanium layer (13)    Transparent conductive layer (30)    Fabricate metal electrode (40)