NOVELTY - The cell has a first back surface electrode layer (200) provided with second and third back surface electrode layers. A front electrode layer is formed on a buffer layer. The buffer layer is adhered on a light absorption layer. The light absorption layer is formed on the first back surface electrode layer. The first back surface electrode layer is adhered on a substrate. The substrate is arranged on a side of the second back surface electrode layer. The second and the third back surface electrode layers are made of molybdenum and sodium materials.    USE - Solar cell.    ADVANTAGE - The amount of the sodium in the second back surface electrode layer is less than that of the third back surface electrode layer. The cell differentiates amount of the sodium of the second back surface electrode layer and the third back surface electrode layer, so that amount of the sodium diffused to the light absorption layer can be efficiently controlled. The first back surface electrode layer is formed on the second back surface electrode layer, thus decreasing electric potential difference of a cell, and hence smoothly flowing current through a cell and improving open circuit voltage and fidelity and photoelectric conversion efficiency of the cell. The third back surface electrode layer is in contact with an upper side of the first back surface electrode layer, so that fixed stepped portion can be formed by the first back surface electrode layer of the cell. The cell reflects light in the first back surface electrode layer, so that incident light can be easily collected at low angle, thus improving efficiency of the cell. The cell avoids requirement of through groove formation process, so that processing time can be shortened, thus improving processing efficiency.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a solar cell fabricating method.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of a solar cell.    Back surface electrode layer (200)