Abstract: A tandem solar cell structure includes a substrate, a conductive layer, a bottom solar cell combination and a top solar cell, The bottom solar cell combination includes a plurality of solar cell units and is disposed on the substrate. A conductive layer is disposed between the top solar cell and the bottom solar cell combination. The top solar cell is connected to one of the solar cell units in series. A wide energy distribution of the solar radiation can be absorbed through the tandem solar cell structure. The electrical series connection of the top solar cell and the solar cell units of the bottom solar cell combination reduces current mismatch between the top and bottom cells and enhances the overall system open circuit voltage due to more units in the bottom cell combination. The efficiency of the tandem solar cell structure is therefore improved considerably.