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We report on a novel hybrid amorphous Si-organic series-connected tandem junction solar cell. The solar cell is fabricated on indium tin oxide (ITO)-coated glass and uses an a-(Si,C):H as the first cell and a P3HT/PCBM organic cell as the second cell. An intermediate ITO layer is used as an ohmic layer which provides an excellent contact to both the first and the second cells. By adjusting the bandgap and thickness of the first a-(Si,C):H cell, we achieve an almost complete matching of currents produced by the first and the second cells. The first cell produces ~0.95-1.0-V open-circuit voltage, and the second cell produces ~0.6-V open-circuit voltage. The combined cell produces 1.5-V open-circuit voltage and had a fill factor of 77%, showing the effectiveness of the intermediate ITO layer to act as an excellent connecting layer between the two cells. When such an ITO layer is not used, the fill factor is very poor. The solar conversion efficiency of the organic cell was 4.3%, whereas the efficiency of the tandem cell was 5.7%. We also measured the stability of the organic cell with and without an inorganic cell acting as a filter in front. It is shown that the degradation of the organic cell is much higher when it is subjected to a full solar spectrum, as compared with when it is subjected to light passing through an inorganic cell first, which filters out ultraviolet (UV) and blue photons. Thus, we show that this new cell combination has the potential to significantly increase the efficiency of organic cells while also decreasing the instability. We also discuss the potential of achieving much higher efficiencies, that is approaching 20%, by using an appropriate combination of amorphous and organic cells. An example is shown next.