A solar cell includes a first electrode, a second electrode and a stacked semiconductor layer. The stacked semiconductor layer is disposed between the first electrode and the second electrode. The stacked semiconductor layer includes a first semiconductor layer, a second semiconductor layer and an intrinsic semiconductor layer. The first semiconductor layer has a first energy gap. The second semiconductor layer has a second energy gap. The intrinsic semiconductor layer is disposed between the first semiconductor layer and the second semiconductor layer, wherein the intrinsic semiconductor layer is a chalcopyrite layer and has a third energy gap. The third energy gap is less than the first energy gap and the second energy gap.