The invention provides a solar cell. The solar cell includes a silicon substrate including a front surface for receiving light, and a rear surface opposite the front surface, an emitter diffusion region on the rear surface and doped with a first polarity that is opposite to a polarity of the silicon substrate, a base diffusion region on the rear surface of the substrate and doped with a second polarity that is the same as the polarity of the silicon substrate, and an insulation gap between the emitter diffusion region and the base diffusion region, wherein the base diffusion region has a closed polygonal shape, and wherein the insulation gap is adjacent the base diffusion region.