A multi-junction solar cell comprising a high-crystalline silicon solar cell and a high-crystalline germanium solar cell. The high-crystalline silicon solar including a first p-doped layer and a n+ layer and the high-crystalline germanium solar cell including a second p layer and a heavily doped layer. The multi-junction solar cell can also be comprised of a heavily doped silicon layer on a non-light receiving back surface of the high-crystalline germanium solar cell and a tunnel junction between the high-crystalline silicon solar cell and the high-crystalline germanium solar cell.