Patent ID: 8716593

Claim:
A monolithic multi-junction solar cell comprising elements of the third and fifth main groups of the periodic table, the multi-junction solar cell comprising a Ge substrate, and at least three junctions, one of which is a junction consisting of GaInAs which is made of a material with low diffusion length or with a diffusion length which considerably deteriorates during use, a semiconductor mirror disposed between two said junctions and underneath the junction consisting of GaInAs, and having several layers with different refraction indices and/or material compositions and/or thicknesses, and the semiconductor mirror having a high reflection degree at least in one part of the spectral absorption range of the junction consisting of GaInAs disposed above the semiconductor mirror, and a high transmission degree in the spectral absorption range of the junction or junctions disposed underneath the semiconductor mirror, wherein at least one layer of the semiconductor mirror which is disposed underneath the junction consisting of GaInAs is lattice-matched to the junction consisting of GaInAs, the junction consisting of GaInAs disposed above the semiconductor mirror has a thickness of d m with 500≦d m ≧2500 nm, and the semiconductor mirror has a high reflection R in a spectral range of higher energies than that of a band gap of the junction consisting of GaInAs located above the semiconductor mirror, wherein a half width value of reflection of the semiconductor mirror is in a range between 50 nm and 300 nm wherein the semiconductor mirror comprises at least three layers of different composition.