3-6 junction photovoltaic cells for space and terrestrial concentrator applications

Multi-junction solar cells made from III-V compound semiconductors are the highest efficient photovoltaic devices today. Different solar cell structures have been developed for space as well as terrestrial concentrator applications in a close collaboration between the Fraunhofer ISE and RWE-SSP in Germany. Efficiencies up to 29.1% (AM0) have been recently achieved for a 30.2 cm² GaInP/GaInAs/Ge device at RWE-SSP. Triple-junction solar cells with remaining factors up to 88 % after irradiation with 1 MeV electrons at a fluence of 10¹⁵ cm^-2 have been demonstrated at Fraunhofer ISE. Multi-junction solar cells with 5 and even 6 junctions for even higher radiation hardness are under development. On the other hand lattice mismatched triple-junction solar cells are an excellent solution for terrestrial concentrator applications. Efficiencies up to 35.2 % at a concentration ratio of 443-637 (AM1.5d, low AOD) have been obtained.