Four-Junction Wafer Bonded Solar Cells for Space Applications

Concentrator solar cells with efficiencies up to 46.1 % have been developed in a collaboration between Fraunhofer ISE, SOITEC and CEA-LETI using a four-junction cell structure of GaInP/(Al)GaAs//GaInAsP/GaInAs joint by wafer bonding. The bottom tandem cell is based on the InP lattice constant, whereas the top tandem is realized on GaAs. In this paper we report on the potential of this cell architecture for space applications. Therefore, several solar cell wafers with adapted subcell bandgap energy and thickness were processed and characterized, measuring begin-of-life efficiencies up to 35.2 % under AM0 spectral conditions.