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Wafer-bonded GaInP/GaAs//Si solar cells with 30% efficiency under concentrated sunlight
Highly efficient III-V/Si triple-junction solar cells were realized by a fabrication process based on direct wafer bonding: Ga0.51In0.49P/GaAs dual-junction solar cells were grown inverted by metal organic vapor phase epitaxy on GaAs substrates and bonded to separately fabricated Si solar cells. The fast atom beam activated direct wafer bond between highly doped n-Si and n-GaAs enabled a transparent and electrically conductive interface. Challenges arising from the different thermal expansion coefficients of Si and the III-V semiconductors were circumvented, as the bonding was performed atmoderate temperatures of 120 degrees C. The external quantum efficiency and current-voltage characteristics of the wafer-bonded triple-junction solar cells were thoroughly investigated, and a maximum efficiency of 30.0% was found for a concentration factor of 112.