Radiation hard four-junction space solar cell based on GaInAsP alloys

Electric orbit raising increases the radiation dose for space solar arrays significantly. This leads to the need for a more radiation resistant, highly efficient space solar cell. We propose a new wafer-bonded 4-junction structure which allows reaching begin-of-life efficiencies up to 34.7% (AM0) and efficiencies up to 30.8% (AM0) after 1*1015 cm(-2) 1-MeV electron irradiation. The high radiation hardness is a result of specific material properties of InP-rich compounds which benefit from significant defect annealing under typical operating conditions in space. A new fourjunction space solar cell, based on high InP fractions containing GaInAsP and Ge is currently under development in the EU project RadHard and first devices achieve an efficiency of 21.4% (AM0) before irradiation. After irradiation, as expected, a strong annealing effect after 3 days at AM0 & 60 degrees C is found for this device. Already at this early development stage 78% of the end of life open circuit target voltage of 3.09 V under AM0 has been reached.