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% (AMO) and efficiencies up to 30.8% (AMO) after 1*10 ¹⁵ 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 four-j unction 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°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.