Comparison of radiation effects of LM and UMM structure GaAs triple-junction solar cells under 1 MeV neutron irradiation

The output performances of lattice-matched (LM) and upright metamorphic (UMM) GaAs triple-junction solar cells under 1 MeV neutron irradiation were studied. The results show that the electrical performance, including open-circuit voltage, short-circuit current, maximum output power and fill factor of the solar cells were degraded seriously with the increase of neutron irradiation fluence. Meanwhile, the series resistance and the shunt resistance of solar cells are increased and decreased, respectively, when the neutron irradiation fluence increased. The degradation of maximum output power in LM and UMM GaAs cells is about the same level of 72.9 % and 72.3 % of its initial values, respectively, when the irradiation fluence is reached 6 x 1012 n/cm2. By comparing the integrated current densities, it was found out that the current-limiting subcell in LM cells s always GaAs middle cell, and in the UMM cell, the current limiting unit is changed from GaInP top subcell to GaInAs middle subcell after high fluence neutron irradiation.