GaAs solar cells, as other semiconductor devices, suffer from degradations of their electrical and physical properties under particle irradiations (electrons and protons) in space environment. In this work, numerical simulation is used to model the effect of 1 MeV electron irradiation on the performance degradation of a single junction GaAs solar cell, and to identify the defects responsible for the degradation of the output parameters of GaAs solar cells. We found that the GaAs solar cell is sensitive to 10(16) cm(-2) electron irradiation fluence, and the electron defects E3 and E4, and the hole defect H4 created by 1 MeV electron irradiation, are the most responsible for the degradation of short-circuit current (J(sc)). These defects also alter the open-circuit voltage (V-oc). Simulation results also reveal that electron trap defect E2 has a significant influence on the solar cell performance when it is combined with the other defects. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.