In this paper, we report a detailed numerical study of the electron irradiation effect on the photoelectrical parameters of a GaAs based p⁺–n–n⁺ solar cell which operates under an AM0 solar spectrum. As a consequence of irradiation different types of defects are created in the semiconductor lattice. These defects introduce energy levels in the gap of the material. The majority of studies dealing with irradiation-induced degradation in solar cells relate it mainly to recombination centres, which are deep levels lying near the mid gap. In the present study, numerical simulation is used to demonstrate that the irradiation-induced degradation is not solely due to recombination centres. Other less deep levels, or traps, play a major role in this degradation. When only recombination centres are taken into account, the short circuit current density (J_sc) is hardly affected while the other cell output parameters such as the open circuit voltage (V_oc), the conversion efficiency (η) and the fill factor (FF) are strongly deteriorated. However, if less deep levels or traps are taken into account together with recombination centres, J_sc becomes sensitive to electron irradiation and the other output parameter deteriorations become less sensitive.