In this paper numerical simulation has been used to predict the effect of the thickness and aluminium (Al) mole fraction of an AlGaAs layer, used as a window for a p(+)-n-n(+) GaAs solar cell under AMO illumination and exposed to 1 MeV electron irradiation. Such solar cells are used in satellites and undergo severe degradation in their performance due to induced structural defects. The irradiation-induced defects are modelled as energy levels in the energy gap of GaAs. To predict this effect, the spectral response is evaluated for different electron irradiation fluences for two types of cells. In the first a narrow Al0.31Ga0.69As window is a small part of the p(+) layer while in the second type the whole window is an AlxGa1-xAs layer with a gradual Al mole fraction. The obtained results show that the AlxGa1-xAs window with a gradual Al mole fraction improves the resistance of the solar cell to electron irradiation especially in the short wavelengths range. (C) 2009 Elsevier Ltd. All rights reserved.