Numerical simulation was used to study the AlxGa1-xAs window composition effect on the current-voltage characteristics of 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 modeled as energy levels in the energy gap of GaAs. To predict this effect, the current voltage characteristic and the spectral response are evaluated for different electron irradiation fluences for two types of cells. In the first we use a narrow Al0.31Ga0.69As window as a small part of the p(+) layer while in the second type we use an AlxGa1-xAs window with a gradual Al mole fraction. The obtained results show that the AlxGa1-xAs window with a gradual Al mole fraction reduces the degradation of the output parameters of the solar cell and its spectral response by irradiation in particular for the short wavelengths. (C) 2009 Elsevier Ltd. All rights reserved.