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The spectral response, the voltage and current that give maximum power, and the conversion efficiency have all been calculated for Ga1-xAlxAs/p-GaAs/n-GaAs solar cells that have multilayer GaAlAs windows on their surfaces. In the numerical analysis, photo-generated carrier collection in the window layers was considered. The spectral response in the short-wavelength region could be improved if either the Al composition factor x of the window layer was made larger or the window was made thinner. The lifetime of the carriers in the p-GaAs layer is especially important for improving the spectral response and the conversion efficiency. The increases of donor concentration in the n-GaAs bulk region and of acceptor concentration in the p-GaAs layer cause the current and voltage to increase. Thus the multilayer structures can make efficient use of the short-wavelength region of the spectrum and be easier to produce than a continuously graded structure. Conversion efficiencies can be approximately 20% in AMO.