The electrical transport and the optical behaviour of the solar cells discussed in this paper were studied with the simulation code SCAPS (Solar Cell Capacitance Simulator in one Dimension). In SCAPS the technique of finite differences method are used to solve the Poisson and the continuity equations that are subject to appropriate boundary conditions and under various conditions: equilibrium, DC, AC, Illumination Recombinations (Radiative, Auger, and Shockley- Read-Hall). InGaP is a ternary material and forms a good interface with the GaAs material for a molar fraction x=0.5, it has a direct gap for a molar fraction less than 0.74 [7,8], but the best compromise between the two materials GaAs and AlGaAs is obtained for a molar fraction x ~0.8 [9] In this study different layers are used for modeling solar cells with window layers. The main parameters used in our simulations are listed in Table 1 [10-12].