The literature emphasizes on the quality of InP/(AlGa) 1−x In x As metamorphic buffers, which is estimated by transmission electron microscopy and X-ray diffraction, fabricated on 15°-off GaAs substrate to grow the In 0.52 Ga 0.48 As solar cell using metal organic chemical vapor deposition. Based on the virtual InP/(AlGa) 1−x In x As/GaAs substrate above, we simulated the effect of the InP window layer of various thicknesses on the performance of In 0.52 Ga 0.48 As solar cell and compared them according to optical reflectance, short circuit current density J sc , open circuit voltage V oc and external quantum efficiency EQE using the Crosslight APSYS tool. Under one-sun AM1.5 G illumination, the simulated In 0.52 Ga 0.48 As cell with a 100 nm InP window layer achieved 4% higher efficiency compared to that of cells with a 1000 nm InP window layer.