Single junction In0.52Al0.48As solar cells have been grown on a (100) GaAs substrate by employing a 1 μm thick compositionally graded InxGa1-xAs/InP metamorphic buffer layer to accommodate the 3.9% mismatch. Cells processed from the 0.8 μm thick InAlAs layers had photovoltaic conversion efficiency of 5% with an open circuit voltage of 0.72 V, short-circuit current density of 9.3 mA/cm2, and a fill factor of 74.5% under standard air mass 1.5 illumination. The threading dislocation density was estimated to be 3 × 108 cm-2.