In order to enhance absorption at infrared range for GaAs based solar cell, we insert the nine-layer of vertically coupled quantum dots (VCQDs) into the active layer. We fine modulated the GaAs spacer thickness of coupled In 0.75Ga0.25As QDs, and investigated the effects on photovoltaic response. For the open-circuit voltage (Voc), the values decreases from 0.61 V to 0.55 V as the spacer thickness (d) decreases from d= 15 nm to 5 nm for the nine-layer VCQDs solar cells. The reduction of V oc for the VCQDs solar cells is attributed to the accumulation of compressive strain energy in the active QD region. For the sample of d=10 nm shows the best performance of current density (Jsc24 mA/cm 2) and efficiency (η10.6). The Jsc and η are increases by 55% and 112% more than the device without QDs, respectively.