Photovoltaic response for high density InGaAs coupled quantum dots
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<sub>0.75</sub>Ga<sub>0.25</sub>As QDs, and investigated the effects on photovoltaic response. For the open-circuit voltage (V<sub>oc</sub>), 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<sub>oc</sub> 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 (J<sub>sc</sub>~24 mA/cm<sup>2</sup>) and efficiency (η~10.6). The J<sub>sc</sub> and η are increases by 55% and 112% more than the device without QDs, respectively.