To improve the performance of self-assembled InGaAs quantum dots (QDs) solar cells, we introduce a 2-nm In0.1Ga0.9As quantum well underneath each In0.75Ga0.25 As QDs layer to form an InGaAs quantum dots-in-a-well (DWell) structure. The coupled DWell solar cell consists of nine DWells spacing by GaAs layers. We change the GaAs spacer thickness to optimize the photovoltaic performance. The solar cell of 15-nm GaAs spacer shows the best results, including the open-circuit voltage (V-OC) = 0.67 V, the short-circuit current density (J(SC)) = 17.4 mA/cm(2), and the power conversion efficiency (eta) = 8.7%, compared to the coupled InGaAs QDs counterpart of V-OC = 0.59 V, J(SC) = 18.6 mA/cm(2), and (eta) = 8.0%. The enhancement of V-OC for the DWell solar cell is attributed to the lower dark saturation current, which is caused by stronger carrier confinement and lower strain-induced defects in the active region. The DWell solar cell is further improved by Al2O3/HfO2 anti-reflection coating, and reaches eta = 11.8% as J(SC) increases to 23.5 mA/cm(2).