This paper focuses on the simulation and optimization of electrical and structural properties of high efficiency InGaP/InGaAs/Ge triple junction solar cells that incorporate In0.7Ga0.3As quantum dots with in the GaAs middle cell material. Current density-voltage (J-V), external quantum efficiency (EQE) and capacitance-voltage (C-V) characteristics have been simulated and discussed. Results show that 30 pairs of In0.70Ga0.30As (QD)/GaAs (barrier) in the middle cell provide a relative enhancement of 13% in EQE in the 900–1000 nm wavelength range. This leads to a short-circuit current of 20 mA/cm2, an open circuit voltage of 2.3 V, a fill factor of 81.73%, and a conversion efficiency of 39.03%. The C-V revealed that a relatively high number of interfacial states are present in the 3-J cell structure including the QD layers, which decreases the open circuit voltage. In this study we benefited 18% of relative efficiency.