Comparison from Simulated Al0.3Ga0.7As/GaAs/Ge and Al0.3Ga0.7As/GaAs/Si/Ge to Experimental InGaP/GaAs/InGaNAsSb/Ge for Optimized Utilization of the Solar Spectrum

To make full use of the solar spectrum, the performances of Al 0.3 Ga 0.7 As/GaAs/Ge and Al 0.3 Ga 0.7 As/GaAs/Si/Ge have been simulated using a one-dimensional device simulator called personal computer oe dimension (PC1D). The dependencies of simulated current density–voltage ( J – V ) and external quantum efficiency (EQE) results on the thicknesses of each sub-cell have been thoroughly analyzed to determine the preferred thickness. Compared to Al 0.3 Ga 0.7 As/GaAs/Ge (1.5/5/50 μm), Al 0.3 Ga 0.7 As/GaAs/Si (1.5/5/180 μm) has an increase of 0.36 V for open-circuit voltage ( V oc ) but a slight decrease of 1.55 mA/cm 2 for short-circuit current density ( J sc ). Subsequently, a monolithic InGaP/GaAs/InGaNAsSb (1.9/1.42/1 eV, 3 J) cell has been mechanically stacked on a Ge cell with four terminals. The J sc value of 14 mA/cm 2 and 6.5 mA/cm 2 is calculated for each sub-cell of 3 J cell and bottom Ge cell with integration of EQE measurements. In addition, the TiO 2 /SiO 2 /TiO 2 (150 nm/1 µm/150 nm, trilayer) interface provides a thermal conductance (2.9 × 10 6 W K −1 ) comparable to the direct bond interface. It is believed that the architecture of InGaP/GaAs/InGaNAsSb on the Ge cell with a trilayer interface between is the preferred choice.