In this paper, the effect of material parameters on the efficiency of Ge and InGaAs\np-n junction solar cells which are most commonly used as the sub-cell of multi-junction solar\ncells are investigated and the results due to these two cells are compared. The efficiency of Ge\n(EG=0.67 eV) solar cell which is easy to manufacture and inexpensive in cost, is compared\nwith the efficiency of InGaAs (EG=0.74 eV) solar cell which is coming with drawback of high\nproduction difficulties and cost. The theoretical efficiency limit of Ge and InGaAs solar cells\nwith optimum thickness were determined by using detailed balance model under one sun\nAM1.5 illumination. Since the band gap values of two cells are close to each other,\napproximate detailed balance efficiency limits of 16% for InGaAs and 14% for Ge are\nobtained. When drift- diffusion model is used and the thicknesses and doping concentrations\nare optimized, the maximum efficiency values are calculated as 13% for InGaAs and 9% for\nGe solar cell. For each solar cell external quantum efficiency curves due to wavelength are also\nsketched and compared.
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