Analysis of heteroepitaxial AlGaAs/Si tandem solar cell for concentrator applications

A development of monolithic AlGaAs/Si tandem solar cells for concentration application is proposed. A theoretical analysis was carried out to express the device parameters as a function of the doping concentration and the dislocation density. From the results of this theoretical analysis, it is demonstrated that when the dislocation density is reduced to lower than 10/sup 4/ cm/sup -2/, the photocurrent matching between the top cell and the bottom cell can be satisfied at the Al composition of AlxGa1-xAs, x=0.21 and the efficiency of the AlGaAs top cell increases rapidly in 1-100 Sun concentration region. In order to achieve very high efficiency, the dislocation density must be reduced to lower than 5/spl times/10/sup 5/ cm/sup -2/ and concentration ratios greater than 100 times must be used. From these results, it is suggested that monolithic AlGaAs/Si tandem solar cells have the potential to achieve high efficiency at low cost by using high solar concentration ratios.