A tandem four-terminal CPV system consisting of Al0.3Ga0.7As and Ge solar cells

In the realm of photovoltaics, a common technique towards achieving high solar energy conversion efficiencies is to concentrate sunlight on a multi-junction monolithically stacked solar cells. This approach is most suitable for cells made of materials that have the same lattice constant, because this results in less defects, and hence, a high efficiency. If the cells do not have the same lattice constant, then more complex and costly growth techniques are used. Alternatively, the non-lattice matched cells can be kept apart (i.e. not stacked) and integrated in an optical system that splits the sunbeam into several sub-beams and direct each towards one cell. In this study, we are demonstrating this last approach consisting of an optical system with beam-splitting features, encompassing two solar cells: AlGaAs and Ge.