The specimens in this work are 4J cell A (optimized for uniform illumination) and a 4J cell B (designed for the nonuniform illumination profile of a Fresnel lens). Cell A is measured withthe full-glass lens and cell B with either Fresnel lens or full-glass lens. Each combination of cell and lens corresponds to a subunit of a specific CPV module. The I–V characteristics of these subunits are measured on the sun tracking unit at Fraunhofer ISE, Freiburg, Germany. First, the distance between lens and cell is varied stepwise. Second, the power output is determined at concentrator standard conditions. High fill factor (FF) losses are expected for the combination of cell A and the Fresnel lens. The reason for this is that the front-contact grid of cell A does not fit to the illumination profile of the Fresnel lens. Therefore, a measurement of cell A with the Fresnel lens has not been performed.