Probing the effects of non-uniform light beams and chromatic aberration on the performance of concentrators using multijunction cells

A method is presented for estimating the photocurrent of the subcells of a multijunction cell within a concentrator, through the measurement of the cell’s short-circuit current under a large sweep of different spectral conditions. The spectrum is monitored by means of a set of component cells matched to the subcells of the concentrator cell. The method allows the calculation of the current-matching or J-ratio of the concentrator cell under any spectrum, and also the identification of losses due to the non-uniformity of the spectrum throughout the solar cell area. For illustration purposes, the method is applied to a concentrator composed of a Fresnel lens that concentrates light over a triple-junction cell 300 times smaller.