Current-matching estimation for multijunction cells within a CPV module by means of component cells



An indoor method is presented for the quantification of the current-matching ratio of a multijunction cell within a concentrator under arbitrary spectral irradiance conditions. The cell current is measured across a very large spectral sweep to force the relevant subcells into a limiting condition. The light spectrum is monitored using component cells to avoid the need for a spectroradiometer and spectral response measurements. The method also provides an estimation of the current losses beyond the overall current mismatch, for example, losses produced in concentrators with chromatic aberration by the non-uniformity of the incident spectrum across the cell. The method has been applied to a pair of refractive point-focus concentrator systems; first, a 300X single-stage Fresnel lens over a lattice-matched GaInP/Ga(In)As/Ge triple-junction cell and second, a 1000X two-stage system with the same Fresnel lens over a homogenizing secondary lens that encapsulates a triple-junction cell of the same kind but smaller. The experiment demonstrates that the single-stage concentrator exhibits a higher sensitivity of the current mismatch to variations in the focal distance. Copyright © 2012 John Wiley & Sons, Ltd.