Measurement of the limiting subcell in multijunction space solar devices by restricted-wavelength-range illumination

During their employment in space applications, InGaP/InGaAs/Ge-based multijunction solar cells undergo strong particle bombardments that decrease their performances. As InGaP is more resistant to radiation, the whole device is usually designed in “top-limited” configuration. Then the development of high-efficiency and reliable devices needs standard techniques for identifying the limiting subcell before and after irradiation. We here present a specific method to determine the limiting subcell and matching current in multijunction solar cell. This approach is based on using simultaneously a solar simulator and a suitable supplemental lamp for illuminating the cell in a restricted wavelength range where the top subcell only responds. The technique is tested on beginning-of-life and irradiated 3-junction InGaP/InGaAs/Ge solar cells, and its reliability is discussed.