Determination of subcell I-V characteristics of multijunction solar cells using optical coupling

A method for the determination of the subcell I-V characteristics of multijunction solar cells in the presence of optical coupling is presented and applied to a Ga0.50In0.50P/Ga0.99In0.01As/Ge triple-junction solar cell. Each of the subcells is described by a two-diode model and can be illuminated by a narrowband light source externally. Optical coupling is then used explicitly to generate current in one subcell, which is not illuminated externally. This approach yields the magnitude of optical coupling and a relationship between the two diode parameters of each subcell. The remaining cell parameters are determined with the help of pulsed illumination. In this fashion, the open circuit voltage of individual subcells is accessible, despite the fact that not all junctions are illuminated.