Characterization of monolithic III-V multi-junction solar cells - challenges and application
The characterization of monolithic III-V multi-junction solar cells is still a challenging task. In this paper we show that quantum efficiency measurements have to be performed under optimized light- and voltage-bias conditions to minimize measurement artifacts. They appear, if the subcell to be measured has a low shunt resistance or a low reverse breakdown voltage. Moreover, cells with increasing number of junctions, such as our five-junction cell, pose new challenges to this characterization technique. Accurate I-V measurements of multi-junction cells under correct spectral conditions are usually very time consuming. However, ISE CalLab has developed a faster procedure for spectral correction. It is used in the methodology of spectrometric characterization. This characterization technique can be used to determine the current matching of the subcells. Applying spectrometric characterization in degradation experiments yields the degradation of the individual subcells additionally to the degradation of the total multi-junction device. Furthermore, it can be used to give a realistic estimation of the annual power output of terrestrial concentrator systems.