Research on multi-junction solar cells at Fraunhofer ISE

In this work, we investigated the impact of intensive heat loads on concentrator solar cells assemblies. As test samples, we employed lattice-matched and lattice-mismatched triple-junction solar cells made of GaInP/GaInAs/Ge. The thermal loads were induced by different manners. We used drying cabinets, external power supplies, and a combination of both to achieve maximum test temperatures of 180 °C. For the performance analysis, we utilized flash light solar simulators and an electroluminescence (EL) imaging tool. Our experiments revealed a significant difference depending on the applied manner of heating. The highest impact was observed for the pure heat treatment in drying cabinets. This was particularly visible in the spatial EL images, but also in the IV curves. In contrast, running the concentrator solar cells as forward-biased diodes using an external current supply of 2000 mA, which corresponds to 2000 suns, did not lead to any significant changes in EL and IV curves. However, deformation of the front metallization was observed. In conclusions, pure heat treatment can be considered as a cost-efficient alternative to pinpoint weak points in solar cell receivers.