Outdoor photoluminescence imaging of III-V multijunction solar cells under direct sunlight

Multijunction solar cells, particularly those based on elements from Groups III and V, have garnered significant attention due to their high efficiencies and excellent stability. These cells are ideal candidates for concentration applications. Concentrated photovoltaic (PV) plants, however, require substantial investments. Field inspection of these systems is thereby critical to ensure optimal performance and maximum reliability. Contactless measurements are highly valuable as they eliminate the need for specialised qualifications and instruments. Photoluminescence (PL) imaging has proven to be a powerful contactless characterisation tool for providing spatially resolved defect analysis in solar cells. However, extracting PL signals under outdoor conditions remains challenging, even for commercial single-junction silicon solar cells, let alone multijunction cells. This paper presents the first-ever outdoor photoluminescence images of multijunction solar cells under sunlight excitation. The developed method involves selecting optimal optical filters for each subcell to maximise the signal-to-noise ratio. The method is capable to provide critical insights into the field performance of III-V multijunction solar cells.