Photoluminescence-based detection of mechanical defects in multijunction solar cells

Abstract

Mechanical solar cell defects give rise to a characteristic contrast in luminescence imaging. In multijunction cell architectures, the current in each subcell can be adjusted individually in photoluminescence imaging in contrast to electroluminescence imaging. The contrast formation under these conditions is derived theoretically. The image contrast of a defect recorded by illuminating and imaging one specific subcell can be reversed by illuminating the adjacent subcell in addition. This provides a convenient method to eliminate all background contrast by subtracting both images, resulting in an improved visibility of defects. This is demonstrated experimentally for the top cell of Ga0.5In0.5P/GaAs/Ge triple junction solar cells.