Detection of Finger Interruptions in Silicon Solar Cells Using Line Scan Photoluminescence Imaging

Finger interruptions or finger breaks are a common occurrence in screen printed solar cell manufacturing and may result in decreased performance due to an increase in effective series resistance. Identification of finger interruptions is typically accomplished using electroluminescence imaging. This paper demonstrates contactless detection of finger interruptions using line scan photoluminescence imaging. Modeling is used to highlight the difference between line scan photoluminescence images and conventional luminescence imaging methods. Significant benefits of using line scan photoluminescence imaging over electroluminescence imaging to identify finger interruptions are presented: in line scan photoluminescence images, finger interruptions cause an increase in luminescence intensity, while high recombination regions cause a decrease in intensity. This contrast inversion allows for a more unambiguous identification of defect types. Detailed modeling is performed to determine the impact of finger interruptions on line scan photoluminescence images, as a function of the location of the finger interruption and of illumination intensity. The increase in luminescence intensity from a finger interruption is found to correlate linearly with the corresponding power loss. Finally, experimental line scan photoluminescence images of industrial cells and full sized modules are presented and found to agree well with the modeling results.