Influence of external contacting on electroluminescence and fill factor measurements

Electroluminescence imaging combined with photoluminescence imaging on solar cells allows extracting spatially resolved information on local solar cell quality. Numerous methods for the extraction of spatially resolved parameters have been introduced in the past. An important factor, which has mandatory influence on electroluminescence images, has not been discussed in detail yet. This factor is the influence of the external contacting scheme or erroneous contacting on the measurement results. In this work we discuss the influence of the external contacting scheme on the appearance of electroluminescence images and images of the spatially resolved series resistance which are calculated from electroluminescence images taken at different operating points. Furthermore we discuss the impact of erroneous contacting on fill factor measurements. We show that the impact of erroneous contacting on fill factor measurements becomes larger if busbar resistances become larger. The industrial trend towards thinner busbars with higher resistances hence motivates an electroluminescence based quality control for inline current voltage measurements of silicon solar cells.