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Iron related solar cell instability: Imaging analysis and impact on cell performance

: Schubert, M.C.; Padilla, M.; Michl, B.; Mundt, L.; Giesecke, J.; Hohl-Ebinger, J.; Benick, J.; Warta, W.; Tajima, M.; Ogura, A.


Solar energy materials and solar cells 138 (2015), pp.96-101
ISSN: 0927-0248
Journal Article
Fraunhofer ISE ()
Solarzellen - Entwicklung und Charakterisierung; Silicium-Photovoltaik; Charakterisierung von Prozess- und Silicium-Materialien; Herstellung und Analyse von hocheffizienten Solarzellen; iron; silicon; cells; instability; imaging

Iron is an omnipresent and efficiency-limiting impurity in p-type silicon solar cells. A very useful technique to detect the interstitial iron concentration in boron doped silicon is based on carrier lifetime measurements at two metastable states of iron, namely interstitial and bound to boron. We present a further development of this technique which images the iron concentration not only on wafer level but also on finished solar cells and in this way enables the most direct access to the impact of interstitial iron on cell performance. With the help of this method we reveal that remaining iron in solar cells may be responsible for significantly unstable current-voltage characteristic under illumination. Recommendations for stable cell measurements even for cells containing a significant concentration of iron are given.