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Iron distribution in silicon after solar cell processing: Synchrotron analysis and predictive modeling

: Fenning, D.P.; Hofstetter, J.; Bertoni, M.I.; Hudelson, S.; Rinio, M.; Lelievre, J.F.; Lai, B.; Canizo, C. del; Buonassisi, T.


Applied Physics Letters 98 (2011), Nr.16, Art. 162103, 3 S.
ISSN: 0003-6951 (Print)
ISSN: 1077-3118
ISSN: 1931-9401 (online)
Fraunhofer ISE ()
PV Produktionstechnologie und Qualitätssicherung; Silicium-Photovoltaik; Produktionsanlagen und Prozessentwicklung; Charakterisierung; Zellen und Module

The evolution during silicon solar cell processing of performance-limiting iron impurities is investigated with synchrotron-based x-ray fluorescence microscopy. We find that during industrial phosphorus diffusion, bulk precipitate dissolution is incomplete in wafers with high metal content, specifically ingot border material. Postdiffusion low-temperature annealing is not found to alter appreciably the size or spatial distribution of FeSi2 precipitates, although cell efficiency improves due to a decrease in iron interstitial concentration. Gettering simulations successfully model experiment results and suggest the efficacy of high- and low-temperature processing to reduce both precipitated and interstitial iron concentrations, respectively.