AbstractThe effect of dissociation of interstitial iron‐substitutional boron (FeiBs) pairs, as it occurs under illumination in iron‐contaminated silicon solar cells, on the solar cell properties has been studied on the basis of numerical device simulations using reported recombination parameters for Fei and FeiBs. Most cell parameters are found to degrade during FeiBs dissociation. However, the open‐circuit voltage can also increase within certain ranges of the iron concentration. Critical iron concentrations are determined, giving the threshold contamination level above which a significant degradation in the corresponding cell parameter can be observed. The threshold iron contamination level of the open‐circuit voltage degradation is found to be up to two orders of magnitude larger than the threshold iron level of the short‐circuit current degradation. As the behaviour of the cell parameters under illumination is specific to the dissociation of FeiBs pairs, the characteristic changes in the cell parameters due to illumination may be used as a simple way of identifying iron contamination problems in silicon solar cells. Copyright © 2005 John Wiley & Sons, Ltd.