In this work we study impurity diffusion into Cu(In, Ga) Se-2 from stainless steel substrates with and without Cr diffusion barriers using secondary ion mass spectrometry. For these substrate configurations we compare cases with and without adding NaF as a sodium precursor. A clear increase in impurity diffusion from the substrate is observed for samples with NaF. Devices made using our micro pilot line show the expected correlation between Fe content, Na content and efficiency, but the highest device efficiency obtained for steel substrates is still slightly below that of the glass substrate reference. We discuss reasons for the observed device performance. (C) 2012 Elsevier B.V. All rights reserved.