The presence of Na in Cu(In, Ga) Se-2 (CIGS) is well known to improve the solar cell performance. To incorporate Na into the CIGS absorber, Na-doped Mo (MoNa) back contact layers were grown on stainless steel foils. Three different back contact designs deposited from MoNa sputtering targets with Na concentrations of 3 at.%, 5 at.% and 10 at.% were investigated. A multistage CIGS evaporation process at low (similar to 450 degrees C) substrate temperature was used to deposit the absorbers. Measurements from time-of-flight secondary ion mass spectroscopy depth profiles indicate that Na is preferentially collected at the internal interfaces and out-diffuses from the grain boundaries of the multilayer MoNa back contact into the CIGS absorber. From the [Ga]/([In]+[Ga]) grading profiles, a more pronounced Ga dip was found with increasing Na concentration. Moreover, at high Na concentrations (10 at.% MoNa target), a change in the CIGS texture was observed by X-ray diffraction. Best solar cell efficiency of 14.4% was achieved for the 5 at.% MoNa sample without antireflective coating, which is a significant improvement compared to the 9.8% efficiency measured for the Na-free reference. (C) 2012 Elsevier B.V. All rights reserved.