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The properties of sputtered and electron-beam evaporated Mo are compared, and the resulting impacts on performance of co-evaporated CIGS devices deposited on each type of back contact are investigated. In past studies, the effect of Mo on Cu(In,Ga)Se2 device efficiency has been attributed largely to control of sodium diffusion from the glass. To verify this hypothesis, sodium-free Al2O3 substrates were utilized. Despite lack of Na in the substrate - Na was provided as NaF on the Mo layer-significant differences in device performance between the two types of Mo were observed. Purely resistive effects are ruled out by sheet resistance measurements, and comparison of current-voltage parameters. Negative contributions due to diffusion of harmful impurities from the substrate can be eliminated based on secondary ion mass spectroscopy results. These findings lead to the deduction of device performance dependency on Mo morphology.