This work reports on the effect of Na doping on hole concentration in CIGS thin film solar cells deposited on polyimide substrate. Two methods of Na supply were applied in this investigation: Na containing back contact layers (Mo:Na) and NaF evaporation at different stages of the absorber deposition, including the post-growth Na treatment. The results of hole concentration profiles are presented. The correlation of the hole concentration and the amount of supplied Na is discussed in view of growth- and defect-related models. (C) 2014 Elsevier B.V. All rights reserved.