Effects of Na incorporation on electrical properties of Cu(In,Ga)Se2-based photovoltaic devices on polyimide substrates

• Hole concentration in CIGS solar cells absorbers increases if sodium is provided into the absorber.
• Different methods of Na supply are adequate to achieve high hole concentration.
• Electrical activity of grain boundaries was proposed to have impact on hole concentration.
• Proposed model was supported by performed simulations.

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.