CIGS solar cells were fabricated on a hybrid back contact comprised of a TCO layer (ZnO:Ga (GZO)) and Mo layers. It was discovered that an additional Mo layer introduced underneath the TCO layer promotes sodium diffusion through the TCO back contact into the upper CIGS absorber layer. Improvement in V
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SC values relative to those of sodium-free solar cells was achieved with the Mo/GZO/Mo hybrid back contact as a result of the enhanced sodium diffusion.