The impact of oxygen incorporation during intrinsic ZnO sputtering on the performance of Cu(In,Ga)Se2 thin film solar cells

We investigated the impact of incorporating 2% oxygen during intrinsic ZnO sputtering on the efficiency of Cu(In,Ga)Se2 solar cells. The added oxygen not only reduced the optical absorption loss of the Al-doped ZnO overlaying layer but also improved the electronic properties of the underlying CdS/Cu(In,Ga)Se2 by increasing carrier density, lowering defect level, and increasing diffusion length, eventually enhancing JSC, VOC, and fill factor. It was found that the Na doping concentration was significantly increased around the CdS/Cu(In,Ga)Se2 junction due to the plasma-activated oxygen. The improved electronic properties are better explained by the increased Na concentration than simply the oxygen-related defect passivation.