Exploring the p-n junction region in Cu(In,Ga)Se2 thin-film solar cells at the nanometer-scale

In this work we study the CdS/Cu(In,Ga)Se2 p-n junction region in Cu(In,Ga)Se2 thin-film solar cells using atom probe tomography. A Cu-, Ga-depleted, and Cd-doped region of about 1 nm thickness is detected at the Cu(In,Ga)Se2 side of the CdS/Cu(In,Ga)Se2 interface. Furthermore, Cd is also found to be enriched at Cu(In,Ga)Se2 grain boundaries connected to the CdS layer. Na and O impurities decorate the CdS/CIGS interface, where Na-rich clusters are preferentially located in CdS regions abutting to Cu(In,Ga)Se2 grain boundaries. The experimental findings of this work demonstrate the capability of atom probe tomography in studying buried interfaces and yield vital information for understanding and modeling the p-n junction band structure in Cu(In,Ga)Se2 solar cells.