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.