Microstructural and Chemical Investigation of PVD-CdS/PVD-CuIn1-xGaxSe2 Heterojunctions: A Transmission Electron Microscopy Study

We report on a detailed transmission electron microscopy (TEM) study of physical-vapor-deposited (PVD) CdS/CuIn1-xGaxSe2 (CIGS) heterojunctions prepared at the Mia-Sole production line. High-resolution TEM images of the heterointerface reveal the coexistence of CdS domains of cubic and hexagonal phases. Both are shown to grow epitaxially on the CIGS surface. Twin boundaries in the CIGS were observed to propagate into the epitaxial CdS and continue through the whole CdS layer. Scanning TEM in combination with energy dispersive X-ray spectroscopy shows the presence of Cu in the CdS up to similar to 20 nm from the heterojunction. These results provide insights into the PVD-CdS/CIGS heterointerface and suggest that buffer layer crystallinity sufficient to produce photocurrent generation may be obtained with further process optimization.