Microstructural and Chemical Investigation of PVD-CdS/PVD- $\hbox{CuIn}_{\hbox{1-x}} {\hbox{Ga}}_{\hbox{x}} {\hbox{Se}}_{\hbox{2}}$ Heterojunctions: A Transmission Electron Microscopy Study

We report on a detailed transmission electron microscopy (TEM) study of physical-vapor-deposited (PVD) CdS /CuIn
_1-x
Ga
_x
Se
₂
(CIGS) heterojunctions prepared at the Mia-Soléproduction 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 -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.