Characterizing thin film PV devices with Low-Incidence Surface Milling by Focused Ion Beam

We used Low-Incidence Surface Milling by Focused Ion Beam (LISM-FIB) at glancing incident angle from the film surface to expose complete structures of thin-film CdTe device for scanning electron microscopic (SEM) investigation. Specific sample preparation procedures of this method are described. This method enables observation of micro-features in the thickness dimension of thin film devices in a planar view for various microscopic studies, particularly electron microscopy. We have observed that a ~52 nm thick buffer layer in Pilkington TEC glass is extended to approximately 1 μm from the top view in SEM. We also provide two consistent methods for identifying the exposed layers. An interesting feature of a porous layer of ~100 nm at CdTe side of the CdS/CdTe junction has been observed for the first time. Impacts of such a layer on thin CdTe PV devices are discussed.