Interfacial microstructure and defect analysis in Cu(In,Ga)Se([sub]2)-based multilayered film by analytical transmission electron microscopy and focused ion beam

Interfacial microstructures of Cu(In,Ga)Se2(CIGS)-based multilayered film are closely characterized by TEM (transmission electron microscopy), SEM (scanning electron microscopy) and FIB (focused ion beam). A cross-sectional TEM, energy dispersive X-ray spectroscopy and energy-filtered TEM reveal that a pronounced Cu diffusion occurs across the interface of the CdS/CIGS, which leads to a large amount of Cu rich in the CdS layer and a Cu-deficient sub-surface in the CIGS layer as well as a rough interfacial structure. TEM studies further reveal that the interface microstructures in the multilayered film are dissimilar, both ZnO/CdS and CdS/CIGS interfaces are strongly bonded whereas the CIGS/Mo interface is weakly bonded and interface separation occasionally occurs. Mo back contact layer shows a well adhesion to glass substrate.Detailed observation on defects in the CIGS-based multilayered film is carried out by 3D (3-dimensional) FIB and SEM techniques. Sequential 2D (2-demensional) cross-sectioning shows that dominant growth-defects in the CIGS and top SiO2 layers are micro-scale crack, appearing as diversified morphologies. The micro-scale crack in the CIGS layer is possibly released by propagating into the adjacent layer while the crack in the SiO2 layer is relieved usually by forming a small particle behind. It is noted that in the multilayered film the interface frequently acts as crack initiation sites due to distinct thermal expansion coefficients.