Examination of growth kinetics of copper rich Cu(In,Ga)Se2-films using synchrotron energy dispersive X-ray diffractometry

Multistage evaporation processes are capable of producing state of the art Cu(In,Ga)Se2-thin-films for use in solar cells. The morphology of films grown by this process changes in a rapid manner as soon as their composition becomes copper rich beyond stoichiometry. For investigation of the structural changes, synchrotron radiation energy-dispersive X-ray diffractometry was used. Cu-rich and Cu-poor absorbers with an in-depth gallium gradient were grown by physical vapor deposition. These were transferred to a thermal processing reaction chamber which allows in-situ characterization. In the Cu-rich case changes in energy and shape of the measured diffraction signals caused by heating the samples could be attributed to the leveling of indium and gallium gradients within the layer. As a secondary method glow discharge optical emission spectroscopy was used to confirm this result. Cu-poor reference samples did not show a similarly significant intermixing of indium and gallium during annealing. We conclude, that the presence of excess copper in the layer at elevated temperatures (>470∘C) causes interdiffusion of indium and gallium.