Diffusion of Ag into Organic Semiconducting Materials: A Combined Analytical Study Using Transmission Electron Microscopy and X-ray Reflectivity

This study shows that the morphology of organic/metal interfaces strongly depends on process parameters and the involved materials. The interface between organic n-type blocking layer materials and the top Ag cathode within an organic photodiode was investigated. Ag was deposited on either amorphous tris-8-hydroxyquinolinato-aluminum (Alq(3)) or crystalline 4,7-diphenyl-1,10-phenanthroline (Bphen) using different deposition techniques such as electron beam deposition, ion beam sputtering, and vacuum thermal evaporation at various deposition rates. The interfaces were studied by transmission electron microscopy and X-ray reflectivity. It was found that Bphen does not show any Ag diffusion no matter which deposition technique was used, whereas the Ag diffusion into Alq(3) depends on the deposition technique and the deposition rate. The highest amount of Ag diffusion into Alq(3) occurred by using thermal vacuum deposition at low deposition rates.