Abstract

A study of metal (Li, Ag) diffusion has been carried out in an archetypal OLED device based on N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine|tris(8-hydroxyquinolinato) aluminum|4,7-diphenyl-1,10-phenanthroline (NPB|Alq3|Bphen). Using single-stack and two-stack tandem OLED structures with variations of layer thicknesses and metal layer placements, we have found that Ag vapor-deposited on Alq3 layer can diffuse or penetrate deep into Alq3, up to ∼2,000 Å, causing luminescence quenching. This diffusion can be substantially prevented by a thin layer of Li or Bphen deposited on Alq3 prior to the deposition of Ag. In contrast, Li diffusion in either Alq3 or Bphen is limited to about 50–100 Å. Li appears to be able to diffuse into Bphen irrespective of the order of Li and Bphen depositions.