Effect of lithium and silver diffusion in single-stack and tandem OLED devices

A study of metal (Li, Ag) diffusion has been carried out in an archetypal OLED based on N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine[tris(8-hydroxyquinolinato) aluminuml],4,7-dipheny1-1,10-phenanthroline (NPBI[ALq(3)]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 Alq(3) layer can diffuse or penetrate deep into Alq(3), up to similar to 2,000 A, causing luminescence quenching. This diffusion can be substantially prevented by a thin layer of Li or Bphen deposited on ALq(3) prior to the deposition of Ag. In contrast, Li diffusion in either Alga or Bphen is limited to about 50-100 angstrom. Li appears to be able to diffuse into Bphen irrespective of the order of Li and Bphen depositions. (C) 2016 Published by Elsevier B.V.