Effects of alternate doped structures on organic electroluminescent devices

Two organic electroluminescent (EL) devices with alternate doped structures have been fabricated under high vacuum deposition system. One of the structures consists of alternating layers of doped tris(8-quinolinolato) aluminum (Alq) and undoped Alq. The other consists of alternating layers of doped N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) and undoped NPB. Effects of the designed structures on blue-shift of the emission peak energy and on the brightness and efficiency of the organic EL devices are observed. Uniquely, the efficiency of the device with the latter structure is relatively independent on the drive voltage in a wide range from 5 to 13V. (C) 2002 Elsevier Science B.V. All rights reserved.