Operating lifetime of phosphorescent organic light emitting devices

We investigate the continuous operating lifetime of organic light emitting devices (OLEDs) using the phosphorescent dopant, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum (II) as the light emitting molecule. We characterize devices based on two different electron transporting hosts: tris-(8-hydroxyquinoline) aluminum and 4,4'-N,N'-dicarbazolyl-biphenyl (CBP). The OLEDs lose similar to 25% of their luminance in the first 50 h of operation, followed by extremely slow degradation with negligible growth of dark spots. The device lifetime of CBP-based phosphorescent OLEDs projected to 50% initial brightness is > 10(7) h at a mean current density of 10 mA/cm(2) under 50% duty cycle pulsed operation. These extremely long lifetimes are speculated to be an intrinsic property of electrophosphorescent OLEDs, where radiative phosphors significantly shorten the lifetime of potentially reactive triplet states in the conductive host material. (C) 2000 American Institute of Physics. [S0003-6951(00)02018-0].