Operating lifetime of phosphorescent organic light emitting devices

We investigate the continuous operating lifetime of organic light emitting devices (OLEDs) using the phosphorescent dopant, $\text{2,3,7,8,12,13,17,18-}\mathrm{octaethyl}\text{-21H,23H-}\mathrm{porphine}$ platinum (II) as the light emitting molecule. We characterize devices based on two different electron transporting hosts: tris-(8-hydroxyquinoline) aluminum and ${\text{4,4}}^{\prime }{\mathrm{-N,N}}^{\prime }$ -dicarbazolyl-biphenyl (CBP). The OLEDs lose $\text{∼25\%}$ 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 ${\text{>10}}^7$ h at a mean current density of $\text{10\hspace{0.5em}}{\mathrm{mA/cm}}^2$ 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.