High operational stability of electrophosphorescent devices

Abstract

Electrophosphorescent devices with fac-tris(2-phenylpyridine)iridium as the green emitting dopant have been fabricated with a variety of hole and exciton blocking materials. A device with aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq) demonstrates an efficiency of 19 cd/A with a projected operational lifetime of 10 000 h, operated at an initial brightness of 500 cd/m²; or 50 000 h normalized to 100 cd/m². An orange-red electrophosphorescent device with iridium(III) $\mathrm{bis}\text{(2-}\mathrm{phenylquinolyl}{\mathrm{-N,C}}^{2^{\prime }})\mathrm{acetylacetonate}$ as the dopant emitter and BAlq as the hole blocker demonstrates a maximum efficiency of 17.6 cd/A with a projected operational lifetime of 5000 h at an initial brightness of 300 cd/m²; or 15 000 h normalized to 100 cd/m². The average voltage increase for both devices is <0.3 mV/h. The device operational lifetime is found to be inversely proportional to the initial brightness, typical of fluorescent organic light emitting devices.