The degradation mechanism of phosphorescent-dye-doped polymer light-emitting diodes ͑PLEDs͒ is investigated. The active medium of our PLED is a polymer blend comprising poly͑vinylcarbazole͒ ͑PVK͒, ͓2-͑4-biphenylyl͒-5-͑4-tert-butyl-phenyl͒-1,3,4-oxadiazole͔ ͑t-PBD͒, and platinum͑II͒-2,8,12,17-tetraethyl-3,7,13,18-tetramethylporphyrin ͑PtOX͒. The cyclic voltammetry result shows that the reductive reversibility of PtOX is poor. This result suggests that PLED doped with PtOX is not stable if PtOXs

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... rap electrons and turn into anionic PtOX species. This was indeed verified by fabricating single-layer PLEDs with various amounts of electron-transporting material, t-PBD. A slower degradation rate was observed from the devices with higher concentration of t-PBD, because of the reduction of the electron accumulation at the PtOX sites. The half decay lifetime of our phosphorescent polymer LED has been improved by a factor of ϳ40, from 1.2 to 45 h.