Excitonic Degradation Mechanisms in Phosphorescent and Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes

초록

In this study, the degradation mechanisms of triplet exciton harvesting organic light-emitting diodes (OLEDs), namely, phosphorescent OLEDs and thermally activated delayed fluorescence (TADF) OLEDs, are investigated. Two common green emitters, fac-tris(2-phenylpyridine) iridium (III) (Ir(ppy)3) and 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), are doped in an exciplex-forming cohost, and their degradation processes are comprehensively evaluated using various analytical approaches. Triplet-triplet-annihilation induces the formation of defects, such as charge traps and exciton quenchers, triggering luminance loss during the device aging process of Ir(ppy)3-based phosphorescent OLEDs. Electron trapping-induced triplet-polaron annihilation and narrow emission zone severely impair the device stability of 4CzIPN-based TADF OLEDs, despite limited material degradation and charge trap formation. Thermally activated delayed fluorescence devices suffer from triplet-polaron annihilation and trap formation accelerating degradation in a narrower effective recombination zone, while exciton quenchers due to triplet-triplet annihilation dominate device instability in phosphorescent organic light-emitting diodes.image

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