Stable blue phosphorescent organic LEDs that use polariton-enhanced Purcell effects.

Phosphorescent organic light emitting diodes (PHOLEDs) feature high efficiency 1,2 , brightness, and color tunability suitable for both display and lighting applications 3 . However, overcoming the short operational lifetime of blue PHOLEDs remains one of the most challenging high-value problems in the field of organic electronics. Their short lifetimes originate from the annihilation of high energy, long-lived blue triplets that leads to molecular dissociation 4-7 . The Purcell effect, the enhancement of the radiative decay rate in a microcavity, can reduce the triplet density and hence the probability of destructive high-energy triplet-polaron 5,6 and triplet-triplet annihilation events 4,5,7,8 . Here, we introduce the polariton-enhanced Purcell effect in blue PHOLEDs. We find plasmon-exciton-polaritons 9 (PEPs) significantly increase the strength of the Purcell effect and achieves an average Purcell factor of 2.4 ± 0.2 over a 50 nm thick emission layer in a blue PHOLED. A 5.3-fold improvement in LT90 (the time for the PHOLED luminance to decay to 90% of its the initial value of a cyan-emitting Ir-complex device is achieved compared to its use in a conventional PHOLED. Shifting the chromaticity coordinates to (0.14, 0.14) and (0.15, 0.20) into the deep blue, the Purcell-enhanced devices achieve 10-14 times improvement over similarly deep blue PHOLEDs, with one structure reaching the longest Ir-complex device lifetime of LT90 = 140 ± 20 h reported to date 10-21 . The polariton-enhanced Purcell effect and microcavity engineering provide new possibilities for extending deep blue PHOLED lifetimes.