Journal
ADVANCED FUNCTIONAL MATERIALS
Volume 23, Issue 39, Pages 4914-4920Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.201300547
Keywords
exciplexes; co-hosts; energy transfer; efficiency roll-off; organic light emitting diodes
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Funding
- Industrial strategic technology development program [10035225]
- MKE/KEIT
- Korea Evaluation Institute of Industrial Technology (KEIT) [10035225] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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Phosphorescent organic light-emitting diodes (OLEDs) with ultimate efficiency in terms of the external quantum efficiency (EQE), driving voltage, and efficiency roll-off are reported, making use of an exciplex-forming co-host. This exciplex-forming co-host system enables efficient singlet and triplet energy transfers from the host exciplex to the phosphorescent dopant because the singlet and triplet energies of the exciplex are almost identical. In addition, the system has low probability of direct trapping of charges at the dopant molecules and no charge-injection barrier from the charge-transport layers to the emitting layer. By combining all these factors, the OLEDs achieve a low turn-on voltage of 2.4 V, a very high EQE of 29.1% and a very high power efficiency of 124 lm W-1. In addition, the OLEDs achieve an extremely low efficiency roll-off. The EQE of the optimized OLED is maintained at more than 27.8%, up to 10 000 cd m(-2).
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