Exciplex-Forming Co-host for Organic Light-Emitting Diodes with Ultimate Efficiency

• Published in: Advanced functional materials 2013-10, Vol.23 (39), p.4914-4920
• Main Authors: Park, Young-Seo, Lee, Sunghun, Kim, Kwon-Hyeon, Kim, Sei-Yong, Lee, Jeong-Hwan, Kim, Jang-Joo
• Format: Article
• Language: English
• Subjects: co-hosts; Dopants; efficiency roll-off; Electric potential; Energy transfer; exciplexes; Organic light emitting diodes; Power efficiency; Quantum efficiency; Voltage
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201300547

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. Using an exciplex‐forming co‐host, an organic light‐emitting diode (OLED) with ultimate efficiency is produced. The OLED has a low turn‐on voltage of 2.4 V, a very high external quantum efficiency (EQE) of 29.1%, a very high power efficiency of 124 lm W−1, and 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.