Solution Processed Red Phosphorescent Organic Light-Emitting Diodes with Green Phosphorescent Ir Sensitizer

Abstract

We fabricated the organic light-emitting diodes (OLEDs) with sensitizer by solution process. The addition of sensitizer into the emission layer improved the device efficiency. 4,4′-N,N′-dicarbazole-biphenyl (CBP), bis(2-phenylquinoline)iridium(III) (acetylacetonate) [Ir(pq)₂(acac)], tris(2-phenylpyridine)iridium [Ir(ppy)₃] were used as host, red emitting dopant, and sensitizer, respectively. The sensitizer leads to the cascade energy transfer from the host into the red emitting dopant. The doping concentration of sensitizer was varied as 0∼20 wt% and optimized. As a result, the device with 5% Ir(ppy)₃ shows the luminous efficiency, power efficiency, and quantum efficiency of 5.1 cd/A, 4.0 lm/W, and 3.0%, respectively. These efficiencies are about 3 times as high as that of device without sensitizer.

Keywords:

• Cascade energy transfer
• organic light-emitting diode
• sensitizer

Acknowledgment

This work was supported by Energy Resources Technology Development program (No. 2007-E-CM11-P-07) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Knowledge Economy and Strategy Technology Development program (No. 10030834) from Ministry of Knowledge Economy (MKE). Moreover, this research was also supported by the ERC program of the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea Ministry of Education, Science and Technology (MEST) (No. R11-2007-045-03001-0).