Energy transfer from exciplexes to dopants and its effect on efficiency of organic light-emitting diodes
- 15 December 2011
- journal article
- research article
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 110 (12), 124519
- https://doi.org/10.1063/1.3672836
Abstract
We report that an exciplex is formed at the interface between the N,N′-dicarbazolyl-4-4′-biphenyl (CBP) and the bis-4,6-(3,5-di-3-pyridylphenyl)-2-methylpyrimidine (B3PYMPM), which are widely used as an emitting layer (EML) host and an electron transporting layer (ETL) for high efficiency, green phosphorescent, organic light-emitting diodes(OLEDs), respectively. The intensity of the exciplex emission is almost proportional to the inverse square of the fac-tris(2-phenylpyridine) iridium [Ir(ppy)3] concentration of the EML. Meanwhile, the efficiency of the OLEDs increases as the concentration of the Ir(ppy)3 increases. This enhancement of the efficiency and the decrease of the exciplex emission originates from the increase in the energy transfer rate from the exciplex to the dopants, due to the decrease in the distance between the exciplex and the dopant. The energy transfer processes were successfully analyzed using the Förster energy transfer mechanism. The high-efficiency OLEDs were obtained through the energy transfer from the exciplex to the dopant at the EML/ETL interface. The external quantum efficiency of the OLED reached 20.1% when the concentration of the Ir(ppy)3 is 6 mol. %. In addition, we investigated the relationship between the efficiency roll-off of the OLEDs and the energy transfer from the exciplex to the dopant by inserting a thin, undoped CBP layer at the EML/ETL interface.Keywords
This publication has 25 references indexed in Scilit:
- Outcoupling efficiency of organic light emitting diodes and the effect of ITO thicknessOrganic Electronics, 2010
- Hydroxynaphthyridine-Derived Group III Metal Chelates: Wide Band Gap and Deep Blue Analogues of Green Alq3 (Tris(8-hydroxyquinolate)aluminum) and Their Versatile Applications for Organic Light-Emitting DiodesJournal of the American Chemical Society, 2008
- Low roll-off of efficiency at high current density in phosphorescent organic light emitting diodesApplied Physics Letters, 2007
- High Luminous Efficiency Blue Organic Light-Emitting Devices Using High Triplet Excited Energy MaterialsJapanese Journal of Applied Physics, 2007
- Ultra High Efficiency Green Organic Light-Emitting DevicesJapanese Journal of Applied Physics, 2006
- Combinatorial study of exciplex formation at the interface between two wide band gap organic semiconductorsApplied Physics Letters, 2006
- New charge-carrier blocking materials for high efficiency OLEDsOrganic Electronics, 2003
- Exciplex formation at the organic solid/solid interface and tuning of the emission color in organic electroluminescent devicesJournal of Luminescence, 2000
- Efficient blue luminescence of a conjugated polymer exciplexMacromolecules, 1994
- 10th Spiers Memorial Lecture. Transfer mechanisms of electronic excitationDiscussions of the Faraday Society, 1959