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Evidence for non-isotropic emitter orientation in a red phosphorescent organic light-emitting diode and its implications for determining the emitter's radiative quantum efficiency

 
: Schmidt, T.D.; Setz, D.S.; Flämmich, M.; Frischeisen, J.; Michaelis, D.; Krummacher, B.C.; Danz, N.; Brütting, W.

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Applied Physics Letters 99 (2011), No.16, Art. 163302
ISSN: 0003-6951 (Print)
ISSN: 1077-3118
ISSN: 1931-9401 (online)
English
Journal Article
Fraunhofer IOF ()

Abstract
The efficiency of organic light-emitting diodes is limited as only a fraction of the consumed electrical power is converted into light that is finally extracted to air. Especially, the radiative quantum efficiency of the guest-host system is of interest and should be close to unity to achieve highly efficient devices. We show that the red phosphorescent emitter Ir(MDQ) 2(acac) doped in an -NPD matrix exhibits a profound non-isotropic dipole orientation. Ignoring this feature leads to a significant overestimation of the emitter efficiency. Furthermore, we demonstrate the huge potential for efficiency enhancement of mainly parallel emitter orientation in phosphorescent organic light-emitting diodes.

: http://publica.fraunhofer.de/documents/N-189025.html