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Oriented phosphorescent emitters boost OLED efficiency

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


Organic Electronics 12 (2011), Nr.10, S.1663-1668
ISSN: 1566-1199
Fraunhofer IOF ()
organic light emitting diode; in-situ characterization; emitter orientation; phosphorescent emitter; photoluminescence

The orientation distribution of the emissive sites in a phosphorescent Organic LED has been measured utilizing two independent optical methods. In contradiction to common expectations we find a clearly non-isotropic, predominantly parallel emitter orientation in the well-known triplet emitting guest-host system of Ir(MDQ)2(acac) blended in an alpha-NPD matrix. This result emphasizes the necessity of more sophisticated assumptions on active emitter properties in quantitative optical OLED analysis, and demonstrates a highly promising approach for OLED efficiency optimization.