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Efficiency Enhancement of Organic Light‐Emitting Diodes Incorporating a Highly Oriented Thermally Activated Delayed Fluorescence Emitter
Author(s) -
Mayr Christian,
Lee Sae Youn,
Schmidt Tobias D.,
Yasuda Takuma,
Adachi Chihaya,
Brütting Wolfgang
Publication year - 2014
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201400495
Subject(s) - common emitter , oled , materials science , quantum efficiency , optoelectronics , photoluminescence , radiative transfer , exciton , fluorescence , quantum yield , diode , optics , layer (electronics) , nanotechnology , physics , condensed matter physics
An organic light‐emitting diode (OLED) with the blue emitter CC2TA showing thermally activated delayed fluorescence (TADF) is presented exhibiting an external quantum efficiency ( η EQE) of 11% ± 1%, which clearly exceeds the classical limit for fluorescent OLEDs. The analysis of the emission layer by angular dependent photoluminescence (PL) measurements shows a very high degree of 92% horizontally oriented transition dipole moments. Excited states lifetime measurements of the prompt fluorescent component under PL excitation yield a radiative quantum efficiency of 55% of the emitting species. Thus, the radiative exciton fraction has to be significantly higher than 25% due to TADF. Performing a simulation based efficiency analysis for the OLED under investigation allows for a quantification of individual contributions to the efficiency increase originating from horizontal emitter orientation and TADF. Remarkably, the strong horizontal emitter orientation leads to a light‐outcoupling efficiency of more than 30%.