Abstract
An organic light-emitting diode (OLED) with the blue emitter CC2TA showing thermally activated delayed fluorescence (TADF) is presented exhibiting an external quantum efficiency (ηEQE) 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%.
Original language | English |
---|---|
Pages (from-to) | 5232-5239 |
Number of pages | 8 |
Journal | Advanced Functional Materials |
Volume | 24 |
Issue number | 33 |
DOIs | |
State | Published - 3 Sep 2014 |
Keywords
- emitter orientation
- optical simulation
- organic light-emitting diodes (OLEDs)
- radiative exciton fraction
- thermally activated delayed fluorescence