Improving Processability and Efficiency of Resonant TADF Emitters: A Design Strategy
Authors/Creators
- 1. Organic Semiconductor Centre EaStCHEM School of Chemistry University of St Andrews St Andrews KY16 9ST, UK
- 2. Organic Semiconductor Centre SUPA School of Physics and Astronomy University of St Andrews St Andrews KY16 9SS, UK
- 3. Soft Matter Optoelectronics BIMF & BPI University of Bayreuth Universitätsstraße 30, 95447 Bayreuth, Germany
- 4. Laboratory for Chemistry of Novel Materials University of Mons 7000 Mons, Belgium
- 5. Unité de Chimie Physique Théorique et Structurale & Laboratoire de Physique du Solide Namur Institute of Structured Matter Université de Namur
Description
A new design strategy is introduced to address a persistent weakness with resonance thermally activated delayed fluorescence (R-TADF) emitters to reduce aggregation-caused quenching effects, which are identified as one
of the key limiting factors. The emitter Mes3DiKTa shows an improved photoluminescence quantum yield of 80% compared to 75% for the reference DiKTa in 3.5 wt% 1,3-bis(N-carbazolyl)benzene. Importantly, emission from aggregates, even at high doping concentrations, is eliminated and aggregation-caused quenching is strongly curtailed. For both molecules, triplets are almost quantitatively upconverted into singlets in electroluminescence, despite a significant (≈0.21 eV) singlet-triplet energy gap (ΔEST), in line with correlated quantum-chemical calculations, and a slow reverse intersystem crossing. It is speculated that the lattice stiffness responsible for the narrow fluorescence and phosphorescence emission spectra also protects the triplets against nonradiative decay. An improved maximum external quantum efficiencies (EQEmax) of 21.1% for Mes3DIKTa compared to the parent DiKTa (14.7%) and, importantly, reduced efficiency roll-off compared to literature resonance TADF organic light-emitting diodes (OLEDs), shows the promise of this design strategy for future design of R-TADF emitters for OLED applications.
Files
adom.201901627.pdf
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