Improving Processability and Efficiency of Resonant TADF Emitters: A Design Strategy

Abstract

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 Mes 3 DiKTa 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 (ΔE ST ), 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 (EQE max ) of 21.1% for Mes 3 DIKTa 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.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.

The design of an extended multiple resonance TADF emitter based on a polycyclic amine/carbonyl system

“…The E ox and E red determined from the DPV peak Scheme 1 Synthetic route for DDiKTa. values are 1.63 and À1.27 V, respectively, showing the expected decreased DE due to increased conjugation compared to those of DiKTa (E ox : 1.65 eV; E red : À1.33 eV vs. SCE; determined from the DPV in MeCN), 21 a trend that is consistent with the DFT calculations. The UV-vis absorption, fluorescence and phosphorescence spectra of DDiKTa in dilute toluene solution are depicted in Fig.…”

“…19,20 We showed that by decorating a MR-TADF emitter, DiKTa, with mesityl groups, Mes 3 DiKTa, undesired aggregation caused quenching and excimer emission can be largely mitigated. 21 Herein, we report the emitter DDiKTa, which is a dimeric compound consisting of two MR-TADF DiKTa units (Scheme 1). The slightly increased conjugation present in DDikTa compared to DiKTa contributes to a modest red-shifting of the emission; however, the new compound conserves its MR-TADF status.…”

A Brief History of OLEDs—Emitter Development and Industry Milestones

“…Recently, in 2020, Zysman‐Colman and co‐workers designed and synthesized a molecule based on a fused amine/carbonyl system. [ 117 ] Due to the opposite resonance effect of a nitrogen and oxygen atom in Mes 3 DiKTa (see Figure 12), the HOMO and LUMO were separated, resulting in a small Δ E ST (0.26 eV). Excellent OLED device performance was realized with an EQE of 21.1%, sky‐blue EL emission at 480 nm, and an FWHM of 37 nm.…”

Simple Acridan-Based Multi-Resonance Structures Enable Highly-Efficient Narrowband Green TADF Electroluminescence

“…[5][6][7][8] This contradiction undoubtedfully sets an obstacle to obtain highly efficient emitter, and the large structural reorganization occurred in the excited state would cause broad emission spectra and increased nonradiative decay channels, eventually weakening the performances of corresponding devices. [9][10][11][12][13][14][15] Instead of the conventional D-A configured emitters, a unique category of multiresonance TADF (MR-TADF) molecules based on fused polycyclic aromatics was lately proposed by Hatakeyama et. al.…”

“…two magnitudes higher than DABNA (9.9×10 3 s -1 ) recorded at the same condition, indicating efficient tripletharvesting that might involve upper excited states (Table S1). [9,21,24] These represented promising characteristics of TADF dye for fabricating OLED with high performance. The suitable energy cascade between functional layers as well as ideal charge carrier injection of the emitter ensured relatively low turn-on voltages (Von, at 1 cd m -2 ) below 3.5 V for both devices (Fig.…”