The development of efficient metal‐free organic emitters with thermally activated delayed fluorescence (TADF) properties for deep‐blue emission is still challenging. A new family of deep‐blue TADF ...emitters based on a donor–acceptor architecture has been developed. The electronic interaction between donor and acceptor plays a key role in the TADF mechanism. Deep‐blue OLEDs fabricated with these TADF emitters achieved high external quantum efficiencies over 19.2 % with CIE coordinates of (0.148, 0.098).
Deep blue emission: An internal quantum efficiency (IQE) of almost 100 % was achieved in organic light‐emitting diodes by a rational molecular design strategy. The organic light‐emitting diodes showed deep‐blue thermally activated delayed fluorescence.
By simple modification of the functional groups on the donor unit, the thermally activated delayed fluorescence (TADF) properties of emitters can easily be manipulated. A series of deep blue to blue ...emissive TADF derivatives is developed, capable of deep‐blue emissions from 403 to 460 nm in toluene. Deep‐blue organic light‐emitting diodes (OLEDs) based on this series of TADF emitters are fabricated, resulting in an electroluminescence peak at 428 nm and a high external quantum efficiency of up to 10.3%. One deep‐blue OLED has achieved the commission internationale de l'eclairage (CIE) coordinates of (0.156, 0.063), which is among the best reported TADF performances for deep‐blue OLEDs with CIEy < 0.07.
A series of deep‐blue to blue emissive TADF derivatives is developed, by which deep‐blue emissions from 403 to 460 nm in toluene are achieved. Deep‐blue OLEDs based on this series of TADF emitters are fabricated, exhibiting an electroluminescence peak at 428 nm and a high external quantum efficiency of up to 10.3%.
A family of organic emitters with a donor–σ–acceptor (D‐σ‐A) motif is presented. Owing to the weakly coupled D‐σ‐A intramolecular charge‐transfer state, a transition from the localized excited ...triplet state (3LE) and charge‐transfer triplet state (3CT) to the charge‐transfer singlet state (1CT) occurred with a small activation energy and high photoluminescence quantum efficiency. Two thermally activated delayed fluorescence (TADF) components were identified, one of which has a very short lifetime of 200–400 ns and the other a longer TADF lifetime of the order of microseconds. In particular, the two D‐σ‐A materials presented strong blue emission with TADF properties in toluene. These results will shed light on the molecular design of new TADF emitters with short delayed lifetimes.
Avoid long delays: A novel molecular design for thermally activated delayed fluorescence (TADF) emitters based on a donor–σ–acceptor motif led to short TADF decay lifetimes of less than 400 ns. Since shorter delayed lifetimes in TADF emitters are highly beneficial for device performance, this design strategy is expected to provide an effective approach to advanced TADF materials.
Organic light-emitting diodes have become a mainstream display technology because of their desirable features. Third-generation electroluminescent devices that emit light through a mechanism called ...thermally activated delayed fluorescence are currently garnering much attention. However, unsatisfactory device stability is still an unresolved issue in this field. Here we demonstrate that electron-transporting n-type hosts, which typically include an acceptor moiety in their chemical structure, have the intrinsic ability to balance the charge fluxes and broaden the recombination zone in delayed fluorescence organic electroluminescent devices, while at the same time preventing the formation of high-energy excitons. The n-type hosts lengthen the lifetimes of green and blue delayed fluorescence devices by > 30 and 1000 times, respectively. Our results indicate that n-type hosts are suitable to realize stable delayed fluorescence organic electroluminescent devices.
In this work, two novel thermally activated delayed fluorescence (TADF) emitters, 2tDMG and 3tDMG, are synthesized for high‐efficiency organic light‐emitting diodes (OLEDs), The two emitters have a ...tilted face‐to‐face alignment of donor (D)/acceptor (A) units presenting intramolecular noncovalent interactions. The two TADF materials are deposited either by an evaporation‐process or by a solution‐process, both of them leading to high OLED performance. 2tDMG used as the emitter in evaporation‐processed OLEDs achieves a high external quantum efficiency (EQE) of 30.8% with a very flat efficiency roll‐off of 7% at 1000 cd m−2. The solution‐processed OLEDs also display an interesting EQE of 16.2%. 3tDMG shows improved solubility and solution processability as compared to 2tDMG, and thus a high EQE of 20.2% in solution‐processed OLEDs is recorded. The corresponding evaporation‐processed OLEDs also reach a reasonably high EQE of 26.3%. Encouragingly, this work provides a novel strategy to address the imperious demands for OLEDs with high EQE and low roll‐off.
A thermally activated delayed fluorescence emitter, 2tDMG, is designed and synthesized based on the donor (D)/acceptor (A) spatially intramolecular noncovalent interaction. The D/A units are connected via a rigid linker, thereby confining them into a close‐packed coplanar configuration for small singlet–triplet splitting energy. 2tDMG achieves a high external quantum efficiency of 30.8% with a low efficiency roll‐off in evaporation‐processed organic light‐emitting diodes (OLEDs).
Much effort has been devoted to developing highly efficient organic light‐emitting diodes (OLEDs) that function through phosphorescence or thermally activated delayed fluorescence (TADF). However, ...efficient host materials for blue TADF and phosphorescent guest emitters are limited because of their requirement of high triplet energy levels. Herein, we report the rigid acceptor unit benzimidazobenzothiazole (BID‐BT), which is suitable for use in bipolar hosts in blue OLEDs. The designed host materials, based on BID‐BT, possess high triplet energy and bipolar carrier transport ability. Both blue TADF and phosphorescent OLEDs containing BID‐BT‐based derivatives exhibit external quantum efficiencies as high as 20 %, indicating that these hosts allow efficient triplet exciton confinement appropriate for blue TADF and phosphorescent guest emitters.
Gotta catch them all: Over 20 % external quantum efficiencies were achieved in both blue thermally activated delayed fluorescence (TADF) and phosphorescent organic light‐emitting diodes (OLEDs) using benzimidazobenzothiazole bipolar host materials.
Efficient sky‐blue organic light‐emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) display a three orders of magnitude increase in lifetime, which is superior to those ...of controlled phosphorescent OLEDs used in this study. The combination of electro‐oxidation and photo‐oxidation of the TADF emitters in their triplet excited‐states is suppressed through molecule design and device engineering.
Metal halide perovskite semiconductors have demonstrated remarkable potentials in solution‐processed blue light‐emitting diodes (LEDs). However, the unsatisfied efficiency and spectral stability ...responsible for trap‐mediated non‐radiative losses and halide phase segregation remain the primary unsolved challenges for blue perovskite LEDs. In this study, it is reported that a fluorene‐based π‐conjugated cationic polymer can be blended with the perovskite semiconductor to control film formation and optoelectronic properties. As a result, sky‐blue and true‐blue perovskite LEDs with Commission Internationale de l'Eclairage coordinates of (0.08, 0.22) and (0.12, 0.13) at the record external quantum efficiencies of 11.2% and 8.0% were achieved. In addition, the mixed halide perovskites with the conjugated cationic polymer exhibit excellent spectral stability under external bias. This result illustrates that π‐conjugated cationic polymers have a great potential to realize efficient blue mixed‐halide perovskite LEDs with stable electroluminescence.
A fluorene‐based π‐conjugated cationic polymer as a multifunctional passivator to suppress non‐radiative processes, improve charge transport properties, and inhibit ion migration for blue mixed‐halide perovskite semiconductors, is reported. As a result, efficient and spectrally stable blue perovskite light‐emitting diodes with emission wavelengths from 485 to 458 nm are achieved.
Two novel pure hydrocarbon compounds, SF33 and SF34, are designed with high triplet energies and stabilities. The efficiency of an SF34/FIrpic‐based device is as high as 22.0%. Moreover, SF33 and ...SF34 are also used as hosts for thermally activated delayed fluorescence organic light‐emitting diodes and achieve external quantum efficiencies in excess of 20.8% and 22.3%, respectively. The pure hydrocarbon host shows a much longer device lifetime than the traditional host 4,4′‐di(N‐carbazolyl)biphenyl.
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