Blue Thermally Activated Delayed Fluorescence Research Articles

Rational Molecular Design Enables Efficient Blue TADF−OLEDs with Flexible Graphene Substrate

AbstractObservation of thermally activated delayed fluorescence (TADF) in conjugated systems redefined the molecular design approach to realize highly efficient organic light emitting diodes (OLEDs) in the early 2010s. Enabling effective reverse intersystem crossing (RISC) by minimizing the difference between singlet and triplet excited state energies (ΔEST) is proven to be a widely applicable and fruitful approach, which results in remarkable external quantum efficiencies (EQE). The efficacy of RISC in these systems is mainly dictated by the first‐order mixing coefficient (λ), which is proportional to spin‐orbit coupling (HSO) and inversely proportional to ΔEST. While minimizing ΔEST has been the focus of the OLED community over the last decade, the effect of HSO in these systems is largely overlooked. Here, molecular systems with increased HSO are designed and synthesized by substituting selected heteroatoms of high‐performance TADF materials with heavy‐atom selenium. A new series of multicolor TADF materials with remarkable EQEs are achieved. One of these materials, SeDF‐B, results in pure blue emission with EQEs approaching 20%. Additionally, flexible graphene‐based electrodes are developed for OLEDs and revealed to have similar performance as standard indium tin oxide (ITO) in most cases. These devices are the first report of TADF based OLEDs that utilize graphene‐based anodes.

Towards Efficient Blue Delayed-Fluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Towards Efficient Blue Delayed-Fluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Synergistic Control of Hot Exciton Relaxation and Exciton–Polaron Dispersion Using a Polaron Retarder for Long Lifetime in Thermally Activated Delayed Fluorescence Organic Light‐Emitting Diodes

AbstractThe operational stability of thermally activated delayed fluorescence (TADF) organic light‐emitting diodes (OLEDs) is an essential property to utilize their efficient triplet harvesting ability and reduce the usage of expensive metal complexes in commercial applications. In this study, a device strategy for extending the device lifetime using the synergistic effects of the hot exciton relaxation and polaron dispersion is demonstrated. By doping a polaron retarder to a conventional TADF‐emitting layer, the lifetime of the blue TADF device is enhanced by 98% at an initial luminance of 1000 cd m−2. Kinetic modeling describing the device degradation indicates that the concurrent contribution via the suppression of exciton and polaron interactions and hot exciton‐related degradation are the origin of the lifetime enhancement. It is demonstrated that the introduction of the polaron retarder finely fits to the ground and that the excited energetic relationship of the host–dopant structure simultaneously improves the operation lifetime and device efficiency without sacrificing other device characteristics.

Ultrapure Blue Thermally Activated Delayed Fluorescence (TADF) Emitters Based on Rigid Sulfur/Oxygen-Bridged Triarylboron Acceptor: MR TADF and D-A TADF.

Organic light-emitting diodes (OLEDs) still face a significant challenge in finding blue thermally activated delayed fluorescence (TADF) emitters that can achieve narrowband emission and high efficiency. In this work, we successfully design and synthesize a novel kind of TADF emitters based on rigid sulfur/oxygen-bridged triarylboron acceptor for ultrapure blue with narrowband electroluminescence. Time-dependent density functional theory (TD-DFT) calculations and photophysical results indicate the different intramolecular charge-transfer (ICT) character of two emitters. Benefiting from the rigid aromatic framework, both emitters exhibited deep-blue emission at 444 and 447 nm with a small full-width at half-maximum (fwhm) of about 33 nm, and a small singlet (S1)-triplet (T1) energy gap (ΔEST) of 0.23 and 0.36 eV. Consequently, OLEDs based on PhCz-TOSBA and TPA-TOSBA exhibit deep blue electroluminescence at 456 nm with fwhm of about 55 nm, affording high external quantum efficiencies (EQEs) of 16.69% with CIE coordinates of (0.14, 0.15) and 16.65% with CIE coordinates of (0.14, 0.12), respectively. These findings show that PhCz-TOSBA and TPA-TOSBA are superior emitters in ultrapure blue TADF devices.

Molecular design of blue thermally activated delayed fluorescent emitters for high efficiency solution processable OLED via an intramolecular locking strategy

Realizing high-efficiency blue emission in solution processable organic light-emitting diode (OLED) with thermally activated delayed fluorescent (TADF) emitters is still a big challenge. To suppress the non-radiative process in TADF emitters, compound DPS-BF-Ac featuring a donor-π-acceptor skeleton is prepared via intramolecular cyclization, in which diphenylsulfone (DPS), acridine (Ac) and furan derivatives are regarded as the donor, acceptor and π linker, respectively. Then, compounds DPS-Ph-Ac, DPS-OMe-Ac and DPS-OH-Ac with different π linkers are investigated to further explore the molecular structure–property relationship. All compounds show promising blue emission with a clear TADF character. Single crystal analysis demonstrate that compound DPS-BF-Ac possesses almost a perpendicular geometry between donor and acceptor groups and expanded molecular rigidity, leading to a smaller singlet–triplet energy difference and greatly improved emission efficiency. A remarkable external quantum efficiency (EQEmax) of ∼ 25 % is achieved for the DPS-BF-Ac based solution OLED, concomitant with the emission peak at ∼ 480 nm. Using DPS-BF-Ac and PO-01 as the blue and red dopant, respectively, the white OLED exhibits an EQEmax of ∼ 29 %. This research shows that intramolecular cyclization is an effective strategy for designing high efficiency solution-processable blue TADF emitter.

Interfacial Exciplex Host to Release Interfacial Accumulated Charges for Highly Efficient and Bright Solution‐Processed White Organic Light‐Emitting Diodes

AbstractWhite organic light‐emitting diodes (WOLEDs) have attracted extensive attention and are considered as an ideal next‐generation lighting source. However, maintaining high efficiency and high color rendering index (CRI) in WOLEDs still faces great challenges. The charges accumulation at the interface leads to nonradiative recombination and further Joule heat, which is a source of efficiency decrease and device degradation. In this paper, the interfacial exciplex is designed as the host for high efficiency; the blue thermally activated delayed fluorescence (TADF) material and the red phosphorescent material are employed as guests for high CRI. Due to the interfacial exciplex host, electrons don't need to overcome the potential barrier to inject into the light‐emitting layer, but can directly compound with holes at the interface, so as to release the interfacial accumulated charges and improve the recombination efficiency of carriers. Also, a suitable energy level gradient for hole injection transmission is constructed. Finally, WOLEDs with a current efficiency of 52.8 cd A−1, an external quantum efficiency of 22.9 %, the Commission Internationale de I'Eclairage (CIE) coordinate of (0.35,0.39), and the high CRI of 80 are obtained, which are the highest values ever achieved by the solution processed WOLEDs based on blue TADF emitters.

Highly Efficient Blue Thermally Activated Delayed Fluorescence Emitters Based on Multi-Donor Modified Oxygen-Bridged Boron Acceptor.

The employment of thermally activated delayed fluorescence (TADF) emitters is one of the most promising ways to realize the external quantum efficiency (EQE) of over 25% for organic light-emitting diodes (OLEDs). In addition, the TADF emitter based on oxygen-bridged boron (BO) fragment can maintain blue emission with high color purity. Herein, we constructed two blue TADF emitters, 3TBO and 5TBO, for OLEDs application. Both emitters consist of three donors linked at the oxygen-bridged boron acceptor. OLED devices based on 3TBO and 5TBO exhibited both high excellent device efficiency and high color purity with a maximum EQE; full-width at half-maximum (FWHM); and CIE coordinates of 17.3%, 47 nm, (0.120, 0.294), and 26.2%, 57 nm, (0.125, 0.275), respectively.

Small dose of phosphorescent dopant enabling high efficiency and bright solution-processed sky-blue organic light-emitting diodes

In this work, we demonstrate the simultaneous use of thermally activated delayed fluorescence (TADF) material and a small dose of phosphorescent material to construct TADF-phosphorescent mixed emitting system, which enables the OLED exhibiting high device performance. To achieve this, a blue TADF material, 10,10'- (4,4′-Sulfonylbis (4,1-phenylene)) bis (9,9-dimethyl-9,10-dihydroacridine) (DMAC-DPS), and a conventional blue phosphor with similar emission color to DMAC-DPS, Bis [2-(4,6-difluorophenyl) pyridinato-C2, N] (picolinato) iridium (III) (FIrpic), are incorporated together into 1,3-Bis(carbazol-9-yl) benzene (mCP) host to constructed the mixed emitting system. The device has achieved the maximum current efficiency of 21.1 cd/A with FIrpic concentration of 1%; meanwhile, the luminance of the device has also been improved. There merits are superior to the optimized TADF OLED and the optimized phosphorescent OLED based on 16% FIrpic in device efficiency. In view of the expensive price of phosphorescent materials, the strategy presented here will greatly reduce the material cost without the cost of device performance. Through investigations on the energy transfer process and the film morphology in the mixed emitting system, the main cause of the improvement has been unveiled. The study may provide a simple but effective strategy to achieve low-cost, high-performance solution-processed OLEDs.

Electron-withdrawing bulky group substituted carbazoles for blue TADF emitters: Simultaneous improvement of blue color purity and RISC rate constants

Carbazole is a weak electron donor suitable to construct blue thermally activated delayed fluorescence (TADF) emitters, but the less repulsion effect of its five-member-ring structure can't guarantee the frontier molecular orbital separation and TADF feature. A group of carbazole-π-triazine based blue fluorescence emitters is designed by introducing the steric hindrance groups with different electronic properties at the donor or π-bridge. When electron-withdrawing pyridyl with moderate steric hindrance is introduced to the 1-site of 3,6-Di-tert-butyl-9H-carbazole, PyBuCz-TRZ and PyBuCz-MeTRZ gain the blue-shifted TADF. The observed charge transfer triplet excited state within the donor (3CTD) between carbazole and pyridyl units has different spatial orbital angular momentum and allowed spin-orbit coupling (SOC) with the charge transfer singlet excited state (1CT) of the whole molecule from carbazole donor to triazine acceptor, thus, acting as the media state to facilitate efficient multi-channel reverse intersystem crossing (RISC) process. This is the first time to introduce an electron-withdrawing group into the 1-position of carbazole donors to construct TADF molecules, not only achieving the blue-shifted TADF at 455 nm but also improving the external quantum efficiency to 15.3% in organic light-emitting diodes. This donor strategy should be valid to design more blue TADF materials.

Management of Multi‐Energy‐Transfer Channels and Exciton Harvesting for Power‐Efficient White Thermally Activated Delayed Fluorescence Diodes

AbstractWhite organic light‐emitting diodes (WOLEDs) based on thermally activated delayed fluorescence (TADF) emitters attract considerable attention owing to the advantages of full exciton harvesting, low cost, and environmental sustainability. However, compared to phosphorescent counterparts, the power efficiencies of TADF‐based WOLEDs lag behind. Herein, a newly synthesized TADF emitter named DPPZ‐DMAC featuring near‐zero singlet−triplet splitting and high photoluminescence quantum yield (91.6%) is utilized as an ideal orange‐yellow dopant for realizing a power‐efficient WOLED with a mixed system consisting of a blue TADF sensitizer and a conventional fluorescent host. The balanced carrier transport, modulated energy transfer and exciton harvesting, and less exciton quenching can be realized simultaneously. Eventually, a warm WOLED is achieved with an external quantum efficiency of ≈30%, power efficiency of >80 lm W‐1, turn‐on voltage of 2.5 V, and correlated color temperature of 3600 K. Moreover, the color coordinate of the resulting white emission is close to the standard blackbody radiation and can be precisely tuned inside the specific quadrangles given by the American National Standard Institute (ANSI), revealing a large prospect for indoor health lightings.

High-efficiency and low roll-off deep-blue OLEDs enabled by thermally activated delayed fluorescence emitter with preferred horizontal dipole orientation

• Molecular engineering by linear extension resulted in two blue TADF emitters. • The two emitters exhibited high photoluminescence quantum yields and preferred horizontal dipole orientation. • Deep-blue TADF OLEDs achieved external quantum efficiency of up to 29.3% and low efficiency roll-off. Highly efficient blue thermally activated delayed fluorescence (TADF) materials with high horizontal dipole orientation (Θ // ) remain a big challenge due to the concentration quenching effects and serious efficiency roll-offs in their corresponding organic light-emitting diodes (OLEDs). We herein report two novel TADF compounds, namely 2TDBA-SBA and TDBA-SBA, which were facilely synthesized by utilizing a rigid oxygen-bridged cyclized triarylboron-based unit (TDBA) as the acceptor and a spiro acridine (SBA) as the donor. Benefiting from the rigid and planar skeleton of the acceptor and the linear molecular shape, high Θ // s and photoluminescence quantum yields (PLQYs) of ∼ 90% were achieved. Significantly, TDBA-SBA exhibited excellent TADF properties with a short delayed fluorescence lifetime of only 684 ns and narrow full-width at half-maximum (FWHM) of 44 nm in solution state, accompanied by the high PLQYs of over 80% at high doping concentrations, manifesting the alleviated exciton quenching effects. Consequently, OLEDs based on TDBA-SBA achieved a high maximum external quantum efficiency (EQE) of 29.3% and a maximum brightness of 27663 cd cm −2 . Importantly, an EQE over 20% was realized even at the high brightness of 10000 cd cm −2 , signifying a small efficiency roll-off.

Boron-Based Multi-Resonance TADF Emitter with Suppressed Intermolecular Interaction and Isomer Formation for Efficient Pure Blue OLEDs.

Multi-resonance (MR) thermally activated delayed fluorescent (TADF) emitters are highly attractive due to their superior color purity as well as efficient light-harvesting ability from singlets and triplets. However, boron and nitrogen-based MR-TADF emitters suffer from their strong π-π interaction owing to their rigid flat cores. Herein, a boron-based multi-resonance blue TADF emitter with suppressed intermolecular interaction and isomer formation is developed through a simple synthetic process by introducing meta-xylene and meta-phenyphenyl groups to the core. The MR-TADF emitter, mBP-DABNA-Me, shows a narrowband blue emission with a peak at 467nm, along with full width at half maximum of 28nm, and photoluminescence quantum yield of 97%. Notably, highly efficient pure blue organic light-emitting diode (OLED) is realized using mBP-DABNA-Me, showing a maximum external quantum efficiency of 24.3% and a stable blue emission with a Commission Internationale de L'Eclairage coordinate of (0.124, 0.140). The color purity of the OLED is maintained at a high doping concentration of over 20%, attributed to the suppressed intermolecular interaction between the MR emitters.

Phenylpyridine and carbazole based host materials for highly efficient blue TADF OLEDs

In this work, two host materials for blue TADF (thermally activated delayed fluorescence) OLEDs (organic light-emitting diodes) were designed and synthesized for improving the lifetime by incorporating pyridine core carbazole connected at different liking positions. These materials exhibit good thermal stability, high bond dissociation energy (BDE), and longer lifetime than the reference host. In particular, a blue TADF OLEDs system consisting of 4N-oCBP (9-(3-(2-(9 H -carbazol-9-yl)phenyl)pyridin-4-yl)-9 H -carbazole host and TCz-Trz (2,4,6-tris(2-(9 H -carbazol-9-yl)phenyl)-1,3,5-triazine) dopant exhibited the best device performances with a maximum external quantum efficiency (EQE) of 16.2% and an improvement of 88% in operational lifetime (initial luminance of 200 cd/m 2 ). This improved lifetime could be explained by the C–N BDE in the host molecular structure. The carbazole-based host molecule with different linking positions to the pyridine core developed in this study has considerable potential for improving the efficiency and lifetime of the TADF OLEDs device. • Two host materials for blue TADF OLEDs were designed and synthesized for improving the lifetime by incorporating pyridine core carbazole connected at different liking positions. • This improved lifetime could be explained by the C–N BDE in the host molecular structure.

The selective regulation of borylation site based on one-shot electrophilic C–H borylation reaction, achieving highly efficient narrowband organic light-emitting diodes

The electrophilic borylation site of borylation reaction can be selectively controlled by varying the steric hindrance and electron-donating ability of the substrate substituent. The device based on the synthesized compound exhibits EQE of 21.6% with FWHM of 28 nm and CIE coordinates of (0.135, 0.094). The work provides an effective way for the development of high-performance MR-TADF emitter. • The electrophilic borylation site of one-shot electrophilic C–H borylation reaction can be selectively controlled. • New compounds tDPAC-BN and tDMAC-BN exhibited high PLQYs, narrow FWHMs, and satisfactory TADF properties. • The device based on tDPAC-BN achieved EQE of 21.6% with FWHM of 28 nm and CIE coordinates of (0.135, 0.094). Developing novel thermally activated delayed fluorescence (TADF) materials with a small full-width at half-maximum (FWHM) is very important for the fabrication of wide gamut and high-resolution displays of organic light-emitting diodes (OLEDs). In this work, we report two blue TADF emitters (tDPAC-BN and tDMAC-BN) with narrow FWHM based on a one-shot electrophilic C–H borylation reaction by selecting acridan-containing arylamine derivatives as the starting materials of borylation. The rigid skeleton structure significantly reduces vibrational motion, endowing tDPAC-BN and tDMAC-BN with high PLQYs (94.4% and 89.7%) and narrow FWHMs (19 nm and 26 nm in toluene). The electroluminescent devices employing tDPAC-BN and tDMAC-BN as emitters exhibit external quantum efficiency (EQE) of 21.6% and 22.3%, and CIE coordinates of (0.135, 0.094) and (0.116, 0.186), respectively. More importantly, we found the electrophilic borylation site of borylation reaction can be controlled by varying the steric hindrance effect and electron-donating ability of the substrate substituent. The different HOMO distribution originated from the differences in the substrate substituent accounts for different cyclization mode for tDPAC-BN and tDMAC-BN. Therefore, the work provides a useful strategy for broadening the range of high-performance TADF materials with narrow FWHM.

Creation of a thermally cross-linkable encapsulated TADF molecule for highly efficient solution-processed hybrid white OLEDs

Robust luminogens that can be used in application for high efficiency solution-processed hybrid white organic light-emitting diodes (WOLEDs) are rarely reported. Herein, a thermally cross-linkable encapsulated thermally activated delayed fluorescence (TADF) molecule, DVCz-2CzCN, consisting of blue emissive core, encapsulation unit and thermal cross-linkable group is designed and synthesized. Systematic studies demonstrate that DVCz-2CzCN as the emitter can form a stable and uniform thin film by the solution-process, and simultaneously suppress the triplet excitons concentration quenching. Consequently, the nondoped blue solution-processed device using DVCz-2CzCN as the emissive layer exhibits blue emission with maximum external quantum efficiency (EQE) of 5.6% is achieved. Especially to solution-processed hybrid WOLED with the construction of employing the cross-linked DVCz-2CzCN as the blue-emitting component combined with an orange-emitting phosphor PO-01, exhibits a superior performance with maximum forward-viewing EQE of 14.9% and a stable Commission International de L'Eclairage (CIE) coordinate of (0.33, 0.45). This work indicates that molecular topology construction is crucial for the development of high-performance solution-processed hybrid WOLEDs. Herein, a highly efficient solution-processed hybrid white OLED was reported based on the strategy of constructing a thermally cross-linkable encapsulated TADF molecule. • Solution-processed hybrid white OLED was fabricated by utilizing a thermally cross-linkable encapsulated TADF molecule. • DVCz-2CzCN possesses good morphologic stability, sufficient solvent resistance and efficient triplet excitons confinement. • The DVCz-2CzCN-based device can afford a high blue TADF OLED by the solution-process with EQE max of 5.6%. • Solution-processed hybrid white OLED exhibits a superior performance with EQE max of 14.9%.

Controlling the electronic structures of triphenylene based sky blue TADF emitters by chemical modifications for high efficiency with shorter emission lifetimes

Chemically modified triphenylene derivatives are one of the attractive candidates as an acceptor unit for realizing efficient blue thermally activated delayed fluorescence (TADF) emitters due to the rigid structure and the high triplet energy of 2.9 eV however, only a limited number of examples with low external quantum efficiency (EQE) below 10% are reported to date. Here, we developed three types of blue TADF emitters based on modified triphenylene acceptor units. These emitters showed sky blue emission with the emission peak wavelength around 470 nm, high photoluminescent quantum yield (PLQY) of ∼88%, and a short delayed lifetime (τd) of ∼7.7 μs. These emitters realized efficient sky blue organic light-emitting device with high EQE of over 20%.

Solution-processed white OLEDs with power efficiency over 90 lm W-1 by triplet exciton management with a high triplet energy level interfacial exciplex host and a high reverse intersystem crossing rate blue TADF emitter.

Solution-processed white organic light-emitting diodes (WOLEDs) have shown much lower device efficiency than their vacuum-deposited counterparts, due to the lack of triplet exciton management in a single-emissive-layer device structure, which will induce triplet-triplet annihilation (TTA) and triplet-polaron annihilation (TPA). Here, two kinds of solution-processed WOLEDs, including thermally activated delayed fluorescence (TADF)/phosphorescence hybrid WOLEDs and all-TADF WOLEDs, with high power efficiency are developed by using a high triplet energy level (T1) interfacial exciplex as a host and a high reverse intersystem crossing (RISC) rate TADF emitter as a blue dopant for triplet exciton management. The interfacial exciplex host with high T1 can ensure that triplet excitons transfer from the host to the blue emitter, and the blue TADF emitter with high RISC rate (1.15 × 107 s-1) can rapidly upconvert triplet excitons to singlet ones to avoid TTA and TPA. The solution-processed TADF/phosphorescence hybrid and all-TADF WOLEDs exhibit maximum external quantum efficiencies of 31.1% and 27.3%, together with maximum power efficiencies of 93.5 and 70.4 lm W-1, respectively, which are the record efficiencies for solution-processed WOLEDs, and quite comparable to those of most vacuum-deposited counterparts.

Benzonitrile-based AIE polymer host with a simple synthesis process for high-efficiency solution-processable green and blue TADF organic light emitting diodes

Polymer host materials have great potential for enabling small molecular thermally activated delayed fluorescence (TADF) emitters to construct solution-processed organic light-emitting diodes (OLEDs).

Intrinsically Ionic, Thermally Activated Delayed Fluorescent Materials for Efficient, Bright, and Stable Light‐Emitting Electrochemical Cells

AbstractSolid‐state light‐emitting electrochemical cells (LECs) using sustainable and eco‐friendly materials and affording high brightness, efficiency, and stability are highly desired. Here, intrinsically ionic, thermally activated delayed fluorescence (TADF) materials 1–3 for efficient, bright, and stable LECs are reported. 1–3 feature carbazole‐type donors and cationic triazine‐type acceptors, which are located ortho to each other on the phenyl linkers. Through‐space charge‐transfer (CT) dominates the CT transitions in 1–3. In doped and neat films, 1–3 show blue and green TADF emission, respectively, with reverse intersystem crossing rates at around 7.0 × 105 s−1. 1–3 possess excellent electrochemical stability (except for the oxidation of 1) and film‐forming abilities. LECs using neat films of 1–3 as the single active layers afford green electroluminescence with peak brightness/peak external quantum efficiency (EQE) of up to 572 cd m−2/6.8% under 4.0 V and peak brightness/peak EQE/half‐lifetime of up to 860 cd m−2/5.4%/48 h under 50 A m−2. A longer half‐lifetime of 218 h has further been achieved at 162 cd m−2 under 10 A m−2. The work reveals the bright prospect for the development of efficient, bright, and stable LECs with intrinsically‐ionic TADF materials.

Acridin-9(10H)-one-based blue thermally activated delayed fluorescence materials: improvement of color purity and efficiency stability

A series of donor-acceptor-donor (D-A-D) type blue thermally activated delayed fluorescence (TADF) emitters, namely, 2,7-DtBuCz-AD, 3,6-DtBuCz-AD, 3,6-DMAC-AD, and 3,6-DMAC-AD-CF3, were developed with highly rigid acridin-9(10H)-one (i.e. acridone [AD]) as acceptor. The regioisomeric effect study revealed that the attachment of donors at 3,6-sites of AD ring dramatically enhanced TADF ratio in comparison with the 2,7-site isomer. On the one hand, by varying donors from dimethylacridine (DMAC) to tert-butylcarbazole (tBuCz) at 3,6-sites of AD ring, the emission color purity of blue TADF emitters was improved from sky blue to deep blue. On the other hand, by introducing trifluoromethyl (CF3) onto 9-site phenyl ring of 3,6-DtBuCz-AD, the efficiency stability of the sky blue emission for 3,6-DMAC-AD-CF3 was remarkably improved. The deep blue organic light-emitting diode (OLED) of 3,6-DtBuCz-AD exhibited a maximum external quantum efficiency (EQEmax) of 17.88% with CIE coordinates of (0.15, 0.08), which is among the best performances ever reported for deep blue TADF-OLEDs. The sky-blue OLED of 3,6-DMAC-AD realized an EQEmax of 23.16%. And with the incorporation of CF3, the sky blue device of 3,6-DMAC-AD-CF3 exhibited extremely low efficiency loss of only 5.1% at the high brightness of 1,000 cd/m2.