Solution-processed Organic Light-emitting Diodes Research Articles

Red hyperbranched conjugated polymers with thermally activated delayed fluorescence for solution-processed organic light-emitting diodes

Wet-processable red luminescent materials with thermally activated delayed fluorescence (TADF) are essential in the field of printed electronics. Particularly, hyperbranched conjugated polymers with the advantages of large steric hindrance, effective energy transfer and good solubility had exhibited great potential application to prepare the high-performance solution-processed organic light-emitting devices, but it is still a great challenge. In this work, a novel kind of red hyperbranched conjugated polymers PFCz-(BTZ-DMAC)n (n = 1, 2, 10 and 50) were designed and synthesized using D-A-D-typed BTZ-DMAC as the red TADF cores and poly(fluorene-carbazole) as the backbone. The polymers owned more effective energy transfer process and reverse intersystem crossing that could simultaneously and effectively utilize the singlet and triplet excitons. The polymers also exhibited good thermal stabilities and film forming properties. At the same time electroluminescent emission (about 650 nm) prominently enhanced and had an obvious red-shift with the increasing concentration of red cores. In the non-doped devices, PFCz-(BTZ-DMAC)50 with 50 mol‰ content of red TADF cores showed the best electroluminescent performance that a red chromaticity coordinate of (0.59, 0.39) and a maximum external quantum efficiency of 4.88 % were obtained. More importantly, it exhibited the low roll-off (7 % decrease at 500 cd/m−2) owing to the large steric hindrance. All results revealed that red TADF hyperbranched conjugated polymers had potential application for preparing the high-quality solution-processed organic light-emitting devices.

Boron-, sulfur- and nitrogen-doped decacyclic multiple resonance emitters for narrowband deep blue electroluminescence

Two boron-, sulfur- and nitrogen-doped polycyclic aromatic hydrocarbon (PAH) multiple resonance (MR) emitters, namely mDBNS and mDBNStBu, are developed by introducing two pairs of boron (B) and sulfur (S) atoms at meta-positions of central benzene and one carbazole moiety in decacyclic aromatic skeletons. The resultant emitters exhibit efficient deep blue narrowband emission at 451–457 nm with full width at half maximum (FWHM) of 18–22 nm in toluene, together with PLQY of 70%–76% and reverse intersystem crossing rate (kRISC) of 1.1–1.2 × 105 s−1. Solution-processed organic light-emitting diodes (OLEDs) employing mDBNStBu as emitters exhibit deep blue electroluminescence at 462 nm with CIE coordinates of (0.13, 0.12), together with a maximum external quantum efficiency (EQEmax) of 10.4%.

Precision-Engineered Medium-Sized Molecular Host and Emitter for Ensuring Consistent Performance in Solution-Processed Narrowband OLEDs.

In this study, two novel multiple resonance (MR) emitters, DtCzBN and Cy-DtCzBN, were designed based on the well-known BCzBN structure and synthesized for narrowband solution-processed organic light-emitting diodes (OLEDs). Cy-DtCzBN possesses a dimeric V-shaped structure formed by coupling two individual DtCzBN units via a nonconjugated cyclohexane linker. When compared with DtCzBN, Cy-DtCzBN, as a medium-sized molecule, was found to maintain the optical and photophysical properties of the corresponding monomeric unit, DtCzBN, but exhibits high thermal stability, excellent solubility, and good film-forming ability. Additionally, solution-processed OLEDs were fabricated by using two sets of molecules: one set of small molecular hosts and emitters (i.e., mCP and DtCzBN) and the other set of medium-sized molecular hosts and emitters (i.e., Cy-mCP and Cy-DtCzBN). Notably, devices using medium-sized molecular hosts and emitters exhibited similar optical and photophysical properties but showed significantly improved reproducibility and thermal stability compared with those based on small molecular hosts and emitters. Our current study provides some insights into molecular design strategies for thermally stable hosts and emitters, which are highly suitable for solution-processed OLEDs.

Turning Non-Emissive Schiff Bases Into Aggregate Emitters.

Schiff bases are a crucial component in various functional materials but often exhibit non-emissive behavior which significantly limits their potential applications as luminescent materials. However, traditional approaches to convert them into aggregate emitters often require intricate molecular design, tedious synthesis, and significant time and resource consumption. Herein, we present a cocrystallization-induced emission strategy that can transform non-emissive (hetero)aryl-substituted Schiff bases into green-yellow to yellow aggregate emitters via even simple grinding of a mixture of Schiff bases and 1,2,4,5-tetracyanobenzene (TCB) mixtures. The combined experimental and theoretical analysis revealed that the cocrystallization inhibits the C=N isomerization and promotes face-to-face π-π interaction, which restricts access to both the dark state and canonical intersection to ultimately induce emission. Furthermore, the induced emission enables the observation of solid-state molecular diffusion through fluorescence signals, advancing white light emission diodes, and notably, solution-processed organic light-emitting diodes based on cocrystal for the first time. This study not only highlights the potential of developing new C=N structural motifs for AIEgens but also could boost advancements in related structure motifs like C=C and N=N.

Solution-processed orange organic light-emitting diodes based on phosphorescent iridium(III) complexes with coumarin 6 as the main ligand

Four ionic orange phosphorescent iridium(III) complexes (Ir1, Ir2, Ir3, Ir4) were successfully synthesized using coumarin 6 as the cyclometalated ligand and 2,2′-bipyridine (bpy) derivatives with different number and position of methyl groups as the auxiliary ligand. The effects of substituents in the auxiliary ligands on their properties were systematically investigated. These four complexes exhibited orange emission at wavelengths of 590, 588, 587, and 586 nm, respectively, with excellent solubility and remarkable photophysical properties in different solvents. Furthermore, they were further applied in the organic light-emitting diodes (OLEDs) based on solution method. The maximum luminance of the devices based on Ir1/Ir2/Ir3/Ir4 reached 1907.0/932.6/760.8/519.3 cd/m2, with corresponding maximum current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) values of 1.56/1.71/1.97/1.52 cd/A, 0.33/0.32/0.35/0.27 lm/W, and 0.77/0.82/0.90/0.72 %, respectively. Although there is room for improvement in the performance of OLEDs, this strategy inspires us to modulate the novel photoluminescent and electroluminescent properties of iridium(III) complexes through rational modifications of their ancillary ligands.

Efficiency Roll-off Suppression in Solution-Processed Organic Light-Emitting Diodes through a Bipolar Host Design

Efficiency Roll-off Suppression in Solution-Processed Organic Light-Emitting Diodes through a Bipolar Host Design

Three new red neutral and ionic iridium(III) complexes based on the same main ligand and auxiliary ligand but with different counterions for solution-processed organic light-emitting diodes.

Three new neutral and ionic phosphorescent iridium(III) complexes were successfully prepared using 1-(6-methoxynaphthalen-2-yl)isoquinoline as the main ligand, while the auxiliary ligand was 2-(2-1H-imidazolyl)pyridine. Three complexes (Ir1, Ir2, Ir3) showed red emission, peaking at 610, 609, and 615 nm, respectively, and they exhibited good solubility and excellent photophysical properties in different solvents, which is suitable to prepare organic light-emitting diodes (OLEDs) by solution method. Among the three OLEDs prepared by iridium(III) complexes using the solution method, the device based on Ir2 possessed better electroluminescent properties, and its maximum brightness, current efficiency (CE), power efficiency (PE), and the maximum external quantum efficiency (EQE) were 507.2cd m-2 , 0.14 cd A-1 , 0.06 lm W-1 , and 0.14%. respectively, proving that the three complexes have a certain of potential for OLEDs applications and are expected to expand the applications of iridium(III) complexes for OLEDs.

Rational molecular design of efficient yellow-red dendrimer TADF for solution-processed OLEDs: a combined effect of substitution position and strength of the donors

AbstractThe development of high-performance solution-processed red organic light-emitting diodes (OLEDs) remains a challenge, particularly in terms of maintaining efficiency at high luminance. Here, we designed and synthesized four novel orange-red thermally activated delayed fluorescence (TADF) dendrimers that are solution-processable: 2GCzBP, 2DPACzBP, 2FBP2GCz and 2FBP2DPACz. We systematically investigated the effect of substitution position and strength of donors on the optoelectronic properties. The reverse intersystem crossing rate constant (kRISC) of the emitters having donors substituted at positions 11 and 12 of the dibenzo[a,c]phenazine (BP) is more than 10-times faster than that of compounds substituted having donors substituted at positions 3 and 6. Compound 2DPACzBP, containing stronger donors than 2GCzBP, exhibits a red-shifted emission and smaller singlet-triplet energy splitting, ΔEST, of 0.01 eV. The solution-processed OLED with 10 wt% 2DPACzBP doped in mCP emitted at 640 nm and showed a maximum external quantum efficiency (EQEmax) of 7.8%, which was effectively maintained out to a luminance of 1,000 cd m−2. Such a device∙s performance at relevant display luminance is among the highest for solution-processed red TADF OLEDs. The efficiency of the devices was improved significantly by using 4CzIPN as an assistant dopant in a hyperfluorescence (HF) configuration, where the 2DPACzBP HF device shows an EQEmax of 20.0% at λEL of 605 nm and remains high at 11.8% at a luminance of 1,000 cd m−2, which makes this device one of the highest efficiency orange-to-red HF SP-OLEDs to date.

Achieving Record External Quantum Efficiency of 11.5% in Solution-Processable Deep-Blue Organic Light-Emitting Diodes Utilizing Hot Exciton Mechanism.

High performance solution-processable deep-blue emitters with a Commission International de l'Eclairage (CIE) coordinate of CIEy ≤ 0.08 are highly desired in ultrahigh-definition display. Although, deep-blue materials with hybridized local and charge-transfer (HLCT) excited-state feature are promising candidates, their rigidity and planar molecular structures limit their application in solution-processing technique. Herein, four novel deep-blue solution-processable HLCT emitters were first proposed by attaching rigid imide aliphatic rings as functional units onto the HLCT emitting core. The functional units not only improve solubility, enhance thermal properties and morphological stability of the emitting core, but also promote photoluminescence efficiency, balance charge carrier transport, and inhibit aggregation-caused quenching effect due to the weak electron-withdrawing property as well as steric hindrance. The corresponding solution-processable organic light-emitting diodes (OLEDs) substantiate an unprecedented maximum external quantum efficiency (EQEmax) of 11.5% with an emission peak at 456 nm and excellent colour purity (full width at half maximum = 56 nm and CIEy = 0.09). These efficiencies represent the state-of-the-art device performance among the solution-processable blue OLEDs based on the "hot exciton" mechanism. This simple strategy opens up a new avenue for designing highly efficient solution-processable deep-blue organic luminescent materials.

HLCT-Type Acceptor Molecule-Based Exciplex System for Highly Efficient Solution-Processable OLEDs with Suppressed Efficiency Roll-Offs.

Exciplex systems are promising candidates for thermally activated delayed fluorescence (TADF) molecules because of the small energy difference between the lowest singlet and triplet excited states (ΔEST ). However, realizing high-efficiency and low-external-quantum-efficiency (EQE) roll-off in solution-processed organic light-emitting diodes (OLEDs) using an exciplex system remains a formidable challenge. In this study, two (HLCT)-type isomers with a spiro skeleton, 2-t BuspoCz-TRZ and 10-t BuspoCz-TRZ, are designed and synthesized as acceptors of exciplexes, where tert-butylspirofluorene indole is regarded as a donor and the triazine unit as an acceptor. Green exciplex emissions are observed for the 2-t BuspoCz-TRZ:TAPC and 10-t BuspoCz-TRZ:TAPC exciplexes, indicating distinct TADF characteristics with a very small ΔEST of 35 ± 5 meV. By using the TADF exciplex system based on the HLCT acceptor as an emitter, solution-processable OLEDs achieve a maximum external quantum efficiency (EQEmax ) of 20.8%. Furthermore, a high EQEmax > 25% with a very low-efficiency roll-off (≈3.5% at 1000cd m-2 ) is obtained for solution-processable phosphorescent devices using HLCT-based exciplexes as the host matrix of phosphors. This study paves the way for a novel strategy for designing acceptor exciplex molecules for effective TADF molecules and host matrices in solution-processable OLEDs.

PtII(C^N)(N-donor ligand)Cl-type complexes with the four-coordinate organoboron unit and their optoelectronic properties

In this research, we have developed a series of PtII(C^N)(N-donor ligand)Cl-type phosphorescent complexes with the four-coordinate organoboron unit in the C^N ligand. Through shifting the coordinating position of the Pt(II) center from phenyl ring to pyridyl ring of the 2-phenylpyridine-type (ppy-type) four-coordinate organoboron unit, the variation of >50 nm in charge-transfer (CT) absorption band and >40 nm in phosphorescent wavelength can be observed in the synthesized PtII(C^N)(N-donor ligand)Cl-type complexes, indicating effective tuning of their photophysical properties incurred by the four-coordinate organoboron unit. In addition, based on the cyclic voltammetry result, obvious variation of electron density on the Pt(II) center of these PtII(C^N)(N-donor ligand)Cl-type phosphorescent complexes can also be observed. Critically, these PtII(C^N)(N-donor ligand)Cl-type complexes with the ppy-type four-coordinate organoboron unit can exhibit aggregation enhanced phosphorescent emission (AEPE) behavior. It seems that the hydrogen bonding among the N-donor ligands and water molecules can affect their AEPE response greatly, representing a new way to tune the AEPE behavior in the PtII(C^N)(N-donor ligand)Cl-type complexes. In the solution-processed organic light-emitting diodes (OLEDs), peak electroluminescent (EL) efficiencies of 15.3%, 10.3 cd A−1 and 9.8 lm W−1 have been achieved with EL at ca. 648 nm. These impressive results have provided key information for tuning optoelectronic properties of the PtII(C^N)(N-donor ligand)Cl-type complexes by the four-coordinate organoboron unit and N-donor ligand.

Eco-friendly solution-processed narrowband OLEDs using non-halogenated aliphatic solvent systems

In general, fabricating multilayer structures in solution-processed organic light-emitting diodes (OLEDs) presents challenges owing to the potential degradation of the initial film during subsequent processing steps. Furthermore, these devices typically require aromatic and halogenated solvents recognized for their adverse effects on human health and their harmful environmental impact. In this study, we successfully synthesized a solution-processable multi-resonance thermally activated delayed fluorescence (MR-TADF) emitter by introducing tert-butyl carbazolyl dendron, which exhibits excellent solubility. In our approach, we fabricated a multilayer OLED for solution processing utilizing eco-friendly, non-halogenated aliphatic solvents, with each layer in the devices developed utilizing water, cyclohexanone, and ethyl acetate for the hole injection layer, hole transport layer, and emitting layer, respectively. The resulting eco-friendly solution-processed OLED achieved a maximum external quantum efficiency (EQEmax) of 14.0 % and a narrow bandwidth of 30 nm. Furthermore, utilizing an additional TADF sensitizer led to a remarkable EQEmax enhancement of over 15 % and a substantial improvement in efficiency roll-off. Thus, the eco-friendly device fabrication strategy employed here opens novel avenues for diverse research in organic semiconductor devices that must be fabricated with solution processes in the future.

A Comparative Study between Blended Polymers and Copolymers as Emitting Layers for Single-Layer White Organic Light-Emitting Diodes.

Extensive research has been dedicated to the solution-processable white organic light-emitting diodes (WOLEDs), which can potentially influence future solid-state lighting and full-color flat-panel displays. The proposed strategy based on WOLEDs involves blending two or more emitting polymers or copolymerizing two or more emitting chromophores with different doping concentrations to produce white light emission from a single layer. Toward this direction, the development of blends was conducted using commercial blue poly(9,9-di-n-octylfluorenyl2,7-diyl) (PFO), green poly(9,9-dioctylfluorenealt-benzothiadiazole) (F8BT), and red spiro-copolymer (SPR) light-emitting materials, whereas the synthesized copolymers were based on different chromophores, namely distyryllanthracene, distyrylcarbazole, and distyrylbenzothiadiazole, as yellow, blue, and orange-red emitters, respectively. A comparative study between the two approaches was carried out to examine the main challenge for these doping systems, which is ensuring the proper balance of emissions from all the units to span the entire visible range. The emission characteristics of fabricated WOLEDs will be explored in terms of controlling the emission from each emitter, which depends on two possible mechanisms: energy transfer and carrier trapping. The aim of this work is to achieve pure white emission through the color mixing from different emitters based on different doping concentrations, as well as color stability during the device operation. According to these aspects, the WOLED devices based on the copolymers of two chromophores exhibit the most encouraging results regarding white color emission coordinates (0.28, 0.31) with a CRI value of 82.

Adjusting the Electron-Withdrawing Ability of Acceptors in Thermally Activated Delayed Fluorescence Conjugated Polymers for High-Performance OLEDs.

Constructing high-performance solution-processed organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) conjugated polymers remains a challenging issue. The electron-withdrawing ability of acceptors in TADF units significantly affects the TADF properties of the conjugated polymers. Herein, we have designed three TADF conjugated polymers, in which phenoxazine donors and anthracen-9(10H)-one acceptors are incorporated into the polymeric backbones and side chains, respectively, and the carbazole derivative is copolymerized as the host. By incorporating different heteroatoms, such as nitrogen, oxygen, or sulfur, with slightly different electronegativities into anthracen-9(10H)-one, the effect of the electron-withdrawing ability of the acceptor on the performance of conjugated TADF polymer-based OLEDs is thus systematically studied. It is found that the introduction of a nitrogen atom can enhance the spin-orbital coupling and RISC process due to the modulated energy levels and nature of the excited states. As a result, the solution-processed OLEDs based on the prepared polymer p-PXZ-XN display an excellent comprehensive performance with an EQEmax of 17.6%, a low turn-on voltage of 2.8 V, and a maximum brightness of 14750 cd m-2. Notably, the efficiency roll-off is quite low, maintaining 15.1% at 1000 cd m-2, 12.1% at 3000 cd m-2, and 6.1% at 10000 cd m-2, which ranks in the first tier among the reported TADF conjugated polymers. This work provides a guideline for constructing high-efficiency TADF polymers.

Thienothiophene-based organic light-emitting diode: synthesis, photophysical properties and application

A donor–π–acceptor (D–π–A)-type pull–push compound, DMB-TT-TPA (8), comprising triphenylamine as donor and dimesitylboron as acceptor linked through a thieno[3,2-b]thiophene (TT) π-conjugated linker bearing a 4-MeOPh group, was designed, synthesized, and fabricated as an emitter via a solution process for an organic light-emitting diode (OLED) application. DMB-TT-TPA (8) exhibited absorption and emission maxima of 411 and 520 nm, respectively, with a mega Stokes shift of 109 nm and fluorescence quantum yields both in the solid state (41%) and in solution (86%). The optical properties were supported by computational chemistry using density functional theory for optimized geometry and absorption. A solution-processed OLED was fabricated using low turn-on voltage, which had performances with maximum power, current, and external quantum efficiencies of 6.70 lm/W, 10.6 cd/A, and 4.61%, respectively.

Selenoxanthen-9-one-based emitters exhibiting efficient room temperature phosphorescence for electroluminescent and oxygen sensing applications

Two selenoxanthen-9-one-based emitters (Se-2DPA and Se-2TPA) were synthesized by introducing diphenylamine and triphenylamine as electron donors. The doped films of Se-2DPA and Se-2TPA exhibited bright fluorescence-phosphorescence dual emission and comparable photoluminescence quantum yields (ΦPL) of 31.4 % and 29.6 %, respectively. Unlike the Se-2DPA with phosphorescence lifetime of 1.1 ms, Se-2TPA shows significantly extended phosphorescence lifetime up to 17.7 ms. As revealed by computational and experimental investigations, Se-2DPA maintained more effective spin orbit coupling (SOC) between T1 and S0 states and its radiative rate constant of phosphorescence is 1 order of magnitude higher than that of Se-2TPA, which resulted in a relatively shorter phosphorescence lifetime. Consequently, solution-processed organic light-emitting diodes (OLEDs) based on Se-2DPA with shorter phosphorescence lifetime achieved a maximum external quantum efficiency of 8.8 %, which is much higher than the device based on Se-2TPA (only 0.8 %). In contrast, Se-2TPA showed higher sensitivity for oxygen sensing and the Stern-Volmer quenching constant (KSV) value reached 3.04 × 10−3 ppm owing to the longer phosphorescence lifetime, which is over 3-folds higher than that of Se-2DPA (8.88 × 10−4 ppm) under the same conditions.

Blue polyimides for high-performance solution-processable organic light-emitting diodes

Blue light-emitting materials with excellent film-forming ability, superior morphological stability, outstanding color purity, and high device efficiency are in urgent demand for new-generation display and solid-state lighting devices fabricated by low-cost wet processing. However, their current performances are far from satisfactory. Herein, two polyimide (PI)-based blue polymers are first precisely constructed and synthesized through a “Hinge-type Linking” strategy. A small molecular is introduced into the PI backbone via non-conjugated aliphatic imide ring linker. These polymers not only show superb thermal stability and morphological stability, but also maintain narrowband blue emission. Furthermore, PIs are prepared by polycondensation method, precipitated and purified in ethanol solvent, which avoids the use of metal catalysts. The resulting solution-processable devices achieve high performance with a maximum external quantum efficiency (EQE) of 9.94 % and maximum emission peak at 460 nm. To the best of our knowledge, this is the first time that solution-processable polymer light-emitting diodes (PLEDs) based on the “hot exciton” mechanism achieving splendid performance with maximum EQE close to 10 %. The superior performance is attributed to the validity of the “Hinge-type Linking” strategy in PLEDs, opening up a new avenue for PLED development and application.

Constructing solution-processable heavy metal platinum (II) complex with narrowband emission by integrating multiple resonance molecular system

The narrowband emission required by wide color gamut display is an extremely important research topic for any luminescence mechanism, which has made significant progress in traditional fluorescence and thermally activated delayed fluorescence (TADF) based on purely organic compounds, but is far from mature in organometallic complexes. Herein, we propose a feasible molecular design paradigm for constructing the desirable organic electroluminescence (EL) emitter with narrowband emission by integrating an original multiple resonance TADF (MR-TADF) fragment into the classical platinum (II) complex. The solution-processed organic light-emitting diode (OLED) by employing the target model platinum (II) complex BNCPPt as the dopant emitter shows light green emission with a peak of 507 nm and narrow full-width at half-maximum (FWHM) of 35 nm, which achieves a maximum external quantum efficiency (EQE) of 13.5% with very low efficiency roll-off of 4.4% at 1000 cd m−2.

Molecular design strategies for the highly efficient vacuum and solution-processable long wavelength thermally activated delayed fluorescence emitters

Simple device architecture-based solution-processed organic light-emitting diodes (OLEDs) are more advantageous over the multilayer vacuum-processed OLEDs for their commercial application. Highly efficient long wavelength thermally activated delayed fluorescent (TADF) emitters suitable for both vacuum and solution-processed OLEDs are rarely reported because of the stringent molecular design rules and the inherent limitation of the energy gap law. To resolve this issue, we designed and synthesized two TADF emitters namely, 5,8-bis(4-(bis(4-(tert-butyl)phenyl)amino)phenyl)-2,3-bis(4-(tert-butyl)phenyl)quinoxaline-6,7-dicarbonitrile (2tBuTPA-QxCN) and 2,3,5,8-tetrakis(4-(bis(4-(tert-butyl)phenyl)amino)phenyl)quinoxaline-6,7-dicarbonitrile (4tBuTPA-QxCN), for their use in both vacuum and solution-processed OLEDs. High external quantum efficiency (EQE) of 22 % and emission peak at 608 nm were demonstrated for the vacuum-deposited OLED fabricated with 4tBuTPA-QxCN TADF emitter as compared to the OLED fabricated with 2tBuTPA-QxCN TADF emitter exhibiting EQE value of 21.1 % and emission peak at 605 nm. In their solution-processed OLEDs, a high EQE of 15.6 % and pure-red emission peak at 630 nm was demonstrated for the 2tBuTPA-QxCN TADF emitter as compared to the EQE value of 11.6 % and emission peak at 628 nm for the 4tBuTPA-QxCN TADF emitter.

Carbazole-Decorated Organoboron Emitters with Low-Lying HOMO Levels for Solution-Processed Narrowband Blue Hyperfluorescence OLED Devices.

The hyperfluorescence has drawn great attention in achieving efficient narrowband emitting devices based on multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters. However, achieving efficient solution-processed pure blue hyperfluorescence devices is still a challenge, due to the unbalanced charge transport and serious exciton quenching caused by that the holes are easily trapped on the high-lying HOMO (the highest occupied molecular orbital) level of traditional diphenylamine-decorated emitters. Here, we developed two narrowband blue organoboron emitters with low-lying HOMO levels by decorating the MR-TADF core with weakly electron-donating carbazoles, which could suppress the hole trapping effect by reducing the hole traps between host and MR-TADF emitter from deep (0.40 eV) to shallow (0.14/0.20 eV) ones for facilitating hole transport and exciton formation, as well as avoiding exciton quenching. And the large dihedral angle between the carbazole and MR-TADF core makes the carbazole act as a steric hindrance to inhibit molecular aggregation. Accordingly, the optimized solution-processed pure blue hyperfluorescence devices simultaneously realize record external quantum efficiency of 29.2 %, narrowband emission with a full-width at half-maximum of 16.6 nm, and pure blue color with CIE coordinates of (0.139, 0.189), which is the best result for the solution-processed organic light-emitting diodes based on MR-TADF emitters.