Thermally Activated Delayed Fluorescence Molecules Research Articles

Inkjet Printing of High-Color-Purity Blue Organic Light-Emitting Diodes with Host-Free Inks.

Inkjet printing technology offers a unique approach to producing direct-patterned pixels without fine metal masks for active matrix displays. Organic light-emitting diodes (OLEDs) consisting of thermally activated delayed fluorescence (TADF) emitters facilitate efficient light emission without heavy metals, such as platinum and iridium. Multi-resonance TADF molecules, characterized by their small full width at half maxima (FWHM), are highly suitable for the requirements of wide color-gamut displays. Herein, host-free TADF inks with a low concentration of 1 mg/mL were developed and inkjet-printed onto a seeding layer, concurrently serving as the hole-transporting layer. Attributed to the proof-of-concept of host-free inks printed on a mixed seeding layer, a maximum external quantum efficiency of 13.1% (improved by a factor of 21.8) was achieved in the inkjet-printed OLED, with a remarkably narrow FWHM of only 32 nm. Highly efficient energy transfer was facilitated by the effective dispersion of the sensitizer around the terminal emitters.

Effective donor and acceptor modifications of carbazole-benzonitrile thermally activated delayed fluorescence molecules enabling high-performance OLEDs

Carbazole-benzonitrile derivatives (CzBNs) have great potential to enable thermally activated delayed fluorescence (TADF) molecules with both high efficiency and good stability simultaneously. However, the device performances of most CzBN-based organic light-emitting diodes (OLEDs) still lag behind other types of TADF molecules. In this work, we proposed a design strategy to construct efficient CzBN-TADF molecules through acceptor and donor modifications. The cyano-modified acceptor enables the extension of the lowest unoccupied molecular orbital while mostly preserving the overlapped area with the highest occupied molecular orbital. The optimized distributions of frontier molecular orbitals contribute to tiny singlet-triplet energy gaps while maintaining a high radiative decay rate. The incorporation of tert-butyl units in the donor groups further enhances the TADF property of resulted tPCNBN molecule due to suppressed non-radiative decay and reduced exciton self-quenching. Accordingly, OLEDs based on tPCNBN present the best device performances, such as a maximum external quantum efficiency of 33.1 % at 400 cd m−2, which is still as high as 26.3 % at a high luminance of 4000 cd m−2, demonstrating relatively low efficiency roll-off. These results confirm the effectiveness of the proposed design strategy in developing efficient and stable CzBN-TADF materials and devices.

Excited-state Engineering Enables Efficient Deep-blue Light-emitting Diodes Exhibiting BT.2020 Color Gamut.

Organic luminescent materials that exhibit thermally activated delayed fluorescence (TADF) can convert non-emissive triplet excitons into emissive singlet states through a reverse intersystem crossing (RISC) process. Therefore, they have tremendous potential for applications in organic light-emitting diodes (OLEDs). However, with the development of ultra-high definition 4K/8K display technologies, designing efficient deep-blue TADF materials to achieve the Commission Internationale de l'Éclairage (CIE) coordinates fulfilling BT.2020 remains a significant challenge. Here, we propose an effective approach to design deep-blue TADF molecules based on hybrid long- and short-range charge-transfer by incorporation of multiple donor moieties into organoboron multiple resonance acceptors. The resulting TADF molecule exhibits deep-blue emission at 414nm with a full width at half maximum (FWHM) of 29nm, together with a thousand-fold increase in RISC rate. OLEDs based on our champion material achieved a record maximum external quantum efficiency (EQE) of 22.8% with CIE coordinates of (0.163, 0.046), approaching the coordinates of the BT.2020 blue standard. Moreover, TADF-assisted fluorescence devices employing our designed material as a sensitizer exhibited an exceptional EQE of 33.1%. Our work thus provides a blueprint for future development of efficient deep-blue TADF emitters, representing an important milestone towards meeting the blue color gamut standard of BT.2020. This article is protected by copyright. All rights reserved.

Regulation for photophysical properties of thermally activated delayed fluorescence molecules with through-space charge transfer by substitution effect

Thermally activated delayed fluorescence (TADF) molecules with through-space charge transfer (TSCT) have attracted much attention in recent years. The photophysical properties of four TADF molecules with TSCT properties were studied in toluene and in solid phase. Our calculation results indicate that ortho substitution and fluorine substitution not only favor the generation of TADF, but also promote room temperature phosphorescence in solid phase. The results provide deeper understanding of substitution effect on light-emitting properties of TSCT-TADF emitters and may favor the design of TADF emitters.

Triplet Excited-State Dynamics in Benzothiadiazole-Based Thermally Activated Delayed Fluorescence Compound.

The "hot exciton" thermally activated delayed fluorescence (TADF) materials have attracted considerable research interest for their utilization of high-lying triplet excitons. In this work, we reported the mechanism of photoluminescence by revealing the spectral evolution from singlet to triplet states in "hot exciton" TADF molecules by transient absorption (TA) spectra and triplet sensitization experiments. The internal conversion and intersystem crossing are much faster than reverse intersystem crossing (RISC), so that high-lying triplet states (Tn) are difficult to accumulate to be observed in the transient absorption spectra. In contrast, the emergence of delayed fluorescence in time-resolved emission spectra demonstrates the existence of a high-lying RISC process (hRISC) from Tn to S1. Triplet sensitization experiments successfully identified the spectral features of the T1 state in the TA spectra. This work sheds light on critical factors for the systematic design of these materials to achieve a high emission quantum yield.

Diradical-Based Strategy in Designing Narrowband Thermally Activated Delayed Fluorescence Molecules with Tunable Emission Wavelengths.

In the design of thermally activated delayed fluorescence (TADF) materials, narrow-band emission is of particular importance for the development of organic light-emitting diodes (OLEDs). In this work, we proposed a new strategy for designing TADF molecules utilizing degenerate nonbonding (NB) orbitals of diradical parent molecules, and these designed molecules are termed NB-TADF molecules. Based on this strategy, a series of NB-TADF molecules is finely designed and systematically studied by theoretical calculations. Taking advantage of the nonbonding properties, these NB-TADF molecules exhibit desirable narrowband emissions and high quantum yields. More importantly, the emission bands can be easily tuned from blue to near-infrared by changing the conjugate length of the parent group in the NB-TADF molecules. We hope that this new strategy can open a new door for the design of novel TADF materials.

Conformational Isomerization Effect on Singlet/Triplet Energy Consumption Process of Thermally Activated Delayed Fluorescence Molecules with Aggregation Induced Emission: A QM/MM Study.

Thermally activated delayed fluorescence (TADF) molecules with aggregation-induced emission (AIE) properties hold tremendous potential in biomedical sensing/imaging and telecommunications. In this study, a multiscale method combined with thermal vibration correlation function (TVCF) theory is used to investigate the photophysical properties of the novel TADF molecule CNPy-SPAC in toluene and crystal and amorphous states. In the crystal state, an increase in radiative rates and a decrease in nonradiative rates lead to AIE. Additionally, conformational isomerization effects result in significantly different luminescent efficiencies between the two crystal structures. Furthermore, the isomerization effect allows for the coexistence of three configurations in the amorphous state. Among them, the non-TADF quasi-axial (Qa) configuration may facilitate energy transfer to the TADF-characteristic quasi-equal/quasi-equal-H (Qe/Qe-H) configurations, enhancing AIE. Moreover, the Qa configuration enables rapid electron transport, offering the potential for self-doped devices. Our work elucidates a new mechanism for the isomerization effect in AIE-TADF molecules.

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.

Key requirements for ultraefficient sensitization in hyperfluorescence organic light-emitting diodes

AbstractBlue organic light-emitting diode (OLED) technology requires further advancements, and hyperfluorescent (HF) OLEDs have emerged as a promising solution to address stability and colour-purity concerns. A key factor influencing the performance of HF-OLEDs is Förster resonance energy transfer (FRET). Here we investigate the FRET mechanism in blue HF-OLEDs using contrasting thermally activated delayed fluorescence (TADF) sensitizers. We demonstrate that the molecular structure of the sensitizer profoundly impacts the FRET efficiency, exemplified by the spiro-linked TADF molecule ACRSA, which suppresses the dihedral-angle inhomogeneity and any lower-energy conformers that exhibit minimal FRET to the terminal emitter. Consequently, the FRET efficiency can be optimized to nearly 100%. Further, we demonstrate how the properties of a near-ideal sensitizer diverge from ideal TADF emitters. As a result, blue HF-OLEDs utilizing a greenish sensitizer exhibit a remarkable tripling of external quantum efficiency (~30%) compared with non-HF devices. This new understanding opens avenues for sensitizer design, indicating that green sensitizers can efficiently pump blue terminal emitters, thereby reducing device exciton energies and improving blue OLED stability.

Deep Learning-Based Chemical Similarity for Accelerated Organic Light-Emitting Diode Materials Discovery.

Thermally activated delayed fluorescence (TADF) material has attracted great attention as a promising metal-free organic light-emitting diode material with a high theoretical efficiency. To accelerate the discovery of novel TADF materials, computer-aided material design strategies have been developed. However, they have clear limitations due to the accessibility of only a few computationally tractable properties. Here, we propose TADF-likeness, a quantitative score to evaluate the TADF potential of molecules based on a data-driven concept of chemical similarity to existing TADF molecules. We used a deep autoencoder to characterize the common features of existing TADF molecules with common chemical descriptors. The score was highly correlated with the four essential electronic properties of TADF molecules and had a high success rate in large-scale virtual screening of millions of molecules to identify promising candidates at almost no cost, validating its feasibility for accelerating TADF discovery. The concept of TADF-likeness can be extended to other fields of materials discovery.

Efficient Blue Thermally Activated Delayed Fluorescence Molecules with Sandwich‐Structured Through‐Space Charge Transfer for Fabricating High‐Performance OLEDs

AbstractExploring robust blue luminescent materials is of high significance but challenging for the commercialization application of organic light‐emitting diodes (OLEDs). In this work, it is wished to report two blue thermally activated delayed fluorescence (TADF) molecules with a through‐space charge transfer feature. They have sandwich‐structured molecular backbones comprised of one triphenyltriazine acceptor and two 9‐phenylcarbazole or 3,6‐di(tert‐butyl)‐9‐phenylcarbazole donors that are linked at the 1,8,9‐positions of a 3,6‐di(tert‐butyl)carbazole holder, and exhibit high thermal stability and strong blue delayed fluorescence with high photoluminescence quantum yields and fast reverse intersystem crossing. The blue OLEDs use 2TBCTC as an emitter and provide outstanding maximum external quantum efficiencies (EQEmaxs) of up to 32.76% with Commission Internationale de I'Eclairage coordinates of (0.160, 0.206). To the best of knowledge, 2TBCTC is the most efficient blue TADF emitter based on through‐space charge transfer in the literature. Moreover, the interlayer‐sensitizing OLED employs 2TBCTC as a sensitizer for blue multi‐resonance TADF (MR‐TADF) molecule (v‐DABNA) as guest emitter attains an excellent EQEmax of 32.69% with a narrow full width at half maximum of 18 nm, validating the excellent potential of 2TBCTC as sensitizer for MR‐TADF emitters and the feasibility and effectiveness of the interlayer sensitization strategy for blue hyperfluorescence OLEDs.

A molecular descriptor of a shallow potential energy surface for the ground state to achieve narrowband thermally activated delayed fluorescence emission.

Narrowband thermally activated delayed fluorescence (TADF) molecules have extensive applications in optoelectronics, biomedicine, and energy. The full-width at half-maximum (FWHM) holds significant importance in assessing the luminescence efficiency and color purity of TADF molecules. The goal is to achieve efficient and stable TADF emissions by regulating and optimizing the FWHM. However, a bridge from the basic physical parameters (such as geometric structure and reorganization energy) to the macroscopic properties (delayed fluorescence, efficiency, and color purity) is needed and it is highly necessary and urgent to explore the internal mechanisms that influence FWHM. Herein, first-principles calculations coupled with the thermal vibration correlation function (TVCF) theory were performed to study the energy consumption processes of the excited states for the three TADF molecules (2,3-POA, 2,3-DPA, and 2,3-CZ) with different donors; inner physical parameters affecting the FWHM were detected. By analyzing the basic geometric and electronic structures as well as the transition properties and reorganization energies, three main findings in modulating FWHM were obtained, namely a large local excitation (LE) proportion in the first singlet excited state is advantageous in reducing FWHM, a donor group with weak electron-donating ability is beneficial for achieving narrowband emission, and small reorganization energies for the ground state are favorable for reducing FWHM. Thus, wise molecular design strategies to achieve efficient narrowband TADF emission are theoretically proven and proposed. We hope that these results will promote an in-depth understanding of FWHM and accelerate the development of high color purity TADF emitters.

Luminescence mechanism analysis of a TADF molecule showing peculiar thermal behavior.

In recent years, much attention has been paid to the development of thermally activated delayed fluorescence (TADF) materials with short delayed-fluorescence lifetimes to improve the device performances of OLEDs. In principle, by reducing the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) overlap, while the energy difference between S1-T1 (ΔEST) and activation energy (Ea) can be reduced, and the reverse intersystem crossing rate constant (kRISC) can be accelerated, a decrease in the radiative rate constant happens, necessitating an advanced molecular design. Furthermore, a molecule based on heptazine as a parent skeleton has recently been found to have a peculiar temperature dependence of luminescence decay, suggesting a negative gap (NG) material. In this report, we show that 9-[1,4]benzoxaborino[2,3,4-kl]phenoxaborine-7-yl-1,3,6,8-tetramethyl-9H-carbazole (TMCz-BO), a donor-acceptor linked TADF molecule with a very short delay lifetime of 750 ns, exhibits a peculiar thermal behavior similar to that of NG materials based on the temperature dependence of its luminescence decay in solution.

Significant contributions of second-order exchange terms in GW electron–hole interaction kernel for charge-transfer excitations

The GW electron–hole interaction kernel, which includes two second-order exchange terms in addition to the first-order direct and exchange terms considered in the conventional GW + Bethe–Salpeter method, is applied to 10 two-molecular systems and six thermally activated delayed fluorescence (TADF) molecules in which inter- and intramolecular charge transfer excitations are expected to occur. The contributions of the two second-order exchange terms are almost zero for intermolecular charge transfer excitations and ∼0.75 eV for intramolecular charge transfer excitations according to our exciton analysis method with exciton wave functions. For TADF molecules, we found that the second-order exchange terms are more significant than the first-order exchange terms, and the contributions—even for local-type and delocalized-type excitations—are not negligibly small. We revealed that the two second-order exchange terms are proportional to the molecular size, the exciton binding energy, and the electron–hole overlap strength for intramolecular charge-transfer excitations. We believe that our findings are indispensable for further considerations of the GW method in the future.

Molecular Engineering Modulating the Singlet-Triplet Energy Splitting of Indolocarbazole-Based TADF Emitters Exhibiting AIE Properties for Nondoped Blue OLEDs with EQE of Nearly 20.

The development of efficient blue thermally activated delayed fluorescence (TADF) emitters with an aggregation-induced emission (AIE) nature, for the construction of organic light-emitting diodes (OLEDs), is still insufficient. This can be attributed to the challenges encountered in molecular design, including the inherent trade-off between radiative decay and reverse intersystem crossing (RISC), as well as small singlet-triplet energy splitting (ΔEST) and the requirement for high photoluminescence quantum yields (ΦPL). Herein, we present the design of three highly efficient blue TADF molecules with AIE characteristics by combining π-extended donors with different acceptors to modulate the differences in the electron-donating and electron-withdrawing abilities. This approach not only ensures high emission efficiency by suppressing close π-π stacking, weakening nonradiative relaxation, and enhancing radiative transition but also maintains the equilibrium ratio between the triplet and singlet excitons by facilitating the process of RISC. These emitters exhibit AIE and TADF properties, featuring quick radiative rates and low nonradiative rates. The ΦPL of these emitters reached an impressive 88%. Based on their excellent comprehensive performance, nondoped PICzPMO and PICzPMO OLEDs achieved excellent electroluminescence performance, exhibiting maximum external quantum efficiency (EQEmax) of up to 19.5%, while the doped device achieved a higher EQEmax of 20.8%. This work demonstrated that by fusing π-extended large rigid donors with different acceptors, it is possible to regulate the difference in electron-donating and electron-withdrawing abilities, resulting in a small ΔEST, high ΦPL, and fast RISC process, which is a highly feasible strategy for designing efficient TADF molecules.

An A-D-A-Type Thermally Activated Delayed Fluorescence Emitter with Intrinsic Yellow Emission Realizing Record-High Red/NIR OLEDs upon Modulating Intermolecular Aggregations.

Realizing efficient red/near-infrared (NIR) electroluminescence (EL) by precisely modulating molecular aggregations of thermally activated delayed fluorescence (TADF) emitters is an attractive pathway, yet the molecular designs are elusive. Here, a new approach is proposed to manage molecular aggregation via a mild-twist acceptor-donor-acceptor (A-D-A)-type molecular design. A proof-of-concept TADF molecule, QCN-PhSAC-QCN, is developed that furnishes a fast radiative rate and obvious aggregation-induced emission feature. Its emission bands can be facilely shifted from intrinsic yellow to the red/NIR region via fine-tuning doping levels and molecular aggregates while maintaining elegant photoluminescence quantum yields benefiting from suppressed exciton annihilation processes. As a result, a QCN-PhSAC-QCN-based organic light-emitting diode (OLED) exhibits a record-setting external quantum efficiency (EQE) of 39.1% at a doping ratio of 10wt.%, peaking at 620nm. Moreover, its nondoped NIR OLED affords a champion EQE of 14.3% at 711nm and retains outstanding EQEs of5.40% and 2.35% at current densities of 10 and 100 mA cm-2 , respectively, which are the highest values among all NIR-TADF OLEDs at similar density levels. This work validates the feasibility of such mild-twist A-D-A-type molecular design for precisely controlling molecular aggregation while maintaining high efficiency, thus providing a promising pathway for high-performance red/NIR TADF OLEDs.

Twisted vibration of Aza-azulene promotes ultra-fast triplet-singlet up-conversion for extremely stable red electroluminescence

The fast triplet-singlet up-conversion based on thermally activated delayed fluorescence (TADF) molecules is a unique effort to improve the utilization of triplet excitons. We construct two TADF molecules using nonbenzenoid aromatic aza-azulene as donor and triazine as acceptor. The distortion structural resonance of aza-azulene enhances the reverse intersystem crossing (RISC) process, resulting in efficient inter/intramolecular charge transfer (CT) emission. The rate constant of RISC (kRISC) is 9.0 × 106 and 8.4 × 106 s−1 in solid states. Efficient Förster Energy Transfer (FRET) and/or Dexter Energy Transfer (DET) between these molecules and dopants make them suitable host materials to improve the performances of red phosphorescent organic light-emitting diodes (OLEDs). Especially, the top-emitting device achieves an external quantum efficiency (EQE) of 51.3% and a current efficiency of 68.2 cd/A at 1000 cd m−2 with a long device lifetime of LT95 = 52,350 and LT50 = 536,200 h.

Modulating excited state properties of thermally activated delayed fluorescence molecules by hybrid long-range and short-range charge transfer strategy

Balancing the rapid radiative decay process and the fast reverse intersystem crossing (RISC) process of thermally activated delayed fluorescence (TADF) molecule remains a great challenge and efficient molecular design strategies are highly desired. Herein, from a theoretical perspective, excited state properties of three reported TADF molecules (1TICz, 1BOICz and 2BOICz) are investigated based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations coupled with the thermal vibration correlation function (TVCF) method. Results indicate that, by introducing the multi-resonance (MR) acceptor, 1BOICz possesses hybrid long-range and short-range charge transfer features, balanced small energy gap (ΔEST) and large oscillator strength (f) is obtained. Furthermore, by incorporating double equivalent MR acceptors in 2BOICz, largely enhanced f with slightly changed ΔEST is achieved, inner mechanism for remarkable photophysical property is illustrated. Keep this strategy, seven new TADF molecules (2pDBA-bICz-1, 2pDBA-bICz-2, 2OSBA-bICz, 2DQAO-bICz, 2QAO-bICz, 2SQAO-bICz and 2OQAO-bICz) are theoretically designed, detailed physical parameters are analyzed and excited state energy consumption process is studied. Strong electrophilicity on acceptor is determined and the strength of nucleophilic sites on the bridge-phenyl of 2DQAO-bICz, 2QAO-bICz, 2SQAO-bICz and 2OQAO-bICz is increased, this promotes the short-range charge transfer property. In addition, the excitation processes for all studied molecules are dominated by long-range charge transfer from donor to acceptors, and supplemented by the short-range charge transfer on the bridge-phenyl with MR effect. Compromise energy gap and oscillator strength as well as large spin orbit coupling (SOC) constant are obtained for designed molecules. Thus, by regulating the long-range and short-range charge transfer ratios, excited state properties are successfully modulated and new efficient TADF molecules are proposed. Our research aims to provide deeper insight into long-range and short-range charge transfer features in balancing small ΔEST and large f, which could facilitate the development of novel efficient TADF molecules.

Carbonized polymer dots assisted thermally activated delayed fluorescence to achieve stronger luminescence

Carbonized polymer dots (CPDs) feature a strongly cross-linked system with a large number of energy levels, which limits the vibration and rotation of the luminous center, reduces non-radiative relaxation deactivation, and allows for cross-linking-enhanced emission (CEE). This study first predicted the rationality of designing thermally activated delayed fluorescence (TADF) molecules using theoretical calculations of electronic structure and interaction region indicators (IRI), and then introduced a highly cross-linked system of carbonized polymer dots to stabilize the triplet state of TADF and confine the vibrational and rotational relaxation. Finally, it is demonstrated through experiments, molecular electrostatic potential (MESP) analysis, and electron density difference maps that the luminescence mechanism between CPDs and TADF is due to the formation of O–H⋯N hydrogen bond interactions, which promote the reverse intersystem crossing process of thermally activated delayed fluorescence, which achieves high photoluminescence quantum yield (PLQY) in powder state and solves the problem of TADF stability. The PLQY of Ph-tBuCz@CPDs is 34.40 %, and the PLQY of Ph-DPCz@CPDs is 30.57 %. The produced TADF molecules and TADF@CPDs were used to detect electrochemiluminescence (ECL) signals, demonstrating the multifunctionality of TADF materials and proposing a specific notion for material design in biosensing.

Thermally activated delayed fluorescence emitters with bulky four-coordinate boron acceptors for high-performance solution-processed OLEDs

Although considerable progress has been made in vacuum-deposited thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs), the development of inexpensive solution-processed TADF-OLEDs still lags, primarily owing to low luminous efficiency. Herein, we designed and synthesized two TADF emitters by introducing bulky four-coordinate boron into pyrimidine acceptor, producing a simple and versatile approach to dramatically enhance performance. The introduction of bulky four-coordinate boron substantially reduces the singlet–triplet energy gap and improves photoluminescent quantum yield as well as improves solubility by inhibiting intermolecular aggregation or crystallization, resulting in an excellent TADF characteristics and highly efficient solution-processed OLEDs. Finally, the Spiro-PMB-SPAc emitter provides an OLED device with a remarkable maximum external quantum efficiency of 38.21 %, which reaches 32.50 % at a luminance of 500 cd m−2. This state-of-the-art performance validates the superiority of the boron-nitrogen coordination strategy in the reconstruction of pyrimidine-based TADF molecules for highly efficient solution-processed OLEDs.