Blue Thermally Activated Delayed Fluorescence Research Articles

Manipulating Complementarity of Binary White Thermally Activated Delayed Fluorescence Systems for 100% Exciton Harvesting in OLEDs

AbstractDifferent to fluorescent and phosphorescent counterparts, white thermally activated delayed fluorescence (TADF) involves in multiple reverse intersystem crossing (RISC), leading to the correlation but competition between blue and other color components in both singlet and triplet allocations. Herein, three blue TADF emitters SSFAPO, DSFAPO, and TSFAPO, collectively named xSFAPO are developed, featuring a moderately electron‐withdrawing phosphine oxide (PO) acceptor respectively linked 1‐3 donors. Despite nearly identical blue emissions, photoluminescence quantum yields of xSFAPO are proportional to donor number. But, their RISC efficiencies are below 70%, markedly less than 85% of a conventional yellow TADF emitter 2,3,5,6‐tetrakis(3,6‐di‐(tert‐butyl)carbazol‐9‐yl)‐1,4‐dicyanobenzene (4CzTPNBu). Furthermore, sp3 hybrid configuration of PO enlarges steric hindrance of peripheral donor groups. So, Dexter energy transfer is impeded by increasing donor numbers. Among xSFAPO and 4CzTPNBu dually doped white‐emitting films, yellow emission from SSFAPO‐based film is the strongest, reflecting the predominance of fast Dexter energy transfer in triplet allocation. Therefore, SSFAPO endowed its warm‐white organic light‐emitting diodes (WOLEDs) with an external quantum efficiency of 25.1%, corresponding to 100% internal quantum efficiency, which are 1.25 and 1.60 folds of those of DSFAPO and TSFAPO‐based WOLEDs. These results suggest advantage complementarity of different components is crucial for developing white‐emitting systems with 100% exciton utilization.

High-efficiency, long-lifetime deep-blue organic light-emitting diodes

Simultaneously achieving both a high efficiency and long lifetime in deep-blue organic light-emitting diodes is challenging. Here we report thermally activated delayed fluorescence (TADF) organic light-emitting diodes that aim to meet this goal by combining a new design of blue TADF materials with a triplet-exciton recycling protocol. Two TADF materials, one distributing and one emitting, were doped into a host to form triplet-exciton-distributed TADF devices. The singlet excitons were transferred from the host to the emitter via the distributing TADF material by cascade energy transfer, whereas the triplet excitons were transferred to the emitter as singlet excitons by a triplet-exciton recycling process between the low-triplet-energy host and the distributing TADF material. The resulting triplet-exciton-distributed TADF devices achieved a high external quantum efficiency of 33.5 ± 0.1, a colour coordinate corrected current efficiency over 400 cd A–1, a lifetime of >5,000 h and a y colour coordinate below 0.10. Exciton energy cascade transfer and recycling bring improvements in the efficiency and lifetime of deep-blue organic light-emitting diodes.

Mixed-host engineering of blue thermally activated delayed fluorescence devices for enhanced efficiency and suppressed efficiency roll-off

Abstract Blue thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) with enhanced efficiency and suppressed efficiency roll-offs were fabricated using a mixed host consisting of 3,3-di(9H-carbazol-9-yl)-biphenyl (mCBP) and bis[2-(diphenyl-phosphino)phenyl]ether oxide (DPEPO). Notably, mCBP and DPEPO, which are generally used as hosts in blue TADF OLEDs, exhibit material stability and efficiency as their trade-off characteristics. The mixed-host structure, when applied to 10,10′-(4,4′-sulfonylbis(4,1-phenylene))bis(9,9-dimethyl-9,10-dihydroacridine), which is a blue TADF dopant, facilitated a maximum efficiency of 18.1%. Furthermore, the critical current density (J0), at which the external quantum efficiency decreases by half of its maximum value, was observed to be 3.9 times that of the DPEPO device.

Adjusting the photophysical properties of AIE-active TADF emitters from through-bond to through-space charge transfer for high-performance solution-processed OLEDs

Intramolecular through-space charge transfer (TSCT) excited state has been exploited for developing thermally activated delayed fluorescence (TADF) emitters, while the adjustment of excited state dynamics by conformational engineering is still rare. Herein, we designed a series of AIE-active TADF emitters, bearing triphenylamine as donor and phenyl ketone as acceptor unit, and the evolution of charge transfer from through-bond to through-space is realized by controlling the relative position of the donor and acceptor units. Upon transforming the charge transfer categories from through-bond to through-space, the reverse intersystem crossing (RISC) rate is progressively improved by virtue of the narrower energy split between singlet and triplet states (ΔΕST), meanwhile, the restricted intramolecular motion suppresses the non-radiative decay effectively, resulting in obviously improved luminescence efficiency. Appointing a bipolar blue TADF material as host to sensitize these emitters, solution-processed organic light-emitting diodes (OLEDs) based on TSCT emitter 1TCPM-Cz achieve maximum current efficiency (CE) of 35.5 cd A−1 and external quantum efficiency (EQE) of 13.3%, respectively, which is higher than that of through-bond charge transfer (TBCT) analogues. The work demonstrates a convenient design strategy to achieve high-performance TSCT emitters by regulating the conformation of the donor and acceptor.

High efficiency and extremely low roll-off solution- and vacuum-processed OLEDs based on isophthalonitrile blue TADF emitter

Capable of harvesting all singlet and triplet excitons, thermally activated delayed fluorescence (TADF) emitters hold promise in replacing blue-emitting fluorescent/phosphorescent emitters, however, they suffer from prolonged delayed fluorescence (exciton) lifetime causing pronounced efficiency roll-off in organic light-emitting diodes (OLEDs). Here, we address this issue in isophthalonitrile-based blue TADF emitters by imposing enlarged steric hindrance via methylation at 1-position of carbazolyl donors, and thus, promoting substantial shrinking of the singlet–triplet energy gap. The endowed features resulted in 35-fold boost of reverse intersystem crossing rate (up to 2.47 × 106 s−1) and substantial shortening of delayed fluorescence lifetime (down to 3.66 µs) in the modified compound DMeCzIPN. Moreover, DMeCzIPN-based blue OLED fabricated by cost-effective solution-process demonstrated superior performance, i.e. high efficiency (max. EQE = 21.6%) with exceptionally low efficiency roll-off, similar to those of vacuum-deposited device based on this emitter. High EQE of 19.6% and 12.7% were maintained at 1000 cd/m2 and at an extreme brightness of 10,000 cd/m2, respectively, indicating suppressed exciton annihilation processes in the emissive layer. The results imply great potential of isophthalonitrile-based TADF emitters for solution-processable high-brightness OLED applications such as displays and lighting.

Exploring the possibility of using fluorine-involved non-conjugated electron-withdrawing groups for thermally activated delayed fluorescence emitters by TD-DFT calculation.

The trifluoromethyl group has been previously explored as a non-conjugated electron-withdrawing group in donor–acceptor thermally activated delayed fluorescence (TADF) emitters. In the present study, we investigate computationally the potential of other fluorine-containing acceptors, trifluoromethoxy (OCF3), trifluoromethylthio (SCF3), and pentafluorosulfanyl (SF5), within two families of donor–acceptor TADF emitters. Time-dependent density functional theory calculations indicate that when only two ortho-disposed carbazole donors are used (Type I molecules), the lowest-lying triplet state possesses locally excited (LE) character while the lowest-lying singlet state possesses charge-transfer character. When five carbazole donors are present in the emitter design (Type II molecules), now both S1 and T1 states possess CT character. For molecules 2CzOCF3 and 5CzOCF3, the singlet energies are predicted to be 3.92 eV and 3.45 eV; however, the singlet-triplet energy gaps, ΔESTs, are predicted to be large at 0.46 eV and 0.37 eV, respectively. The compounds 2CzCF3, 2CzSCF3, and 2CzSF5, from Type I molecules, show significant promise as deep blue TADF emitters, possessing high calculated singlet energies in the gas phase (3.62 eV, 3.66 eV, and 3.51 eV, respectively) and small, ΔESTs, of 0.17 eV, 0.22 eV, and 0.07 eV, respectively. For compounds 5CzSCF3 and 5CzSF5, from Type II molecules, the singlet energies are stabilized to 3.24 eV and 3.00 eV, respectively, while ΔESTs are 0.27 eV and 0.12 eV, respectively, thus both show promise as blue or sky-blue TADF emitters. All these six molecules possess a dense number of intermediate excited states between S1 and T1, thus likely leading to a very efficient reverse intersystem crossing in these compounds.

Spiral Donor Design Strategy for Blue Thermally Activated Delayed Fluorescence Emitters.

Thermally activated delayed fluorescence (TADF) emitters with a spiral donor show tremendous potential toward high-level efficient blue organic light-emitting diodes (OLEDs). However, the underlying design strategy of the spiral donor used for blue TADF emitters remains unclear. As a consequence, researchers often do "try and error" work in the development of new functional spiral donor fragments, making it slow and inefficient. Herein, we demonstrate that the energy level relationships between the spiral donor and the luminophore lead to a significant effect on the photoluminescent quantum yields (PLQYs) of the target materials. In addition, a method involving quantum chemistry simulations that can accurately predict the aforementioned energy level relationships by simulating the spin density distributions of the triplet excited states of the spiral donor and corresponding TADF emitters and the triplet excited natural transition orbitals of the TADF emitters is established. Moreover, it also revealed that the steric hindrance in this series of molecules can form a nearly unchanged singlet (S1) state geometry, leading to a reduced nonradiative decay and high PLQY, while a moderated donor-acceptor (D-A) torsion in the triplet (T1) state can induce a strong vibronic coupling between the charge-transfer triplet (3CT) state and the local triplet (3LE) state, achieving an effective reverse intersystem crossing (RISC) process. Furthermore, an electric-magnetic coupling is formed between the high-lying 3LE state and the charge-transfer singlet (1CT) state, which may open another RISC channel. Remarkably, in company with the optimized molecular structure and energy alignment, the pivotal TADF emitter DspiroS-TRZ achieved 99.9% PLQY, an external quantum efficiency (EQE) of 38.4%, which is the highest among all blue TADF emitters reported to date.

Highly efficient blue TADF emitters incorporating bulky acridine moieties and their application in solution-processed OLEDs

Two bulky acridine moieties, 9,9-diphenyl-9,10-dihydroacridine (DPAc) and 10H-spiro [acridine-9,9′-fluorene] (SpiroAc), were selected as electron donors. Compared with commonly used 9,9-dimethyl-9,10-dihydroacridine (DMAc), phenyl modified acridines exhibited low-lying highest occupied molecular orbital (HOMO) levels and relatively weak electron-donating abilities, which make them potential units to create blue TADF emitter. DPAc and SpiroAc were connected with a triarylboron group and constructed centrosymmetric 3D-A architectures, namely 3DPAc-TB and 3SpiroAc-TB, respectively. Density functional theory calculations showed that both molecules exhibited large dihedral angles between the triarylboron unit and acridine planes. The well-separated frontier molecular orbitals contributed to small energy gaps between S1 and T1 states of the designed molecules (0.12 and 0.07 eV, respectively). Both molecules exhibited distinct thermally activated delayed fluorescence (TADF) character. The bulky acridine donors endowed both molecules with rigid structures and realized high photoluminescent quantum yields (71.6% and 84.3%, respectively). Solution-processed organic light-emitting diodes (OLEDs) utilizing 3DPAc-TB and 3SpiroAc-TB as emitters exhibited blue emissions with emission peaks of 472 nm and 490 nm, respectively. The maximum external quantum efficiencies of 3DPAc-TB and 3SpiroAc-TB based devices were 12.8% and 17.3%, respectively.

High-power-efficiency thermally activated delayed fluorescence white organic light-emitting diodes based on asymmetrical host engineering

Developing thermally activated delayed fluorescence (TADF) white organic light emitting diodes (WOLED) featuring high power efficiencies faces a challenge in balancing carrier transport, energy transfer and quenching suppression. Here, we demonstrate that host matrix is crucial for the modification of optoelectronic process in emissive layers (EML) and the achievement of high power efficiency. Through asymmetrically introducing two or three diphenylphosphine oxide (DPPO) groups, three phosphine oxide (PO) hosts 24DBFDPO , 26DBFDPO and 248DBFTPO were constructed, in which dibenzofuran (DBF) chromophore is embedded by rationally spatial distribution of DPPO groups in 26DBFDPO and 248DBFTPO . Direct steric effect of DPPOs suppresses the host-dopant and dopant-dopant interaction induced quenching and mitigates excessive dopant-dopant energy transfer. Dually-doped white TADF films of 248DBFTPO reveal the improved white color purity with a high quantum yield of ~ 90%. Simultaneously, remote steric and electron-withdrawing effects of DPPOs remedy carrier transport in 248DBFTPO films. Based on a simple trilayer single-EML device structure, 248DBFTPO endowed its full-TADF WOLEDs with the state-of-the-art performance, especially the top-rank power efficiency beyond 70 lm W −1 . This work indicates host engineering can provide a feasible approach to realize the practical application of TADF daily lighting. • Host engineering based Asymmetric phosphine oxide hosts were implemented for white TADF diodes. • Intermolecular interactions in host matrixes are accurately adjusted with spatial asymmetry of phosphine oxide groups. • Carrier mobility of 10 −6 cm 2 V −1 s −1 for neat films and ~ 90% PLQYs of blue and white TADF doped films are achieved. • High power efficiency beyond 70 lm W −1 was realized by a simple trilayer single-emissive-layer TADF WOLED.

Bee-shaped host with ideal polarity and energy levels for high-efficiency blue and white fluorescent organic light-emitting diodes

An ideal host for blue emitters with thermally activated delayed fluorescence (TADF) should bear a moderate polarity to relax charge transfer (CT) states of dopant for a reduced singlet-triplet energy gap (ΔEST) while utter-mostly keeping blue emission, a high triplet energy to confine exciton, and a small ΔEST for feasible charge injection. However, it is rather challenging to simultaneously fulfill all those requirements as the strong CT characteristic necessary for a small ΔEST usually enlarge polarity and lower energy levels. Here, a symmetrical ortho-linked diphenylphosphine oxide (DPO)/carbazole derivative is developed, of which the configuration resembles the bee with carbazoles as front wings, phenyl rings on DPO as back wings, hooked together by π-π interaction. This motif features a short distance of charges for a moderate polarity of 3.45 D, a twisted non-conjugation structure for a small ΔEST of 0.24 eV with a high triplet of 2.98 eV and multiple intermolecular interactions for enhanced charge transport. The corresponding blue TADF device realizes a compromise between efficiency and colors with a maximum external quantum efficiency (EQEmax) of 35.7% and a CIEy of 0.20. Furthermore, a full-TADF white device with this host realizes a EQEmax of 26.1%, representing the state-of-the-art performance.

Highly Performances Blue Thermally Activated Delayed Fluorescence Devices and Efficient Host-Emitter Interactions

The influence of host-emitter interactions on electroluminescent (EL) performances of thermally activated delayed fluorescence (TADF) emitter had not explored in detail. In this study, by doping DMTDAc into host materials with different polarity and energy levels as emitting layer, we demonstrated that the choice of host can be able to greatly impact on the EL performances. Finally, we found the variation of device performances was mainly dominated by energy transfer and charge trapping progresses in emitting layers, and stable blue TADF device with maximum efficiencies and brightness of 23.74 cd/A, 24.05 lm/W, 21.9% and 5695 cd/m2, was obtained.

CN-substituted ortho-terphenyl core based high triplet energy bipolar host materials for stable and efficient blue TADF devices

Two novel, CN-substituted ortho-terphenyl (OTP) core based bipolar type host materials were designed and synthesized for application in blue thermally activated delayed fluorescence (TADF) devices.

N-Type host materials based on nitrile and triazine substituted tricyclic aromatic compounds for high-performance blue thermally activated delayed fluorescence devices

Novel n-type host materials based on tricyclic aromatic compounds, dibenzo[b,d]furan and dibenzo[b,d]thiophene (2Trz6CNDBF and 2Trz6CNDBT), have been successfully synthesized and characterized for high-performance blue thermally activated delayed fluorescence (TADF) organic light-emitting devices (OLEDs). Dibenzo[b,d]furan and dibenzo[b,d]thiophene were utilized as central molecular building blocks to achieve excellent thermal stability and high triplet energy (ET). Nitrile and diphenyltriazine functional groups were introduced at the 6- and 2- positions of the central building blocks to achieve low-lying lowest unoccupied molecular orbital (LUMO) energy levels, high ET, and excellent electron transport properties. UV–Vis absorption, low-temperature photoluminescence, and ultraviolet photoelectron spectroscopy analysis showed that 2Trz6CNDBF and 2Trz6CNDBT possessed high ET (2.95 and 2.88 eV) and low-lying LUMO energy levels (−3.43 and −3.16 eV) that were well-matched with a blue TADF emitter, 5CzCN. Moreover, the electron-only device (EOD) result revealed that 2Trz6CNDBF and 2Trz6CNDBT had excellent electron transport properties. Blue TADF OLEDs fabricated with a p-type host material, mCBP, and n-type host, 2Trz6CNDBF or 2Trz6CNDBT, exhibited lower driving voltages (3.34 and 3.26 V, respectively) than a TADF OLED with only a p-type host material, mCBP (3.83 V). Blue TADF OLEDs with 2Trz6CNDBF and 2Trz6CNDBT exhibited superior external quantum efficiency (ηext, 15.6 and 14.7%), current efficiency (ηce, 33.8 and 32.7 cd A−1), and power efficiency (ηpe, 25.6 and 25.7 lm W−1), respectively. The ηext and ηce of blue TADF OLEDs with 2Trz6CNDBF and 2Trz6CNDBT increased by more than 70% and ηpe by approximately 150% compared to those of the TADF OLED with a single p-type host, mCBP. In addition, the device lifetimes of blue TADF OLEDs with 2Trz6CNDBF and 2Trz6CNDBT increased by more than 1000%. The efficient electron injection by the low-lying LUMO energy level, effective exciton confinement by high ET, and high thermal stability of the film morphology provided the enhanced efficiency and lifetime for blue TADF OLEDs with 2Trz6CNDBF and 2Trz6CNDBT.

Improved stability of blue TADF organic electroluminescent diodes via OXD-7 based mixed host.

Thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) have been demonstrated in applications such as displays and solid-state lightings. However, weak stability and inefficient emission of blue TADF OLEDs are two key bottlenecks limiting the development of solution processable displays and white light sources. This work presents a solution-processed OLED using a blue-emitting TADF small molecule bis[4-(9,9-dimethyl-9,10-dihydroacridine) phenyl]sulfone (DMAC-DPS) as an emitter. We comparatively investigated the effects of single host poly(N-vinylcarbazole) (PVK) and a co-host of 60% PVK and 30% 2,2'-(1,3-phenylene)-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole] (OXD-7) on the device performance (the last 10% is emitter DMAC-DPS). The co-host device shows lower turn-on voltage, similar maximum luminance, and much slower external quantum efficiency (EQE) rolloff. In other words, device stability improved by doping OXD-7 into PVK, and the device impedance simultaneously and significantly reduced from 8.6 × 103 to 4.2 × 103 Ω at 1000 Hz. Finally, the electroluminescent stability of the co-host device was significantly enhanced by adjusting the annealing temperature.

Enhancing spin-orbital coupling in deep-blue/blue TADF emitters by minimizing the distance from the heteroatoms in donors to acceptors

How to enhance the reverse intersystem crossing (RISC) rates of deep-blue/blue thermally activated delayed fluorescent (TADF) materials remains a difficult task to be solved. Incorporating heteroatoms can effectively enhance the spin-orbital coupling (SOC) between their singlet and triplet states, and boost their RISC processes thereby, though the relationship between the locations of heteroatoms and SOC remains rarely studied. Here, we have designed and synthesized six analogous TADF materials with different types and locations of heteroatoms. It is revealed that minimizing the distance from the heteroatoms in donors to acceptors can significantly enhance the contribution of heteroatoms to the natural transition orbitals of singlet and triplet states, promote their n-π* transition proportion, and enhance the SOC between them thereby. As a result, the maximum spin-orbital coupling matrix elements (SOCMEs) of deep-blue TADF material BFCZPZ1 containing heteroatom O and blue TADF material BTCZPZ1 containing heteroatom S are as high as 0.311 and 0.980 cm−1, respectively, which accelerate their RISC processes. Fabricated deep-blue/blue TADF devices based on them exhibit high efficiencies with low efficiency roll-off. These findings provide a guideline in further designing high performance deep-blue/blue TADF materials containing heteroatoms.

1.42-Fold Enhancement of Blue OLED Device Performance by Simply Changing Alkyl Groups on the Acridine Ring

Summary Developing high-efficiency blue thermally activated delayed fluorescence (TADF) emitters is still a formidable challenge. Here, we report five blue TADF emitters designed by simply changing the frequently used methyl group (C1) to a longer one gradually to subtly adjust the energy levels. DAc-C1–DAc-C5 are developed by using diphenylsulfone (DPS) as the acceptor and acridine with different-length alkyl chains on C(9) as the donor groups. These five compounds have high photoluminescence quantum yields (PLQYs) (75%–84%) with blue emission. The DAc-C2-based OLED device exhibits the maximum external quantum efficiency (EQE) of up to 24.1% with CIE (0.15, 0.19), which is 1.42 times higher than that of state-of-the-art TADF OLEDs based on DAc-C1 (EQE: 17.0%) under the same conditions, confirming the power of the molecular design strategy. Furthermore, the crystal analyses partially explain the influence of the alkyl chain on the device property, demonstrating a new approach for achieving TADF luminogens with high performance.

High performance TADF-phosphorescence hybrid warm-white organic light-emitting diodes with a simple fully doping-free device structure

White organic light-emitting diodes (WOLEDs) with doping-free emissive layer (EML) structures have been increasingly attracting attention due to their excellent advantages, such as easier manufacturing process and more flexible structure design. In this paper, a series of highly efficient hybrid WOLEDs is manufactured using a simple doping-free EML structure, which is composed of two blue thermally activated delayed fluorescence (TADF) emitters and an ultrathin (<0.1 nm) orange phosphorescent emitter. Through the thickness optimization of the blue TADF emitters, the optimal device shows a maximum external quantum efficiency, power efficiency, current efficiency, and luminance of 9.1%, 22.7 lm/W, 29.0 cd/A, and 14 530 cd/m2, respectively. When the brightness is increased from 1000 cd/m2 to 10 000 cd/m2, the chromaticity coordinates migrate from (0.44, 0.48) to (0.41, 0.47), and the correlated color temperature changes from 3454 to 3881 K, which belongs to the warm-white light emission zone. The result indicates that the use of a doping-free blue–orange–blue structure provides a common path for fabricating efficient, simple, and low cost WOLEDs.

Highly Efficient Deep-Blue OLEDs using a TADF Emitter with a Narrow Emission Spectrum and High Horizontal Emitting Dipole Ratio.

New blue (DBA-SAB) and deep-blue (TDBA-SAF) thermally activated delayed fluorescence (TADF) emitters are synthesized for blue-emitting organic-light emitting diodes (OLEDs) by incorporating spiro-biacridine and spiro-acridine fluorene donor units with an oxygen-bridged boron acceptor unit, respectively. The molecules show blue and deep-blue emission because of the deep highest occupied molecular energy levels of the donor units. Besides, both emitters exhibit narrow emission spectra with the full-width at half maximum (FWHM) of less than 65nm due to the rigid donor and acceptor units. In addition, the long molecular structure along the transition dipole moment direction results in a high horizontal emitting dipole ratio over 80%. By combining the effects, the OLED utilizing DBA-SAB as the emitter exhibits a maximum external quantum efficiency (EQE) of 25.7% and 1931 Commission Internationale de l'éclairage (CIE) coordinates of (0.144, 0.212). Even a higher efficiency deep blue TADF OLED with a maximum EQE of 28.2% and CIE coordinates of (0.142, 0.090) is realized using TDBA-SAF as the emitter.

Selective efficiency boosting in thermally activated delayed fluorescence emitters by a secondary donor

The design strategy of thermally activated delayed fluorescence (TADF) emitters for high quantum efficiency in the TADF devices was developed by addition of a secondary donor in an ortho- linkage based donor–acceptor type TADF emitter. The secondary donors were substituted at para- position of the acceptor in the ortho- linkage based TADF compound to improve the absorption and emission properties. The external quantum efficiency of the TADF emitters was increased from 15.8% to 22.7% by the introduction of the secondary donor without changing the emission color of the devices. Based on these results, the molecular design strategy presented in this work can be effective to develop highly efficient blue TADF devices.

Three‐ and Four‐Coordinate, Boron‐Based, Thermally Activated Delayed Fluorescent Emitters

AbstractRecent developments in purely organic‐material‐based thermally activated delayed fluorescence (TADF) emitters are helping to make them suitable for commercial applications in the near future. In spite of their high external quantum efficiencies, the broad emission spectra and short device lifetimes are the main barriers to using TADF emitters. Among the classes of materials, boron‐embedded polycyclic aromatic compounds have shown potential as TADF emitters that overcome the technical issues. In particular, highly efficient boron‐based TADF emitters with the advantage of a narrowband emission spectrum have been reported recently relying on the concept of a multi‐resonance effect. Hence, boron TADF emitters have the potential to become next‐generation emitters. Based on the future scope of the boron‐based TADF emitters (especially in development of blue TADF emitters), three‐ and four‐coordinate boron TADF emitters are reviewed. Additionally, future prospects of boron‐based TADF emitters are discussed to resolve the issues of low efficiency and short lifetimes of blue emitters.