Blue Thermally Activated Delayed Fluorescence Emitters Research Articles

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.

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.

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.

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.

Rigidity and Polymerization Amplified Red Thermally Activated Delayed Fluorescence Polymers for Constructing Red and Single‐Emissive‐Layer White OLEDs

AbstractPolymerization could be a feasible method to overcome the rigid structure induced self‐quenching effect in conventional thermally activated delayed fluorescence (TADF) emitters. Despite steady progress in TADF polymer research, developing an efficient red TADF polymer still remains a great challenge because of the large non‐radiative internal conversion rate governed by the energy gap law. Herein, a novel strategy for constructing a red TADF conjugated polymer is presented by means of embedding quinoxaline‐6,7‐dicarbonitrile (QC) as an acceptor into a polycarbazole (PCz) backbone and attaching donor 9,10‐dihydroacridine (A) as a pendant. The obtained polymers PCzAQCx with the appropriate molar content of the AQC unit (x≥ 0.5) exhibit efficient TADF features with a dominant emissive peak at 627−661 nm and a photoluminescence quantum yield of up to 76% in neat film. The non‐doped electroluminescent devices with the polymers produce red emissions with a maximum external quantum efficiency (EQE) of up to 12.5% and the emission peak at 620 nm, which represents state‐of‐the‐art performance for solution‐processed devices based on red TADF polymers. Furthermore, combined with a blue TADF emitter, the bright white devices with tunable spectra cover the whole visible–near infrared range from 400 to 900 nm and a record‐high EQE of up to 22.4% is achievable.

Asymmetrically phosphorylated carbazole host for highly efficient blue and white thermally activated delayed fluorescence diodes

Host development is crucial and challenging for thermally activated delayed fluorescence (TADF) organic light emitting diodes (OLED), which requires accurate modulation of host-dopant energy transfer and host/dopant-dopant quenching. Here, we demonstrate that phosphine oxide (PO) groups can be used to simultaneously facilitate carrier transport, positive energy transfer and quenching suppression. Two diphenylphosphine oxide (DPPO) groups at carbazole and N-phenyl of 3,6-di-tert-butyl-N-phenylcarbazole induce the spatially different steric hindrance and inductive effect of DPPOs in tBCzPPOSPO host. The asymmetric configuration with two bulky DPPOs at the same side of tBCzPPOSPO results in the lamellar structure and head-to-tail molecular packing in each layer of its single crystal. tBCzPPOSPO reveals the first singlet (S1) and triplet energy levels (T1) of 3.42 and 2.98 eV, providing the positive energy transfer to blue TADF emitter. Intermolecular interactions are mitigated by steric hindrance of tert-butyls and DPPO groups for quenching suppression. A corner of tBCzPPOSPO is uncovered, rendering electron and hole mobility by level of 10−6 cm2 V−1 s−1. Therefore, based on conventional blue and yellow TADF emitters, tBCzPPOSPO endowed its single-emissive-layer blue and white OLEDs with the state-of-the-art performance, including maximum external quantum efficiencies more than 20% and a top-rank power efficiency of 63.5 lm W−1.

Nanosecond-time-scale delayed fluorescence molecule for deep-blue OLEDs with small efficiency rolloff

Aromatic organic deep-blue emitters that exhibit thermally activated delayed fluorescence (TADF) can harvest all excitons in electrically generated singlets and triplets as light emission. However, blue TADF emitters generally have long exciton lifetimes, leading to severe efficiency decrease, i.e., rolloff, at high current density and luminance by exciton annihilations in organic light-emitting diodes (OLEDs). Here, we report a deep-blue TADF emitter employing simple molecular design, in which an activation energy as well as spin–orbit coupling between excited states with different spin multiplicities, were simultaneously controlled. An extremely fast exciton lifetime of 750 ns was realized in a donor–acceptor-type molecular structure without heavy metal elements. An OLED utilizing this TADF emitter displayed deep-blue electroluminescence (EL) with CIE chromaticity coordinates of (0.14, 0.18) and a high maximum EL quantum efficiency of 20.7%. Further, the high maximum efficiency were retained to be 20.2% and 17.4% even at high luminance.

Efficient and Stable Deep-Blue Fluorescent Organic Light-Emitting Diodes Employing a Sensitizer with Fast Triplet Upconversion.

Multiple donor-acceptor-type carbazole-benzonitrile derivatives that exhibit thermally activated delayed fluorescence (TADF) are the state of the art in efficiency and stability in sky-blue organic light-emitting diodes. However, such a motif still suffers from low reverse intersystem crossing rates (kRISC ) with emission peaks <470 nm. Here, a weak acceptor of cyanophenyl is adopted to replace the stronger cyano one to construct blue emitters with multiple donors and acceptors. Both linear donor-π-donor and acceptor-π-acceptor structures are observed to facilitate delocalized excited states for enhanced mixing between charge-transfer and locally excited states. Consequently, a high kRISC of 2.36 × 106 s-1 with an emission peak of 456 nm and a maximum external quantum efficiency of 22.8% is achieved. When utilizing this material to sensitize a blue multiple-resonance TADF emitter, the corresponding device simultaneously realizes a maximum external quantum efficiency of 32.5%, CIEy ≈ 0.12, a full width at half maximum of 29 nm, and a T80 (time to 80% of the initial luminance) of > 60 h at an initial luminance of 1000 cd m-2 .

A novel design strategy for deeper blue and more stable thermally activated delayed fluorescent emitters

Abstract Thermally activated delayed fluorescent (TADF) materials are considered as the competitive alternative to traditional fluorescent and noble-metal-based phosphorescent materials due to their high electroluminescence (EL) efficiency and low cost. Solution-processable TADF OLEDs have drawn great research attention and can be potentially applied in both flat-panel displays and lighting sources in the near future. However, the blue light emitting TADF materials with high luminance, satisfying color purity and excellent stability are still rare. Herein, two blue light emitting TADF molecules (CzAC-TRZ, DFAC-TRZ) are designed and synthesized. Due to the modified acridine units by introducing 9-phenylcarbazole and dibenzofuran as σ-groups into the molecular skeletons, CzAC-TRZ, DFAC-TRZ possess high energy states and rigid molecular configuration. Solution-processed OLEDs based on CzAC-TRZ and DFAC-TRZ achieved high EL efficiency with the external quantum efficiency (EQE) up to 11.8% and 11.5%, respectively. Moreover, compared with the analogue emitter (DMAC-TRZ) fabricated control devices, CzAC-TRZ and DFAC-TRZ OLEDs presented lower roll-offs, blue-shift and narrower EL spectra. These results have shown that introducing high energy state building blocks into the donor units via σ bonds offers a promising approach of developing stable deeper blue TADF emitters.

Rational molecular design of deep blue thermally activated delayed fluorescent emitters for high efficiency fluorescent and hyperfluorescent devices

Abstract Two deep blue thermally activated delayed fluorescent (TADF) emitters with peripheral alkyl branches surrounding the donor and acceptor moieties were synthesized to explore ideal design of deep blue TADF emitters for fluorescence and hyperfluorescence in terms of quantum efficiency. The TADF emitters having the multiple alkyl branches protecting the donor and acceptor moieties performed better than the emitter without the alkyl branch or with the alkyl branch only in the donor or acceptor unit. The TADF emitters with the peripheral alkyl branches both in the donor and acceptor units showed a high quantum efficiency above 22.0%, a deep blue color coordinate of (0.15, 0.20), and doping concentration independent emission color as TADF emitters, and 13.7% quantum efficiency in the TADF sensitized hyperfluorescent device. Therefore, the multiple alkyl modification method of both donor and acceptor units of TADF emitters can resolve the issues of TADF emitters for ideal device performances.

Efficient and Stable Organic Light-Emitting Diodes Employing Indolo[2,3-b]indole-Based Thermally Activated Delayed Fluorescence Emitters.

Triplet excitons can be effectively harvested in organic light-emitting diodes employing thermally activated delayed fluorescence (TADF) molecules as the emitter and host. A design strategy for blue and green emitters with small S1-T1 splitting (ΔEST) is to construct a donor-acceptor (D-A) type molecule with moieties combining a high T1 level with a strong electron-donating/withdrawing character. Here, we report a new kind of TADF emitter with an indolo[2,3-b]indole (IDID) donor. In comparison to other reported indolocarbazole and indoloindole donors, IDID has a higher T1 level, which is comparable to that of the classical donor 9,9-dimethyl-9,10-dihydroacridine (DMAC) for blue TADF emitters. The sky-blue and green TADF emitters based on the IDID donor and a phenyltriazine acceptor exhibit high photoluminescence quantum yields (0.78-0.92) and short TADF lifetimes (1.1-1.7 μs) in doped films. Devices employing these IDID-based emitters offer an external quantum efficiency of 19.2%, which is comparable to that obtained for a device employing an analogous compound with a DMAC donor, while the stability of the former is higher than that of the latter owing to the just-right D-A twisting angles (∼59°) in the IDID-based emitters leading to a balance between ΔEST and the fluorescence rate. The utilization of host materials with a similar polarity to the emitter is found to be an effective strategy to improve device stability.

Facile Generation of Thermally Activated Delayed Fluorescence and Fabrication of Highly Efficient Non-Doped OLEDs Based on Triazine Derivatives.

A series of donor-acceptor-donor triazine-based molecules with thermally activated delayed fluorescence (TADF) properties were synthesized to obtain highly efficient blue-emitting OLEDs with non-doped emitting layers (EMLs). The targeted molecules use a triazine core as the electron acceptor, and a benzene ring as the conjugated linker with different electron donors to alternate the energy level of the HOMO to further tune the emission color. The introduction of long alkyl chains on the triazine core inhibits the unwanted intermolecular D-D/A-A-type π-π interactions, resulting in the intermolecular D-A charge transfer. The weak aggregation-caused quenching (ACQ) effect caused by the suppressed intermolecular D-D/A-A-type π-π interaction further enhances the emission. The crowded molecular structure allows the electron donor and acceptor to be nearly orthogonal, thereby reducing the energy gap between triplet and singlet excited states (ΔEST ). As a result, blue-emitting devices with TH-2DMAC and TH-2DPAC non-doped EMLs showed satisfactory efficiencies of 12.8 % and 15.8 %, respectively, which is one of the highest external quantum efficiency (EQEs) reported for blue TADF emitters (λpeak <475 nm), demonstrating that our tailored molecular designs are promising strategies to endow OLEDs with excellent electroluminescent performances.

High‐Efficiency White Organic Light‐Emitting Diodes Based on All Nondoped Thermally Activated Delayed Fluorescence Emitters

AbstractWhile phosphorescent white organic light‐emitting diodes (WOLEDs) have attracted great attention due to their high efficiencies, the complex device structure (e.g., host–dopant systems) and the adoption of novel metals (e.g., Ir or Pt) inevitably increase the fabrication complication and manufacturing cost. Herein, a simple and cost‐effective structure based on all thermally activated delayed fluorescence (TADF) emitters is proposed to achieve high‐performance WOLEDs. The key feature of the WOLED structure is to insert an orange‐red TADF ultrathin layer within the nondoped blue TADF emitter, which can significantly reduce the energetic loss and therefore the operating voltage during electron–photon conversion process. After optimizing the energy transfer and exciton formation region between two color‐complementary TADF emitters, the all‐fluorescence WOLEDs exhibit an extremely high external quantum efficiency of 24.2% with a turn‐on voltage of 2.5 V and a color rendering index of &gt;80. It is anticipated that the results will pave the way to the realization of high‐efficiency and low‐cost WOLEDs that can outperform the typical phosphorescent devices.

High-Performance Nondoped Blue Delayed Fluorescence Organic Light-Emitting Diodes Featuring Low Driving Voltage and High Brightness.

Thermally activated delayed fluorescence (TADF) provides great potential for the realization of efficient and stable organic light‐emitting diodes (OLEDs). However, it is still challenging for blue TADF emitters to simultaneously achieve high efficiency, high brightness, and low Commission Internationale de l'Eclairage (CIE) y coordinate (CIEy) value. Here, the design and synthesis of two new benzonitrile‐based TADF emitters (namely 2,6‐di(9H‐carbazol‐9‐yl)‐3,5‐bis(3,6‐diphenyl‐9H‐carbazol‐9‐yl)benzonitrile (2PhCz2CzBn) and 2,6‐di(9H‐carbazol‐9‐yl)‐3,5‐bis(3,6‐di‐tert‐butyl‐9H‐carbazol‐9‐yl)benzonitrile (2tCz2CzBn)) with a symmetrical and rigid heterodonor configuration are reported. The TADF OLEDs doped with both the emitters can achieve a high external quantum efficiency (EQE) over 20% and narrowband blue emission of 464 nm with a CIEy < 0.2. Moreover, the incorporation of a terminal tert‐butyl group can weaken the intermolecular π–π stacking in the nondoped TADF emitter, and thus significantly suppress self‐aggregation‐caused emission quenching for enhanced delayed fluorescence. A peak EQE of 21.6% is realized in the 2tCz2CzBn‐based nondoped device with an extremely low turn‐on voltage of 2.7 V, high color stability, a high brightness over 20 000 cd m−2, a narrow full‐width at half‐maximum of 70 nm, and CIE color coordinates of (0.167, 0.248).

Optimizing energy transfer for highly efficient single-emissive-layer white thermally activated delayed fluorescence organic light-emitting diodes.

Thermally activated delayed fluorescence (TADF) white organic light-emitting diodes (WOLEDs) with simplified structures have great potential for daily lighting applications. However, the complicated energy and charge transfer processes between TADF emitters impede the development of single-layer white TADF systems. Here we demonstrate high-efficiency WOLEDs with single-emissive layers composed of blue and yellow TADF emitters with appropriate steric hindrances and energy gaps, which optimize the energy transfer from blue to yellow dopants for rational exciton allocation. As a consequence, the single-emissive-layer WOLEDs achieve the maximum external quantum efficiency beyond 20% and small roll-offs, which are among the best results of full-TADF WOLEDs.

Influence of the Dielectric Constant around an Emitter on Its Delayed Fluorescence

Despite the commercial success of organic emitters based on thermally activated delayed fluorescence (TADF), a general understanding of emitter-matrix interactions is still lacking. How does the dielectric constant around an emitter impact its delayed fluorescence? The authors study the photophysical properties of three emitters in solution, showing that a higher excited triplet state at low dielectric constants can boost the efficiency of blue TADF emitters. Experiments are supported by state-of-the-art quantum simulations. The findings may be generalized to solid-state systems, pointing to tuning of host-guest architectures to improve the efficiency of TADF-based blue OLEDs.

Dipolar and Quadrupolar Luminophores Based on 1,8‐Dimethylcarbazole−Triazine Conjugates for High‐Efficiency Blue Thermally Activated Delayed Fluorescence OLEDs

AbstractAs one of the three primary colors indispensable for full‐color displays, the development of blue emitters is of great importance and still a difficult challenge for organic light‐emitting diodes (OLEDs). Blue organic emitters exhibiting thermally activated delayed fluorescence (TADF) are anticipated to be promising materials as they have the potential to achieve high electroluminescence (EL) efficiencies and suitable color purity. In this paper, highly efficient blue TADF emitters combining 1,8‐dimethylcarbazole as a weak donor (D) unit with a triazine‐based acceptor (A) core are reported. Unlike unsubstituted carbazole, 1,8‐dimethylcarbazole can effectively induce intermolecular twisting between the D‐A linkages, thus enhancing the TADF properties. Moreover, a quadrupolar D‐A‐D‐type blue TADF emitter exhibits superior photo‐ and electroluminescence (EL) properties compared to a dipolar D‐A‐type counterpart. TADF‐OLEDs based on the D‐A‐D‐type emitter featuring the 1,8‐dimethylcarbazole−triazine conjugates display a brilliant blue EL emission and furnish a maximum external EL quantum efficiency as high as 21.2 % with CIE color coordinates of (0.16, 0.27).

Excited-state engineering of universal ambipolar hosts for highly efficient blue phosphorescence and thermally activated delayed fluorescence organic light-emitting diodes

The development of high-performance universal host materials for both blue electrophosphorescence and thermally activated delayed fluorescence (TADF) is one of the main challenges for organic light-emitting diode (OLED) technology. In this work, based on four quaternary ambipolar hosts with insulated donor-acceptor (D-A) structures, the influence of the excited-state characteristics for these hosts on their device performance was systematically investigated. It was showed that on the premise of the similar electrical properties and excited-state energy levels for positive host-dopant energy transfer (ET), the weak exciton capture ability, embodied as low exciton binding energy (Eb), for the hosts could facilitate the Dexter ET to the dopant through charge migration. Since the charge-transfer -featured excited states and small Eb of blue TADF emitters, in contrast to the blue phosphorescence (PH) counterparts, the influence of the host Eb on the device efficiencies of blue TADF dyes was dramatically enlarged, reflecting the higher sensitivity of the latter to host characteristics. In consequence, 9CzFDBFDPO with the smallest Eb endowed its blue TADF and PH devices with the state-of-the-art performance, e.g. EQE beyond 20% and EQE roll-off within 20% at 500 cd m−2. This work showed that based on the systematically optimized excited-state characteristics, the ambipolar hosts can be competent in both high-efficiency blue PH and TADF OLEDs, which is crucial for their commercial applications.