Small Efficiency Roll-off Research Articles

Twisted Structure and Multiple Charge-Transfer Channels Endow Thermally Activated Delayed Fluorescence Devices with Small Efficiency Roll-Off and Low Concentration Dependence.

Despite the rapid development of thermally activated delayed fluorescent (TADF) materials, developing organic light-emitting diodes (OLEDs) with small efficiency roll-off remains a formidable challenge. Herein, we have designed a TADF molecule (mClSFO) based on the spiro fluorene skeleton. The highly twisted structure and multiple charge-transfer channels effectively suppress aggregation-caused quenching (ACQ) and endow mClSFO with excellent exciton dynamic properties to reduce efficiency roll-off. Fast radiative rate (kr) and rapid reverse intersystem crossing (RISC) rate (kRISC) of 1.6×107 s-1 and 1.07×106 s-1, respectively, are obtained in mClSFO. As a result, OLEDs based on mClSFO obtain impressive maximum external quantum efficiency (EQEmax) exceeding 20 % across a wide doping concentration range of 10-60 wt %. 30 wt % doped OLED exhibits an EQEmax of 23.1 % with a small efficiency roll-off, maintaining an EQE of 18.6 % at 1000 cd m-2. The small efficiency roll-off and low concentration dependence observed in the TADF emitter underscore its significant potential.

Efficient Deep-Blue Organic Light-Emitting Diodes Employing Doublet Sensitization.

Fast and efficient exciton utilization is a crucial solution and highly desirable for achieving high-performance blue organic light-emitting diodes (OLEDs). However, the rate and efficiency of exciton utilization in traditional OLEDs, which employ fully closed-shell materials as emitters, are inevitably limited by spin statistical limitations and transition prohibition. Herein, a new sensitization strategy, namely doublet-sensitized fluorescence (DSF), is proposed to realize high-performance deep-blue electroluminescence. In the DSF-OLED, a doublet-emitting cerium(III) complex, Ce-2, is utilized as sensitizer for multi-resonance thermally activated delayed fluorescence emitter ν-DABNA. Experimental results reveal that holes and electrons predominantly recombine on Ce-2 to form doublet excitons, which subsequently transfer energy to the singlet state of ν-DABNA via exceptionally fast (over 108s-1) and efficient (≈100%) Förster resonance energy transfer for deep-blue emission. Due to the circumvention of spin-flip in the DSF mechanism, near-unit exciton utilization efficiency and remarkably short exciton residence time of 1.36µs are achieved in the proof-of-concept deep-blue DSF-OLED, which achieves a Commission Internationale de l'Eclairage coordinate of (0.13, 0.14), a high external quantum efficiency of 30.0%, and small efficiency roll-off of 14.7% at a luminance of 1000cdm-2. The DSF device exhibits significantly improved operational stability compared with unsensitized reference device.

Triphenylene-Based Emitters with Hybridized Local and Charge-Transfer Characteristics for Efficient Nondoped Blue OLEDs with a Narrowband Emission and a Small Efficiency Roll-Off.

Developing high-efficiency nondoped blue organic light-emitting diodes (OLEDs) with high color purity and low-efficiency roll-off is vital for display and lighting applications. Herein, we developed two asymmetric D-π-A blue emitters, PIAnTP and PyIAnTP, in which triphenylene is first utilized as a functional acceptor. The relatively weak charge transfer (CT) properties, rigid molecular structures, and multiple supramolecular interactions in PIAnTP and PyIAnTP can significantly enhance the fluorescence efficiency and suppress the structural relaxations to obtain a narrowband blue emission. The photophysical experiments and theoretical simulations reveal that they both exhibit a typical hybridized local and charge-transfer (HLCT) excited state and achieve high external quantum efficiency (EQE) via a "hot exciton" channel. As a result, PIAnTP- and PyIAnTP-based nondoped devices realize blue emission at 456 and 464 nm, corresponding to CIE coordinates of (0.16, 0.14) and (0.16, 0.19), narrow full width at half-maximums of 52 and 60 nm, and the high EQEs of 8.36 and 8.69%, respectively. More importantly, the PIAnTP- and PyIAnTP-based nondoped devices show small EQE roll-offs of only 5.9 and 2.4% at 1000 cd m-2, respectively. These results signify an advance in designing a highly efficient blue emitter for nondoped OLEDs.

Exciton Dynamics and Optically Pumped Lasing in 1‐Naphthylmethylamine‐Based Quasi‐2D Perovskite Films

AbstractFilms of the quasi‐2D perovskite based on 1‐naphthylmethylamine (NMA) are promising as the gain medium for optically pumped lasing and future electrically pumped lasing because of its low lasing threshold and small electroluminescence efficiency rolloff. However, reasons for the low threshold and small efficiency rolloff are still unclear. Therefore, exciton dynamics are investigated in NMA‐based quasi‐2D perovskite films. It is found that quenching of bright excitons by other excitons or charge carriers is unlikely in NMA‐based quasi‐2D perovskite films, which is one reason for the low lasing threshold and small efficiency rolloff. Moreover, thermally stimulated current measurements reveal that the defect levels inside the band gap of the NMA‐based quasi‐2D perovskite are shallow, with a depth of ≈0.3 eV, causing a decrease in nonradiative exciton recombination through the defects. Therefore, population inversion can be easily achieved, leading to the low lasing threshold as well. For fabrication of NMA‐based quasi‐2D perovskite laser devices with even lower lasing thresholds, a circular‐shaped optical resonator, and small‐molecule‐based defect passivation are used. Optically pumped lasing can be obtained from these devices, with a threshold of ≈1 µJ cm−2, which is one of the lowest values ever reported in any perovskite lasers.

Phenoxazine and phenothiazine embedded Multi-Resonance emitters for highly efficient Pure-Red OLEDs with improved color purity

Multi-resonance (MR) emitters based on boron-nitrogen doped polycyclic aromatic hydrocarbons are the cutting-edge light-emitting materials for organic light-emitting diodes (OLEDs) due to their high photoluminescence quantum yield and narrowband emission spectra. Among all the widely-reported MR molecules, emitters showing pure-red emission are the least developed. The difficulty in designing pure-red MR emitters lies in the limit of the weak charge transfer nature of the MR framework, as well as the large molecular weight which may bring difficulty in vacuum sublimation process. Herein, through introducing the strong electron donating phenoxazine and phenothiazine moiety into the double-boron-based MR molecular skeleton, two novel MR emitters namely PXZBNO and PTZBNO were designed and synthesized. These two emitters exhibited pure-red emission with emission maxima up to 627 nm, small full-width at half-maximum (FWHM) of 45 nm. Red OLEDs based on PTZBNO demonstrated very high maximum external quantum efficiency (EQEmax) of 34.5%, together with very small efficiency roll-off. Meanwhile, PXZBNO-based purity pure-red OLEDs exhibited high color purity with color coordinates of (0.69, 0.31), which is approaching BT. 2020 standard.

Efficient Circularly Polarized Electroluminescence from Achiral Luminescent Materials.

Circularly polarized electroluminescence (CP-EL) is generally produced in organic light-emitting diodes (OLEDs) based on special CP luminescent (CPL) materials, while common achiral luminescent materials are rarely considered to be capable of direct producing CP-EL. Herein, near ultraviolet CPL materials with high photoluminescence quantum yields and good CPL dissymmetry factors are developed, which can induce blue to red CPL for various achiral luminescent materials. Strong near ultraviolet CP-EL with the best external quantum efficiencies (ηext s) of 9.0 % and small efficiency roll-offs are achieved by using them as emitters for CP-OLEDs. By adopting them as hosts or sensitizers, commercially available yellow-orange achiral phosphorescence, thermally activated delayed fluorescence (TADF) and multi-resonance (MR) TADF materials can generate intense CP-EL, with high dissymmetry factors and outstanding ηext s (30.8 %), demonstrating a simple and universal avenue towards efficient CP-EL.

Realizing high-performance bluish-green ionic thermally activated delayed fluorescence materials through counterion regulation

Ionic thermally activated delayed fluorescence (iTADF) materials have rarely been reported and applied in organic light emitting diodes (OLEDs) owing to their poor sublimability, photoluminescence (PL) and electroluminescence (EL) performance. It is appealing and challenging to develop iTADF emitters for high-performance OLEDs based on a deep understanding of their structure–property relationship. In this work, we report three new iTADF materials, DMAC-TPP[Br], DMAC-TPP[BF4] and DMAC-TPP[BArF24], which have the same phosphonium-cation-based chromophore and different counter anions. These materials show excellent PL properties, e.g., high photoluminescence quantum yields (PLQYs), short exciton lifetimes and fast reverse intersystem crossing (RISC). The comparative studies reveal that the photophysical properties of these iTADF materials are slightly affected by the anions via molecular configuration, intra-/inter-molecular interactions and molecular stacking. More importantly, we find that the anions play a key role in determining the EL performance of the iTADF emitters. The change of anions can lead to 3-fold increased external quantum efficiency (EQE), over 21-fold increased luminance and significantly suppressed efficiency roll-offs for the iTADF-OLEDs. The solution-processed OLED based on DMAC-TPP[BF4] achieved a EQE of 15.1 % with small efficiency roll-offs of only 0.7 % and 10.6 % at luminance of 100 cd/m2 and 1000 cd/m2, and a maximum luminance of 10400 cd/m2. The significant difference in EL performance is ascribed to the different charge recombination governed by the migration and hole-trapping ability of anions under an electric field. These results motivate the further development of high-performance iTADF materials for EL applications by anion engineering.

Through-Space Conjugated Molecule with Dual Delayed Fluorescence and Room-Temperature Phosphorescence for High-Performance OLEDs

Purely organic materials with room-temperature phosphorescence usually have much longer triplet state lifetimes than noble-metal containing phosphorescent materials, which lead to severe exciton quenching and inferior electroluminescence (EL) performance when applied in organic light-emitting diodes (OLEDs). Herein, a novel through-space conjugated molecule (2,3-PICz-XT) with dual delayed fluorescence and room-temperature phosphorescence is developed. Owing to suitable energy levels and strong spin–orbit coupling among excited states, 2,3-PICz-XT has short phosphorescence lifetimes at microsecond scale and high photoluminescence quantum yields in neat and doped films. 2,3-PICz-XT can function as efficient emitters in OLEDs, providing high external quantum efficiencies (ηexts) of up to 32.73% with small efficiency roll-offs. It can also efficiently sensitize various phosphorescent and thermally activated delayed fluorescence (TADF) materials to yield excellent EL performances. Impressively, the hyperfluorescence OLEDs using 2,3-PICz-XT as sensitizer for multiple resonance TADF materials attain narrow EL spectra and greatly improved ηexts over 35%. To the best of our knowledge, 2,3-PICz-XT is the most efficient emitter and sensitizer ever reported for dual delayed fluorescence and phosphorescence materials.

Pressure-shortened delayed fluorescence lifetime of solid-state thermally activated delayed fluorescent 4CzIPN: the structure evolution.

The incorporation of mechanochromic luminescence into thermally activated delayed fluorescence (TADF) molecules is a promising strategy for developing multifunctional mechanochromic luminescent materials. Nevertheless, due to the difficulties in systematic design, it is still challenging to controllably exploit the versatility of TADF molecules. In this work, we were surprised to find that the delayed fluorescence lifetime of 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene crystals was continuously shortened with increasing pressure, which was ascribed to the increasing HOMO/LUMO overlap by planarization of the molecular conformation, as well as the pressure-induced emission enhancement and obvious multicolor emission at high pressure (green to red), owing to the formation of new interactions and the part-planarization of the molecular conformation, respectively. This study not only developed a new function of TADF molecules, but also provided a route to shorten the delayed fluorescence lifetime, which is beneficial for designing TADF-OLEDs with small efficiency roll-off.

Weak-conjugation linked donor–acceptor emitters for efficient near-ultraviolet organic light-emitting diodes with narrowed full width at half maximum

By weak conjugation, stable near-ultraviolet (NUV) emitters are prepared for organic light-emitting diodes fabrication and highly pure NUV electroluminescence with small efficiency roll-off is achieved with narrowed full-width at half maxima.

Metal-Perturbed Multiresonance TADF Emitter Enables High-Efficiency and Ultralow Efficiency Roll-Off Nonsensitized OLEDs with Pure Green Gamut.

Multiresonance (MR)-induced thermally activated delayed fluorescence (TADF) emitters based on B- and N-embedded polycyclic aromatics are desirable for ultrahigh-definition organic light-emitting diodes (OLEDs) due to their high photoluminescence quantum yield (PLQY) and narrow bandwidth. But the reverse intersystem crossing (RISC) rates of MR-TADF emitters are usually small, resulting in severe device efficiency roll-off at high brightness. To solve this issue, a sensitizer for the MR-TADF emitter has been required. Herein, a new MR-TADF emitter is developed through coordination of Au with B/N-embedded polycyclic ligand. Benefitting from the Au perturbation, the RISC rate is dramatically accelerated to 2.3 × 107 s-1 , leading to delayed fluorescence lifetime as short as 4.3 µs. Meanwhile, the PLQY of 95% and full width at half maximum of 39nm (0.18eV) are essentially unchanged after metal coordination. Therefore, a high PLQY, short delayed fluorescence lifetime, and high color purity are concurrently realized in a single TADF emitter. Accordingly, vacuum-deposited OLEDs exhibit high-performance electroluminescence with a maximum external quantum efficiency (EQE) of 35.8% without sensitization. The EQE is maintained as high as 32.3% at 10000cd m-2 . Furthermore, solution-processed OLED based on the emitter also achieves excellent performance with a maximum EQE of 25.7% and a small efficiency roll-off.

Stable Tetradentate Gold(III)-TADF Emitters with Close to Unity Quantum Yield and Radiative Decay Rate Constant of up to 2× 106 s-1 : High-Efficiency Green OLEDs with Operational Lifetime (LT90 ) Longer than 1800 h at 1000cd m-2.

High maximum external quantum efficiency (EQEmax ), small efficiency roll-offs, and long operational lifetime at practical luminances are three crucial parameters for commercialization of organic light-emitting diodes (OLEDs). To simultaneously achieve these goals, it is desirable to have the radiative decay rate constant (kr ) as large as possible, which, for a thermally activated delayed fluorescent (TADF) emitter, requires both a large S1 →S0 radiative decay rate constant (kr S ) and a small singlet-triplet energy gap (ΔEST ). Here, the design of a class of tetradentate gold(III) TADF complexes for narrowing the ΔEST while keeping the kr S large is reported. The as-synthesized complexes display green emission with close to unity emission quantum yields, and kr approaching 2× 106 s-1 in thin films. The vacuum-deposited green OLEDs based on 1 and 4 demonstrate maximum EQEs of up to 24 and 27% with efficiency roll-offs of 5.5 and 2.2% at 1000cd m-2 , respectively; the EQEs maintain high at 10000cd m-2 (19% (1) and 24% (4)). A long LT90 device lifetime of 1820h at 1000cd m-2 for complex 1 is achieved, which is one of the longest device lifetimes of TADF-OLEDs reported in the literature.

Phosphonium-Based Ionic Thermally Activated Delayed Fluorescence Emitters for High-Performance Partially Solution-Processed Organic Light-Emitting Diodes

Phosphonium-Based Ionic Thermally Activated Delayed Fluorescence Emitters for High-Performance Partially Solution-Processed Organic Light-Emitting Diodes

Robust sky-blue aggregation-induced delayed fluorescence materials for high-performance top-emitting OLEDs and single emissive layer white OLEDs

The development of blue luminescent materials plays a crucial role in the industry of organic light-emitting diodes (OLEDs). Herein, two sky-blue luminescent materials (mCP-BP-DMAC and DCB-BP-DMAC) comprised of electron donors of 9-(3-(9H-carbazol-9-yl)phenyl, 9-(4-(9H-carbazol-9-yl)phenyl and 9,9-dimethyl-9,10-dihydroacridine and electron acceptor of benzoyl are synthesized and characterized. They exhibit excellent thermal and electrochemical stabilities, strong aggregation-induced delayed fluorescence and bipolar carrier transport ability, and behavior efficiently in nondoped and doped bottom-emitting OLEDs with high external quantum efficiencies (ηexts) of up to 26.6% and small efficiency roll-offs. Efficient top-emitting OLEDs employing mCP-BP-DMAC and DCB-BP-DMAC as emitters are also achieved, providing sky-blue lights with high color purity and impressive ηexts over 30%. In addition, hybrid white OLEDs with stable emission color and high color rendering index are fabricated based on a single emissive layer consisting of orange-red phosphorescent Ir(MDQ)2acac dopant and sky-blue mCP-BP-DMAC and DCB-BP-DMAC hosts, furnishing excellent ηexts of up to 24.1% and small efficiency roll-offs. These results demonstrate mCP-BP-DMAC and DCB-BP-DMAC are outstanding luminescent and host materials with great application potentials in display and lighting devices.

A simple bipolar host material based on triphenylamine and pyridine featuring σ-linkage for efficient solution-processed phosphorescent organic light-emitting diodes

Solution-processable host materials play an important role in achieving highly efficient and cost-effective phosphorescent organic light-emitting diodes (PhOLEDs). This paper designed and prepared a simple solution-processable host material of TPA-PyF2 based on triphenylamine and pyridine to fabricate efficient solution-processed PhOLEDs. TPA-PyF2 featured an σ-linkage between the electron donor and acceptor units, which not only served to limit the conjugation length of the molecule and maintain a high triplet energy level, but also endowed the host molecule with a three-dimensional structure to enable high film morphological stability for solution processing. As a result, TPA-PyF2 exhibited a high triplet energy level (2.82 eV), high thermal stability, bipolar charge transfer, and excellent film morphology. Blue solution-processed OLED with a simple double-layer structure based on TPA-PyF2 host achieved a maximum current efficiency, power efficiency, and luminance of 17.2 cd/A, 7.1 lm/W, and 11519 cd/m2, respectively, with a small efficiency roll-off of only 9.1% at the practical luminance of 1000 cd/m2. This work reveals that the σ-linkage strategy is promising in designing efficient solution-processable host materials for high-efficiency PhOLEDs.

High-performance non-doped near ultraviolet OLEDs with the EQE ∼ 6 % and CIEy ∼ 0.03 from high-lying reverse intersystem crossing

Developing high-performance organic fluorophors with short-wavelength emission is both significant and challenging subject in the application of organic light-emitting diodes (OLEDs). In this work, we proposes a “coupling hardness with distortion” design concept to construct an efficient near ultraviolet (NUV) fluorophor mP2MPC with 1,4-dimethyl-2,5-diphenylbenzene as a rotatable bridge via the meta-positons linking rigid and bulky phenanthroimidazole and carbazole groups. As a result, the non-doped OLED with it as emitter not only exhibits an emission peak at 395 nm with the Commission Internationale de l’éclairage coordinates of (0.163, 0.028), but also realizes a high forward-viewing external quantum efficiency of 6.09 % due to the high-lying reverse intersystem crossing. The value still keeps as high as 5.56 % at 1000 cd m−2, showing a small efficiency roll-off. This is one of the highest efficiencies among the non-doped devices with the electroluminescence peak below 400 nm. Moreover, the green and red phosphorescent OLEDs with mP2MPC as host can also show excellent electroluminescence performance with the forward-viewing external quantum efficiencies over 21.5 %, illustrating that mP2MPC should be a prospective material for OLEDs.

Triarylboron-cored multi-donors TADF emitter with high horizontal dipole orientation ratio achieving high performance OLEDs with near 39% external quantum efficiency and small efficiency Roll-off

The combination of acridine/phenoxazine donors and triarylboron acceptor has afforded two thermally activated delayed fluorescence (TADF) emitters with D3-A typed architectures, namely 3DMAC-TB and 3PXZ-TB. Attributing to the highly steric hindrance between D/A groups as well as intense intramolecular charge transfer state, both emitters exhibit well-separated frontier molecular orbitals (FMOs) distributions and distinct TADF characteristics. The high rigidity molecular structures of 3DMAC-TB and 3PXZ-TB contribute to high photoluminescence quantum yields (PLQYs) up to 0.94 and 0.89, respectively. The “star-shaped” configuration endows both emitters with high ratios of horizontal dipole orientation of 86% and 80%, respectively. The organic light emitting diodes (OLEDs) involving 3DMAC-TB and 3PXZ-TB as emitting dopants achieve maximum external quantum efficiencies of 38.8% and 29.4%, respectively. The efficiency of 3DMAC-TB based device is among the state-of-the-art efficiency for green TADF OLEDs. This work unveils great potential with triarylboron-cored multi-donors molecular design strategy in the development of excellent TADF molecules simultaneously possessing high quantum yields and preferentially horizontal emitting dipole orientations.

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

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

Multifunctional luminophores with dual emitting cores: TADF emitters with AIE properties for efficient solution- and evaporation-processed doped and non-doped OLEDs

• Three dual emitting core emitters are developed by coupling single core emitters. • The emitters possess high absorption coefficients and PLQY values in neat films. • Photophysical investigations demonstrate both AIE and TADF properties. • Highly efficient OLEDs with ultra-low efficiency roll-offs are achieved. Three novel emitters with dual emitting cores, namely 3,3′,5,5′-tetra(triphenylamine-4-yl)-[1,1′-biphenyl]-2,2′,6,6′-tetracarbonitrile (DDTPAIPN), 3,3′-di(triphenylamine-4-yl)-5,5′-di(3,5-(9,9′-dicarbazolyl)phenyl)-[1,1′-biphenyl]-2,2′,6,6′-tetracarbonitrile (DTPAmCPIPN), and 3,3′,5,5′-tetra(3,5-(9,9′-dicarbazolyl)phenyl)-[1,1′-biphenyl]-2,2′,6,6′-tetracarbonitrile (DDmCPIPN) are designed and synthesized by coupling their respective single core emitters. Compared with their single core counterparts, the three novel compounds exhibit significantly improved thermal stability, absorption coefficients, and photoluminescence efficiencies in neat films. Photophysical measurements show that these three emitters exhibit both aggregation-induced emission and thermally activated delayed fluorescence properties, which is beneficial for non-doped organic light-emitting diodes (OLEDs). The new compounds show relatively balanced charge carrier transport abilities as revealed by unipolar devices. The solution- and evaporation-processed doped and non-doped OLEDs made from these three luminophores achieve excellent electroluminescence (EL) performances. The peak current, power, and external quantum efficiencies of a DTPAmCPIPN-based solution-processed doped device reach 59.2 cd A −1 , 61.3 lm W −1 , and 17.2%, respectively, with an emission peak at 548 nm. The evaporation-processed doped device based on DTPAmCPIPN exhibits maximum EL efficiencies of up to 63.7 cd A −1 , 61.1 lm W −1 , and 19.2%. Moreover, the non-doped OLEDs also possess superior EL efficiencies with extremely small efficiency roll-offs. The molecular design strategy in this work is demonstrated to be effective in developing new emitters for efficient and stable OLEDs.

Electroplex hosts for highly efficient phosphorescent organic light-emitting diodes with extremely small efficiency roll-offs

• Four bipolar molecules were designed and synthesized for accessing exciplex and electroplex host systems. • Highly efficient green PhOLED with EQE max of 29.9% was achieved. • Extremely small efficiency roll-offs (1.3% at 1,000 cd m −2 ; 5.4% at 5,000 cd m −2 ) were obtained. Host materials are of great significance to achieve high-performance host–guest organic light-emitting diodes (OLEDs) through restraining the exciton annihilation in the emissive layer. Herein, four bipolar molecules bearing benzothienocarbazole ( BTCz )/benzothienocarboline ( BTCb ) and benzimidazole ( Bi ) moieties were designed and synthesized. Using them as hosts, green phosphorescent OLEDs (PhOLEDs) with maximum current efficiency (CE max ) of 90.8 cd A −1 , power efficiency (PE max ) of 76.5 lm W −1 , and external quantum efficiency (EQE max ) of 27.9% were obtained. More importantly, it was found that these four molecules could be used as electron-donating materials to interact with electron-accepting triazine derivatives to form electroplexes. Employing these electroplexes as hosts, highly efficient green PhOLEDs with CE max of 104.4 cd A −1 , PE max of 85.1 lm W −1 , EQE max of 29.9%, and extremely small efficiency roll-offs (EQE = 29.5%, 1.3% roll-off at 1,000 cd m −2 ; EQE = 28.3%, 5.4% roll-off at 5,000 cd m −2 ) were achieved. The excellent device performances fully exhibit the promising potential of electroplexes as hosts for high-performing OLEDs.