Low Roll-off Research Articles

Drag force shear manipulating ligand distribution at perovskite buried interface enables efficiently suppressed EQE roll-off of perovskite light-emitting diodes

Effectively manipulating the ligand distribution at the perovskite buried interface is critical for achieving high-performance nanocrystal-based perovskite light-emitting diodes (PeLEDs). However, it is challenging to realize it due to the non-exposed feature of the buried interface. Here, the drag force shear (DFS) is utilized to successfully regulate the ligand distribution at the perovskite buried interface which can effectively suppress the EQE roll-off of devices. By manipulating the ligand distribution at the perovskite buried interface, it is revealed that a more ligand preservation could result in an improved defect passivation leading to higher EQE, while the carrier injection barrier is increased simultaneously making devices suffer from severe EQE roll-off and decreased luminance, and vice versa. With the help of optimizing the ligand distribution by manipulating the DFS, the balance between carrier injection and interfacial defect passivation is successfully achieved. Resultantly, an enhanced EQE of 17.24 % with substantially suppressed EQE roll-off is reached, culminating in a remarkable luminance of 61,900 cd/m2. This work presents an efficient approach to control ligand distribution at the perovskite buried interface and offers valuable insights for realizing high luminance and low EQE roll-off of PeLEDs.

Strongly-Confined CsPbBr3 Perovskite Quantum Dots with Ultralow Trap Density and Narrow Size Distribution for Efficient Pure-Blue Light-Emitting Diodes.

The development of pure-blue perovskite light-emitting diodes (PeLEDs) faces challenges of spectral stability and low external quantum efficiency (EQE) due to phase separation in mixed halide compositions. Perovskite quantum dots (QDs) with strong confinement effects are promising alternatives to achieve high-quality pure-blue PeLEDs, yet their performance is often hindered by the poor size distribution and high trap density. A strategy combining thermodynamic control with a polishing-driven ligand exchange process to produce high-quality QDs is developed. The strongly-confined pure-blue (≈470nm) CsPbBr3 QDs exhibit narrow size distribution (12% dispersion) and are achieved in Br-rich ion environment based on growth thermodynamic control. Subsequent polishing-driven ligand exchange process removes imperfect surface sites and replaces initial long-chain organic ligands with short-chain benzene ligands. The resulting QDs exhibit high photoluminescence quantum yield (PLQY) to near-unity. The resulting PeLEDs exhibit a pure-blue electroluminescence (EL) emission at 472nm with narrow full-width at half-maximum (FWHM) of 25nm, achieving a maximum EQE of 10.7% and a bright maximum luminance of 7697cdm-2. The pure-blue PeLEDs show ultrahigh spectral stability under high voltage, a low roll-off of EQE, and an operational half-lifetime (T50) of 127min at an initial luminance of 103cdm-2 under continuous operation.

High-efficiency narrowband multi-resonance TADF emitters via the introduction of bulky adamantane units

New design strategy for MR-TADF emitters by incorporating bulky adamantane unit as steric hindrance into MR skeletons to mitigate intermolecular π–π stacking and green organic light-emitting diodes with high EQE up to 32.3% and low roll-off are achieved.

Alkyl-promoted iridium complex for high-performance deep-red phosphorescent organic light-emitting diodes

In this work, a novel deep-red (642 nm) iridium complex, Ir(bp4b)2(dend), is developed. The introduction of alkyl groups in ligands weakens the intermolecular interactions and endows Ir(bp4b)2(dend) with favorable physical properties: short photoluminescence lifetime (271.6 ns), low concentration sensitivity (10−6 to 10−4 M) and balanced charge-transporting ability. Ir(bp4b)2(dend)-doped phosphorescent device displays high efficiencies (9.62 cd/A, 12.25 lm/W, 15.29%), low roll-off of efficiencies (from 10 to 1000 cd/m2: no decrease; from 1000 to 5000 cd/m2: 10.6%), relatively low concentration sensitivity (from 5% to 15%), long device lifetime (T80: 5225 h at 100 cd/m2) and very stable electroluminescent spectra (from 1 cd/m2 to maximum luminance). This performance is comparable to those of previous record deep-red (around 640 nm) phosphorescent emitters. More importantly, compared with previous record emitters, Ir(bp4b)2(dend) reports more kinds of excellent parameters and such comprehensive deep-red emitter is rare at present.

Rational strategy of exciplex-type thermally activated delayed fluorescent (TADF) emitters: Stacking of donor and acceptor units of the intramolecular TADF molecule

• Rational strategy to construct high efficiency exciplex-type chromophores is put forward. • The exciplex PL decay lifetimes can be tuned from 20 μs to 800 μs by the donor structures. • Exciplex-OLEDs show prominent efficiency with EQE of 16.9% and low efficiency roll-off. The lack of the exciplex-type chromophores with high quantum yields hinders their wide applications. Here, a rational strategy to construct exciplexes with thermally activated delayed fluorescence (TADF) were designed by stacking of the donor and acceptor units of an intramolecular charge transfer (CT) chromophore (TXO-PhCz). The intermolecular CT interaction can be anticipated in DFT calculations between the TXO unit and PhCz units. By mixing TXO-P-Si with four donor molecules 1,3-Bis(carbazol-9-yl)benzene (mCP), 4,4′-Bis(carbazol-9-yl)biphenyl (CBP), 3,5-Bis(3-(9H -carbazol-9-yl)phenyl)pyridine (3,5-DCzPPy) and 3-(Diphenylphosphoryl)-9-(4-(diphenylphosphoryl)phenyl)-9H -carbazole (PPO21), emission from these exciplexes can be easily observed. And the photophysical properties of these formed exciplexes can be tuned by the structure of the carbazole-based molecules. The exciplexes eliminate the high driving voltage issue, realizing highly efficient green exciplex OLED with a low driving voltage of nearly 3.5, 3.8, and 3.6 V and maximum external quantum efficiency (EQE) up to 16.9% (53.8 cd A −1 , and 48.3 lm W −1 ), 13.7% (39.9 cd A −1 , and 36.2 lm W −1 ), 16.1% (51.0 cd A −1 , and 45.1 lm W −1 ) for mCP:TXO-P-Si, CBP:TXO-P-Si, and 3,5-DCzPPy:TXO-P-Si, respectively. Meanwhile, the efficiency roll off is small, which is comparable with the device with low efficiency roll off. The ideal OLED device based on our strategy with high efficiency and low roll-off has been realized at the same time.

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.

Polycyclic phenazine-derived rigid donors construct thermally activated delayed fluorescence emitters for highly efficient orange OLEDs with extremely low roll-off

Two new thermally activated delayed fluorescence (TADF) molecules, tBuInPz-BO and InPz-BO, are constructed via connecting novel rigid polycyclic phenazine-derived donors with oxygen-bridged boron acceptor. Both emitters exhibit fast reverse intersystem crossing rates and high photoluminescence quantum yields, owing to the high molecular structural rigidity. As a result, the orange organic light-emitting diode (OLED) fabricated with tBuInPz-BO shows a maximum external quantum efficiency (EQEmax) of 22.0% with the electroluminescence peak at 585 nm. Moreover, the device displays extremely low efficiency roll-off. At high luminance of 1000 and 10000 cd/m2, the EQE values still maintain a high level of 20.2% and 14.8%, respectively, achieving state-of-the-art electroluminescence performance among TADF-based orange OLEDs. This work reveals the great potential of the new phenazine-derived donors for constructing highly efficient TADF emitters.

High-performance full phosphorescent warm white organic light-emitting diodes with external quantum efficiency of 34.5%

In this work, we have reported full phosphorescent warm white organic light-emitting diodes (WOLEDs) consisting of three light-emitting layers not only achieving high external quantum efficiency (EQE) but also demonstrating significant color stability and low efficiency roll-off. The WOLED exhibits slight shift in Commission Internationale de l’Eclairage coordinates (CIEx,y) from (0.409, 0.405) at 1000 cd m−2 to (0.372, 0.398) at 10000 cd m−2. Moreover, the maximum external quantum efficiency is as high as 34.5% and remains >28% over wide brightness range of 100 cd m−2 to 5000 cd m−2. Our work not only provides effective design strategy for physiologically friendly warm WOLEDs but also paves the way for achieving high EQE and low roll-off all phosphorescent WOLEDs.

Highly efficient blue and white phosphorescent organic light-emitting diodes with low-efficiency roll-off utilizing thermally activated delayed fluorescent-based co-host architecture

Highly efficient blue phosphorescent organic light-emitting diodes (PhOLEDs) with reduced efficiency roll-off are still challenging. A blue phosphor of (cyanato-κO)[3,5-difluoro-2-(2-pyridinyl-κN)phenyl-κC][[1,1'-(1,3-phenylene-κC2)bis[3-butyl-2,3-dihydro-1H-imidazolato-κC2]](5-)]-iridium complex is utilized as the blue emitter to fabricate highly efficient blue PhOLEDs. Especially, it is first utilized for white PhOLEDs with superior device performance. The realized blue PhOLED employing a novel TADF co-host system achieves maximum power efficiency (PE) of 43.3 lm/W and the PE still remains 26.3 lm/W at 1000 cd/m2, which are 1.9 and 2.5 times higher than that of blue PhOLED using conventional phosphor single-host structure. Furthermore, the current efficiency (CE) roll-off of the blue PhOLED with TADF co-host architecture is only 2.2% at 1000 cd/m2, which can be assigned to the balanced charge carriers injection and transport. The final white device obtained the maximum CE of 46.1 cd/A, PE of 48.1 lm/W, and a low roll-off of 1.9% at 1000 cd/m2. We also systemically investigate the energy transfer mechanism and exciton distribution of the devices. It was found that our proposed device structure could effectively promote the Förster energy transfer mechanism and the even distribution of excitons. We firmly believe that our work may bring light to the future development of highly efficient PhOLEDs with simultaneous low roll-off.

Aggregation induced intermolecular charge transfer in simple nonconjugated donor–acceptor system

The exploration of exciplex for organic light-emitting diodes (OLEDs) has been fleetly developed. However, many of them confront with the problems like phase separation and poor solubility, hampering their utilization in solution process. Hence, a series of soluble exciplex luminophores with the simple architecture of D-spacer-A (mCP-6C-TRZ, phCz-6C-TRZ and 2phCz-6C-TRZ) are synthesized and characterized, in which, the alkyl chain as ample spacer breaks the molecular backbone conjugation, induces intermolecular charge transfer process instead of intramolecular charge transfer in solid state. These materials are endowed with narrowed singlet−triplet splitting energy (ΔE ST ), efficient reverse intersystem crossing (RISC) process, and distinct thermally activated delayed fluorescence (TADF) characteristics. In view of their high triplet energy level (E T ) and bipolar carrier transport ability, where efficient exciplexes are applied as the host, the solution-processed phosphorescence devices realize a low efficiency roll-off of 7.0% at 1000 cd m −2 , high luminance, current efficiency (CE) and external quantum efficiency (EQE) of 25,990 cd m −2 , 20.0 cd A −1 and 6.7%, respectively. These results offer a promising tactic to the establishment of exciplex with TADF feature as host for fabricating efficient solution processed OLEDs. Three exciplex materials with D-spacer-A configuration, were synthesized and characterized, where the long alkyl chain as spacer provided a platform for intermolecular charge transfer instead of intramolecular charge transfer, induced TADF characteristic, as well as the better EL performance of doped solution processed OLEDs obtained based on mCP-6C-TRZ as bipolar host. • Simple exciplex hosts with spacer linker, were synthesized and characterized. • The alkyl chain as spacer deters intra-CT, induces inter-CT and distinct TADF trait. • The solution-processed OLED based on mCP-6C-TRZ realized a low roll-off. • A luminance of 25,990 cd m −2 , CE and EQE of 20.0 cd A −1 and 6.7%, were also realized.

Effective Design Strategy for Aggregation-Induced Emission and Thermally Activated Delayed Fluorescence Emitters Achieving 18% External Quantum Efficiency Pure-Blue OLEDs with Extremely Low Roll-Off.

High-color purity organic emitters with a simultaneous combination of aggregation-induced emission (AIE) and thermally activated delayed fluorescence (TADF) characteristics are in great demand due to their excellent comprehensive performances toward efficient organic light-emitting diodes (OLEDs). In this work, two D-π-A-structure emitters, ICz-DPS and ICz-BP, exhibiting AIE and TADF properties were developed, and both the emitters have narrow singlet (S1)-triplet (T1) splitting (ΔEST) and excellent photoluminescence (PL) quantum yields (ΦPL), derived from the distorted configurations and weak intra/intermolecular interactions, suppressing exciton annihilation and concentration quenching. Their doped OLEDs based on ICz-BP provide an excellent electroluminescence external quantum efficiency (ηext) and current efficiency (ηC) of 17.7% and 44.8 cd A-1, respectively, with an ηext roll-off of 2.9%. Their nondoped OLEDs based on ICz-DPS afford high efficiencies of 11.7% and 30.1 cd A-1, with pure-blue emission with Commission Internationale de l'Éclairage (CIE) coordinates of (0.15, 0.08) and a low roll-off of 6.0%. This work also shows a strategy for designing AIE-TADF molecules by rational use of steric hindrance and weak inter/intramolecular interactions to realize high ΦPL values, fast reverse intersystem crossing process, and reduced nonradiative transition process properties, which may open the way toward highly efficient and small-efficiency roll-off devices.

Functionalized superhydrophobic quartz fabric with electro-photo-thermal conversion performance: Designed for low-cost and efficient self-heating deicing

Multifunctional, high-performance anti-icing/deicing surfaces are desired for resisting/delaying the formation of ice or reducing ice adhesion strength, but their application is limited due to poor flexibility and durability. In this work, an easy method is used to make an anti-icing/deicing surface by carbonizing and fluorinating on a soft quartz fabric (QF). Carbonizing pretreatment of quartz fabric makes carbon nanoparticles adhere to surface, decreasing the surface energy. Moreover, a dual-scale micro/nano structure is formed by microscale fabric and nanoparticles. By dipping 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FAS–17), the surface energy is further reduced and a superhydrophobic surface is obtained. The carbonated and fluorinated quartz fabric (QF–CF) has a water contact angle (WCA) of 150.2° and a low roll–off angle (RA) of 5°. The QF-CF membrane also exhibits superior self-heating performance with a dual-driving energy (electro-photo-thermal) conversion. Under voltage of 13 V, the temperature on QF–CF surface increases from room temperature to 249 °C. Under near infrared light (NIR, 2.5 W·cm−2) irradiation, a rapid light-to-heat response is observed and the temperature on surface reaches over 300 °C in 2 s. Impressively, the QF–CF exhibits excellent anti-icing performance, with a maximum icing delay time of 6 min and electro-thermal efficiency of 449 °C/ (W cm2). The multifunctional QF–CF heater is a promising and ideal candidate for future low-cost and efficient anti-icing/deicing material.

Triphenylsilyl-Promoted Iridium Complex for High-Performance Green-Yellow Phosphorescent Organic Light-Emitting Diodes

In this work, a novel triphenylsilyl-based iridium complex, fac-Ir(tpsp)2(bpp), is developed. Triphenylsilyl groups endow fac-Ir(tpsp)2(bpp) with favorable intermolecular interactions. On the one hand, the steric hindrance of a triphenylsilyl group significantly weakens intermolecular π···π interactions. On the other hand, triphenylsilyl ligands provide several C–H···π interactions for fac-Ir(tpsp)2(bpp). As a result, fac-Ir(tpsp)2(bpp) exhibits a high sublimation yield (78.2%), high photoluminescence quantum yield (97.6%), short lifetime (510.9 ns), low concentration sensitivity (10–6 to 10–4 M), and moderate charge-transporting ability. Phosphorescent devices that utilize fac-Ir(tpsp)2(bpp) as the emitter display high efficiencies (100.9 cd/A, 105.6 lm/W, 27.9%), low roll-off of efficiencies (from 100 to 10,000 cd/m2: 5.3%), relatively low concentration sensitivity (from 5 to 12%), long device lifetime (61,892 h at 100 cd/m2), and very stable electroluminescent spectra (from 1 to 70,000 cd/m2). This performance is comparable to those of previous record green/yellow phosphorescent emitters. More importantly, most of record emitters report limited excellent parameters, and comprehensive emitter-like fac-Ir(tpsp)2(bpp) is rare. These results demonstrate that fac-Ir(tpsp)2(bpp) is a good phosphorescent emitter.

Efficient Exciplex-Based Deep-Blue Organic Light-Emitting Diodes Employing a Bis(4-fluorophenyl)amine-Substituted Heptazine Acceptor.

The realization of a deep-blue-emitting exciplex system is a herculean task in the field of organic light-emitting diodes (OLEDs) on account of a large red-shifted and broadened exciplex emission spectrum in comparison to those of the corresponding single compounds. Herein, 2,5,8-tris(di(4-fluorophenyl)amine)-1,3,4,6,7,9,9b-heptaazaphenalene (HAP-3FDPA) was designed as an electron acceptor by integrating three bis(4-fluorophenyl)amine groups into a heptazine core, while 1,3-di(9H-carbazol-9-yl)benzene (mCP) possessing two electron-donating carbazole moieties was chosen as the electron donor. Excitingly, the exciplex system of 8 wt% HAP-3FDPA:mCP exhibited deep-blue emission and a high photoluminescence quantum yield of 53.2%. More importantly, an OLED containing this exciplex system as an emitting layer showed deep-blue emission with Commission Internationale de l’Eclairage coordinates of (0.16, 0.12), a peak luminance of 15,148 cd m−2, and a rather high maximum external quantum efficiency of 10.2% along with a low roll-off. This study not only reports an efficient exciplex-based deep-blue emitter but also presents a feasible pathway to construct highly efficient deep-blue OLEDs based on exciplex systems.

Enhanced Electroluminescence Based on a π-Conjugated Heptazine Derivative by Exploiting Thermally Activated Delayed Fluorescence.

Heptazine derivatives have attracted much attention over the past decade by virtue of intriguing optical, photocatalytic as well as electronic properties in the fields of hydrogen evolution, organic optoelectronic technologies and so forth. Here, we report a simple π-conjugated heptazine derivative (HAP-3DF) possessing an n→π* transition character which exhibits enhanced electroluminescence by exploiting thermally activated delayed fluorescence (TADF). Green-emitting HAP-3DF shows relatively low photoluminescence quantum efficiencies (Φ p) of 0.08 in toluene and 0.16 in doped film with bis(2-(diphenylphosphino)phenyl) ether oxide (DPEPO) as the matrix. Interestingly, the organic light-emitting diode (OLED) incorporating 8 wt% HAP-3DF:DPEPO as an emitting layer achieved a high external quantum efficiency (EQE) of 3.0% in view of the fairly low Φ p of 0.16, indicating the presence of TADF stemming from n→π* transitions. As the matrix changing from DPEPO to 1,3-di (9H-carbazol-9-yl)benzene (mCP), a much higher Φ p of 0.56 was found in doped film accompanying yellow emission. More importantly, enhanced electroluminescence was observed from the OLED containing 8 wt% HAP-3DF:mCP as an emitting layer, and a rather high EQE of 10.8% along with a low roll-off was realized, which should be ascribed to the TADF process deriving from exciplex formation.

Acceptor-Donor-Acceptor-Type Orange-Red Thermally Activated Delayed Fluorescence Materials Realizing External Quantum Efficiency Over 30% with Low Efficiency Roll-Off.

Two new orange-red thermally activated delayed fluorescence (TADF) materials, PzTDBA and PzDBA, are reported. These materials are designed based on the acceptor-donor-acceptor (A-D-A) configuration, containing rigid boron acceptors and dihydrophenazine donor moieties. These materials exhibit a small ΔEST of 0.05-0.06eV, photoluminescence quantum yield (PLQY) as high as near unity, and short delayed exciton lifetime (τd ) of less than 2.63 µs in 5 wt% doped film. Further, these materials show a high reverse intersystem crossing rate (krisc ) on the order of 106 s-1 . The TADF devices fabricated with 5 wt% PzTDBA and PzDBA as emitting dopants show maximum EQE of 30.3% and 21.8% with extremely low roll-off of 3.6% and 3.2% at 1000 cd m-2 and electroluminescence (EL) maxima at 576 nm and 595nm, respectively. The low roll-off character of these materials is analyzed by using a roll-off model and the exciton annihilation quenching rates are found to be suppressed by the fast krisc and short delayed exciton lifetime. These devices show operating device lifetimes (LT50 ) of 159 and 193 h at 1000 cd m-2 for PzTDBA and PzDBA, respectively. The high efficiency and low roll-off of these materials are attributed to the good electronic properties originatng from the A-D-A molecular configuration.

Polycyclic Phenazine-Derived Rigid Donors Construct Thermally Activated Delayed Fluorescence Emitters for Highly Efficient Orange Oleds with Extremely Low Roll-Off

Polycyclic Phenazine-Derived Rigid Donors Construct Thermally Activated Delayed Fluorescence Emitters for Highly Efficient Orange Oleds with Extremely Low Roll-Off

3-Benzoyl-4H-chromen-4-one: A novel twisted acceptor for highly efficient thermally activated delayed fluorescence emitters

In this work, a novel twisted 3-benzoyl-4H-chromen-4-one (BZC) acceptor is reported and a BZC-based thermally activated delayed fluorescence (TADF) emitter, 3-(4-(10H-phenoxazin-10-yl)benzoyl)-4H-chromen-4-one (BZC-PXZ), is developed. The unique structure of BZC endows BZC-PXZ with favorable molecular and stacking structures. First, the small and twisted structure of BZC group not only brings about large dihedral angle (88.78°) between donor and acceptor groups, but also efficiently prevents π∙∙∙π interaction. Second, the three oxygen atoms of BZC group bring about abundant weak intermolecular interactions which can enhance the charge-transporting ability of BZC-PXZ and facilitate the exciton recombination on it. As a result, BZC-PXZ exhibits small singlet-triplet energy splitting (0.02 eV) and high photoluminescence quantum yield (93%) simultaneously. Meanwhile, the BZC-PXZ-based device displays high efficiency (64.6 cd/A, 69.0 lm/W, 21.3%), high exciton utilization efficiency (77.2%) and low roll-off of efficiencies even at ultralow doped concentration of 1%. These results demonstrate that BZC group is a good acceptor for developing high-performance TADF emitters.

High performance non-doped blue-hazard-free hybrid white organic light-emitting diodes with stable high color rendering index and low efficiency roll-off

White organic light-emitting diodes (WOLEDs), for display and lighting applications, combine features such as high performance, high color quality, low efficiency roll-off and blue-hazard-free are extremely important. In this study, we manufactured a highly efficient bluish-green thermally activated delayed fluorescence (TADF) OLED. The maximum external quantum efficiency (EQE), power efficiency (PE), and current efficiency (CE) were 16.0%, 46.2 lm/W, and 45.9 cd/A, respectively. Next, a non-doped and blue-hazard-free hybrid WOLED was prepared by employing reasonably inserting several red and yellow ultra-thin phosphorescent emitters in between the bluish-green TADF emitters. The device showed a maximum EQE of 18.7% and a low EQE roll-off of 7%. At 1000 cd/m2, a high color rendering index (CRI) of 87 and a low correlated color temperature (CCT) of 2759 were obtained. The result showed that bluish-green TADF material has potential applications in healthy WOLEDs without blue-hazard. Also, the strategy of inserting several long-wavelength ultra-thin phosphorescent emitters in between bluish-green TADF emitters with bipolar transport characteristic, which can reduce efficiency roll-off and enhance device electroluminescence efficiency, was demonstrated.

Asymmetric anthracene derivatives as multifunctional electronic materials for constructing simplified and efficient non-doped homogeneous deep blue fluorescent OLEDs

• High-efficiency asymmetric anthracene derivatives as multifunctional deep blue materials for non-doped homogeneous OLEDs. • Addressing the contradiction of efficiency, color gamut and structure complexity of devices. • The outstanding homogenous OLED with a narrow-band deep blue emission and extremely low roll-off of 4.8% at 5000 cd m −2 . Herein, large π-conjugated core anthracene with an innate bipolar property was employed to construct multifunctional organic electronic materials. Delicate manipulating molecules via combining anthracene core and large periphery groups, two asymmetric anthracene derivatives namely (4-(10-(4-(9 H -1,5-diazacarbazole-9-yl)phenyl)anthracen-9-yl)phenyl)diphenylphosphine oxide ( p -PO15NCzDPA ) and (3-(10-(3-(9 H -1,5-diazarcarbazole-9-yl)phenyl)anthracen-9-yl)phenyl)diphenylphosphine oxide ( m -PO15NCzDPA ) were firstly designed and developed. The large periphery groups 1,5-diazarcarbazole (15NCz) and diphenylphosphine oxide (PO) efficiently interrupt the intramolecular π-conjugation, presenting an asymmetric bulky periphery enveloping strategy achieving highly twisted structures, which help to realize deep-blue emission. Meanwhile, due to the high PLQY and well-balanced bipolar transport characteristics, desired device addressing the contradiction of efficiency, color gamut and structure complexity is within reach. Detailed device engineering study was carried out, in which p -PO15NCzDPA and m -PO15NCzDPA were functioned as multifunction layers. As expected, p -PO15NCzDPA -based homogenous and unilateral homogenous OLEDs exhibited outstanding performance with impressive EQE max of 4.55% and 6.40%, deep blue CIE coordinates of (0.152, 0.075) and (0.151, 0.066) at the voltage of 6 V, narrow FWHM of 46 nm and 50 nm, respectively. More importantly, the simplified homogenous device achieved extremely low efficiency roll-offs of 1.3% and 4.8% at 1000 and 5000 cd m −2 , respectively. These results are among the most outstanding performance, which provided a guide for further improving the performance of deep blue fluorescent OLEDs and simplifying the structure of OLEDs.