High Maximum External Quantum Efficiency Research Articles

High‐Efficiency and Long‐Lifetime Near‐Infrared OLEDs Based on Iridium Complexes with Enhanced Horizontal Emitting Dipole Orientation

AbstractHigh‐efficiency and long‐lifetime near‐infrared (NIR) organic light‐emitting diodes (OLEDs) are rarely reported. Herein, three efficient NIR Ir(III) complexes 1–3 are developed with specially designed cyclometallated ligands based on pyrido[3,4‐b]pyrazine and oriented substitutions along the Ir─N bond axis. Electron‐deficient pyrazine ring effectively stabilizes LUMO energy, leading to significant emission bathochromic shift. Importantly, for complexes 2 and 3, oriented substitutions along the direction of the Ir─N bond axis considerably enhance the horizontal emitting dipole orientation ratio up to 90%. Their OLEDs demonstrate high maximum external quantum efficiencies (EQEs), negligible efficiency roll‐offs, superior radiance, and long lifetimes. The maximum EQEs and radiances of devices are 9.84% and 158 W Sr−1 m−2 at 725 nm for 1, 6.98% and 14.03 W Sr−1 m−2 at 760 nm for 2, and 12.49% and 18.94 W Sr−1 m−2 at 735 nm for 3, respectively. The device lifetime LT97 at 10 mA cm−2 is 453 h for complex 2, which sets a champion lifetime for NIR‐OLEDs. This work demonstrates that pyrido[3,4‐b]pyrazine is a desired building block for robust NIR emitting Ir(III) complexes, providing a superior paradigm to combine high efficiency, negligible roll‐off, and long device lifetime simultaneously toward practical applications.

Highly efficient organic light‐emitting diodes and light‐emitting electrochemical cells employing multiresonant thermally activated delayed fluorescent emitters with bulky donor or acceptor peripheral groups

AbstractMultiresonant thermally activated delayed fluorescence (MR‐TADF) emitters have been the focus of extensive design efforts as they are recognized to show bright, narrowband emission, which makes them very appealing for display applications. However, the planar geometry and relatively large singlet–triplet energy gap lead to, respectively, severe aggregation‐caused quenching (ACQ) and slow reverse intersystem crossing (RISC). Here, a design strategy is proposed to address both issues. Two MR‐TADF emitters triphenylphosphine oxide (TPPO)‐tBu‐DiKTa and triphenylamine (TPA)‐tBu‐DiKTa have been synthesized. Twisted ortho‐substituted groups help increase the intermolecular distance and largely suppress the ACQ. In addition, the contributions from intermolecular charge transfer states in the case of TPA‐tBu‐DiKTa help to accelerate RISC. The organic light‐emitting diodes (OLEDs) with TPPO‐tBu‐DiKTa and TPA‐tBu‐DiKTa exhibit high maximum external quantum efficiencies (EQEmax) of 24.4% and 31.0%, respectively. Notably, the device with 25 wt% TPA‐tBu‐DiKTa showed both high EQEmax of 28.0% and reduced efficiency roll‐off (19.9% EQE at 1000 cd m−2) compared to the device with 5 wt% emitter (31.0% EQEmax and 11.0% EQE at 1000 cd m−2). The new emitters were also introduced into single‐layer light‐emitting electrochemical cells (LECs), equipped with air‐stable electrodes. The LEC containing TPA‐tBu‐DiKTa dispersed at 0.5 wt% in a matrix comprising a mobility‐balanced blend‐host and an ionic liquid electrolyte delivered blue luminance with an EQEmax of 2.6% at 425 cd m−2. The high efficiencies of the OLEDs and LECs with TPA‐tBu‐DiKTa illustrate the potential for improving device performance when the DiKTa core is decorated with twisted bulky donors.

Multifunctional Deep-Blue Thermally Activated Delayed Fluorescence Based on an Oxygen-Bridged Boron Acceptor for Highly Efficient Organic Light-Emitting Diodes.

Until now, thermally activated delayed fluorescence (TADF) materials based on bridged boron-based acceptors have been primarily developed as dopants. However, in this study, we synthesized and characterized multifunctional deep-blue TADF materials─t-OBO-DMAC and t-OBO-DPAC─using bridged boron-based acceptors in combination with dimethylacridine or diphenylacridine as donors. These materials serve as both dopants and hosts. Theoretical calculations and experimentally measured photophysical properties of t-OBO-DMAC reveal a smaller singlet-triplet energy difference, higher photoluminescence quantum yield, and more efficient reverse intersystem crossing compared to t-OBO-DPAC. When evaluated as TADF emitters, t-OBO-DMAC and t-OBO-DPAC exhibited maximum external quantum efficiency (EQE) of 14.4 and 7.3% with deep-blue color coordinates of (0.14, 0.11) and (0.15, 0.07), respectively. Both materials were further assessed as hosts in various configurations, including host-only, TADF, phosphorescent, and phosphor-sensitized fluorescence (PSF)-emitting systems. Notably, t-OBO-DMAC demonstrated a high maximum EQE of 13.9% with deep-blue color coordinates of (0.15, 0.07) in a nondoped host-only device. Remarkably, both materials achieved EQEs exceeding 20% in the PSF devices. Our study marks a critical advancement in the field that breaks the conventional boundaries of the dopant and host and demonstrates unprecedented multifunctionalities for advanced organic light-emitting diodes.

A Boron, Nitrogen, and Oxygen Doped π-Extended Helical Pure Blue Multiresonant Thermally Activated Delayed Fluorescent Emitter for Organic Light Emitting Diodes That Shows Fast kRISC Without the Use of Heavy Atoms.

Narrowband emissive multiresonant thermally activated delayed fluorescence (MR-TADF) emitters are a promising solution to achieve the current industry-targeted color standard, Rec. BT.2020-2, for blue color without using optical filters, aiming for high-efficiency organic light-emitting diodes (OLEDs). However, their long triplet lifetimes, largely affected by their slow reverse intersystem crossing rates, adversely affect device stability. In this study, a helical MR-TADF emitter (f-DOABNA) is designed and synthesized. Owing to its π-delocalized structure, f-DOABNA possesses a small singlet-triplet gap, ΔEST, and displays simultaneously an exceptionally faster reverse intersystem crossing rate constant, kRISC, of up to 2 × 106 s-1 and a very high photoluminescence quantum yield, ΦPL, of over 90% in both solution and doped films. The OLED with f-DOABNA as the emitter achieved a narrow deep-blue emission at 445nm (full width at half-maximum of 24nm) associated with Commission Internationale de l'Éclairage (CIE) coordinates of (0.150, 0.041), and showed a high maximum external quantum efficiency, EQEmax, of ≈20%.

Construction of Weakly Hybridized Excited State Using Donor‐π‐Acceptor Structure and Applications: From Highly Efficient Pure‐Blue Electro‐Fluorescence to Visible‐Light Polymerization

AbstractHerein this work, a novel donor‐π‐acceptor (D‐π‐A) pure‐blue hybrid local and charge‐transfer (HLCT) fluorescent material TDFBO and its functionalization as organic light emitting diode (OLED) emitter and photoinitiator (PI) in photopolymerization is reported. The weak‐hybridization property involved by the fluorene π‐bridge can simultaneously give satisfied photo‐luminescent quantum yield (PLQY) and make efficient “hot‐exciton” channel achievable. Moreover, the D‐π‐A structure can also promote an exceeding electron mobility as high as 3.57×10−4 cm2 V−1 s−1. Finally, it is noted that the TDFBO‐doped OLED can be regarded as the best one among the pure‐blue emissive OLEDs, which exhibits a high maximum external quantum efficiency of 11.1%, while the rolling‐off only stands on a low level, as 6% at 100 cd m−2. Additionally, a relatively high final conversion of C = C double bond in a representative acrylate monomer is also attained by photoinitiation of TDFBO under 405 nm LED, where the photopolymerization has been applied to 3D printing.

Bright, efficient, and stable pure-green hyperfluorescent organic light-emitting diodes by judicious molecular design

To fulfill ultra-high-definition display, efficient and bright green organic light-emitting diodes with Commission Internationale de l’Éclairage y-coordinate ≥ 0.7 are required. Although there are some preceding reports of highly efficient devices based on pure-green multi-resonance emitters, the efficiency rolloff and device stabilities for those pure-green devices are still unsatisfactory. Herein, we report the rational design of two pure-green multi-resonance emitters for achieving highly stable and efficient pure-green devices with CIEx,ys that are close to the NTSC and BT. 2020 standards. In this study, our thermally activated delayed fluorescence OLEDs based on two pure-green multi-resonance emitters result in CIEy up to 0.74. In hyperfluorescent device architecture, the CIExs further meet the x-coordinate requirements, i.e., NTSC (0.21) and BT. 2020 (0.17), while keeping their CIEys ~ 0.7. Most importantly, hyperfluorescent devices display the high maximum external quantum efficiencies of over 25% and maximum luminance of over 105 cd m−2 with suppressed rolloffs (external quantum efficiency of ~20% at 104 cd m−2) and long device stabilities with LT95s of ~ 600 h.

Acceptor Copolymerized Axially Chiral Conjugated Polymers with TADF Properties for Efficient Circularly Polarized Electroluminescence.

Chiral conjugated polymer has promoted the development of the efficient circularly polarized electroluminescence (CPEL) device, nevertheless, it remains a challenge to develop chiral polymers with high electroluminescence performance. Herein, by the acceptor copolymerization of axially chiral biphenyl emitting skeleton and benzophenone, a pair of axially chiral conjugated polymers namely R-PAC and S-PAC are synthesized. The target polymers exhibit obvious thermally activated delayed fluorescence (TADF) activities with high photoluminescence quantum yieldsof 81%. Moreover, the chiral polymers display significant circularly polarized luminescence features, with luminescence dissymmetry factor (|glum|) of nearly 3 × 10-3. By using the chiral polymers as emitters, the corresponding circularly polarized organic light-emitting diodes (CP-OLEDs) exhibit efficient CPEL signals with electroluminescence dissymmetry factor|gEL| of 3.4 × 10-3 and high maximum external quantum efficiency (EQEmax) of 17.8%. Notably, considering both EQEmax and |gEL| comprehensively, the device performance of R-PAC and S-PAC is the best among all the reported CP-OLEDs with chiral conjugated polymers as emitters. This work provides a facile approach to constructing chiral conjugated TADF polymers and discloses the potential of axially chiral conjugated luminescent skeletons in architecting high-performance CP-OLEDs.

Peripheral Selenium Modification of Multi‐Resonance Thermally Activated Delayed Fluorescence Molecules for High‐Performance Blue Organic Light‐Emitting Diodes

AbstractMulti‐resonance thermally activated delayed fluorescence (MR‐TADF) molecules have attracted much attention in the academia owing to their unique photoelectrical properties. However, MR‐TADF emitters usually show slow reverse intersystem crossing (RISC) rate, resulting in high efficiency roll‐off of organic light‐emitting diodes (OLEDs) and seriously limiting their further development. Here, a peripheral selenium (Se) modification is presented for MR‐TADF molecules to promote the RISC process while keeping the narrowband emission for high‐performance blue OLEDs. Compared to the parent molecules (NBN and tBuNBN), SeNBN and SetBuNBN exhibited narrower full‐width at half maximum (FWHM) value of 23 nm and more obvious delayed fluorescence properties with a high efficiency of delayed fluorescence up to 86%, shorter delayed lifetime of 2.4 µs as well as a faster RISC rate of 3.34×105 s−1. Therefore, high‐performance OLEDs based on these two Se modified MR‐TADF emitters are achieved with a high maximum external quantum efficiency (EQE) up to 25.5% and extremely suppressed efficiency roll‐offs of 3.9% at 100 cd m−2 and 24.4% at 1000 cd m−2. This work demonstrated that the introduction of peripheral Se atom can achieve high‐performance organic semiconductors with both narrowband emission and fast RISC rate constant for high‐performance organic optoelectronic devices.

Exciplex Hosts for Constructing Green Multiple Resonance Delayed Fluorescence OLEDs with High Color Purity And Low Efficiency Roll‐Offs

AbstractA carbazole‐based hole‐transport‐type (p‐type) host, BPhCz, is developed using a nonsymmetrical connection strategy between two identical groups. Two benzimidazole–triazine‐based electron acceptor materials with superior electron transport abilities, namely SFX‐PIM‐TRZ and DSFX‐PIM‐TRZ, are designed to fabricate exciplex‐host systems combined with BPhCz. Exciplexes exhibit excellent carrier transport characteristics and appropriate energy levels and can serve as hosts for green multiple resonance‐induced thermally activated delayed fluorescence (MR‐TADF) devices. Efficient green MR‐TADF organic light‐emitting diodes with high color purity and low efficiency roll‐offs are successfully fabricated using the exciplexes prepared from BPhCz:SFX‐PIM‐TRZ and BPhCz:DSFX‐PIM‐TRZ as hosts, which show low driving voltages of 2.6 and 2.7 V, high maximum external quantum efficiencies (EQEs) of 35.7% and 35.5%, ultrapure green emission with Commission Internationale de L'Eclairage coordinates of (0.27, 0.69) and (0.28, 0.69), and high EQEs of 31% and 30.5% at 1000 cd m−2, respectively.

Precise Regulation of Multiple Resonance Distribution Regions of a B,N‐Embedded Polycyclic Aromatic Hydrocarbon to Customize Its BT2020 Green Emission

AbstractRecently, boron (B)/nitrogen (N)‐embedded polycyclic aromatic hydrocarbons (PAHs), characterized by multiple resonances (MR), have attracted significant attention owing to their remarkable features of efficient narrowband emissions with small full width at half maxima (FWHMs). However, developing ultra‐narrowband pure‐green emitters that comply with the Broadcast Service Television 2020 (BT2020) standard remains challenging. Precise regulation of the MR distribution regions allows simultaneously achieving the emission maximum, FWHM value, and spectral shape that satisfy the BT2020 standard. The proof‐of‐concept molecule TPABO‐DICz exhibited ultrapure green emission with a dominant peak at 515 nm, an extremely small FWHM of 17 nm, and Commission Internationale de l′Eclairage (CIE) coordinates of (0.17, 0.76). The corresponding bottom‐emitting organic light‐emitting diode (OLED) exhibited a remarkably high CIEy value (0.74) and maximum external quantum efficiency (25.8 %). Notably, the top‐emitting OLED achieved nearly BT2020 green color (CIE: 0.14, 0.79) and exhibited a state‐of‐the‐art maximum current efficiency of 226.4 cd A−1, thus fully confirming the effectiveness of the above strategy.

Precise Regulation of Multiple Resonance Distribution Regions of a B,N-Embedded Polycyclic Aromatic Hydrocarbon to Customize Its BT2020 Green Emission.

Recently, boron (B)/nitrogen (N)-embedded polycyclic aromatic hydrocarbons (PAHs), characterized by multiple resonances (MR), have attracted significant attention owing to their remarkable features of efficient narrowband emissions with small full width at half maxima (FWHMs). However, developing ultra-narrowband pure-green emitters that comply with the Broadcast Service Television 2020 (BT2020) standard remains challenging. Precise regulation of the MR distribution regions allows simultaneously achieving the emission maximum, FWHM value, and spectral shape that satisfy the BT2020 standard. The proof-of-concept molecule TPABO-DICz exhibited ultrapure green emission with a dominant peak at 515 nm, an extremely small FWHM of 17 nm, and Commission Internationale de l'Eclairage (CIE) coordinates of (0.17, 0.76). The corresponding bottom-emitting organic light-emitting diode (OLED) exhibited a remarkably high CIEy value (0.74) and maximum external quantum efficiency (25.8 %). Notably, the top-emitting OLED achieved nearly BT2020 green color (CIE: 0.14, 0.79) and exhibited a state-of-the-art maximum current efficiency of 226.4 cd A-1 , thus fully confirming the effectiveness of the above strategy.

Realizing highly efficient deep-blue organic light-emitting diodes towards Rec.2020 chromaticity by restricting the vibration of the molecular framework.

Deep-blue organic light-emitting diodes (OLEDs) with narrow emission spectra and high efficiency, meeting the Rec.2020 standard, hold significant promise in the realm of 4K/8K ultrahigh-definition displays. However, the development of light-emitting materials exhibiting both narrowband emission and high efficiency, particularly in the realm of deep-blue thermally activated delayed fluorescence (TADF), confronts substantial challenges. Herein, a novel deep-blue TADF emitter, named BOC-PSi, was designed by integrating a rigid B-heterotriangulene acceptor (A) with a rigid phenazasiline donor (D). The replacement of a sp3 carbon atom with a sp3 silicon atom in the D moiety helps to restrict the low-frequency bending vibration throughout the entire D-A molecular backbone, while concurrently accelerating the multi-channel reverse intersystem crossing (RISC) processes. Notably, OLEDs using the BOC-PSi emitter exhibit exceptional performance, with a high maximum external quantum efficiency (EQEmax) approaching 20%, and a superior color purity closely aligning with the Rec.2020 blue standard.

Liquid-crystalline circularly polarised TADF emitters for high-efficiency, solution-processable organic light-emitting diodes.

Achieving a high emission efficiency and a large luminescence asymmetry factor (glum) in a single molecule exhibiting circularly polarised thermally activated delayed fluorescence (CP-TADF) remains a formidable challenge. In this work, a proof-of-concept, liquid-crystalline CP-TADF molecule is proposed to realise high glum by taking advantage of the order inherent in liquid crystals. Employing a chiral dinaphthol-based CP-TADF molecule as the emissive unit, a pair of liquid-crystalline CP-TADF molecules (R/S-4) is synthesised via the introduction of six mesogenic moieties. The enantiomers show intense emission at about 520 nm which has clear TADF and liquid-crystalline characteristics. Both enantiomers display symmetrical electronic circular dichroism (CD) and circular polarisation luminescence (CPL) signals as thin films. Impressively, relatively large glum values of 0.11 are realised for the films. Solution-processed devices were fabricated using R/S-4 as the dopants, with the TADF molecule CzAcSF as the sensitiser. The OLEDs so prepared show a very high maximum external quantum efficiency of 21.2%, revealing a novel strategy for realising large glum values in CP-TADF.

Stereo effects for efficient synthesis of orange-red multiple resonance emitters centered on a pyridine ring.

Despite theoretical difficulties, we herein demonstrate an effective strategy for the inaugural synthesis of an orange-red multiple resonance (MR) emitter centered on a pyridine ring via stereo effects. Compared to conventional benzene-centered materials, the pyridine moiety in the novel MR material acts as a co-acceptor. This results in a significant spectral redshift and a narrower spectrum, as well as an improved photoluminescence quantum yield (PLQY) due to the formation of intramolecular hydrogen bonds. As envisioned, the proof-of-concept emitter Py-Cz-BN exhibits bright orange-red emission peaking at 586 nm with a small full width at half maximum (FWHM) of 0.14 eV (40 nm), exceeding both the wavelength and FWHM achieved with benzene-centered BBCz-Y. Benefiting from high PLQYs (>92%) and suppressed chromophore interactions, the optimized organic light-emitting diodes achieved high maximum external quantum efficiencies of 25.3-29.6%, identical small FWHMs of 0.18 eV (54 nm), and long lifetimes over a wide range of dopant concentrations (1-15 wt%). The performance described above demonstrates the effectiveness of this molecular design and synthesis strategy in constructing high performance long-wavelength MR emitters.

An Ideal Molecular Construction Strategy for Ultra-Narrow-Band Deep-Blue Emitters: Balancing Bathochromic-Shift Emission, Spectral Narrowing, and Aggregation Suppression.

Narrowband emissive multiple resonance (MR) emitters promise high efficiency and stability in deep-blue organic light-emitting diodes (OLEDs). However, the construction of ideal ultra-narrow-band deep-blue MR emitters still faces formidable challenges, especially in balancing bathochromic-shift emission, spectral narrowing, and aggregation suppression. Here, DICz is chosen, which possesses the smallest full-width-at-half-maximum (FWHM) in MR structures, as the core and solved the above issue by tuning its peripheral substitution sites. The 1-substituted molecule Cz-DICz is able to show a bright deep-blue emission with a peak at 457nm, an extremely small FWHM of 14nm, and a CIE coordinate of (0.14, 0.08) in solution. The corresponding OLEDs exhibit high maximum external quantum efficiencies of 22.1%-25.6% and identical small FWHMs of 18nm over the practical mass-production concentration range (1-4 wt.%). To the best of the knowledge, 14 and 18nm are currently the smallest FWHM values for deep-blue MR emitters with similar emission maxima under photoluminescence and electroluminescence conditions, respectively. These discoveries will help drive the development of high-performance narrowband deep-blue emitters and bring about a revolution in OLED industry.

Rational Design of Circularly Polarized Luminescent Molecular Structures Toward NIR and Single Molecule White Light Emission

AbstractSingle‐molecule white‐light and near‐infrared circularly polarized luminescent materials are effective complements to the demonstrated enhancements of visible emission in the high contrast 3D images or organic light‐emitting diodes. In this contribution, two binaphthalene‐containing luminogenic enantiomers (BIT or BITM) with aggregation‐induced emission are synthesized which exhibit circularly polarized luminescence in solution with dissymmetry factors of ±5.0 × 10−3 and ±4.8 × 10−3, respectively. Additionally, the dual‐fluorescence spectra of single‐molecule white emission (CIE: 0.33, 0.34) in toluene solution are observed with (R)/(S)‐BIT in low polarity solvent originating from locally excited and twisted intramolecular charge‐transfer emission. While (R)/(S)‐BITM only shows single NIR luminescence with peaks at 720 nm in powder state. The nondoped OLEDs exhibit high maximum external quantum efficiencies of up to 4.2% with small efficiency roll‐off and NIR electroluminescence peak at 709 nm.

Regulating excited states by varying different acceptors of D-π-A emitters for efficient non-doped blue electroluminescence with high luminance and low efficiency roll-off.

Chromophores with hybridized local and charge-transfer (HLCT) excited state are promising for the realization of high performance blue organic light-emitting diodes (OLEDs). The rational manipulation of HLCT excited state for efficient emitters remains challenging. Herein, we present three donor-π-acceptor (D-π-A) molecules (mPAN, mPANPH, and mPNAPH) with phenanthro[9,10-d]imidazole (PI) and pyridinyl as donor and π-bridge respectively. Changes in various kinds of polycyclic aromatic derivative acceptors (anthracene, 9-phenylanthracene, and 1-phenylnaphthalene) could manipulate the excited states and optoelectronic properties. Theoretical calculations reveal that the S1 state of mPNAPH exhibits HLCT nature while the other two molecules show local excited (LE) state dominated feature. The photophysical properties also demonstrate this characteristic. Therefore, compared with mPAN and mPANPH, mPNAPH has higher photoluminescence quantum yield (PLQY) whether in solutions or neat films.Ultimately, the non-doped devices based on these emitters show high luminance larger than 35000 cd m-2, and high maximum external quantum efficiencies (EQEmaxs) larger than 5% with low efficiency roll-off. In particular, the mPNAPH-based device displays an excellent performance of pure blue emission at 456 nm with Commission Internationale de L'Eclairage coordinate of (0.15, 0.16) and EQEmax of 6.13% that benefited from the HLCT state and high-lying reverse intersystem crossing process.

Strongly Luminescent Tetradentate Palladium(II)‐TADF Emitters. Blue TADF And TADF‐Sensitized OLEDs with External Quantum Efficiencies Over 23%

AbstractDue to the low‐lying Pd(4d)‐orbitals, luminescent palladium(II) complexes usually show 3IL phosphorescence (IL = intraligand) with excited state lifetimes in the range of hundreds of microseconds, which limits their application in blue organic light‐emitting diodes (OLEDs). Here, a molecular design strategy for the development of strongly luminescent Pd(II)‐based thermally activated delayed fluorescence (TADF) emitters with fast radiative decay rate constants and reverse intersystem crossing rate (kRISC) constants is presented. The synthesized tetradentate [Pd(N*C*C^N)] TADF emitters show sky‐blue to yellow (λmax = 484–565 nm) emission with excited state lifetimes in the range of 0.9−8.7 µs and high photoluminescence quantum yield of up to 77% in CH2Cl2 solution. In 5 wt.% 2,8‐bis(diphenylphosphoryl)dibenzo[b,d]furan (PPF) thin films, these [Pd(N*C*C^N)] TADF complexes display blue to sky‐blue (476−496 nm) emission with quantum yields close to unity. Variable‐temperature emission lifetime measurements, femtosecond time‐resolved spectroscopy, and density functional theory (DFT) and time‐dependent DFT (TDDFT) calculations together reveal ultrafast kRISC rate constants of these [Pd(N*C*C^N)] TADF emitters. Using these Pd(II)‐TADF emitters as dopants, sky‐blue TADF and blue TADF‐sensitized OLEDs with small efficiency roll‐offs achieved high maximum external quantum efficiencies (EQEs) of 24.8% and 23.1%, respectively.

Dielectric Regulation for Efficient Top-Emission Perovskite Light-Emitting Diodes with Suppressed Efficiency Roll-off.

Perovskite light-emitting diodes (PeLEDs) have shown incalculable application potential in the fields of next-generation displays and light communication owing to the rapidly increased external quantum efficiencies (EQEs). However, most PeLEDs obtain a maximum EQE at small current density (J) region and suffer from severe efficiency roll-off in different extents. Herein, it is demonstrated that the dopant with large dipole moment like KBF4 facilitates the effective dielectric regulation of perovskite emissive layer. The increased dielectric constant lowers the exciton binding energy and suppresses the Auger recombination of the 2D/3D segregated perovskite structure, which improves the photoluminescence quantum yield remarkably at an excitation intensity up to 103mWcm-2. Accordingly, the top-emission PeLED that delivers a high maximum EQE above 20% is fabricated and can retain EQE>10% at an extremely high J of 708mAcm-2. These results represent one of the most efficient top-emission PeLEDs with ultra-low efficiency roll-off, which provide a viable methodology for tuning the dielectric response of perovskite films for improved high radiance performance of perovskite electroluminescence devices.

A Breakthrough in Solution-Processed Ultra-Deep-Blue HLCT OLEDs: A Record External Quantum Efficiency Exceeding 10% Based on Novel V-Shaped Emitters.

It is always a great challenge to achieve high-efficiency solution-processed ultra-deep-blue organic light-emitting diodes (OLEDs) with the Commission Internationale de l'Eclairage (CIE) 1931 chromaticity coordinates matching the blue primary of Rec. International Telecommunication Union-Radiocommunication BT.2100, which specifies high dynamic range television image parameters. Inspired by hybrid local and charge transfer (HLCT) excited state emitters improving exciton utilization through high-lying reverse intersystem crossing, here, a series of high-performance blue emitters by a V-shaped symmetric donor (D)-π-acceptor (A)-π-D design strategy are developed. Here, the large torsions and unstable bonds of D-A structures can be improved through π bridges, and also the conjugation length and donor groups can be easily adjusted. The obtained emitters merit excellent photophysical and electrochemical properties, thermal stability, solution processibility, and HLCT excited state excellence. Results suggest that the OLEDs based on the obtained blue emitters all achieve high maximum external quantum efficiency (EQEmax ) of more than 8% with very low efficiency roll-off. In particular, the device based on 4',5'-bis(4-(9H-carbazol-9-yl)phenyl)spiro[fluorene-9,2'-imidazole] exhibits a satisfactory ultra-deep-blue emission (CIEx , y = 0.1579, 0.0387) and a record-high EQEmax (10.40%) among solution-processed HLCT OLEDs, which is very close to the record EQEmax of devices by vacuum vapor deposition technology.