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Thermally activated delayed fluorescence (TADF) materials have emerged as a promising avenue for developing efficient and stable blue organic light‐emitting diodes (OLEDs) without incorporating heavy metals. Among the numerous donor‐acceptor architectures explored, the carbazole (Cz) and benzonitrile (BN) combination has demonstrated exceptional potential for blue OLED applications. Herein, we delve into the recent advances in TADF materials based on the Cz‐BN framework, with a particular focus on design strategies to accelerate exciton dynamics and improve material stability through kinetic and thermodynamic optimization. Eventually, challenges associated with the Cz‐BN systems in blue OLEDs, as well as prospective research directions that could unlock the full potential of this intriguing category of materials, are also discussed. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) emitters with a high horizontal orientation are highly essential for improving the external quantum efficiency (EQE) of organic light‐emitting diodes; however, pivotal molecular design strategies to improve the horizontal orientation of solution‐processable TADF emitters are still scarce and challenging. Herein, a phenyl bridge is adopted to connect the double TADF units, and generate a dimerized TADF dendrimer, D4CzBNPh‐SF. Compared to its counterpart with a single TADF unit, the proof‐of‐the‐concept molecule not only exhibits an improved horizontal dipole ratio (78 %) due to the π‐delocalization‐induced extended molecular conjugation, but also displays a faster reversed intersystem crossing rate constant (6.08×106 s−1) and a high photoluminescence quantum yield of 95 % in neat film. Consequently, the non‐doped solution‐processed device with D4CzBNPh‐SF as the emitter achieves an ultra‐high maximum EQE of 32.6 %, which remains at 26.6 % under a luminance of 1000 cd/m2. Furthermore, when using D4CzBNPh‐SF as a sensitizer, the TADF‐sensitized fluorescence device exhibits a high maximum EQE of 30.7 % at a luminance of 575 cd/m2 and a full width at half maximum of 36 nm. [ABSTRACT FROM AUTHOR]

Ir(III) carbene complexes have been explored as one of the best blue phosphors for their high performance. Herein, the authors designed and synthesized a series of blue‐emitting Ir(III) phosphors (f‐ct9a–c), featuring fac‐coordinated cyano‐imidazo[4,5‐b]pyridin‐2‐ylidene cyclometalates. These Ir(III) complexes exhibit true‐blue emission with a peak maximum spanning 448–467 nm, with high photoluminescence quantum yields of 81–88% recorded in degassed toluene. Moreover, OLED devices bearing phosphors f‐ct9a and f‐ct9b deliver maximum external quantum efficiencies (EQEmax) of 25.9% and 30.3%, together with Commission Internationale de L'Eclairage (CIEx,y) coordinates of (0.157, 0.225) and (0.142, 0.169), respectively. Remarkably, the f‐ct9b‐based device displays an incredible EQE of 29.0% at 5000 cd·m−2. The hyper‐OLED device based on f‐ct9b and ν‐DABNA exhibits an EQEmax of 34.7% and CIEx,y coordinates of (0.122, 0.131), affirming high potentials in achieving efficient blue electroluminescence. [ABSTRACT FROM AUTHOR]

With the increasing performance demand from the display market, it has become ever more important to realize wide color gamut requirement. In this paper, we fabricated a series of pTSF green devices, the optimal devices which exhibit excellent performance in the range of CIEx 0.17‐ 0.22, with the central color point meeting Adobe's green light requirements, showing the advantages in wide color gamut. Additionally, they have comparable performance to existing phosphporescent devices under DCI‐P3 light color, showing the advantages of high performance and high color purity. [ABSTRACT FROM AUTHOR]

Phosphorescent manganese(II) complexes with high photoluminescence quantum yields (PLQYs) and low cost exhibit great potential in organic light‐emitting diodes (OLEDs), information security, and X‐ray imaging. However, it is still a challenge to tune their emission colors. Herein, an effective strategy for engineering the phosphorescence colors of tetrahedral Mn(II) complexes through steric hindrance‐driven bond angle distortion is proposed. Modulating the steric hindrance between phosphine and benzofuran and varying the O─Mn─O bond angles allows these Mn(II) complexes to emit from 498 to 548 nm. Interestingly, these achiral single crystals of Mn(II) complexes exhibit significant circularly polarized luminescence signals due to symmetry breaking. Furthermore, high‐performance green OLEDs are achieved by using these Mn(II) complexes as dopants, providing a record‐high external quantum efficiency of 15.7%. These super‐duper results greatly inspire the development of multi‐color Mn(II) complexes and low‐cost Mn‐based devices. [ABSTRACT FROM AUTHOR]

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 457 nm, an extremely small FWHM of 14 nm, 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 18 nm over the practical mass‐production concentration range (1–4 wt.%). To the best of the knowledge, 14 and 18 nm 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters with narrow emission spectra have garnered significant attention in future organic light‐emitting diode (OLED) displays. However, current C=O/N‐embedded MR‐TADF systems still lack satisfactory performance in terms of electroluminescence bandwidths and external quantum efficiencies (EQEs). In this study, a C=O/N‐embedded green MR‐TADF emitter, featuring two acridone units incorporated in a sterically protected 11‐ring fused core skeleton, is successfully synthesized through finely controlling the reaction selectivity. The superior combination of multiple intramolecular fusion and steric wrapping strategies in the design of the emitter not only imparts an extremely narrow emission spectrum and a high fluorescence quantum yield to the emitter but also mitigates aggregation‐induced spectral broadening and fluorescence quenching. Therefore, the emitter exhibits leading green OLED performance among C=O/N‐based MR‐TADF systems, achieving an EQE of up to 37.2 %, a full width at half maximum of merely 0.11 eV (24 nm), and a Commission Internationale de l′Éclairage coordinate of (0.20, 0.73). This study marks a significant advance in the realization of ideal C=O/N‐based MR‐TADF emitters and holds profound implications for the design and synthesis of other MR‐TADF systems. [ABSTRACT FROM AUTHOR]

Lead halide perovskites have been widely used in optoelectronic devices due to their excellent properties; however, the toxicity of lead and the poor stability of these perovskites hinder their further application. Herein, we report a zero-dimensional (0D) lead-free organic manganese (II) bromide hybrid compound of (TBA)2MnBr4 (TBA+ = tetrabutylammonium cation) single crystals (SCs) with great environmental stability. The (TBA)2MnBr4 SCs show a strong green emission peak at 518 nm with a high photoluminescence quantum yield (PLQY) of 84.98% at room temperature, which is attributed to the d-d transition of single Mn2+ ions, as also confirmed through density functional calculation. A green light-emitting diode was produced based on (TBA)2MnBr4 SCs, which exhibited CIE coordinates (0.17, 0.69) close to those of standard green. A photodetector fabricated by the (TBA)2MnBr4 SCs shows an obvious photo response with a rapid millisecond rise/decay response time (at 365 nm). Our findings promote the research of Mn(II)-based organic–inorganic hybrid materials and pave the way by using these materials for future high-performance optoelectronic devices. [ABSTRACT FROM AUTHOR]

Extending the π‐skeletons of multi‐resonance (MR) organoboron emitters can feasibly modulate their optoelectronic properties. Here, we first adopt the indolo[3,2‐b]indole (32bID) segment as a multi‐nitrogen bridge and develop a high‐efficiency π‐extended narrowband green emitter. This moiety establishes not only a high‐yield one‐shot multiple Bora–Friedel–Crafts reaction towards a π‐extended MR skeleton, but a compact N‐ethylene‐N motif for a red‐shifted narrowband emission. An emission peak at 524 nm, a small full width at half maximum of 25 nm and a high photoluminescence quantum yield of 96 % are concurrently obtained in dilute toluene. The extended molecular plane also results in a large horizontal emitting dipole orientation ratio of 87 %. A maximum external quantum efficiency (EQE) of 36.6 % and a maximum power efficiency of 135.2 lm/W are thereafter recorded for the corresponding device, also allowing a low efficiency roll‐off with EQEs of 34.5 % and 28.1 % at luminance of 1,000 cd/m2 and 10,000 cd/m2, respectively. [ABSTRACT FROM AUTHOR]

Narrowband emitters based on the multiple resonance (MR) effect have shown great promises for applications in high‐definition displays. Though most reported MR emitters adopt the boron‐ and nitrogen‐doped triangulene‐like skeleton following the design of the DABNA series, MR materials with the nitrogen‐only indolocarbazole structures have recently emerged and demonstrated good color tunability from violet to deep red and impressive electroluminescence performances in terms of both efficiency and stability. Herein, we will summarize indolocarbazole‐based MR materials in recent reports, with emphasis on their molecular design, synthesis, photophysical and electroluminescence properties as well as some future research directions to unlock the full potential of this fascinating class of materials. [ABSTRACT FROM AUTHOR]

Though the flourishment of materials with multiple resonance (MR) in blue to green regions, red‐emissive MR emitters are still rare in literatures, which definitely should be resolved for further applications. Herein, we report a simple molecular design strategy for the construction of pure‐red MR emitters by conjugate charge transfer, which could greatly enhance the π‐conjugation degree and charge‐transfer property of the target molecule while maintaining the basic feature of MR, leading to a significant redshift of more than 128 nm compared to the selected parent MR core. The proof‐of‐concept emitter PPZ‐BN exhibited a pure‐red emission with a dominant peak at 613 nm and a small full‐width‐at‐half‐maximum of 0.16 eV (48 nm). The optimized organic light‐emitting diode showed a high external quantum efficiency of 26.9 %, a small efficiency roll‐off, and an excellent operation stability (LT99) of more than 43 hours at an initial luminance of 10 000 cd m−2. [ABSTRACT FROM AUTHOR]

Although helically chiral heterohelicenes are widely adopted in chiroptical studies, those with circularly polarized thermally activated delayed fluorescence (CP‐TADF), which are highly valuable for circularly polarized organic light‐emitting diodes (CP‐OLEDs), are rarely realized. Moreover, the core skeletons of known CP‐TADF heterohelicenes are limited to the p‐ and n‐doped structures with multiresonance effect. In this study, a new type of helically chiral CP‐TADF heterohelicenes featuring a fused donor–acceptor core skeleton is successfully designed and constructed. Enantiomers possessing high configurational stability are achieved and separated, and they efficiently emit CP light with dissymmetry factors reaching 3.1 × 10−3 in doped films. Owing to the excellent photophysical properties, a high‐performance CP‐OLED with the maximum external quantum efficiency of up to 20.0% and an electroluminescence dissymmetry factor reaching 2.9 × 10−3 is obtained. This new type of CP‐TADF heterohelicenes provides a large space for the development of high‐performance CP‐TADF materials for various applications. [ABSTRACT FROM AUTHOR]

With the increasing performance demand from the display market, it has become ever more important to realize wide color gamut and low power consumption. Employing a phosphorescence‐sensitized fluorescence (PSF) mechanism, we introduced a narrow‐spectrum green light‐emitting layer (EML) to the state‐of‐the‐art OLED device structure suitable for mass production and investigate its effect on device performance. Compared with the reference phosphorescent device, the optimal PSF devices have achieved more than 20% efficiency improvement in the range of CIEx 0.17‐ 0.27, showing the advantages of high efficiency and high color purity. [ABSTRACT FROM AUTHOR]

Pure organic phosphors capable of room-temperature phosphorescence show a great potential in organic light-emitting diodes, while it is limited by the big challenge to realize efficient electroluminescence under electric excitation. Herein, we develop a class of organic phosphors based on acridine as the electron donor, triazine as the electron acceptor and oxygen as the bridge between them. Benefitting from the characteristic donor-oxygen-acceptor geometry, these compounds are found to behave an exciting aggregation-induced organic room-temperature electrophosphorescence, and achieve a record-high external quantum efficiency of 15.8% for non-doped devices. Furthermore, they can sensitize multi-resonant emitters in the absence of any additional wide bandgap host, leading to an effective narrowband emission with a peak external quantum efficiency of 26.4% and a small full-width at half maximum of 26 nm. The results clearly indicate that donor-oxygen-acceptor geometry is a promising strategy to design organic phosphors suitable for organic light-emitting diodes. Pure organic room-temperature phosphorescencent materials draw much attention but realising electroluminescence under electric excitation is challenging. Here the authors propose a donor-oxygen-acceptor molecular design realizing aggregation-induced organic room-temperature electrophosphorescence with high external quantum efficiency. [ABSTRACT FROM AUTHOR]

A novel macrocycle of B/N‐doped calix[4]arene (C‐BN) was synthesized by a one‐shot double boronation. Owing to the structural tension and electron‐donating properties of the nitrogen atoms in the macrocycle, reaction selectively proceeds between the adjacent benzene rings outside the macrocycle. C‐BN shows a highly centrosymmetric structure with two multiple resonance (MR) fragments bridged by tertiary amine groups at the 1,3 positions of the benzene ring. Benefiting from the large intermolecular distance (>4.6 Å) between adjacent MR‐emitting cores, C‐BN also exhibits excellent narrowband emitting features against aggregation‐induced quenching and spectrum broadening. Optimized organic light‐emitting diode devices based on C‐BN exhibit high maximum external quantum efficiencies of 24.7–26.6 % and small full width at half maximums of 25–28 nm over a wide doping range of 1–12 wt %. [ABSTRACT FROM AUTHOR]

Polycyclo‐heteraborin multi‐resonance (MR) emitters are promising for high color‐purity organic light‐emitting diodes (OLEDs). Here, unlike the most common heteroatom ternary‐doped (X/B/N) frameworks, a binary‐doped (B/N) skeleton is reported with a large energy band for wide‐range color tunability. Based on this parent‐segment, a "one‐pot" catalyst‐free borylation method is developed which generates deep blue to pure green MR emitters from readily available starting materials, with peaks at 426–532 nm and full‐width‐at‐half‐maxima of 27–38 nm. Impressively, a maximum external quantum efficiency of nearly 40 % is recorded for the corresponding device with Commission Internationale de l′Eclairage coordinates of (0.14, 0.16), representing the state‐of‐the‐art performances. This work presents a new paradigm and synthesis of B/N‐doped MR emitters and will motivate the study of other novel frameworks. [ABSTRACT FROM AUTHOR]

Herein, we report a general strategy for achieving ultra‐pure green emissions by suppressing the shoulder peaks in the emission spectra of conventional polycyclic aromatic hydrocarbons (PAHs). Through precise synthetic fusion of multi‐resonance (MR) fragments with conventional PAH, extended π‐conjugation lengths, increased molecular rigidity, and reduced vibrational frequency could be simultaneously realized. The proof‐of‐concept emitters exhibited ultra‐pure green emissions with dominant peaks at ca. 521 nm, photoluminescence quantum yields that are greater than 99 %, a small full‐width‐at‐half‐maximum of 23 nm, and CIE coordinates of (0.16, 0.77). The bottom‐emitting organic light‐emitting diode (OLED) exhibited a record‐high CIEy value of 0.74 and a high maximum external quantum efficiency of 30.5 %. The top‐emitting OLED not only achieved a BT.2020 green color (CIE: 0.17, 0.78) for the first time but also showed superior performance among all green OLED devices, with a current efficiency of 220 cd A−. [ABSTRACT FROM AUTHOR]

Surface chemistry mediated direct optical patterning represents an emerging strategy for incorporating colloidal nanocrystals (NCs) in integrated optoelectronic platforms including displays and image sensors. However, the role of photochemistry of crosslinkers and other photoactive species in patterning remains elusive. Here we show the design of nitrene‐ and carbene‐based photocrosslinkers can strongly affect the patterning capabilities and photophysical properties of NCs, especially quantum dots (QDs). Their role beyond physical linkers stems from structure‐dictated electronic configuration, energy alignment and associated reaction kinetics and thermodynamics. Patterned QD layers with designed carbene‐based crosslinkers fully preserve their photoluminescent and electroluminescent properties. Patterned light emitting diodes (QLEDs) show a maximum external quantum efficiency of ≈12 % and lifetime over 4800 h, among the highest for reported patterned QLEDs. These results would guide the rational design of photoactive species in NC patterning and create new possibilities in the monolithic integration of NCs in high‐performance device platforms. [ABSTRACT FROM AUTHOR]

Highly efficient blue top emission organic light‐emitting diode with a remarkable blue index (BI) of 305 was demonstrated. This was achieved step by step through a combination of customized high reflectivity Ag anode, CPL with high refractivity, electron/hole transporting materials with high injection and transportation capabilities, and carefully engineered device configurations. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorophores (TADF) with donor–acceptor (D‐A) structures always face strong conjugation between donor and acceptor segments, rendering delocalized new molecular orbitals that go against blue emission. Developing TADF emitters with blue colors, high efficiencies, and long lifetimes simultaneously is therefore challenging. Here, a D‐void‐A structure with D and A moieties connected at the void‐position where the frontier orbital from donor and acceptor cannot be distributed, resulting in nonoverlap of the orbitals is proposed. A proof‐of‐the‐concept TADF emitter with 3,6‐diphenyl‐9H‐carbazole (D) connected at the 3'3‐positions of 9H‐xanthen‐9‐one (A), the void carbon‐atom with no distribution of the highest occupied molecular orbital (HOMO) of A‐segment, realizes more efficient and blue‐shifted emission compared with the contrast D‐A isomers. The deeper HOMO‐2 of A is found to participate into conjugation rather than HOMO, providing a wider‐energy‐gap. The corresponding blue device exhibits a y color coordinate (CIEy) of 0.252 and a maximum external quantum efficiency of 27.5%. The stability of this compound is further evaluated as a sensitizer for a multiple resonance fluorophore, realizing a long lifetime of ≈650 h at an initial luminance of 100 cd m−2 with a CIEy of 0.195 and a narrowband emission with a full‐width‐at‐half‐maxima of 21 nm. [ABSTRACT FROM AUTHOR]

Nitrogen‐containing polycyclic heteroaromatics have exhibited fascinating multi‐resonance (MR) characteristics for efficient narrowband emission, but strategies to bathochromic shift their emissions while maintaining the narrow bandwidths remain exclusive. Here, homogeneous hexatomic rings are introduced into nitrogen‐embedded MR skeletons to prolong the π‐conjugation length for low‐energy electronic transitions while retaining the non‐bonding character of the remaining parts. The proof‐of‐the‐concept emitters exhibit near unity photoluminescence quantum yields with peaks at 598 nm and 620 nm and small full‐width‐at‐half‐maximums of 28 nm and 31 nm, respectively. Optimal organic light‐emitting diodes exhibit a high external quantum efficiency of 18.2 %, negligible efficiency roll‐off, and ultra‐long lifetime with negligible degradation at an initial luminance of 10 000 cd m−2 after 94 hours. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorophors (TADF) featuring through‐space charge transfers (TSCT) suffer from low radiative decay rates (krs), especially for blue emitters. Here, a xanthene bridge is adopted to construct space‐confined face‐to‐face donor–acceptor alignment and minimize their distances down to 2.7–2.8 Å, even shorter than the interlayer distance of graphite and thus strengthening the electronic interactions. The resulting blue TSCT‐TADF emitters exhibit peaks around ≈460 nm, photoluminescence quantum yields of >90 %, and krs of nearly 107 s−1, almost 2–10 times higher than previously observed values with comparable reverse intersystem crossing rates. The corresponding blue organic light‐emitting diodes show maximum external quantum efficiencies of 27.8 % and 34.7 % with Commission Internationale de L'Eclairage y coordinates of 0.29 and 0.15 using those molecules as emitters and sensitizers, respectively. [ABSTRACT FROM AUTHOR]

Multiple resonance (MR) emitters are promising for highly efficient organic light‐emitting diodes (OLEDs) with narrowband emission; however, they still face intractable challenges with concentration‐caused emission quenching, exciton annihilation, and spectral broadening. In this study, sterically wrapped MR dopants with a fluorescent MR core sandwiched by bulk substituents were developed to address the intractable challenges by reducing intermolecular interactions. Consequently, high photo‐luminance quantum yields of ≥90 % and small full width at half maximums (FWHMs) of ≤25 nm over a wide range of dopant concentrations (1–20 wt %) were recorded. In addition, we demonstrated that the sandwiched MR emitter can effectively suppress Dexter interaction when doped in a thermally activated delayed fluorescence sensitizer, eliminating exciton loss through dopant triplet. Within the above dopant concentration range, the optimal emitter realizes remarkably high maximum external quantum efficiencies of 36.3–37.2 %, identical small FWHMs of 24 nm, and alleviated efficiency roll‐offs in OLEDs. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials with through‐space charge transfers (CT) have attracted particularly interest recently. However, the slow reverse intersystem crossing (RISC) and radiative decay always limit their electroluminescence performances. Herein, TADF molecules with ortho‐linked multiple donors‐acceptor (ortho‐Dn‐A) motif are developed to create near‐degenerate excited states for the reinforcement of spin‐orbit coupling. The incorporation of both through‐bond and through‐space CT enlarges oscillator strength. The optimal ortho‐D3‐A compound exhibits a photoluminescence quantum yield of ca. 100 %, a high RISC rate of 2.57×106 s−1 and a high radiative decay rate of 1.00×107 s−1 simultaneously. With this compound as the sensitizer, a TADF‐sensitized‐fluorescent organic light‐emitting diode shows a maximum external quantum efficiency of 31.6 % with an ultrapure green Commission Internationale de L'Eclairage y coordinate value of 0.69. [ABSTRACT FROM AUTHOR]

Efficient organic emitters in the deep‐red region are rare due to the "energy gap law". Herein, multiple boron (B)‐ and nitrogen (N)‐atoms embedded polycyclic heteroaromatics featuring hybridized π‐bonding/ non‐bonding molecular orbitals are constructed, providing a way to overcome the above luminescent boundary. The introduction of B‐phenyl‐B and N‐phenyl‐N structures enhances the electronic coupling of those para‐positioned atoms, forming restricted π‐bonds on the phenyl‐core for delocalized excited states and thus a narrow energy gap. The mutually ortho‐positioned B‐ and N‐atoms also induce a multi‐resonance effect on the peripheral skeleton for the non‐bonding orbitals, creating shallow potential energy surfaces to eliminate the high‐frequency vibrational quenching. The corresponding deep‐red emitters with peaks at 662 and 692 nm exhibit narrow full‐width at half‐maximums of 38 nm, high radiative decay rates of ca. 108 s−1, ≈100 % photo‐luminescence quantum yields and record‐high maximum external quantum efficiencies of ca. 28 % in a normal planar organic light‐emitting diode structure, simultaneously. [ABSTRACT FROM AUTHOR]

Multiple‐resonance (MR) organic emitters bearing small full‐width at half‐maximum (FWHMs) are of general interest in organic light‐emitting diodes. Indolo[3,2,1‐jk]carbazole (ICz) embedded MR‐fluorophors have demonstrated extremely small FWHMs, yet in the violet region with low electroluminescence efficiency. Herein, a strategic implementation of ICz subunits into MR fluorophors is proposed by taking advantage of the synergetic effect of para‐positioned nitrogen atoms to enhance electronic coupling to decrease emitting energy gap. Deep blue emitters peaking at 441 and 447 nm with FWHMs of only 18 and 21 nm are thereof obtained, respectively, accompanied by ≈90 % photo‐luminance quantum yields. With the assistance of a thermally activated delayed fluorescence sensitizer to recycle excitons, the corresponding narrowband electroluminescent devices show unprecedent high maximum external quantum efficiencies of 32.0 % and 34.7 % with CIEy of 0.10 and 0.085, respectively. [ABSTRACT FROM AUTHOR]

Bright and efficient blue emission is key to further development of metal halide perovskite light-emitting diodes. Although modifying bromide/chloride composition is straightforward to achieve blue emission, practical implementation of this strategy has been challenging due to poor colour stability and severe photoluminescence quenching. Both detrimental effects become increasingly prominent in perovskites with the high chloride content needed to produce blue emission. Here, we solve these critical challenges in mixed halide perovskites and demonstrate spectrally stable blue perovskite light-emitting diodes over a wide range of emission wavelengths from 490 to 451 nanometres. The emission colour is directly tuned by modifying the halide composition. Particularly, our blue and deep-blue light-emitting diodes based on three-dimensional perovskites show high EQE values of 11.0% and 5.5% with emission peaks at 477 and 467 nm, respectively. These achievements are enabled by a vapour-assisted crystallization technique, which largely mitigates local compositional heterogeneity and ion migration. Achieving bright and efficient blue emission in metal halide perovskite light-emitting diodes has proven to be challenging. Here, the authors demonstrate high EQE and spectrally stable blue light-emitting diodes based on mixed halide perovskites, with emission from 490 to 451 nm by using a vapour-assisted crystallization technique. [ABSTRACT FROM AUTHOR]

Pure green emitters are essential for realizing an ultrawide color gamut in next‐generation displays. Herein, by fusing the difficult‐to‐access aza‐aromatics onto B (boron)–N (nitrogen) skeleton, a hybridized multi‐resonance and charge transfer (HMCT) molecule AZA‐BN was successfully synthesized through an effective one‐shot multiple cyclization method. AZA‐BN shows pure green fluorescence with photoluminance quantum yield of 99.7 %. The corresponding green device exhibits a maximum external quantum efficiency and power efficiency of 28.2 % and 121.7 lm W−1, respectively, with a full width half maximum (FWHM) of merely 30 nm and Commission Internationale de l'Eclairage (CIE) coordinate y of 0.69, representing the purest green bottom‐emitting organic light‐emitting diode. [ABSTRACT FROM AUTHOR]

The stability of blue organic light-emitting diodes (OLEDs) is highly restricted by both the low electron transport mobility and the stability of the electron transport materials (ETMs). Anthracene-derivative-type ETMs have been proven to be potential materials for solving the aforementioned problem, but their performance still needs to be improved. In this study, a novel anthracene derivative with an asymmetric structure was developed as an ETM in deep-blue devices, realizing a 10.41 cd/A current efficiency, a low driving voltage of 4.04 V, (0.139, 0.047) Rec. 2020 CIE coordinates, and a long T99 lifetime of over 100 h at the 20 mA/cm2 current density. Single-crystal diffraction showed that ET-01 has a face-to-face π-π stack, which is the reason for its good performance. Notably, when the lithium quinolate (Liq) doping ratio was further tuned, one of the devices showed no obvious degradation after 140 h of continuous operation at 20 mA/cm2, representing the champion data in the scientific literature. [ABSTRACT FROM AUTHOR]

Since their emergence in the 1990s, light‐emitting electrochemical cells (LECs) have attracted much attention due to their unique properties and potential for use as an alternative technology for illuminations and displays. After decades of development, however, the performance of LECs remains far from satisfactory for practical applications, in particular for those requiring blue light. Efforts have been made to develop of highly efficient blue‐emitting materials and more advanced device structures, aiming at realizing blueshifted emission, enhancing efficiency, and extending prolonged device lifetimes. A timely review into the current state of blue LECs is deemed imperative, as a full understanding of the molecular and device design strategy and identification of the major challenges that must be addressed to realize practical applications is necessary. A specific summary of recent progress on blue LECs is provided, with the focus placed on design strategies for blue emitters for LECs and device structures with respect to color tuning, efficiency enhancement, and stability improvement. Finally, the direction of development strategies in the future is suggested. [ABSTRACT FROM AUTHOR]

Ultrapure colors are vital for displays to obtain the highly desired wide color‐gamut. Till now, only boron‐dipyrromethene derivatives (BODIPYs) have demonstrated ultrapure full‐colors but suffer from low excitons utilization efficiency as dopants in organic light‐emitting diodes. It is proposed here that with a thermally activated delayed fluorophore to sensitize BODIPYs, all excitons can be recycled, which, still, is challenged by exciton loss through Dexter energy transfer (DET) from sensitizer to dopant and direct charge trapping on BODIPYs. Hence, a sterically hindered BODIPY‐type dopant with a bulk substituent on the meso‐position is developed to suppress DET, exhibiting a high photo‐luminance quantum yield of 98% and a small full width at half maximum of 28 nm. Moreover, the device structure is elaborately designed, successfully modulating carriers and excitons to avoid charge trapping on dopant and also trigger multiple‐sensitizing processes to reduce exciton loss. Consequently, a state‐of‐the‐art maximum external quantum efficiency/power efficiency of 19.0%/85.7 lm W−1 are realized together with an ultrapure‐green emission of Commission Internationale de l'Eclairage coordinates of (0.26, 0.67) and a long half‐lifetime of 2947 h at an initial luminance of 1000 cd m−2. [ABSTRACT FROM AUTHOR]

This paper reports our developments for Micro LED laser lift‐off which is a very important step in Micro LED mass transfer process. By selecting the temporary bonding material, optimizing laser power intensity, and using PSS structure, the yield of Micro LED laser lift‐off can reach 99% for more than 5000 LEDs. This technical developments is of great potential for promoting high‐yield mass transfer technology to realize commercial Micro‐LED displays. [ABSTRACT FROM AUTHOR]

This paper reports our developments for Micro LED laser lift‐off which is a very important step in Micro LED mass transfer process. By selecting the temporary bonding material, optimizing laser power intensity and other process parameters, the yield of Micro LED laser lift‐off can reach 99.87% for more than 1500 LEDs. This technical developments is of great potential for promoting high‐yield mass transfer technology to realize commercial Micro‐LED displays. [ABSTRACT FROM AUTHOR]

This paper reports our developments for Micro LED laser lift‐off which is a very important step in Micro LED mass transfer process. By selecting the temporary bonding material, optimizing laser power intensity and other process parameters, the yield of Micro LED laser lift‐off can reach 99.87% for more than 1500 LEDs. This technical developments is of great potential for promoting high‐yield mass transfer technology to realize commercial Micro‐LED displays. [ABSTRACT FROM AUTHOR]

An electron-transporting counter-anion, OXD-7-SO3−, was developed for a blue-green-emitting cationic iridium complex, which showed superior device performance in solution-processed phosphorescent light-emitting diodes over its counterpart complex with a PF6− counter-anion, due to the facilitated electron-injection/transport and more balanced carrier recombination imparted by OXD-7-SO3−. [ABSTRACT FROM AUTHOR]

Recent development in the field of small molecular materials has led to great advances in the performance of vacuum-evaporated organic light-emitting diodes. However, as a significant class of phosphorescent emitters, ionic transition metal complexes are seldom sublimable due to the inherent ionic nature and low vapor pressure, restricting their applications in state-of-the-art devices fabricated by vacuum evaporation deposition. Here a facile, feasible and versatile strategy is shown to tune the volatility of ionic transition metal complexes through counter-ion control. By introducing counter-ions with large steric hindrance and well-dispersed charges, a series of evaporable ionic iridium complexes are developed, and efficient vapor-processed devices with a high brightness, small efficiency roll-off, and polychromic emission ranging from deep-blue to red-orange are achieved. Our findings unlock the utilization of ionic functional materials in vacuum-evaporated devices, and may open new doors for modern electronic materials technology. [ABSTRACT FROM AUTHOR]

It is demonstrated that materials with thermally activated delayed fluorescence (TADF) are ideal host materials for organic light-emitting diodes (OLEDs). TADF-sensitized-fluorescent OLEDs exhibit maximum power efficiency up to 45 lm/W. TADF-sensitized-phosphorescent OLEDs show high efficiency, low voltage and long lifetime even at low phosphor concentrations of <3 wt%. [ABSTRACT FROM AUTHOR]

Bismuth Trifluoride (BiF 3 ), with a high thermal stability and a low deposition temperature, has been studied as a novel dopant for the conventional hole transporting material of N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB). The efficiency and lifetime of organic light-emitting diodes (OLEDs) have been remarkably improved by using BiF 3 doped NPB. For an optimized green device, a current efficiency of 21.6 cd/A is reached, 40% higher than the control device without BiF 3 . And the lifetime is increased from 115 h to 222 h at room temperature. The enhanced efficiency and lifetime are attributed to the improved balance of holes and electrons in the emissive layer. Most importantly, the thermal stability at an elevated temperature of the OLEDs with BiF 3 doped NPB is largely improved, showing an order of magnitude longer lifetime than the control device at 80 °C. [ABSTRACT FROM AUTHOR]

Abstract: Light-emitting electrochemical cells (LECs) and organic light-emitting diodes (OLEDs) have been investigated based on three blue-green-emitting cationic iridium complexes (1–3). From complexes 1 to 2 and 3, the pendant phenyl ring on the ancillary ligand is gradually fluorinated. It is found that fluorination of the pendant phenyl ring reduces the electrochemical stability of the complexes, which in turn decreases the efficiency and stability of LECs based on the complexes, despite the fact that fluorination reinforces the intramolecular π–π stacking interactions. Fluorination of the pendant phenyl ring also makes the electroluminescent (EL) spectra of LECs red-shifted due to enhanced intermolecular interactions in films. When the complexes are used as dopants in OLEDs, fluorination of the pendant phenyl ring largely enhances the electron-trapping ability of the complexes in the light-emitting layer. Blue-green OLEDs based on complexes 1, 2 and 3 showed promising performances, with peak current efficiencies of 18.3, 9.0 and 14.7cdA−1, respectively. [Copyright &y& Elsevier]

Abstract: We demonstrate an efficient red emitting host-guest LEC based on cationic iridium complexes. The host-guest LEC has brightness of 8.4cdm−2, external quantum efficiency (EQE) of up to 3.5% and peak current efficiency of 3.4cdA−1, the highest efficiencies reported to date for red-emitting host-guest LECs based on cationic iridium complexes. It is confirmed that dispersing the guest molecules into the host matrix would greatly inhibit the self-quenching of the guest molecules in the emissive layer and thus improving the device efficiency, and offering an effective approach to improve device efficiencies of LECs. [Copyright &y& Elsevier]

Abstract: Recently, the stabilities of light-emitting electrochemical cells (LECs) based on cationic iridium(III) complexes with controlled intramolecular π–π stacking interactions by adopting pendant phenyl rings have been dramatically enhanced compared with those of the complexes without π–π stacking interactions within the molecule. Herein, a novel cationic iridium complex [Ir(ppy)2(pyphmi)]PF6[ppy=2-phenylpyridine, pyphmi=1-pyridyl-3-phenylimidazolin-2-ylidene-C,C2′] which exhibits intramolecular π-stacking interaction has been prepared and its X-ray crystal structure has been investigated. Unexpectedly, however, the corresponding LECs based on [Ir(ppy)2(pyphmi)]PF6 do not show significantly enhanced stabilities compared to the LECs based on [Ir(ppy)2(pymi)]PF6 [pymi=1-pyridyl-3-methylimidazolin-2-ylidene-C,C2′] without pendant phenyl rings within the molecule. This phenomenon is attributed to the very long centroid–centroid distance between the π-stacked phenyl rings, which results from the larger tension of substituted five-membered ring moiety (imidazolin-2-ylidene). In addition, irreversible oxidation and reduction processes would also decrease the electrochemical stability of [Ir(ppy)2(pyphmi)]PF6. Thus, intramolecular π–π stacking interaction using pendant phenyl rings is not always effective to improve the stability of LECs. [Copyright &y& Elsevier]

Abstract: Efficient single emitting layer electrophosphorescent white organic light-emitting diodes (WOLEDs) based on small molecules were fabricated by solution process. A solution processible wide-gap compound 9,9-bis[4-(3,6-di-tert-butylcarbazol-9-yl)phenyl] fluorene (TBCPF) was used as the host material and 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxidiazolyl]phenylene (OXD-7) was doped to enhance the electron transport in the emission layer. The optimized single active layer WOLED with three phosphorescent dopants showed a maximum luminance efficiency of 20.8cd A−1 and a maximum luminance of 26,600cdm−2. And the maximum efficiency of double-layer WOLEDs with an additional hole-blocking/electron-transporting layer was further improved to 29.6cd A−1. The color of the devices shifted slightly with the bias voltage. The energy transfer processes and the origin of the white emission in the single emitting layer were also discussed based on the measurement of the transient photoluminescence. [Copyright &y& Elsevier]

Abstract: Using cationic iridium complexes as dopants and poly(N-vinylcarbazole) as host, highly efficient blue-green to red and white organic light-emitting diodes (OLEDs) have been fabricated by a solution process. In single-layer devices, electron-trapping by complexes dominates the device performance. Complexes with cyclometalated 2-phenylpyridine ligands show better device performance compared with those containing cyclometalated 2-(2,4-difluorophenyl)pyridine ligands. With the addition of an electron-transporting/exciton-blocking layer, the devices show improved performances, achieving peak current efficiencies of 24.3, 25.3, 20.5, and 4.2cdA−1 for the blue-green, green, yellow, and red electroluminescence, respectively. White OLEDs have been fabricated by co-doping blue-green and red-emitting complexes, attaining a peak current efficiency of 20.7cdA−1. Thus, cationic iridium complexes can be used as dopants in solution-processed OLEDs, as well as in light-emitting electrochemical cells, to achieve highly efficient blue-green to red and white electroluminescence. [Copyright &y& Elsevier]

The transparent organic light-emitting diodes (TOLEDs) based on Cs2CO3:Ag/Ag composite cathode are reported in this paper. They show higher efficiency and better stability than the control devices with the Cs2CO3/Ag cathode. The devices are highly transparent, and show total efficiencies from both sides of the devices comparable with conventional bottom-emitting devices. The electroluminescence (EL) spectrum from the cathode side of the device is closer to the photoluminescence (PL) spectrum of the light-emitting material than that from the anode side. The effect of the cathode Ag thickness on the device performance has been investigated. It is observed that a critical Ag thickness of 15 nm is required to form a good Ag film with high optical transparency and electrical conductivity. [ABSTRACT FROM AUTHOR]

Abstract: Efficient tris-(8-hydroxyquinoline)aluminum (Alq3)-based organic light-emitting diodes (OLEDs) using YbF3 as the electron injection layer have been investigated. With an YbF3 (3.0nm)/Al cathode, the device with Alq3 as the emitting layer achieved a better performance than the control device with a LiF (0.5nm)/Al cathode. The release of the low-work-function metal Yb is responsible for the performance enhancement. From the analysis by atomic force spectroscopy and X-ray photoemission spectroscopy, it is observed that the Alq3-cathode interface could be well covered by YbF3 at an optimum thickness of 3.0nm, which helps to prevent the contact between Alq3 and Al, and to reduce the destruction of Alq3 by Al. [Copyright &y& Elsevier]

Efficient blue small molecular phosphorescent light-emitting diodes with a blue phosphorescent dye bis(3,5- difluoro-2-(2-pyridyl)-phenyl-(2-carboxypride) iridium (III) (FIrpic) doped into a novel small-molecule host 9,9- bis[4-(3,6-di-tert-butylcarbazol-9-yl)phenyl] fluorene (TBCPF) as the light-emitting layer have been fabricated by spin-coating. The host TBCPF can form homogeneous amorphous films by spin-coating and has triplet energy higher than that of the blue phosphorescent dye FIrpic. All the devices with different FIrpic concentration in the emitting layer give emission from FIrpic indicating complete energy transfer from TBCPF to FIrpic. The device shows the best performance with a peak brightness of 8050 cd/m2 at 10.2 V and the maximum current efficiency up to 3.52 cd/A, when the FIrpic doped concentration is as high as 16%. [ABSTRACT FROM AUTHOR]

The transparent ITO/Ag/ITO multi-layers are developed as anodes on flexible PET (poly(ethylene terephthalate)) substrates. The influence of these anodes on FOLED (Flexible Organic Light-emitting Diodes) is investigated. From the results of research, it can be seen that the multi-layer anode has optimum characteristics, whose sheet resistance is 11 &ohms; and optical transmittance is about 80%, when the thickness of Ag sandwiched by two ITO layers is in the range of 14-18 nm. It is demonstrated that the OLED devices with multi-layer anodes give better luminescence and higher efficiency compared with those with single ITO anodes. [ABSTRACT FROM AUTHOR]

Based on blue light-sensitive interfacial fullerene/4, 4^\prime, 4^\prime\prime-tris \N,\-(3\-methylphenyl)\-N\-phenylamino\ triphenylamine (C60/m-MTDATA) heterojunction organic photodiode (OPD) and deep blue organic light-emitting diode (462 nm), a high-performance organic optocoupler (OOC) was developed. The OOC behaved a maximum photoresponse of 130 mA/W at 6 V OPD bias, which could be markedly higher than some commerical inorganic optocouplers. We believed the high performance of the OPD and OOC was mainly attributed to the selection of high-mobility materials, proper matching of energy levels, and large energy level offset (2.6 eV) at C60/m-MTDATA interface. The maximum light/dark current ratio and current transfer ratio (CTR) of 5\times 10^4 and 0.82% were achieved, respectively. To the best of our knowledge, the CTR is almost the highest reported in OOCs and this sort of OOC could be used for commercial applications. [ABSTRACT FROM AUTHOR]

Cesium quinoline-8-oxide (Csq), as an organic salt, was synthesized and applied as an electron injection material for organic light-emitting diodes. A typical bilayer structure of N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine/tris-(8-hydroxy-quinolinolato) aluminum (III) (Alq3) was used to evaluate the electron injection of Csq. The results showed Csq/Al had better electron injection than LiF/Al cathode, and a maximum current efficiency of 4.13 cd/A (3.33 cd/A for LiF/Al) was obtained when the Csq layer is 2.0 nm. It is proposed that the enhanced electron injection by Csq is related to the interfacial chemical reaction between Csq and Al and the self-doping of Csq by librated Cs. [ABSTRACT FROM AUTHOR]