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Insight into effect of deuterium isotopes on organic near‐IR (NIR) emitters was explored by the use of self‐assembled Pt(II) complexes H‐3‐f and HPh‐3‐f, and their deuterated analogues D‐3‐f and DPh‐3‐f, respectively (Scheme 2). In vacuum deposited thin film, albeit having nearly identical emission spectral feature maximized at ~810 nm, H‐3‐f and D‐3‐f exhibit remarkable difference in photoluminescence quantum yield (PLQY) of 29 % and 50 %, respectively. Distinction in PLQY is also observed for HPh‐3‐f (800 nm, 50 %) and DPh‐3‐f (798 nm, 67 %). We then elucidated the theoretical differences in the impact on near‐infrared (NIR) luminescence between Pt(II) complexes and organic small molecules upon deuteration. The results establish a general guideline for the deuteration on NIR emission efficiency. From a perspective of practical application, NIR OLEDs based on D‐3‐f and DPh‐3‐f emitters attain EQEmax of 15.5 % (radiance 31,287 mW Sr−1 m−2) and 16.6 % (radiance of 32,279 mW Sr−1 m−2) at 764 nm and 796 nm, respectively, both of which set new records for NIR OLEDs of >750 nm. [ABSTRACT FROM AUTHOR]

Efficient saturated red and near‐infrared (NIR) emissive materials are needed in the development of organic light‐emitting diodes (OLEDs), with applications extending beyond flat panel displays and lighting luminaries. Toward this aim, a series of bis‐tridentate Ir(III) complexes (3a ‒ 3c and 4a ‒ 4c) are designed and synthesized, showing emission spanning the region of 601‒694 nm in degassed toluene. Their emission tuning is mainly achieved using monoanionic chromophoric chelates, L1H for red and L2H for deep‐red and NIR, where the extended π‐conjugation and electron deficient N atoms are introduced synergistically. Moreover, three ancillary chelates, X1H2, X2H2, and X3H2, delivered a secondary influence via varied donor strength to the central Ir(III) atom. The resulting red and deep‐red OLED devices exhibit maximum (max.) external quantum efficiencies (EQEs) of 21.4% and 18.1% with peak maximum at 620 and 666 nm, respectively. More impressively, the device based on 4b delivers a NIR emission peak maximum at 702 nm with a maximum EQE of 10.0%. [ABSTRACT FROM AUTHOR]

5‐(6‐(Diphenylphosphinyl)‐2‐naphthyl)‐1,10‐phenanthroline (pPhen‐NaDPO) is reported as a promising n‐type charge‐generation layer in efficient and stable tandem OLEDs. [ABSTRACT FROM AUTHOR]

Efficient Förster energy transfer from a phosphorescent sensitizer to a thermally activated delayed fluorescent terminal emitter constitutes a potential solution for achieving superb blue emissive organic light-emitting diodes, which are urgently needed for high-performance displays. Herein, we report the design of four Ir(III) metal complexes, f-ct1a ‒ d, that exhibit efficient true-blue emissions and fast radiative decay lifetimes. More importantly, they also undergo facile isomerization in the presence of catalysts (sodium acetate and p-toluenesulfonic acid) at elevated temperature and, hence, allow for the mass production of either emitter without decomposition. In this work, the resulting hyper-OLED exhibits a true-blue color (Commission Internationale de I'Eclairage coordinate CIEy = 0.11), a full width at half maximum of 18 nm, a maximum external quantum efficiency of 35.5% and a high external quantum efficiency 20.3% at 5000 cd m‒2, paving the way for innovative blue OLED technology. Deep-blue emitters and corresponding light-emitting devices are still in the progress to meet industrial standards. Here, the authors report catalytic interconversion of isomeric iridium(III) complexes and achieve true-blue emission and operational half-lifetime of over 10,000 h for tandem devices. [ABSTRACT FROM AUTHOR]

Solution processes have promising advantages of low manufacturing cost and large-scale production, potentially applied for the fabrication of organic and quantum dot light-emitting diodes (OLEDs and QLEDs). To meet the expected lifespan of OLEDs/QLEDs in practical display and lighting applications, tandem architecture by connecting multiple light-emitting units (LEUs) through a feasible intermediate connection layer (ICL) is preferred. However, the combination of tandem architecture with solution processes is still limited by the choices of obtainable ICLs due to the unsettled challenges, such as orthogonal solubility, surface wettability, interfacial corrosion, and charge injection. This review focuses on the recent progresses of solution-processed tandem OLEDs and tandem QLEDs, covers the design and fabrication of various ICLs by solution process, and provides suggestions on the future challenges of corresponding materials and devices, which are anticipated to stimulate the exploitation of the emerging light technologies. [ABSTRACT FROM AUTHOR]

The solubility of luminescent materials is a key parameter to improve the electroluminescent performances of solution-processed organic light-emitting diodes (OLEDs). The through-space charge transfer (TSCT) materials provide an alternative to introduce the solubilizing groups (SGs) to the linker. Herein, the tert-butyl and n-hexyl groups are introduced as SGs at C7 positions of spiro structure, named C6-DMB and tBu-DMB, away from the acceptor. This has no influence on the photophysical properties of the parent TSCT molecule. Highly efficient solution-processed OLEDs were demonstrated with the maximum external quantum efficiencies of 21.0% and 21.7%, respectively. To the best of our knowledge, these are champions in the state-of-the-art solution-processed OLEDs with TSCT emitters. This work confirmed our conjecture of constructing highly efficient soluble emitters by transforming an outstanding TSCT material from thermal evaporation to solution-processed OLEDs with SGs simply integrated on the 'bridge' linker. [ABSTRACT FROM AUTHOR]

The effective reflective anode remains a highly desirable component for the fabrication of reliable top-emitting organic light-emitting diodes (TE-OLEDs) which have the potential to be integrated with complementary metal-oxide-semiconductor (CMOS) circuits for microdisplays. This work demonstrates a novel laminated anode consisting of a Cr/Al/Cr multilayer stack. Furthermore, we implement an ultra-thin titanium nitride (TiN) layer as a protective layer on the top of the Cr/Al/Cr composite anode, which creates a considerably reflective surface in the visible range, and meanwhile improves the chemical stability of the electrode against the atmosphere or alkali environment. Based on [2-(2-pyridinyl-N)phenyl-C](acetylacetonate)iridium(III) as green emitter and Mg/Ag as transparent cathode, our TE-OLED using the TiN-coated anode achieves the maximum current efficiency of 71.2 cd/A and the maximum power efficiency of 66.7 lm/W, which are 81% and 90% higher than those of the reference device without TiN, respectively. The good device performance shows that the Cr/Al/Cr/TiN could function as a promising reflective anode for the high-resolution microdisplays on CMOS circuits. [ABSTRACT FROM AUTHOR]

To date, all efficient host materials reported for phosphorescent OLEDs (PhOLEDs) are constructed with heteroatoms, which have a crucial role in the device performance. However, it has been shown in recent years that the heteroatoms not only increase the design complexity but can also be involved in the instability of the PhOLED, which is nowadays the most important obstacle to overcome. Herein, we design pure aromatic hydrocarbon materials (PHC) as very efficient hosts in high‐performance white and blue PhOLEDs. With EQE of 27.7 %, the PHC‐based white PhOLEDs display similar efficiency as the best reported with heteroatom‐based hosts. Incorporated as a host in a blue PhOLED, which are still the weakest links of the technology, a very high EQE of 25.6 % is reached, surpassing, for the first time, the barrier of 25 % for a PHC and FIrpic blue emitter. This performance shows that the PHC strategy represents an effective alternative for the future development of the OLED industry. [ABSTRACT FROM AUTHOR]

Organic materials with multi‐stimulus response (MSR) properties have demonstrated many potential and practical applications. Herein, a π‐stacked thermally activated delayed fluorescence (TADF) material with multi‐stimulus response (MSR) properties, named SDMAC, was designed and synthesized using distorted 9,9‐dimethyl‐10‐phenyl‐9,10‐dihydroacridine as a donor. SDMAC possesses a rigid π‐stacked configuration with intramolecular through‐space interactions and exhibits aggregation‐induced emission enhancement (AIEE), solvatochromic, piezochromic, and circularly polarized luminescence (CPL) under different external stimuli. The rigid molecular structure and efficient TADF properties of SDMAC can be used in displays and lighting. Using SDMAC as an emitter, the maximum external quantum efficiency (EQE) of the fabricated organic light‐emitting diodes (OLEDs) is as high as 28.4 %, which make them the most efficient CP‐TADF OLEDs based on the through‐space charge transfer strategy. The CP organic light‐emitting diodes (CP‐OLEDs) exhibit circularly polarized electroluminescence (CPEL) signals. [ABSTRACT FROM AUTHOR]

Organic materials with violet electroluminescence are highly interesting for organic light‐emitting diode (OLED) application. However, the design and synthesis of new molecules combining with desirable violet emission and high luminous efficiency are a challenging task. Here, three novel organic molecules consisting of a pyrene unit and a highly rigid skeleton, namely TFPy2, TFPy3, and TFPy4, are developed for violet‐emitting OLEDs (VOLEDs). These emitters exhibit excellent thermal stability and violet emission with a narrow full width at half‐maximum (FWHM) and high photoluminescence quantum yields (PLQYs). Photophysical results show that the emission peaks can be tuned by the introduction of pyrene units at different positions, and the emission will have a blue shift with increasing steric hindrance. Moreover, OLEDs fabricated with TFPy2, TFPy3, and TFPy4 as the emitters exhibit maximum external quantum efficiencies (EQEs), emission peaks, and CIEs (x,y) of 3.8%, 414 nm, and (0.15, 0.03); 4.8%, 406 nm, and (0.16, 0.02); and 5.1%, 404 nm, and (0.16, 0.02), respectively. The two molecules TFPy3 and TFPy4 exhibit violet emissions with EL peaks at ≈405 nm with a record low CIEy of 0.02. Therefore, these materials and their construction strategy are promising for future VOLEDs with wide‐color‐gamut display and potential biological applications. [ABSTRACT FROM AUTHOR]

With the inherent organic–metal system property, phosphorescent organic light‐emitting diodes (PhOLEDs) are capable of exhibiting high performance. However, the existence of unintended triplet–triplet annihilation (TTA), which is mainly originated from high triplet exciton density leading to inferior device performance, is a current predicament. For mitigating the TTA in devices, reported herein is an effective host system with the role of precisely controlling the triplet excitons via the multichannel processes, in which a bipolar host material, a hole‐transporting material, and an electron‐transporting material are mixed to manage the triplet exciton transfer. The mixed‐host with so‐called "triplet excitons harvesting" strategy exhibits two concomitant reverse intersystem crossing (RISC) processes that simultaneously occur in the bipolar host material:electron‐transporting material and the host‐transporting material:electron‐transporting material exciplexes, respectively. Highly efficient green and red PhOLEDs are demonstrated by these multichannel processes, in which phosphorescent emitters bis(2‐phenylpyridine) (acetylacetonate) iridium(III) (Ir(ppy)2(acac)) and bis(2‐methyldibenzo[f,h]‐quinoxaline) (acetylacetonate) iridium(III) (Ir(MDQ)2(acac)) are doped into the mixed‐host, respectively. The green and red PhOLEDs realize nearly 30% of maximum external quantum efficiencies of 29.4% and 29.2%, respectively, and also maintain 29.1% and 28.3% at 1000 cd m−2. These excellent efficiencies and low roll‐offs confirm that the concomitant RISC processes effectively manage and utilize triplet excitons. [ABSTRACT FROM AUTHOR]

Near‐infrared exciplex can weaken molecular design difficulties, and has the advantage of easy bathochromic‐shift spectra via selecting the suitable electron donors and acceptors. In this contribution, exciplex is applied to fabricate near‐infrared (NIR) organic light‐emitting diodes (OLEDs) incorporating a synthesized fluorescent material 3‐([1,1″:3′,1″‐terphenyl]‐5′‐yl)acenaphtho[1,2‐b]pyrazine‐8,9‐dicarbonitrile (APDC‐tPh) and a commercially available material 4,4′,4″‐tris(carbazol‐9‐yl)triphenylamine (TCTA). The device having a mixed TCTA:APDC‐tPh as an emitting layer shows a 730 nm NIR emission with a maximum external quantum efficiency (EQE) of about 0.1%, while the device having 2‐[4‐(diphenylamino)phenyl]‐10,10‐dioxide‐9H‐thioxanthen‐9‐one (TXO‐TPA):APDC‐tPh as the emitting layer exhibits an emission peak of 704 nm with a maximum EQE of 1.27%. These results prove the feasibility of fabricating the efficient exciplex‐based NIR OLEDs. [ABSTRACT FROM AUTHOR]

Carbazole is a classic tricyclic aromatic compound that has been widely used in organic optoelectronics. Appropriate functionalization on its aromatic rings will significantly increase the possibilities for its application as an optoelectronic material. Position engineering of carbazole not only leads to its structural diversity, but also substantially enriches its functionality. Bicarbazoles have 15 isomers, most of which are well studied and have been applied in organic light‐emitting diodes (OLEDs). However, one isomer, 9,9′‐bicarbazole, is rarely investigated as an OLED material. Therefore, two 9,9′‐bicarbazole derivatives, 3,3′‐di(10H‐phenoxazin‐10‐yl)‐9,9′‐bicarbazole and 3,3′‐di(10H‐phenothiazin‐10‐yl)‐9,9′‐bicarbazole, have been designed and prepared for use as host materials for green and red OLEDs. These two compounds demonstrated good device performances, and it is believed that the 9,9′‐bicarbazole building block could be a novel platform for the design of efficient host materials for OLEDs. Perfecting host qualities: Appropriate functionalization carbazole will significantly increase the possibilities for its application as an optoelectronic material. The 9,9′‐bicarbazole building block is used to construct host materials for phosphorescent organic light‐emitting diodes (see figure). [ABSTRACT FROM AUTHOR]

Reported here are C1‐linked spiro‐bifluorene dimers. A comprehensive study is carried out to analyze the electronic properties of these highly twisted structures. This work shows that the C1‐position enables the design of pure hydrocarbon materials, with a high triplet energy, for hosting blue phosphors in efficient phosphorescent OLEDs (PhOLEDs). To date, this work describes the highest performance of blue PhOLEDs ever reported for pure hydrocarbons (external quantum efficiency of ca. 23 %), thus highlighting the potential of the C1‐spirobifluorene scaffold in organic electronics. Phosphorescence with a twist: The highly twisted C1‐linked spiro‐bifluorene dimers are reported. This work shows that the C1‐position enables the design of pure hydrocarbon materials, with a high triplet energy, for hosting blue phosphors in highly efficient phosphorescent OLEDs (PhOLEDs). [ABSTRACT FROM AUTHOR]

Abstract: Thermally activated delayed fluorescence materials can effectively achieve high efficiency by harvesting singlet and triplet excitons in organic light‐emitting diodes (OLEDs). However, the choice of host material has a huge impact on the efficiency of the device, especially for the near‐infrared (NIR) luminescent material. In this contribution, a series of host materials are used to match the thermally activated delayed fluorescence emitter, 3,4‐bis(4‐(diphenylamino)phenyl)acenaphtho[1,2‐b]pyrazine‐8,9‐dicarbonitrile (APDC‐DTPA), for fabricating NIR OLEDs. All the host materials have the higher triplet energy than that of APDC‐DTPA. As the organometallic compound of Zn(BTZ)2 has relatively stronger dipole moment, the electroluminescence spectral peak of doped device shows strong bathochromic shift exceeding 700 nm and changes with doping concentration. Finally, the extremely high external quantum efficiency of 7.8% (with 10 wt% of doping concentration) and 5.1% (with 20 wt% of doping concentration) are achieved with the emission peaks of 710 and 728 nm, respectively, which are superior to that of the device based on the other host materials. The approach is feasible to achieve bathochromic shift and highly efficient fluorescent OLEDs. [ABSTRACT FROM AUTHOR]

Efficiency roll-off in blue organic light-emitting diodes especially at high brightness still remains a vital issue for which the excitons density-dependent mechanism of host materials takes most responsibility. Additionally, the efficiency roll-off leads to high power consumption and reduces the operating lifetime because higher driving voltage and current are required. Here, by subtly modifying the triphenylamine to oxygen-bridged quasi-planar structure, a novel thermally activated delayed fluorescence type blue host Tri-o-2PO is successfully developed. Efficiency roll-off based on Tri-o-2PO is ultralow with external quantum efficiency (EQE) just dropping by around 2% in the high luminance range from 1000 cd m−2 to 10 000 cd m−2. As expected, low turn-on voltage (≈2.9 V) of device is also achieved, which is close to the theory limit value (≈2.62 V). Super-high power efficiency (≈60 lm W−1) and EQE (>22%) are also achieved when utilizing Tri-o-2PO as host. Furthermore, two-color warm-white light with CIE of (0.45, 0.43) and correlated color temperature of 2921 K is also fabricated and a champion EQE of 21% is delivered. These excellent performances prove the strategy of bridging the triphenylamine to reduce Δ Est is validated and suggest the great potential of this novel skeleton. [ABSTRACT FROM AUTHOR]

Two new 10-phenyl-9,10-dihydroacridine derivatives attached by dibenzothiophene (DBT) and dibenzofuran (DBF) were synthesized. The influence of the substituents of these materials was studied by theoretical calculations (DFT calculation) and experimental measurements. Owing to the twisted N-phenyl ring, both molecules possess sufficiently high triplet energies and are suitable as hosts for phosphorescent organic light-emitting diodes. To evaluate the electroluminescent (EL) performance of these materials, FIrpic-based blue PHOLEDs and two-color white PHOLEDs (FIrpic and PO-01 as the dopants) were fabricated using the common device structures. High external quantum efficiencies (EQE) of 21.1 % and 20.9 % for FIrpic-based blue PHOLEDs were achieved by FPhAc and TPhAc, respectively. The white device based on the host FPhAc achieved a higher performance, with a maximum EQE of 24.7 % than the device with TPhAc as host material. [ABSTRACT FROM AUTHOR]

High-efficiency blue phosphorescence devices with external quantum efficiencies above 25% are developed using a new bipolar host material, diphenyl(10-phenyl-10 H-spiro[acridine-9,9′-fluoren]-2′-yl)phosphine oxide (POSTF), which is constructed in orthogonal molecular structure with a spiro-coree. The separation of bipolarity from effective spiro-fluorene-triphenylamine (STF) structure is elucidated and its versatility in device is evaluated by two kinds of sky-blue phosphors. Noticeably, large-size white light-emitting panel (150 mm × 150 mm) is fabricated with max power efficiency of 75.9 l m W−1 using this new host. [ABSTRACT FROM AUTHOR]

A highly efficient and stable green phosphorescent organic light-emitting diode (PHOLED) was fabricated by using a new dibenzofuran/spirobifluorene hybrid material (named as DBFSF2) as the host material. The DBFSF2-based PHOLEDs exhibited slightly better electroluminescence efficiency than that in the conventional host material 4,4′-bis(carbazol-9-yl)biphenyl (CBP)-based ones. Moreover, further studies demonstrated that the DBFSF2-based PHOLEDs had a better stability with about 1.5 times improvement in half lifetime compared with that of CBP-based ones. To investigate the mechanism behind the enhanced stability in the DBFSF2-based PHOLEDs, the evaluations of dark spots growth, film crystallization properties and carrier recombination zone were carried out. [ABSTRACT FROM AUTHOR]

A new electron-withdrawing moiety (BFPz) has been used for the first time as an acceptor in OLEDs and its corresponding core unit (2-Br-BFPz) was synthesized. Combined with an electron-donating moiety triphenylamine, a novel fluorescent material with a D–A structure named TPA-BFPz was synthesized. Encouragingly, the EQE values of non-doped and doped blue OLEDs reach 3.68% and 4.42%, respectively. [ABSTRACT FROM AUTHOR]

A novel silicon-based compound, 10-phenyl-2′-(triphenylsilyl)-10 H-spiro[acridine-9,9′-fluorene] (SSTF), with spiro structure has been designed, synthesized, and characterized. Its thermal, electronic absorption, and photoluminescence properties were studied. Its energy levels make it suitable as a host material or exciton-blocking material in blue phosphorescent organic light-emitting diodes (PhOLEDs). Accordingly, blue-emitting devices with iridium(III) bis[(4,6-difluorophenyl)-pyridinato- N, C2′]picolinate (FIrpic) as phosphorescent dopant have been fabricated and show high efficiency with low roll-off. In particular, 44.0 cd A−1 (41.3 lm W−1) at 100 cd m−2 and 41.9 cd A−1 (32.9 lm W−1) at 1000 cd m−2 were achieved when SSTF was used as host material; 28.1 lm W−1 at 100 cd m−2 and 20.6 lm W−1 at 1000 cd m−2 were achieved when SSTF was used as exciton-blocking layer. All of the results are superior to those of the reference devices and show the potential applicability and versatility of SSTF in blue PhOLEDs. [ABSTRACT FROM AUTHOR]

The authors demonstrate a thick MoO3 layer (60 nm) as a good short reduction layer in organic light emitting diodes (OLEDs), which is especially useful for large-area and flexible OLEDs to prevent short circuit issues. The crystallization of organic material and the increase of driving voltage induced by a thick MoO3 layer in OLEDs were resolved by a simple ultraviolet-ozone (UV-ozone) treatment. Ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, contact angle, and atomic force microscope analyses revealed that a longer UV-ozone treatment resulted in an optimized fraction of oxygen vacancies in MoO3, which is responsible for the improved device performance. [ABSTRACT FROM AUTHOR]

Deep‐red and near‐infrared emitters with twisted donor–acceptor (D–A) structures often exhibit suboptimal performance in organic light‐emitting diodes (OLEDs) due to constraints imposed by the energy gap law. In this work, a pure hydrogen carbon (PHC) host material named SBF‐DTP is purposefully tailored for deep‐red OLEDs. The excellent capacity of SBF‐DTP to support D–A type DR emitters effectively arises from its distinctive attributes: localized excitation states, 3D configuration, and low polarity. When employing SBF‐DTP as the host for the fluorescence emitter DCPA‐TPA and the thermally activated delayed fluorescence emitter APDC‐DTPA, doped films exhibit substantially enhanced photoluminescence quantum yields. This improvement leads to high‐efficiency OLEDs with external quantum efficiencies of 5.47% for DCPA‐TPA and 20.03% for APDC‐DTPA, respectively, which is about twice as high as the initial reports. This findings underscore the paramount significance of developing efficient host materials in the pursuit of high‐performance deep red and even near‐infrared OLEDs. [ABSTRACT FROM AUTHOR]

Hybrid white organic light-emitting diodes (WOLEDs) have drawn great attention both for display and solid-state lighting purposes because of the combined advantages of desirable stability of fluorescent dyes and high efficiency of phosphorescent materials. However, in most WOLEDs, obtaining high efficiency often requires complex device structures. Herein, we achieved high-efficiency hybrid WOLEDs using a simple but efficacious structure, which included a non-doped blue emissive layer (EML) to separate the exciton recombination zone from the light emission region. After optimization of the device structure, the WOLEDs showed a maximum power efficiency (PE), current efficiency (CE), and external quantum efficiency (EQE) of 82.3 lm/W, 70.0 cd/A, and 22.2%, respectively. Our results presented here provided a new option for promoting simple-structure hybrid WOLEDs with superior performance. [ABSTRACT FROM AUTHOR]

Implementing rigorous standards for high‐quality white organic light‐emitting diodes (WOLEDs) demands further investigation. Herein, a novel and feasible color remedy strategy (CRS) is proposed in WOLEDs composed of binary‐emitters, to arouse the green‐emission, thereby complementing the spectral deficiency in white‐emission. Thus, the color rendering indexes (CRIs) of binary‐emissive WOLEDs can be boosted from 63 to 80 threshold, and the Commission International de I'Eclairage‐(x, y) coordinates are precisely located inside the American National Standard Institute quadrangles, which can rival the WOLEDs integrating ternary or more emitters. Moreover, it is more feasible for CRS‐based binary‐emissive system to tune white‐emission from cool white‐emission (correlated color temperature (CCT) ≈ 5000 K) to eye‐friendly warm white‐emission (CCT ≈ 2000 K). Meanwhile, benefiting from the reduced energy loss and low driving voltage of CRS zone, all of the CRS‐based WOLEDs with diverse CCTs can exceed 20% external quantum efficiency, and the highest approach 25%, as well as the highest power efficiency beyond 60 lm W−1, which is comparable with those reported employing light‐extracting techniques. In addition, it is evident that CRS‐based WOLEDs also exhibit outstanding color stability within the variation of luminance in several orders of magnitude (50–12 000 cd m−2). Thus, this novel CRS provides an innovative pathway to fabricate high‐quality WOLEDs composed of binary emitters. The color remedy strategy in binary‐emissive white organic light‐emitting diodes (WOLEDs) can effectively complement the green‐emission deficiency in a blue‐red binary‐emissive system by arousing the potential intensity of the shoulder peak in the blue emitter with lower exciton energy, thereby boosting the color rendering indexes of conventional binary‐emissive WOLEDs from 63 to in excess of 80 thresholds, as well as producing a high external quantum efficiency of 25%. [ABSTRACT FROM AUTHOR]

A novel deep-blue fluorescent emitter was designed and synthesized. The external quantum efficiency (ηEQE) of the blue-emitting, doped, organic light-emitting diode (OLED) was as high as 4.34%. The device also exhibited an excellent color purity with Commission Internationale de l'Eclairage (CIE) coordinates of x = 0.15 and y = 0.05. In addition, the triplet energy had a value of 2.7 eV, which is rare for an emitter with deep-blue emission, which makes it a preferred choice for high-performance white OLEDs. By optimizing the device architectures, the color of hybrid-white OLEDs could be tunable from warm white to cool white using the aforementioned material as a bifunctional material. That is, the ηEQE of the hybrid warm-white OLED is 20.1% with a CIE x and y of 0.46 and 0.48 and the ηEQE of the hybrid cool-white OLED is 9% with a CIE x and y of 0.34 and 0.33. [ABSTRACT FROM AUTHOR]

A controllable etching process for indium zinc oxide (IZO) films was developed by using a weak etchant of oxalic acid with a slow etching ratio. With controllable etching time and temperature, a patterned IZO electrode with smoothed surface morphology and slope edge was achieved. For the practical application in organic light emitting devices (OLEDs), a suppression of the leak current in the current—voltage characteristics of OLEDs was observed. It resulted in a 1.6 times longer half lifetime in the IZO-based OLEDs compared to that using an indium tin oxide (ITO) anode etched by a conventional strong etchant of aqua regia. [ABSTRACT FROM AUTHOR]

A novel bipolar host molecule di-spiro [fluorene-9,5′-quinolino [3,2,1-de] acridine-9′,9″-fluorene]-2,2″,7,7″-tetracarbonitrile (QACN) featuring an Acceptor-σ-Donor-σ-Acceptor structure was developed. Systematic investigations into its photophysical, electrochemical, and thermal properties unveiled exceptional thermal stability, a three-dimensional spatial configuration, and bipolar carrier transport capability. Employing QACN as the host material in red phosphorescent and thermally activated delayed fluorescent (TADF) organic light-emitting diodes (OLEDs) yielded a maximum external quantum efficiency of 25.3 % and 16.5 %, respectively. Compared with the commercial material TPBi (EQE = 12.0 %, λ EL = 668 nm) and mCP (EQE = 14.5 %, λ EL = 652 nm), the TADF OLEDs based on QACN achieved a higher EQE and a large red-shift emission (EQE = 16.5 %, λ EL = 694 nm). These findings underscore the potential of QACN as an effective host material for red phosphorescent and TADF emitters and provide a new auxiliary finesse for realizing deep red and near-infrared (NIR) OLEDs. [Display omitted] • A highly twisted bipolar host material QACN with A-σ-D-σ-A structure was designed and synthesized. • The orthogonal structure, thermal stability, and desirable energy levels of QACN make it an effective host for red emitters. • QACN-based TADF OLEDs achieved higher EQE and significant red-shifted emission compared to commercial host materials. [ABSTRACT FROM AUTHOR]

A blue phosphorescent emitter based on tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III), Ir(iprpmi) 3 , as the dopant and 3,3′-bis(N-carbazolyl)biphenyl, mCBP, as the host have been evaluated in OLED devices. By optimizing the dopant concentration and the materials for the electron and hole-transport layers, external quantum efficiencies greater than 20% have been achieved. Improved device lifetimes over those using the classic light-blue dopant FIrpic have also been achieved. These improvements can be attributed to the control of the electron-hole recombination and emission regions within the emitter layer as well as the choice of material for the transport layers. [ABSTRACT FROM AUTHOR]

• Design and synthesis of a novel bipolar host material for red phosphor. • The introduction of phenylketone on ortho-positions of triphenylamine to enhance the rigidity of the structure. • The OLED deviceexhibited efficient device performance with maximum external quantum efficiency (EQE) of 16.1%. A new bipolar host material, 2,2′,2′′-tris(diphenylketone)amine (N-DPK) was developed in a one-shot by Ullmann reaction, and characterized by spectroscopic techniques and spatial arrangement was ascertained by single X-ray crystal structure analysis. The compound is possessing C 3 -symmetry with three diphenylketone units connected to the central nitrogen atom. In this organic architecture, the electron-withdrawing units, phenylketone are incorporated to ortho-position of triphenylamine, electron-donating unit to generate rigidity, which is responsible to reduce the gap between single and triplet energy levels. The material possessed triplet energy (E T) at 2.53 eV, indicating that it could be used as a host material for red phosphorescent organic light-emitting diodes. The OLED device was fabricated with bis(2 -methyldibenzo[f,h]quinoxaline)(acetylacetonate)iridium(III) (Ir(MDQ) 2 acac) and N-DPK, as guest and host, respectively, and 10 wt% doping concentration exhibited good device performance with maximum external quantum efficiency (EQE) of 16.1%. [ABSTRACT FROM AUTHOR]

Two novel deep-blue emitters based on a highly rigid unit, IDC-PA and IDC-Py, were prepared by respectively introducing the 7,7-dimethyl-5-phenyl-5,7-dihydro indeno [2,1-b] carbazole (IDC) unit with anthracene and pyrene derivatives. The emitters exhibit high quantum efficiency, excellent thermal stability, narrow full width at half maximum and deep-blue emission. Moreover, the IDC-PA and IDC-Py-based devices demonstrated maximum EQEs of 4.41% and 6.08% and maintain 4.35% and 5.35% as applied in non-doped devices even at the brightness of 5000 cd m −2 with CIE coordinates of (0.15, 0.10) and (0.15, 0.08), respectively. [ABSTRACT FROM AUTHOR]

A subtle change in molecular structure of OLED material could lead to significant variation in device performance. For a better understanding of the connection between molecular structures and properties, four molecules ( 1 , 2 , 3 , and 4 ) based on different spiro-systems, namely spiro[cyclopropane-1,9′-fluorene], spiro[cyclopentane-1,9′-fluorene], 1′,3′-dihydrospiro[fluorene-9,2′-indene] and spirobifluorene, were designed and prepared. The influences of different spiro units on photophysical properties and electroluminescence performance were fully studied. The experimental results showed that photophysical properties, electrochemical behaviors, and frontier molecular orbital distributions of these different spirofluorenes are mostly identical because the π-backbones were less affected by the different cycles at the C-9 position of fluorene. However, green phosphorescent organic light-emitting diodes (PHOLEDs) based on spirobifluorene derivative 4 exhibited the highest electroluminescence performance among these four hosts. Thus, we hope this work could reveal deep understanding for the rational design of host materials based on spirofluorene blocks. [ABSTRACT FROM AUTHOR]

Solution-processed organic light-emitting diodes (OLEDs) are currently attracting a lot of attention for their simple fabrication process. However, most laboratory-scale solution-processed devices are fabricated by spin-coating method which is not the optimum method for fabricating devices with a larger area as much of the material is wasted. Herein, a dip-coating method is introduced for its advantages for producing large-sized devices. The method is a more reliable and material saving fabrication process. In the present study, both the hole-transporting layer (HTL) and emitting layer (EML) were prepared by dip coating, and solution-processed green thermally activated delayed fluorescence (TADF) based OLEDs with high efficiencies were fabricated. [ABSTRACT FROM AUTHOR]

Four novel bipolar host materials, namely 9,9'-(4-(pyridin-2-yl)-1,3-phenylene)bis(9H-carbazole) ( 2CzPy ), 9,9'-(4-(pyridin-2-yl)-1,3-phenylene)bis(3,6-di- tert -butyl-9H-carbazole) ( 2TCzPy ), 5,5'-(4-(pyridin-2-yl)-1,3-phenylene)bis(5H-benzofuro[3,2- c ]carbazole) ( 2BFCzPy ) and 9′,9‴-(4-(pyridin-2-yl)-1,3-phenylene)bis(9-phenyl-9H,9′H-3,3′-bicarbazole) ( 2PBCzPy ) were designed and synthesized. Within each host material, one pyridine group serving as electron-transporting unit and two identical electron-donating groups serving as hole-transporting motifs were attached to the central benzene ring. These two donor units are located ortho and para to pyridine group, respectively. The four compounds showed excellent thermal stability with the glass-transition temperature up to 192 °C and decomposed temperature up to 571 °C. These hosts possessed triplet energies over 2.80 eV, indicating that they could be used as suitable hosts for blue phosphorescent organic light-emitting diodes (PHOLEDs). The bis[2-(4,6-difluorophenyl)-pyridinato-C2,N](picolinato)iridium(III) (FIrpic) based PHOLEDs hosted by 2CzPy and 2BFCzPy exhibited high device performance with maximum external quantum efficiencies (EQEs) of 17.8% and 17.4%, respectively. More importantly, 2CzPy exhibited a low efficiency roll-off at a brightness of 1000 cd m −2 with an external quantum efficiency of 17.1% (3.9% roll-off). The results demonstrate that 2CzPy could be a promising host for blue PHOLEDs. [ABSTRACT FROM AUTHOR]

One polycyclic aromatic hydrocarbon compound, 3,6,11,14-tetraphenyldibenzo[ g,p ]chrysene ( TPDBC ), was designed, synthesized, and fabricated in a red phosphorescent organic light-emitting diode (PHOLED) with a maximum external quantum efficiency (EQE) of 14.4%, which represented the first report of a dibenzo[ g,p ]chrysene motif as the building block for host materials. It was conjectured that dibenzo[ g,p ]chrysene may serve as a next generation molecular platform which is readily functionalizable for the preparation of electroactive materials for applications in the emerging areas of molecular electronics. [ABSTRACT FROM AUTHOR]

Four novel bipolar hosts, namely 9,9′-(2-(4,6-diphenylpyrimidin-2-yl)-1,3-phenylene)bis(9H-carbazole) ( 2CzPm ), 9,9′-(2-(4,6-diphenylpyrimidin-2-yl)-1,3-phenylene)bis(3,6-di- tert -butyl-9H-carbazole) ( 2TCzPm ), 5,5′-(2-(4,6-diphenylpyrimidin-2-yl)-1,3-phenylene)bis(5H-benzofuro[3,2-c]carbazole) ( 2BFCzPm ) and 5,5′-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(5H-benzofuro[3,2-c]carbazole) ( 2BFCzTrz ) were designed and synthesized with diphenylpyrimidine and diphenyltriazine as electron-transporting units and carbazole derivatives as hole-transporting motifs for the application in blue phosphorescent organic light-emitting diodes (PHOLEDs). These electron-accepting and -donating functional groups were attached to the central phenylene bridge in an ortho-substituted fashion, which led to high triplet energies (2.97–3.00 eV) and wide bandgap (3.43–3.55 eV). The effect of modulation of electron-accepting and donating groups on the photophysical properties, frontier orbital energy levels, charge carrier transport properties and device performance of these four hosts has been investigated. 2BFCzPm and 2BFCzTrz featured with large conjugation system exhibited high thermal stability as compared to 2CzPm and 2TCzPm . The bis[2-(4,6-difluorophenyl)-pyridinato-C2,N](picolinato)iridium(III) (FIrpic) based blue PHOLEDs hosted by 2BFCzPm exhibited excellent electroluminescence performance with a peak current efficiency of 38.2 cd/A and a maximum external quantum efficiency of 19.0%, which could be ascribed to the enhanced thermal stability, high triplet energy and good bipolar charge transport properties of the host material. [ABSTRACT FROM AUTHOR]

Two phenanthroimidazole derivatives containing triphenylamine, carbazole and pyrene units were designed and synthesized. Highly efficient non-doped deep blue organic light emitting diodes (OLEDs) were fabricated by using these materials as emissive layer. The non-doped devices demonstrated high efficiency (4.24 cd/A, 3.67 lm/W, 4.66%), low efficiency roll-off at higher current densities, and stable deep blue emissions with CIEy around 0.10, which are excellent results for deep-blue OLED devices. This study reveals that the combination of phenanthroimidazole and donor-linker-acceptor strategy has a great potential for developing high performance deep-blue OLEDs. [ABSTRACT FROM AUTHOR]

Two novel spiro-based host materials, namely 3-(9,9′-spirobi[fluoren]-6-yl)-9-phenyl-9 H -carbazole ( SF3Cz1) and 9-(3-(9,9′-spirobi[fluoren]-6-yl)phenyl)-9 H -carbazole ( SF3Cz2) were designed and synthesized. Due to the meta -linkage of spirobifluorene backbone, both SF3Cz1 and SF3Cz2 possess triplet energies over 2.70 eV, indicating they could serve as suitable hosts for blue and even white phosphorescent organic light-emitting diodes (PHOLEDs). The fabricated bis (4,6-(difluorophenyl)-pyridinato -N,C′)picolinate (FIrpic) based PHOLEDs hosted by SF3Cz1 and SF3Cz2 exhibited excellent performance with maximum external quantum efficiencies (EQEs) of 18.1% and 19.7%, respectively. Two-color warm white PHOLEDs fabricated by utilizing SF3Cz1 and SF3Cz2 as hosts also achieved high EQEs and low efficiency roll-offs. The results demonstrate that SF3Cz1 and SF3Cz2 are promising hosts for blue and white PHOLEDs. [ABSTRACT FROM AUTHOR]

Two novel bipolar host materials were designed and synthesized, by incorporating α-carboline and carbazole to spiro-acridine-fluorene skeleton. As expected, both materials exhibited high triplet energy over 2.8 eV, indicating they could act as suitable blue hosts in phosphorescent organic light-emitting diodes. By changing the appending group from carbazole to α-carboline, the thermal property and molecular bipolarity were improved. When they were applied as hosts for sky-blue emitter iridium(III) bis[4,6-difluorophenyl]pyridinato-N, C2′ ] picolinate (FIrpic), good performance of 35.5 cd A −1 , 35.8 lm W −1 and 29.5 cd A −1 , 24.5 lm W −1 was achieved for α-carboline derivative and carbazole derivative, respectively. [ABSTRACT FROM AUTHOR]

An optical energy loss mechanism including the surface plasmon polariton (SPP) loss, wave guide (WG) mode and substrate mode in organic light-emitting diodes (OLEDs) is introduced based on CPS theory. The theoretical calculations of both the out-coupling efficiency (OCE) and the external quantum efficiency (EQE) of OLEDs are proposed. MATLAB tools are applied to simulate the optical model and provide the results of the two efficiencies. It is demonstrated that, the OCE and the EQE in a green phosphorescence OLED with optimized device structure can reach up to 20% and 27%, respectively (intrinsic quantum efficiency q = 90% assumed). The simulation results based on the theoretical model are further validated experimentally. [ABSTRACT FROM AUTHOR]

A new bipolar host material (PBCz-PO) consisting a phosphinic amide is developed to show a resonance effect. It possesses quite high triplet energy (2.76 eV), and this high triplet energy make it suitable to be blue host in phosphorescent organic light-emitting diodes (PHOLEDs). The device with PBCz-PO as a host and FIrpic as a dopant achieved a maximum current efficiency ( η c ) of 31.5 cd/A, a maximum power efficiency ( η p ) of 31.0 lm/W and a maximum external quantum efficiency (EQE) of 13.4% as well as low driving voltage. [ABSTRACT FROM AUTHOR]

Two host materials, SFCA and SFCC, consist of a diphenylamine or carbazole unit linking to spiro-fused phenyl carbazole (SFC) backbone, were designed and synthesized. By choosing the meta linkage way between diphenylamine/carbazole units and SFC ring, higher triplet energies could be easily achieved for the two new materials, which mean that they could be used as effective host material for popular blue phosphorescent material Iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C 2′ ] picolinate (FIrpic, E T = 2.65). Besides that, the steric SFC structure could guarantee their good thermal stabilities. Their thermal, photophysical and electroluminescent properties were systematically investigated. The blue phosphorescent OLEDs with the two materials as hosts and FIrpic as a dopant exhibited excellent performance with maximum current efficiencies of 33.9 and 40.8 cd/A, respectively. [ABSTRACT FROM AUTHOR]

A combination of a scattering medium layer and a roughened substrate was proposed to enhance the light extraction efficiency of organic light-emitting diodes (OLEDs). Comparing with a reference OLED without any scattering layer, 65% improvement in the forward emission has been achieved with a scattering layer formed on an intentionally roughened external substrate surface of the OLED by spin-coating a sol–gel fabricated matrix containing well dispersed titania (TiO 2 ) particles. Such a combination method not only demonstrated efficient extraction of the light trapped in the glass substrate but also achieved homogenous emission from the OLED panel. The proposed technique, convenient and inexpensive, is believed to be suitable for the large area OLED production in lighting applications. [ABSTRACT FROM AUTHOR]

Abstract: A novel multifunctional spiro-annulated fluorene/triarylamine based compound (STNPB) has been designed, synthesized and characterized. It exhibits a high glass transition temperature of 140 °C, due to the rigid spiro-configuration molecular structure. According to its suitable energy level and triplet energy (2.34 eV), improved performances, such as lower driving voltage, enhanced device power efficiency, and longer stability, are shown in organic light-emitting diodes with STNPB as the hole-transport material, compared with the ones with the widely used arylamine derivative N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB). Through further studies, it has been demonstrated that the enhanced stability is attributed to suppressed crystallization process as a result of employing STNPB instead of NPB as the hole-transport material. [Copyright &y& Elsevier]

Highlights: [•] The HOMO energy levels of carbazole-based host materials can be independently turned with simple spacers. [•] A blue PHOLED device incorporating PBCz host achieved a maximum EQE of 19.5%. [•] Two-color, all-phosphor WOLEDs was achieved with an EQE of 24.6%. [•] The three colors WOLEDs was demonstrated a high EQE of 19.1%. [Copyright &y& Elsevier]

Theintrinsic asymmetry of 1,2,4-oxadiazole was utilized to synthesizethree isomers, DCzmOXD-1, DCzmOXD-2, and mCzmOXD, and high tripletenergies over 2.80 eV made them good candidates for host materialsin blue OLEDs. The best efficiencies of 23.0 cd A–1/20.5 lm W1–/11.2% in CE/PE/EQE were achieved byDCzmOXD-1 with derivation at the β-carbon position of 1,2,4-oxadiazole. [ABSTRACT FROM AUTHOR]

Abstract: Two novel bipolar host materials, namely 3,5-bis(4-(9H-carbazol-9-yl)phenyl)-1,2,4-oxadiazole (pCzmOXD) and 3,5-bis(3-(9H-carbazol-9-yl)phenyl)-1,2,4-oxadiazole (mCzmOXD) were designed and synthesized, by incorporating a new block 1,2,4-oxadiazole as the n-type moiety and changing its linking pattern with carbazole. As expected, high triplet energy (over 2.81 eV) for mCzmOXD was achieved due to the intrinsic meta-linkage of 1,2,4-oxadiazole. When both materials were applied in blue phosphorescent organic light-emitting diodes, good performance of 13.0 cd A−1/16.0 cd A−1 were achieved for pCzmOXD and mCzmOXD in iridium(III) picolinate (FIrpic)-based devices, respectively. [Copyright &y& Elsevier]

Highlights: [•] A single layer graphene was modified with TiO x and PEDOT:PSS. [•] The sheet resistance of the modified graphene was reduced by 86% from 628Ω/sq to 86Ω/sq. [•] The work function of the modified graphene was increased by 0.82eV from 4.30eV to 5.12eV. [•] Enhanced charge injection and transport were achieved from the modified graphene. [Copyright &y& Elsevier]

Large-area organic light-emitting diodes (OLEDs) fabricated by solution process with low-cost are essential for practical applications. However, maintaining desirable uniformity and smoothness of prepared films are challenging with the enhancement of film size and layers. Reported herein is a systematic strategy of solvent and device structure engineering for designing small molecular hybrid white OLED (WOLED) via blade-coating. Benefiting from the uniform blade-coated films with low roughness about 1 nm as well as the balanced charge carrier transport, the blade-coated WOLED with hybrid fluorescence and phosphorescence (small area 0.1 cm2) shows the maximum current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) of 29.0 cd A−1, 30.4 lm W−1, and 11.6%, respectively. And the WOLEDs achieve low turn-on voltage (V on) of about 2.8 V. Meanwhile, the all-vacuum-based WOLED reaches maximum CE, PE, and EQE of 40 cd A−1, 44.3 lm W−1, and 15.9%, respectively. Remarkably, a larger area of the device (2 cm × 2 cm) with uniform emitting reaches peak EQE of 6.8% by blade-coating, notably, only a small amount of solution about 0.9 μL/cm2 was consumed for blade-coated films. The high-performance and low-cost WOLED via blade-coating is ascribed to the facile strategy to improve the film morphology and the energy-level matching, which provides huge potential in display and flat panel lighting. Benefiting from the solvent and device structure engineering, the blade-coated hybrid white organic light-emitting diodes (WOLEDs) reach external quantum efficiencies (EQEs) close to 12% (small-area, 0.1 cm2) and 6.8% (2 cm × 2 cm) with a small amount of solution about 0.9 μL/cm2. [Display omitted] • Fabricating a hybrid white organic light-emitting diodes (WOLEDs) by blade-coating at ambient conditions. • Selecting the ideal solvents (solvent engineering) and electron-transporting layer for the highly efficient blade-coating WOLED which reaches the maximum EQE, power efficiency (PE), and current efficiency (CE) of 11.6%, 30.4 lm W−1, and 29.0 cd A−1, respectively. • Fabricating a blade-coated WOLED (2 cm × 2 cm) owning peak EQE of 6.8% with a small amount of solution of 0.9 μL/cm2. [ABSTRACT FROM AUTHOR]