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A hybrid cadmium sulfide nanoparticles (CdSNPs) electroluminescence (EL) device was fabricated by Phase – Segregated Method and characterized. It was fabricated as layers of (ITO/poly-TPD:CdS ) and (ITO/poly-TPD:CdS /Alq3). PolyTPD is an excellent Hole Transport Layer (HTL), CdSNPs is an emitting layer and Alq3 as electron transport layer (ETL). The EL of Organic-Inorganic Light Emitting Diode (OILED) was studied at room temperature at 26V. This was achieved according to band-to-band transition in CdSNPs. From the I-V curve behavior, the addition of Alq3 layer decreased the transfer of electrons by about 250 times. The IV behavior for (poly-TPD/CdS) is exponential with a maximum current of 4500 µA. While, the current is constant for (poly-TPD:CdS /Alq3) and the maximum current was 16.5 µA. Semiconductor nanoparticles like CdS are attractive for fabricating hybrid LEDs with spectrally pure color, low operating voltage values, and shortwavelength electro-luminescence, needed for the RGB devices. The correlated color temperature (CCT) was equal to (1700 oK) for the emitted blue light. [ABSTRACT FROM AUTHOR]

A few unit cells of thick colloidal CsPbBr3 nanoplatelets (NPLs) exhibit strong quantum confinement. However, due to the increased surface‐to‐volume ratio, they show poor photoluminescence quantum yield (PLQY) resulting from surface traps. Here, a unique, quantum‐confined core/crown perovskite is reported for the first time, where the CsPbBr3 NPL surface is passivated by laterally grown thin FAPbBr3 crown layers. Unlike regular core/shells, the FAPbBr3 is coated around the core NPLs resulting in blue emission. Careful control of the growth kinetics while monitoring growth using in situ PL led to the formation of core/crown perovskites with nearly two times improvement in thin film PLQYs. HR‐TEM analyses show that the interplanar distances of the core match with CsPbBr3 and the crown match with FAPbBr3. The XRD and TEM analyses revealed that their thickness remains the same even if Cs+ to FA+ ratios are varied, indicating lateral growth of FAPbBr3 around the CsPbBr3 core. Further, FA+ ions in the crown lattice are confirmed by FTIR and 1HNMR. Finally, considering their high PLQYs and narrow linewidths, the core/crown NPLs are employed as blue emitters in light‐emitting diodes, and a maximum external quantum efficiency of 0.4% at 2.71 eV (457 nm) with a luminance of 513 cd m−2 is achieved. [ABSTRACT FROM AUTHOR]

Metal halide perovskite nanocrystals (NCs) have emerged as highly promising light emitting materials for various applications, ranging from perovskite light‐emitting diodes (PeLEDs) to lasers and radiation detectors. While remarkable progress has been achieved in highly efficient and stable green, red, and infrared perovskite NCs, obtaining efficient and stable blue‐emitting perovskite NCs remains a great challenge. Here, a facile synthetic approach for the preparation of blue emitting CsPbBr3 nanoplatelets (NPLs) with treatment by an organic sulfate is reported, 2,2‐(ethylenedioxy) bis(ethylammonium) sulfate (EDBESO4), which exhibit remarkably enhanced photoluminescence quantum efficiency (PLQE) and stability as compared to pristine CsPbBr3 NPLs coated with oleylamines. The PLQE is improved from ≈28% for pristine CsPbBr3 NPLs to 85% for EDBESO4 treated CsPbBr3 NPLs. Detailed structural characterizations reveal that EDBESO4 treatment leads to surface passivation of CsPbBr3 NPLs by both EDBE2+ and SO42– ions, which helps to prevent the coalescence of NPLs and suppress the degradation of NPLs. A simple proof‐of‐concept device with emission peaked at 462 nm exhibits an external quantum efficiency of 1.77% with a luminance of 691 cd m−2 and a half‐lifetime of 20 min, which represents one of the brightest pure blue PeLEDs based on NPLs reported to date. [ABSTRACT FROM AUTHOR]

Multi‐resonant thermally activated delayed fluorescent (MR‐TADF) materials are blooming for high‐resolution organic light‐emitting diodes (OLEDs). However, boron/nitrogen (B/N)‐integrated MR‐TADF emitters suffer severe efficiency roll‐off from their strong inter‐molecular π–π interactions. Herein, versatile narrowband pure blue emitters (mono‐mx‐CzDABNA and tri‐mx‐CzDABNA) are demonstrated featuring a ring‐fused extended π‐skeleton: a classic steric hindrance and rigidity accessed by integrating with meta‐xylene (mx) rotors. tri‐mx‐CzDABNA shows a narrowband (FWHM, 26 nm) pure blue emission (λmax, 462 nm) with substantial hypsochromic shift (12 nm) while maintaining MR‐TADF characteristics. The key solid‐state analyses conclude that they conceivably suppress the non‐radiative energy loss, thus improving the photoluminescence quantum yield (PLQY > 90%) and rate of reverse intersystem crossing (RISC) (kRISC ≈2.85 × 105 s−1). The integration of tri meta‐xylene significantly leads to an enhanced horizontal dipole ratio (HDR) from 65% to 85%. Hyperfluorescent‐OLEDs are fabricated using designed MR‐TADF as terminal emitter, achieving a narrowband (FWHM, 34 nm) pure blue electroluminescence (λmax, 472 nm) and maximum external quantum efficiency (EQEmax) of 26.97% with magnificently suppressed efficiency roll‐off (7.8%) at 1000 cd m−2. So, it is believed that regulation of internal efficiencies and high color purity can amplify the route to achieving a narrowband pure blue emission through new synthetic MR‐TADF approaches. [ABSTRACT FROM AUTHOR]

Antisolvent treatment is paramount in the fabrication of high‐efficiency perovskite optoelectronic devices as it affords a high crystallization rate critical for the formation of pin holes‐free perovskite films. Although the antisolvent choice determines the domain distribution of quasi‐2D perovskite, and hence the emission wavelength (blue vs green), as well as its light emission efficiency, few studies have examined it in detail. Herein, the crystallization dynamics and resulting optoelectronic properties of PBA (phenyl‐butyl‐ammonium)‐based quasi‐2D perovskites (A′2Am‐1PbmX3m+1), which are commonly employed to create blue emissive films, are scrutinized for the first time through in situ photoluminescence measurements during film formation. The m domain distribution can be tailored by selecting antisolvents with various solubilities of PBA cation. Antisolvents with higher PBA solubility promote the formation of smaller bandgap films due to larger m domains and vice versa. This study effectively reveals a route to tailor quasi‐2D perovskite optoelectronic properties via antisolvent engineering. Fine‐tuning the optoelectronic properties can be done by blending two antisolvents with contrasting PBA cations solubility. By doing so, a blue emissive light emitting diode with emission wavelength ranging from 471 to 509 nm can be fabricated with an external quantum efficiency of 2.9% at 471 nm. [ABSTRACT FROM AUTHOR]

The article presents a study which reported cerium halides with the cryolite-like structure and stable and tunable color coordinates from (0.17, 0.02) to (0.15, 0.04). Topics discussed include optical characterizations of cerium halides films, synthesis of cerium halides powders, and material and device characterization.

The article presents a study which developed a phosphor-sensitized thermally activated delayed fluorescence (TADF) emission system with TADF emitters to achieve high efficiency and long operational lifetime. Topics discussed include molecule design and photophysical properties, photophysical and electrochemical properties of the emitters, and device performance.

The bilayer structure for an emitting layer (EML) was developed to improve performances of a fluorescence blue organic light emitting diode. By functionally separating the EML into the charge recombination and the Triplet‐Triplet Fusion (TTF) zone, we successfully suppressed the quenching of triplet excitons by excess carriers to make more TTF efficient and the local degradation within the EML to make the lifetime longer. In the bottom emission device with the bilayer EML, 12% of external quantum efficiency (EQE) and 450 hours of LT95 were achieved. Furthermore, we achieved over 14% of EQE by optimizing the material combinations. [ABSTRACT FROM AUTHOR]

To investigate the effects of trifluoromethyl and tert -butyl moieties on the general optoelectronic properties of star-shaped hosts based on phenyls substituted carbazole, we used 3,6,9-tris (4-(tert -butyl)-phenyl)-9 H -carbazole (M1) as a reference, and different numbers of electron-withdrawing 3,5-bis(trifluoromethyl) benzene were introduced into 3, 6 and 9 positions of carbazole to obtain compounds 9-(3,5-bis(trifluoromethyl)phenyl)-3,6-bis(4-(tert -butyl)phenyl)-9 H -carbazole (M3) , 3,6-bis(3,5-bis(trifluoromethyl)phenyl)-9-(4-(tert -butyl)phenyl)-9 H -carbazole (M5) and 3,6,9-tris(3,5-bis(trifluoromethyl)phenyl)-9 H -carbazole (M6). After the introduction of 3,5-bis (trifluoromethyl) benzene, the thermal temperature at 5 % mass loss of M3 , M5 and M6 decreased to 344 °C, while the glass transition temperature and melting point of M3 and M5 showed a significant increase. However, M6 did not show obvious glass transition, but its melting point also showed a significant increase. M3 crystallized at 125 °C as evidenced by differential scanning calorimetry, and the linking model of M3 is helpful to crystalize. In addition, when compared with those of M1 , the fluorescence emission peaks of M3 and M6 showed a blue-shift, while M5 showed a red-shift, all of which were in the deep blue emission range. The color purity of blue light for M1 in tetrahydrofuran solution is the highest, and M1 exhibit aggregation-induced emission characteristics. Compared to the photoluminescence quantum efficiency (PLQY) of compound M1 of 39 % in toluene, the PLQYs of M3 and M6 decreased to 34 % and 29 %, and the PLQY of M5 increased to 46 %. The function of the lowest unoccupied molecular orbital trap of M3 film under the external electrical field will increase, which not only offsets the increasing effect of the electrical field to the electron carrier and further decreases the carrier mobility when the electrical field increase, and the same situation is also feasible for the highest occupied molecular orbital traps in M5 , M6 and M1. The organic blue light emitting diodes were prepared by using M1 , M3 , M5 and M6 as the hosts of bis [2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium, and the optimized device of M1 as the host showed the best performance with a maximum luminescence brightness of 2978 cd/m2, maximum current efficiency of 39.42 cd/A and maximum external quantum efficiency of 18.36 %. • Trifluoromethyl decreased the thermal-stability of the hosts. • 3,5-bis(trifluoromethyl) benzene tri-substituted host emitted light more effectively. • 3,5-bis(trifluoromethyl) benzene improved the electron-injecting ability of the hosts. • 3,5-bis(trifluoromethyl) benzene mono-substituted M3 made the charge mobilities to change oppositely relative to the others. • M1 without 3,5-bis(trifluoromethyl) benzene showed aggregation-induced emission characteristic and better device performance. [ABSTRACT FROM AUTHOR]

We synthesized and characterized blue emitting materials based on indeno-triphenylene derivatives. Multilayer organic light emitting diodes (OLEDs) were fabricated in the following sequence; ITO (180 nm)/N,N'-diphenyl-N,N'-(2-napthyl)-(1,1'-phenyl)-4,4'-diamine (NPB) (50 nm)/Blue emitter (30 nm)/4,7-diphenyl-1,10-phenanthroline (BPhen) (30 nm)/lithium quinolate (Liq)/Al (2 nm/100 nm). Particularly, a device using 14,14-dimethyl-14H-indeno[1,2-b]triphenylene as an emitter showed the efficient emission and exhibited luminous efficiency, power efficiency, and external quantum efficiency of 11.16 cd/A, 6.05 lm/W, 4.30% at 20 mA/cm2, respectively. Also, it exhibited blue emission with the Commission Internationale De L'Énclairage (CIE) coordinates of (0.21, 0.43) at 8.0 V. [ABSTRACT FROM AUTHOR]

A series of substituted aza‐boron‐dipyridylmethene (aD) compounds are demonstrated as fluorescent dopant emitters in blue organic light emitting diodes (OLEDs). Replacing the meso‐carbon of a dipyridylmethene dye with nitrogen to form the aD chromophore leads to a destabilization of the highest occupied molecular orbital in aD, as evidenced both from their experimentally determined photophysical and electrochemical properties. These properties are consistent with theoretical calculations of the molecular energetics. These aD derivatives emit violet to blue light, peaking between 400 and 460 nm with photoluminescent quantum yields over 85%. The aD compounds have small energy differences (<400 meV) between their singlet and triplet excited states. OLEDs fabricated with an aza‐boron‐dipyridylmethene emitting fluorophore give an external quantum efficiency of 4.5% on glass substrates, close to the theoretical maximum for fluorescent OLEDs. [ABSTRACT FROM AUTHOR]

Organic thermally activated delayed fluorescent (TADF) materials can harvest 100% of the electrically generated excitons as a result of their small singlet–triplet energy difference. However, maximizing the external quantum efficiency (EQE) of a device also requires enhancing the light out‐coupling efficiency. This work presents a new acceptor–donor–acceptor (ADA) emitter employing an indolocarbazole donor and diphenyltriazine acceptors that show nearly‐completely horizontal orientation regardless of the host matrix, leading to a sky‐blue organic light‐emitting diode (λEL = 483 nm, CIE coordinates of 0.17, 0.32) with EQEMAX of 22.1%, a maximum luminance of 7800 cd m−2, and blue emission. [ABSTRACT FROM AUTHOR]

Novel homoleptic cyclometalated Ir(III) complexes are designed to improve their emission dipole orientations in the emitting layer of blue phosphorescent organic light emitting devices. Biphenyl group is introduced into the imidazole of cyclometalated Ir(III) complexes to simultaneously achieve enhanced efficiency and operation lifetime, resulting in one of the best device performances of single‐stacked organic light emitting diodes with 91% emission dipole orientation, 26.3% maximum external quantum efficiency (maximally calculated as 41%), and 169 h lifetime at 1000 cd m−2 (LT80), color coordinate (0.17, 0.30). To elucidate the physical origin of this significant improvements, the orientational and positional distributions of the homoleptic dopants are analyzed with consideration on intermolecular interactions through atomistic modeling of the emitting layer. With the findings, the phosphorescent dopants could be designed in the future to achieve enhanced performance. [ABSTRACT FROM AUTHOR]

In this study, as the ongoing effort to develop efficient blue OLEDs, two deep blue emitters based on indenoquinoline-substituted anthracene derivatives have been synthesized and characterized. Multilayer organic light emitting diodes were fabricated with the following sequence: indium-tin-oxide (ITO)/4,4',4"-tris[2-naphthyl(phenyl)amino (2-TNATA)/4,4'-bis(N-(1-naphthyl)-N-phenylamino) biphenyl (NPB)/Blue emitting materials/Bathophenanthroline (Bphen)/lithium quinolate (Liq)/Al. All the devices showed efficient blue emissions. Particularly, a device using '2,7,7,13,13-pentamethyl-9-(10-phenylanthracen-9-yl)−7,13-dihydrobenzo[5,6]-s-indaceno[1,2-g] quinoline' as an emitter showed a maximum external quantum efficiency (EQE) of 4.92% with the Commission Internationale De L'Énclairage (CIE) coordinates of (0.15, 0.10) at 8.0 V. [ABSTRACT FROM AUTHOR]

We present a novel stackable luminescent device integrating a blue light emitting diode (LED) with a red organic LED (OLED) in series. The anode of the OLED is connected with the cathode of the LED through a via in the insulation layer on the LED. The LED–OLED hybrid device is electroluminescent and two electroluminescence (EL) peaks (the blue peak around 454 nm and the red peak around 610 nm) are observed clearly. The effect of the indium tin oxide (ITO) layer on the device performance is analyzed. Compared with the individual LED and OLED, their combination shows great potential applications in the field of white lighting, plant lighting, and display. [ABSTRACT FROM AUTHOR]

A novel compound 6,6′-(ethyne-1,2-diylbis(4,1-phenylene))bis(2-(2-butyloctyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione) (NAI-PVP-NAI) based on an end capping group 1,8-naphthalimide and central building block diphenylacetylene was designed and synthesized by Suzuki coupling. The newly synthesized NAI-PVP-NAI compound is characterized using optical, thermal, and electrochemical techniques as well as ab initio modeling. This novel and unique compound exhibits strong blue emission in the solid state and has been successfully used as an active light-emitting layer in organic light emitting diodes (OLEDs). Interestingly, the newly developed compound shows both electron-donating and electron-accepting abilities. Therefore, it can act as a donor or an acceptor organic semiconductor. Indeed, upon evaluating this molecule in solution processable organic photovoltaic (OPV) devices, we show that it acts as a donor when used with a PCBM acceptor and as an acceptor when used with a P3HT donor. Thus, NAI-PVP-NAI is a versatile compound, which can play three roles as a blue light emitting layer in OLEDs and a donor or an acceptor in OPV devices. [ABSTRACT FROM AUTHOR]

Recently, we have reported that a nano‐lens array (NLA) technology using a very simple and fab‐compatible vacuum deposition process contributes to highly efficient and color stable green and blue organic light emitting diodes (OLEDs). Here, the technique is applied to red OLEDs. With NLA, the increase ratio of current efficiency is about 1.57 which is similar to those of green and blue OLEDs (1.56, 1.59). Furthermore, color coordinate change measurement values of red OLEDs in a wide viewing angle ranging from 0° to 60° are reduced as green and blue OLEDs do, indicating that NLA has a great potential for the development of the optically efficient full‐color OLED displays composed of three color OLED pixels. [ABSTRACT FROM AUTHOR]

We present a comprehensive theoretical study on the optical and electronic properties of the organic conjugated dimer containing the 4H -cyclopenta[2,1 -b :3,4- b' ]dithiophen-4-one, as monomer unit, suitable for blue organic light emitting diodes (OLEDs). Ground and excited states properties of the dimer, denoted hereafter as CPDT, were theoretically computed using the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) at the level of B3LYP/6-311g(d,p) in acetonitrile, respectively. The UV–vis absorption spectrum of CPDT exhibits peaks in the range 250–450 nm and small optical band gap of 2.38 eV. The excited CPDT dimer shows emission in the deep blue domain (∼420 nm). The well resolved vibronic spectra of absorption and emission line profiles with good overlap have separated by the smaller Stokes shift (47 nm, 0.37 eV). Additionally, the two optical bands appeared at 672 nm (UV–vis) and 827 nm (PL) have been attributed to the formation of an intra-molecular charge transfer (ICT) state. Regarding the calculated ionization potential (IP), electronic affinity (EA) and the reorganization energies, the compound presents high performance of charge mobility with the International Commission on Illumination coordinates of (x,y) = (0.16,0.04). The data are interpreted using molecular electrostatic potential surface and the CIE color coordinates. In the three layers based OLED [ITO/NPD/CPDT/Alq3/LiF:Al], the electrical response was evaluated based on the current-voltage (I-V) characteristics. The threshold voltage for luminescence is about 4.6 V at which the carriers appear to reach the CPDT light emitting layer. Image 1 • Linear π-conjugated small molecule for deep blue OLED. • Some fundamental optical and electrical properties of the studied compound were computed. • Low threshold voltage has adjusted from electrical response based on the current-voltage (I-V) characteristics. [ABSTRACT FROM AUTHOR]

Organic light-emitting diodes (OLEDs) perform a vital function in flat-panel displays and solid-state lighting. Herein, a simple structured donor-acceptor based organic light-emitting material (OLEM), 6-(4-(di ([1,1′-biphenyl]-4-yl)amino)phenyl)nicotinonitrile (PTPA-NN), has been prepared and applied as emissive layer in OLEDs. This OLEM has a slightly twisted structure, which enhances its thermal stability. Interestingly, a device consisting of PTPA-NN OLEM demonstrated a promising performance showing a turn-on voltage of 3.8 V with a current efficiency of 9.7 cd/A, external-quantum-efficiency of 4.17% and power efficiency of 8.0 lm/W. Small molecular simple-structured nicotinonitrile based material provide an effective strategy to discover suitable OLEMs for sky-blue OLEDs. • Simple Structure Materials. • Isonicotinonitrile Based Fluorophore. • High Thermal Stability. • Sky Blue Organic Light Emitting Diodes. [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]

Using an anthracene chromophore as a core group and a phenyl carbazole chromophore as a side group, three new emitters of blue light, 2-DCPA, 3-DCPA and 4-DCPA, were synthesized. The three compounds differed with regard to the position of the carbazole linked to the core, with 2-DCPA and 4-DCPA using carbazole nodes and 3-DCPA using the lobe position. Density functional theory calculations were performed to determine which positions of the carbazole moiety had node characteristics and which had lobe characteristics. The PL max values of 2-DCPA, 3-DCPA and 4-DCPA in the film state were in the blue region, at 453, 457, and 452 nm, respectively. Of these materials, 3-DCPA, i.e., that with the linkage to the lobe position, showed the highest efficiency, with a value of 2.91 cd/A, and EQE, with a value of 2.65%. In a doped device using CBP as a host material and 3-DCPA as a dopant, the EL max emission was observed to be in the deep blue region, at 433 nm, and with a CIE value of (0.150, 0.068). [ABSTRACT FROM AUTHOR]

Elongation of operation lifetime in a blue TTA-OLED was demonstrated with T90 increasing from 34 to 550 hours at the initial luminance of 2000 nits, corresponding to 16.1-times improvement, by: 1. incorporation of new ETL material, 2. layer structure optimization, and 3. new EML material and double EML structures. [ABSTRACT FROM AUTHOR]

A series of novel angular BN-heteroacenes were successfully synthesized. Associated with the intrinsic syn-structures, they exhibit unique molecular alignments in a solid state and promising electronic properties, and are thus suitable as efficient nondoped emitters for the fabrication of blue organic light-emitting diodes with improved performance. [ABSTRACT FROM AUTHOR]

New host material of 2-tert-butyl-9,10-bis(3′′,5′′-diphenylbiphenyl-4′-yl)anthracene [T-TAT] substituted t-butyl group was investigated in solution process WOLED device compared with 9,10-bis (3′′,5′′-diphenylbiphenyl-4’-yl) anthracene [TAT]. A two-color WOLED of a co-host system using solution process method was demonstrated. The device configuration was ITO / PEDOT:PSS (40 nm) / emitting layer (50 nm) / TPBi (20 nm) / LiF (1 nm) / Al. The emitting layer consisted of TAT or T-TAT, NPB, DPAVBi (blue dopant), and rubrene (yellow dopant). NPB was used to help hole carrier transport as well as blue host role. The device using the T-TAT compound as a co-host showed a luminance efficiency of 2.73 cd/A, which is 77% higher than TAT device of 1.54 cd/A at 20 mA/cm2. [ABSTRACT FROM AUTHOR]

In this paper, side-by-side patterning of red, green and blue OLEDs is demonstrated. To achieve 640 ppi arrays with 20 µm subpixel pitch, chemically amplified, i-line photoresist system with submicron resolution was used. These results show feasibility of obtaining full-color displays with ultra-high resolution. [ABSTRACT FROM AUTHOR]

We were able to improve properties of blue organic light-emitting diode (OLED) device by inserting new Hole Blocking Layer (HBL) between Emitting Layer (EML) and Electron Transport Layer (ETL). It was possible to improve properties of such blue device by using new HBL that has high electron mobility and that can block the holes at the same time. The fluorescent blue device that used new HBL-1 and HBL-2 showed very high efficiency: At 500 cd/m2, pure blue color coordinate (0.135, 0.108) and efficiency of 9.5 cd/A. On the other hand, fluorescent blue device that used HBL-1 showed efficiency of 9.3 cd/A at pure blue color coordinate (0.134, 0.109), showing 50% lifetime increase as well. [ABSTRACT FROM AUTHOR]

We report the performance of inkjet printed red, green and blue OLEDs, with focus on transition from evaporated blue common layer to printed blue panel design. Printed OLED device efficiencies and colors are reported, and we demonstrate that in these metrics, printed red, green and blue OLEDs are now comparable to state-of-the-art vapor-processed devices. [ABSTRACT FROM AUTHOR]

Highlights: [•] Driving voltage increases in blue organic light emitting diode (OLED) with increasing the emitting layer (EML) thickness. [•] Current efficiency and external quantum efficiency decrease when the EML thickness deviates from 35nm. [•] Luminance of 10,000cd/m2 is obtained at low voltage of 5.0V from OLED with EML of 15nm thickness. [Copyright &y& Elsevier]

Abstract: By using Heck polycondensation, we have synthesized carbazole-based alt-copolymers tethered with polyhedral oligomeric silsesquioxanes (POSS), which had well-defined architectures, similar polymerization degrees and the different contents of POSS. The effect of POSS content and the length of the side chain containing POSS on the electroluminescence properties of these polymers were investigated. POSS particles in these alt-copolymers showed excellent dispersity and prevented the interchain aggregation of polymers in film state well. Besides, POSS benefited charge balance by increasing the electron current density, which led to a higher luminance and current efficiency, as well as purer blue light-emitting. [Copyright &y& Elsevier]

Highlights: [•] Synthesis and luminescent properties of carbazole/anthracene hybrided molecules were studied. [•] Organic light-emitting diodes were fabricated by vacuum evaporation using these materials as non-doped emitter. [•] Deep-blue electroluminescence with good performance was obtained. [ABSTRACT FROM AUTHOR]

Stacked inverted top-emitting white electrophosphorescent organic light-emitting diodes (OLEDs) are demonstrated. The OLEDs consist of orange and blue light-emitting units interconnected with a connecting unit of 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile/Al/LiF. These OLEDs combine the features of having inverted electrode positions, top-emission, and a stacked architecture. They exhibit an average current efficacy of 26.5 cd/A at a luminance of 100 cd/m2. Single-unit inverted top-emitting OLEDs based on the constituent orange and blue light-emitting units are also characterized for comparison. The current efficacies of the orange and blue OLEDs are 21.2 cd/A and 32.6 cd/A, respectively, at a luminance of 100 cd/m2. [ABSTRACT FROM AUTHOR]

Abstract: A carbazole type, thermally stable, high triplet energy host material having a diphenylether linkage, 9,9′-(oxybis([1,1′-biphenyl]-4′,3-diyl))bis(9H-carbazole), was synthesized and the device performances of blue phosphorescent organic light-emitting diodes were studied. The new host material exhibited a high glass transition temperature of 111 °C and a high triplet energy of 2.73 eV for energy transfer to blue triplet emitter. Blue devices were fabricated using the new host material and a high quantum efficiency of 23.5% was achieved. [Copyright &y& Elsevier]

Abstract: Improved power efficiency in blue phosphorescent organic light-emitting diodes (PHOLEDs) was demonstrated by using new high triplet energy hole-transport materials based on the diphenylmethyl linkage. Two high triplet energy hole-transport materials with diphenylamine or ditolyamine moieties linked through a diphenylmethyl linkage, 4,4′-(diphenylmethylene)bis(N,N-diphenylaniline) (TCBPA) and 4,4′-(diphenylmethylene)bis(N,N-di-p-tolylaniline), were synthesized and evaluated as hole-transport materials for blue PHOLEDs. The power efficiency of TCBPA was superior to that of standard 1,1-bis[4-[N,N′-di(p-tolyl)amino]phenyl]cyclohexane. [Copyright &y& Elsevier]

A series of novel blue light-emitting materials, spirofluorene derivatives, DBSF, 3DBSF, and 5DBSF, based on 2′,7′-dibromospiro- [benzo[c]fluorene-7,9′-fluorene] (DBrSPFF) were successfully synthesized and identified by IR, 1H-NMR, and13C-NMR, MS. Optical properties were examined by UV-Vis absorption spectra and photoluminescence (PL) emission spectra. They performed great blue light characteristics. PL quantum yield was calculated by using quinine sulphate in 0.1M H2SO4 as standard. Electro-chemical behavior was examined through cyclic voltammeter measurement. They may be potential promising blue light-emitting materials for OLED. [ABSTRACT FROM PUBLISHER]

Efficient thermally activated delayed fluorescence (TADF) has been characterized for a carbazole/sulfone derivative in both solutions and doped films. A pure blue organic light emitting diode (OLED) based on this compound demonstrates a very high external quantum efficiency (EQE) of nearly 10% at low current density. Because TADF only occurs in a bipolar system where donor and acceptor centered 3ππ* states are close to or higher than the triplet intramolecular charge transfer (3CT) state, control of the π-conjugation length of both donor and acceptor is considered to be as important as breaking the π-conjugation between them in blue TADF material design. [ABSTRACT FROM AUTHOR]

[Display omitted] • Conception of a new fluorescent anthracene derivative by click chemistry. • Vibronic fine structure of absorption and pure blue color emission. • Excellent optoelectronic properties of the studied compound. • Potential application of the studied material in blue organic light-emitting diodes. New functional anthracene material (An-Tri-Van) was elaborated through click chemistry reaction to be applied as an emitter in blue OLEDs. We have performed a combined experimental and theoretical study to get insights into the optoelectronic properties of the new organic material An-Tri-Van. Its molecular structure was confirmed by proton nuclear magnetic resonance (1H NMR) and Fourier-transform infrared (FT-IR) spectroscopies. Thermal analysis was determined by DSC and showed that this material has a good thermal stability up to 200 °C. The optical properties for UV-Vis absorption and photoluminescence (PL) of An-Tri-Van were investigated in dilute solution and in thin film. The HOMO and LUMO energy levels were estimated using cyclic voltammetry analysis. Density Functional Density (DFT) and Time Dependent (TD-DFT) have been used to evaluate the structural, optical and charge transfer properties of the studied organic material. The B3LYP method at 3-21g (d), 6-31+g (d) and 6-311++g (d, p) basis sets have been successfully applied to reliably compare predicted vibrational, structural, electrochemical and optical properties. The studied molecule exhibited a non-planar structure with energy band gap around 3.4 eV and a vibronic structure of absorption in the ultraviolet-near visible with a maximum absorption of 402 nm attributed to the π → π ∗ electronic transitions mainly from anthracene group. The excited An-Tri-Van displayed a purely blue color emission. Based on Marcus theory and starting from the analysis of the charge transfer properties, we found that the molecule An-Tri-Van possess an interesting hole/electron transport ability. In addition, the current-voltage response (I-V) characteristic of typical three-layer OLED (ITO/ NPB/ An-Tri-Van/ Alq3/ Al) was generated by simulation and the threshold voltage is estimated to be 5.4 V. The prepared An-Tri-Van molecule has tunable electronic and physical properties that exhibit the most favorable characteristics for blue OLED emission. [ABSTRACT FROM AUTHOR]

Conventional thermally activated delayed fluorescence (TADF) molecules achieve small energy differences between the lowest singlet and triplet excited states (Δ E ST) by enhancing the intramolecular charge transfer, which inevitably leads to a wide emission spectrum and low fluorescence rate. Here, we prepared a deep blue TADF molecule via a small Δ E ST pyridine-phenol fluoroboron complex as the acceptor. The small Δ E ST is maintained when carbazole donors are attached to the 4-position of the phenyl rings in the fluoroboron complex. Benefiting from the strong electron coupling between the donor (D) and acceptor (A) moieties, the compound Cz-4-BF exhibits a high fluorescence rate of 4.8 × 108 s−1 and a small D-A dihedral angle change in the excited state. Consequently, a photoluminescence (PL) quantum yield of nearly 100% and a PL spectrum with full-width at half-maximum (FWHM) < 60 nm were obtained in solution and low-concentration doped films. A TADF-sensitized fluorescence (TSF) device containing Cz-4-BF achieves an external quantum efficiency of 21%, which is higher than the devices employing classical fluorescent emitters and multiple resonance-type TADF emitters. The Cz-4-BF-based TSF device shows significantly improved color coordinates of (0.14, 0.10) versus a control device without Cz-4-BF. [Display omitted] • Deep-blue TADF emitter with very high fluorescence rate of 4.8 × 108 s−1. • Full-width at half-maximum of PL and EL spectra <60 nm. • PL and EL efficiencies are higher than those of multiple resonance type TADF emitters. [ABSTRACT FROM AUTHOR]

Highlights: [•] We study on the effect of the Liq in device performances. [•] We use Liq with one of organometallic compound materials. [•] We fabricated an optimal device with double electron transport layer as the Liq concentration increased. [•] We demonstrated efficient carriers’ balance in blue PHOLEDs. [ABSTRACT FROM AUTHOR]

We examined the performance of solution-processed organic light emitting diodes (OLEDs) by modifying the hole injection layer (HIL), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS). Atomic force microscopy (AFM) showed morphological changes with surface roughness (R RMS) of 1.47, 1.73, and 1.37 nm for pristine PEDOT: PSS, PEDOT: PSS modified with a 40 v% deionized water and with a 30 v% acetone, respectively. The surface hydrophobicity of the acetone modified PEDOT:PSS HIL layer was decreased by 34% as comparing with the water modified counterpart. Electrical conductivity was increased to two orders of magnitude for the water and acetone modified PEDOT:PSS as compared to pristine. We observed a low refractive index and high transmittance for the modified HILs. We fabricated and explored electroluminescent properties of bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) based sky blue device by utilizing HIL with and without modification. The changes in electrical conductivity, surface roughness, refractive index, and transmittance of the modified HILs strongly influenced the performance of devices. By utilizing a 30% acetone modified HIL, the power efficiency was increased from 14.2 to 24.2 lm/W, an increment of 70% and the EQE from 8.5 to 13.1% at 100 cd/m2, an increment of 54%. The maximum luminance also increased from 11,780 to 18,190 cd/m2. The findings revealed herein would be helpful in designing and fabricating high efficiency solution processed OLEDs. [Display omitted] • Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) modified with optimized concentrations of deionized water (DI water) and acetone and fabricated sky blue OLED devices with modified PEDOT:PSS. • By utilizing a 30% acetone modified HIL, the power efficiency was increased from 14.2 to 24.2 lm/W, an increment of 70% and the EQE from 8.5 to 13.1% at 100 cd/m2, an increment of 54%. The maximum luminance also increased from 11,780 to 18,190 cd/m2. • The changes in electrical conductivity, surface roughness, refractive index and transmittance of modified HIL strongly influenced the performance of devices. [ABSTRACT FROM AUTHOR]

A series of fluorescent emitters based on Imidazole-Alkyl spacer-Carbazole were designed and synthesized by connecting donor and acceptor moieties through alkyl spacer. In these design strategy we have chosen carbazole as electron rich and imidazole as electron deficient with deferent functional black (phenyl and phenyl substituted) at the N1 position of imidazole moiety. All the fluorophores were structurally confirmed by spectroscopic methods (NMR, MASS, and FTIR). The photophysical, electrochemical and electroluminescence properties were thoroughlyexamined. All the fluorophores showed good thermal stability and near-UV emission with high photoluminescence quantum yield (PLQY)of ~59% in the solid state. All the synthesized compounds feature Commission International de L'Eclairage (CIE) coordinates of y < 0.08 for a particular doping concentration, which is very close to the National Television Standards Committee (NTSC) standard blue (0.14, 0.08). Solution-processed organic light emitting diode (OLED) device consisting of molecule BIPOCz displays a maximum external quantum efficiency EQE of 1.9% with CIE coordinates of (0.17, 0.07). All these results reveal that this work provides novel approaches for realizing ultra-deep-blue emission with high performance. Imidazole-Alkyl spacer-Carbazole (BIPOCZ) based emitter serve as a fluorescent emitter to transmit pure blue light EL emission with CIE coordinates of (0.17. 0.07) and EQE of 1.9% in organic light emitting diodes (OLEDs), which are very crucial for high-quality flat panel display and solid-state lighting. Image 1 • A series of fluorescent emitters based on Imidazole-spacer-Carbazole were designed and synthesized. • All the fluorophores showed good thermal stability and near-UV emission. • HOMO and LUMO separation endows them with good carrier transporting property. • OLED device consisting of BIPOCz displays an EQEmax of 1.9 % with CIE coordinates of (0.17, 0.07). [ABSTRACT FROM AUTHOR]

Nowadays, most blue organic light emitting diodes (OLEDs) are fabricated by using sky-blue emitters which are more easily synthesized when compared with other deep blue emitters. Herein, we put forward a new idea of using an optical micro-cavity based on metal electrodes to regulate electroluminance (EL) spectra of sky-blue organic light emitting diodes to obtain a saturated deep blue emission with a narrowed full-width at half-maximum (FWHM). First, we simulate micro-cavity OLEDs and find that the transmission of the anode plays an important role in the forward emission. Meanwhile, the optical path of micro-cavity OLEDs as well as the phase shifting from electrodes influence the EL spectra and induce the extra intensity enhancement. The results show that when the resonant cavity optical path is regulated by changing the thickness of emitting layer (EML) from 25 nm to 75 nm in the micro-cavity, the EL peak of blue OLEDs has a redshift from 479 nm to 493 nm with FWHM shifting from 69.8 nm to 83.2 nm, when compared to the device without the micro-cavity, whose approximate EL peak and FWHM are 487 nm and 87 nm, respectively. However, the efficiency of electroluminescence decreases in micro-cavity OLEDs. We speculate that this is on account of the ohmic contact between ITO and Ag, the surface plasma effect and the rough morphology induced by Ag electrodes. [ABSTRACT FROM AUTHOR]

A high triplet energy exciplex host derived from a ternary mixture of hosts was developed for efficient energy transfer to a deep blue phosphor by suppressing reverse energy transfer. In the thermally activated delayed fluorescent type exciplex host of 4,4′-bis(carbazol-9-yl)-2,2′-dimethylbiphenyl (CDBP) and 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T), the (oxybis(2,1-phenylene))bis(diphenylphosphine oxide) (DPEPO) was added as a third component to increase the triplet energy of the exciplex host. The addition of DPEPO in the CDBP:PO-T2T exciplex host increased the triplet energy of the exciplex from 2.88 eV to 2.97 eV, and the photoluminescence quantum yield of the deep blue phosphor doped exciplex from 0.77 to 0.86. The triplet energy boosting function of the DPEPO improved the maximum external quantum efficiency of the deep blue phosphorescent organic light-emitting diode from 12.8% to 16.6% at a DPEPO content of 70%. Image 1 • A high triplet energy exciplex host derived from a ternary mixture of hosts. • Efficiency improvement from 12.8% to 16.6% by adding an inert host content of 70%. • Triplet energy and photoluminescence quantum yield are increased up to 2.97 eV and 86% in the ternary exciplex host. [ABSTRACT FROM AUTHOR]

Unicolored phosphor‐sensitized fluorescence (UPSF) is a dual emitting concept proposed for improving efficiencies and operational lifetimes of blue organic light emitting diodes (OLEDs). To overcome the limitations of the individual emitters, it uses a phosphorescent donor to sensitize a fluorescent acceptor. To quantify the potential of the concept, a multiscale model of a UPSF OLED is developed. It starts from atomistic morphologies, the rates of all processes on the available experimental data are parameterized, and the respective master equation is solved with the help of the kinetic Monte Carlo algorithm. The simulations show that the energy transfer between donor molecules is essential to reproduce the results of the time‐resolved photoluminescence experiment. The scope of the experiment is expanded by studying the effect of the acceptor concentration, as well as Förster and (parasitic) Dexter energy transfer from the donor to acceptor, on the characteristics of the UPSF OLED. The study shows that an appropriate material design can further improve efficiency by more than 30% and at the same time achieve radiative decay times below 0.02 µs, thus significantly extending OLED operational lifetime. [ABSTRACT FROM AUTHOR]

High efficiency blue fluorescent organic light-emitting diodes (OLEDs), based on 1,3-bis(carbazol-9-yl)benzene (mCP) doped with 4,4'-bis(9-ethyl-3-carbazovinylene)-1,1'-biphenyl (BCzVBi), were fabricated using four different hole transport layers (HTLs) and two different electron transport layers (ETLs). Fixing the electron transport material TPBi, four hole transport materials, including 1,1-Bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4'-diamine(NPB), 4,4'-Bis(N-carbazolyl)-1,1,-biphenyl (CBP) and molybdenum trioxide (MoO3), were selected to be HTLs, and the blue OLED with TAPC HTL exhibited a maximum luminance of 2955 cd/m2 and current efficiency (CE) of 5.75 cd/A at 50 mA/cm2, which are 68% and 62% higher, respectively, than those of the minimum values found in the device with MoO3 HTL. Fixing the hole transport material TAPC, the replacement of TPBi ETL with Bphen ETL can further improve the performance of the device, in which the maximum luminance can reach 3640 cd/m2 at 50 mA/cm2, which is 23% higher than that of the TPBi device. Furthermore, the lifetime of the device is also optimized by the change of ETL. These results indicate that the carrier mobility of transport materials and energy level alignment of different functional layers play important roles in the performance of the blue OLEDs. The findings suggest that selecting well-matched electron and hole transport materials is essential and beneficial for the device engineering of high-efficiency blue OLEDs. [ABSTRACT FROM AUTHOR]

We characterized the 6,12-bis{[N-(3,4-dimethylphenyl)-N-(2,4,5-trimethylphenyl)]amino} chrysene (BmPAC), which has been proven to be a blue fluorescent emission with high EL efficiency. The blue fluorescent device exhibits good performance with an external quantum efficiency of 5.8% and current efficiency of 8.9 cd/A, respectively. Using BmPAC, we also demonstrate a hybrid phosphorescence/fluorescence white organic light-emitting device (WOLED) with high efficiency of 36.3 cd/A. In order to improve the relative intensity of blue light, we plus a blue light-emitting layer (BEML) in front of the orange light emitting layer (YEML) to take advantage of the excess singlet excitons. With the new emitting layer of BEML/YEML/BEML, we demonstrate the fluorescence/phosphorescence/fluorescence WOLED exhibits good performance with a current efficiency of 47 cd/A and an enhanced relative intensity of blue light. [ABSTRACT FROM AUTHOR]