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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]

Divalent ions‐doping has recently been developed as a new approach to blue perovskite light emitting diodes (LEDs) with improved spectral stability. However, the efficiency of these perovskite LEDs, especially in the pure blue region, is still far behind their red‐ and green‐emissive counterparts. Here, a method to improve the device efficiency of strontium ion (Sr2+)‐doped pure blue perovskite LEDs, prominently by modifying the hole transport layer, is reported. Mixing a small amount of poly(9,9‐di‐n‐octylfluorene‐alt‐(1,4‐phenylene‐(4‐sec‐butylphenyl)imino)‐1,4‐phenylene) (TFB) into the hole transport layer poly(9‐vinylcarbazole) (PVK) remarkably improves the morphology and reduces the trap states of Sr2+‐doped perovskite films. As a result, a pure blue LED emitting at 470 nm is obtained and shows a high external quantum efficiency of 2.24% with stable electroluminescence spectra under a forward bias of up to 8 V, representing the best performance reported in the divalent ions‐doped pure blue perovskites so far. The work opens up the way for the development of efficient pure blue perovskite LEDs. [ABSTRACT FROM AUTHOR]

Arrays of nanorod multi-quantum-well (MQW) blue light emitting diodes (nLEDs) with diameter 800 nm were prepared by reactive ion etching (RIE) with subsequent surface treatment by KOH etching alone, and KOH etching followed by SiO 2 passivation with the SiO 2 prepared by the sol-gel technique. In addition, the effects of Ag/SiO 2 core/shell nanoparticles prepared by sol-gel were studied for all surface treatments. For as etched nLEDs, the Internal Quantum Efficiency (IQE) of photoluminescence was low, 5.5 %, because of the impact of surface damage introduced by RIE. KOH etching and KOH plus SiO 2 passivation produced an increase of IQE to respectively 5.7 and 6.8 %. When the Ag/SiO 2 core/shell nanoparticles known to produce localized surface plasmon resonance at the wavelength well-matched to the light emission from the MQWs were added to the polymer filling the gaps between the MQW nanorods, the result was found to depend on finding a proper balance between the enhancement due to the interaction Ag/SiO 2 nanoparticles adjacent to the MQW nanorods and the absorption by "idle" Ag/SiO 2 particles in the bulk of the polymer. When optimal concentrations of LSP NPs giving rise to maximal enhancement of the MQW PL intensity were used, a considerable improvement of performance was obtained, with IQE of 10.6 %. • Arrays of blue light emitting diodes were prepared by reactive ion etching with subsequent KOH etching or SiO 2 passivation. • Effects of Ag/SiO 2 core/shell nanoparticles prepared by sol-gel were studied for all surface treatments. • For as etched nLEDs, the Internal Quantum Efficiency (IQE) was 5.5%. • KOH etching and KOH plus SiO 2 passivation produced IQE of respectively 5.7 and 6.8%. • When optimal concentrations of LSP NPs were used, IQE was 10.6%. [ABSTRACT FROM AUTHOR]

Non‐toxic heavy metal, low‐cost indium‐free blue emissive quantum dots (QDs) are critical for the realization of self‐emissive electroluminescent quantum dot (ELQD) light‐emitting diode (LED) displays. A facile and effective hybridization of ZnO QDs with functionalized polyaromatic hydrocarbons (f‐PAHs) to synthesize a very bright and stable blue‐light emissive quantum‐dot LED (QLED) using non‐toxic quasi‐type‐II ZnO@1‐Aminopyrene hybrid QDs is reported. The optimized QLEDs of ITO/PEDOT:PSS/TFB/ZnO@1‐Aminopyrene/TPBi/LiF/Al demonstrate very bright deep blue‐light electroluminescence of 3379 cd m−2 centered at λ = 441 nm with a full‐width‐at‐half maximum of 41.7 nm and CIE 1931 color coordinates of 0.17 and 0.09, a luminous efficacy of 3.32 cd A−1, power efficiency of 2.45 lm W−1, external quantum efficiency of 2.35%, and a remarkably long lifetime T50 of >17 830 h at 100 cd m−2. [ABSTRACT FROM AUTHOR]

Simulations on mobility influence in optoelectronics parameters from an InGaN/GaN blue LED using the Nextnano++ software arepresented in this paper. These simulations were performed by changing the hole and electron mobility value for the material compounds according to experimental, theoretical, and doping-concentration data already reported in the literature. The power law mobility is used for the current calculation in the quantum drift-diffusion model. The results indicate the lower hole and electron leakage currents correspond to the lowest mobility values for the InGaN alloy, the greatest amount of recombination occurs in the extreme wells within the active layer of the LED and the stable emission is at 3.6 V with peak wavelength λ ^ L E D = 456.7   nm and full width at half maximum F W H M ~ 11.1   nm for the three mobilities. Although experimental and theoretical mobility values reach higher carrier density and recombination, the photon emission is broader and unstable. Additionally, the doping-concentration mobility results in lower wavelength shifts and narrows FWHM, making it more stable. The highest quantum efficiency achieved by doping-concentration mobility is only in the breakdown voltage ( η d o p − m a x = 60.43 % ), which is the IQE value comparable to similar LEDs and is more useful for these kinds of semiconductor devices. [ABSTRACT FROM AUTHOR]

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]

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 h of LT95 were achieved. Furthermore, we achieved over 14% of EQE by optimizing the material combinations. [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]

Simulations on mobility influence in optoelectronics parameters from an InGaN/GaN blue LED using the Nextnano++ software arepresented in this paper. These simulations were performed by changing the hole and electron mobility value for the material compounds according to experimental, theoretical, and doping-concentration data already reported in the literature. The power law mobility is used for the current calculation in the quantum drift-diffusion model. The results indicate the lower hole and electron leakage currents correspond to the lowest mobility values for the InGaN alloy, the greatest amount of recombination occurs in the extreme wells within the active layer of the LED and the stable emission is at 3.6 V with peak wavelength λ^LED=456.7 nm and full width at half maximum FWHM~11.1 nm for the three mobilities. Although experimental and theoretical mobility values reach higher carrier density and recombination, the photon emission is broader and unstable. Additionally, the doping-concentration mobility results in lower wavelength shifts and narrows FWHM, making it more stable. The highest quantum efficiency achieved by doping-concentration mobility is only in the breakdown voltage (ηdop−max=60.43%), which is the IQE value comparable to similar LEDs and is more useful for these kinds of semiconductor devices.

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

A sequence of Eu3+ activated Na2Ln4(MoO4)7 [Ln = La, Gd and Y] red phosphors has been synthesized using a conventional solid-state method. The phase formation and structural analysis of the synthesized phosphor compositions were analyzed by X-ray diffraction followed by Rietveld refinement. All of the optical studies were executed systematically for the Eu3+ activated Na2Ln4(MoO4)7 red phosphors, all of them showed an intense red emission at 616 nm, owing to the 5D0 → 7F2 electric dipole (ED) transition. The synthesized phosphors show a decent thermal stability, and it retains a moderate percentage of the emission intensity at 423 K; the absolute internal quantum efficiency (IQE) was also found to be 79%. The red (conjugated with a near ultraviolet light emitting diode (UV LED)) and white light emitting diodes (LEDs) (conjugated with a blue light emitting diode (LED) + yellow organic dye) were fabricated by using the synthesized phosphor composition, the red LED showed an intense red emission and the white LED showed a warm white light emission with a Commission Internationale de l'Eclairage (CIE) color coordinate of 0.300, 0.379 and attractive color rendering index (CRI) (80%) and correlated color temperature (CCT) (6713 K) values. In addition, Sm3+ alone and Eu3+, Sm3+ co-doped Na2Ln4(MoO4)7 orange-red phosphors were synthesized, and their corresponding LEDs were fabricated for plant growth applications. The electroluminescence (EL) spectrum of the present phosphor entirely covers the absorption spectrum of phytochrome Pr. The obtained results reveal the synthesized red phosphor could be a potential red-emitting component in the white LED, as well as having possible applications as a plant growth LED. [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]

In this study, we investigate the below-threshold emission characteristics of InGaN-based blue laser diodes (LDs) emitting at 442 nm to study the efficiency droop effects in InGaN LDs. From the measurement of spontaneous emission in the LD, it is observed that the peak efficiency appears at a current density of ∼20 A/cm2 and the efficiency at the threshold current density of ∼2.3 kA/cm2 are reduced to ∼47% of the peak efficiency. The measured spontaneous emission characteristics are analyzed using the carrier rate equation model, and the peak internal quantum efficiency is found to be ∼75% using the fit of the measured efficiency curve. In addition, the Auger recombination coefficient of the measured InGaN blue LD is found to be 10-31-10-30 cm6/s, which is somewhat lower than that reported for InGaN-based blue light-emitting diodes. It is discussed that low dislocation density and uniform current injection in quantum wells may have resulted in the low Auger recombination coefficient of InGaN LDs. [ABSTRACT FROM AUTHOR]

A solution processed blue organic light emitting diodes was fabricated by using single component crosslinkable blue emitting materials. We successfully reduced a crosslinking temperaturedown to 135 °C by applying unique cyclic crosslinking units. From first blue emitting material, we obtained 7.86 cd/A of maximum current efficiency (CE) and 2.90 % of external quantum efficiency. And, we modified such material to give deeper blue OLED showing (0.16, 0.13) in CIE 1931 coordinate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bright and stable blue light emitting PeLEDs are obtained. • The thermal stability of the codoped QDs is greatly enhanced. • Both A and B sites of CsPbBr 3 perovskite are substituted by metal ions. • The EQE max is obtained as 4.52% for PeLEDs based on codoped QDs. Light-emitting perovskite quantum dots (PeQDs) are extensively investigated owing to their evident merits. However, it is still a challenge to adjust their intrinsic emissions and enhance their thermal stability to achieve full-color highly emissive QD-based light-emitting diodes (QLEDs), especially blue QLEDs. Herein, we demonstrate an effective strategy to fundamentally stabilize the crystal structure of CsPbBr 3 QDs by codoping Na+ and Cu2+ ions, which are designed to substitute Cs+ (A sites) and Pb2+ (B sites), respectively. It is found out that the codoping metal ions have significantly improved the thermal stability and the optical properties of the QDs. 40% of the emission intensity can be remained after 8 thermal cycles (20–120 °C) for CsPbBr 3 : Na+/Cu2+ QDs, whilst less than 10% is maintained for undoped CsPbBr 3 QDs. Accordingly, stable blue QLEDs are packed by CsPbBr 3 : Na+/Cu2+ QDs. Strong electroluminescence with the maximum luminance of 7161 cd m−2 and low turn-on voltage of 2.4 V are realized. The CIE coordinates are tuned from green (0.10, 0.74) to blue (0.17, 0.25) via Na+ and Cu2+ codoping. The maximum external quantum efficiency (EQE max) is obtained as 4.52% for PeLEDs based on codoped QDs. The proposed metal ions A and B sites dual substitution strategy guarantees PeQDs as an extremely promising prospect in potential applications as high-resolution displays and high-quality lightings. [ABSTRACT FROM AUTHOR]

[Display omitted] • WS 2 was used as the hole interface layer to improve the hole transport ability through energy level matching. • The crystal quality of perovskite film was improved by using WS 2 as the hole interface layer. • Obtained high-performance Quasi-2D blue perovskite light-emitting devices with EQE of 3.24%. Due to the deep energy levels, the external quantum efficiency (EQE) of the blue perovskite light-emitting diode (PeLED) is far lower than its green, red, and near-infrared counterparts, which has exceeded 20%. The mismatched energy levels between perovskites and the hole transporting layer (HTL) still hinder the hole injection and consequent improvement of blue PeLED device performance. Here, a two-dimensional material, WS 2 (Tungsten disulfide), was introduced to match the energy levels between perovskites and HTL and enhanced the hole injection. The WS 2 HTL-based perovskite FAPbBr 3-x Cl x blue LED achieved a luminance of 990 cd/m2 with an EQE of 3.24%, which surpasses the performance of previously reported for the formamidinium (FA) based system, indicating the potential of WS 2 for PeLEDs. [ABSTRACT FROM AUTHOR]

For electroluminescence with delayedfluorescence, the azasiline unit has been introduced for the firsttime as a donor in a thermally activated delayed fluorescence (TADF)material. The TADF material (DTPDDA) shows strong intramolecular chargetransfer (CT) character with large spatial separation with the acceptorof triazine leading to narrow splitting of singlet and triplet excitedstates for the efficient reverse intersystem crossing (RISC). A blueorganic light emitting diode (OLED) based on DTPDDA not only displaysdeep blue in the Commission Internationale de L’Eclairage (CIE)coordinates of (0.149, 0.197) but also exhibits a high external quantumefficiency (EQE) of 22.3% which is the highest value ever reportedfor a blue fluorescent OLED. Theoretical prediction based on transientphotoluminescence (PL) and optical simulation result agrees well withthe achieved EQE indicating the successful conversion of triplet excitonsto singlet in the blue fluorescent OLED by using DTPDDA. [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]

Blue light-emitting diodes (LEDs) with different p-doping concentrations in the last barrier have been studied numerically. The energy band diagrams, carrier concentrations, internal quantum efficiency and light output power are investigated using APSYS software. The simulation results show that the LED structure with p-doping in the last barrier has a better hole-injection efficiency and confinement of electron leakage over the structure with the last undoped GaN barrier due to enhancement of the holes' injection and the electrons' confinement. As a result, the efficiency droop is markedly improved, and the light output power is greatly enhanced when a larger p-doping amount is centralised in the last barrier. [ABSTRACT FROM AUTHOR]

Abstract: Two isomeric bipolar transporting molecules containing arylamine and benzimidazole moieties linked by 1,1′-binaphthalene bridge have been synthesized and used for blue light-emitting diodes. The highly twisted binaphthalene bridge is beneficial for amorphous morphology, good solubility, high thermal stability and high photoluminescence quantum efficiency (Φ PL). The charge transfer bands of these compounds exhibit interesting solvent-polarity dependent fluorescence properties. The physical properties of the compounds were tunable upon binding of the benzimidazole with binaphthalene group via C- (BINAPC) or N- (BINAPN) linkage. Three-layered blue-emitting OLEDs using BINAPC or BINAPN as the emitting layer, NPB as the hole transporting layer, and TPBI as the electron transporting layer as well as hole-blocking layer exhibit good performance. External quantum efficiencies of 2.49% with color coordinates of (0.15, 0.11) and 2.67% with color coordinates of (0.16, 0.16) were achieved for BINAPC and BINAPN, respectively. [Copyright &y& Elsevier]

Highlights: [•] A simply fabricated platform for high efficiency plasmonic LED is demonstrated. [•] Blue light emission is increased by 4.4-fold via localized surface plasmon coupling. [•] A 1.5-fold higher spontaneous emission rate confirms the fast recombination channel. [•] 53% enhancement in internal quantum efficiency was performed. [Copyright &y& Elsevier]

Polysilafluorenes(PSFs) are an important class of light-emitting conjugate polymersnoted for their characteristic brilliant solid state blue luminescence,high quantum efficiency, excellent solubility, and improved thermalstability. These polymers are also reported to have superior electronconductivity to polyfluorenes. The higher electron affinity and conductivity,which are particularly promising for OLEDs, originate from σ*−π*conjugation between the σ* antibonding orbital of the exocyclicSi–C bond and the π* antibonding orbital of the butadienefragment. In this paper, we present the synthesis and thorough characterizationof several new derivatives of 2,7-dibromo-3,6-dimethoxy-9,9-dialkylsilafluorenemonomers and demonstrate an efficient room temperature route to theirpolymerization. In addition to silafluorene monomers with simple alkylside chains, we have increased the functionality of several of ourmonomers by incorporating vinyl, cyclohexenyl, and norbornenyl moietiesinto their side chains, which we believe is useful for postpolymerizationmodification. (i.e., adding pendant emitters to tune PL or cross-linking).The production of polymer was achieved using a nickel-catalyzed polycondenationof diarylmagnesate-type monomers in a mixed solvent system of THFand 1,4-dioxane (7:3). Using 1,4-dioxane as a cosolvent was discoveredto significantly increase the Mg/Br exchange rate by a factor of 5,reducing the time required to achieve stiochiometric conversion ofsterically hindered and electron rich 2,7-dibromo-3,6-dimethoxy-9,9-dialkylsilafluoreneto 2 h. Also, relatively fast rates of polymerization were observed.Polymers reached their maximum molecular weight within 30 m. In manycases, Mnexceeds 50 kg/mol (PDI ∼1.5–2.0). The resultant polymers possess characteristic bluephotoluminescence with solid state quantum yields (exceeding 80% inmany cases). Polymer films have excellent transparency (with a measured Eg∼ 3.0 eV) and thermal stability asdemonstrated by TGA/DSC. Energy levels determined using CV were −5.62and −2.62 eV for HOMO and LUMO, respectively. [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]

We have decomposed the blue light-emitting diode (LED) current into the constituent components and studied the temperature dependence of each component and the internal quantum efficiency (IQE) quantitatively over the temperature range from 0 ^\circ\C to 80 ^\circ\C. The most temperature-sensitive current component is the nonradiative recombination current that increases with the temperature rise, and the component plays a dominant role in determining the temperature dependence of the IQE and luminescence output. Therefore, high-efficiency LEDs achieve high power and low temperature sensitivity simultaneously. On the other hand, the portion of the loss current that is responsible for the efficiency droop decreases with the temperature rise, resulting in lower droop at higher temperature. Some consequences and implications of the temperature dependence are also discussed. [ABSTRACT FROM AUTHOR]

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]

In this study, four blue fluorescent arylenes end-capped with thiophene derivatives have been synthesized. To explore electroluminescent properties of these molecules, multilayer OLEDs device structure of ITO/NPB/EML/BPhen/Al were fabricated. Two multilayer devices, using 3–4, showed the efficient deep blue emissions with CIE x,y of (0.159, 0.092) and (0.151,0.082) at 9.0 V, and the external quantum efficiencies of 1.60 and 0.80%, respectively. A PFVtPh doped-device exhibited the highly efficient blue emission with a maximum luminance of 3480 cd m−2 at 9.0 V, the external quantum efficiency of 5.23%, and CIE x,y of (0.151, 0.185) at 9.0 V. [ABSTRACT FROM AUTHOR]

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]

The effect of d-doping of In0.06Ga0.94N barriers with Mg on the quantum efficiency of blue lightemitting- diodes (LEDs) with active regions composed of 6 (hex) 3-nm In0.15Ga0.85N is investigated. Compared to the reference sample, δ-doping of the first barrier on the n-side of the LED structure improves the peak external quantum efficiency (EQE) by 20%, owing to the increased hole concentration in the wells adjacent to the n-side, as confirmed by numerical simulations of carrier distributions across the active region. Doping the second barrier, in addition to the first one, did not further enhance the EQE, which likely indicates compensation of improved hole injection by degradation of the active region quality due to Mg doping. Both LEDs with Mg δ-doped barriers effectively suppress the drop of efficiency at high injection when compared to the reference sample, and the onset of EQE peak roll-off shifts from ~80 A/cm² in the reference LED to ~120 A/cm² in the LEDs with Mg d-doped barriers. [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]

Deep blue fluorescent organic light-emitting diodes were developed using boron derived 5,9-diphenyl-5H,9H-[1,4]benzazaborino[2,3,4-kl]phenazaborine (DABNA) and 2,12‐di‐tert‐butyl‐5,9‐bis(4‐(tert‐butyl)phenyl)‐5,9‐dihydro‐5,9‐diaza‐13b‐boranaphtho[3,2,1‐de]anthracene (t-DABNA) as fluorescent emitters rather than thermally activated delayed fluorescent emitters for long lifetime. The DABNA and t-DABNA boron emitters were doped in the 9,10-bis(1-naphtyl)anthracene (α-ADN) host to harvest only singlet excitons while quenching triplet excitons for long-term stability. The t-DABNA emitter showed high external quantum efficiency of 7.6% as fluorescent emitters and lifetime longer than that of a conventional pyrene derived blue emitter. This work demonstrated the usefulness of the boron derived emitters as deep blue fluorescent emitters rather than thermally activated delayed fluorescent emitters by overcoming short lifetime drawback through triplet exciton quenching. The paradigm change of the thermally activated delayed fluorescent emitters enabled the development of the deep blue fluorescent organic light-emitting diodes with excellent long-term stability. Image 1 • Boron emitters as the highly efficient fluorescent emitters for blue organic light-emitting diodes. • Triplet exciton quenching of the boron emitters using a low triplet energy host for long lifetime. • High external quantum efficiency of 7.6% and lifetime longer than that of a conventional pyrene derived blue emitter. [ABSTRACT FROM AUTHOR]

The balance of hole–electron injection is always a vital factor for the luminance, efficiency and working lifetime of quantum‐dot light‐emitting diodes (QLEDs), especially blue QLEDs. However, currently most approaches proposed to solve this issue involve tedious optimization of device architecture or material composition. Here, high‐performance blue QLEDs are reported based on CdZnS/ZnS quantum‐dot (QDs) by utilizing ZnO nanoparticles (NPs) and Al:Al2O3 as electron‐transporting layer (ETL) and cathode materials, respectively. The effect of post‐annealing temperature on the trap state density in ZnO NPs and the related mechanisms are investigated through optical and photoelectron spectroscopies. The method of controlling ZnO NPs annealing temperature leads to controllable electron‐mobility of ETL, which ultimately optimizes the balance of charge injection. Together with partially oxidized Al cathode (Al:Al2O3), high‐performance blue QLEDs are fabricated with luminance and external quantum efficiency (EQE) up to 27 753 cd m−2 and 8.92%. As far as is known, the peak luminance achieved is the record of deep blue QLEDs. This simple method for regulating charge injection balance via annealing temperature requires no modification of device architecture, making it applicable for a variety of QLEDs structures. High‐performance blue QLEDs are fabricated based on a ZnO nanoparticle (NP) electron‐transporting layer and a Al:Al2O3 cathode. The electron mobility in ZnO NP films can be regulated for better electron–hole balance by controlling the annealing temperature, thereby ensuring excellent luminance and recombination efficiency. This simple way to adjust charge injection balance requires no additional modification of the device architecture. [ABSTRACT FROM AUTHOR]

A compositionally step-graded (CSG) InGaN barrier is designed for the active region of c-plane blue light-emitting diodes (LEDs). High external quantum efficiencies of 45, 42, 39 and 36% are achieved at current densities of 100, 200, 300 and 400 A/cm2, respectively. Compared with GaN barrier devices, LEDs with CSG InGaN barriers showed higher power, lower operating voltage and smaller wavelength blueshift, compared with GaN barrier LEDs. Owing to the low-voltage performance, higher wall-plug efficiency can be achieved for blue LEDs with CSG InGaN barriers. [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]