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Excited‐state intramolecular proton transfer (ESIPT) molecules are promising fluorophores for various applications including bioimaging, sensing, and optoelectronic devices. Particularly, their self‐absorption‐free fluorescence properties would make them a perfect choice as emissive materials for organic light‐emitting diodes (OLEDs). Nevertheless, to become effective emitters some of their properties need to be altered by structural modifications. Herein, we design and synthesize a series of new ESIPT molecules (2PImBzP, 2ImBzP, and 2FImBzP) by functionalization of imidazole‐phenol‐based ESIPT cores with electron‐deficient benzo[d]thiazole and various ambipolar imidazole moieties (1‐phenyl‐1H‐phenanthro[9,10‐d]imidazole (PIm), 1,4,5‐triphenyl‐1H‐imidazole (Im), and (4,5‐bis(4‐fluorophenyl)‐1‐phenyl‐1H‐imidazole (FIm)), respectively. Each molecule displays a complete ESIPT process with intense green emissions from a pure keto form and high solid‐state photoluminescence quantum yields (ΦPL) of 65–80 %. These fluorophores with superior thermal stability and balanced charge carrier mobility are effectively employed as non‐doped emitters in OLEDs. The non‐doped devices emit greenish lights with high brightness, high current efficiency (CE) (10.95–17.66 cd A−1), and low turn‐on voltages (2.8–2.9 V). The electroluminescence purely originates from the emission of the keto tautomer of the emissive layers. Specifically, the 2PImBzP‐based non‐doped OLED stands out by achieving a remarkable brightness of 56,220 cd m−2, a CE of up to 17.66 cd A−1, and an impressive external quantum efficiency (EQE) of 5.65 % with a slight efficiency roll‐off. [ABSTRACT FROM AUTHOR]

Achieving deep-blue light with high color saturation remains a critical challenge in the development of white light-emitting diode (LED) technology, necessitating luminescent materials that excel in efficiency, low toxicity, and stability. Here, we report the synthesis of [N(C2H5)4]2Cu2I4 (TEA2Cu2I4) single crystals (SCs), which exhibit deep-blue photoluminescence (PL) at 450 nm. These crystals are characterized by a significant Stokes shift of 180 nm, a long lifetime of 1.7 μs, and an impressive photoluminescence quantum yield (PLQY) of 96.7% for SCs and 87.2% for polycrystalline films. The zero-dimensional structure is attributed to the proper spacing of triangular inorganic units [Cu2I4]2− by organic cations [N(C2H5)4]+. This structural arrangement facilitates broadband deep-blue light emission with phosphorescent characteristics, as evidenced by temperature-dependent PL and time-resolved photoluminescence (TRPL) measurements. The band gap properties of TEA2Cu2I4 were further elucidated through density functional theory (DFT) computations. Notably, the material exhibited minimal PL intensity degradation after continuous UV irradiation and one month of exposure to ambient conditions. Moreover, the polycrystalline film of TEA2Cu2I4 maintained substantial deep-blue emission even after one year of storage. Utilizing TEA2Cu2I4 thin film, we fabricated an electroluminescent device emitting deep-blue light with high color saturation, featuring CIE coordinates (0.143, 0.076) and a brightness of 90 cd/m2. The exceptional photophysical properties of TEA2Cu2I4 render it a highly promising candidate for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Organic fluorescent emitters based on π-conjugated small molecules show tremendous potential for display, lighting, and bio-imaging applications. However, these emitters face challenges of aggregation-caused quenching and limitations of color range caused by synthetic complexity and undesirable efficiency and quantum yield. In this work, by using quinoxaline/2,1,3-benzothiadiazole as central electron acceptors, and employing carbazole/thiophene/3,4-ethylenedioxythiophene as terminal electron donors, a series of π-conjugated fluorescent trimers with very low molecular weights (Mw = 294–466) were designed and synthesized. Modulating the molecular structure through the incorporation of distinct electron donor and acceptor moieties, broad spectral tuning from blue to red in the π-conjugated trimers was achieved. These conjugated trimers when applied as emitting layers in electroluminescent devices, particularly organic light-emitting diodes (OLEDs), exhibit high brightness and color-tunable electroluminescence (EL) peaks from 528 to 605 nm. The meticulously optimized device demonstrates excellent performance with a high brightness of 3857.19 cd m−2, and an external quantum efficiency (EQE) of 2.29%. These π-conjugated trimers, synthesized by a simple synthesis process, present a viable avenue for low-cost luminescence lighting and display applications. [ABSTRACT FROM AUTHOR]

Organic ultralong room temperature phosphorescence (OURTP) materials capable of combining various emission behaviors for diversified optoelectronic properties and applications have recently gained a vigorous development, but it remains a forbidden challenge in designing OURTP molecules with hybrid local and charge‐transfer (HLCT) feature, possibly due to the elevated difficulties in simultaneously meeting the stringent requirements of both HLCT and OURTP emitters. Here, through introducing multiple heteroatoms into one‐dimensional fused ring of coumarin with moderate charge transfer perturbation in donor‐π‐acceptor architecture, we demonstrate a HLCT‐featured OURTP molecule showing both promoted fluorescence with a quantum yield of 77 % in solution and long‐lived OURTP with a lifetime of 251 ms in conventional host material used in electroluminescent device. Thus, efficient OURTP organic light‐emitting diodes (OLEDs) were fabricated, exhibiting bright electroluminescence with an exciton utilization efficiency of 85 % and yellow OURTP lasting over 2 s for afterglow. Impressively, the HLCT OURTP‐OLEDs can be further optimized to reach an unprecedented total external quantum efficiency (EQE) of ~12 % and OURTP EQE up to 3.11 %, representing the highest performance among the reported OURTP‐OLEDs. These impressive results highlight the significance to fuse HLCT and OURTP together in enriching OURTP materials and improving the afterglow OLED performances. [ABSTRACT FROM AUTHOR]

Excited-state intramolecular proton transfer (ESIPT) materials have emerged as highly promising candidates for emitters in organic light-emitting diodes (OLEDs), attributed to their distinctive photophysical properties. These materials have garnered considerable attention due to their pronounced Stokes shifts, exceptional color purity, and potential for achieving high efficiency and stability in OLED applications. To develop highly luminescent solids with large Stokes shifts, two imidazole-based ESIPT-AIE emitters, PPy-HPI and PPy-HPIC, have been synthesized following the strategy of combining excited-state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) systems. These emitters integrate the ESIPT cores 2-(2-hydroxy-5-methylphenyl)-1,4,5-triphenylimidazole (HPI) and 2-(2-hydroxy-5-methylphenyl)-1- phenylphenanthroimidazole (HPIC) with the AIE-active luminogen 4-(1-phenylvinyl)pyridine (PPy). The ESIPT and AIE properties were confirmed through both theoretical and experimental studies. The emitters demonstrated ESIPT and AIE characteristics, featuring a large Stokes shift and strong yellow-green to yellow emission in the solid state, which originated from the pure keto form. A non-doped OLED utilizing PPy-HPIC demonstrated yellow emission with CIE coordinates of (0.47, 0.51), a maximum external quantum efficiency (EQEmax) of 3.13% and a maximum current efficiency (CEmax) of 9.48 cd A-1. Notably, the non-doped OLED incorporating PPy-HPI exhibited yellow-green emission with CIE coordinates of (0.15, 0.10), EQEmax of 3.61%, and CEmax of 10.56 cd A-1, with minimal efficiency roll-off. These results signify a major breakthrough in creating ESIPT molecules for use as non-doped emitters in fluorescent OLEDs. [ABSTRACT FROM AUTHOR]

Large-area imaging techniques in the short-wave infrared spectral region remain a pressing need. Organic light-emitting diodes and infrared photodetectors can be combined to form a near-infrared (NIR) to visible upconversion device, which has great potential to replace traditional infrared imaging systems. The integration of a white organic light-emitting diode (WOLED) with infrared photodetectors has become essential to realize full-color displays for its simple preparation process and high compatibility. This work has designed and optimized a WOLED to achieve stable emission with high brightness (19 470 cd m−2) and high external quantum efficiency (EQE = 18.08%) at a wide voltage range, thereby reducing chromaticity drift caused by voltage fluctuations. Moreover, photon-generated holes in the NIR-sensitive photodetector are able to inject into the WOLED for visible light emission. Consequently, we have obtained a high-performance upconversion device with a luminance on-off ratio exceeding 5 × 103 at 850 nm NIR and a high color stability over a wide range of operating voltage. Our efforts have accomplished a high-performance upconversion device from NIR to white visible light, laying the groundwork for a preliminary exploration of full-color displays. [ABSTRACT FROM AUTHOR]

While the development of solution‐processed organic light‐emitting diodes (sOLEDs) utilizing multiple resonance‐induced thermally activated delayed fluorescence (MR‐TADF) is highly significant, it is restricted by the limited solubility and film‐forming property resulting from the rigid conjugate and planarity of MR‐TADF materials. Herein, an effective strategy is presented to obtain solution‐processed narrowband emitters by introducing an inert steric bulky hindrance group into the multiple resonance skeleton, thereby mitigating issues arising from intermolecular packing‐induced poor solution processing ability and quenching effects. The resulting target emitter, designed as 3CzSF‐BN, exhibits pure‐green emission with a peak at 520 nm and a small full width at half maximum (FWHM) of 30 nm (0.14) eV. Remarkably, it achieves an exceptional photoluminescence quantum yield (PLQY) of 100% and notable advancements in solution processing attributes. The optimized bottom‐emitting sOLED (BE‐sOLED) device achieves an external quantum efficiency (EQE) over 20% with Commission Internationale de I'Éclairage (CIE) coordinates of (0.214, 0.716). Notably, the top‐emitting sOLED (TE‐sOLED) device exhibits an ultra‐pure green color with FWHM of 22 nm and CIE coordinates of (0.138, 0.771), thereby highlighting the effectiveness of this strategy in designing high‐performance solution‐processed MR‐TADF materials. [ABSTRACT FROM AUTHOR]

Organic and inorganic hybrid perovskites are a class of solution‐processable semiconductors that hold significant promise for light‐emitting diode applications. However, the development of efficient blue perovskite light‐emitting diodes (PeLEDs) has remained a critical challenge. Although significant advancements have been achieved in the development of sky‐blue PeLEDs, the performance of pure‐blue and deep‐blue PeLEDs still lags. In this manuscript, by incorporating 1‐cyclohexene‐1‐ethanamine cation (CEA+) into the host 1‐phenylbutylamine cation (PBA+) spacer and fabricating mixed‐cations quasi‐2D perovskites, a homogeneous phase distribution in quasi‐2D perovskite films is achieved through precise tuning of the phase formation energy. The resulting PeLEDs exhibit remarkable performance with an external quantum efficiency (EQE) of 5.8% at 467 nm, which is one of the highest EQEs among the deep‐blue light quasi‐2D PeLED devices with emission wavelengths below 470 nm, Additionally, the device demonstrates a half‐lifetime of ≈ 25 min. Furthermore, the PeLEDs utilizing mixed‐cation perovskite exhibit a stable electroluminescence (EL) spectrum under varying voltage biases, even when the chlorine content in the halogen sites reaches as high as 30%. Overall, this work offers a novel and promising avenue to achieve both high EQE and a stable EL spectrum in blue‐light quasi‐2D PeLEDs. [ABSTRACT FROM AUTHOR]

Circularly polarized electroluminescent devices are conventionally fabricated by incorporating an optically active chiral luminophore into their emission layer. Herein, we developed a circularly polarized perovskite light-emitting diode (PeLED) system with an optically inactive perovskite luminophore that can emit near-infrared circularly polarized electroluminescence (CPEL) upon application of an external magnetic field. The magnitude of the magnetic CPEL (gMCPEL) was in the order of 10−3 in the near-infrared wavelength range of 771–773 nm. Although the Pb perovskite quantum dots were achiral, the rotation direction of the CPEL of the magnetic circularly polarized PeLED system was successfully reversed by switching the Faraday geometry of the applied magnetic field. The use of achiral luminophores exhibiting magnetic-field-induced CPEL represents a new approach for the development of circularly polarized electroluminescent devices. [ABSTRACT FROM AUTHOR]

Exploiting narrow-bandwidth-emission fluorescent materials is crucial for next-generation wide-color gamut displays. Inspired by the narrow-bandwidth-emission characteristic of chlorophyll derivates, the present work develops a facile strategy to synthesize a series of red-emitting chlorophyll-structured CDs (CHL-CDs) with ultra-high color purity and good carrier mobility from different traditional Chinese medicine leaves through a simple cross-linking polymerization and carbonization process. The obtained CHL-CDs exhibit bright photoluminescence centered at 671 nm, ultra-high color purity with an FWHM of 23 nm, and a high photoluminescence quantum yield of up to 62%. More importantly, based on in-depth experimental and theoretical studies on the macroscopic host–guest interactions and microscopic interfacial interactions between the CHL-CDs and charge transporting materials, high-performance red electroluminescent light-emitting diodes are successfully prepared, with FWHM of only 28 nm, turn-on voltage of 3.7 V, maximum luminance of 623 cd m−2, and maximum current efficiency of 0.26 cd A−1. This study provides a universal platform for fabricating narrow-bandwidth-emission CDs with significant applications in photoelectric devices. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon dots (NCDs), exhibiting strong yellow emission in aqueous solution and solid matrices, have been utilized for fabricating heterostructure white electroluminescence devices. These devices consist of nitrogen-doped carbon dots as an emissive layer sandwiched between an organic hole transport layer (PEDOT:PSS) and an array of rutile TiO2 nanorods, acting as an electron transport layer. Under an applied forward bias of 5 V, the device exhibits broadband electroluminescence covering the wavelength range of 390–900 nm, resulting in pure white light emission characteristics at room temperature. The result demonstrates the successful fabrication of all solution-processed, low-cost, eco-friendly NCDs-based LEDs with CIE (Commission Internationale d'Éclairage) coordinate of (0.31, 0.34) and color rendering index (CRI) > 90, which are close to ideal white light emission characteristics. The device functionalities are achieved based on defect-related NIR emission from TiO2 nanorods array and visible emission from nitrogen-doped carbon dots. This result paves a new opportunity to develop low-cost, solution-processed nitrogen-doped carbon dots based on warm White light emitting diodes with high CRI for large-area display and lighting applications. [ABSTRACT FROM AUTHOR]

Microcavity structures are used in inorganic‐, organic‐, quantum‐dot‐, and perovskite‐based electroluminescent (EL) devices to advance next‐generation displays. However, there are difficulties in controlling electrical characteristics and patterning processes for producing different thicknesses for each red, green, and blue (RGB) subpixel, and the issues are more challenging in the high‐resolution display for future realistic media. Here, a novel design method is presented for a dual‐microcavity structure that controls high‐order modes of a second cavity stacked on top of EL devices with the same cavity length for each subpixel to produce multiple peaks at RGB resonant wavelengths. The dual‐microcavity effect demonstrated by top‐emitting organic light‐emitting diodes (OLEDs) can be conveniently fabricated via in situ deposition. By modulating the high‐order modes, the spectral characteristics of each RGB dual‐microcavity top‐emitting OLED (DMTOLED) are manipulated while its electrical properties are maintained. Green DMTOLED exhibits a maximum luminance of 2.075 × 105 cd m−2, allowing applications not only for commercialized displays but also for outdoor augmented reality and automotive displays. Furthermore, dual‐microcavity structures with narrow spectral bandwidths can be applied to next‐generation EL devices for more realistic media. The method is expected to be applied industrially, promoting the advancement of EL devices for next‐generation displays. [ABSTRACT FROM AUTHOR]

Here, we report the synthesis and characterization of a solution-processable deep-red hot exciton fluorophore (CTTPy) based on a donor–π–acceptor–π–donor (D–π–A–π–D) type structure and its application as a non-doped emitter in an organic light-emitting diode (OLED). CTTPy contains electron-deficient thiadiazole[3,4-c]pyridine (TPy) as a strong acceptor, 3-hexylthiophene as a π-linker, and a carbazole dendron as a donor. The solvatochromic studies and theoretical calculations support that CTTPy is a hot exciton emitter with hybridization of both locally excited (LE) and charge transfer (CT) features of emission. Thanks to the strong electron deficiency of the TPy central core, bulkiness, and electron-donating and hole-transporting properties of end-capped carbazole dendrons, CTTPy displays a strong deep red emission (λem = 681 nm) with a decent fluorescence quantum yield of 54%, thermally stable amorphous morphology (Tg = 214 °C), good thin film forming ability by solution casting, and appropriate energy levels. CTTPy is effectively applied as a non-doped emitter in a solution-processed OLED which emits deep red electroluminescence peaked at 674 nm with CIE coordinates of (0.667, 0.327), an EQEmax of 3.66% and a considerably high exciton utilization efficiency (EUE) of 59%. This work not only provides a new strategic design for the construction of deep-red pure organic fluorescent materials, but also further ratifies that the "hot exciton" mechanism can also be successful in solution-processed OLEDs. [ABSTRACT FROM AUTHOR]

Rare-earth (RE) doped AlN are excellent candidate materials for electroluminescent devices, full color displays and white lighting technology. In this paper, a deep red Sm2+ doped AlN (AlN:Sm2+) phosphor was synthesized for the first time by a one-step direct nitridation method. Detailed XRD and EDS studies show the presence of samarium (Sm) ions the AlN, and XPS measurements indicate Sm ions are divalent. SEM and TEM studies show that the AlN:Sm2+ have a branched nanostructure, consisting of a primary stem and secondary short nano-branches. AlN:Sm2+ phosphor has a broad and strong excitation bands in the range of 300–600 nm, ultra-narrow deep red emission at 686 nm, near unity color purity, and good thermal stability (78.2% at 413 K). A blue-pumped warm white light emitting diode with high color rendering index (Ra∼87.5) and low correlated color temperature (CCT∼4875 K) was fabricated. Moreover, a super-wide color gamut (117.6% of the NTSC) can be achieved by using AlN:Sm2+ as the red component. Furthermore, photoluminescence (PL) and Raman spectra of AlN:Sm2+ were studied under hydrostatic pressure up to 25 GPa. The shift of the 5D 0 →7F 0 emission band (dλ/dP≈0.13 nm/GPa) and the decrease of PL intensity ratio (5D 0 →7F 0 /5D 0 →7F 1 , dI R (0/1)/dP≈−5.6%/GPa) with applied pressure can be used for optical pressure sensor. Raman spectroscopy revealed a phase transition of AlN:Sm2+ from wurtzite to rocksalt phase at 19.9 GPa. The large doping of Sm2+ ions and unique intrinsic geometry in branched nanostructure co-affect its compressibility and structural stability under high pressure. The results indicate that AlN:Sm2+ phosphor has promising applications in backlight displays and optical pressure sensors due to their excellent luminescent properties. [ABSTRACT FROM AUTHOR]

We report on organoboron complexes characterized by very small energy gaps (ΔEST) between their singlet and triplet states, which allow for highly efficient harvesting of triplet excitons into singlet states for working as thermally activated delayed fluorescence (TADF) devices. Energy gaps ranging between 0.01 and 0.06 eV with dihedral angles of ca. 90° were registered. The spin–orbit couplings between the lowest excited S1 and T1 states yielded reversed intersystem crossing rate constants (KRISC) of an average of 105 s−1. This setup accomplished radiative decay rates of ca. 106 s−1, indicating highly potent electroluminescent devices, and hence, being suitable for application as organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

We investigated the effects of sterically nonrestricted electron-accepting substituents of three isomeric indolocarbazole derivatives on their aggregation-induced emission enhancement, mechanochromic luminescence and thermally activated delayed fluorescence. The compounds are potentially efficient emitters for host-free organic light-emitting diodes. The films of indolocarbazole derivatives exhibit emissions with wavelengths of fluorescence intensity maxima from 483 to 500 nm and photoluminescence quantum yields from 31 to 58%. The ionization potentials of the solid samples, measured by photoelectron emission spectrometry, are in the narrow range of 5.78–5.99 eV. The electron affinities of the solid samples are in the range of 2.99–3.19 eV. The layers of the derivatives show diverse charge-transporting properties with maximum hole mobility reaching 10−4 cm2/Vs at high electric fields. An organic light-emitting diode with a light-emitting layer of neat compound shows a turn-on voltage of 4.1 V, a maximum brightness of 24,800 cd/m2, a maximum current efficiency of 12.5 cd/A and an external quantum efficiency of ca. 4.8%. When the compounds are used as hosts, green electroluminescent devices with an external quantum efficiency of ca. 11% are obtained. The linking topology of the isomeric derivatives of indolo[2,3-a]carbazole and indolo[3,2-b]carbazole and the electron-accepting anchors influences their properties differently, such as aggregation-induced emission enhancement, mechanochromic luminescence, thermally activated delayed fluorescence, charge-transporting, and electroluminescent properties. The derivative indolo[3,2-b]carbazole displays good light-emitting properties, while the derivatives of indolo[2,3-a]carbazole show good hosting properties, which make them useful for application in electroluminescent devices. [ABSTRACT FROM AUTHOR]

Herein, donor (D)‐acceptor (A) type fluorophores (TTBz and TTNz) were designed and synthesized with different acceptor units. The two acceptor units benzo[c][1,2,5]thiadiazole (Bz) and naphtho[2,3‐c][1,2,5]thiadiazole (Nz) are asymmetrically functionalized with triphenylamine (TPA) as a strong donor and tetraphenylethylene (TPE) as an aggregation‐induced emission (AIE)‐luminogen to realize combined AIE and hybridized local and charge transfer (HCLT) excited state features as well as long‐wavelength emission. Their HCLT and AIE properties are verified by theoretical calculations, solvatochromic effects, and transient photoluminescence decay experiments. They exhibit strong orange‐red and deep‐red fluorescence emission with good thermal stability and hole mobility, leading to effective utilization as emitters in organic light‐emitting diodes (OLEDs). The resulting devices show decent electroluminescent (EL) performance (current efficiency of 12.04–12.58 cd A−1, maximum brightness of 11206–20160 cd m−2, and external quantum efficiency of 5.11–5.47 %). Particularly, the TTNz‐based OLED demonstrates steady deep‐red emission with a peak at 661 nm and CIE coordinates of (0.67, 0.33). [ABSTRACT FROM AUTHOR]

The bias dependent behaviors in magnetic field effects (MFEs) of the current and the electroluminescence (EL) intensity in organic light emitting diodes (OLEDs) have been investigated from electrically-detected and EL-detected magnetic resonance (EDMR and ELDMR) techniques. An EDMR signal was not detected from the electron-only device, and the hole-only device gave only a much smaller EDMR signal than the OLED device. Both the EDMR and ELDMR signals observed from the OLED are concluded to primarily arise from the spin-dependent reaction of electron-hole (e-h) pairs. Both the normalized EDMR and ELDMR signal intensities decrease by increasing the operation bias of OLED, because the increased bias enhances the dissociation and recombination of e-h pairs beyond the increase in the pair-density by the bias. The bias-dependence curves of magneto-conductances and magneto-EL intensities are demonstrated to be very similar to those of the normalized EDMR and ELDMR, respectively. This similarity gives direct evidence that e-h pairs determine the MFEs of the present OLEDs at room temperature and that the MFEs are reduced by bias-dependent dissociation and recombination of e-h pairs. The bias-dependent EDMR and ELDMR experiments are thus effective as probing methods to examine the magnetic field properties via e-h pairs of OLEDs. [ABSTRACT FROM AUTHOR]

Carbon quantum dots (CQDs) feature bright and tunable photoluminescence, solution processability, and low toxicity, showing great potential in optoelectronics. However, the large‐scale synthesis of CQDs with near‐unity photoluminescence quantum yield (PLQY) has not been achieved so far. In this study, we perform radical‐assisted synthesis of hexagon‐shaped CQDs (H‐CQDs) delivering near‐unity PLQY (96 %). Experimental and theoretical analyses revealed that the large vertically oriented transition dipole moment of H‐CQDs originating from high symmetry results in nearly 100 % PLQY. The H‐CQDs also exhibited a high electron mobility of up to 0.07 cm2 V−1 s−1. These properties enable the H‐CQD‐based light‐emitting diodes with a high external quantum efficiency of 4.6 % and a record maximum brightness of over 11 000 cd m−2. This study represents a significant advance that CQDs‐based electroluminescent device can be utilized for potential display and lighting applications. [ABSTRACT FROM AUTHOR]

In the synthesis of InP‐based quantum dots (QDs), the environmentally friendly carboxylic‐free phosphor precursor tris(dimethylamino)phosphine ((DMA)3P) has been frequently used to replace tris (trimethylsilyl)phosphine (TMS)3P, in order to prevent the InP cores from oxidation and avoid the dangerous etching with hydrofluoric acid. However, the InP‐based QDs synthesized with (DMA)3P still perform poorly in quantum dot light‐emitting diodes (QLEDs) due to oxidation by other carboxylic sources. In this work, based on the synthesis with (DMA)3P, ZnCl2 precursor instead of zinc carboxylate is used for shell growing, and oleylamine is used as solvent instead of oleic acid, so that there is no oxidizing agent such as carboxylic groups during the whole synthesis process. As a result, highly efficient InP/ZnSe/ZnSeS/ZnS QDs with gradient varying shells are obtained, whose full width at half‐maximum (≈41 nm) and photoluminescence quantum yield (≈96%) are narrowest and highest among the reported ones, respectively. The QLEDs based on InP QDs synthesized with (DMA)3P achieve breakthrough efficiency of 12.39%. Especially, high efficiency and high brightness are achieved at the same time. This work opens a new avenue in the synthesis of high‐quality and environmental friendly InP‐based QDs. [ABSTRACT FROM AUTHOR]

Reduced‐dimensional perovskite light‐emitting diodes (PeLEDs) have shown great potential in solution‐processed high‐definition displays. However, the inferior electroluminescent (EL) performance of blue PeLEDs has become a huge challenge for their commercialization. The inefficient domain control [number of PbX6− layers (n)] and deleterious phase segregation make the blue PeLEDs suffer from low EL efficiency and poor spectral stability. Here, a rational strategy for perovskite crystallization control by adjusting the precursor concentration is proposed for improving phase distribution and suppressing ion migration in reduced‐dimensional mixed‐halide blue perovskite films. Based on this method, efficient sky‐blue PeLEDs exhibit a maximum external quantum efficiency (EQE) of 8.5% with stable EL spectra at 482 nm. Additionally, spectrally stable pure‐blue PeLEDs at 474 and 468 nm are further obtained with maximum EQEs of 4.0% and 2.4%, respectively. These findings may provide an alternative scheme for manipulating perovskite crystallization dynamics toward efficient and stable PeLEDs. [ABSTRACT FROM AUTHOR]

[Display omitted] • An intramolecular-locked azaryl ketone acceptor IQLO is designed for TADF emitters. • The new compounds exhibit notable TADF properties, facilitating efficient triplet-to-singlet spin conversion. • IQLO-PXZ and IQLO-DMAC show long-wavelength emission with decent PLQYs of 42% and 47%, respectively. • High electroluminescence efficiency with EQE of up to11.7% is demonstrated. We have developed two novel thermally activated delayed fluorescence (TADF) emitters, IQLO-PXZ and IQLO-DMAC, featuring an intramolecularly locked indeno[1,2- b ]quinolin-11-one (IQLO) acceptor. Our comprehensive investigation, including structural analysis, theoretical calculations, and photophysical studies, aims to assess the viability of IQLO-PXZ and IQLO-DMAC as light emitters in electroluminescent devices. Unlike existing aryl ketone-based emitters, IQLO-PXZ and IQLO-DMAC exhibit red-shifted emission due to their structurally rigid and electron-deficient IQLO moiety. The stronger intramolecular charge transfer effect in IQLO-PXZ results in longer-wavelength emission compared to IQLO-DMAC. Both emitters demonstrate significant TADF properties, facilitating efficient triplet-to-singlet spin conversion. When utilized as the emissive core in electroluminescent devices, IQLO-PXZ and IQLO-DMAC achieved long-wavelength electroluminescence peaking at 612 nm and 578 nm, with commendable external quantum efficiencies of 10.3 % and 11.7 %, respectively. These findings underscore the potential of IQLO as an effective acceptor for constructing high-performance TADF electroluminescent materials. [ABSTRACT FROM AUTHOR]

The development of red organic emissive materials with high‐efficiency and low‐cost is of great significance but formidable challenge for organic light‐emitting diodes (OLEDs). Herein, through isomer engineering, a pair of red thermally activated delayed fluorescence (TADF) isomers with Y‐shape and cruciform structures, namely TPA‐APQDCN‐Y and TPA‐APQDCN‐C, are developed by integrating two triphenylamine (TPA) donor moieties into different positions of rigid planar acenaphtho[1,2‐b]quinoxaline‐9,10‐dicarbonitrile (APQDCN) acceptor core. Compared to common Y‐shape structure, the unique cruciform structure can result in the formation of intramolecular H‐bonding, the limited molecular packing, the balance of the contradiction between the small spatial overlap of frontier molecular orbitals, and high oscillator strength, contributing to a higher photoluminescence quantum yield of 95%, a smaller singlet–triplet energy split of 0.24 eV and a larger horizontal emitting dipole ratio of 86%. An external quantum efficiency of 34.3% with an emission peak at 610 nm is achieved for TPA‐APQDCN‐C based red electroluminescent device, which is the highest value for red TADF‐OLEDs with emission maximum beyond 600 nm ever reported. [ABSTRACT FROM AUTHOR]

Single-carrier devices are an excellent model system to study charge injection and charge transport properties of (doped) transport layers and to draw conclusions about organic electronics devices in which they are used. By combining steady-state and impedance measurements at varying temperatures of hole-only devices with different intrinsic layer thicknesses, we are able to determine all relevant material parameters, such as the charge mobility and the injection barrier. Furthermore, the correlation and sensitivity analyses reveal that the proposed approach to study these devices is especially well suited to extract the effective doping density, a parameter which cannot be easily determined otherwise. The effective doping density is crucial in organic light-emitting diodes (OLEDs) for realizing efficient injection, charge balance, and lateral conductivity in display or lighting applications. With the fitted drift-diffusion device model, we are further able to explain the extraordinary two-plateau capacitance–frequency curve of these hole-only devices, which originates from charges that flow into the intrinsic layer at zero applied offset voltage. We demonstrate that the observation of this behaviour is a direct indication for ideal charge injection properties and the observed capacitance–frequency feature is linked to the charge carrier mobility in the intrinsic layer. The extracted material parameters may directly be used to simulate and optimize full OLED devices employing the investigated hole-injection and -transport materials. [ABSTRACT FROM AUTHOR]

The degradation behavior of ultraviolet-B light emitting diodes (UV-B LEDs) emitting near 310 nm has been investigated and a method to localize the degradation effects is presented. Measurements of the electro-optical characteristics of UV-B LEDs, during a 200 h constant-current degradation study, showed an initial fast decrease in the optical power accompanied by a decrease in the drive voltage and an increase in the capacitance. Furthermore, by using a specially designed contact geometry, it was possible to separate the degradation of the electrical properties of the p-layers and p-contacts from the degradation of the active region and n-side of the LED heterostructure. Our investigations show that the initial changes in capacitance and voltage can be attributed to changes in the p-side and at the p-contact of the LED, which can be explained by an activation of Mg dopants. [ABSTRACT FROM AUTHOR]

Cd-based quantum dot light-emitting diodes (QLEDs) have outstanding optical properties, which are promising for a wide range of applications in the fields of lighting and display. However, it is still a research hotspot to prepare high-quality quantum dots (QDs) which can satisfy the requirements of preparing high-performance devices. Here, we develop a facile method to prepare high-quality alloyed CdSeS/CdS/ZnS QDs with a single precursor material, and the as-prepared alloyed QDs have high luminous intensity and narrow size distribution. The alloyed QDs have a uniform and gradient internal structure, there is no abrupt boundary in the final alloyed QDs. This is beneficial to reducing the carrier injection barrier and improving the carrier injection efficiency of electroluminescent devices. The alloyed gradient core/shell QDs-based green QLEDs were fabricated successfully and maximum current efficiency of 33.7 cd/A was obtained. This paper will provide a new strategy to prepare high-performance QLED devices. [ABSTRACT FROM AUTHOR]

New derivatives of carbazole and diphenyl imidazole for potential multiple applications were synthesized and investigated. Their properties were studied by thermal, optical, photophysical, electrochemical, and photoelectrical measurements. The compounds exhibited relatively narrow blue light-emission bands, which is favorable for deep-blue electroluminescent devices. The synthesized derivatives of imidazole and carbazole were tested as fluorescent emitters for OLEDs. The device showed deep-blue emissions with CIE color coordinates of (0.16, 0.08) and maximum quantum efficiency of 1.1%. The compounds demonstrated high triplet energy values above 3.0 eV and hole drift mobility exceeding 10−4 cm2/V·s at high electric fields. One of the compounds having two diphenyl imidazole moieties and tert-butyl-substituted carbazolyl groups showed bipolar charge transport with electron drift mobility reaching 10−4 cm2/V·s at electric field of 8 × 105 V/cm. The synthesized compounds were investigated as hosts for green, red and sky-blue phosphorescent OLEDs. The green-, red- and sky-blue-emitting devices demonstrated maximum quantum efficiencies of 8.3%, 6.4% and 7.6%, respectively. [ABSTRACT FROM AUTHOR]

Coinage metal nanoclusters (MNCs) are a new type of ultra-small nanoparticles on the sub-nanometer (typically < three nm) scale intermediate between atoms and plasmonic nanoparticles. At the same time, the ultra-small size and discrete energy levels of MNCs enable them to exhibit molecular-like energy gaps, and the total structure involving the metal core and surface ligand together leads to their unique properties. As a novel environmentally friendly chromophore, MNCs are promising candidates for the construction of electroluminescent light-emitting diodes (LEDs). However, a systematic summary is urgently needed to correlate the properties of MNCs with their influences on electroluminescent LED applications, describe the synthetic strategies of highly luminescent MNCs for LEDs' construction, and discuss the general influencing factors of MNC-based electroluminescent LEDs. In this review, we first discuss relevant photoemissions of MNCs that may have major influences on the performance of MNC-based electroluminescent LEDs, and then demonstrate the main synthetic strategies of highly luminescent MNCs. To this end, we illustrate the recent development of electroluminescent LEDs based on MNCs and present our perspectives on the opportunities and challenges, which may shed light on the design of MNC-based electroluminescent LEDs in the near future. [ABSTRACT FROM AUTHOR]

Constructing organic near‐infrared (NIR) luminescent materials to confront the formidable barrier of "energy gap law" remains challenging. Herein, two NIR thermally activated delayed fluorescence (TADF) molecules named T‐β‐IQD and TIQD were developed by connecting N,N‐diphenylnaphthalen‐2‐amine and triphenylamine with a novel electron withdrawing unit 6‐(4‐(tert‐butyl)phenyl)‐6H‐indolo[2,3‐b]quinoxaline‐2,3‐dicarbonitrile. It is confirmed NIR‐TADF emitters concurrent with aggregation‐induced emission effect, J‐aggregate with intra‐ and intermolecular CN⋅⋅⋅H−C and C−H⋅⋅⋅π interactions, and large center‐to‐center distance in solid states can boost the emissive efficiencies both in thin films and non‐doped organic light‐emitting diodes (OLEDs). Consequently, the T‐β‐IQD‐based non‐doped NIR‐OLED achieved the maximum external quantum efficiency (EQEmax) of 9.44 % with emission peak at 711 nm, which is one of the highest efficiencies reported to date for non‐doped NIR‐OLEDs. [ABSTRACT FROM AUTHOR]

Perovskite light‐emitting diodes (PeLEDs) have attracted much attentions due to the superior optoelectronic properties such as pure spectrum, high photoluminescence quantum yield, tunable emission, and ease of fabrication. Though lots of progresses have been made on PeLEDs and optically pumped lasers, microcavity perovskite lasing device under electrical pumping remains extremely challenging. Microcavity perovskite LEDs can be considered as a step toward laser diode due to the common structure of resonant cavity. In this study, a new type of metal‐dielectric microcavity PeLED is designed and fabricated by using 2.5 pairs of TiO2/SiO2 distributed bragg reflector (DBR) and Al as cavity coplanar mirrors. A microcavity device with forward spectral full‐width at half‐maximum of 11.8 and 9.5 nm, under electrical and optical excitations, respectively, the directional forward emission within 30° is enhanced by 3 times compared to the control device without cavity is realized. To the best of the knowledge, this study demonstrates the narrowest spectrum for three‐demisional PeLEDs so far, it helps to expand the color space in display applications and may also serve as a reference device for solution processed perovskite exciton–polariton electroluminescent devices and electrically driven vertical cavity surface emitting lasers due to the similar device structure and processing. [ABSTRACT FROM AUTHOR]

By adopting atomic layer deposition (ALD) sidewall passivation, the electroluminescence (EL) and communication performances of mini-light emitting diodes (mini-LEDs) of different sizes were improved. In particular, the most significant improvement in the electroluminescence properties of the external quantum efficiency (EQE) (a 7.2% increase), leakage current, and the communication properties of the modulation bandwidth (a 20% increase) transmission rate and bit error rate (BER) was found in the smallest mini-LEDs (80 $\mu \text{m}\,\,\times $ 120 $\mu \text{m}$). According to the results of time-resolved photoluminescence (TRPL) measurements, the carrier lifetime of the samples can be affected by both the size and ALD sidewall passivation. In addition, the effects of ALD sidewall passivation for visible-light communication (VLC) were demonstrated. [ABSTRACT FROM AUTHOR]

New solution-processable chrysene-basked deep-blue fluorescent dendrimers consisting of chrysene as a core end-capped by carbazole dendrons were designed, synthesized, and characterized. These dendrimers exhibit strong deep-blue emissions in solution or thin-film states with decent hole mobility and high thermal and electrochemical stability. They can be effectively used as nondoped emitters in organic light-emitting diodes (OLEDs). The nondoped OLEDs, which have a simple structure, showed good electroluminescence (EL) performance (luminance: 2334–2400 cd m–2 ; external quantum efficiency: 1.88-2.51%; turn-on voltage: 3.8–4.0 V) and deep-blue EL spectra (CIE y : 0.065–0.075) with a narrow full width at half maximum of 61–65 nm. [ABSTRACT FROM AUTHOR]

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In state-of-the-art blue phosphorescent organic light-emitting diode (PHOLED) device architectures, electrons and holes are injected into the emissive layer, where they are carried by the emitting and hole transporting units, respectively. Using transient electroluminescence measurements, we disentangle the contribution of the electrons and holes on the transport and efficiency of both pristine and degraded PHOLEDs. By varying the concentration of hole transporting units, we show that for pristine PHOLEDs, the transport is electron dominated. Furthermore, degradation of the PHOLEDs upon electrical aging is not related to the hole transport but is governed by a decrease in the electron transport due to the formation of electron traps. [ABSTRACT FROM AUTHOR]

The authors present Ag nanocluster-based color converters (Ag NC color converters), which convert part of the blue light from a light source to yellow light so as to create white organic light-emitting devices that could be suitable for lighting systems. Ag NCs synthesized by poly(methacrylic acid) template methods have a statistical size distribution with a mean diameter of around 4.5?nm, which is larger than the Fermi wavelength of around 2?nm. Hence, like free electrons in metals, the Ag NC electrons are thought to form a continuous energy band, leading to the formation of surface plasmons by photoexcitation. As for the fluorescence emission mechanism, the fact that the photoluminescence is excitation wavelength dependent suggests that the fluorescence originates from surface plasmons in Ag NCs of different sizes. By using Ag NC color converters and suitable blue light sources, white organic light-emitting devices can be fabricated based on the concept of light-mixing. For our blue light sources, we used polymer light-emitting electrochemical cells (PLECs), which, like organic light-emitting diodes, are area light sources. The PLECs were fabricated with a blue fluorescent π-conjugated polymer, poly[(9,9-dihexylfluoren-2,7-diyl)-co-(anthracen-9,10-diyl)] (PDHFA), and a polymeric solid electrolyte composed of poly(ethylene oxide) and KCF3SO3. In this device structure, the Ag NC color converter absorbs blue light from the PDHFA-based PLEC (PDHFA-PLEC) and then emits yellow light. When the PDHFA-PLEC is turned on by applying an external voltage, pure white light emission can be produced with Commission Internationale de l'Eclairage coordinates of (x?=?0.32, y?=?0.33) and a color rendering index of 93.6. This study shows that utilization of Ag NC color converters and blue PLECs is a very promising and highly effective method for realizing white organic light-emitting devices. [ABSTRACT FROM AUTHOR]

We present a cryogenic wafer mapper based on light emitting diodes (LEDs) for spatial mapping of a large microwave kinetic inductance detector (MKID) array. In this scheme, an array of LEDs, addressed by DC wires and collimated through horns onto the detectors, is mounted in front of the detector wafer. By illuminating each LED individually and sweeping the frequency response of all the resonators, we can unambiguously correspond a detector pixel to its measured resonance frequency. We have demonstrated mapping a 76.2mm 90-pixel MKID array using a mapper containing 126 LEDs with 16 DC bias wires. With the frequency to pixel-position correspondence data obtained by the LED mapper, we have found a radially position-dependent frequency nonuniformity of ≾1:6% over the 76.2mm wafer. Our LED wafer mapper has no moving parts and is easy to implement. It may find broad applications in superconducting detectors and quantum computing/information experiments. [ABSTRACT FROM AUTHOR]

Here, we present the concept of combining excited-state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) features into a single molecule as a strategy to generate high-performance ESIPT-based non-doped organic light-emitting diodes (OLEDs). Two ESIPT-AIE-type green fluorophores, TBzHPI and TBzHI , are meticulously designed and synthesized by incorporating a conventional AIE moiety of triphenylethylene (TPE) with specific ESIPT cores of 2-(benzo[d]thiazol-2-yl)-6-(1-phenyl-1H-phenanthro [9,10-d]imidazole-2-yl)phenol (BzHPI) and 2-(benzo[d]thiazol-2-yl)-6-(1,4,5-triphenyl-1H-imidazole-2-yl)phenol (BzHI), respectively. The ESIPT and AIE properties are thoroughly validated through both theoretical calculations and experimental investigations. Both TBzHPI and TBzHI exhibit large Stokes shifted emissions (135–146 nm) and strong green emission of the pure keto form in the solid state owing to the collective effects of ESIPT and AIE properties in molecules. Their uses as non-doped emitters in OLEDs have been accomplished, with all devices showing strong keto-form emissions and low turn-on voltages of 2.8 V. Particularly, TBzHPI -based device demonstrates a remarkably high luminance of 54,825 cd m2, a current efficiency (CE) of 18.42 cd A−1, and an external quantum efficiency (EQE) of 5.76 %, with only a slight decrease in efficiency. This finding is significant as it represents the highest EQE reported so far for ESIPT molecules used as non-doped emitters in fluorescent OLEDs. [Display omitted] • Fluorophores with synergic excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) features. • The materials exhibit strong green emission of the pure keto form in the solid state large with high photoluminescence quantum yields. • They are effectively utilized as non-doped emitters in OLEDs. • The OLEDs present stable green electroluminescent emission with high current efficiency of 18.42 cd A−1 and external quantum of 5.76 %. [ABSTRACT FROM AUTHOR]

The pervasive use of zinc oxide (ZnO) as an electron transport layer in quantum dot (QD) electroluminescent devices is constrained due to its chemical instability with the QD layer and the formation of interface quenching sites. The effect of fluorine passivation of sol-gel processed ZnO in QD light-emitting devices (QLEDs) is investigated in depth. An examination of the interaction between the ZnO surface and fluorine species revealed that the passivation of oxygen vacancies and the formation of stable hydrogen bonds with hydroxyl groups on ZnO surface have a significant influence on the stability and efficiency of the device. Such exceptional functions of fluorine have been found to effectively capture defects at the interface between ZnO and the emissive layer, therefore mitigating the interface quenching sites. The initial fluorination device demonstrated a significant improvement in external quantum efficiency (EQE) from 5.72 % to 20.07 %, and half of the device lifetime (LT50 at an initial luminance of 1500 cd m−2) was 286 h. Further passivating the remaining active oxygen on the ZnO surface can extend the stability of the device to 542 h with an EQE of 15.2 %, which is among the longest lifetime reported so far for green InP-QLEDs. Our report offers the possibility of utilizing straightforward and highly effective fluorination by spin-coating technique to attain long-lasting InP-QLED devices with remarkable performance. [Display omitted] • Fluorine passivated ZnO was created via the solution spin-coating method by using an NH 4 F solution. • The chemical and thermodynamic stability of ZnO is enhanced through the fluorine alteration on the surface of ZnO. • By optimizing fluorine passivation conditions, a maximum of 2.7 and 11 times improvement in EQE and device stability are achieved respectively. [ABSTRACT FROM AUTHOR]

Aromatic imide derivatives play a critical role in boosting the electroluminescent (EL) performance of organic light-emitting diodes (OLEDs). However, the majority of aromatic imide-based materials are limited to long wavelength emission OLEDs rather than blue emissions due to their strong electron-withdrawing characteristics. Herein, two novel polycyclic fused amide units were reported as electron acceptor to be combined with either a tetramethylcarbazole or acridine donor via a phenyl linker to generate four conventional fluorescence blue emitters of BBI-4MeCz, BBI-DMAC, BSQ-4MeCz and BSQ-DMAC for the first time. BSQ-4MeCz and BSQ-DMAC based on a BSQ unit exhibited higher thermal stability and photoluminescence quantum yields than BBI-4MeCz and BBI-DMAC based on a BBI unit due to their more planar acceptor structure. The intermolecular interactions that exist in the BSQ series materials effectively inhibit the molecular rotation and configuration relaxation, and thus allow for blue-shifted emissions. Blue OLED devices were constructed with the developed materials as emitters, and the effects of both the structure of the polycyclic fused amide acceptor and the electron donor on the EL performance were clarified. Consequently, a sky-blue OLED device based on BSQ-DMAC was created, with a high maximum external quantum efficiency of 4.94% and a maximum luminance of 7761 cd m−2. [ABSTRACT FROM AUTHOR]

Herein, three hydroxy‐tetraphenylimidazole (HPI)‐based fluorophores (HPI‐TPA, HPI‐PCz, and HPI‐CzP) are designed and synthesized by disubstituted HPI core with arylamine units of triphenylamine (TPA), phenyl carbazole (PCz), and carbazole phenyl (CzP) at 3,5‐positions of the N‐phenyl ring of HPI, respectively. Their photophysical properties are theoretically and experimentally examined. HPI‐TPA shows a hybridized local and charge transfer (HLCT) excited state characteristic and emits deep blue color via an HLCT mechanism, while both HPI‐PCz and HPI‐CzP exhibit excited‐state intramolecular proton transfer (ESIPT) property and display pure keto form emissions. They possess high thermal stability and are successfully fabricated as emitters in organic light‐emitting diodes (OLEDs). All devices exhibit intense blue color emissions with low turn‐on voltages (3.5–3.7 V). Particularly, HPI‐TPA‐based OLED emits light in the deep‐blue region with a high maximum external quantum efficiency (EQEmax) of 3.77% and a decent efficiency roll‐off. [ABSTRACT FROM AUTHOR]

Herein, the authors report on charge‐transfer (CT) complex emission‐based organic light‐emitting diodes (OLEDs), which emit light by electric field‐induced intermolecular CT complex formation in the light‐emitting layer. Two phosphorescent materials are chosen to have energy level offset for the CT complex formation. This process generates the CT complex, which efficiently emits only in the electroluminescent device by electric‐field‐induced complex formation. A phenylpyridine‐ligand‐based Ir compound and phenylimidazole‐based Ir compounds are selected as the CT complex‐forming materials, and the CT complex exhibits yellow emission under an electric field. Moreover, the doping of the two compounds in the host material produces white OLEDs, exhibiting both blue emission and yellow emission at a quantum efficiency of 13.7%. In particular, the color of the CT complex device can be tuned by the content of each material in the emitting layer. As an initial result, the quantum efficiency is acceptable, and further material development would enhance the quantum efficiency of the CT complex OLEDs. This light‐emitting device can be used in various applications, e.g., a mono‐color or a white‐color light‐emitting diode. [ABSTRACT FROM AUTHOR]

Effective protection against photooxidation of organic wide‐bandgap semiconductors is a potential method to afford high efficient deep‐blue emission for full color displays. Herein, the crystallization effect of fluorene‐based blue emitter on suppressing the formation of long‐wavelength green band (g‐band) defect is demonstrated through the model of self‐assembled organic micro/nanocrystals. The selected molecule 2,2'‐bi(9,9‐dipropyl)fluorene (DDC3F), which easily generates strong g‐band emission (green index (Igreen/Iblue) of ≈5 under ultraviolet exposure for 3 h) in amorphous state, shows an excellent spectra stability of deep‐blue emission with a green index of ≈0 and an unchangeable CIE coordination of (0.18, 0.09) in crystalline nanorod morphologies. Such effect of crystallization‐induced stability enhancement can be further extended into other solution‐processing methods such as brushing. Molecular dynamic simulation reveals that crystalline nanorods with compact molecular packing enable to effectively block the diffusion of O2 and H2O molecules, which is crucial to suppress the occurrence of photooxidation reactions. Along with high quantum yield of 87% from crystallization‐induced luminescence enhancement effect, such ultrastable deep‐blue emission on crystalline film can also be maintained in solution‐processing organic light‐emitting diode devices. The supramolecular self‐assembled micro/nanocrystals strategy provides a potential platform to maintain ultrastable color purity in organic optoelectronic devices. [ABSTRACT FROM AUTHOR]

Herein, an inexpensive and efficient device structure using copper phthalocyanine (CuPc) as a dopant into tris-(8-hydroxyquinoline) aluminum (Alq3) is introduced for near-infrared (NIR) organic light-emitting diodes (OLEDs). An optimized green OLED was first fabricated, and then the device's electroluminescent performance was compared with its simulation results gained via the APSYS (Advanced Physical Model of Semiconductor Devices) method. After confirming the simulation results, the emission spectra and external quantum efficiency (EQE) were investigated for OLEDs doped with different concentrations of CuPc using the APSYS program. Electroluminescence was observed near 1.1 µm, following the transitions from CuPc's low-lying triplet state (T1) to its ground state (S0). A further optimized NIR OLED with 2 wt% CuPc demonstrated superior performance to other structures via the efficient energy transfer from the host excited states to the NIR phosphors, realizing a maximum EQE value of 0.11%, and radiance of 316 μW/cm2. [ABSTRACT FROM AUTHOR]

A semipolar GaInN based light-emitting diode (LED) sample is investigated by three-dimensionally resolved cathodoluminescence (CL) mapping. Similar to conventional depth-resolved CL spectroscopy (DRCLS), the spatial resolution perpendicular to the sample surface is obtained by calibration of the CL data with Monte-Carlo-simulations (MCSs) of the primary electron beam scattering. In addition to conventional MCSs, we take into account semiconductor-specific processes like exciton diffusion and the influence of the band gap energy. With this method, the structure of the LED sample under investigation can be analyzed without additional sample preparation, like cleaving of cross sections. The measurement yields the thickness of the p-type GaN layer, the vertical position of the quantum wells, and a defect analysis of the underlying n-type GaN, including the determination of the free charge carrier density. The layer arrangement reconstructed from the DRCLS data is in good agreement with the nominal parameters defined by the growth conditions. [ABSTRACT FROM AUTHOR]

Temperature-dependent characteristics of GeSn light-emitting diodes with Sn composition up to 9.2% have been systematically studied. Such diodes were based on Ge/GeSn/Ge double heterostructures (DHS) that were grown directly on a Si substrate via a chemical vapor deposition system. Both photoluminescence and electroluminescence spectra have been characterized at temperatures from 300 to 77K. Based on our theoretical calculation, all GeSn alloys in this study are indirect bandgap materials. However, due to the small energy separation between direct and indirect bandgap, and the fact that radiative recombination rate greater than non-radiative, the emissions are mainly from the direct Γ-valley to valence band transitions. The electroluminescence emissions under current injection levels from 102 to 357 A/cm2 were investigated at 300 K. The monotonic increase of the integrated electroluminescence intensity was observed for each sample. Moreover, the electronic band structures of the DHS were discussed. Despite the indirect GeSn bandgap owing to the compressive strain, type-I band alignment was achieved with the barrier heights ranging from 11 to 47 meV. [ABSTRACT FROM AUTHOR]

This research paper discusses an analytical approach to designing the active region of light emitting diodes to enhance its performance. The layers in the active region were modified and the effects of changing the width of quantum well and barrier layers in a multiquantum light emitting diode on the output power and efficiency have been investigated. Also, the ratio of the quantum well width to the B layer width was calculated and proposed in this research paper. The study is carried out on two different LED structures. In the first case, the width of the quantum well layers is kept constant while the width of the B layers is varied. In the second case, both the quantum well and B layer widths are varied. Based on the simulation results, it has been observed that the LED power efficiency increases considerably for a given quantum well to B layers width ratio without increasing the production complexity. It is also seen that for a desired power efficiency the width of quantum well should be between 0.003 µm and 0.006 µm, and the range of B width (height) should be 2.2 to 6 times the quantum well width. The proposed study is carried out on the GaN-AlGaN-based multi-quantum well LED structure, but this study can be extended to multiple combinations of the semiconductor structures. [ABSTRACT FROM AUTHOR]

The effects of the heterostructure design on the injection efficiency and external quantum efficiency of ultraviolet (UV)-B light emitting diodes (LEDs) have been investigated. It was found that the functionality of the Alx Ga1-x N:Mg electron blocking layer is strongly influenced by its aluminum mole fraction x and its magnesium doping profile. By comparing LED electroluminescence, quantum well photoluminescence, and simulations of LED heterostructure, we were able to differentiate the contributions of injection efficiency and internal quantum efficiency to the external quantum efficiency of UV LEDs. For the optimized heterostructure using an Al0.7Ga0.3N:Mg electron blocking layer with a Mg to group III ratio of 4% in the gas phase the electron leakage currents are suppressed without blocking the injection of holes into the multiple quantum well active region. Flip chip mounted LED chips have been processed achieving a maximum output power of 3.5 mW at 290 mA and a peak external quantum efficiency of 0.54% at 30 mA. [ABSTRACT FROM AUTHOR]