Electroluminescent Devices Research Articles

Electrically chargeable inorganic persistent luminescence in an alternating current driven electroluminescent device

Persistent luminescence (PersL) in inorganic materials, lasting from seconds to even days, has attracted considerable attention. Despite the promise of electric power-driven PersL for lighting and display device applications due to its convenience and manageability, studies on electrically driven inorganic PersL are lacking. Here, we report an inorganic PersL in electroluminescent devices, which shows an energy storage effect that persists beyond 24 h after charging with an alternating current electric field at 250 K. The spin-coating method-prepared emission layer composites consist of a small bandgap copper-doped zinc sulfide core, a high dielectric constant alumina shell and a chemically passivated dielectric polydimethylsiloxane medium (ZnS:Cu@AlOx@PDMS), and these composites exhibit well-distributed electric fields and excellent operational stability. Thermoluminescence characterization reveal that PersL with an ~ 0.3 eV trap depth in electroluminescent devices mainly arises from the charge separation via hot-electron impact excitation and charge trapping within trap states in the emission layer. This study on electrically chargeable PersL in alternating current-driven electroluminescent devices can enhance our understanding of luminescence mechanisms in inorganic semiconductors.

Cyano‐Modified Multi‐Resonance Thermally Activated Delayed Fluorescent Emitters Towards Pure‐Green OLEDs with a CIEy Value of 0.74

AbstractThe development of pure‐green organic emitters with ideal emission peaks and ultra‐narrow full‐widths at half‐maximum (FWHMs) remains a formidable challenge. Herein, we report two new green emitters, CNBN and MCNBN, which achieve extremely narrow FWHMs by synergistic rigid π‐extension and cyano‐substitution of a sky‐blue multi‐resonance thermally activated delayed fluorescence (MR‐TADF) core. The introduction of cyano groups induces red‐shifts in the emission to the green region and dramatically minimizes the FWHMs. In toluene solution, CNBN and MCNBN exhibit narrowband emission with a maximum at 501 nm and 510 nm with ultra‐narrow FWHMs of 14 nm/0.066 eV and 15 nm/0.071 eV, respectively. Given the near‐unity photoluminescence quantum yields and almost 100 % horizontal dipole orientation, the electroluminescent (EL) devices based on CNBN and MCNBN deliver external quantum efficiencies (EQEs) exceeding 30 % with FWHMs of 16 nm/0.072 eV and 17 nm/0.080 eV, respectively. Notably, the MCNBN‐based device achieves pure‐green emission with a maximum at 517 nm with Commission Internationale de l’Éclairage coordinates of (0.17, 0.74), closely aligning with the BT.2020 green standard.

Cyano-Modified Multi-Resonance Thermally Activated Delayed Fluorescent Emitters Towards Pure-Green OLEDs with a CIEy Value of 0.74.

The development of pure-green organic emitters with ideal emission peaks and ultra-narrow full-widths at half-maximum (FWHMs) remains a formidable challenge. Herein, we report two new green emitters, CNBN and MCNBN, which achieve extremely narrow FWHMs by synergistic rigid π-extension and cyano-substitution of a sky-blue multi-resonance thermally activated delayed fluorescence (MR-TADF) core. The introduction of cyano groups induces red-shifts in the emission to the green region and dramatically minimizes the FWHMs. In toluene solution, CNBN and MCNBN exhibit narrowband emission with a maximum at 501 nm and 510 nm with ultra-narrow FWHMs of 14 nm/0.066 eV and 15 nm/0.071 eV, respectively. Given the near-unity photoluminescence quantum yields and almost 100 % horizontal dipole orientation, the electroluminescent (EL) devices based on CNBN and MCNBN deliver external quantum efficiencies (EQEs) exceeding 30 % with FWHMs of 16 nm/0.072 eV and 17 nm/0.080 eV, respectively. Notably, the MCNBN-based device achieves pure-green emission with a maximum at 517 nm with Commission Internationale de l'Éclairage coordinates of (0.17, 0.74), closely aligning with the BT.2020 green standard.

Blue Electroluminescent Carbon Dots Derived from Victorian Lignite.

Carbon dots (CDs) derived from natural products have attracted considerable interest as eco-friendly materials with a wide range of applications, such as bioimaging, sensors, catalysis, and solar energy harvesting. Among these applications, electroluminescence (EL) is particularly desirable for light-emitting devices in display and lighting technologies. Typically, EL devices incorporating CDs feature a layered structure, where CDs function as the central emissive layer, flanked by charge transport layers and electrodes. Under an applied external bias, electrons and holes are introduced into the active CD layer, resulting in EL through radiative recombination. However, achieving EL with natural product-derived CDs has remained elusive due to challenges such as production difficulties and quenching in the solid state. In this study, we present, for the first time, the successful realization of EL from natural product-derived CDs, synthesized using Victorian lignite through a straightforward single-step pyrolysis method. The CDs demonstrated excellent dispersibility in solvents, allowing them to serve as an emissive layer in light-emitting diodes (LEDs). This was achieved by spin-coating a concentrated CD solution between the organic hole and electron transport layers on a glass substrate coated with indium tin oxide. Remarkably, the CDs retained their dispersibility and emissive efficiency both in solution (toluene) and after film formation. Moreover, the resulting LED demonstrated blue EL, characterized by a peak emission at 460 nm and a maximum luminance of 100.4 cd/m2. This luminance is comparable to that achieved with CDs synthesized from conventional chemical carbon sources. These results highlight the promise of natural product-derived CDs as sustainable and eco-friendly materials for use in LED applications.

New highly efficient phosphorescent manganese halides as green and blue emitters.

Three new manganese compounds on 5-(pyridin-2-yl)-3-phenyl-1,2,4-triazole (L) basis (HL)4[MnBr4]2·H2O (1), (HL)2[MnCl4] (2) and [MnL2Cl2]·H2O (3) have been synthesized and characterized in terms of their structure, photoluminescence (PL), and electroluminescence (EL) properties. Compounds 1 and 2 exhibit bright green luminescence (λem ≈ 550 nm) with high quantum yields of 75.1 and 71.2%, and 3 emits unusual blue emission at 438 nm with a quantum yield of 43.9%. Analysis of the spectral properties of complexes 1 and 2 indicates that luminescence is determined by the transfer of excitation energy from the triazole cation to the manganese cation. Electroluminescent devices based on complexes 1 and 3 show high brightness values of 3033 and 5230 Cd m-2, respectively.

Coplanar Pattern and Temperature Transient Control in Intelligent Wearable Multi‐Color Alternating Current Electroluminescence Devices

AbstractFlexible alternating current electroluminescence (ACEL) devices integrated into textiles are gaining significant attention for their potential in lighting displays and health monitoring applications. Traditional challenges include high‐voltage “breakdown” and limited color output due to the inherent properties of ZnS:Cu. This study introduces a novel multi‐color ACEL device featuring a fluorescent dye color conversion layer alongside a robust protective layer designed to enhance device stability. The optimal ratio of dielectric layer concentration and protective layer thickness is systematically investigated to mitigate the risk of “breakdown”. Utilizing the principles of photoluminescence and electroluminescence, luminous electronic textile devices is successfully developed that exhibit both purple and green luminescence. Additionally, integration with a temperature sensor enables the device to serve as a health‐monitoring tool by signaling changes in body temperature. This research delineates the protective capabilities of the protective layer and the efficacy of the color conversion mechanism in maintaining consistent brightness under various conditions. The findings suggest a viable pathway for broadening applications and potentially accelerating the commercialization of wearable electroluminescent technologies.

Position Optimization of Bulky Tetraphenylsilane in Multiple Resonance Molecules for Highly Efficient Narrowband OLEDs.

Multiple resonance (MR)-type thermally activated delayed fluorescence (TADF) emitters have garnered significant interest due to their narrow full width at half maximum (FWHM) and high electroluminescence efficiency. However, the planar structures and large singlet-triplet energy gaps (ΔESTs) characteristic of MR-TADF molecules pose challenges to achieving high-performance devices. Herein, two isomeric compounds, p-TPS-BN and m-TPS-BN, are synthesized differing in the connection modes between a bulky tetraphenylsilane (TPS) group and an MR core. This strategy aims to suppress intermolecular interactions, reduce ΔEST values, and investigate how connection positions influence photoelectric properties. Both compounds exhibit remarkably small ΔEST values (0.08-0.09eV) and high internal quantum yields (95.0-97.8%). Notably, p-TPS-BN demonstrates a faster reverse intersystem crossing (RISC) with a rate constant of 2.54×10⁵s⁻¹, attributed to its optimal long-range charge transfer (LRCT) process. A narrowband device employing p-TPS-BN achieves a maximum external quantum efficiency of 35.8% with an FWHM of 36nm. This work offers an effective framework for studying structure-property relationships in MR molecules, paving the way for the development of high-efficiency electroluminescent devices.

High Mobility Emissive Organic Semiconductors for Optoelectronic Devices.

High mobility emissive organic semiconductors (HMEOSCs) are a kind of unique semiconducting material that simultaneously integrates high charge carrier mobility and strong emission features, which are not only crucial for overcoming the performance bottlenecks of current organic optoelectronic devices but also important for constructing high-density integrated devices/circuits for potential smart display technologies and electrically pumped organic lasers. However, the development of HMEOSCs is facing great challenges due to the mutually exclusive requirements of molecular structures and packing modes between high charge carrier mobility and strong solid-state emission. Encouragingly, considerable advances on HMEOSCs have been made with continuous efforts, and the successful integration of these two properties within individual organic semiconductors currently presents a promising research direction in organic electronics. Representative progress, including the molecular design of HMEOSCs, and the exploration of their applications in photoelectric conversion devices and electroluminescent devices, especially organic photovoltaic cells, organic light-emitting diodes, and organic light-emitting transistors, are summarized in a timely manner. The current challenges of developing HMEOSCs and their potential applications in other related devices including electrically pumped organic lasers, spin organic light-emitting transistors are also discussed. We hope that this perspective will boost the rapid development of HMEOSCs with a new mechanism understanding and their wide applications in different fields entering a new stage.

Low‐Dimensional Lead‐Free Metal Halides for Efficient Electrically Driven Light‐Emitting Diodes

AbstractElectrically driven light‐emitting diodes (ED LEDs) based on 3D metal halide perovskites have seen remarkable advancements during the past decade. However, the highest‐performing devices are largely based on lead‐containing 3D perovskites, presenting two key challenges – toxicity and stability – that must be addressed for commercialization. Reducing structural dimensionality and incorporating non‐lead metals present promising pathways to address these issues. Although research on ED LEDs based on low‐dimensional, lead‐free metal halides (LD LFMHs) is growing, their performance still significantly lags behind that of 3D lead halide perovskites. This review seeks to deliver a comprehensive overview of ED LEDs based on LD LFMHs, covering a brief history of their development, methods for material synthesis, luminescence mechanisms, and applications in electroluminescent devices. It also examines current challenges and proposes practical strategies to enhance device performance, with the goal of inspiring further progress in the field.

Sym- and Asym-Expanded Heterohelicene Isomers Featuring Extended Multi-Resonance Skeleton for Narrowband Deep-Blue Fluorescence.

Expanded heterohelicenes composed of alternating linearly and angularly fused multi-resonance (MR) skeletons have gained wide interest owing to their promising narrowband emissions. Herein, a pair of sym- and asym-expanded heterohelicene isomers was obtained by merging boron/oxygen (B/O)-embedded MR triangulene and indolo[3,2,1-jk]carbazole units via one-pot synthesis. Owing to their fully resonating extended helical skeleton, the target heterohelicenes exhibit a significantly narrowed spectra bandwidth while emission red-shifting, thus affording deep-blue narrowband emission with a peak at approximately 460 nm, full-width-at-half-maximum (FWHM) of only 18 nm, and near-unity photoluminescence quantum yields. In comparison to the symmetrical structure, the asym-expanded heterohelicene displays suppressed aggregation within doped films, thereby showing superior narrowband electroluminescence in devices with CIE coordinates of (0.12, 0.18) and a high external quantum efficiency of up to 25 %, which retains 18.1 % even at a high luminance of 10,000 cd m-1. Overall, this work provides a novel paradigm for the development of narrowband expanded heterohelicenes.

Direct Evidence of Excessive Charge-Carrier-Induced Degradation in InP Quantum-Dot Light-Emitting Diodes.

The limited operational lifetime of quantum-dot light-emitting diodes (QLEDs) poses a critical obstacle that must be addressed before their practical application. Specifically, cadmium-free InP-based QLEDs, which are environmentally benign, experience significant operational degradation due to challenges in charge-carrier confinement stemming from the composition of InP quantum dots (QDs). This study investigates the operational degradation of InP QLEDs and provides direct evidence of the degradation process. To facilitate degradation studies, a double-emission structure was designed. We employed transient electroluminescence and photoluminescence for nondestructive analysis of charge-carrier dynamics during device degradation. The time-resolved emission sequence revealed changes in carrier mobility within the QD layer as devices degraded. Furthermore, prolonged exposure of QDs to the charge-carrier population hindered their radiative recombination. Our observations indicate clear evidence of QLED degradation, characterized by ligand detachment from the QD surface and deterioration of the hole-transporting material due to excessive electrons. This comprehensive analysis of degradation mechanisms in InP QLEDs lays the groundwork for improving operational stability and longevity, serving as a benchmark for future research and development in the field of nanocrystal-based electroluminescent devices.

The degradation mechanism of multi-resonance thermally activated delayed fluorescence materials

1,4-Azaborine-based arenes are promising electroluminescent emitters with thermally activated delayed fluorescence (TADF), offering narrow emission spectra and high quantum yields due to a multi-resonance (MR) effect. However, their practical application is constrained by their limited operational stability. This study investigates the degradation mechanism of MR-TADF molecules. Electroluminescent devices incorporating these compounds display varied operational lifetimes, uncorrelated with excitonic stability or external quantum efficiency roll-off. Bulk electrolysis reveals significant instability in the radical cationic forms of MR-TADF compounds, with device lifetime linked to the Faradaic yield of oxidation. Comprehensive chemical analyses corroborate that the degradation byproducts originated from intramolecular cyclization of radical cation, followed by hydrogen atom transfer. The mechanism is further supported by enhanced stability observed in a deuterated MR-TADF emitter, attributed to a secondary kinetic isotope effect. These findings provide insights into the stabilizing effects of deuteration and mechanism-driven strategies for designing MR-TADF compounds with improved operational longevity.

Interface Modification by Ga2O3 Atomic Layers within Er-Doped GeO2 Nanofilms for Enhanced Electroluminescence and Operation Stability.

For silicon-based devices using dielectric oxides doped with rare earth ions, their electroluminescence (EL) performance relies on the sufficient carrier injection. In this work, the atomic Ga2O3 layers are inserted within the Er-doped GeO2 nanofilms fabricated by atomic layer deposition (ALD). Both Ga(CH3)3 and Ga(C2H5)3 could realize the ALD growth of Ga2O3 onto the as-deposited GeO2 nanofilm with unaffected deposition rates. The interfacial defects introduced by atomic Ga2O3 layers decrease the threshold voltage while increasing the tolerable injection current of the EL devices; the 1530 nm emissions from the 600 °C-annealed Ga2O3/GeO2:Er nanolaminate devices achieve the optical power density of 16.2 mW/cm2, with the excitation efficiency increased to 12.5%. Moreover, the interface modification by atomic Ga2O3 layers significantly prolongs the operation time of these prototype devices, reaching 5.21 × 104 s for the optimal one. High-temperature annealing above 800 °C results in the decomposition of GeO2 and leaves reticular porous nanofilms. The conduction mode within these amorphous Ga2O3/GeO2:Er nanolaminates conforms to the trap-assisted tunneling mechanism, with the depths of defect states lowered by the interfacial Ga2O3 layers. These Ga2O3/GeO2:Er nanolaminates with improved EL performance demonstrate new potential in the utilization of ALD GeO2 nanofilms in silicon-compatible optoelectronics.

Improving electron injection of organic light-emitting transistors via interface layer design.

Ambipolar transport is crucial for constructing high performance organic light-emitting transistors (OLETs), but the ambipolar feature is usually not exhibited due to ineffective electron injection especially in symmetric device geometry. Herein, we show that electron injection could be greatly enhanced through the judicious design of an organic interface layer of 3,7-di(2-naphthyl)dibenzothiophene S,S-dioxide (DNaDBSO) which shows an interfacial dipole effect upon contact with a metal electrode, especially an Au electrode. When incorporating a DNaDBSO film beneath Au electrodes, the electron injection and mobility were significantly enhanced in 2,6-diphenylanthracene-based OLETs, and thus ambipolar transport (μmaxh: 2.17 cm2 V-1 s-1, μmaxe: 0.053 cm2 V-1 s-1) was effortlessly obtained. Furthermore, the shift of the electroluminescent region was obviously observed upon modulation of gate voltage, which demonstrates efficient electron injection and intrinsic ambipolar transporting properties in devices. This study provides a new avenue for regulating the interface in electroluminescent devices towards high performance simple-structured OLETs in applications.

A linearly polarized AC-driven perovskite light emitting device with nanoscale metal contact.

Electroluminescent (EL) devices consisting of a single metal-semiconductor contact and a gate effect structure have garnered significant attention in the field of perovskite light-emitting devices. This interest is largely due to the thermal stability of the active layer and the simplicity of the device structure. However, the application of these devices in large-area light-emitting applications is hindered by the inherently low carrier mobility in perovskite materials. In our study, we addressed this limitation by optimizing the nanostructure within the electrodes, which resulted in enhanced electroluminescence and linear polarization. To confirm the luminescence mechanism and the observed enhancement, we conducted comprehensive electrical and optical characterization studies. These characterization studies demonstrated the effectiveness of our approach in improving the performance of perovskite-based EL devices, paving the way for their broader application in large-area light-emitting technologies.

Highly polarized single-crystal organic light-emitting devices with low turn-on voltage and high brightness.

Linearly-polarized organic electroluminescent devices have gained significant attention due to their potential applications across various fields. However, traditional thin-film organic light-emitting diodes (OLEDs) face significant challenges, primarily due to the necessity of incorporating complex optical elements. In this study, we present linearly-polarized OLEDs (LP-OLEDs) based on organic single crystals that we have designed and prepared. These devices exhibit a degree of polarization (DOP) of up to 0.96 for photoluminescence and 0.95 for electroluminescence, values that are close to the ideal linearly-polarized light (DOP = 1). The LP-OLEDs demonstrate outstanding performance, with a low turn-on voltage of just 2.5 volts, an exceptionally high brightness of 200 000 cd m-2, and a current density surpassing 300 A cm-2. This is the best overall performance reported for single crystal-based OLEDs to date. These results open the door to the development of next-generation, low-power consumption displays, marking a significant step forward in the field of organic single crystal-based LP-OLEDs.

Luminescence modification of porous silicon decorated with GOQDs synthesized by green chemistry

<p>In this work, the luminescent emission control from porous silicon (PS) decorated with graphene oxide quantum dots (GOQDs) was analyzed. The samples obtained showed a 95 nm range of variation in which the luminescent emission can be controlled. Based on the results obtained from the PS samples decorated with GOQDs, the emission can be selected in a range from blue to red. Fourier transform infrared (FTIR) spectroscopy showed evidence of bond formation between PS and GOQDs. These changes can be related to the changes in luminescent emission. Photoluminescence analysis showed that the main PS emission can be selected in a 90 nm range with the introduction of GOQDs. Scanning electron microscopy (SEM) images and energy dispersive spectroscopy (EDS) spectra demonstrated the introduction of GOQDs in the PS. X-ray diffraction patterns also confirmed the presence of GOQDs on the surface of PS. In this study, different methodologies to control the luminescent emission were applied, and the results show that PS samples decorated with GOQDs showing blue, orange, and red luminescence can be obtained. The samples obtained can be applied to the development of electroluminescence devices, photodetectors, and biosensors.</p>

ILLUMINATION PROPERTIES AND GADGET EFFICIENCY STEADINESS OF WLEDS BASED ON QUANTUM DOTS

The recent improvements in picture quality have led to the need for new methods to create displays that meet more rigorous standards. While the screen market is mainly dominated by liquid crystal display (LCD) and light emitting diode (LED) technology, these technologies have downsides solvable via creating augmented electroluminescent screens. Utilizing sticky quantum dots (QDs) in the form of down transmuters facilitates creating screens featuring highly improved chroma clarity as well as range. As such, sticky nanocrystals prove a promising option when it comes to creating electroluminescent devices, providing a simple way to build high-quality displays. The QDs that emit light featuring significant fluorescent quantum output along with chroma clarity covering the entire visible spectrum, as well as significantly-bright singular-chroma LED apparatuses featuring extrinsic quantum proficiencies reaching 1.30%, 0.39%, 1.04%, and 2.10% respectively in the case of blue, red, orange, and green hues, saw the prospect of development. Additionally, white LEDs were created by combining QDs, achieving a color temperature of 5,300 K and over 80% color rendering index. The LED performance is also extensively evaluated, including color stability, and device efficiency, providing crucial data for the advancement of high-quality electroluminescent displays.

Low-Dimensional Lead-Free Metal Halides for Efficient Electrically Driven Light-Emitting Diodes.

Electrically driven light-emitting diodes (ED LEDs) based on 3D metal halide perovskites have seen remarkable advancements during the past decade. However, the highest-performing devices are largely based on lead-containing 3D perovskites, presenting two key challenges-toxicity and stability-that must be addressed for commercialization. Reducing structural dimensionality and incorporating non-lead metals present promising pathways to address these issues. Although research on ED LEDs based on low-dimensional, lead-free metal halides (LD LFMHs) is growing, their performance still significantly lags behind that of 3D lead halide perovskites. This review seeks to deliver a comprehensive overview of ED LEDs based on LD LFMHs, covering a brief history of their development, methods for material synthesis, luminescence mechanisms, and applications in electroluminescent devices. It also examines current challenges and proposes practical strategies to enhance device performance, with the goal of inspiring further progress in the field.

Tailoring the Interfacial Composition of Heterostructure InP Quantum Dots for Efficient Electroluminescent Devices.

The formation of core-shell quantum dots (QDs) with type-I band alignment results in surface passivation, ensuring the efficient confinement of excitons for light-emitting applications. In such cases, the atomic composition at the core-shell heterojunction significantly affects the optical, and electrical properties of the QDs. However, for InP cores, shell materials are limited to compositions consisting of II-VI group elements. The restricted selection of shell materials leads to an interfacial misfit, resulting in a charge imbalance at the core-shell heterojunction. In this study, the effect of interfacial stoichiometry is investigated on the optical, and electrical properties of InP core-shell QDs. Direct Se injection strategy is employed during the synthesis of the InP core to regulate the interfacial chemical composition, resulting in the formation of an InZnSe alloy on the core surface. This InZnSe layer reduces the misfit between the InP core, and ZnSe shell, leading to a remarkable photoluminescence quantum yield of 95% with a narrow emission bandwidth of 34nm. The InZnSe interlayer significantly influences the electroluminescence (EL) processes, increasing the charge injection efficiency, and mitigating charge imbalance. A green-emitting EL device is demonstrated with a maximum luminance of 26370cd m-2, and a peak current efficiency of 31.5cd A-1.