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Light-emitting diodes (LEDs) have been known as the most widely used light source in lighting and displays for more than 60 years. There is still room for progress in the performance of LEDs, especially since the current devices with various types of different light-emitting layer materials have converged to unity in terms of internal quantum efficiency, and there is an urgent need to improve the light extraction efficiency. Metasurfaces (MSs) have received attention from researchers as structures that can be integrated with LEDs to efficiently modulate the phase and amplitude of light through resonance and scattering, which can reduce light loss. This paper reviews the development of metasurfaces in LEDs so far. The different working mechanisms of metasurfaces composed of different materials are first analyzed in depth. Subsequently, three aspects of light extraction, angle change, and polarization modulation are described in detail according to different applications of metasurfaces in LEDs. Finally, the current status of metasurface applications in LEDs is summarized, and the future development prospects are envisioned. [ABSTRACT FROM AUTHOR]

Abstract Quasi‐2D metal halide perovskite light emitting diodes (PeLEDs) have attracted a lot of attentions in recent years, while their potential applications in displays and lighting are limited by the device stability. Although defect passivation in PeLEDs is an effective method to ameliorate the unstable problem, the underlying mechanisms need to be further explored. Herein, organic spacer cations with different charge distributions and formation energies in quasi‐2D CsPbBr3 perovskites are utilized to unravel the defect passivation mechanisms, including phenylmethanamine, 2‐phenylethanamine bromide, and 4‐phenylbutylammonium. The experimental findings and density functional theory calculation reveal that the defect passivation occurs by the electrostatic interaction between defective PbBr64− octahedrons and proper organic spacer cations during the annealing process, particularly at the grain boundaries. The thermal stability of the perovskite films and device performance are improved after the effective defect passivation process. The exploration of the defect passivation process in perovskites will be beneficial to the development of high‐performance PeLEDs.

Quasi‐two‐dimensional (quasi‐2D) perovskites are emerging as efficient emitters in blue perovskite light‐emitting diodes (PeLEDs), while the imbalanced crystallization of the halide‐mixed system limits further improvements in device performance. The rapid crystallization caused by Cl doping produces massive defects at the interface, leading to aggravated non‐radiative recombination. Meanwhile, unmanageable perovskite crystallization is prone to facilitate the formation of nonuniform low‐dimensional phases, which results in energy loss during the exciton transfer process. Here, we propose a multifunctional interface engineering for nucleation and phase regulation by incorporating the zwitterionic additive potassium sulfamate into the hole transport layer. By using potassium ions (K+) as heterogeneous nucleation seeds, finely controlled growth of interfacial K+‐guided grains is achieved. The sulfamate ions can simultaneously regulate the phase distribution and passivate defects through coordination interactions with undercoordinated lead atoms. Consequently, such synergistic effect constructs quasi‐2D blue perovskite films with smooth energy landscape and reduced trap states, leading to pure‐blue PeLEDs with a maximum external quantum efficiency (EQE) of 17.32 %, spectrally stable emission at 478 nm and the prolonged operational lifetime. This work provides a unique guide to comprehensively regulate the halide‐mixed blue perovskite crystallization by manipulating the characteristics of grain‐growth substrate. [ABSTRACT FROM AUTHOR]

Perovskite light‐emitting diodes (PeLEDs) are emerging as promising candidates for new‐generation high‐definition displays with excellent color purity and low power consumption. Nevertheless, the massive defects at grain boundaries and severe interfacial exciton quenching are critical challenges that hinder the commercialization process of PeLEDs. Herein, a novel and feasible strategy of interfacial molecule control is demonstrated by employing a bifunctional material with abundant phosphine oxide groups to induce strong interaction and exciton management between the perovskite and electron‐transport layers (ETLs). This modification layer is capable of passivating the surface crystal defects and blocking the interfacial exciton transfer simultaneously, contributing to minimized energy loss at the interface. Consequently, the modified PeLEDs with green (at 513 nm), blue (at 488 nm), and red (at 666 nm) emissions achieve maximum external quantum efficiencies of 18.8%, 12.6%, and 12.3%, respectively. This study reveals the importance of interfacial molecule control for reducing the energy loss in PeLEDs. [ABSTRACT FROM AUTHOR]

Organic light‐emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) materials are promising for the realization of highly efficient emitters. However, severe efficiency roll‐off at high brightness still remains as a huge challenge for TADF‐based OLEDs. Herein, rod‐like orange‐red TADF emitters of 2BNCz‐PZ and 2BNtCz‐PZ with acceptor‐donor‐acceptor (A‐D‐A) configuration are developed by bearing dihydrophenazine donor and discoidal rigid boron, nitrogen‐contained polycyclic aromatic hydrocarbons acceptors. Both emitters exhibit hybrid long‐range/short‐range charge‐transfer excitation for small singlet‐triplet energy splitting, short delayed lifetime, and high photoluminescence quantum yield, leading to fast singlet radiation rate over 107 s−1 and fast reverse intersystem crossing rate over 106 s−1. Furthermore, a horizontal emitting dipole orientation factor over 90% is realized. The optimized orange‐red OLED based on 2BNtCz‐PZ presents a maximum external quantum efficiency (EQE) of 31.0% and a slight EQE roll‐off to 22.2% at 1 000 cd m−2 with emission peak over 600 nm. In addition, the single‐emitting layer white OLEDs achieve a maximum EQE of 30.6% due to the use of these orange‐red dopants with intense charge‐transfer absorption band. This work reveals the potential of the rod‐like A‐D‐A configuration for constructing highly efficient orange‐red TADF emitters with low‐efficiency roll‐off. [ABSTRACT FROM AUTHOR]

Perovskite Light‐emitting diodes (PeLEDs) have emerged as a promising technique for future high‐definition displays due to their outstanding electroluminescent characters. However, the development of blue PeLEDs toward practical applications is seriously hindered by their inferior performance, which mainly arises from the detrimental halide ionic behavior and thus severe nonradiative recombination in mixed‐halide blue perovskite materials. Herein, efficient sky‐blue PeLEDs featuring spectrally stable emission at 483 nm are realized by employing bifunctional passivators of Lewis‐base benzoic acid anions and alkali metal cations to simultaneously passivate the under‐coordinated lead atoms and suppress halide ion migration. A decent external quantum efficiency (EQE) of 16.58% and a maximum EQE of 18.65% are achieved, which is further boosted to 28.82% through the optical outcoupling enhancement. This work demonstrates unique insight into the generality and individuality of this category of benzoates and puts forward a feasible guidance in choosing appropriate additives for efficient perovskite materials. [ABSTRACT FROM AUTHOR]

White organic light‐emitting diodes (WOLEDs) based on thermally activated delayed fluorescence (TADF) emitters attract considerable attention owing to the advantages of full exciton harvesting, low cost, and environmental sustainability. However, compared to phosphorescent counterparts, the power efficiencies of TADF‐based WOLEDs lag behind. Herein, a newly synthesized TADF emitter named DPPZ‐DMAC featuring near‐zero singlet−triplet splitting and high photoluminescence quantum yield (91.6%) is utilized as an ideal orange‐yellow dopant for realizing a power‐efficient WOLED with a mixed system consisting of a blue TADF sensitizer and a conventional fluorescent host. The balanced carrier transport, modulated energy transfer and exciton harvesting, and less exciton quenching can be realized simultaneously. Eventually, a warm WOLED is achieved with an external quantum efficiency of ≈30%, power efficiency of >80 lm W‐1, turn‐on voltage of 2.5 V, and correlated color temperature of 3600 K. Moreover, the color coordinate of the resulting white emission is close to the standard blackbody radiation and can be precisely tuned inside the specific quadrangles given by the American National Standard Institute (ANSI), revealing a large prospect for indoor health lightings. [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]

Halide perovskite materials are emerging as a new promising semiconductor display material owing to their excellent optical and electrical properties. Highly efficient blue perovskite light‐emitting diodes (PeLEDs) are the basis for full‐color displays and solid‐state lighting applications, but their efficiency and stability still lag far behind the red and green analogs. This review focuses on the key effect factors and novel strategies for blue emission PeLEDs. In detail, first effective strategies to obtain blue emission perovskite are discussed, and then the recent progress and strategies in blue emission PeLEDs, including the physical properties and significant improvements based on different structural perovskite materials are systematically elucidated. Finally, the main challenges relating to efficiency, stability, lead toxicity, and fabrication techniques in blue emission PeLEDs are summarized, and the promising research avenues in the future are discussed. [ABSTRACT FROM AUTHOR]

Metal halide perovskite (MHP) materials have shown great advantages for the next‐generation optoelectronic devices, especially for light‐emitting diodes (LEDs), on account of their outstanding photoelectric properties and facile solution processability. However, the performances of red perovskite LEDs (PeLEDs) are not ready for commercialization, presumably due to the instability both of the emission spectra and operation conditions, and the toxicity of lead ions. In this review, the structures, physical properties, and preparation approaches of red emissive perovskite materials are first introduced, including 3D bulk perovskites, 2D and quasi‐2D perovskites, and colloidal perovskite nanocrystals (NCs). In addition, several strategies that contribute to the recent development and achievement of red PeLEDs are summarized in detail, mainly involving component engineering, dimension, and phase distribution modulation, ligand engineering, additive engineering, interfacial engineering, and strategies for the light out‐coupling device structure. Moreover, the challenges and corresponding solutions are discussed from three aspects of spectral stability, operational stability, and lead‐free red PeLEDs. Finally, the conclusion and outlook on the promising future of the red PeLEDs are raised. [ABSTRACT FROM AUTHOR]

Perovskite light‐emitting didoes (PeLEDs) have shown considerable potential in solution‐processable display applications. However, the performance of blue PeLEDs in terms of efficiency and stability hinders their practicality on account of severe trap‐mediated nonradiative recombination losses and halide phase segregation. To ameliorate these issues, mixed‐halide sky‐blue perovskite materials are strategically modulated through crystal defect passivation with a trifurcate isocyanate oligomer, which leads to the synergistical suppression of charge trap density and halide ion migration. The proposed approach enables the performance improvement for sky‐blue PeLEDs, exhibiting a peak external quantum efficiency of 14.82% and spectrally stable emission at 487 nm. In addition, prolonged operational lifetime and enhanced capability of moisture resistance are achieved simultaneously, approaching a half‐lifetime of ≈2900 s at an initial brightness of 178 cd m–2. [ABSTRACT FROM AUTHOR]

Pain is a common symptom of an illness. For decades, pain treatments such as non-steroidal anti-inflammatory drugs, opioids, and surgical nerve blocking have been widely used, but each method has its limitations. Photobiomodulation is a recently developed method for pain management, with light-emitting diodes (LEDs) being a more recent development used in pain management because of their low cost, low side effects, and high safety. Here, we reviewed the phototherapeutic effects of LEDs on different pain conditions. We also discussed possible physicochemical and neurobiological mechanisms underlying LED therapy, especially its effects on inflammatory pain. [ABSTRACT FROM AUTHOR]

Quasi‐2D metal halide perovskite light emitting diodes (PeLEDs) have attracted a lot of attentions in recent years, while their potential applications in displays and lighting are limited by the device stability. Although defect passivation in PeLEDs is an effective method to ameliorate the unstable problem, the underlying mechanisms need to be further explored. Herein, organic spacer cations with different charge distributions and formation energies in quasi‐2D CsPbBr3 perovskites are utilized to unravel the defect passivation mechanisms, including phenylmethanamine, 2‐phenylethanamine bromide, and 4‐phenylbutylammonium. The experimental findings and density functional theory calculation reveal that the defect passivation occurs by the electrostatic interaction between defective PbBr64− octahedrons and proper organic spacer cations during the annealing process, particularly at the grain boundaries. The thermal stability of the perovskite films and device performance are improved after the effective defect passivation process. The exploration of the defect passivation process in perovskites will be beneficial to the development of high‐performance PeLEDs. [ABSTRACT FROM AUTHOR]

Regardless of the rapid advance on perovskite light‐emitting diodes (PeLEDs), the lack of long‐term operational stability hinders the practicality of this technology. Particularly, thermal management is indispensable to control the Joule heating induced by charge transport and parasitic re‐absorption of internally confined photons. Herein, a synergetic device architecture is proposed for minimizing the optical energy losses in PeLEDs toward high efficiency and long lifetime. By adopting a carefully modified perovskite emitter in combination with an improved light outcoupling structure, red PeLEDs emitting at 666 nm achieve a peak external quantum efficiency of 21.2% and an operational half‐lifetime of 4806.7 h for an initial luminance of 100 cd m‐2. The enhanced light extraction from trapped modes can efficiently reduce the driving current and suppress optical energy losses in PeLEDs, which in turn ameliorate the heat‐induced device degradation during operation. This work paves the way toward high‐performance PeLEDs for display and lighting applications in the future. [ABSTRACT FROM AUTHOR]

Efficient and stable blue emission of perovskite light‐emitting diodes (PeLEDs) is a requisite toward their potential applications in full‐color displays and solid‐state lighting. Rational manipulation over the entire electroluminescence process is promising to break the efficiency limit of blue PeLEDs. Herein, a facile device architecture is proposed to achieve efficient blue PeLEDs for simultaneously reducing the energetic loss during electron‐photon conversion and boosting the light outcoupling. Effective interfacial engineering is employed to manipulate the perovskite crystallization nucleation, enabling highly compact perovskite nanocrystal assemblies and suppressing the trap‐induced carrier losses by means of interfacial hydrogen bonding interactions. This strategy contributes to a high external quantum efficiency (EQE) of 12.8% for blue PeLEDs emitting at 486 nm as well as improved operational stability. Moreover, blue PeLEDs reach a peak EQE of 16.8% with the incorporation of internal outcoupling structures for waveguided light, which can be further raised to 27.5% by integrating a lens‐based structure for substrate‐mode light. These results verify the validity of this strategy in producing efficient and stable blue PeLEDs for practical applications. [ABSTRACT FROM AUTHOR]

While tremendous progress has recently been made in perovskite light‐emitting diodes (PeLEDs), large‐area blue devices feature inferior performance due to uneven morphologies and vast defects in the solution‐processed perovskite films. To alleviate these issues, a facile and reliable interface engineering scheme is reported for manipulating the crystallization of perovskite films enabled by a multifunctional molecule 2‐amino‐1,3‐propanediol (APDO)‐triggered "anchoring effect" at the grain‐growth interface. Sky‐blue perovskite films with large‐area uniformity and low trap states are obtained, showing the distinctly improved radiative recombination and hole‐transport capability. Based on the APDO‐induced interface engineering, synergistical boost in device performance is achieved for large‐area sky‐blue PeLED (measuring at 100 mm2) with a peak external quantum efficiency (EQE) of 9.2% and a highly prolonged operational lifetime. A decent EQE up to 6.1% is demonstrated for the largest sky‐blue device emitting at 400 mm2. [ABSTRACT FROM AUTHOR]

Metal halide perovskites are one of the most promising materials for optoelectronic applications owing to their unique optoelectronic properties. In the pursuit of achieving the efficient perovskite light‐emitting diodes (PeLEDs), the critical role of crystallization dynamics on luminescence properties of cesium lead bromide (CsPbBr3) perovskite films has been clarified based on the characterizations of in situ photoelectron spectroscopy, synchrotron‐based grazing incidence X‐ray diffraction, and device fabrication. The crystallinity and crystal orientation of CsPbBr3 perovskite films has been effectively controlled when tuning the underlayer of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) with the ethanolamine modification. The fast crystallization with the formation of pure cubic phase (α‐CsPbBr3) reveals a substantial boost in luminance and device efficiency of PeLEDs, whereas the performance degradation occurs due to the phase transition from α‐CsPbBr3 to orthogonal phase (γ‐CsPbBr3) along with the appearance of PbBr2. The decomposition of organic additives in the perovskite films is a key factor that results in this phase transition, which changes the absorption and band gap as confirmed by the density functional theory calculation. These experimental and theoretical findings provide a better understanding of the crystallization dynamics of perovskite emitters and their influence on device performance by tuning the substrate properties. [ABSTRACT FROM AUTHOR]

Circularly polarized organic light‐emitting diodes (CP‐OLEDs) that enable circularly polarized luminescence (CPL) are promising for 3D display and photonic applications. However, the device efficiency and CPL character of CP‐OLEDs still lag behind the practical requirements. Here, two pairs of axially chiral emitting enantiomers, flexible (R/S)‐ODQPXZ and rigid (R/S)‐ODPPXZ, are reported by fusing (R/S)‐octahydro‐binaphthol chiral source, diphenyl quinoxaline (DQ)/dibenzo[a,c]phenazine (DP) acceptors and phenoxazine (PXZ) donors. The symmetrical chiral‐acceptor‐donor configuration endows them thermally activated delayed fluorescence (TADF) properties with small singlet–triplet energy gaps of 0.16 and 0.07 eV, high photoluminescence quantum yields of 92% and 89% in doped films, and obvious mirror‐image CPL characteristics, respectively. The CP‐OLEDs based on these TADF enantiomers not only show a maximum external quantum efficiency of 28.3% with yellow emission for (R/S)‐ODQPXZ and 20.3% with orange‐red emission for (R/S)‐ODPPXZ, but also display the CPL with dissymmetry factors (gEL) of 6.0 × 10−4 and 2.4 × 10−3, respectively. The high efficiency and obvious CPL of (R)‐ODPPXZ arise from a synergetic interplay of the TADF skeleton and the rigid coplanar acceptor for efficient chiral induction and suppressed intramolecular rotational quenching. [ABSTRACT FROM AUTHOR]

Perovskite light‐emitting diodes (PeLEDs) are emerging candidates for the applications of solution‐processed full‐color displays. However, the device performance of deep‐blue PeLED still lags far behind that of their red and green counterparts, which is largely limited by low external quantum efficiency (EQE) and poor operational stability. Here, a facile and reliable crystallization strategy for perovskite grains is proposed, with improved deep‐blue emission through rational interfacial engineering. By modifying the substrate with potassium cation (K+) as the supplier of heterogeneous nucleation seeds, the interfacial K+‐guided grain growth is realized for well‐packed perovskite assemblies with high surface coverage and the controlled crystal orientation, leading to the enhanced radiative recombination and hole‐transport capabilities. Synergistical boost in device performance is achieved for deep‐blue PeLEDs emitting at 469 nm with a peak EQE of 4.14%, a maximum luminance of 451 cd m–2, and spectrally stable color coordinates of (0.125, 0.076) that matches well with the National Television System Committee (NTSC) standard blue. [ABSTRACT FROM AUTHOR]

Despite the rapid development of high-efficiency perovskite light-emitting diodes (PeLEDs) via material design and morphology control, a comprehensive evaluation of the power loss among various optical modes has seldom been conducted for the precise design of device architectures. Here, a quantitative analysis of light outcoupling efficiency (η out ) of PeLEDs is presented with the theoretical simulations by taking into account the key factors of refractive index and film thickness of various functional layers, and the emitter dipole orientation. For a planar PeLED, a rational design to enhance the η out is predicted by constructing multilayer stack in series of transparent electrode/high-index transport layer/perovskite emitter/low-index transport layer/reflective electrode. Furthermore, the role of photonic structures on the outcoupling management is explored, and the potential of a substantial increase in η out is demonstrated with an enhancement factor of over 1.75 by implementing a moth-eye nanostructure into the emitter. We anticipate that the findings shown here will provide the design guidelines for the optical optimization of PeLEDs. [ABSTRACT FROM AUTHOR]

Metal halide perovskites, a class of crystalline semiconductors with unique optical and electronic properties, are emerging as potential solutions for low-cost photovoltaics and photonic sources in fields of solar cells, sensors, light-emitting diodes and lasers. Regardless of significant progress on device efficiency with the control over perovskite structures and film morphologies, unveiling the interface energetics and band alignment of these perovskite systems is indispensable for the performance optimization in the optoelectronic applications by grasping the photon harvest and charge transport processes. Herein we review the recent advances in the energetics of metal halide perovskite interfaces. The electronic properties of perovskite materials are addressed in terms of halide substitution, thermal annealing and substrate effects as well as trap states. The energy level alignments of interfaces between perovskite films and charge transport layers are then discussed, which is correlated to the photovoltaic properties in perovskite solar cells. [ABSTRACT FROM AUTHOR]

The impact of illumination on the connection part of the tandem organic light-emitting diodes was studied by using a special organic multilayer sample consisted of two organic active layers coupled with different transition metal oxide (TMO)-based intermediate connectors (ICs). Through measuring the current density-voltage characteristic, interfacial electronic structures, and capacitance-voltage characteristic, we observe an unsymmetrical phenomenon in current densityvoltage and capacitance-voltage curves of Mg:Alq3/MoO3 and MoO3 composed devices, which was induced by the charge spouting zone near the ICs region and the recombination state in the MoO3 layer. Moreover, Mg:Alq3/MoO3 composed device displays a photovoltaic effect and the Voc shifts to forward bias under illumination. Our results demonstrate that the TMO-based IC structure coupled with photovoltaic effect can be a good approach for the study of photodetector, light sensor, and so on. [ABSTRACT FROM AUTHOR]

A small-size gas-tight optical measuring system for detection of ammonia nitrogen in water was prepared based on gas-phase ammonia induced color change of the sensing element that was made by loading bromothymol blue (BTB) in a transparent porous glass fiber membrane. The gas-tight optical measuring system consists of a gas-testing and a liquid-sample chamber connected with each other by means of tubes and a mini-pump that cycles the gas between the two chambers. A 625-nm light emitting diode (LED), a photodetector and a sensing element were mounted in the gas-testing chamber for optical response to ammonia gas released from the water in the liquid-sample chamber. Release of ammonia gas was realized by alkalinizing the water sample with NaOH. Owing to the amount accumulation of ammonia gas in the sealing system, the ammonia nitrogen detection limit of the device can be very low. A small concentration of ammonia nitrogen, as low as 0.05 mg/L, was detected. The two linear-response ranges from 0.05 mg/L to 0.26 mg/L and from 0.26 mg/L to 2.62 mg/L were obtained. A relative standard deviation of ≤1% was determined by multiple measurements of the same sample. [ABSTRACT FROM AUTHOR]

Abstract: First, binary and ternary doping system of terbium and/or europium β-diketonate complex doping in poly(N-vinylcarbazole) (PVK) was studied. Energy transfer was analyzed in such complicated doping system. In such a complicated system, inter-molecular energy transfer from PVK to Tb(DBM)3Phen(TbDP) and Eu(DBM)3Phen(EuDP), and from TbDP to EuDP exists. The color changed by adjusting the mixing ratio of dopants concentration and excitation wavelength. Further, in the ternary doping system, it is found that white light could be obtained by optimizing the excitation of different wavelength. [Copyright &y& Elsevier]

Organic Light-Emitting Diodes: The Strategies for High-Performance Single-Emissive-Layer White Organic Light-Emitting Diodes (Laser Photonics Rev. 15(3)/2021) The strategies focus on the molecular design methods of single-molecule devices, the energy transfer mechanisms in various multiple-molecule devices with all-fluorescence, all-phosphorescence, and fluorescence-phosphorescence hybrid structures, and the combination of exciplex emitters and complementary fluorescent/delayed fluorescent/phosphorescent emitters. In article number 2000474, Yan-Qing Li, Jian-Xin Tang, and co-workers review the recent developments for constructing single-emissive-layer white organic light-emitting diodes (SEL-WOLEDs). [Extracted from the article]

Deep-Blue Emission: Interfacial Potassium-Guided Grain Growth for Efficient Deep-Blue Perovskite Light-Emitting Diodes (Adv. Funct. Keywords: crystallization manipulation; deep-blue emission; interface engineering; perovskite light-emitting diodes EN crystallization manipulation deep-blue emission interface engineering perovskite light-emitting diodes 1 1 1 02/05/21 20210203 NES 210203 In article number 2006736, Yan-Qing Li, Jian-Xin Tang, and co-workers demonstrate a facile and reliable crystallization strategy for interfacial potassium-guided perovskite grain growth, leading to efficient deep-blue light-emitting diodes with an external quantum efficiency of 4.14% and stable color coordinates of (0.125, 0.076). Crystallization manipulation, deep-blue emission, interface engineering, perovskite light-emitting diodes. [Extracted from the article]

Efficient UV-blue polymer light-emitting diodes based on a fluorene-based nonconjugated polymer, poly[2,7-(9,9-dihexylfluorene)-alt-4,4′-phenylether] (PFPE), are fabricated. The device with PFPE as emitting layer shows a very narrow ultraviolet-blue electroluminescence emission with a peak at 397 nm and a maximal external quantum efficiency of 1.07%. By blending PFPE into poly(N-vinylcarbazole) (PVK), the device performance can be further improved. A maximum external quantum efficiency of 1.81%, with a maximum irradiance power density of 1223 μW/cm2, was reached by using a blend of PVK and PFPE in the weight ratio of 95:5 as emitting layer. [ABSTRACT FROM AUTHOR]

In article number 1801534, Yan‐Qing Li, Feng Gao, Chun‐Sing Lee, Jian‐Xin Tang, and co‐workers propose a method for the synergetic morphology control over cesium lead bromide perovskite films. Bright perovskite light‐emitting diodes (PeLEDs) are achieved due to the synergetic interplay of small grain sizes for efficient energy funneling and defect passivation for suppressing nonradiative recombination losses. Efficient flexible PeLEDs on plastics are also realized, showing great potential for commercially viable applications. [ABSTRACT FROM AUTHOR]

A universal strategy for highly power‐efficient white organic light‐emitting diodes is developed by Y.‐Q. Li, J.‐X. Tang, and colleagues on page 7249 by combining deterministic aperiodic nanostructures for broadband quasi‐omnidirectional light extraction and a multilayer energy cascade structure for energy‐efficient photon generation. A record efficiency exceeding 120 lm W−1 is achieved with an extremely small roll‐off in efficiency and superior angular color stability. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of positional isomerization on the photoelectric properties of thermally activated delayed fluorescence (TADF) emitters, thereby fully stimulating the potential of the molecular backbone, herein, two red TADF isomers, oTPA-PPP and mTPA-PPP, were developed and synthesized by linking triphenylamine (TPA) donor into different positions of the pyrido [2′,3′:5,6] pyrazino [2,3-f] [1,10] phenanthroline (PPP). Their photoluminescent quantum yields (PLQYs) and external quantum efficiencies (EQEs) were significantly different by manipulating the substitution position of the donor. Compared with mTPA-PPP, oTPA-PPP exhibited higher PLQY benefiting from intramolecular hydrogen bonding and larger fluorescence radiative decay rate, as confirmed by both theoretical and experimental analyses. As a result, oTPA-PPP-based organic light-emitting diode (OLED) realized high EQE max of 19.2 % with red emission at 603 nm, whereas mTPA-PPP achieves an EQE max of 7.9 % at 596 nm. This work provides a simple and feasible molecular design strategy to design and select red TADF emitters with excellent properties. [Display omitted] • Two emitters' photophysical properties can be finely regulated and their molecular skeleton potential is excited. • Multi-nitrogen atom receptors promote RISC and radiative transition processes. • High k r of 5.29 × 107 s−1 for oTPA-PPP suppressed the non-radiative decay and enhanced PLQY to 92.8 %. • OTPA-PPP-based OLED realized high EQE of 19.2 % with red emission peaked at 603 nm. [ABSTRACT FROM AUTHOR]

[Display omitted] • The DETA additive is used for domain regulation and radiative recombination. • The layer numbers of metal halide octahedron PbBr 6 4− can be precisely adjusted. • The emission of pure-bromide perovskites is tuned from violet to greenish-blue. • Efficient blue perovskite light-emitting diodes are achieved. • The EQEs are 1.74%, 2.44% and 5.71% for deep-, pure- and sky-blue emissions. Perovskite light-emitting diodes (PeLEDs) with green and red emissions have made tremendous progress in recent years. However, the realization of efficient and spectra-stable blue-emission PeLEDs remains challenging, which greatly limits their future commercialization. Here, a self-assembling strategy is proposed to achieve efficient blue PeLEDs with stable emission by modulating low-dimensional domains of pure-bromide perovskites to Bohr's radii. A spacer of butylamine with polyamine is used as a modifier to facilitate the formation of homogeneous perovskite films with precious tailoring of the numbers (N) of metal halide octahedron PbBr 6 4− layers. The cubic-phase quasi-2D perovskite films featuring the improved domain distributions and the enhanced luminance are realized, and their emissions can be modulated from violet (~436 nm) to greenish region (~500 nm), corresponding to the emission from N = 2 to N > 3 layered perovskites. The PeLEDs with deep-blue, pure-blue, and sky-blue emissions are obtained with the colour coordinates of (0.13, 0.06), (0.11, 0.13), and (0.08, 0.25), respectively, yielding the maximum external quantum efficiencies of 1.74%, 2.44%, and 5.71%. The approach demonstrated in this work paves the way for constructing efficient, endurable, spectra-stable perovskite emitters for the next-generation display and lighting technologies. [ABSTRACT FROM AUTHOR]

Perovskites light emitting diodes (PeLEDs) are promising candidates for next-generation display devices because of their attractive properties of low-cost, solution processability and excellent color purity. For metal halide perovskite materials, the emission tuning can be easily achieved by altering halide composition. However, blue PeLEDs with chlorine incorporation usually suffer from the severe phase segregation and ion migration, resulting in the red-shifted electroluminescence and the efficiency degradation. Here, the partial substitution of Pb2+ ions with non-toxic Sr2+ is adopted to enhance the formation energy of Sr-alloyed perovskite films, leading to the negligible electroluminescence in electrically driven blue PeLEDs. The maximum brightness and efficiency are optimized simultaneously. Further, such a substitution can greatly enhance the thermal and operational stabilities of PeLEDs. Image 1 • Nontoxic strontium was adopted to partly substitute Pb in perovskites for blue emission. • Spectral and thermal stabilities of PeLEDs are improved by inhibiting ion migrations. • The stability enhancement arises from the increase in the formation energy. [ABSTRACT FROM AUTHOR]