High-efficiency Light-emitting Diodes Research Articles

Perovskite Light-Emitting Diodes with Quantum Wires and Nanorods.

Perovskite materials, celebrated for their exceptional optoelectronic properties, have seen extensive application in the field of light-emitting diodes (LEDs), where research is as abundant as the proverbial "carloads of books." In this review, the research of perovskite materials is delved into from a dimensional perspective, with a focus on the exemplary performance of low-dimensional perovskite materials in LEDs. This discussion predominantly revolves around perovskite quantum wires and perovskite nanorods. Perovskite quantum wires are versatile in their growth, compatible with both solution-based and vapor-phase growth, and can be deposited over large areas-even on spherical substrates-to achieve commendable electroluminescence (EL). Perovskite nanorods, on the other hand, boast a suite of superior characteristics, such as polarization properties and tunability of the transition dipole moment, endowing them with the great potential to enhance light extraction efficiency. Furthermore, zero-dimensional (0D) perovskite materials like nanocrystals (NCs) are also the subject of widespread research and application. This review reflects on and synthesizes the unique qualities of the aforementioned materials while exploring their vital roles in the development of high-efficiency perovskite LEDs (PeLEDs).

Transparent medium embedded with Mn2+ doped perovskite quantum dots for underwater X-ray imaging

Inorganic cesium lead halide (CsPbX₃, X = Cl, Br, I) quantum dots (QDs) have attracted significant interest owing to their superior optoelectronic properties, which are promising for a wide range of optoelectronic applications including low-threshold optical-pumped lasers, high-efficiency light-emitting diodes, photodetectors, and solar cells. However, the QDs exhibit significant drawbacks in terms of stability, being susceptible to external environmental factors. Herein, Mn2+ doped CsPbClxBr3-x QDs were in-situ formed from a glass matrix, achieving both enhanced stability and tunable luminescence. Due to the excellent optical properties of Mn2+ doped CsPbClxBr3-x QDs and the protection of the glass matrix, the glass exhibits a high resolution of 17.2 lp mm−1 and underwater X-ray imaging capabilities. These attributes render Mn2⁺-doped CsPbClxBr3-x QD glass to be of significant application value in the X-ray imaging field, potentially to provide new material support for the development of optoelectronic technologies.

(Invited) III-Nitride Ultraviolet LEDs and Lasers for Applications in Biology and Medicine

Ultraviolet (UV) light emitters with large-energy photons are being developed for emerging biology and medicine applications such as sterilization, water/air purification, and medical treatments, as a replacement for mercury vapor lamps. Solid-state UV light-emitting diodes (LEDs) and lasers based on wide bandgap III-Nitrides offer compact sizes, wavelength tuning, long lifetimes, and sustainability over mercury vapor lamps. While visible LEDs and lasers with longer emission wavelengths find widespread commercial uses for solid-state lighting and display, UV emitters with AlGaN heterostructures struggle with poor external quantum efficiencies of typically less than 10%, which drop further when wavelengths get shorter. Therefore, it is extremely challenging to realize high-efficiency UV emitters despite the demand for compact UV light source, especially for disinfection and sterilization from the pandemic as those high-energy photons can break DNA/RNA bonds and deactivate virus/bacteria. Here, I will discuss our recent developments toward realization of high-efficiency UV LEDs and lasers.To enhance the radiative recombination rate (R sp) from the AlGaN quantum well (QW) active region, we had pursued novel QW design to overcome issues from the existence of valence subbands crossover. Specifically, the arrangement of the three energy-degenerate valence subbands - heavy hole (HH), light hole (LH), and the crystal-field split-off hole (CH) bands for high Al-content and low Al-content AlGaN QWs are completely different. The ordering of the valence bands strongly affects the optical matrix element via the oscillator strength, as well as the direction of the photon emission. Our work has proposed promising solution on the use of delta-QW design to address the valence subbands crossover issue, in order to significantly boost up the R sp. In addition, to enhance the extraction efficiency of UV emitters, we demonstrated the realization and characterization of top-down fabricated, electrically driven UV micropillar array LEDs emitting at 286 nm with a narrow, 9 nm linewidth and output power densities up to 35 mW/cm2. Top-down fabrication allows for formation of perfectly uniform arrays of micropillars with easily tunable diameter and pitch, which cannot be achieved with epitaxially grown nanowires without the use of selective area epitaxy. Dry etch damage induced surface losses were avoided through the use of a two-step etch process combining a Cl dry etch and a hydroxyl-based wet etch to form the micropillar arrays. We also revealed that the unique inverse-taper profile of our micropillars could produce significant enhancements in the extraction efficiency with the increased taper angle. Lastly, our developed III-Nitride wet etch by the use of hydroxyl-based chemicals such as potassium hydroxide (KOH) investigated the effects of temperature, concentration, and the damage recovery aspects of hydroxyl etching of III-Nitride nano and micro structures, leading to important smooth surface profiles for micropillar/nanowire LEDs and optimized mirror facets for ridge-emitting UV lasers.

Carbon Quantum Dots with Highly Efficient Bandgap Emission for Electroluminescent Light-Emitting Diodes

Carbon quantum dots (CQDs) feature bright and tunable photoluminescence, solution processability, and low toxicity, showing great potential in optoelectronics. The multicolor fluorescent CQDs were first fabricated as active layers in our lab, and then the high-performance electroluminescent warm white light-emitting diodes (LEDs) were obtained with the synthesized bright red CQDs. More significantly, through designing the triangular structure of the carbon core, fluorescent CQDs first achieved the narrow-bandwidth (∼30 nm) electroluminescent LEDs with appreciable stability, high color purity, and high luminescence performance. These results lay the foundation for the development of next-generation high performance displays based on CQDs. Here, we will report the large-scale synthesis of CQDs with near-unity photoluminescence quantum yield and the synthesis of red (625 nm) phosphorescent carbon quantum dot organic frameworks (CDOFs) with a quantum yield of up to 42.3% and realization of high-efficiency red phosphorescent electroluminescent LEDs. The LEDs based on the CDOFs exhibited a red emission with a maximum luminance of 1818 cd m−2 and an EQE of 5.6%. This work explores the possibility of a new perspective for developing high-performance CQD-based electroluminescent LEDs.References Yuxin Shi, Louzhen Fan, et al., Red Phosphorescent Carbon Quantum Dot Organic Framework-Based Electroluminescent Light-Emitting Diodes Exceeding 5% External Quantum Efficiency, Am. Chem. Soc. 2021, 143, 45, 18941–18951Ting Yuan, Louzhen Fan, et al., Carbon Quantum Dots with Near-Unity Quantum Yield Bandgap Emission for Electroluminescent Light-Emitting Diodes, Angew. Chem. Int. Ed. 2023, e202218568.Fanglong Yuan，Louzhen Fan, et al., Engineering triangular carbon quantum dots with unprecedented narrow bandwidth emission for multicolored LEDs, Nat. Commun., 2018, 9, 2249. Figure 1

High-efficiency red perovskite quantum dot light-emitting diodes via an effective cation exchange method for tunable emission wavelength

The utilization of perovskite quantum dots (PQDs) in photoelectric devices is indeed an area of intense research due to their advantageous properties such as tunability of visible light and efficient light emission. In this study, mixed CsPbI3 and FAPbI3 PQD dispersions were successfully employed for cation exchange to prepare red-color Cs1−xFAxPbI3 PQD with the photoluminescence (PL) wavelength from 689 nm (x = 0) to 778 nm (x = 1). It is also found that the aggregation of Cs1−xFAxPbI3 PQD films were strongly dependent on x. When x from 0 to 0.6, the holes in PQD thin films were gradually improved. On the opposite, when x > 0.6, the PQDs thin films returned more and more holes due to an excess of FA + cations. The resulting Cs1-xFAxPbI3 PQD based light-emitting diodes (LEDs) also demonstrated tunable emission wavelengths, and it is worth mentioning that the maximum external quantum efficiency (EQE) of 11.22 % was achieved with an emission wavelength of 758 nm when x = 0.6.

Acceleration of radiative recombination for efficient perovskite LEDs

The increasing demands for more efficient and brighter thin-film light-emitting diodes (LEDs) in flat-panel display and solid-state lighting applications have promoted research into three-dimensional (3D) perovskites. These materials exhibit high charge mobilities and low quantum efficiency droop1–6, making them promising candidates for achieving efficient LEDs with enhanced brightness. To improve the efficiency of LEDs, it is crucial to minimize nonradiative recombination while promoting radiative recombination. Various passivation strategies have been used to reduce defect densities in 3D perovskite films, approaching levels close to those of single crystals3. However, the slow radiative (bimolecular) recombination has limited the photoluminescence quantum efficiencies (PLQEs) of 3D perovskites to less than 80% (refs. 1,3), resulting in external quantum efficiencies (EQEs) of LED devices of less than 25%. Here we present a dual-additive crystallization method that enables the formation of highly efficient 3D perovskites, achieving an exceptional PLQE of 96%. This approach promotes the formation of tetragonal FAPbI3 perovskite, known for its high exciton binding energy, which effectively accelerates the radiative recombination. As a result, we achieve perovskite LEDs with a record peak EQE of 32.0%, with the efficiency remaining greater than 30.0% even at a high current density of 100 mA cm−2. These findings provide valuable insights for advancing the development of high-efficiency and high-brightness perovskite LEDs.

Efficient Perovskite Nanograin Light-Emitting Diodes in Green-to-Blue Gamut with Co-Additive Engineering.

Perovskite nanograins exceeding the Bohr exciton diameter show great potential for high-performance light-emitting diodes (LEDs) owing to their bandgap homogeneity, spatial charge confinement, and nonlocal interaction. However, it is challenging to directly synthesize proper nanograins along with reduced crystal defects on functional substrate, and the corresponding high-efficiency perovskite LEDs (PeLEDs) have rarely been reported. In this study, crystallization modulation for perovskites with an effective co-additive system, including lithium bromide, p-fluorophenethylammonium bromide, and 18-crown-6, is performed. Furthermore, it is demonstrated that the proposed co-additive system can synergistically retard perovskite crystallization and reduce crystal defects. Consequently, high-quality perovskite nanograin solids (≈22.8nm) are obtained with a high photoluminescence quantum yield (≈88%). These superior optical properties contribute to developing efficient green PeLEDs with a champion external quantum efficiency (EQE) of 28.4% and an average EQE of 27.1%. The co-additive system can be universally applied to mixed-halide perovskite nanograin LED, presenting a maximum EQE of 24.4%, 21.6%, 17.5%, and 11.1% for the blue device at 496, 488, 478, and 472nm, respectively, along with a narrow spectral linewidth (17-14nm) and stable color. These results supplement the research on high-efficiency perovskite nanograin LEDs for multicolor displays and lighting.

High-Efficiency Pure-Red CsPbI3 Quantum Dot Light-Emitting Diodes Enabled by Strongly Electrostatic Potential Solvent and Sequential Ligand Post-treatment Process.

Efficient pure-red emission light-emitting diodes (LEDs) are essential for high-definition displays, yet achieving pure-red emission is hindered by challenges like phase segregation and spectral instability when using halide mixing. Additionally, strongly confined quantum dots (QDs) produced through traditional hot-injection methods face byproduct contamination due to poor solubility of metal halide salts in the solvent octadecene (ODE) at low temperatures. Herein, we introduced a novel method using a benzene-series strongly electrostatic potential solvent instead of ODE to prevent PbI2 intermediates and promote their dissolution into [PbI3]-. Increasing methyl groups on benzene yields precisely sized (4.4 ± 0.1 nm) CsPbI3 QDs with exceptional properties: a narrow 630 nm PL peak with photoluminescence quantum yield (PLQY) of 97%. Sequential ligand post-treatment optimizes optical and electrical performance of QDs. PeLEDs based on optimized QDs achieve pure-red EL (CIE: 0.700, 0.290) approaching Rec. 2020 standards, with an EQE of 25.2% and T50 of 120 min at initial luminance of 107 cd/m2.

High-efficiency InGaN red light-emitting diodes with external quantum efficiency of 10.5% using extended quantum well structure with AlGaN interlayers

In this study, we have demonstrated a high-efficiency InGaN red (625 nm) light-emitting diode (LED) with an external quantum efficiency (EQE) of 10.5% at a current density of 10 A/cm2. To achieve this, we introduced GaN cap layers on InGaN quantum wells and AlGaN interlayers. The introduction of these layers resulted in a red shift of the wavelength. The AlGaN interlayer caused band bending, while the GaN cap layer modulated the electron wavefunction, thus helping to achieve the wavelength red shift of the InGaN red LED with high EQE. This technology is crucial for the realization of discrete or monolithic full-color micro-LED displays.

Investigation into the Effects of Cross-Sectional Shape and Size on the Light-Extraction Efficiency of GaN-Based Blue Nanorod Light-Emitting Diode Structures

We investigated the effect of cross-sectional shape and size on the light-extraction efficiency (LEE) of GaN-based blue nanorod light-emitting diode (LED) structures using numerical simulations based on finite-difference time-domain methods. For accurate determination, the LEE and far-field pattern (FFP) were evaluated by averaging them over emission spectra, polarization, and source positions inside the nanorod. The LEE decreased as rod size increased, owing to the nanorods’ increased ratio of cross-sectional area to sidewall area. We compared circular, square, triangular, and hexagonal cross-sectional shapes in this study. To date, nanorod LEDs with circular cross sections have been mainly demonstrated experimentally. However, circular shapes were found to show the lowest LEE, which is attributed to the coupling with whispering-gallery modes. For the total emission of the nanorod, the triangular cross section exhibited the highest LEE. When the angular dependence of the LEE was calculated using the FFP simulation results, the triangular and hexagonal shapes showed relatively high LEEs for direction emission. The simulation results presented in this study are expected to be useful in designing high-efficiency nanorod LED structures with optimum nanorod shape and dimensions.

Partial Ligand Stripping from CsPbBr3 Nanocrystals Improves Their Performance in Light-Emitting Diodes.

Halide perovskite nanocrystals (NCs), specifically CsPbBr3, have attracted considerable interest due to their remarkable optical properties for optoelectronic devices. To achieve high-efficiency light-emitting diodes (LEDs) based on CsPbBr3 nanocrystals (NCs), it is crucial to optimize both their photoluminescence quantum yield (PLQY) and carrier transport properties when they are deposited to form films on substrates. While the exchange of native ligands with didodecyl dimethylammonium bromide (DDAB) ligand pairs has been successful in boosting their PLQY, dense DDAB coverage on the surface of NCs should impede carrier transport and limit device efficiency. Following our previous work, here, we use oleyl phosphonic acid (OLPA) as a selective stripping agent to remove a fraction of DDAB from the NC surface and demonstrate that such stripping enhances carrier transport while maintaining a high PLQY. Through systematic optimization of OLPA dosage, we significantly improve the performance of CsPbBr3 LEDs, achieving a maximum external quantum efficiency (EQE) of 15.1% at 516 nm and a maximum brightness of 5931 cd m-2. These findings underscore the potential of controlled ligand stripping to enhance the performance of CsPbBr3 NC-based optoelectronic devices.

Investigation of emission plane control in GaInN/GaN multiple-quantum shells for efficient nanowire-based LEDs.

Significant attention has been directed toward core-shell GaInN/GaN multiple-quantum shell (MQS) nanowires (NWs) in the context of high-efficiency micro light-emitting diodes (micro-LEDs). These independent three-dimensional NWs offer the advantage of reducing the impact of sidewall etching regions. Furthermore, the emitting plane on the sidewalls demonstrates either nonpolar or semipolar orientation, while the dislocation density is exceptionally low. In this study, we assessed how changes in the NW morphology are affected by GaInN/GaN superlattice (SL) structures grown at varying growth temperatures, as well as control of the emission plane via the p-GaN shell and emission sizes. The SL growth rate was enhanced at elevated growth temperatures, accompanied by the shrinkage of the (0001)-plane and expansion of the (11̄01)-plane on the NWs. The samples exhibited a higher light output when the SLs were grown at elevated temperatures compared to those grown with lower temperatures. A similar trend was observed for the samples with a gradual temperature transition during the growth. These findings indicate that the dimensions of the (0001)-plane can be controlled through SL growth, which in turn influences the emission properties of NW-LEDs. In addition, the emission properties of NW-LEDs with different growth time p-GaN shells and different emission sizes were investigated. Based on the NW-LED characteristics, it was revealed that the weak emission of the (0001)-plane was the dominant factor for the limited light output, and the most effective way to realize high efficiency devices is to suppress current injection into the apex or minimize the grown (0001)-plane region. Overall, it is one promising way to control the emission planes of NWs, which holds significant relevance for the potential application of NW-LEDs in the realm of micro-LEDs.

Unveiling the luminescence property of Li2MgGeO4:Mn4+ featuring the tetrahedral crystallographic-site occupancy of Mn4.

Owing to the occupying tendency of Mn4+ at octahedral sites, doping Mn4+ activators in tetrahedral structures poses challenges and hence is seldom reported. In this work, tetrahedrally sited Mn4+ phosphors were studied. By combining X-ray diffraction (XRD) data with Rietveld refinement analysis, the location of Mn4+ was determined. It was found that by adding excessive raw MgO, the phosphor synthesis temperature can be improved, enhancing the crystallinity of the crystal and thus improving the emission performance of the phosphor. In addition, excessive raw MgO forms a second phase in an LMGO matrix, which does not change the doping site for Mn4+. The Tanabe-Sugano diagram of Mn4+ in the tetrahedral field and the energy-level diagram of these phosphors were constructed for the first time, and the excitation and emission mechanisms are discussed in detail. With 1.2-fold excess of raw MgO, the prepared sample (LMGO-Mn-1.2) shows the best luminescence, demonstrating red emissions peaked at 656 nm and affording an emission intensity enhancement of over 50 times compared to a stoichiometric LMGO:Mn4+ system. At 150 °C, LMGO-Mn-1.2 keeps 90% emission intensity compared to that at room temperature. Finally, a high-efficiency warm white light-emitting diode was built. This work provides new insights into the study of Mn4+-activated phosphors in a tetrahedron crystal field.

High-efficiency inkjet-printed quantum-dot light-emitting diode enabled by solvent-resistant hole transport materials with high surface energy and extended conjugation

High-efficiency inkjet-printed quantum-dot light-emitting diode enabled by solvent-resistant hole transport materials with high surface energy and extended conjugation

Phase distribution management for high-efficiency and bright blue perovskite light-emitting diodes

Quasi-two-dimensional (quasi-2D) perovskite materials have attracted significant attention for application in light-emitting diodes (PeLEDs) due to their unique optical characteristics and extraordinary performance. The inherent multi-quantum well structure will generate a strong quantum confinement effect which is beneficial for the blue emission. However, the efficiency and stability of the quasi-2D blue PeLEDs lag behind their red and green counterparts, which prevents the further commercial application of the PeLEDs. The performance of quasi-2D blue PeLEDs was limited on account of the inefficient phase distribution management, which causes an inefficient energy transfer and severe non-radiative recombination. Herein, we employ guanidine thiocyanate (GASCN) as the pre-deposited film at the bottom of the perovskite film to manage the phase distribution of the PBA2Csn−1PbnBr3n+1 quasi-2D perovskite film (where n is the number of [PbBr6]4- sheets, and PBA is phenylbutylammonium). The pre-deposited GASCN can not only inhibit the small n-phase (i.e., n = 1: PBA2PbBr4, and n = 2: PBA2CsPb2Br7) but also avoid the undesired emission redshift from the over-growth of the large n-phase as well as passivate defects of the quasi-2D perovskite film, which accelerates energy transfer efficiently, strengthens the carrier transport, and enhances the luminous efficiency. As a result, the optimized device demonstrated the highest external quantum efficiency (EQE) of 16.40% and a maximum luminance of 8290 cd m−2. This strategy provides a new pathway to accurately manage phase distribution of quasi-2D perovskite achieving the high efficiency in blue PeLEDs.

Advanced Design of a III‐Nitride Light‐Emitting Diode via Machine Learning

AbstractGallium nitride (GaN)‐based light‐emitting diodes (LEDs) have obtained great market success in the past 20 years. However, the traditional research paradigm, i.e., experimental trial‐and‐error method, no longer adapts to the industry development. In this work, an efficient approach is demonstrated to design and optimize GaN‐based LED structures via machine learning (ML). By using the dataset of GaN‐based LED structures over the past decade to train four typical ML models, it is found that the convolutional neural network (CNN) provides the most accurate prediction, with a root mean square error (RMSE) of 1.03% for internal quantum efficiency (IQE) and 11.98 W cm−2 for light output power density (LOPD). Based on the CNN model, 1) the feature importance analysis is adopted to reveal the critical features for LED performance; 2) the predicted trends of IQE and LOPD match well with the physical mechanism, being consistent with the experimental and simulation results; and 3) a high‐throughput screening is demonstrated to predict the properties of over 20 000 structures within seconds to obtain high efficiency LED structures. This ML‐based LED design method enables direct guiding of the LED structure optimization in terms of key parameter selection during manufacturing and greatly accelerates the development cycle of GaN‐based LEDs.

Charge injection engineering at organic/inorganic heterointerfaces for high-efficiency and fast-response perovskite light-emitting diodes

The development of advanced perovskite emitters has considerably improved the performance of perovskite light-emitting diodes (LEDs). However, the further development of perovskite LEDs requires ideal device electrical properties, which strongly depend on its interfaces. In perovskite LEDs with conventional p-i-n structures, hole injection is generally less efficient than electron injection, causing charge imbalance. Furthermore, the popular hole injection structure of NiOx/poly(9-vinylcarbazole) suffers from several issues, such as weak interfacial adhesion, high interfacial trap density and mismatched energy levels. In this work, we insert a self-assembled monolayer of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid between the NiOx and poly(9-vinylcarbazole) layers to overcome these challenges at the organic/inorganic heterointerfaces by establishing a robust interface, passivating interfacial trap states and aligning the energy levels. We successfully demonstrate blue (emission at 493 nm) and green (emission at 515 nm) devices with external quantum efficiencies of 14.5% and 26.0%, respectively. More importantly, the self-assembled monolayer also gives rise to devices with much faster response speeds by reducing interfacial capacitance and resistance. Our results pave the way for developing more efficient and brighter perovskite LEDs with quick response, widening their potential application scope.

Dual-functionalized poly(ethylene oxide) for interface modification and addition of rubidium-doped CsPbBr3 perovskite composite emission layer to enhance brightness of perovskite light-emitting diodes

Metal halide perovskite as an emitter has extremely high color purity, but the generally poor morphology of the perovskite layer restricts the performance of the emitter. The additive of a suitable polymer can greatly boost the uniformity of the spin-coated perovskite film. The all-inorganic perovskite layer deposited by the solution method has a multi-crystalline structure. Besides, there are a lot of defects and grain boundaries on the surface, and the carriers will undergo non-radiative recombination at these defects. In this study, Cs1-xRbxPbBr3 was prepared by introducing Rb+ cations with smaller ionic radius to partially replace Cs+ cations, and combined with poly(ethylene oxide) (PEO) and (1,3,5-benzinetriyl)tris(1-phenyl-1-H-benzimidazole) (TPBi) blended composite film as the light-emitting layer, that can increase the film coverage and radiative recombination efficiency of the perovskite film. The polymer PEO was introduced as a buffer layer deposited on the poly-TPD hole transport layer (HTL) to to enhance the hydrophilicity and passivate the poly-TPD HTL/perovskites interface in order to obtain high-efficiency perovskite light-emitting diodes. By adjusting the concentration of the PEO buffer layer, the champion luminance and external quantum efficiency are 25650 cd/m2 and 0.844 %, respectively.

High-Efficiency and Emission-Tunable Inorganic Blue Perovskite Light-Emitting Diodes Based on Vacuum Deposition.

The fabrication of perovskite light-emitting diodes (PeLEDs) with vacuum deposition shows great potential and commercial value in realizing large-area display panel manufacturing. However, the electroluminescence (EL) performance of vacuum-deposited PeLEDs still lags behind the counterparts fabricated by solution process, especially in the field of blue PeLEDs. Here, the fabrication of high-quality CsPbBr3- x Clx film through tri-source co-evaporation is reported to achieve high photoluminescence quantum yield (PLQY). Compared with the conventional traditional dual-source co-evaporation, the tri-source co-evaporation method allows for freely adjustable elemental ratios, enabling the introduction of the lattice-matched Cs4 Pb(Br/Cl)6 phase with the quantum-limited effect into the inorganic CsPb(Br/Cl)3 emitter. By adjusting the phase distribution, the surface defects of the emitter can be effectively reduced, leading to better blue emission and film quality. Further, the effects of Cs/Pb ratio and Br/Cl ratio on the PLQY and carrier recombination dynamics of perovskite films are investigated. By optimizing the deposition rate of each precursor source, spectrally stable blue PeLEDs are achieved with tunable emission ranging from 468 to 488nm. Particularly, the PeLEDs with an EL peak at 488nm show an external quantum efficiency (EQE) of 4.56%, which is the highest EQE value for mixed-halide PeLEDs fabricated by vacuum deposition.

Photophysical dynamics of excitons in polyaniline nanotubes with enhanced resistance against exciton quenching for applications in flexible high-efficiency PLEDs

The development of a high-efficiency polymer light-emitting diode is strongly hindered by injected charge carriers in the emissive polymer layer. But real-time identification of the interactions that quench the photoluminescence is extremely difficult owing to the complex photophysics of polymers involved in it. Here, we have synthesized the polyaniline nanotubes to study interactions at the nanoscale within the emissive layer. Acid doping of PAni helped us to quantify the processes that suppress the emission, e.g., Förster resonance energy transfer (FRET) and charge transfer (CT). We have developed a material design perspective by demonstrating how an effective increase in conjugation length of PAni nanochain through 1D nanostructure growth can avoid the undesired emission quenching due to exciton quenching by the polarons. We have demonstrated how this approach helped us to preserve up to 95 % of the emission, which would otherwise be lost by exciton-polaron quenching interaction. Exploration of this new strategy could be a way forward for both fundamental and application aspects to enhance the emission efficiency of the conducting conjugate polymers and emissive layers in flexible polymer light-emitting diodes (PLEDs).