Peak External Quantum Efficiency Research Articles

InGaN amber micrometer-scale light-emitting diodes with a peak external quantum efficiency of 5.5%

We demonstrate high-performance 10 × 10 μm2 InGaN amber micro-size LEDs (μLEDs). At 15 A cm−2, the InGaN μLEDs show a single emission peak located at 601 nm. The peak external quantum efficiency (EQE) and wall-plug efficiency are 5.5% and 3.2%, respectively. Compared to the 100 × 100 μm2 μLEDs, the 10 × 10 μm2 InGaN red μLEDs maintain a similar EQE value with the same efficiency droop. These results point out that InGaN materials are much more promising for higher efficiency than the common AlInGaP materials for the ultra-small size red μLEDs required by augmented reality and virtual reality displays.

53‐3: High‐Efficiency MicroLED Displays Enabled Through PulseForge Assisted Die Transfer

A pathway to scalable microLED mass‐transfer technology utiliz‐ing a PulseForge assisted die transfer process (PATP) was studied. PATP involves an intermediate glass carrier (IC) coated with an inorganic release layer to transfer an array of LEDs over a 150 mm×75 mm area. To demonstrate the feasibility of this process, an array of 15×15 µm 2blue microLEDs were integrated onto a sili‐con substrate. The transferred LEDs had a 55% peak external quantum efficiency (EQE) compared to a peak EQE of 26% for LEDs on sapphire substrates.

Efficient and Stable OLEDs with Inverted Device Structure Utilizing Solution‐Processed ZnO‐Based Electron Injection Layer

AbstractTo realize low‐cost, efficient, and stable organic light‐emitting diodes (OLEDs) in future large area displays and lighting, the development of suitable solution‐processed functional materials is highly desirable. Herein, a series of efficient and stable OLEDs with an inverted device architecture is reported, employing both a vapor‐deposited phosphorescent aggregate emitter, i.e., Pd(II) 7‐(3‐(pyridine‐2‐yl‐κN)phenoxy‐κC)(benzo‐κC)([c]benzo[4,5]imidazo‐κN)[1,2‐a][1,5]naphthyridine, and a solution‐processed ZnO layer as potential electron injection layer and electron‐transporting layer. One of the optimized OLED devices exhibits its peak external quantum efficiency (EQE) of 23.9% and retains EQEs of 23.5% and 18.7% at 1000 and 10 000 cd m−2, with a low efficiency roll‐off. Such an efficient device also demonstrates a measured lifetime (LT95) of 98.6 h with an initial brightness of 10 435 cd m−2 corresponding to an estimated LT95 of 5313 h at 1000 cd m−2. By depositing a 2 nm Al on the ZnO surface, an estimated LT95 at 1000 cd m−2 of such a device can be further extended to 73 244 h, making it the longest‐lived OLED reported in the literature domain. This study lays the strong foundation for the future deployment of efficient and stable inverted OLEDs with solution‐processed ZnO layers for a wide range of displays and lighting applications.

Efficient Charge Transfer in Narrowband Organic Photodiodes Based on Self‐Assembled Heterojunction for Spectrally Selective Photodetection and Imaging

AbstractSpectrally selective photodetection has been used in many areas where only band‐specific optical signals are aimed to be detected. Organic photodiodes (OPDs) based on internal light depletion mechanisms have been utilized to realize narrowband photodetection. However, the fabrication of the photoactive layers by conventional solution methods can result in the deterioration of the underneath organic depletion layers and cause high‐density defect states at their interface. Herein, a new approach is presented to realize efficient charge transfer by adopting a self‐assembly strategy to prepare donor/acceptor bulk heterojunctions as the photoactive layers for narrowband OPDs. This method is able to prepare highly smooth, phase‐uniform, and low‐defect‐density thin films with controlled thickness. With this strategy, a narrowband near‐infrared OPD centered at 760 nm with a full‐width‐at‐half‐maximum of around 60 nm, peak external quantum efficiency of 49%, and peak specific detectivity of over 1013 Jones under −5 V is achieved. Multiple material combinations for the depletion and photoactive layers are examined, and the results show the effectiveness to realize the spectrally selective photodetection (from 740 to 900 nm) in general. More importantly, the narrowband OPDs can be integrated into a matrix for imaging, which demonstrates the mass‐scale fabrication feasibility of these OPDs.

Self-Generated Buried Submicrocavities for High-Performance Near-Infrared Perovskite Light-Emitting Diode

HighlightsSynergistic effect triggers the Ostwald ripening for the downward recrystallization of perovskite to form buried submicrocavities as light output coupler.The simulation suggests the buried submicrocavities can improve the light out-coupling efficiency from 26.8% to 36.2% for near-infrared light.Light-emitting diodes yields peak external quantum efficiency increasing from 17.3% at current density of 114 mA cm−2 to 25.5% at current density of 109 mA cm−2 and a radiance increasing from 109 to 487 W sr−1 m−2 with low rolling-off.

Significant Quantum Efficiency Enhancement of InGaN Red Micro-Light-Emitting Diodes with a Peak External Quantum Efficiency of up to 6%

We demonstrate a significant quantum efficiency enhancement of InGaN red micro-light-emitting diodes (μLEDs). The peak external quantum efficiency (EQE) of the packaged 80 × 80 μm2 InGaN red μLEDs was largely increased to 6.0% at 12 A/cm2, representing the significant process in exploring the efficiency of InGaN red μLEDs. The improvement of the EQE is attributed to the significant enhancement of the quantum efficiency, which is confirmed by the electron–hole wavefunction overlap in the InGaN quantum well from the band gap simulation and the photoluminescence intensity ratio at room temperature/low temperature. Ultrasmall 5 × 5 μm2 InGaN red μLEDs were also obtained, which show a high peak EQE of 4.5%. This work demonstrates a simple approach to achieving highly efficient InGaN red μLEDs, which are very promising candidates for ultrasmall red μLEDs required by AR/VR displays.

Scalable Synthesis of High‐Quality Core/Shell Quantum Dots With Suppressed Blinking

AbstractA facile and reproducible method for scalable synthesis of high‐quality core/shell quantum dots (QDs) is a prerequisite to facilitate their versatile applications. Herein, a seed‐mediated heat‐up approach is developed for the preparation of high‐quality core/shell QDs with variable shell composition and continuously tunable shell thickness by selection of conventional salts as the precursors. The method is very simple and highly reproducible and, therefore, can be easily scaled up to get gram‐level product. The as‐obtained CdSe/CdS and CdSe/ZnCdS core/shell QDs exhibit intriguing optical properties, that is a narrow photoluminescence (PL) emission peak and near‐unity PL quantum yield. Importantly, the CdSe/ZnCdS core/shell QDs with a size of 11.4 nm exhibit obviously suppressed blinking behavior, and the fraction of nonblinking QDs (defined by an on‐time fraction ≥ 0.95) can reach as high as 96.0% on the measurement of more than 200 QDs. Moreover, quantum‐dot light‐emitting diodes (QLEDs) based on CdSe/ZnCdS core/shell QDs show a peak external quantum efficiency of 14.8% and low efficiency roll‐off at luminance ranging from 1000 to 25 000 cd·m−2. It is anticipated that the presented work will pave a novel way for the large‐scale production of high‐quality QDs and further boost their applications in light‐emitting diodes, lasing, and biological imaging.

Bridging Chloride Anions Enables Efficient and Stable InP Green Quantum‐Dot Light‐Emitting Diodes

AbstractZnMgO nanoparticles (NPs) are commonly used as the electron transport layer (ETL) in indium phosphide (InP) based quantum dots light‐emitting diodes (QLEDs). It has been experimentally found that the inherent oxygen vacancy defects in ZnMgO can be passivated by halogen additives. However, an in‐depth understanding of how the halogen additives in ZnMgO affect the quantum dots (QDs) films is currently missing. Here, the study reports on efficient and stable indium phosphide (InP) green QLEDs by effectively bridging QDs and ETL using chloride (Cl) ions. As bi‐functional anchoring additives, Cl ions not only passivate the oxygen vacancy defects of ZnMgO NPs for suppressing the exciton quenching at the QDs/ZnMgO interfaces, but also facilitate the hole transport of QDs due to part replacement of insulated oleic acid ligands on the surfaces of InP QDs with Cl anions for more balanced charge injection in the devices. Consequently, the optimized green InP QLED achieves a peak external quantum efficiency (EQE) of 13.8% and an operational lifetime of 5944 h, which, to the best of current knowledge, represents the best overall performance among the reported green InP QLEDs.

Realization of 1.54-μm Light-Emitting Diodes Based on Er3+ /Yb3+ co-Doped CsPbCl3 Films.

1.54-μm erbium ions (Er3+ ) electric pumped light sources with excellent optical property and simple fabrication process are urgently desired to satisfy the development of silicon-based integration photonics. The previous Er-based electroluminescence (EL) devices are mainly based on Er-complexes or Er-doped oxide compounds, which usually suffer from low external quantum efficiency(EQE)or high applied voltage etc. In this work, a novel type of Er3+ /Yb3+ co-doped lead-halide perovskite films (Er3+ /Yb3+ :CsPbCl3 ) with the maximum photoluminescence quantum yield (PLQY) of 30.12% are prepared by a simple two-step solution-coating method and the corresponding light emitting diodes (Er-PeLEDs) are fabricated, which demonstrate a almost pure 1.54-μm emission and a peak EQE up to 0.366% at a low applied voltage of 1.4V. Strong negative thermal quenching effect may help Er-PeLEDs suppress Joule heating quenching. These excellent LED properties benefit mainly from outstanding regulatory performance of acetate to perovskite films, the excellent semiconductor behavior and strong ionic property of the perovskite, and the involving of Yb3+ ions, which can directly and efficiently transfer the exciton energy to Er3+ through a quantum cutting process. Overall, the realization of 1.54-μm Er-PeLEDs offers new opportunities for silicon-based integrated light sources. This article is protected by copyright. All rights reserved.

Efficiency enhancement of submicron‐size light‐emitting diodes by triple dielectric layers

AbstractMicro‐LED (light‐emitting diode) is an emerging technology that produces superiorly bright, efficient, and high‐resolution display. However, efficiency drop at small chip sizes is one of the major hurdles for cost‐effectiveness and ultra‐compact form factor. We demonstrate highly efficient submicron‐scale nanorod LEDs (nLEDs) passivated by the triple dielectric layers. The diameter, length, and wavelength at a peak external quantum efficiency (EQE) of nLEDs are 580 nm, 5 μm, and 460 nm, respectively. We report a peak EQE of 22.2 ± 0.3% with HfO2‐based triple dielectric layer. We also explore the relation of indium fluctuation in multi‐quantum wells (MQWs) to sidewall effect of micro‐LEDs. We show that higher indium contents in MQWs successfully reduce non‐radiative recombination on sidewall of InGaN blue nLEDs.

Efficient Near‐Infrared Electroluminescence from Lanthanide‐Doped Perovskite Quantum Cutters

AbstractPerovskite nanocrystals (PeNCs) deliver size‐ and composition‐tunable luminescence of high efficiency and color purity in the visible range. However, attaining efficient electroluminescence (EL) in the near‐infrared (NIR) region from PeNCs is challenging, limiting their potential applications. Here we demonstrate a highly efficient NIR light‐emitting diode (LED) by doping ytterbium ions into a PeNCs host (Yb3+ : PeNCs), extending the EL wavelengths toward 1000 nm, which is achieved through a direct sensitization of Yb3+ ions by the PeNC host. Efficient quantum‐cutting processes enable high photoluminescence quantum yields (PLQYs) of up to 126 % from the Yb3+ : PeNCs. Through halide‐composition engineering and surface passivation to improve both PLQY and charge‐transport balance, we demonstrate an efficient NIR LED with a peak external quantum efficiency of 7.7 % at a central wavelength of 990 nm, representing the most efficient perovskite‐based LEDs with emission wavelengths beyond 850 nm.

In-situ composition development of Zn/In-doped Ga2O3 nanowire with ultrahigh responsivity and long-term stability for deep-UV photodetector

High-performance deep ultraviolet photodetectors (UV PDs) based on Ga2O3 have been applied widely in civil and military exploration. The incident photon-to-electron conversion efficiency of Ga2O3-based UV PDs could be improved by doping metal or non-metal elements in the lattice. Herein, multi-metallic oxide of InZn co-doped Ga2O3 (InZn-Ga2O3) nanowires is synthesized via the in-situ chemical vapor deposition (CVD) method. The favorable 25%InZn-Ga2O3 exhibits a maximum responsivity of 440.42 A W−1 and a peak external quantum efficiency (EQE) of 2.15 × 105% under 254 nm light illumination at 10 V, which are 1.19 × 104 times higher than that for pure Ga2O3, indicating its enhanced detection ability for deep-UV light and high conversion efficiency from photons to electrons. A high UV/visible rejection ratio of 7.3 × 105 is also obtained, implying a high sensitivity for UV light. Moreover, the responsivity of the InZn-Ga2O3 UV PD remains unchanged after a long period of 8000 s testing. The superior performances of InZn-Ga2O3 UV PD are attributed to the improved crystal quality with decreased oxygen vacancies and elevated conductivity, which facilitate the separation and transfer of photoinduced electron-hole carriers. The DFT calculation and UV–vis spectra results reveal that the InZn-Ga2O3 possesses a narrowed band gap with enhanced light absorption and a decreased work function for the fast escape of electrons. In addition, the ohmic contact between InZn-Ga2O3 and Ag electrode accelerates the transfer and diffusion of photogenerated electrons. The achievements in our work present a multi-metallic oxide nanowire with high performance and an innovative mechanism analysis method for the applications of optoelectronic devices.

ZnO/silica quasi core/shell nanoparticles as electron transport materials for high-performance quantum-dot light-emitting diodes

Quantum dot light-emitting diodes (QLEDs) are considered as the ideal candidate for next-generation displays, solid-state lighting, and optical communication applications. Although the efficiency of QLEDs has been significantly improved to the level comparable to that of organic light-emitting diodes in recent years, simultaneously achieving high efficiency and high brightness still remains challenging for QLEDs. In this work, we report a facile and effective electron-transport-layer interface control strategy of incorporating 3-aminopropyl triethoxysilane (APTES) into a ZnO nanocrystal-solution to enhance charge injection balance and suppress interfacial exciton quenching via in-situ formation of ZnO/organic silica (hereinafter referred to as ZnO/SiO2) quasi core/shell nanoparticles in the solution, enabling red QLEDs to exhibit a maximum luminance intensity of 261,700 cd m−2, a peak external quantum efficiency (EQE) of 19.0%, and low efficiency roll-off at high luminance (an EQE up to 16.8% remained at a brightness of 200, 000 cd m−2). Our results demonstrate that substituting quasi core/shell-structured ZnO/SiO2 nanoparticles for traditional ZnO nanocrystals as electron transport materials is a simple and effective means of fabricating QLEDs with both high efficiency and high luminance, which is expected to facilitate the development of QLED technology toward practical applications in lighting, displays and optical communication.

Efficient Red-Emissive Circularly Polarized Electroluminescence Enabled by Quasi-2D Perovskite with Chiral Spacer Cation.

Perovskites are promising environmentally sustainable materials for circularly polarized electroluminescence (CPEL). While another chiral nonemissive layer is required for the developed perovskite-based CPEL, we report herein a highly efficient circularly polarized electroluminescence based on a single layer of quasi-2D perovskite with achiral phenethylammonium iodide (PEAI) and chiral S/R-1-(1-naphthyl)ethylammonium iodide (S/R-NEAI) as dual spacer cations. The quasi-2D perovskite was further passivated by carbazole-functionalized phosphonium. The as-fabricated film exhibits not only a circular dichroism (CD) signal but also prominent circularly polarized luminescence (CPL) activity with a maximum photoluminescence dissymmetry factor (glum) of ∼2.1 × 10-3. More importantly, a highly efficient, spin-polarized light-emitting diode (LED) was fabricated based on the in situ passivated quasi-2D perovskite with a peak external quantum efficiency of 3.7% and a maximum electroluminescence dissymmetry factor (gEL) of ∼4.0 × 10-3.

Low-efficiency-droop c-plane InGaN/GaN light-emitting diodes through the use of thick single quantum wells and doped barriers

Efficiency droop at high current densities is a problem for InGaN-based light-emitting diodes (LEDs), especially for conventional c-plane devices. The large internal electric fields in c-plane quantum wells (QWs) lead to an increase in the active region carrier density (n), causing the electrical efficiency droop onset to occur at low current densities. Here, we present an approach to reduce the internal electric fields (Eint) in c-plane QWs by placing doped p-type and n-type GaN barriers close to the QW. The reduced Eint also allows a thick QW active region design, which helps to lower n to further reduce the droop. The concept of using doped barriers to control Eint is explained using theory and device simulations. Following that, multiple series of thick single QW (SQW) LEDs were grown and characterized. Key parameters in the epitaxial design such as the doping levels and the relative position of the doped barriers were systematically studied and optimized. By using optimized doped barriers and a thick SQW, c-plane LEDs with a low-efficiency droop of 14% at 300 A/cm2 [with respect to the peak external quantum efficiency (EQE)] and a high peak EQE of 49% were demonstrated.

D-O-A based organic phosphors for both aggregation-induced electrophosphorescence and host-free sensitization

Pure organic phosphors capable of room-temperature phosphorescence show a great potential in organic light-emitting diodes, while it is limited by the big challenge to realize efficient electroluminescence under electric excitation. Herein, we develop a class of organic phosphors based on acridine as the electron donor, triazine as the electron acceptor and oxygen as the bridge between them. Benefitting from the characteristic donor-oxygen-acceptor geometry, these compounds are found to behave an exciting aggregation-induced organic room-temperature electrophosphorescence, and achieve a record-high external quantum efficiency of 15.8% for non-doped devices. Furthermore, they can sensitize multi-resonant emitters in the absence of any additional wide bandgap host, leading to an effective narrowband emission with a peak external quantum efficiency of 26.4% and a small full-width at half maximum of 26 nm. The results clearly indicate that donor-oxygen-acceptor geometry is a promising strategy to design organic phosphors suitable for organic light-emitting diodes.

Ionic Liquid Passivation for High‐Performance Sky‐Blue Quasi‐2D Perovskite Light‐Emitting Diodes

AbstractGreat progress has been made in high‐performance perovskite light‐emitting diodes (PeLEDs). However, the external quantum efficiency (EQE) of blue PeLEDs still lags. Particularly, defects are inevitable in solution‐processed perovskite films, which inhibit the efficient radiative recombination in blue PeLEDs. Herein, a facile ionic liquid (IL, 1,3‐dimethyl‐3‐imidazolium hexafluorophosphate) post‐treatment on the as‐fabricated quasi‐2D perovskite film is reported, to passivate the uncoordinated Pb through the strong interaction with IL. The IL‐assisted perovskite film demonstrates a great enhancement of radiative recombination efficiency, and the photoluminescence quantum yield of the film increases from 35.7% to 74.6%. IL post‐treatment also adjusts the energy level of perovskite film and enhances the hole injection in PeLED. As a result, the peak EQE of the sky‐blue quasi‐2D PeLED is improved from 4.0% to 9.0%, while the turn‐on voltage is reduced from 3.3 to 3.0 V. This work contributes to a feasible and effective approach for improving the quality of blue quasi‐2D perovskites and enhancing the efficiency of blue PeLEDs.

Impact of Sidewall Conditions on Internal Quantum Efficiency and Light Extraction Efficiency of Micro‐LEDs

AbstractThe sidewall condition is a key factor determining the performance of micro‐light emitting diodes (µLEDs). In this study, equilateral triangular III‐nitride blue µLEDs are prepared with exclusively m‐plane sidewall surfaces to confirm the impact of sidewall conditions. It is found that inductively coupled plasma‐reactive ion etching (ICP‐RIE) causes surface damages to the sidewall and results in rough surface morphology. As confirmed by time‐resolved photoluminescence (TRPL) and X‐ray photoemission spectroscopy (XPS), tetramethylammonium hydroxide (TMAH) eliminates the etching damage and flattens the sidewall surface. After ICP‐RIE, 100 µm2‐µLEDs yield higher external quantum efficiency (EQE) than 400 µm2‐µLEDs. However, after TMAH treatment, the peak EQE of 400 µm2‐µLEDs increases by ≈10% in the low current regime, whereas that of 100 µm2‐µLEDs slightly decreases by ≈3%. The EQE of the 100 µm2‐µLEDs decreases after TMAH treatment although the internal quantum efficiency (IQE) increases. Further, the IQE of the 100 µm2‐µLEDs before and after TMAH treatment is insignificant at temperatures below 150 K, above which it becomes considerable. Based on PL, XPS, scanning transmission electron microscopy, and scanning electron microscopy results, mechanisms for the size dependence of the EQE of µLEDs are explained in terms of non‐radiative recombination rate and light extraction.

The Synergy of the Buried Interface Surface Energy and Temperature for Thermal Evaporated Perovskite Light-Emitting Diodes.

Multisource coevaporation is such a promising method for the preparation of perovskite films. However, there is limited research about the effects of the buried interface on thermal-evaporated perovskite light-emitting diodes (PeLEDs). In this study, the effects of buried interfaces on thermal-evaporated all-inorganic perovskite films are systematically investigated. It is found that the low-surface-energy buried interface promotes the formation of columnar grain by suppressing heterogeneous nucleation, and functional groups on the high-surface-energy interface have a significant effect on the actual element ratio of the film. The substrate temperature can affect the nucleation and film-formation kinetics of the columnar grains. As a result of the synergistic strategy, a peak external quantum efficiency (EQE) of 8.6% is achieved in the green PeLEDs with a stable emission peak at 516 nm, which is among the best thermal-evaporated PeLEDs reported. This work provides an insight into the preparation of perovskites by thermal evaporation and builds the groundwork for future studies.

In-Situ Interfacial Reaction Induced Amino-Rich Oxide Surface to Grow High-Quality FAPbBr3 Crystals for Efficient Inverted Light-Emitting Diodes

Iodine-based perovskite light-emitting diodes (PeLEDs) utilizing zinc oxide (ZnO) films as electron-transporting layers (ETLs) show excellent efficiency and stability. However, the poor understanding of the reaction between bromine-based perovskites and ZnO films hinders the preparation of high-quality bromine-based perovskites on ZnO films. Here, we demonstrate an in situ interfacial amidation reaction between one amino group of formamidinium bromide (FABr) and sol–gel ZnO film, leaving unreacted amino groups to form an amino-rich ZnO/perovskite interface. The density of amino groups, which can regulate the crystallization of FAPbBr3, is determined by the original carboxylate groups of the ZnO film. Carboxylate groups-rich zinc–magnesium oxide film is further developed to grow high-quality FAPbBr3 crystals. The resultant inverted PeLEDs show a low turn-on voltage of 1.8 V and a peak external quantum efficiency of 12.7%, the highest efficiency reported for green-emissive PeLEDs prepared directly on ZnO-based films. This significant discovery provides a promising route toward achieving high-performance inverted bromine-based PeLEDs on oxide ETLs.