High External Quantum Efficiency Research Articles

Exploring the Critical Factors Toward Spectrally Stable Mixed‐Halide Blue Perovskite LEDs

AbstractMetal mixed‐halide perovskite has demonstrated considerable potential in the development of solution‐treated blue light‐emitting diodes (LEDs) with high external quantum efficiency, excellent color purity, and tunable wavelength. However, the severe phase segregation of mixed‐halide perovskite under bias voltage would lead to the spectral instability of LEDs. Therefore, suppressing phase segregation of Br/Cl perovskite towards spectrally stable blue perovskite LEDs (PeLEDs) is a big challenge. In this work, we systematically explore the influence of perovskite component, preparation conditions, and device structures on the spectral stability of PeLEDs. We have observed that the stable spectra increased the proportion of Cs in the A‐site cations, passivator, and the annealing temperature of perovskite films. Finally, we achieve a spectra‐stable and high‐performance blue PeLED under optimized conditions. Our findings provide important guidance for preparing spectrally stable PeLEDs.

Ligand‐Pinning Induced Size Modulation of CsPbI3 Perovskite Quantum Dots for Red Light‐Emitting Diodes

AbstractPerovskite quantum dots (PQDs) show high potential for new‐generation light‐emitting diodes (LEDs) due to their outstanding optoelectronic properties. Even though the red PQD‐LEDs can be realized through mixing halide in the PQDs to tune their spectroscopies, the PQDs may suffer from phase separation under a high electric field, predominantly affecting LED applications. Herein, a ligand‐pinning‐assisted approach is reported to tune the spectroscopies of CsPbI3 PQDs, in which vinyl phosphonic acid (VPA) is applied as function ligands to regulate the nucleation and growth of PQDs during the synthesis. Systematically experimental studies and theoretical calculations are conducted to comprehensively understand the functions of the VPA ligands during the PQD synthesis, which reveals that the VPA ligands with high binding energy with Pb2+ cations could firmly anchor on the surface matrix of PQDs without desorption, regulating the growth of PQDs and thus resulting in tunable spectroscopies being realized. Meanwhile, VPA could also renovate the defective surface matrix of PQDs, substantially diminishing trap‐induced nonradiative recombination. Consequently, red PQD‐LEDs deliver a high external quantum efficiency of 22.83%, which is significantly improved compared with the control devices. This work provides a new avenue to tune the spectroscopies of PQDs toward high‐performing LEDs.

Wavelength‐Selective Photodetector and Neuromorphic Visual Sensor Utilizing Intrinsic Defect Semiconductor

AbstractWith the rapid developments of Artificial Intelligence (AI) and the Internet of Things (IoT), increasingly intricate and expanding application scenarios are placing higher demands on current machine vision capabilities. Therefore, there is a pressing need to simultaneously achieve diverse functionalities, simple designs, and efficient computing in vision devices. Here, the study develops a two‐terminal optoelectronic device utilizing a single 2D intrinsic defect semiconductor In2S3. The device demonstrates wavelength‐selective photodetection and neuromorphic visual capabilities, attributed to defect‐related charge‐trapping/de‐trapping processes. As a photodetector, the device exhibits a high photoresponsivity of 473.6 A W−1, a high external quantum efficiency of 1.6 × 105%, and a fast rise/fall time of 0.3/1.4 ms at the wavelength of 359 nm. As an all‐in‐one neuromorphic visual device, optoelectronic‐driven fundamental synaptic functions, including paired‐pulse facilitation (PPF), short‐term plasticity (STP), long‐term plasticity (LTP), and “learning‐experience”, are successfully mimicked at the wavelength of 671 nm. Moreover, one‐shot recognition of the 12‐letter image “SHAN XI NORMAL” is achieved through an artificial convolutional neural network. This study provides a new strategy for developing compact high‐level intelligence systems for complex application scenarios.

Transition Layer Assisted Synthesis of Defect Free Amine-Phosphine Based InP QDs.

Environmentally friendly InP-based quantum dots (QDs) are promising for light-emitting diodes (LEDs) and display applications. So far, the synthesis of highly emitting InP-based QDs via safe and economically viable amine-phosphine remains a challenge. Herein, we report the synthesis of amine-phosphine based InP/ZnSe/ZnS QDs by introducing an alloyed oxidation-free In-ZnSe transition layer (TL) at the core-shell interface. The TL not only has the essential function of preventing oxidation of the core and relieving interfacial strain but also results in oriented epitaxial growth of shell. The alloyed TL significantly mitigates the nonradiative recombination at core-shell interfacial trap states, thereby boosting the photoluminescence (PL) efficiency of the QDs up to 98%. Also, the Auger recombination is suppressed, extending the biexciton lifetime from 60 to 100 ps. The electroluminescence device based on the InP-based QDs shows a high external quantum efficiency over 10%, further demonstrating high quality QDs synthesized by this process.

Recombination zone shift in OLEDs of the pyrene- phenanthroimidazole conjugate giving cyan and green emission

Phenanthroimidazole derivative with Pyrene (PhenI-Py), which is known to be a good blue emitter, has been used to make OLED devices. We report the tuning of the emission from green (peak emission at 535 nm) to cyan (peak emission at 495 nm) in OLEDs by changing the device geometry using different hole transporting layers (HTL). Cyan OLEDs reported a high external quantum efficiency (EQE) of ∼10%. By making devices with different thicknesses of the active layer and hole transporting layers (HTL), this wavelength shift could be understood on the basis of the shift in the recombination zone (RZ). Time resolved area normalized emission spectroscopy (TRANES) carried out in thin films of PhenI-Py indicated the dynamics of excited states, which seem to be responsible for the observed RZ shift. Thus, our results present an understanding of the mechanism of the observed colour tunability in devices of PhenI-Py.

Vertically Phase Separated Photomultiplication Organic Photodetectors with p-n Heterojunction Type Ultrafast Dynamic Characteristics.

Photomultiplication (PM)-type organic photodetectors (OPDs), which typically form a homogeneous distribution (HD) of n-type dopants in a p-type polymer host (HD PM-type OPDs), have achieved a breakthrough in device responsivity by surpassing a theoretical limit of external quantum efficiency (EQE). However, they face limitations in higher dark current and slower dynamic characteristics compared to p-n heterojunction (p-n HJ) OPDs due to inherent long lifetime of trapped electrons. To overcome this, we have developed a new PM-type OPD that demonstrates ultrafast dynamic properties through a vertical phase separation (VPS) strategy between the p-type polymer (host) and n-type acceptor (dopant), referred to as VPS PM-type OPDs. Notably, VPS PM-type OPDs show a remarkable increase (by three orders of magnitude) in -3dB cut-off frequency (120kHz) and over a 200-fold faster response time (rising time = 4.8 µs, falling time = 8.3 µs) compared to HD PM-type OPDs, while maintaining high EQE of 1,121% and specific detectivity of 2.53 × 1013 Jones at -10V. The VPS PM OPD represents a groundbreaking advancement by demonstrating the coexistence of p-n HJ and PM modes within a single photoactive layer for the first time. This innovative approach holds the potential to enhance both static and dynamic properties of OPDs. This article is protected by copyright. All rights reserved.

Stable and efficient CsPbI3 quantum-dot light-emitting diodes with strong quantum confinement

Even though lead halide perovskite has been demonstrated as a promising optoelectronic material for next-generation display applications, achieving high-efficiency and stable pure-red (620~635 nm) emission to cover the full visible wavelength is still challenging. Here, we report perovskite light-emitting diodes emitting pure-red light at 628 nm achieving high external quantum efficiencies of 26.04%. The performance is attributed to successful synthesizing strongly confined CsPbI3 quantum dots with good stability. The strong binding 2-naphthalene sulfonic acid ligands are introduced after nucleation to suppress Ostwald ripening, meanwhile, ammonium hexafluorophosphate exchanges long chain ligands and avoids regrowth by strong binding during the purification process. Both ligands enhance the charge transport ability of CsPbI3 quantum dots. The state-of-the-art synthesis of pure red CsPbI3 quantum dots achieves 94% high quantum efficiency, which can maintain over 80% after 50 days, providing a method for synthesizing stable strong confined perovskite quantum dots.

Ultrathin, High-Aspect-Ratio Bismuth Sulfohalide Nanowire Bundles for Solution-Processed Flexible Photodetectors.

In this study, a novel synthesis of ultrathin, highly uniform colloidal bismuth sulfohalide (BiSX where X = Cl, Br, I) nanowires (NWs) and NW bundles (NBs) for room-temperature and solution-processed flexible photodetectors are presented. High-aspect-ratio bismuth sulfobromide (BiSBr) NWs are synthesized via a heat-up method using bismuth bromide and elemental S as precursors and 1-dodecanethiol as a solvent. Bundling of the BiSBr NWs occurs upon the addition of 1-octadecene as a co-solvent. The morphologies of the BiSBr NBs are easily tailored from sheaf-like structures to spherulite nanostructures by changing the solvent ratio. The optical bandgaps are modulated from 1.91 (BiSCl) and 1.88eV (BiSBr) to 1.53eV (BiSI) by changing the halide compositions. The optical bandgap of the ultrathin BiSBr NWs and NBs exhibits blueshift, whose origin is investigated through density functional theory-based first-principles calculations. Visible-light photodetectors are fabricated using BiSBr NWs and NBs via solution-based deposition followed by solid-state ligand exchanges. High photo-responsivities and external quantum efficiencies (EQE) are obtained for BiSBr NW and NB films even under strain, which offer a unique opportunity for the application of the novel BiSX NWs and NBs in flexible and environmentally friendly optoelectronic devices.

Fabrication of broadband HgCdTe photodetectors with biomimetic insect corneal arrays

Broadband photodetectors are of great significance in a wide variety of technologically important areas. Inspired by bionics, insect cornea-mimicking microstructures could reduce surface reflection, thus enabling broadband detection. Here, we fabricate a broadband large-area (1280 × 1024) HgCdTe focal plane array photodetector based on biomimetic ZnS microarrays, which achieves high external quantum efficiency (> 60%, averaging 79%) across the broad wavelength range of 400 nm - 5000 nm. These results demonstrate that implementing biomimetic ZnS microstructures has effectively broadened the operational wavelength range of conventional HgCdTe infrared photodetectors to encompass the visible light spectrum. Our work achieves continuous visible-to-infrared spectral imaging and provides a beneficial route to fabricate broadband, large-area, high-performance photodetectors.

Gate‐Modulated and Polarization‐Sensitive Photodetector Based on the MoS2/PdSe2 Out‐Of‐Plane Van Der Waals Heterostructure

AbstractPhotodetectors with good polarization detection ability are promising in many applications, such as remote sensing imaging and environmental monitoring. However, the traditional polarization detection systems fall short in meeting integration demands of the integrated‐circuits field due to additional optical elements. The emerging 2D materials with in‐plane anisotropic structures provide a possible method to fabricate remarkable polarization detectors. Modulating the band structure by gate voltage is an important strategy for developing optoelectronic devices. Herein, a polarized photodetector based on PdSe2/MoS2 out‐of‐plane heterojunction is fabricated. Due to its unique out‐of‐plane heterostructure, the device exhibits excellent photoresponse characteristics and polarization sensitivity, including an excellent responsivity of 10.19A/W, an extremely high external quantum efficiency of 2429%, a fast rise/decay time of 68/192 µs, and a high photocurrent anisotropy ratio of 3.09. Based on the adjustment of the built‐in electric field through gate voltage, the performance of the device can be accordingly modulated. As the gate voltage increases from −30 to 30 V, the responsivity gradually increases from 7.5 to 13A/W and the detectivity increases from 1.53 to 2.63 × 109Jones. Finally, its olarization imaging ability is demonstrated at different polarization angles. The findings indicate that PdSe2/MoS2 devices exhibit significant potential for polarized photoelectric detection.

Efficient Quasi-2D Perovskite Based Blue Light-Emitting Diodes with Carbon Dots Modified Hole Transport Layer.

Quasi-2D perovskites based blue light-emitting diodes (LEDs) suffer from its poor electroluminescence performance, mainly caused by the nonradiative recombination in in defect-rich low-n phases and the unbalanced hole-electron injection in the device. Here, we developed a highly efficient quasi-2D perovskite based sky-blue LEDs behaving recorded external quantum efficiency (EQE) of 21.07% by employing carbon dots (CDs) as additives in the hole transport layer (HTL). We ascribe the high EQE to the effective engineering of CDs: (1) The CDs at the interface of HTLs can suppress the formation of low-efficient n = 1 phase, resulting a high luminescence quantum yield and energy transfer efficiency of the mixed n-phase quasi-2D perovskites. (2) The CDs additives can reduce the conductivity of HTL, partially blocking the hole injection, and thus making more balanced hole-electron injection. The CDs-treated devices have excellent Spectral stability and enhanced operational stability and could be a new alternative additive in the perovskite optoelectronic devices.

Efficient white light-emitting electrochemical cells based on quantum-dot color conversion layers with high EQE >20 %

Solid-state light-emitting electrochemical cells (LECs) offer promising benefits, including simple device architecture, low operating voltage, and insensitivity to electrode work functions. These advantages make them highly suitable for low-cost display and lighting applications, with significant potential for widespread adoption. However, great challenges remain in realizing stable and efficient white LECs. In this work, the blue LECs integrated with red or yellow/red quantum-dot (QD) color conversion layers (CCLs) are shown to achieve efficient and stable white emissions. When the blue LECs are combined with red QD CCLs, they achieve an external quantum efficiency (EQE) exceeding 20 % at a low current density of 0.003 mA cm−2. Alternatively, the blue LECs integrated with yellow/red QD CCLs deliver white emissions with a low CCT <2500 K and a high CRI up to 93 while the peak EQE at a low current density of 0.005 mA cm−2 still remains high (>16 %). The data effectively showcase that efficient and stable white emission can be achieved through partial energy down-conversion from the blue LECs to the QD CCLs, and the proposed white light sources are potential candidates for lighting applications.

Hexacarbazolylbenzene: An Excellent Host Molecule Causing Strong Guest Molecular Orientation and the High-Performance OLEDs.

Hexacarbazolylbenzene (6CzPh), which is benzene substituted by six carbazole rings, is a simple and attractive compound. Despite the success of a wide variety of carbazole derivatives in organic light-emitting diodes (OLEDs), 6CzPh has not received attention so far. Here, excellent performances of 6CzPh are revealed as a host material in OLEDs regarding conventional host materials. Various strategies are implemented to improve the performance of OLEDs, e.g., triplet utilization by thermally activated delayed fluorescence (TADF) and phosphorescence emitters for maximizing internal quantum efficiency, and molecular orientation control for increasing outcoupling efficiency. The present host material is suited for both criteria. Robustness of the structure and sufficiently high triplet energy enables a high external quantum efficiency with a long device lifetime. Besides, the host material boosts the horizontal molecular orientations of several guest emitters. It is noteworthy that disk-shaped 4CzIPN marks the complete horizontal molecular orientations (Θh = 100%, S = -0.50). These results provide an effective way of improving efficiencies without sacrificing device durability for future OLEDs.

Unlocking Cr3+-Cr3+ Coupling in Spinel: Ultrabroadband Near-Infrared Emission beyond 900 nm with High Efficiency and Thermal Stability.

Broadband near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) hold promising potential as next-generation compact, portable, and intelligent NIR light sources. Nonetheless, the lack of high-performance broadband NIR phosphors with an emission peak beyond 900 nm has severely hindered the development and widespread application of NIR pc-LEDs. This study presents a strategy for precise control of energy-state coupling in spinel solid solutions composed of MgxZn1-xGa2O4 to tune the NIR emissions of Cr3+ activators. By combining crystal field engineering and heavy doping, the Cr3+-Cr3+ ion pair emission from the 4T2 state is unlocked, giving rise to unusual broadband NIR emission spanning 650 and 1400 nm with an emission maximum of 913 nm and a full width at half-maximum (fwhm) of 213 nm. Under an optimal Mg/Zn ratio of 4:1, the sample achieves record-breaking performance, including high internal and external quantum efficiency (IQE = 83.9% and EQE = 35.7%) and excellent thermal stability (I423K/I298K = 75.8%). Encapsulating the as-obtained phosphors into prototype pc-LEDs yields an overwhelming NIR output power of 124.2 mW at a driving current of 840 mA and a photoelectric conversion efficiency (PCE) of 10.5% at 30 mA, rendering high performance in NIR imaging applications.

High External Quantum Efficiency and Dual-Band Emission of (C7H18N)3Sb2Cl9 for Sensitivity Temperature Sensing.

Organic-inorganic hybrid halides have gained attention for their ease of processing and remarkable optoelectronic properties. However, the relationship between the structure and optical properties requires further exploration. In this study, the butyltrimethylammonium cation (C7H18N+) was chosen, and seven compounds were synthesized: (C7H18N)3Sb2X9 (X = Cl, Br), (C7H18N)3Bi2X9 (X = Cl, Br, I), and (C7H18N)(C2H8N)MBr5 (M = Sb, Bi). Crystals with a single organic cation exhibit a zero-dimensional structure, while the introduction of dimethylamine ions increases the crystal dimensionality from zero-dimensional (C7H18N)3Sb2Br9 to one-dimensional (C7H18N)(C2H8N)SbBr5. Under 372 nm excitation, (C7H18N)3Sb2Cl9 showed broad orange-red single-band emission with a high photoluminescence quantum yield of 88.4% and an external quantum efficiency of up to 56.9%. A white light-emitting diode based on (C7H18N)3Sb2Cl9 achieved a high color rendering index of 96.3. Moreover, dual-band emission was observed in (C7H18N)3Sb2Cl9 under 308 nm excitation, which exhibits an absolute temperature sensitivity of 1.96 × 10-3 K-1 (320 K), and a flexible film was prepared by incorporating polydimethylsiloxane. This shows the promise of hybrid metal halides as photoluminescent materials and their possibilities for temperature sensing.

Pattern‐Matched Polymer Ligpands Toward Near‐Perfect Synergistic Passivation for High‐Performance and Stable Br/Cl Mixed Perovskite Light‐Emitting Diodes

Mixed Br/Cl perovskite nanocrystals (PeNCs) exhibit bright pure‐blue emission benefiting for fulfilling the Rec. 2100 standard. However, phase segregation remains a significant challenge that severely affects the stability and emission spectrum of perovskite light‐emitting diodes (PeLEDs). Here, we demonstrate the optimization of the spacing between polydentate functional groups of polymer ligands to match the surface pattern of CsPbBr1.8Cl1.2 PeNCs, resulting in effective synergistic passivation effect and significant improvements in PeLED performances. The block and alternating copolymers with different inter‐functional group spacing are facilely synthesized as ligands for PeNCs. Surprisingly, block copolymers with a higher functional group density do not match PeNCs, while alternating copolymers enable efficient PeNCs with the high photoluminescence intensity, low non‐radiative recombination rate and high exciton binding energy. Density functional theory calculations clearly confirm the almost perfect match between alternating copolymers and PeNCs. Finally, pure‐blue PeLEDs are achieved with the emission at 467 nm and Commission Internationale de l'Eclairage (CIE) coordinates of (0.131, 0.071), high external quantum efficiency (9.1%) and record spectral and operational stabilities (~ 80 mins) in mixed‐halide PeLEDs. Overall, this study contributes to designing the polymer ligands and promoting the development of high‐performance and stable pure‐color PeLEDs towards display applications.

Pattern-Matched Polymer Ligpands Toward Near-Perfect Synergistic Passivation for High-Performance and Stable Br/Cl Mixed Perovskite Light-Emitting Diodes.

Mixed Br/Cl perovskite nanocrystals (PeNCs) exhibit bright pure-blue emission benefiting for fulfilling the Rec. 2100 standard. However, phase segregation remains a significant challenge that severely affects the stability and emission spectrum of perovskite light-emitting diodes (PeLEDs). Here, we demonstrate the optimization of the spacing between polydentate functional groups of polymer ligands to match the surface pattern of CsPbBr1.8Cl1.2 PeNCs, resulting in effective synergistic passivation effect and significant improvements in PeLED performances. The block and alternating copolymers with different inter-functional group spacing are facilely synthesized as ligands for PeNCs. Surprisingly, block copolymers with a higher functional group density do not match PeNCs, while alternating copolymers enable efficient PeNCs with the high photoluminescence intensity, low non-radiative recombination rate and high exciton binding energy. Density functional theory calculations clearly confirm the almost perfect match between alternating copolymers and PeNCs. Finally, pure-blue PeLEDs are achieved with the emission at 467 nm and Commission Internationale de l'Eclairage (CIE) coordinates of (0.131, 0.071), high external quantum efficiency (9.1%) and record spectral and operational stabilities (~ 80 mins) in mixed-halide PeLEDs. Overall, this study contributes to designing the polymer ligands and promoting the development of high-performance and stable pure-color PeLEDs towards display applications.

Advancements in Micro-LED Performance through Nanomaterials and Nanostructures: A Review.

Micro-light-emitting diodes (μLEDs), with their advantages of high response speed, long lifespan, high brightness, and reliability, are widely regarded as the core of next-generation display technology. However, due to issues such as high manufacturing costs and low external quantum efficiency (EQE), μLEDs have not yet been truly commercialized. Additionally, the color conversion efficiency (CCE) of quantum dot (QD)-μLEDs is also a major obstacle to its practical application in the display industry. In this review, we systematically summarize the recent applications of nanomaterials and nanostructures in μLEDs and discuss the practical effects of these methods on enhancing the luminous efficiency of μLEDs and the color conversion efficiency of QD-μLEDs. Finally, the challenges and future prospects for the commercialization of μLEDs are proposed.

Intramolecular Hydrogen Bonding Rigidifying Flexible Bridge for Solution- and Vacuum-Processed TSCT-TADF Emitters.

To realize strong donor-acceptor face-to-face stacking for efficient through-space charge transfer-type thermally activated delayed fluorescence, a conceptually new design strategy is proposed to couple flexible bridges with adequate rigidity via built-in intramolecular hydrogen bonds (IHBs). The resulting emitter ACE-CN has a planarized benzyl methyl ether bridge self-anchored by the C-H···O IHB and shows a high photoluminescence quantum efficiency of 93%. The solution- and vacuum-processed devices exhibited high external quantum efficiencies of 11.8% and 24.7%, respectively.

Fine-Tuning Crystal Structures of Lead Bromide Perovskite Nanocrystals through Trace Cadmium(II) Doping for Efficient Color-Saturated Green LEDs.

Decreasing perovskite nanocrystal size increases radiative recombination due to the quantum confinement effect, but also increases the Auger recombination rate which leads to carrier imbalance in the emitting layers of electroluminescent devices. Here, we overcome this trade-off by increasing the exciton effective mass without affecting the size, which is realized through the trace Cd2+ doping of formamidinium lead bromide perovskite nanocrystals. We observe an ~2.7 times increase in the exciton binding energy benefiting from a slight distortion of the [BX6]4- octahedra caused by doping in the case of that the Auger recombination rate is almost unchanged. As a result, bright color-saturated green emitting perovskite nanocrystals with a photoluminescence quantum yield of 96 % are obtained. Cd2+ doping also shifts up the energy levels of the nanocrystals, relative to the Fermi level so that heavily n-doped emitters convert into only slightly n-doped ones; this boosts the charge injection efficiency of the corresponding light-emitting diodes. The light-emitting devices based on those nanocrystals reached a high external quantum efficiency of 29.4 % corresponding to a current efficiency of 123 cd A-1, and showed dramatically improved device lifetime, with a narrow bandwidth of 22 nm and Commission Internationale de I'Eclairage coordinates of (0.20, 0.76) for color-saturated green emission for the electroluminescence peak centered at 534 nm, thus being fully compliant with the latest standard for wide color gamut displays.