Quantum Efficiency Research Articles

Facile Nanowelding Process for Silver Nanowire Electrodes Toward High‐Performance Large‐Area Flexible Organic Light‐Emitting Diodes

AbstractDespite considerable interest, uniform and robust flexible transparent conducting electrodes (FTCEs) that can be seamlessly integrated and used for highly efficient large‐area flexible oganic light‐emitting diodes (OLEDs) remain elusive. In this study, a large‐area fabrication of uniform transparent electrodes for high‐performance flexible OLEDs by exploiting the rapid nanowelding process of silver nanowires (AgNWs) onto polyethylene terephthalate substrate under Xe‐lamp irradiation and mechanical pressing treatment is reported. The performance of AgNWs FTCEs is significantly enhanced by applying the Xe‐lamp beam irradiation for 5 s and subsequent compression at 20 MPa for 15 s, achieving a low sheet resistance of 26.5 Ω sq−1, a high transmittance of 95.2% (at 550 nm), and very smooth surfaces with root‐mean‐square of 5.4 nm. Meanwhile, the nanowelded AgNWs FTCEs maintain excellent electrical conductivity (only a 2.96% increase in ΔR/R0) after 1000 bending cycles. The resulting AgNWs FTCEs‐based green phosphorescent OLED achieves an unprecedented external quantum efficiency (EQE) of 23.7% and a current efficiency as high as 81.5 cd A−1. Benefiting from the uniform properties for resulting AgNWs FTCEs, the fabricated flexible OLED with a large area of 25 × 25 mm2 still retains a high EQE of 22.2% and a current efficiency of 78.0 cd A−1.

Efficient Charge Injection for Perovskite Light‐Emitting Transistor

AbstractMetal halide perovskite semiconductors have demonstrated remarkable performance in light‐emitting‐diode applications in recent years. However, their potential application in other emerging optoelectronic devices, such as light‐emitting field‐effect transistors (LEFETs) is impeded by poor luminous efficiency due to inefficient charge injection. Here, an n‐type MgZnInO (MIZO) as the channel layer is synthesized to achieve efficient electron injection in perovskite LEFETs. These findings indicate that the incorporation of Mg not only suppresses the generation of oxygen vacancies but also optimizes the energy level alignment. These synergistic effects reduce non‐radiative recombination and improve interfacial charge transport. Consequently, the MIZO‐based perovskite LEFETs exhibit an improvement in threshold voltage, subthreshold swing, and field‐effect mobility. The electroluminescence performance shows a peak external quantum efficiency (EQE) of 1.97% with a maximum brightness of 2.1 × 104 cd m−2, accompanied by low‐efficiency roll‐off (an EQE of 1.88% at the current density of 810 mA cm−2). To the best of the author's knowledge, this represents the best luminous efficiency reported for perovskite LEFETs to date.

UV‐A/B High‐Sensitivity Organic Photodetectors Containing Butterfly‐Shaped Furan‐Fused BN‐Dihydropyrene with Push‐Pull Electron “Wings” toward Image Sensor

AbstractReplacement of C─C unit with its isoelectronic B─N unit in aromatics provides a new class of molecules with appealing properties. Herein, Five novel butterfly‐shaped furan‐fused bis‐BN dihydropyrenes (FBN) derivatives are synthesized with different push‐pull electron “wings”. These compounds exhibit prominent UV‐A/B absorption, high energy levels, and p‐type characteristics. Thanks to the side‐chain engineering and BN dipole manipulation, their intramolecular dipole moments and intermolecular stacking mode are effectively regulated to improve intra‐ and inter‐molecular charge transfer, thus achieving high hole mobilities. Five FBN‐X compounds are doped with PC71BM as heterojunction photosensitive layers to fabricate solution‐processed high performance organic photodetectors (OPDs), which exhibit self‐powered effect and high sensitivity to UV‐A/B. Especially, the FBN‐CN‐based device presents a high detectivity up to 1.72 × 1012 Jones, a peak external quantum efficiency of 19.1%, and an extremely low dark current density of 8.90 × 10−10 A cm−2 under 320 nm at 0 V. To the best of authors knowledge, it is the first report of photodiode‐type UV‐OPDs containing BN‐doped polycyclic aromatic hydrocarbons as active layer to date. And the optimal device shows a significant advantage over the reported 300–380 nm UV‐OPDs. In addition, a 10 × 10 array of organic image sensor is successfully demonstrated, which showcases excellent low‐light imaging capability.

Quantum‐Dots Matrix Encapsulated CsPbI3 Polycrystal Composite Films for Efficient and Bright Deep‐Red Light‐Emitting Diodes

AbstractAll‐inorganic CsPbI3 perovskite is a promising emitter for deep‐red light‐emitting diodes (LEDs). However, presently fabricated CsPbI3 polycrystalline films are composed of island‐like polycrystals, encountering the problems of serious interface current leakage and low‐efficiency carrier radiative recombination. Here, a CsPbI3‐xBrx quantum dots (QDs) matrix encapsulated CsPbI3 polycrystal film is reported to address the low‐efficiency issue of island‐like CsPbI3 polycrystalline film applied in deep‐red LEDs. The developed QDs matrix encapsulation strategy has two benefits. One is the filling of void space in the island‐like CsPbI3 polycrystal film to suppress the interface current leakage. The other more important benefit is utilizing the strong carrier confinement effect of QDs to strengthen the formation of excitons in the composite film and thus improve the electroluminescence efficiency. Moreover, interesting grain growth is found between CsPbI3‐xBrx QDs and CsPbI3 polycrystals, which further enhances the exciton transfer effect brought by the QDs matrix and optoelectronic properties of the fabricated composite films. Based on the obtained high‐quality QDs/polycrystal composite films, efficient and bright deep‐red LEDs are achieved with a peak external quantum efficiency of 15.24% and a maximum luminance of 3691 cd m−2.

Harnessing the Power of Light: The Synergistic Effects of Crystalline Carbon Nitride and Ti3C2Tx MXene in Photocatalytic Hydrogen Production

AbstractPhotocatalytic hydrogen evolution is an environmentally friendly means of energy generation. Although g‐C3N4 possesses fascinating features, its inherent shortcomings limit its photocatalytic applications. Therefore, modifying the intrinsic properties of g‐C3N4 and introducing cocatalysts are essential to ameliorate the photocatalytic efficiency. To achieve this, metal‐like Ti3C2Tx is integrated with crystalline g‐C3N4 via a combined salt‐assisted and freeze‐drying approach to form crystalline g‐C3N4/Ti3C2Tx (CCN/TCT) hybrids with different Ti3C2Tx loading amounts (0, 0.2, 0.3, 0.4, 0.5, 1, 5, 10 wt.%). Benefiting from the crystallization of CN, as evidenced by the XRD graph, and the marvelous conductivity of Ti3C2Tx supported by EIS plots, CCN/TCT/Pt loaded with 0.5 wt.% Ti3C2Tx displays an elevated H2 (2) should be subscripted evolution rate of 2651.93 µmol g−1 h−1 and a high apparent quantum efficiency of 7.26% (420 nm), outperforming CN/Pt, CCN/Pt, and other CCN/TCT/Pt hybrids. The enhanced performance is attributed to the synergistic effect of the highly crystalline structure of CCN that enables fleet charge transport and the efficient dual cocatalysts, Ti3C2Tx and Pt, that foster charge separation and provide plentiful active sites. This work demonstrates the potential of CCN/TCT as a promising material for hydrogen production, suggesting a significant advancement in the design of CCN heterostructures for effective photocatalytic systems.

Detection performance of flower-like hydrothermally synthesized ZnO in silicon-type photodetector

Zinc oxide (ZnO) is a versatile compound or metal oxide with a wide range of applications across various industries such as electronics, optoelectronics, and gas sensors, etc. A simple hydrothermal method was used to synthesize ZnO flower-like structures in this study. The synthesized ZnO structures were analyzed by x-ray diffractometer (XRD) and scanning electron microscope (SEM). We used ZnO structures as an interfacial layer for a Schottky-type silicon-based photodetector. While Au and Al metals were employed as metallic and ohmic contacts, respectively, p-Si was utilized as a semiconductor and substrate. Thus, Au/ZnO/p-Si sandwich was successfully fabricated and tested by current–voltage (I–V) measurements under dark and various light power illumination densities from 10 mW cm−2 to 150 mW cm−2 as well as the various wavelengths in the case of same power. The I–V characteristics were used to determine the diode and photodetection parameters. The fabricated heterostructure exhibited 77.51 mA W−1 responsivity, 1.30 × 1010 Jones specific detectivity, and 26.33% external quantum efficiency (EQE) values.

Efficient Green Spin Light-Emitting Diodes Enabled by Ultrafast Energy- and Spin-Funneling in Chiral Perovskites.

Introducing molecular chirality into perovskite crystal structures has enabled the control of carrier spin states, giving rise to circularly polarized luminescence (CPL) in thin films and circularly polarized electroluminescence (CPEL) in LEDs. Spin-LEDs can be fabricated either through a spin-filtering layer enabled by chiral-induced spin selectivity or a chiral emissive layer. The former requires a high degree of spin polarization and a compatible spinterface for efficient spin injection, which might not be easily integrated into LEDs. Alternatively, a chiral emissive layer can also generate circularly polarized electroluminescence, but the efficiency remains low and the fundamental mechanism is elusive. In this work, we report an efficient green LED based on quasi-two-dimensional (quasi-2D) chiral perovskites as the emitting layer (EML), where CPEL is directly produced without separate carrier spin injection. The optimized chiral perovskite thin films exhibited strong CPL at 535 nm with a photoluminescence quantum yield (PLQY) of 91% and a photoluminescence dissymmetry factor (glum) of 8.6 × 10-2. Efficient green spin-LEDs were successfully demonstrated, with a large EL dissymmetry factor (gEL) of 7.8 × 10-2 and a maximum external quantum efficiency (EQE) of 13.5% at room temperature. Ultrafast transient absorption (TA) spectroscopic study shows that the CPEL is generated from a rapid energy transfer accompanied by spin transfer from 2D to 3D perovskites. Our study not only demonstrates a reliable approach to achieve high performance spin-LEDs but also reveals the fundamental mechanism of CPEL with an emissive layer of chiral perovskites.

High‐Performance SiC/Graphene UV‐Visible Band Photodetectors with Grating Structure and Asymmetrical Electrodes for Optoelectronic Logic Gate

AbstractHigh‐quality epitaxial graphene is prepared on semi‐insulated 4H‐SiC (0001) by ultra‐high vacuum thermal decomposition method and used in graphene/SiC/graphene ultraviolet‐visible dual‐band photodetectors. The dual‐band detector exhibits an extremely low dark current (5.2 × 10−14 A) and a peak responsivity of 1.17 A W−1 corresponding to an external quantum efficiency of 518%. A high detectivity of 3.14 × 1014 Jones is achieved under 280 nm light illumination at 30 V, while a high response speed is obtained with a rise time of 25.17 ns and a decay time of 540.10 ns. The detector shows a responsivity of 1.4 × 10−5 A W−1 and a detectivity of 6.5 × 109 Jones under 430 nm light illumination. The dual‐band detector equipped with SiC grating and asymmetrical graphene electrodes is demonstrated for high‐performance optoelectronic logic “AND” gate with high detectivity at 280 and 430 nm.

Deep-Blue and Fast Delayed Fluorescence from Carbene-Metal-Amides for Highly Efficient and Stable Organic Light-Emitting Diodes.

Linear gold complexes of the "carbene-metal-amide" (CMA) type are prepared with a rigid benzoguanidine amide donor and various carbene ligands. These complexes emit in the deep-blue range at 424 and 466nm with 100% quantum yields in all media. The deep-blue thermally activated delayed fluorescence (TADF) originates from a charge transfer state (CT) with an excited state lifetime as low as 213ns, resulting in fast radiative rates of 4.7 × 106 s-1. The high thermal and photo-stability of these CMA materials enabled us to fabricate highly energy efficient organic light-emitting diodes (OLED) in host-guest architectures. We report deep-blue OLED devices with electroluminescence at 416nm and 457nm with practical external quantum efficiencies of up to 23% at 100cd m-2 with excellent colour coordinates CIE (x; y) = 0.16; 0.07 and 0.17; 0.18. The operating stability of these OLEDs is the longest reported to date (LT50 = 1 hour) for deep-blue CMA emitters, indicating a high promise for further development of blue OLED devices. Our findings inform the molecular design strategy and correlation between delayed luminescence with high radiative rates and CMA OLED device operating stability. This article is protected by copyright. All rights reserved.

Spin-orbit-splitting-driven nonlinear Hall effect in NbIrTe4

The Berry curvature dipole (BCD) serves as a one of the fundamental contributors to emergence of the nonlinear Hall effect (NLHE). Despite intense interest due to its potential for new technologies reaching beyond the quantum efficiency limit, the interplay between BCD and NLHE has been barely understood yet in the absence of a systematic study on the electronic band structure. Here, we report NLHE realized in NbIrTe4 that persists above room temperature coupled with a sign change in the Hall conductivity at 150 K. First-principles calculations combined with angle-resolved photoemission spectroscopy (ARPES) measurements show that BCD tuned by the partial occupancy of spin-orbit split bands via temperature is responsible for the temperature-dependent NLHE. Our findings highlight the correlation between BCD and the electronic band structure, providing a viable route to create and engineer the non-trivial Hall effect by tuning the geometric properties of quasiparticles in transition-metal chalcogen compounds.

Individual Tuning of Directional Emission and Luminance of a Quantum Emitter in a Composite Plasmonic Antenna

High directional emission and high radiative quantum efficiency are strongly needed when moving a single optical nano-emitter (such as a quantum dot) into the practical realm. However, a typical optical nano-emitter struggles to meet the requirements above, which limits its practical applications in next-generation nano-photonic devices such as single-photon sources. Here, to achieve these features simultaneously, we propose and theoretically investigate a composite plasmonic antenna consisting of a hemispherical solid immersion lens (SIL) and a bowtie plasmonic nano-antenna, wherein a high directional emission of 10° and 2.5 × 103 of Purcell factor have both been enabled. Moreover, we find that directionality and the Purcell factor can be manipulated independently in our antenna, which provides a novel platform for the optimization of single-photon sources.

Boosting External Quantum Efficiency to 12.0% of an Ultraviolet OLED by Engineering the Horizontal Dipole Orientation of a Hot Exciton Emitter

Currently, much research effort has been devoted to improving the exciton utilization efficiency and narrowing the emission spectra of ultraviolet (UV) fluorophores for organic light‐emitting diode (OLED) applications, while almost no attention has been paid to optimizing their light out‐coupling efficiency. Here, we developed a linear donor‐acceptor‐donor (D‐A‐D) triad, namely CDFDB, which possesses high‐lying reverse intersystem crossing (hRISC) property. Thanks to its integrated narrowband UV photoluminescence (PL) (λPL: 397 nm; FWHM: 48 nm), moderate PL quantum yield (φPL: 72%, Tol), good triplet hot exciton (HE) conversion capability, and large horizontal dipole ratio (Θ//: 92%), the OLEDs based on CDFDB not only can emit UV electroluminescence with relatively good color purity (λEL: 398 nm; CIEx,y: 0.161, 0.040), but also show a record maximum external quantum efficiency (EQEmax) of 12.0%. This study highlights the important role of horizontal dipole orientation engineering in the molecular design of HE UV‐OLED fluorophores.

Advancing Detectivity and Stability of Near-Infrared Organic Photodetectors via a Facile and Efficient Cathode Interlayer.

Near-infrared (NIR) organic photodetectors (OPDs) are pivotal in numerous technological applications due to their excellent responsivity within the NIR region. Polyethylenimine ethoxylated (PEIE) has conventionally been employed as an electron transport layer (hole-blocking layer) to suppress dark current (JD) and enhance charge transport. However, the limitations of PEIE in chemical stability, processing conditions, environmental impact, and absorption range have spurred the development of alternative materials. In this study, we introduced a novel solution: a hybrid of sol-gel zinc oxide (ZnO) and N,N'-bis(N,N-dimethylpropan-1-amine oxide)perylene-3,4,9,10-tetracarboxylic diimide (PDINO) as the electron transport layer for NIR-OPDs. Our fabricated OPD exhibited significantly improved responsivity, reduced internal traps, and enhanced charge transfer efficiency. The detectivity, spanning from 400 to 1100 nm, surpassed ∼5 × 1012 Jones, reaching ∼1.1 × 1012 Jones at 1000 nm, accompanied by an increased responsivity of 0.47 A/W. Also, the unpackaged OPD remarkedly demonstrated stable JD and external quantum efficiency (EQE) over 1000 h under dark storage conditions. This innovative approach not only addresses the drawbacks of conventional PEIE-based OPDs but also offers promising avenues for the development of high-performance OPDs in the future.

Boosting External Quantum Efficiency to 12.0% of an Ultraviolet OLED by Engineering the Horizontal Dipole Orientation of a Hot Exciton Emitter.

Currently, much research effort has been devoted to improving the exciton utilization efficiency and narrowing the emission spectra of ultraviolet (UV) fluorophores for organic light-emitting diode (OLED) applications, while almost no attention has been paid to optimizing their light out-coupling efficiency. Here, we developed a linear donor-acceptor-donor (D-A-D) triad, namely CDFDB, which possesses high-lying reverse intersystem crossing (hRISC) property. Thanks to its integrated narrowband UV photoluminescence (PL) (λPL: 397 nm; FWHM: 48 nm), moderate PL quantum yield (φPL: 72%, Tol), good triplet hot exciton (HE) conversion capability, and large horizontal dipole ratio (Θ//: 92%), the OLEDs based on CDFDB not only can emit UV electroluminescence with relatively good color purity (λEL: 398 nm; CIEx,y: 0.161, 0.040), but also show a record maximum external quantum efficiency (EQEmax) of 12.0%. This study highlights the important role of horizontal dipole orientation engineering in the molecular design of HE UV-OLED fluorophores.

Optimization of near-infrared luminescence performance in Cr3+-doped double perovskite Sr2ScTaO6 phosphor by Nb5+ ion substitution

Here, Nb5+ were partially substituted for Ta5+ in the double perovskite Sr2ScTaO6: Cr3+ phosphor to improve its luminescence performance and finally obtained the optimized phosphor Sr2ScTa0.6Nb0.4O6: Cr3+. The structure, substitution mechanism, luminescence optimization mechanism, crystal field, and thermal stability of the phosphor were all thoroughly explored. The results indicate that introducing Nb5+ into Sr2ScTaO6: Cr3+ can cause lattice distortion in the host, and the distorted crystal lattice can break the forbidden transition of Cr3+, thereby enhancing its absorption of excitation light. At the same time, the full width at half maximum of the phosphor emission increased from 176.4 nm to 179.7 nm. And the internal quantum efficiency, absorption efficiency, and external quantum efficiency of the optimized Sr2ScTa0.6Nb0.4O6: Cr3+ phosphor can reach 86.3%, 49% and 42.3%, respectively. The photoelectric conversion efficiency of the optimized pc-LED increased from 5.63% to 7.80%@100 mA, indicating the introduction of Nb5+ in Sr2ScTaO6: Cr3+ improved the luminescence performance of phosphor. The above results provide directions for the development of more efficient and promising double-perovskite NIR phosphors.

Self-powered stable high-performance UV-Vis-NIR broadband photodetector based on PVP-Cobalt@Carbon nanofibers/n-GaAs heterojunction.

The self-powered PVP-Co@C nanofibers/n-GaAs heterojunction photodetector (HJPD) was fabricated by electrospinning of the PVP-Co@C nanofibers onto GaAs. An excellent rectification ratio of 6.60×106 was obtained from I-V measurements of the device in the dark. The I-V measurements of the fabricated device under 365 nm, 395 nm and 850 nm lights, as well as I-V measurements in visible light depending on the light intensity, were performed. The HJPD demonstrated excellent photodetection performance in terms of a good responsivity of ∼ 225 mA/W (at -1.72 V) and at zero bias, an impressive detectivity of 6.28×1012 Jones, and a high on/off ratio of 8.38×105, all at 365 nm wavelength. In addition, the maximum external quantum efficiency and NPDR values were 3495% (V=-1.72 V) and 2.60×1010 W-1 (V=0.0 V), respectively, while the minimum NEP value was ∼10-14 W.Hz-1/2 for 365 nm at V=0.V volts. The HJPD also exhibited good long-term stability in air after 30 days without any encapsulation.&#xD.

Amorphous Ga2O3-based solar-blind photodetectors on crystalline and amorphous substrates: A comparative study

Amorphous Ga2O3 thin films were deposited on SiO2 and sapphire substrates by pulsed magnetron sputtering (PSD) at room temperature, respectively. Corresponding amorphous Ga2O3 thin film photodetectors were prepared. The oxygen vacancies and defects of the interface between films and substrates were found to determine the discrepancy by comparing the performance between these two photodetectors. Amorphous Ga2O3 photodetectors on SiO2 had highly performances with a responsivity of 417 A/W, detectivity of 7.84 × 1012 Jones, and external quantum efficiency of 2.01 × 105 %.

Enhanced photovoltaic response in WSe2 photodetector with asymmetric two-dimensional contacts

Asymmetric contact pairs with different work functions provide an efficient method to extract photogenerated carriers in optoelectrical devices. Specifically, vertical optoelectrical devices based on two-dimensional (2D) materials utilize graphene layers as the bottom and top contacts. Whereas an additional terminal is required for electrostatic doping in either top or bottom graphene to enlarge the built-in electric field. Herein, we present an enhanced photovoltaic response in a vertical WSe2 photodetector utilizing asymmetric 2D contacts. A graphite layer and a degenerate SnSe2 are used as the top and bottom contacts, respectively, with a significant difference in their work functions. By establishing a large built-in electric field across the vertical WSe2 layer, a strong photovoltaic effect is achieved, resulting in an open-circuit voltage of 0.37 V and a short-circuit current of 0.42 μA under 532 nm illumination. The device shows high-performance photodetection characteristics, with a responsivity of 32.04 A W−1, external quantum efficiency of 7475%, and specific detectivity of 3.61 × 1012 Jones. Furthermore, the device can generate a maximum output electrical power of 70.9 nW, enabling a high-power conversion efficiency of 3.5%.

226 nm far‐ultraviolet‐C light emitting diodes with an emission power over 2 mW

Far‐ultraviolet‐C (far‐UVC) light emitting diodes (LED) emitting at an emission wavelength of 226 nm with different n‐AlGaN contact layers, quantum well barriers, and quantum well numbers are compared regarding their emission power, operation voltage, and lifetime. Electroluminescence measurements show higher emission power but also an increased operation voltage with increasing Al mole fraction in the n‐AlGaN contact layer. Furthermore, it was found that both the mean emission power and the device lifetime decrease with increasing Al mole fraction (82 % to 89 %) of the quantum well barriers and therefore with increasing barrier height. Finally, 226 nm LEDs with 6 and 9 quantum wells were compared. It was observed that the sample with 9 quantum wells shows an around 30 % lower mean emission power but on the other hand the L70 lifetime of these LEDs is higher by a factor of around five. Based on these optimizations, 226 nm LEDs with a maximum external quantum efficiency of 0.28 % (wall plug efficiency of 0.18 %) as well as an emission power of 2.1 mW and an operation voltage of 9.6 V at 200 mA were realized.This article is protected by copyright. All rights reserved.

MMC Array to Study X-Ray Transitions in Muonic Atoms

AbstractThe QUARTET collaboration aims to significantly improve the precision of the absolute nuclear charge radii of light nuclei from Li to Ne by using an array of metallic magnetic calorimeters to perform high-precision X-ray spectroscopy of low-lying states in muonic atoms. A proof-of-principle measurement with lithium, beryllium and boron is planned for fall 2023 at the Paul Scherrer Institute. We discuss the performance achieved with the maXs-30 detector module to be used. To place the detector close to the target chamber where the muon beam will impact the material under study, we have developed a new dilution refrigerator sidearm. We further discuss the expected efficiency given the transparency of the X-ray windows and the quantum efficiency of the detector. The expected muonic X-ray rate combined with the high resolving power and detection efficiency of the detector suggest that QUARTET will be able to study the de-excitation of light muonic atoms at an unprecedented level, increasing the relative energy resolution by up to a factor of 20 compared to conventional detector techniques.