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Comparison of size-dependent characteristics of blue and green InGaN microLEDs down to 1a?? <b> <i>??</i> </b> m in diameter
摘要： There is growing interest in microLED devices with lateral dimensions between 1 and 10 lm. However, reductions in external quantum ef?ciency (EQE) due to increased nonradiative recombination at the surface become an issue at these sizes. Previous attempts to study size-dependent EQE trends have been limited to dimensions above 5 lm, partly due to fabrication challenges. Here, we present size-dependent EQE data for InGaN microLEDs down to 1 lm in diameter fabricated using a process that only utilizes standard semiconductor processing techniques (i.e., lithography and etching). Furthermore, differences in EQE trends for blue and green InGaN microLEDs are compared. Green wavelength devices prove to be less susceptible to reductions in ef?ciency with the decreasing size; consequently, green devices attain higher EQEs than blue devices below 10 lm despite lower internal quantum ef?ciencies in the bulk material. This is explained by smaller sur- face recombination velocities with the increasing indium content due to enhanced carrier localization.
关键词： InGaN,microLEDs,size-dependent characteristics,external quantum efficiency,blue and green wavelengths
更新于2025-09-23 15:19:57
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Hybrid chemical bath deposition-CdS/sputter-Zn(O,S) alternative buffer for Cu <sub/>2</sub> ZnSn(S,Se) <sub/>4</sub> based solar cells
摘要： To replace the conventionally used CdS buffers in Cu2ZnSn(S,Se)4 (CZTSSe) based thin-film solar cells, sputtered Zn(O,S) buffer layers have been investigated. Zn(O,S) layers with three different [O]/([O] + [S]) ratios (0.4, 0.7, and 0.8)—and a combination of Zn(O,S) and CdS (“hybrid buffer layer”) were studied. In comparison to the CdS reference, the external quantum efficiency (EQE) of the Zn(O,S)-buffered devices increases in the short- and long-wavelength regions of the spectrum. However, the average EQE ranges below that of the CdS reference, and the devices show a low open-circuit voltage (VOC). By adding a very thin CdS layer (5 nm) between the absorber and the Zn(O,S) buffer, the VOC loss is completely avoided. Using thicker intermediate CdS layers result in a further device improvement, with VOC values above those of the CdS reference. X-ray photoelectron spectroscopy (XPS) measurements suggest that the thin CdS layer prevents damage to the absorber surface during the sputter deposition of the Zn(O,S) buffer. With the hybrid buffer configuration, a record VOC deficit, i.e., a minimum difference between bandgap energy Eg (divided by the elementary charge q) and VOC (Eg/q – VOC) of 519 mV could be obtained, i.e., the lowest value reported for kesterite solar cells to date. Thus, the hybrid buffer configuration is a promising approach to overcome one of the main bottlenecks of kesterite-based solar cells, while simultaneously also reducing the amount of cadmium needed in the device.
关键词： VOC deficit,Cu2ZnSn(S,Se)4,CdS,hybrid buffer layer,open-circuit voltage,X-ray photoelectron spectroscopy,thin-film solar cells,Zn(O,S) buffer layers,external quantum efficiency
更新于2025-09-23 15:19:57
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AlGaN deep-ultraviolet light-emitting diodes grown on SiC substrates
摘要： The disinfection industry would greatly benefit from efficient, robust, high-power deep-ultraviolet light-emitting diodes (UV-C LEDs). However, the performance of UV-C AlGaN LEDs is limited by poor light-extraction efficiency (LEE) and the presence of a large density of threading dislocations. We demonstrate high power AlGaN LEDs grown on SiC with high LEE and low threading dislocation density. We employ a crack-free AlN buffer layer with low threading dislocation density and a technique to fabricate thin-film UV LEDs by removing the SiC substrate, with a highly selective SF6 etch. The LEDs (278 nm) have a turn-on voltage of 4.3 V and a CW power of 8 mW (82 mW/mm2) and external quantum efficiency (EQE) of 1.8% at 95 mA. KOH submicron roughening of AlN surface (nitrogen-polar) and improved p-contact reflectivity are found to be effective in improving the LEE of UV light. We estimate the improved LEE by semi-empirical calculations to be 33% (without encapsulation). This work establishes UV LEDs grown on SiC substrates as a viable architecture to large-area, high-brightness, and high power UV LEDs.
关键词： AlGaN LEDs,UV-C LEDs,light extraction efficiency,disinfection technology,AlN,external quantum efficiency,SiC,substrate removal
更新于2025-09-19 17:13:59
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High-efficiency perovskite nanocrystal light-emitting diodes <i>via</i> decorating NiO <sub/>x</sub> on the nanocrystal surface
摘要： Nickel oxides exhibit a great potential as hole transport layers for the fabrication of efficient perovskite light-emitting diodes (LEDs) due to their high carrier mobility and good energy band matching with perovskite nanocrystals. In this work, nickel oxides were directly decorated on the CsPbBr3 nanocrystal surface through adsorption and a sequential oxidation treatment. The resulting sample shows a high photoluminescence quantum-yield of 82%. The LED using CsPbBr3 nanocrystals with nickel oxides achieves a high external quantum efficiency (EQE) of up to 16.8% with a low turn-on voltage of 2.8 V, which is much superior to that of the counterpart LED based on pristine CsPbBr3 nanocrystals (EQE = 0.7%, turn-on voltage = 5.6 V). The excellent performance of the nickel oxide decorated CsPbBr3 nanocrystal device could be attributed to the better energy level matching between the decorated nanocrystals and the transport layers of the device and more balanced charge carrier injection. Furthermore, the operational lifetime of the nickel oxide decorated CsPbBr3 nanocrystal device is 40 times longer than that of the pristine CsPbBr3 nanocrystal device.
关键词： perovskite nanocrystals,photoluminescence quantum-yield,light-emitting diodes,external quantum efficiency,nickel oxides
更新于2025-09-19 17:13:59
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Four-membered red iridium( <scp>iii</scp> ) complexes with Ira??Sa??Ca??S structures for efficient organic light-emitting diodes
摘要： Three sulfur atom contained ligands (diphenylcarbamodithioate (dpdtc), di-p-tolylcarbamodithioate (medtc) and bis(4-(trifluoromethyl)phenyl)carbamodithioate (cf3dtc)) were prepared for three red iridium(III) complexes. All (tfmpqz)2Ir(dpdtc), (tfmpqz)2Ir(medtc) and (tfmpqz)2Ir(cf3dtc) complexes were synthesized rapidly at room temperature in 5 min with high yields owing to strong coordination ability between sulfur and iridium atoms, in which 4-(4-(trifluoromethyl)phenyl)quinazoline (tfmpqz) was used as main ligand. Three Ir(III) complexes show distinct PL emissions at the range of 617 - 629 nm with high phosphorescence quantum yields up to of 83%, respectively. With these complexes as dopants, the organic light-emitting devices (OLEDs) with the double-emissive-layer structure of ITO/ HATCN (hexaazatriphenylenehexacabonitrile, 5 nm)/ TAPC ((bis(4-(N,N-ditolylamino)phenyl)cyclohexane, 30 nm)/ Ir(III) complexes: TCTA (4,4',4''-tris(carbazol-9-yl)-triphenylamine) (12 wt%, 10 nm)/ Ir(III) complexes: 26DCzppy (2,6-bis-(3-(carbazol-9-yl)phenyl)pyridine) (12 wt%, 10 nm)/ TmPyPB (1,3,5-tri((3-pyridyl)-phen-3-yl)benzene, 30 nm)/ LiF (1 nm)/ Al (100 nm) achieved good performances. In particular, the device employing (tfmpqz)2Ir(cf3dtc) complex exhibits the champion performances with a maximum luminance of 30 740 cd m-2 and a maximum external quantum efficiency of 26.10%, respectively.
关键词： phosphorescence quantum yields,sulfur atom,iridium(III) complexes,external quantum efficiency,OLEDs
更新于2025-09-19 17:13:59
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The Structure Optimization of Phenanthroimidazole Based Isomers with External Quantum Efficiency Approaching 7% in non-doped Blue OLEDs
摘要： In this work, four phenantroimidazole (PI) based isomers TPA-PPI-PBI, TPA-PPI-NPBI, PBI-PPI-TPA and NPBI-PPI-TPA for high-efficiency deep-blue organic light-emitting diodes (OLEDs) have been designed and synthesized. The structure-property relationship is systematically studied. Devices based on TPA-PPI-PBI, TPA-PPI-NPBI, PBI-PPI-TPA and NPBI-PPI-TPA achieved deep-blue emissions with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.15, 0.07), (0.15, 0.07), (0.15, 0.09) and (0.15, 0.05) and high external quantum efficiencies (EQEmax) of 4.12%, 4.66%, 6.88% and 5.59%, respectively. Especially the PBI-PPI-TPA based device exhibited negligible efficiency roll-off with EQE 6.48% at practical 1000 cd m-2. Moreover, the EQE is still above 5% even at a high brightness of 10,000 cd m-2. Comparing the four isomers, we found that substituent at the C2 position of PI core has a significant influence on the emission wavelength and CIE coordinates. This work provides a rational design strategy that modifying electron acceptor (A) at the C2 position and electron donor (D) at the N1 position of PI core will be an effective way to fabricate high-performance PI-based bipolar emitters.
关键词： deep-blue,isomers,phenanthroimidazole,external quantum efficiency,OLEDs
更新于2025-09-19 17:13:59
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Analysis of dominant non-radiative recombination mechanisms in InGaN green LEDs grown on silicon substrates
摘要： Relationship between the external quantum efficiency (EQE) curves and the dominant non-radiative recombination mechanisms of InGaN green LEDs grown on silicon substrates were investigated. Through the analysis of the ABC+(cid:1)(cid:2)(cid:3)(cid:4) model, the significant drop in EQE at low current levels is due to an increasingly defect-related Shockley-Read-Hall (SRH) recombination. Under extremely low current densities, the defect traps can even become the dominant channel for the leakage current through the tunneling process, thereby reducing the efficiency of carrier injection into the active region. These observations were further supported by the carrier lifetime measurement. However, this fails to explain the droop in EQE at high current densities, especially when SRH recombination has been saturated. Our results show that carrier leakage has becomes dominant at high current density when Auger recombination has been less impossible. Reduced carrier leakage may lead to increased carrier injection efficiency, which in turn alleviates EQE droop.
关键词： silicon substrates,InGaN,non-radiative recombination,green LEDs,external quantum efficiency,carrier leakage
更新于2025-09-19 17:13:59
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Industrial Applications of Nanomaterials || Nanomaterials-based UV photodetectors
摘要： Photodetectors are essential elements applied in video imaging, optical communications, biomedical imaging, security, night-vision, gas sensing, and motion detection, which possess the ability to transform light into electrical signals precisely. As the scale and diversity of application areas are growing, the need for innovative photodetection platform technologies with higher performance in terms of speed, efficiency or wavelength range, as well as material flexibility, transparency, and complementary metal-oxide-semiconductor (CMOS) integrability, is becoming more critical. In the past decades, extensive efforts have been devoted to explore the next generation of photodetector materials, such as In2Te3, ZnO, and GaN, with low noise, high photosensitivity, and good stability. However, many of these novel photodetector materials still suffer from limited photocurrent and photoresponse speed.
关键词： Nanomaterials,Schottky contacts,photoconductive gain,photodetection mechanism,photoresistors,linear dynamic range,responsivity,external quantum efficiency,photodiodes,specific detectivity,UV photodetectors
更新于2025-09-19 17:13:59
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Highly efficient blue organic light-emitting diodes based on carbene-metal-amides
摘要： Carbene-metal-amides are soluble and thermally stable materials which have recently emerged as emitters in high-performance organic light-emitting diodes. Here we synthesise carbene-metal-amide photoemitters with CF3-substituted ligands to show sky-blue to deep-blue photoluminescence from charge-transfer excited states. We demonstrate that the emission colour can be adjusted from blue to yellow and observe that the relative energies of charge transfer and locally excited triplet states influence the performance of the deep-blue emission. High thermal stability and insensitivity to aggregation-induced luminescence quenching allow us to fabricate organic light-emitting diodes in both host-free and host-guest architectures. We report blue devices with a peak external quantum efficiency of 17.3% in a host-free emitting layer and 20.9% in a polar host. Our findings inform the molecular design of the next generation of stable blue carbene-metal-amide emitters.
关键词： charge-transfer excited states,photoluminescence,carbene-metal-amides,organic light-emitting diodes,external quantum efficiency
更新于2025-09-19 17:13:59
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On the contribution of fullerene to the current of planar heterojunction organic solar cells.
摘要： Recently, significant progress in the field of organic photovoltaic cells was obtained by substituting new electron acceptor molecules to the fullerene, which was attributed to the fact that the fullerene absorption is quite small. Nevertheless, we demonstrate in the present work that, in the case of inverted cells, i.e. when the transparent bottom electrode is used as cathode, the contribution of fullerene to the Jsc short-circuit current of the cells, if not dominant, is not negligible; and that mainly in the short wavelength spectral range. The experimental results are confirmed by an optical simulation. Due to this significant contribution to Jsc, the light transmission of the transparent electrode towards the UV-part of the spectrum is crucial for inverse cell performances. When a transparent conductive electrode based on an alternative dielectric/metal/dielectric structure is substituted to ITO, such as ZnS/Ag/TiO2, the study allows to obtain promising results, although there is a loss of performance due to the decrease of transmission of TiO2 below 400 nm in wavelength.
关键词： Absorption,Optical Modeling,External Quantum Efficiency,Organic solar cells,Planar heterojunction
更新于2025-09-19 17:13:59