scholarly journals A Method to Realize Efficient Deep-Red Phosphorescent OLEDs with a Broad Spectral Profile and Low Operating Voltages

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5723
Author(s):  
Wei-Ling Chen ◽  
Shan-Yu Chen ◽  
Dun-Cheng Huang ◽  
Dian Luo ◽  
Hsueh-Wen Chen ◽  
...  
Keyword(s):  
Carrier Transport ◽  
Layer Structure ◽  
Hole Injection ◽  
Electroluminescence Spectrum ◽  
Light Sources ◽  
Spectral Profile ◽  
Coverage Ratio ◽  
Design Concepts ◽  
Red Phosphors ◽  
Materials Used

Organic light-emitting diodes (OLEDs) used as phototherapy light sources require sufficient spectral distribution in the effective wavelength ranges and low operating voltages. Herein, a double emitting layer structure consisting of a red-emitting Ir(piq)2acac and a deep-red Ir(fliq)2acac was designed to generate a broad electroluminescence spectrum. An efficient TCTA:CN-T2T exciplex system was used as the host of the emitting layer, facilitating effective energy transfer from the exciplex host to the red and deep-red phosphors. The materials used in the exciplex host were also used as the carrier transport layers to eliminate the energy barriers and thus increase the current density. The hole injection layer structures were varied to examine the hole injection capabilities and the carrier balance. The resulting optimized phosphorescent OLEDs with a broad spectral profile exhibit a 90% coverage ratio in the target ranges from 630 to 690 nm, together with a high peak efficiency of 19.1% (10.2 cd/A and 13.8 lm/W). The proposed device only needs 5.2 V to achieve a power density of 5 mW/cm2, implying that the device could be driven via two series-connected button cell batteries. These results illustrate the feasibility of our design concepts and demonstrate the realization of a portable and lightweight OLED phototherapy light source.

scholarly journals Designs of InGaN Micro-LED Structure for Improving Quantum Efficiency at Low Current Density

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Shiqiang Lu ◽  
Jinchai Li ◽  
Kai Huang ◽  
Guozhen Liu ◽  
Yinghui Zhou ◽  
...  
Keyword(s):  
Quantum Efficiency ◽  
Current Density ◽  
Carrier Transport ◽  
Defect Density ◽  
Numerical Study ◽  
Structure Design ◽  
Operating Conditions ◽  
Hole Injection ◽  
Electron Blocking Layer ◽  
Recombination Processes

AbstractHere we report a comprehensive numerical study for the operating behavior and physical mechanism of nitride micro-light-emitting-diode (micro-LED) at low current density. Analysis for the polarization effect shows that micro-LED suffers a severer quantum-confined Stark effect at low current density, which poses challenges for improving efficiency and realizing stable full-color emission. Carrier transport and matching are analyzed to determine the best operating conditions and optimize the structure design of micro-LED at low current density. It is shown that less quantum well number in the active region enhances carrier matching and radiative recombination rate, leading to higher quantum efficiency and output power. Effectiveness of the electron blocking layer (EBL) for micro-LED is discussed. By removing the EBL, the electron confinement and hole injection are found to be improved simultaneously, hence the emission of micro-LED is enhanced significantly at low current density. The recombination processes regarding Auger and Shockley–Read–Hall are investigated, and the sensitivity to defect is highlighted for micro-LED at low current density.Synopsis: The polarization-induced QCSE, the carrier transport and matching, and recombination processes of InGaN micro-LEDs operating at low current density are numerically investigated. Based on the understanding of these device behaviors and mechanisms, specifically designed epitaxial structures including two QWs, highly doped or without EBL and p-GaN with high hole concentration for the efficient micro-LED emissive display are proposed. The sensitivity to defect density is also highlighted for micro-LED.

scholarly journals Electro-Optical Performance of Organic Thin-Film Using HAT(CN)6 between Anode and Organic Materials

Coatings ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 648 ◽  
Author(s):  
Hong-Gyu Park ◽  
Sang-Geon Park
Keyword(s):  
Thin Film ◽  
Optical Properties ◽  
Current Density ◽  
Carrier Transport ◽  
Hole Injection ◽  
Driving Voltage ◽  
Organic Thin Film ◽  
20 Nm ◽  
Injection Barrier ◽  
A Current

We report the electro-optical properties of an organic thin-film by varying the thickness of 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT(CN)6), included therein as an interlayer. Devices with HAT(CN)6, which are 7 nm thin films used as interlayers, exhibited good current density–voltage characteristics due to an improved hole injection barrier resulting from carrier ladder effects and carrier transport phenomena. The device without an interlayer showed the worst driving voltage characteristics due to the hole injection barrier. At low driving voltages, a device using 7 nm HAT(CN)6 as an interlayer exhibited a current density about 9.9 times higher than that of a device using 20 nm HAT(CN)6, and showed a current density about 9600 times higher than that of a device without an interlayer. Due to the proper carrier balance, the device using 7 nm HAT(CN)6 as an interlayer achieved a maximum current efficiency of 10.8 cd/A, which was the highest among the devices studied. This shows that the electro-optical properties of devices using HAT(CN)6 as an interlayer are dominated by the holes.

Development of Synchrotron Radiation Storage Rings

1998 ◽  
Vol 5 (3) ◽  
pp. 179-183 ◽  
Author(s):  
Motohiro Kihara
Keyword(s):  
Synchrotron Radiation ◽  
Storage Rings ◽  
Light Sources ◽  
Third Generation ◽  
Accelerator Physics ◽  
Future Prospects ◽  
Design Concepts ◽  
The Past ◽  
Technological Developments ◽  
Principal Design

Many third-generation light sources have been commissioned over the past ten years, and the soundness of the principal design concepts has been well recognized through experiences at these facilities. Also, technological developments concerning third-generation light sources have been remarkable. With the emittance and current of the beams far exceeding the previous levels, stability requirements of the beams have become much more stringent. In this report the present status of light sources, operational and projected, is summarized, and developments and future prospects of synchrotron radiation storage rings in view of accelerator physics and technology are reviewed.

Three-layer Permutation of the Phonionic Structure and the Influence of the Environment

2018 ◽  
Vol 69 (9) ◽  
pp. 2571-2574
Author(s):  
Michal Szota
Keyword(s):  
Layer Structure ◽  
Middle Layer ◽  
Production Costs ◽  
Frequency Range ◽  
Different Types ◽  
Transmission Structure ◽  
Materials Used ◽  
The Impact ◽  
Wave Filters ◽  
Different Thickness

The study investigated the influence of permutation of a three-layer structure on the phononic system transmission. Phononic structures are used as mechanical wave filters. These composites are designed and manufactured to have specific properties. The most important property is the presence of phononic bandgaps (PhBG) in these structures. They are designed so that the PhBG occurs in a given frequency range. Knowledge of the impact of deployment of the layets in the structure allows better design of these filters. The analysis was carried out using the transmission matrix method (TMM) algorithm. The transmission structures was examined for all permutations of a system of three layers made of different materials. The structure consisted of mercury, epoxy, rubber and PNM-0.38PT. The materials are chosen so that their characteristics largely differ. The structure was surrounded by water. The tests were carried out for the frequency range up to 1 MHz. Cases with different thickness of layers were analyzed. The tests have shown that regardless of the layer thickness, only three types of transmission structures exist in the six permutations of the system. Systems in which the middle layer remained unchanged, while the outermost layers were changed, were characterized by the same transmission structure. Increasing the thickness of the layers increased the number of transmission bands. Transmission strongly depends on the environment.The absorption of the materials used was not taken into account in the work. Interesting results can be obtained by analyzing the permutation of more complex structures. Changing the order of layers in the filter without changing its characteristics may affect the reduction of production costs and easier design of structures with given properties. The article shows repeating phononic transmission structure for different types of layers alignment.

Modeling Carrier Transport in Oxide-Passivated Nanocrystalline Silicon Leds

2000 ◽  
Vol 638 ◽  
Author(s):  
Karl D. Hirschman ◽  
Philippe M. Fauchet
Keyword(s):  
Density Of States ◽  
Carrier Transport ◽  
Light Emission ◽  
Transport Model ◽  
Glass Structure ◽  
Electrical Characterization ◽  
Nanocrystalline Silicon ◽  
Hole Injection ◽  
Device Operation

AbstractThis report presents an investigation on carrier transport in LED structures based on oxide passivated nanocrystalline silicon (OPNSi), formed by oxidation of porous silicon. This material, like its precursor, can luminesce quite efficiently while demonstrating several advantages in stability (i.e. chemical, thermal, electrical and electroluminescence). OPNSi can be best described as a porous glass structure with defects that facilitate transport, and remaining embedded nanocrystals of silicon that support light emission. Although this study does not provide a direct measurement of the density of states in OPNSi, the following transport study suggests a high density of states having a broad energy distribution that readily exchange charge with the silicon electrodes. Experimental data also suggests the existence of deeper trap centers that do not facilitate transport, yet influence transport behavior significantly. The device operation is explained by bipolar injection from an electron-injection cathode and a hole-injection anode into the semi-insulating OPNSi layer. The device is modeled as a “field effect diode”, where untraditional concepts are applied in the interpretation of experimental observations. Extensive electrical characterization of OPNSi LEDs has lead to the development of a comprehensive transport model that is self-consistent with all experimental observations.

Efficient carrier transport for 368 nm ultraviolet LEDs with p-AlInGaN/AlGaN short-period superlattice electron blocking layer

2021 ◽  
Author(s):  
Longfei He ◽  
Kang Zhang ◽  
Hualong Wu ◽  
Chenguang He ◽  
Wei Zhao ◽  
...  
Keyword(s):  
Ultraviolet Light ◽  
Carrier Transport ◽  
Hole Injection ◽  
Blocking Layer ◽  
Electron Blocking Layer ◽  
Light Emitting ◽  
Near Ultraviolet ◽  
Short Period ◽  
P Type ◽  
Ultraviolet Light Emitting Diodes

It is generally known that the p-type AlGaN electron-blocking layer (EBL) can hinder hole injection for near-ultraviolet light-emitting diodes (NUV-LEDs). Moreover, at the last quantum barrier (LQB)/EBL interface, the polarization-induced...

scholarly journals Dopant-Tunable Ultrathin Transparent Conductive Oxides for Efficient Energy Conversion Devices

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Dae Yun Kang ◽  
Bo-Hyun Kim ◽  
Tae Ho Lee ◽  
Jae Won Shim ◽  
Sungmin Kim ◽  
...  
Keyword(s):  
Energy Conversion ◽  
Indium Tin Oxide ◽  
Carrier Transport ◽  
Hole Injection ◽  
Visible Range ◽  
Transparent Conductive Oxides ◽  
Light Emitting ◽  
Efficient Energy ◽  
Uv Leds ◽  
Energy Conversion Devices

AbstractUltrathin film-based transparent conductive oxides (TCOs) with a broad work function (WF) tunability are highly demanded for efficient energy conversion devices. However, reducing the film thickness below 50 nm is limited due to rapidly increasing resistance; furthermore, introducing dopants into TCOs such as indium tin oxide (ITO) to reduce the resistance decreases the transparency due to a trade-off between the two quantities. Herein, we demonstrate dopant-tunable ultrathin (≤ 50 nm) TCOs fabricated via electric field-driven metal implantation (m-TCOs; m = Ni, Ag, and Cu) without compromising their innate electrical and optical properties. The m-TCOs exhibit a broad WF variation (0.97 eV), high transmittance in the UV to visible range (89–93% at 365 nm), and low sheet resistance (30–60 Ω cm−2). Experimental and theoretical analyses show that interstitial metal atoms mainly affect the change in the WF without substantial losses in optical transparency. The m-ITOs are employed as anode or cathode electrodes for organic light-emitting diodes (LEDs), inorganic UV LEDs, and organic photovoltaics for their universal use, leading to outstanding performances, even without hole injection layer for OLED through the WF-tailored Ni-ITO. These results verify the proposed m-TCOs enable effective carrier transport and light extraction beyond the limits of traditional TCOs.

scholarly journals Analysis of LLL System Properties for Different Excitation Parameters

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7723
Author(s):  
Krzysztof Wandachowicz ◽  
Małgorzata Zalesińska ◽  
Przemysław Otomański
Keyword(s):  
Light Sources ◽  
Primary Method ◽  
Escape Route ◽  
Fluorescent Lamps ◽  
Interior Lighting ◽  
Passenger Ships ◽  
System Properties ◽  
Materials Used ◽  
Photoluminescent Materials ◽  
Excitation Parameters

Photoluminescent strips forming a Low Location Lighting (LLL) system are the primary method for marking escape routes on passenger ships. The LLL system can be built as a self-luminous system (powered by electricity) or made as a series of strips made of photoluminescent materials, which glow and indicate the escape route after the loss of basic and emergency lighting. To ensure correct visual guidance, these strips must be installed at specific locations in the passageways and achieve appropriate photometric parameters after a certain time from their activation. The properties of the LLL system depend on the type of luminescent material used, the excitation source, and the exposure parameters. This paper presents the results of laboratory tests on two types of photoluminescent materials used for the construction of LLL systems. We recorded the change in luminance after the loss of excitation and measured the luminance values obtained 10 and 60 min after the loss of excitation under exposure to light sources commonly used for interior lighting on passenger ships. It turns out that replacing fluorescent lamps with LED lamps can reduce the luminance of the LLL system.

scholarly journals Highly Efficient White Organic Light-Emitting Diodes with Controllable Excitons Behavior by a Mixed Interlayer between Fluorescence Blue and Phosphorescence Yellow-Emitting Layers

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Chun-Hong Gao ◽  
Xiao-Bo Shi ◽  
Dong-Ying Zhou ◽  
Lei Zhang ◽  
Zhao-Kui Wang ◽  
...  
Keyword(s):  
Power Efficiency ◽  
Carrier Transport ◽  
Layer Structure ◽  
Light Emitting Diode ◽  
Device Structure ◽  
Emission Layer ◽  
Light Emitting ◽  
Organic Light Emitting Diode ◽  
Highly Efficient ◽  
Organic Light

A highly efficient hybrid white organic light-emitting diode (HWOLED) has been demonstrated with a mixed interlayer between fluorescent blue and phosphorescent yellow-emitting layers. The device structure is simplified by using a controllable fluorescence-mixed interlayer-phosphorescence emission layer structure. The electroluminance (EL) performance can be modulated easily by adjusting the ratio of the hole-predominated material to the electron-predominated material in the interlayer. It is found that the HWOLED with a ratio of 3 : 2 exhibits a current efficiency of 34 cd/A and a power efficiency of 29 lm/W at 1000 cd/m2with warm white Commission Internationale de l’Eclairage (CIE1931) coordinates of (0.4273, 0.4439). The improved efficiency and adaptive CIE coordinates are attributed to the controllable mixed interlayer with enhanced charge carrier transport, optimized excitons distribution, and improved harvestings of singlet and triplet excitons.

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