A ZnO nanorod inorganic/organic heterostructure light-emitting diode emitting at 342 nm

An inorganic/organic heterostructure light-emitting diode consisting of the hole-transporting layer N, N'-di(naphth-2-yl)- N, N'-diphenylbenzidine (NPB) and n-type ZnO nanorods fabricated by hydrothermal decomposition is reported. Poly(methyl methacrylate) was used to form a smooth surface on top of ZnO nanorod array with ZnO nanorod tops exposed for subsequent NPB deposition. An unusual ultraviolet emission at 342 nm was observed in the electroluminescence spectrum. Compared to band gap energy of ZnO (3.37 eV), the excitonic emission is blue-shifted and broadened. The mechanism of the blue shift is discussed in terms of the energy band diagram of the heterostructure.     

Flexible inorganic nanowire light-emitting diode

We report a highly flexible light-emitting device in which inorganic nanowires are the optically active components. The single-crystalline ZnO nanowires are grown at 80 degrees C on flexible polymer-based indium-tin-oxide-coated substrates and subsequently encapsulated in a minimal-thickness, void-filling polystyrene film. A reflective top contact serving as the anode in the diode structure is provided by a strongly doped p-type polymer and an evaporated Au film. The emission through the polymer side of this arrangement covers most of the visual region. Electrical and optical properties as well as performance limitations of the device structure are discussed.     

A hybrid light source with integrated inorganic light-emitting diode and organic polymer distributed feedback grating

We report a compact light source that incorporates a semiconductor light-emitting diode, nanostructured distributed feedback (DFB) Bragg grating and spin-coated thin conjugated polymer film. With this hybrid structure, we transferred electrically generated 390?nm ultraviolet light to an organic polymer via optical pumping and out-couple green luminescence to air through a second-order DFB grating. We demonstrate the feasibility of electrically driven, hybrid, compact light-emitting devices and lasers in the visible range.     

Non-reflective black cathode in organic light-emitting diode

A black conductive electrode with a resistivity of 6.75×10⁻⁴ Ω cm was fabricated by doping silicon monoxide into aluminum by simple thermal evaporation. The relative optical reflectance of such electrode layers within the visible spectral range was between 0.12 and 0.05. The black electrode was incorporated in an organic light-emitting diode (OLED) by sequential deposition of α-napthylphenylbiphenyl diamine, tris-(8-hydroxyquinoline) aluminum and the black layer on indium-tin-oxide-coated glass substrates. The black layer reduced the reflection of ambient light entering the device and resulted in a significant increase of the OLED display contrast ratio. The electroluminescence properties of the device incorporating the black layer were investigated.     

一种基于照明目的的有机白光发光二极管

研制了一种以照明为目标的有机白光发光二极管(WOLED),该二极管在8V时的色度坐标为(x=0．319,y=0．337),对应的显色指数(Ra)为85．4,色温(Tc)为6151K。该二极管是含NPB和CBP两个基质的多层掺杂型结构器件;此外,NPB{4,4‘-bis[N-(1-naphthyl)-N-phenylamino]bipheonyl}除了用作绿光和黄光基质外,还用作空穴传榆材料,CBP{4,4‘-N,N‘-dicarbazole-biplaenyl)用作红光磷光配合物的基质材料。3个掺杂层分别提供白光发射的红、黄和绿光成分,而蓝光成分则来自于空穴传榆层NPB本身的发射。该器件在直流电流密度为0．1mA／cm^2时最大白光发光效率可达5．6cd／A(3．9lm／W),在15V时达到的最大亮度为5100ccl／m^2。其性能参数达到了白光照明光源的要求。     

Separated carbon nanotube macroelectronics for active matrix organic light-emitting diode displays

Active matrix organic light-emitting diode (AMOLED) display holds great potential for the next generation visual technologies due to its high light efficiency, flexibility, lightweight, and low-temperature processing. However, suitable thin-film transistors (TFTs) are required to realize the advantages of AMOLED. Preseparated, semiconducting enriched carbon nanotubes are excellent candidates for this purpose because of their excellent mobility, high percentage of semiconducting nanotubes, and room-temperature processing compatibility. Here we report, for the first time, the demonstration of AMOLED displays driven by separated nanotube thin-film transistors (SN-TFTs) including key technology components, such as large-scale high-yield fabrication of devices with superior performance, carbon nanotube film density optimization, bilayer gate dielectric for improved substrate adhesion to the deposited nanotube film, and the demonstration of monolithically integrated AMOLED display elements with 500 pixels driven by 1000 SN-TFTs. Our approach can serve as the critical foundation for future nanotube-based thin-film display electronics.     

MBE n-ZnO/MOCVD p-GaN heterojunction light-emitting diode

The growth, fabrication, and subsequent electroluminescence (EL) characterization of an n-ZnO/p-GaN heterojunction light-emitting diode prepared on c-Al₂O₃ substrate are presented. The diode-like I-V characteristics and room temperature EL spectrum with an intense broadband emission in the yellow-green spectral region has been observed with forward bias applied. Photoluminescence (PL) and Raman spectra of the n-ZnO and p-GaN films were also measured. By comparing PL and EL spectra, it was concluded that the deep-level defect-related emission mainly originated from the GaN epitaxial layer.     

Transparent active matrix organic light-emitting diode displays driven by nanowire transistor circuitry

Optically transparent, mechanically flexible displays are attractive for next-generation visual technologies and portable electronics. In principle, organic light-emitting diodes (OLEDs) satisfy key requirements for this application-transparency, lightweight, flexibility, and low-temperature fabrication. However, to realize transparent, flexible active-matrix OLED (AMOLED) displays requires suitable thin-film transistor (TFT) drive electronics. Nanowire transistors (NWTs) are ideal candidates for this role due to their outstanding electrical characteristics, potential for compact size, fast switching, low-temperature fabrication, and transparency. Here we report the first demonstration of AMOLED displays driven exclusively by NW electronics and show that such displays can be optically transparent. The displays use pixel dimensions suitable for hand-held applications, exhibit 300 cd/m2 brightness, and are fabricated at temperatures suitable for integration on plastic substrates.     

Broadband ZnO single-nanowire light-emitting diode

We present a novel technique for reliable electrical injection into single semiconductor nanowires for light-emitting diodes and lasers. The method makes use of a high-resolution negative electron-beam resist and direct electron-beam patterning for the precise fabrication of a metallic top contact along the length of the nanowire, while a planar substrate is used as a bottom contact. It can be applied to any nanowire structure with an arbitrary cross section. We demonstrate this technique by constructing the first zinc oxide single-nanowire light-emitting diode. The device exhibits broad sub-bandgap emission at room temperature.     

Mechanism of droplet generation in silver thin films for organic light-emitting diode displays

Thin silver film is widely used as the cathode in organic light-emitting diode displays and it is generally fabricated using the thermal evaporation method. But during the evaporation process, there is an inevitable outgassing problem and this creates high viscosity bubbles in melted silver. When the bubbles break, the high energy released scatters silver droplets which damage the silver surface. In this study, we were able to decrease the number of droplets from 6,171 to 278 with a degassing process of 400 °C for 6 h before proceeding with a thermal evaporation process.     

Pure white organic light-emitting diode with lifetime approaching the longevity of yellow emitter

A high-efficiency pure white organic light-emitting diode was fabricated with lifetime approaching that of the low-excitation-energy (yellow) emitter containing counterpart, or six times that of the deep-blue counterpart. The white device was composed of two emission layers with mixed hosts of different compositions. They were respectively doped with yellow rubrene and deep-blue 4,4'-bis-[4-{N,N,N',N'- tetrakis-(4-fluoro-diphenylamino)-phenyl}-vinyl]-biphenyl. The resulting efficiency was 6.0 lm/W (12.4 cd/A) at 20 mA/cm(2). The long device lifetime may be attributed to the double mixed-host architecture employed that effectively dispersed the injected carriers into three different recombination zones and consequently diluted the damaging effect arising from the accumulated charge from un-recombined carriers, hence leading to a markedly improved lifespan.     

Excitation of waveguide modes in organic light-emitting diode structures by classical dipole oscillators

Analytical techniques known in the literature are used to (i) identify all the planar waveguide modes in four top-emitting organic light-emitting diode (OLED) structures over the visible spectrum, and (ii) compute both TM and TE power spectra for classically radiating dipoles in the emissive layers of these OLED structures. Peaks in the computed power spectra are identified with the waveguide modes in the OLED devices, and areas associated with these peaks are used to estimate the excitation probability of the waveguide modes. In cases where ambiguities arise because of overlapping peaks, it is shown that computed power spectra can be approximated as sums of Lorentzian line shapes. It is found that for all four structures, the dipoles couple almost 80% of their radiant energy into TM modes with only about 20% going into TE modes. Furthermore, except for a narrow spectral band, the excited TM modes are primarily short-range surface plasmon polaritons. Excitations in the narrow spectral band correspond to TM and TE Fabry-Perot microcavity modes. Finally, the analysis shows that, in the absence of grating couplers, only light in the microcavity modes escapes into the air cover.     

Device based on the coupling of an organic light-emitting diode with a photoconductive material

We have realized a device based on the coupling of an organic light-emitting diode (with tri(8-hydroxyquinoline)aluminium for light emission) as an input unit with a photoconductive material as an output unit. Various photoconductive materials like pentacene, Cu-phtalocyanine and fullerene were investigated under green light illumination with an emission peak at 550 nm. Photocurrent measurements versus light intensity and bias voltage (applied between two 50 μm distant indium-tin oxide bottom electrodes for the current to flow through the materials) were realized at room temperature a photocurrent gain around 4 is obtained when the materials are subjected to a luminance of about 5000 cd/m² and for bias voltage of − 50 V. Besides, it was shown that to obtain a device with a fast photocurrent response by switching the light off and on, it is necessary to apply a bias voltage higher than − 200 V in these conditions, the gain is multiplied by a factor of 3.     

Improvement of optical extraction efficiency of organic light-emitting diode using a large area nano-pattern

In order to improve optical extraction efficiencies, we propose a nano-patterned organic light-emitting diode (OLED) which doesn't rely on high precision lithography nor rigorous periodicity. The nano-pattern is fabricated by spin-coating PS (poly-styrene) spheres on the substrate and carrying out reactive ion etching and flattening using dielectric material. The verification of the optical properties of the nano patterns was carried out by fabricating OLED-like structures using quantum dot and distributed Bragg reflector (DBR). As a result, the nano-patterned structure showed a 28% increase in optical efficiency compared to the non-patterned sample. In addition, the use of a prism sheet on the backside of a glass substrate also showed a 23% increase in optical efficiency by disturbing the total internal reflection between glass and air. In this way, the large area nano-patterns can be fabricated and applied to increasing the optical extraction in OLED.     

Luminescence mechanisms of organic/inorganic hybrid organic light-emitting devices fabricated utilizing a Zn2SiO4:Mn color-conversion layer

Zn₂SiO₄:Mn phosphor layers used in this study were synthesized by using the sol-gel method and printed on the glass substrates by using a vehicle solution and a heating process. Organic/inorganic hybrid organic light-emitting devices (OLEDs) utilizing a Zn₂SiO₄:Mn color-conversion layer were fabricated. X-ray diffraction data for the synthesized Zn₂SiO₄:Mn phosphor films showed that the Zn ions in the phosphor were substituted into Mn ions. The electroluminescence (EL) spectrum of the deep blue OLEDs showed that a dominant peak at 461 nm appeared. The photoluminescence spectrum for the Zn₂SiO₄:Mn phosphor layer by using a 470 nm excitation source showed that a dominant peak at 527 nm appeared, which originated from the ⁴T₁-⁶A₁ transitions of Mn ions. The appearance of the peak around 527 nm of the EL spectra for the OLEDs fabricated utilizing a Zn₂SiO₄:Mn phosphor layer demonstrated that the emitted blue color from the deep blue OLEDs was converted into a green color due to the existence of the color-conversion layer. The luminescence mechanisms of organic/inorganic hybrid OLEDs fabricated utilizing a Zn₂SiO₄:Mn color-conversion layer are described on the basis of the EL and PL spectra.     

Visible colloidal nanocrystal silicon light-emitting diode

We herein demonstrate visible electroluminescence from colloidal silicon in the form of a hybrid silicon quantum dot-organic light emitting diode. The silicon quantum dot emission arises from quantum confinement, and thus nanocrystal size tunable visible electroluminescence from our devices is highlighted. An external quantum efficiency of 0.7% was obtained at a drive voltage where device electroluminescence is dominated by silicon quantum dot emission. The characteristics of our devices depend strongly on the organic transport layers employed as well as on the choice of solvent from which the Si quantum dots are cast.     

Mid-ultraviolet light-emitting diode detects dipicolinic acid

Dipicolinic acid (DPA, 2,6-pyridinedicarboxylic acid) is a substance uniquely present in bacterial spores such as that from anthrax (B. anthracis). It is known that DPA can be detected by the long-lived fluorescence of its terbium chelate; the best limit of detection (LOD) reported thus far using a large benchtop gated fluorescence instrument using a pulsed Xe lamp is 2 nM. We use a novel AlGaN light-emitting diode (LED) fabricated on a sapphire substrate that has peak emission at 291 nm. Although the overlap of the emission band of this LED with the absorption band of Tb-DPA (lambda(max) doublet: 273, 279 nm) is not ideal, we demonstrate that a compact detector based on this LED and an off-the-shelf gated photodetection module can provide an LOD of 0.4 nM, thus providing a basis for convenient early warning detectors.     

High-temperature buried InP/GaInAsP heterostructure laser diode emitting at 1310 nm

As a continuation of our studies aimed at creating semiconductor lasers based on buried InP/GaInAsP heterostructures, we consider the design and fabrication aspects of 1310-nm laser diodes for operation at elevated temperatures. We report the key features of the fabrication process and parameters of the laser emitters at temperatures of up to 120°C, and present their power-current and spectral characteristics.