Enhanced organic light emitting diode and solar cell performances using silver nano-clusters

Silver nano-clusters (NCs) were incorporated into organic light emitting diodes (OLED) and solar cells by means of thermal evaporation. Silver NCs enhance the efficiency of both OLEDs and polymer solar cells under tailored device architecture. In tris-(8-hydroxyquinoline) aluminum (Alq₃) based small molecule OLEDs, silver NCs were deposited under the Al cathode. The electron injection from the cathode to organic layer is promoted significantly owing to silver NCs induced lightning rod effect, the Alq₃ OLEDs luminous efficiency is increased up to a factor of 6. In poly(3-hexylthiophene) (P3HT) polymer solar cells, the active layer absorption is enhanced in the presence of silver NCs, which can be ascribed to NCs induced light scattering effect as well as to plasmon enhanced local electric field effect. As a result, photocurrent of the solar cells is increased and the power conversion efficiency (PCE) is improved up to 20%. The comparative study of surface plasmon effects in different organic optoelectronic devices reveals interesting features of the surface plasmon and allows optimization of optoelectronic devices from a novel point of view.     

Real-time external sensing and compensation method for organic light emitting diode displays

A real-time external sensing and compensation method for active matrix organic light emitting diode displays is proposed. The proposed method senses and compensates for the variation of electrical characteristics of poly-Si thin-film transistors (TFTs) during display time. Experimental results show that the proposed method successfully senses the electrical characteristics of TFTs in real-time and compensates for the non-uniform emission current error.     

Optically-coupled mirror-quantum well InGaAs-GaAs light emitting diode

Data are presented showing that it is possible to optically couple a semiconductor quantum well to a mirror, and thus influence its spontaneous emission lifetime, for mirror to quantum well spacings of less than an optical wavelength. Light emitting diodes with various mirror to quantum well spacings corresponding to quantum well placement at either interference nodes or antinodes are characterised in terms of light output efficiency and frequency response.<>     

Efficient blue emitters based on 1,3,5-triazine for nondoped organic light emitting diode applications

Two novel efficient blue emitters (TTT-1, TTT-2) containing 1,3,5-triazine, thiophene and triphenylamine have been designed and synthesized. Organic light emitting diodes (OLEDs) using these new triazine derivatives as emissive layers, ITO/TAPC (60 nm)/TTT-1 (Device A) or TTT-2 (Device B) (40 nm)/TPBi (60 nm)/LiF (1 nm)/Al (100 nm), were fabricated and tested. The OLEDs exhibited good performances with low turn-on voltage of 3 V, maximum luminance of ca. 8990 cd/m² for TTT-1 and 15,980 cd/m² for TTT-2, and maximum luminance efficiency of 4.7 cd/A for TTT-1 and 4.0 cd/A for TTT-2, respectively.     

Surface plasmon enhanced blue organic light emitting diode with nearly 100% fluorescence efficiency

Surface plasmon (SP) enhanced blue organic light emitting diodes (OLEDs) have been realized by using silver nanoclusters (SNCs) deposited using thermal evaporation technique. SNCs were found to have the surface plasmon resonance at wavelength 445 nm and were used with blue emitting layer BCzVBi. The optimized OLED (in terms of the size of SNCs and the distance between SNCs and emitting layer) were found to have the efficiency two times higher than reference OLED without SNCs. Internal quantum efficiency was calculated to be 24% for SP enhanced OLED owing to 96% fluorescence efficiency. Energy transfer between exciton and SPs with the separation distance have been studied experimentally and using 2D-FDTD simulation and surface–dipole energy transfer has been observed.     

Improved efficiency in fluorescent blue organic light emitting diode with a carrier confining structure

A blue organic light emitting device (OLED) with improved efficiency and good color purity is reported. The highest occupied molecular orbital (HOMO) level of the hole transport layer (HTL) and that of the emissive layer (EML) differs by 0.3 eV. This energy level mismatch confines the carriers at the HTL/EML interface. Conventional devices have only one HTL/EML interface, with a current efficiency of 2.9 cd/A. Without adding a separate hole blocking layer, incorporating multi-layers of the same HTL and EML increases this efficiency to 5.8 cd/A, with only a small increase in operating voltage yielding increased power efficiency also. But, there are an optimum number of layers, beyond which efficiency loss results. Also, including the multilayer structure simultaneously improves the blue color co-ordinates. To gain insight into the role of multilayer structures in modifying charge transport and recombination zone a simulator was developed. The simulated results could qualitatively explain the experimental observations.     

Remodeling light emitting diode in low current region

A general expression is proposed for the current-voltage (I-V) characteristics of junction diode by which it is possible to determine forward voltage across diode at actual current and temperature. Expressions fur the band gap and temperature coefficient of junction voltage based on the experimental measurements are also presented. The expressions include only experimentally obtained and derived values. These expressions have been used to check the performance of logarithmic amplifier using light emitting diode (LED) as a feedback clement, at different temperatures. Further, it has been shown that it is possible to predict the behavior of a logarithmic amplifier without temperature compensation techniques within 5% accuracy for the current range 10^-12-10^-5 A and for the temperature range -5°-60°C. The alternative could be the use of temperature compensation circuitry which may make electrometer circuit more complex. The proposed scheme is useful in applications where it is difficult to incorporate temperature compensation technique and space and power are at premium     

Mercury cadmium telluride-based resonant cavity light emitting diode

A CdHgTe resonant cavity light emitting diode (RCLED) is proposed as a new infrared emitter. The device is prepared by molecular beam epitaxy on a CdZnTe substrate. A 10.5 periods Bragg mirror is first deposited. The cavity material is made of Cd_0.75Hg_0.25Te and contains a wide well (50 nm) designed to emit at 3.2 μm. The last three periods of the mirror are n-type doped while the cavity material is covered by a thin p-type CdZnTe layer. A gold layer closes the cavity, serving as the second mirror of a Fabry-Perot cavity tuned around 3.18 urn. It also provides an ohmic contact to the p-region. Under forward bias, the emission spectrum displays a narrow peak (8 meV full width at half maximum) corresponding to the cavity resonance. The position and linewidth of this line are independent of temperature. The directivity of the diode is also improved with respect to a conventional emitter, in agreement with theoretical expectations. Taking advantage of the spectral properties of the RCLED a new multispectral device has been fabricated.     

蓝色发光二极管的技术与实际应用

综述了蓝色发光二极管的技术及不同材料蓝色发光二极管的制作与特性，并介绍了蓝色发光二极管的实际应用。     

Filling of light emitting diode via-holes by MOCVD

The growth of epitaxial films on featured substrates has an important device application in junction-confinement, double hetero-structure light emitting diodes. These devices are presently grown by a liquid phase epitaxy process but growth by metalorganic chemical vapor deposition is desirable because of MOCVD's superior surface quality, uniformity, and throughput. This paper describes the effect of growth parameters on AlGaAs films deposited by atmospheric-pressure MOCVD into substrate holes typically made in the fabrication of junction-confinement LEDs. MOCVD growth replicates the substrate features; it does not give a planar surface over the holes. The behavior of epitaxy filling into holes is strongly dependent on growth temperature and total gas flow and largely independent of substrate misorientation and the thickness of the layer grown. Wet-etched holes formed (ll0)-oriented V-groove and dovetail-groove features on the hole circumference. Faceting of the MOCVD growth was seen on the wall with the (111)A feature while smooth growth was seen on the etched (111)B surface. Deceased.     

Efficiency enhancement of organic light emitting diode via surface energy transfer between exciton and surface plasmon

Organic light emitting diodes (OLEDs) with surface plasmon (SP) enhanced emission have been fabricated. Gold nanoclusters (GNCs) deposited using thermal evaporation technique has been used for localization of surface plasmons. Size of GNCs and distance of GNCs from the emissive layer have been optimized using steady state and time resolved photoluminescence (PL) results. 3.2 Times enhancement in PL intensity and 2.8 times enhancement in electroluminescence intensity of OLED have been obtained when GNCs of size 9.3 nm has been introduced at a distance of 5 nm from emissive layer. Distance dependence of energy transfer efficiency between exciton and SPs was found to be of 1/R⁴ type, which is typically the dependence for dipole-surface energy transfer.     

GaAs红外发光二极管加速寿命试验研究

本文采用步进应力的试验方法设计了一个针对GaAs红外发光二极管的可靠性加速寿命的研究方案.这种方法主要是把步进应力和恒定应力两种方法相结合,用此来评估GaAs红外发光二极管的可靠度;然后总结除了GaAs红外发光二极管这种光电器件的寿命分布形式和失效模式.     

Improvement of AlGaInP light emitting diode by sulfide passivation

The brightness of AlGaInP light emitting diodes (LEDs) has been raised by a factor of 1.12 at 20 mA by sulfide passivation. Meanwhile, the sulfide also can decrease leakage current of AlGaInP LEDs at -2 V to nearly one thousandth of that in the as-fabricated device. The possible causes for the brightness increase of AlGaInP LEDs after sulfide treatment including surface roughness, reduction of Fresnel loss, and effective injection of carriers were demonstrated.     

Driving current and temperature dependent magnetic-field modulated electroluminescence in Alq3-based organic light emitting diode

Driving current and temperature dependences of magnetic-field modulated electroluminescence (EL) in tris(8-hydroxyquinoline) aluminum (Alq₃)-based OLEDs have been thoroughly investigated. At low temperatures, the applied magnetic-field induces a sharp increase of the EL in low field regime (B ? 35 mT) and a slow but apparent decrease at high fields (35 ? B ? 500 mT). The low-field increase in EL (LFE) survives at all working temperatures while the high-field decrease (HFE) gradually disappears as temperature is increased. At a given temperature, the higher the current level, the smaller LFE and stronger HFE are observed. To explain the observed MFEs a composite model based on magnetic-field dependent singlet-to-triplet conversion of electron-hole pairs and magnetic-field mediated triplet–triplet annihilation process is proposed in this paper.     

改进实用型LED生物光源系列

通过采用平面LED点阵、半球曲面内LED点阵、半球曲面与菲涅耳透镜结合这三种光学设计,本文研制出具有不同光强和光照均匀差别的三种实用型LED生物光源,研究了每个光源中的四个工作参数对其辐射照度的影响,并使用统计分析软件SPSS拟合得出它们的辐射照度经验计算公式.     

High stability and low driving voltage green organic light emitting diode with molybdenum oxide as buffer layer

Green organic light emitting diodes (OLEDs) with copper phthalocyanine (CuPc), 4,4′,4″-tris[3-methylphenyl(phenyl)amino]triphenymine (m-MTDATA) and molybdenum oxide (MoO_x) as buffer layers have been investigated. The MoO_x based device shows superior performance with low driving voltage, high power efficiency and much longer lifetime than those with other buffer layers. At the luminance of 100 cd/m², the driving voltage is 3.8 V, which is 0.5 V and 2.2 V lower than that of the devices using CuPc (Cell-CuPc) and m-MTDATA (Cell-m-MTDATA) as buffer layer, respectively. Its power efficiency is 13.6 Lm/W, which is 38% and 30% higher than that of Cell-CuPc and Cell-m-MTDATA, respectively. The projected half-life under the initial luminance of 100 cd/m² is 42,400 h, which is more than 3.8 times longer than that of Cell-m-MTDATA and 24 times that of Cell-CuPc. The superior performance of Cell-MoO_x is attributed to its high hole injection ability and the stable interface between MoO_x and organic material. The work function of MoO_x measured by contact potential difference method and the J–V curves of “hole-only” devices indicate that a small barrier between MoO_x/N,N′-di(naphthalene-1-y1)-N,N′-dipheyl-benzidine (NPB) leads to a strong hole injection, resulting in the low driving voltage and the high stability.     

SJ/T 11281-2007《发光二极管(LED)显示屏测试方法》概要

本标准规定了发光二极管(LED)显示屏的机械、光学、电学等主要技术性能指标的分级和测试方法,适用于各类发光二极管(LED)显示屏(以下简称显示屏)的测试.     

Multijunction AC or DC integrated GaP light emitting diode array

An ac or dc GaP LED array has been designed and fabricated which has potential as a direct replacement for several tungsten filament lamps and as an illuminator for new design considerations. In designing such an LED for high-voltage application, series light emitting junctions rather than series resistors are used as a voltage divider to maximize the light output/power input ratio. A figure of merit is modeled and calculated which provides a measure of total light output for a given applied current and voltage as a function of the number of series diodes. The optimum number of series diode for a given ac voltage is Vrms/1.94. Thermal calculations based upon chip size, power dissipation, and thermal contact resistance predict a peak temperature rise of 30°C for the bonded die approach. n- and p-type liquid phase epitaxial layers were grown on semi-insulating substrates, p-n junctions on the same chip were electrically isolated utilizing either proton bombardment or chemically etched trenches. An Au metallization scheme provides the series-parallel interconnection required for ac or dc operation while maintaining junction isolation. The light emitting junction areas are mesas, with edges shaped to redirect internally generated light out to the viewer. The near field radiation pattern demonstrates the optical effectiveness of the shaped-mesa emitters.     

Gravure printed flexible small-molecule organic light emitting diodes

Small-molecule based flexible organic light-emitting diodes (SMOLEDs) were fabricated by gravure printing. In order to modify rheological properties of the functional ink, the green emitter was embedded into an ultrahigh molecular weight polystyrene (UHMW-PS) matrix. The viscosity of the ink was characterized as a function of the small molecule:UHMW-PS weight ratio and solvent type. The gravure printed SMOLEDs exhibited a maximum luminance of 850 cd m⁻², a maximum efficiency of up to 7.7 cd A⁻¹, and turn on voltage of ∼3.5 V. The gravure printed SM:UHMW-PS device exhibits ∼67% higher luminance efficiency comparing to the spin-coated pristine SM device.