DERMATOLOGIC SURGERY, Issue 7 2001
Christiane Handrick MD
Background. Unwanted facial and body hair is a common problem, generating a high level of interest for treatment innovations. Advances in laser technology over the past several years has led to the development and distribution of numerous red and infrared lasers and light sources to address this issue. Despite the impressive clinical results that have been reported with the use of individual laser hair removal systems, long-term comparative studies have been scarce. Objective. To compare the clinical and histologic efficacy, side effect profile, and long-term hair reduction of long-pulsed diode and long-pulsed alexandrite laser systems. Methods. Twenty women with Fitzpatrick skin types I,IV and dark terminal hair underwent three monthly laser-assisted hair removal sessions with a long-pulsed alexandrite laser (755 nm, 2-msec pulse, 10 mm spot) and a long-pulsed diode laser (800 nm, 12.5 msec or 25 msec, 9 mm spot). Axillary areas were randomly assigned to receive treatment using each laser system at either 25 J/cm2 or 40 J/cm2. Follow-up manual hair counts and photographs of each area were obtained at each of the three treatment visits and at 1, 3, and 6 months after the final laser session. Histologic specimens were obtained at baseline, immediately after the initial laser treatment, and 1 and 6 months after the third treatment session. Results. After each laser treatment, hair counts were successively reduced and few patients found it necessary to shave the sparsely regrown hair. Optimal clinical response was achieved 1 month after the second laser treatment, regardless of the laser system or fluence used. Six months after the third and final treatment, prolonged clinical hair reduction was observed with no significant differences between the laser systems and fluences used. Histologic tissue changes supported the clinical responses observed with evidence of initial follicular injury followed by slow follicular regeneration. Side effects, including treatment pain and vesiculation, were rare after treatment with either laser system, but were observed more frequently with the long-pulsed diode system at the higher fluence of 40 J/cm2. Conclusion. Equivalent clinical and histologic responses were observed using a long-pulsed alexandrite and a long-pulsed diode laser for hair removal with minimal adverse sequelae. While long-term hair reduction can be obtained in most patients after a series of laser treatments, partial hair regrowth is typical within 6 months, suggesting the need for additional treatments to improve the rate of permanent hair removal. [source]

Analysis of Improved Efficiency of InGaN Light-Emitting Diode With Bottom Photonic Crystal Fabricated by Anodized Aluminum Oxidxe

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2009
Sang-Wan Ryu
Abstract The improved performance of a bottom photonic crystal (PC) light-emitting diode (LED) is analyzed based on internal quantum efficiency (,int) and light-extraction efficiency (,ex). The bottom PC is fabricated by anodized aluminum oxide nanopatterns and InGaN quantum wells (QWs) are grown over it. Transmission electron microscopy images reveal that threading dislocations are blocked at the nanometer-sized air holes, resulting in improved optical emission efficiency of the QWs. From temperature-dependent photoluminescence measurements, the enhancement of ,int is estimated to be 12%. Moreover, the enhancement of ,ex is simulated to be 7% by the finite-difference time-domain method. The fabricated bottom PC LED shows a 23% higher optical power than a reference, which is close to the summation of enhancements in ,int and ,ex. Therefore, the bottom PC improves LED performance through higher optical quality of QWs as well as increased light extraction. [source]

An Organic Light-Emitting Diode with Field-Effect Electron Transport,

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2008
S. Schols
Abstract We describe an organic light-emitting diode (OLED) using field-effect to transport electrons. The device is a hybrid between a diode and a field-effect transistor. Compared to conventional OLEDs, the metallic cathode is displaced by one to several micrometers from the light-emitting zone. This micrometer-sized distance can be bridged by electrons with enhanced field-effect mobility. The device is fabricated using poly(triarylamine) (PTAA) as the hole-transport material, tris(8-hydroxyquinoline) aluminum (Alq3) doped with 4-(dicyanomethylene)-2-methyl-6-(julolindin-4-yl-vinyl)-4H-pyran (DCM2) as the active light-emitting layer, and N,N,-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13H27), as the electron-transport material. The obtained external quantum efficiencies are as high as for conventional OLEDs comprising the same materials. The quantum efficiencies of the new devices are remarkably independent of the current, up to current densities of more than 10 A cm,2. In addition, the absence of a metallic cathode covering the light-emission zone permits top-emission and could reduce optical absorption losses in waveguide structures. These properties may be useful in the future for the fabrication of solid-state high-brightness organic light sources. [source]

Rewritable Switching of One Diode,One Resistor Nonvolatile Organic Memory Devices

ADVANCED MATERIALS, Issue 11 2010
Byungjin Cho
One diode,one resistor (1D,1R) hybrid-type devices consisting of an inorganic Schottky diode and an organic unipolar memory show electrically rewritable switching characteristics as well as rectifying properties. The 1D,1R array architecture improves the sensing efficiency of the array memory cell, ultimately creating the possibility for high-density integrated organic memory devices without restrictions due to cross-talk between cells. [source]

A Lasing Organic Light-Emitting Diode

ADVANCED MATERIALS, Issue 4 2010
Bodo H. Wallikewitz
Direct structuring of photocrosslinkable polyspirobifluorene copolymers by holographic lithography to yield insoluble, organic, distributed feedback (DFB) lasers with thresholds as low as 2,µJ,cm,2 is reported (see figure). These DFB lasers (X-LEP layer in figure) are embedded in the first optimized, multilayered slab-waveguide organic light-emitting diode with good luminance efficiency of ,6,cd A,1 and concomitant low laser thresholds. The effect of electrical excitation on the optically pumped laser is investigated for the first time. [source]

Fabrication of a High-Brightness Blue-Light-Emitting Diode Using a ZnO-Nanowire Array Grown on p-GaN Thin Film

ADVANCED MATERIALS, Issue 27 2009
Xiao-Mei Zhang
Bright n-ZnO nanowire/p-GaN film hybrid heterojunction light-emitting-diode (LED) devices are fabricated by directly growing n-type ZnO-nanowire arrays on p-GaN wafers. UV,blue electroluminescence emission was observed from the heterojunction diodes, and the heterojunction LED device exhibited a high sensitivity in responding to UV irradiation. [source]

Efficient Polymer Light-Emitting Diode Using Air-Stable Metal Oxides as Electrodes,

ADVANCED MATERIALS, Issue 1 2009
Henk J. Bolink
Poly(phenylenevinylene)-based organic light-emitting diodes (OLEDs) are fabricated using air-stable metal oxides as electrodes, producing very efficient and bright electroluminescent devices. Efficiencies of 8,cd,A,1 and luminances above 20000,cd,m,2 are obtained, comparable to the values reported for classic OLED structures using reactive metals as cathodes. [source]

A Low-Temperature-Grown Oxide Diode as a New Switch Element for High-Density, Nonvolatile Memories,

ADVANCED MATERIALS, Issue 1 2007
M.-J. Lee
A one-diode/one-resistor structure, Pt/NiO/Pt/p-NiOx/n-TiOx/Pt, has been fabricated. This novel structure exhibits bistable resistance switching under forward bias, while the diode suppresses resistance switching in the Pt/NiO/Pt memory cell under reverse bias (see figure). Its low processing temperature and small cell size, as well as excellent rectifying characteristics, make this Pt/p-NiOx/n-TiOx/Pt diode structure a promising switch element for high- density, nonvolatile memory devices with 3D stack and cross-point structures. [source]

Effect of Er:YAG and Diode lasers on the adhesion of blood components and on the morphology of irradiated root surfaces

JOURNAL OF PERIODONTAL RESEARCH, Issue 5 2006
Letícia Helena Theodoro
Objective:, The aim of this study was to evaluate in vitro, by scanning electron microscopy (SEM), the adhesion of blood components on root surfaces irradiated with Er:YAG (2.94 µm) and GaAlAs Diode (808 nm) lasers and the effects on the morphology of irradiated root surfaces. Methods:, One hundred samples of human teeth were obtained. They were previously planed and scaled with manual instruments and divided into five groups of 20 samples each: G1 (control group) , absence of treatment; G2 , Er:YAG laser (7.6 J/cm2); G3 , Er:YAG laser (12.9 J/cm2); G4 , Diode laser (90 J/cm2) and G5 , Diode laser (108 J/cm2). After these treatments, 10 samples of each group received a blood tissue but the remaining 10 did not. After laboratory treatments, the samples were obtained by SEM, the photomicrographs were analysed by the score of adhesion of blood components and the results were statistically analysed (Kruskall,Wallis and Mann,Whitney test). Results:, In relation to the adhesion of blood components, the study showed no significant differences between the control group and the groups treated with Er:YAG laser (p = 0.9633 and 0.6229). Diode laser radiation was less effective than control group and Er:YAG laser radiation (p < 0.01). Conclusions:, None of the proposed treatments increased the adhesion of blood components in a significant way when compared to the control group. Although the Er:YAG laser did not interfere in the adhesion of blood components, it caused more changes on the root surface, whereas the Diode laser inhibited the adhesion. [source]

Diode pumped 500-picosecond Nd:GdVO4 Raman laser

LASER PHYSICS LETTERS, Issue 5 2004
T. T. Basiev
Abstract Self-Raman frequency conversion in a diode-pumped passively Q-switched Nd:GdVO4 laser has been demonstrated. The use of LiF:F,2 crystal as a saturable absorber has provided effective Q-switching of the Nd:GdVO4 laser with high pulse energy. The laser pulse duration at the 1st Stokes wavelength 1174 nm was as short as 500 ps. Diode-to-Raman optical conversion efficiency more than 2 % at the pulse peak power of 9 kW was achieved. (© 2004 by ASTRO, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

Diodenlaser sind im Kommen!

LASER TECHNIK JOURNAL, Issue 2 2007
Chefredakteur Andreas Thoß Dr.
Im November des vergangenen Jahres gab es am Fraunhofer IWS in Dresden einen spannenden Workshop zum Thema "Industrielle Anwendungen von Hochleistungsdiodenlasern". Bei den Vorträgen kamen nicht nur die Diodenlaserhersteller und -anwender, sondern auch Mikrooptikfirmen zu Wort. Und besonders von dieser Seite kamen einige interessante Gedanken zum Vergleich von Hochleistungsdiodenlasern mit den "neuen" Festkörperlasern. Dabei ging es darum, dass das System "Diodenlaser plus Mikrooptik plus Faser" mit inzwischen bis zu 10 kW Ausgangsleistung durchaus konkurrenzfähig ist. Neben den deutlich verbesserten Parametern der Diodenlaser ist das Know-how, Diode, Optik und Faser effizient miteinander zu verbinden, ein entscheidender Punkt. Der Unterschied ist noch im Faserdurchmesser sichtbar, aber schon da ist es für einige Anwendungen zweitrangig, ob die Strahlquelle ein Faser-, ein Scheiben- oder doch "nur" ein Diodenlaser ist. Die hervorragende Strahlqualität der Faser- und Scheibenlaser ermöglicht sicher einige neue Anwendungen, für andere jedoch ist sie unnötig. Und wenn die Strahlung ohnehin durch Mikrooptik geformt wird - beispielsweise zu einer schmalen Linie - kann der Diodenlaser den anderen Systemen durchaus überlegen sein. Dazu kommt der Preis als (entscheidendes) Argument und auch da spricht einiges für den Diodenlaser. Neben der vergleichsweise einfachen Konstruktion und der hohen Effizienz sahen die Hersteller noch andere Vorteile: So wird sich eine positive Marktentwicklung bei diodengepumpten Lasern auch auf den Preis für Pumpdioden auswirken und damit natürlich auch auf den Preis der High-Power-Diodenlasersysteme. Dazu kommt, dass im Rahmen des Förderprogramms BRIOLAS (BMBF) die Weiterentwicklung von Hochleistungsdiodenlasern massiv gefördert wird. Zu BRIOLAS gehört sowohl die Entwicklung einer neuen Generation von brillanten Diodenmodulen (BRILASI) als auch die Automatisierung der Montagetechnologie (INLAS). Man darf also erwarten, dass die Diodenlaser noch besser und noch preiswerter werden. Und dementsprechend werden auch die Diodenlaseranwendungen in den nächsten Jahren mehr Aufmerksamkeit bekommen. Einige Beispiele für neue Entwicklungen auf dem Gebiet finden Sie in diesem Heft in der Rubrik "Diodenlaseranwendung". Eine wichtige Voraussetzung für die Entwicklung neuer Applikationsfelder ist ein detailliertes Verständnis der Prozesse beim Schweißvorgang. Die verschiedenen Systeme zur Prozeßüberwachung (zum Beispiel das auf dem Titelbild) geben schon eine Vielzahl von Informationen, die aber immer durch die Art des Detektors eingeschränkt sind. Tiefere Einblicke versprechen an der Stelle numerische Simulationen. Der Beitrag von Peter Berger (IFSW Stuttgart) bietet auf Seite 31 eine Einführung in dieses komplexe Gebiet. Das Thema des Tutorials in diesem Heft ist ein Dauerbrenner: die Messung von Strahlparametern bei Hochleistungslasern. Hier ist in den letzten Jahren viel passiert, inzwischen gibt es nicht nur neue Normen sondern auch eine Vielzahl von Detektoren. Der Beitrag auf Seite 46 liefert Ihnen einen Einstieg in das Thema und eine Übersicht, was man mit welchem Detektor messen kann. [source]

Novel Light Emitting Diode Using Organic Electroluminescence Microcapsules

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2003
Jae-Seok Heo
Abstract Novel light emitting diodes (LEDs) were prepared using electroluminescence (EL) material/polymer microcapsules (ELC). N-vinylcarbazole as a hole-transporting component and methyl methacrylate (MMA) were copolymerized for producing the seed particles using dispersion polymerization. An oxadiazole derivative, synthesized as a electron-transporting component, and tris(8-hydroxyquinolinato) aluminium(III) (Alq3) were incorporated into the polymer particles by using the solute co-diffusion method (SCM). The LEDs for the EL characterization were fabricated in a thin sandwich configuration: Al anode/ELC/ITO cathode. The surface imaging of the LED prepared using ELC was performed by atomic force microscopy (AFM). The EL characteristics of the ELC were investigated by UV, photoelectron and luminescence spectroscopy, and the current-voltage and the light-voltage characteristics for the LED were determined. Encapsulation procedure using solute co-diffusion method (SCM). [source]

III-V concentrator solar cell reliability prediction based on quantitative LED reliability data,

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2007
Manuel Vázquez
Abstract III-V Multi Junction (MJ) solar cells based on Light Emitting Diode (LED) technology have been proposed and developed in recent years as a way of producing cost-competitive photovoltaic electricity. As LEDs are similar to solar cells in terms of material, size and power, it is possible to take advantage of the huge technological experience accumulated in the former and apply it to the latter. This paper analyses the most important parameters that affect the operational lifetime of the device (crystalline quality, temperature, current density, humidity and photodegradation), taking into account experience on the reliability of LEDs. Most of these parameters are less stressed for a III-V MJ solar cell working at 1000 suns than for a high-power LED. From this analysis, some recommendations are extracted for improving the long-term reliability of the solar cells. Compared to high-power LEDs based on compound semiconductors, it is possible to achieve operational lifetimes higher than 105,hours (34 years of real-time operation) for III-V high-concentration solar cells. Copyright © 2007 John Wiley & Sons, Ltd. [source]

ChemInform Abstract: An Efficient Room-Temperature Silicon-Based Light-Emitting Diode.

CHEMINFORM, Issue 25 2001
Wai Lek Ng
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

An Alternative Approach to Constructing Solution Processable Multifunctional Materials: Their Structure, Properties, and Application in High-Performance Organic Light-Emitting Diodes

ADVANCED FUNCTIONAL MATERIALS, Issue 18 2010
Shanghui Ye
Abstract A new series of full hydrocarbons, namely 4,4,-(9,9,-(1,3-phenylene)bis(9H -fluorene-9,9-diyl))bis(N,N -diphenylaniline) (DTPAFB), N,N,-(4,4,-(9,9,-(1,3-phenylene)bis(9H -fluorene-9,9-diyl))bis(4,1-phenylene))bis(N -phenylnaphthalen-1-amine) (DNPAFB), 1,3-bis(9-(4-(9H -carbazol-9-yl)phenyl)-9H -fluoren-9-yl)benzene, and 1,3-bis(9-(4-(3,6-di- tert -butyl-9H -carbazol-9-yl)phenyl)-9H -fluoren-9-yl)benzene, featuring a highly twisted tetrahedral conformation, are designed and synthesized. Organic light-emitting diodes (OLEDs) comprising DNPAFB and DTPAFB as hole transporting layers and tris(quinolin-8-yloxy)aluminum as an emitter are made either by vacuum deposition or by solution processing, and show much higher maximum efficiencies than the commonly used N,N,-di(naphthalen-1-yl)- N,N,-diphenylbiphenyl-4,4,-diamine device (3.6 cd A,1) of 7.0 cd A,1 and 6.9 cd A,1, respectively. In addition, the solution processed blue phosphorescent OLEDs employing the synthesized materials as hosts and iridium (III) bis[(4,6-di-fluorophenyl)-pyridinato-N, C2] picolinate (FIrpic) phosphor as an emitter present exciting results. For example, the DTPAFB device exhibits a brightness of 47 902 cd m,2, a maximum luminescent efficiency of 24.3 cd A,1, and a power efficiency of 13.0 lm W,1. These results show that the devices are among the best solution processable blue phosphorescent OLEDs based on small molecules. Moreover, a new approach to constructing solution processable small molecules is proposed based on rigid and bulky fluorene and carbazole moieties combined in a highly twisted configuration, resulting in excellent solubility as well as chemical miscibility, without the need to introduce any solubilizing group such as an alkyl or alkoxy chain. [source]

The Role of Transition Metal Oxides in Charge-Generation Layers for Stacked Organic Light-Emitting Diodes

ADVANCED FUNCTIONAL MATERIALS, Issue 11 2010
Sami Hamwi
Abstract The mechanism of charge generation in transition metal oxide (TMO)-based charge-generation layers (CGL) used in stacked organic light-emitting diodes (OLEDs) is reported upon. An interconnecting unit between two vertically stacked OLEDs, consisting of an abrupt heterointerface between a Cs2CO3 -doped 4,7-diphenyl-1,10-phenanthroline layer and a WO3 film is investigated. Minimum thicknesses are determined for these layers to allow for simultaneous operation of both sub-OLEDs in the stacked device. Luminance,current density,voltage measurements, angular dependent spectral emission characteristics, and optical device simulations lead to minimum thicknesses of the n-type doped layer and the TMO layer of 5 and 2.5,nm, respectively. Using data on interface energetic determined by ultraviolet photoelectron and inverse photoemission spectroscopy, it is shown that the actual charge generation occurs between the WO3 layer and its neighboring hole-transport material, 4,4',4"-tris(N -carbazolyl)-triphenyl amine. The role of the adjacent n-type doped electron transport layer is only to facilitate electron injection from the TMO into the adjacent sub-OLED. [source]

Enhancement of Light Extraction Through the Wave-Guiding Effect of ZnO Sub-microrods in InGaN Blue Light-Emitting Diodes

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2010
Ki Seok Kim
Abstract The improvement of the light extraction efficiency (LEE) of a conventional InGaN blue light-emitting diode (LED) by the incorporation of one-dimensional ZnO sub-microrods is reported. The LEE is improved by 31% through the wave-guiding effect of ZnO sub-microrods compared to LEDs without the sub-microrods. Different types of ZnO microrods/sub-microrods are produced using a simple non-catalytic wet chemical growth method at a low temperature (90,°C) on an indium-tin-oxide (ITO) top contact layer with no seed layer. The crystal morphologies of needle-like or flat-top hexagonal structures, and the ZnO microrods/sub-microrod density and size are easily modified by controlling the pH value and growth time. The wave-guiding phenomenon within the ZnO rods is observed using confocal scanning electroluminescence microscopy and micro-electroluminescence spectra. [source]

Variations in Hole Injection due to Fast and Slow Interfacial Traps in Polymer Light-Emitting Diodes with Interlayers

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2010
M. James Harding
Abstract Detailed studies on the effect of placing a thin (10,nm) solution-processable interlayer between a light-emitting polymer (LEP) layer and a poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic)-acid-coated indium tin oxide anode is reported; particular attention is directed at the effects on the hole injection into three different LEPs. All three different interlayer polymers have low ionization potentials, which are similar to those of the LEPs, so the observed changes in hole injection are not due to variations in injection barrier height. It is instead shown that changes are due to variations in hole trapping at the injecting interface, which is responsible for varying the hole current by up to two orders of magnitude. Transient measurements show the presence of very fast interfacial traps, which fill the moment charge is injected from the anode. These can be considered as injection pathway dead-ends, effectively reducing the active contact surface area. This is followed by slower interfacial traps, which fill on timescales longer than the carrier transit time across the device, further reducing the total current. The interlayers may increase or decrease the trap densities depending on the particular LEP involved, indicating the dominant role of interfacial chain morphology in injection. Penetration of the interlayer into the LEP layer can also occur, resulting in additional changes in the bulk LEP transport properties. [source]

Phenylcarbazole-Based Phosphine Oxide Host Materials For High Efficiency In Deep Blue Phosphorescent Organic Light-Emitting Diodes

ADVANCED FUNCTIONAL MATERIALS, Issue 22 2009
Soon Ok Jeon
Abstract Highly efficient deep blue phosphorescent organic light-emitting diodes are developed using novel phenylcarbazole-based phosphine oxide host materials (PPO1 and PPO2). A deep blue phosphorescent dopant, tris((3,5-difluoro-4-cyanophenyl)pyridine) iridium, is doped into PPO1 and PPO2 at a doping concentration of 15% and a high quantum efficiency of 18.4% is obtained with color coordinates of (0.14, 0.15). [source]

Selective Angle Electroluminescence of Light-Emitting Diodes based on Nanostructured ZnO/GaN Heterojunctions

ADVANCED FUNCTIONAL MATERIALS, Issue 21 2009
Hang-Kuei Fu
Abstract Selective angle electroluminescence of violet light with a peak wavelength of 405,nm from light-emitting diodes based on nanostructured p-GaN/ZnO heterojunctions is reported. The fabrication of well-aligned nanobottles with excellent crystalline quality is achieved by chemical vapor deposition at temperatures as low as 450,°C with a specially designed upside-down arrangement of substrate configuration. Selective angle light sources are essential in our daily life. With the geometry of the nanobottle waveguides, it is very easy to realize such a practical application. Therefore, the discovery reported here should be very useful for the future development of many unique optoelectronic devices. [source]

Electron-Rich Alcohol-Soluble Neutral Conjugated Polymers as Highly Efficient Electron-Injecting Materials for Polymer Light-Emitting Diodes

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2009
Fei Huang
Abstract We report the design and synthesis of three alcohol-soluble neutral conjugated polymers, poly[9,9-bis(2-(2-(2-diethanolaminoethoxy) ethoxy)ethyl)fluorene] (PF-OH), poly[9,9-bis(2-(2-(2-diethanol-aminoethoxy)ethoxy)ethyl)fluorene- alt -4,4,-phenylether] (PFPE-OH) and poly[9,9-bis(2-(2-(2-diethanolaminoethoxy) ethoxy)ethyl)fluorene- alt -benzothiadizole] (PFBT-OH) with different conjugation length and electron affinity as highly efficient electron injecting and transporting materials for polymer light-emitting diodes (PLEDs). The unique solubility of these polymers in polar solvents renders them as good candidates for multilayer solution processed PLEDs. Both the fluorescent and phosphorescent PLEDs based on these polymers as electron injecting/transporting layer (ETL) were fabricated. It is interesting to find that electron-deficient polymer (PFBT-OH) shows very poor electron-injecting ability compared to polymers with electron-rich main chain (PF-OH and PFPE-OH). This phenomenon is quite different from that obtained from conventional electron-injecting materials. Moreover, when these polymers were used in the phosphorescent PLEDs, the performance of the devices is highly dependent on the processing conditions of these polymers. The devices with ETL processed from water/methanol mixed solvent showed much better device performance than the devices processed with methanol as solvent. It was found that the erosion of the phosphorescent emission layer could be greatly suppressed by using water/methanol mixed solvent for processing the polymer ETL. The electronic properties of the ETL could also be influenced by the processing conditions. This offers a new avenue to improve the performance of phosphorescent PLEDs through manipulating the processing conditions of these conjugated polymer ETLs. [source]

Phosphorescent OLEDs: Synthesis and Characterization of Red-Emitting Iridium(III) Complexes for Solution-Processable Phosphorescent Organic Light-Emitting Diodes (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 14 2009
Mater.
On page 2205, S.H. Jin and co-workers report on the development of red-emitting iridium(III) complexes for solution-processable phosphorescent organic light-emitting diodes (PhOLEDs). This frontispiece image shows the fabrication of full-color PhOLEDs by an inkjet printing method. The combination of good efficiency and color purity identifies this material as a promising candidate for red phosphorescent doping of PhOLEDs. Structure-property relationships for improving the performance of such devices are also investigated. [source]

Synthesis and Characterization of Red-Emitting Iridium(III) Complexes for Solution-Processable Phosphorescent Organic Light-Emitting Diodes

ADVANCED FUNCTIONAL MATERIALS, Issue 14 2009
Seung-Joon Lee
Abstract A new series of highly efficient red-emitting phosphorescent Ir(III) complexes, (Et-CVz-PhQ)2Ir(pic-N-O), (Et-CVz-PhQ)2Ir(pic), (Et-CVz-PhQ)2Ir(acac), (EO-CVz-PhQ)2Ir(pic-N-O), (EO-CVz-PhQ)2Ir(pic), and (EO-CVz-PhQ)2Ir(acac), based on carbazole (CVz)-phenylquinoline (PhQ) main ligands and picolinic acid N-oxide (pic-N-O), picolinic acid (pic), and acetylacetone (acac) ancillary ligands, are synthesized for phosphorescent organic light-emitting diodes (PhOLEDs), and their photophysical, electrochemical, and electroluminescent (EL) properties are investigated. All of the Ir(III) complexes have high thermal stability and emit an intense red light with an excellent color purity at CIE coordinates of (0.65,0.34). Remarkably, high-performance solution-processable PhOLEDs were fabricated using Ir(III) complexes with a pic-N-O ancillary ligand with a maximum external quantum efficiency (5.53%) and luminance efficiency (8.89,cd,A,1). The novel use of pic-N-O ancillary ligand in the synthesis of phosphorescent materials is reported. The performance of PhOLEDs using these Ir(III) complexes correlates well with the results of density functional theory calculations. [source]

Polyfluorene Light-Emitting Diodes: Understanding the Nature of the States Responsible for the Green Emission in Oxidized Poly(9,9-dialkylfluorene)s: Photophysics and Structural Studies of Linear Dialkylfluorene/Fluorenone Model Compounds (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 13 2009
Mater.
Polyfluorenes, whilst attractive candidates for polymer light-emitting diodes, are susceptible to oxidative degradation. This degradation results in significant green emission. Although it has been linked to the formation of fluorenones, the precise relationship between fluorenones and the observed color shift remains widely debated. On page 2147, Chan et al. report a study on this relationship with the use of a series of model compounds. Inter-molecular fluorenone,fluorenone interaction is reported to be an essential requirement for the color shift. [source]

Optically-Pumped Lasing in Hybrid Organic,Inorganic Light-Emitting Diodes

ADVANCED FUNCTIONAL MATERIALS, Issue 13 2009
Myoung Hoon Song
Abstract Here, the use of metal oxide layers both for charge transport and injection into an emissive semiconducting polymer and also for the control of the in-plane waveguided optical modes in light-emitting diodes (LEDs) is reported. The high refractive index of zinc oxide is used to confine these modes away from the absorbing electrodes, and include a nano-imprinted grating in the polymer layer to introduce distributed feedback and enhance optical out-coupling. These structures show a large increase in the luminescence efficiency over conventional devices, with photoluminescence efficiency increased by up to 45%. Furthermore, optically-pumped lasing in hybrid oxide polymer LEDs is demonstrated. A tuneable lasing emission is also obtained in a single device structure by employing a graduated thickness of a zinc oxide inter-layer. This demonstrates the scope for using such architectures to improve the external efficiency of organic semiconductor LEDs, and opens new possibilities for the realization of polymer injection lasers. [source]

Designing a Stable Cathode with Multiple Layers to Improve the Operational Lifetime of Polymer Light-Emitting Diodes

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2009
Tae-Woo Lee
Abstract The short device lifetime of blue polymer light-emitting diodes (PLEDs) is still a bottleneck for commercialization of self-emissive full-color displays. Since the cathode in the device has a dominant influence on the device lifetime, a systematic design of the cathode structure is necessary. The operational lifetime of blue PLEDs can be greatly improved by introducing a three-layer (BaF2/Ca/Al) cathode compared with conventional two-layer cathodes (BaF2/Al and Ba/Al). Therefore, the roles of the BaF2 and Ca layers in terms of electron injection, luminous efficiency, and device lifetime are here investigated. For efficient electron injection, the BaF2 layer should be deposited to the thickness of at least one monolayer (,3,nm). However, it is found that the device lifetime does not show a strong relation with the electron injection or luminous efficiency. In order to prolong the device lifetime, sufficient reaction between BaF2 and the overlying Ca layer should take place during the deposition where the thickness of each layer is around that of a monolayer. [source]

Characteristics of Solution-Processed Small-Molecule Organic Films and Light-Emitting Diodes Compared with their Vacuum-Deposited Counterparts

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2009
Tae-Woo Lee
Abstract Although significant progress has been made in the development of vacuum-deposited small-molecule organic light-emitting diodes (OLEDs), one of the most desired research goals is still to produce flexible displays by low-cost solution processing. The development of solution-processed OLEDs based on small molecules could potentially be a good approach but no intensive studies on this topic have been conducted so far. To fabricate high-performance devices based on solution-processed small molecules, the underlying nature of the produced films and devices must be elucidated. Here, the distinctive characteristics of solution-processed small-molecule films and devices compared to their vacuum-deposited counterparts are reported. Solution-processed blue OLEDs show a very high luminous efficiency (of about 8.9,cd A,1) despite their simplified structure. A better hole-blocking and electron-transporting layer is essential for achieving high-efficiency solution-processed devices because the solution-processed emitting layer gives the devices a better hole-transporting capability and more electron traps than the vacuum-deposited layer. It is found that the lower density of the solution-processed films (compared to the vacuum-deposited films) can be a major cause for the short lifetimes observed for the corresponding devices. [source]

Triplet Harvesting in Hybrid White Organic Light-Emitting Diodes

ADVANCED FUNCTIONAL MATERIALS, Issue 9 2009
Gregor Schwartz
Abstract White organic light-emitting diodes (OLEDs) are highly efficient large-area light sources that may play an important role in solving the global energy crisis, while also opening novel design possibilities in general lighting applications. Usually, highly efficient white OLEDs are designed by combining three phosphorescent emitters for the colors blue, green, and red. However, this procedure is not ideal as it is difficult to find sufficiently stable blue phosphorescent emitters. Here, a novel approach to meet the demanding power efficiency and device stability requirements is discussed: a triplet harvesting concept for hybrid white OLED, which combines a blue fluorophor with red and green phosphors and is capable of reaching an internal quantum efficiency of 100% if a suitable blue emitter with high-lying triplet transition is used is introduced. Additionally, this concept paves the way towards an extremely simple white OLED design, using only a single emitter layer. [source]

Multifunctional Crosslinkable Iridium Complexes as Hole Transporting/Electron Blocking and Emitting Materials for Solution-Processed Multilayer Organic Light-Emitting Diodes

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2009
Biwu Ma
Abstract Here, a new series of crosslinkable heteroleptic iridium (III) complexes for use in solution processed phosphorescent organic light emitting diodes (OLEDs) is reported. These iridium compounds have the general formula of (PPZ-VB)2Ir(C,N), where PPZ-VB is phenylpyrazole (PPZ) vinyl benzyl (VB) ether; and the C,N ligands represent a family of four different cyclometallating ligands including 1-phenylpyrazolyl (PPZ) (1), 2-(4,6-difluorophenyl)pyridyl (DFPPY) (2), 2-(p-tolyl)pyridyl (TPY) (3), and 2-phenylquinolyl (PQ) (4). With the incorporation of two crosslinkable VB ether groups, these compounds can be fully crosslinked after heating at 180,°C for 30,min. The crosslinked films exhibit excellent solvent resistance and film smoothness which enables fabrication of high-performance multilayer OLEDs by sequential solution processing of multiple layers. Furthermore, the photophysical properties of these compounds can be easily controlled by simply changing the cyclometallating C,N ligand in order to tune the triplet energy within the range of 3.0,2.2,eV. This diversity makes these materials not only suitable for use in hole transporting and electron blocking but also as emissive layers of several colors. Therefore, these compounds are applied as effective materials for all-solution processed OLEDs with (PPZ-VB)2IrPPZ (1) acting as hole transporting and electron blocking layer and host material, as well as three other compounds, (PPZ-VB)2IrDFPPY (2), (PPZ-VB)2IrTPY(3), and (PPZ-VB)2IrPQ(4), used as crosslinkable phosphorescent emitters. [source]