Tris(8-Hydroxyquinoline) Aluminum/2-(4-Biphenylyl)-5-(4-Tertbutylphenyl)-1,3,3-Oxadiazole Organic Multiple Quantum Wells for Electroluminescent Devices

Organic multiple quantum wells(OMQWs) consisting of alternating layers of organic materials have been fabricated from tris(8-hydroxyquinoline) aluminum(Alq)and 2-(4-biphenylyl)-5-(4-tertbutylphenyl)-1,3,3-oxadiazole(PBD) by a multisource-type high-vacuum organic molecular deposition.From the small-angle X-ray diffraction patterns of Alq/PBD OMQWs,a periodically layered structure is confirmed through the entire stack.The Alq layer thickness in the OMQWs was varied from 1 nm to 4 nm.From the optical absorption,photoluminescence and electroluminescence measurements,it is found that the exciton energy shifts to higher energy with decreasing Alq layer thickness,The changes of the exciton energy could be interpreted as the confinement effects of exciton in the Alq thin layers.Narrowing of the emission spectrum has also been observed for the electroluminescent devices (ELDs) with the OMQWs structure at room temperature.

Green Light-Emitting Organic Electroluminescent Device with a New Fluorescent Dye Dispersed in Poly(N-vinylcarbazole) Emitter Layer

Double-layer organic electroluminescent devices have been constructed. A new fluorescent dye, 9,10-bis(phenylethynyl)anthracence, was chosen as the dopant which was molecularly dispersed in the polymer film, and green light was observed from the device with luminance of 130cd/m(2) at 17V.

Fabrication of Organic/Polymeric Superlattice Structure and Its Use for Electroluminescent Device

Superlattices consisting of alternating layers of organic/polymeric materials have been fabricated from tris(8-hydroxyquinoline)aluminum(Alq3) and poly(N-vinylcarbazole)(PVK) by a multisource-type high-vacuum organic molecular deposition.The characteristics of superlattice structures are determined by the small-angle X-ray diffraction,optical absorption and photoluminescence.The electroluminescent devices with the superlattice structure have also been fabricated and the emission characteristics are discussed.

Fabrication of Green Electroluminescent Devices

A gadolinium ternary complex, tris(1 phenyl 3 methyl 4 isobutyryl 5 pyrazolone) (2, 2′ dipyridyl) gadolinium Gd(PMIP) 3(Bipy) was synthesized and used as a light emitting material in the organic electroluminescent devices. The devices exhibited the green electroluminescent (EL) emission peaking at 513 nm, originating from the Gd(PMIP) 3(Bipy). By improving the configuration, the device with a structure of ITO/poly(N vinylcarbazole) (PVK) (40 nm)/Gd(PMIP) 3(Bipy) (40 nm)/tris (8 hydroxyquinoline) aluminum (ALQ) (40 nm)/Mg∶Ag(200 nm)/Ag(100 nm) showed higher performance and a maximum luminance of 340 cd·m -2 at 18 V.

Organic Thin Film Electroluminescent Passive Matrix Display

Long life green emitting matrix display based on organic light emitting diode is reported. The pixel number is 96×60, equivalent pixel size 0.4×0.4 mm 2, and the pixel gap 0.1 mm. An image with no crosstalk between pixels is obtained. The average luminance of these pixels at duty cycle of 1/64 is 100 cd/m 2, and the power consumption is 0.6 W. The dark room contrast of 1∶100 is achieved without using a polarization filter.

Luminescent Enhancement of Heterostructure Organic Light-Emitting Devices Based on Aluminum Quinolines

High performance organic light-emitting devices （OLEDs） have been investigated by using fluorescent bis （2-methyl-8-quinolinolato）（para-phenylphenolato）aluminum（BAlq） as an emissive layer on the performance of multicolor devices consisting of N, N＇-bis-（1-naphthyl）-N,N＇diphenyl- 1,1＇-biphenyl-4,4＇- diamine （NPB） as hole transport layer. The results show that the performance of heterostructure blue light-emitting device composed of 8-hydroxyquinoline aluminum （Alq3） as an electron transport layer has been dramatically enhanced. In the case of high performance heterostructure devices, the electroluminescent spectra has been perceived to vary strongly with the thickness of the organic layers due to the different recombination region, which indicates that various color devices composed of identical components could be implemented by changing the film thickness of different functional layers.

Improved device reliability in organic light emitting devices by controlling the etching of indium zinc oxide anode

A controllable etching process for indium zinc oxide （IZO） films was developed by using a weak etchant of oxalic acid with a slow etching ratio. With controllable etching time and temperature, a patterned IZO electrode with smoothed surface morphology and slope edge was achieved. For the practical application in organic light emitting devices （OLEDs）, a sup- pression of the leak current in the current-voltage characteristics of OLEDs was observed. It resulted in a 1.6 times longer half lifetime in the IZO-based OLEDs compared to that using an indium tin oxide （ITO） anode etched by a conventional strong etchant of aqua regia.

Lowering the driving voltage and improving the luminance of blue fluorescent organic light-emitting devices by thermal annealing a hole injection layer of pentacene

We chose pentacene as a hole injection layer（HIL） to fabricate the high performance blue fluorescent organic lightemitting devices（OLEDs）. We found that the carrier mobility of the pentacene thin films could be efficiently improved after a critical annealing at temperature 120℃. Then we performed the tests of scanning electron microscopy, atomic force microscopy, and Kelvin probe to explore the effect of annealing on the pentacene films. The pentacene film exhibited a more crystalline form with better continuities and smoothness after annealing. The optimal device with 120℃ annealed pentacene film and n-doped electron transport layer（ETL） presents a low turn-on voltage of 2.6 V and a highest luminance of 134800 cd/m^2 at 12 V, which are reduced by 26% and improved by 50% compared with those of the control device.

Dependence of Performance of Organic Light-emitting Devices on Sheet Resistance of Indium-tin-oxide Anodes

The dependence of the performance of organic light-emitting devices（OLEDs） on the sheet resistance of indiumtin-oxide（ITO） anodes was investigated by measuring the steady state current density brightness voltage characteristics and the electroluminescent spectra. The device with a higher sheet resistance anode shows a lower current density, a lower brightness level, and a higher operation voltage. The electroluminescence（EL） efficiencies of the devices with the same structure but different ITO anodes show more complicated differences. Furthermore, the shift of the light-emitting zone toward the anode was found when an anode with a higher sheet resistance was used. These performance differences are discussed and attributed to the reduction of hole injection and the increase in voltage drop over ITO anode with the increase in sheet resistance.

Improvement of electron injection of organic light-emitting devices by inserting a thin aluminum layer into cesium carbonate injection layer

We investigate the electron injection effect of inserting a thin aluminum（Al） layer into cesium carbonate（Cs2CO3）injection layer. Two groups of organic light-emitting devices（OLEDs） are fabricated. For the first group of devices based on Alq3, we insert a thin Al layer of different thickness into Cs2CO3 injection layer, and the device＇s maximum current efficiency of 6.5 cd/A is obtained when the thickness of the thin Al layer is 0.4 nm. However, when the thickness of Al layer is 0.8 nm, the capacity of electron injection is the strongest. To validate the universality of this approach, then we fabricate another group of devices based on another blue emitting material. The maximum current efficiency of the device without and with a thin Al layer is 4.51 cd/A and 4.84 cd/A, respectively. Inserting a thin Al layer of an appropriate thickness into Cs2CO3 layer can result in the reduction of electron injection barrier, enhancement of the electron injection, and improvement of the performance of OLEDs. This can be attributed to the mechanism that thermally evaporated Cs2CO3 decomposes into cesium oxides, the thin Al layer reacts with cesium oxides to form Al–O–Cs complex, and the amount of the Al–O–Cs complex can be controlled by adjusting the thickness of the thin Al layer.

Study on Microcavity Organic Light-emitting Devices Containing Negative Refractive Index Dielectric Layer

A new structure containing negative refractive index dielectric layer（NRlDL） is introduced into microcavity. The properties of the new mierocavity organic light-emitting devices（MOLEDs） are investigated. In the experiment, the transfer matrix method is adopted. The dependence of reflectance and transmittance on the refractive index and thickness of NRIDL are analyzed in detail. Compared with the electroluminescence spectra of non-NRIDL diodes, the line widths of the spectra of the MOLEDs are narrower and all the peaks enhance. The results show that the new structure is beneficial to improve the performance and reduce the thickness of microcavity devices.

High-Efficiency Green Phosphorescent Organic Light-Emitting Diode Based on Simplified Device Structures

A high-efficiency green phosphorescent organic light emitting diode with a simplified structure is achieved that is free of a hole transport layer. The design of this kind of device structure not only saves the consumption of organic materials but also greatly reduces the structural heterogeneities and effectively facilitates the charge injection into the emissive layer. The resulting green phosphorescent organic light-emitting diodes （PHOLEDs） exhibit higher electroluminescent efficiency. The maximum external quantum efficiency and current efficiency reach 23.7% and 88 cd/A, respectively. Moreover the device demonstrates satisfactory stability, keeping 23.7% and 88cd/A, 22% and 82cd/A, respectively, at a luminance of 100 and 1000cd/m2. The working mechanism for achieving high efficiency based on such a simple device structure is discussed correspondingly. The improved charge carrier injection and transport balance are proved to prominently contribute to achieve the high efficiency and great stability at high luminance in the green PHOLEDs.

OLEDs瞬态延迟时间的模拟及在信号通讯的应用

基于有机发光二极管的电致发光原理,建立了载流子注入延迟时间和发光延迟时间模型,探索了延迟时间的影响因素,发现发光延迟时间与器件有效面积、器件厚度、外加电压等密切相关。通过制备不同面积的OLED器件,发现器件面积越小,发光延迟时间越短。以高速信号激励不同面积的OLEDs器件,面积为0.01 mm2的器件能够实现1 000 Mbit/s的信号传输速率,且能量利用率达到47.7%。

基于N-BDAVBi的非掺杂高效蓝色OLEDs

采用真空蒸镀方法,制备了以N-BDAVBi为发光层的高效率非掺杂蓝色有机电致发光器件,器件的结构为ITO/2T-NATA(40 nm)/NPB(10 nm)/N-BDAVBi((3+d)nm)/ADN(7 nm)/N-BDAVBi((3+d)nm)/ADN(7 nm)/Alq3(30 nm)/LiF(0.5 nm)/Al.通过调整N-BDAVBi层的厚度,研究了器件的发光性能.结果表明,当N-BDAVBi的厚度为7 nm时,器件在6 V电压下的电流效率最大,为4.38 cd/A;当N-BDAVBi的厚度为11 nm时,器件在13 V电压下的亮度最大,为13 200 cd/m2.该组器件的色坐标在0～13 V时均位于蓝光区域.

LiF超薄层引起的OLEDs发光光谱展宽(英文)

将LiF插入到发光层Alq3中,制备了有机电致发光器件(OLED),其器件的结构为:ITO/NPB(45 nm)/Alq3(x nm)/LiF(0.3 nm)/Alq3[(45-x)nm]/Al(150 nm)。发现器件的电致发光谱(Electroluminescence spectra,EL)有非常明显的展宽现象,这为白光器件的制备提供了一条简单的途径。通过对比LiF在Alq3中不同厚度处的发光谱,发现在x=10时谱线展宽最显著,器件最大亮度在22 V时达到8 260 cd/m2,最大效率可达4.83 cd/A,并对其光谱展宽的机理及器件特性进行了分析。

Optimization of a poly (p-phenylene benzobisoxazole)-based light-emitting device with a complex cathode structure

In this work, we report the preparation of a series of electroluminescent （EL） devices based on a high-performance polymer, poly（p-phenylene benzobisoxazole） （PBO）, and their optoelectronic properties, which have been rarely explored. The device structure is optimised using a complex cathode structure of tris-（8-hydoxyquinoline） aluminium （Alq3）/LiF/Al. By tuning the thickness of the Alq3 layer, we improve the device efficiency dramatically in an optimized condition. Further analysis reveals that the Alq3 layer in the complex cathode structure acts as a hole blocker in addition to its electron-injection role. A green light emission with a maximum brightness of 8.7×103 cd/m2 and a moderate current efficiency of 4.8 cd/A is obtained. These values are the highest ever reported for PBO devices. The high operational stability demonstrated by the present device makes it a promising tool for display and lighting applications. A new material is added to the selection of polymers used in this field up to now.

Influences of Injection Barrier and Mobility on Recombination Rate and Zone in OLEDs

The luminous efficiency of organic light-emitting devices depends on the recombination probability of electrons injected at the cathode and holes at the anode. A theoretical model to calculate the distribution of current densities and the recombination rate in organic single layer devices is presented taking into account the charge injection process at each electrode, charge transport and recombination in organic layer. The calculated results indicate that efficient single-layer devices are possible by adjusting the barrier heights at two electrodes and the carrier mobilities. Lowering the barrier heights can improve the electroluminescent(EL) efficiency pronouncedly in many cases, and efficient devices are still possible using an ohmic contact to inject the low mobility carrier, and a contact limited contact to inject the high mobility carrier. All in all, high EL efficiency needs to consider sufficient recombination, enough injected carriers and well transport.

Progress in next-generation organic electroluminescent materials:material design beyond exciton statistics

Exciton(or spin)statistics is a physical principle based on the statistics of spin multiplicity.In electroluminescence,injected electrons and holes have randomized spin states,and usually form singlet or triplet excitons in the ratio of 1:3.Exciton statistics determines that the upper limit of internal quantum efficiency is 25%in fluorescent devices,since only singlet exciton can decay radiatively.However,both experimental and theoretical evidence indicate that the actual efficiency can exceed the exciton statistics limit of 25%by utilizing materials with special electronic structure and optimized device structures.These results bring light to break through the exciton statistics limit and develop new-generation fluorescent materials with low cost and high efficiency.Recently,the exciton statistics,which has attracted great attention in the past decade,is being rejuvenated due to the discovery of some fluorescent materials with abnormally high efficiencies.In view of their significance in theoretical research of organic semiconductors and developing new-generation OLED materials,such materials are widely investigated in both academic institutions and industry.Several key issues still require further clarification for this kind of materials,such as the molecular design concepts.Herein,we review the progress of the materials with efficiency exceeding the exciton statistics limit,and the routes to improve exciton utilization efficiency.In the end,we present an innovative pathway to fully harvest the excitons in fluorescent devices,namely,"hot exciton"model and relevant fluorescence material with hybridized local and charge-transfer(HLCT)excited state.

Enhanced efficiency and brightness in organic lightemitting devices with MoO_3 as hole-injection layer

The organic light-emitting devices(OLEDs) using 4,4',4''-tris{N-(3-methylphenyl)-N-phenylamin}triphenylamine(m-MTDATA) and MoO_3 or 1,3,5-triazo-2,4,6-triphosphorine-2,2,4,4,6,6-tetrachloride(TAPC) and MoO_3 as the hole-injection layer(HIL) were fabricated. MoO_3 can be expected to be a good injection layer material and thus enhance the emission performance of OLED. The highest occupied molecular(HOMO) of MoO_3 is between those of m-MTDATA or TAPC and N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine(NPB),which reduces the hole-injection barrier and improves the luminance of the OLEDs. The current efficiency is improved compared with that of the device without the MoO_3 layer. The highest luminous efficiency of the device with 2-nm-thick MoO_3 as HIL is achieved as 5.27 cd/A at 10 V,which is nearly 1.2 times larger than that of the device without it. Moreover,the highest current efficiency and power efficiency of the device with the structure indium-tin oxide(ITO)/TAPC(40 nm)/MoO_3(2 nm)/Tc Ta:Ir(ppy)3(10%,10 nm)/ tris-(8-hydroxyquinoline) aluminium(Alq)(60 nm)/Li F(1 nm)/Al are achieved as 37.15 cd/A and 41.23 lm/W at 3.2 V and 2.8 V,respectively.

采用Li_3Nn型掺杂层作为电子注入层的OLED器件研究

相对于传统的无机半导体材料,有机半导体材料特别是有机电子传输材料的载流子浓度和迁移率较低,从而影响了有机发光器件的亮度、效率等性能.为了提高有机发光器件器件性能必须增强电子注入和传输能力,对有机电子传输材料进行n型电学掺杂能够有效地提高电子的注入和传输能力.本文利用Li3N作为n型掺杂剂,以掺杂层Alq3∶Li3N作为电子注入层,有效地提高了有机发光器件器件的性能,在掺杂浓度为5%,掺杂层厚度为10 nm时器件性能表现为最优.Li3N在空气中稳定,并且在较低的温度和压强下能分解产生Li原子和氮气,避免了采用金属掺杂剂如Li、Cs等材料时易受空气中水分和氧气影响的缺点,有利于工艺处理.