聚芴类有机电致发光的材料和器件

综述了聚芴类有机电致发光领域中材料和器件的研究现况和展望.主要围绕有机电致发光的基本原理、近年来聚芴类有机电致发光的材料制备、器件改进情况和有机电致发光的应用前景三方面内容进行了评述.     

不同电极对蓝光有机电致发光器件性能的影响

利用高真空多源型有机分子沉积系统分别制备了不同负电极为Al、LiF/Al和Mg:Ag的有机小分子多层电致发光器件,比较了不同负极对以五苯基环戊二烯（PPCP）为发光层的蓝光有机电致发光器件性能的影响,发现以LiF/Al作负极的器件在综合性能上优于其它器件。其中器件ITO／TPD／PPDP／Alq/LiF/Al蓝光发射的最大发光亮度达2375cd/m^2,最大发光效率为0.26lm/W.     

以ILTO为阳极的高效有机电致发光器件

以高功函数的掺杂钛酸镧的氧化铟薄膜(ILTO)及氧化铟锡(ITO)作为阳极,制备了Glass/anode/NPB/Alq3/LiF/Al结构的有机电致发光器件。得益于ILTO较好的掺杂性、低的表面粗糙度、高的可见光透过率以及高的有效功函数,以ILTO为阳极的有机电致发光器件的开路电压得到降低,最高亮度、电流效率、功率效率以及外量子效率均获得了成倍的提高。研究结果表明,ILTO是一种潜在的光学窗口材料,有望在各种光电器件中得到广泛的应用。     

彩色有机薄膜电致发光及动态矩阵显示

研究了绿色、红色、蓝色和白色4种有机薄膜电致发光器件.通过掺杂得到了高稳定性的绿色及红色器件,绿色器件的半寿命达14000小时(初始亮度100cd/m²),红色器件的半寿命为7500小时(初始亮度50cd/m²).还研究了具有空穴锁定层及非锁定层的多种不同结构和材料的蓝色及白色器件.研究表明无论蓝色还是白色器件,具有空穴锁定层的器件稳定性较差,老化过程中界面势垒的变化很大.非锁定层的蓝色及白色器件中,新材料JBEM比DPVBi有更优越的性能.JBEM构成的蓝色器件的半亮度寿命为1035小时(初始亮度100cd/m²).由JBEM构成的白色器件中,由蓝色及红色掺杂在同一层的器件得到最好的稳定性,其半亮度寿命为2800小时(初始亮度100cd/m²),而且它具有发光颜色不随电流变化而变化的特点.在稳定性改善的基础上研制成功96×60线,分辨率为2线/mm的绿色及白色矩阵显示屏,还利用选择蒸发的方法制造了彩色矩阵屏,设计和研制了驱动及控制电路,实现了动态显示.     

基于器件结构提高TADF-OLED器件的发光性能

为了提高以TADF材料作为主体、天蓝色荧光材料作为客体的混合薄膜的OLED器件光电性能,我们调整了器件结构,使主体材料发挥其优势。制备了基本结构为ITO/NPB(40 nm)/DMAC-DPS∶x%BUBD-1(40 nm)/Bphen(30 nm)/LiF(0.5 nm)/Al的OLED器件。研究了主-客体材料在不同掺杂浓度下的OLED器件的光电特性。为了提高主体材料的利用率,在空穴传输层和发光层之间加入10 nm的DMAC-DPS作为间隔层;然后,在阳极和空穴传输层之间加入HAT-CN作为空穴注入层,形成HAT-CN/NPB结构的PN结,有效降低了器件的启亮电压(2.7 V)。测量了有无HAT-CN的单空穴器件的阻抗谱。结果表明,在最佳掺杂比例(2%)下,器件的外量子效率(EQE)达到4.92%,接近荧光OLED的EQE理论极限值;加入10 nm的DMAC-DPS作为间隔层,使得器件的EQE达到5.37%;HAT-CN/NPB结构的PN结有效地降低了器件的启亮电压(2.7 V),将OLED器件的EQE提高到5.76%;HAT-CN的加入提高了器件的空穴迁移率,降低了单空穴器件的阻抗。TADF材料作为主体材料在提高OLED器件的光电性能方面具有很大的潜力。     

Organic light emitting devices

The purpose of this paper is to provide general information about basic physical processes involved in organic electroluminescence and to present the main parameters and advantages of organic light emitting devices (OLEDs).     

Bi‐directional organic light‐emitting diodes with nanoparticle‐enhanced light outcoupling

An effective method is presented for enhancing the outcoupling efficiency of translucent/bi‐directional organic light‐emitting diodes (TL/BD‐OLEDs) with a bottom indium tin oxide (ITO) anode and a top cathode comprised of a thin Ag layer covered with an organic capping layer. Upon insertion of a nanoparticle (NP)‐based scattering layer (NPSL) between the substrate and the ITO anode, the TL/BD‐OLEDs exhibit significantly enhanced external quantum efficiency (EQE) in both emission directions. Furthermore, the NPSL improves the color stability of the TL/BD‐OLEDs over a wide range of viewing angles. Simulations based on geometrical and statistical optics are performed to elucidate the mechanism by which the efficiency is enhanced and to establish strategies for further optimization. Simulations performed on the scattering layers with varying NP volume percentage reveal that the bottom‐side emission is governed by competition between waveguide‐mode extraction and backward scattering by NPs in the film, while the top‐side emission is largely dominated by the latter. Optimized bi‐directional OLEDs achieve a 1.64‐fold enhanced EQE compared to reference devices without NPSL.     

MoO_3作空穴注入层的有机电致发光器件(英文)

研究了三氧化钼(MoO3)薄层作为有机电致发光器件空穴注入层的器件性能和注入机制。发现1nm厚度下发光器件性能最佳,器件的最大电流效率比对比发光器件的最大电流效率提高1.6倍。器件的电容曲线表明MoO3薄层能有效提高空穴载流子的注入,多数载流子开始注入的拐点大约降低了9V。单空穴载流子电流曲线说明MoO3器件的电流注入是空间电荷受限电流注入机制,MoO3使阳极界面处形成欧姆接触,而对比器件的电流注入是陷阱电荷受限电流注入机制。器件的光伏曲线进一步说明器件性能的提高是由于MoO3层能使阳极界面能级分布发生改变,1nmMoO3厚度下器件的内建电势从对比器件的0.25V提高到了0.8V,有效降低了空穴注入势垒,提高了器件性能,但过厚的MoO3层由于增加了器件的串联内阻,会导致器件性能降低。     

On the improvement of the electroluminescent signal of organic light emitting diodes by the presence of an ultra‐thin metal layer at the interface organic/ITO

The electroluminescent (EL) signal of organic light emitting diodes (OLEDs) based on simple “hole transporting layer/electron transporting layer” (HTL/ETL) structures has been studied as a function of the anode/HTL interface, the anode being an indium tin oxide (ITO) film. It is shown that the electroluminescent (EL) signal increases when a metal ultra‐thin layer is introduced between the anode and the HTL. Experimental results show that the work function value of the metal is only one of the factors which allow improving the EL signal via better hole injection efficiency. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

互混型有机电致发光器件

通过共蒸镀空穴传输材料TPD和电子传输材料Alq₃,在普通双层器件的异质结界面引入了均匀互混层,并研究了互混层的厚度变化对器件光电性能的影响。互混层的引入在一定程度上改善了普通双层器件的异质结界面由于高浓度载流子积聚导致的高电场和界面缺陷对器件主要性能(效率和寿命)的负面影响。我们发现一定厚度的互混层使器件的性能有所提高。     

高效率的有机电致发光器件

有机电致发光器件 (OL EDs)的发光机理包括电子和空穴从电极的注入、激子的形成及复合发光 ,其中 ,空穴和电子的注入平衡是非常重要的。为了平衡载流子的注入以得到高效率和稳定性好的器件 ,人们不仅使用了电子注入更为有效的 L i F/ Al[1] 和 Cs F/ Al[2 ] 等复合电极 ,同时也使用了空穴缓冲层 ,如 S.A.Van Slyke等 [3]在ITO和 NPB之间使用 Cu Pc,使得器件的稳定性得到了明显的提高 ;A.Gyoutoku等[4 ] 用碳膜使器件的半寿命超过 3 5 0 0小时 ;最近 ,Y.Kurosaka等 [5]和 Z.B.Deng[6 ]分别在 ITO和空穴传输层之间插入一薄层 Al…     

高效率和色稳定性的双超薄发光层的黄光有机电致发光器件

主要对rubrene黄光发光材料制作0.1nm厚度的超薄发光层的有机电致发光器件作了研究,并配合BCP空穴阻挡层探讨了对器件效率和色坐标稳定性的影响。双超薄rubrene发光层配合BCP空穴阻挡层的有机电致发光器件的性能得到了很好的改善,外加电压6V时,器件电流效率为6.35cd.A-1;外加电压10V时,器件发光亮度达到了7068cd.m-2。另外,在较大的外加电压驱动范围内,器件的色坐标一直保持在(0.49,0.49)。增加的发光效率和良好的色坐标稳定性主要是取决于空穴与电子的注入与输运平衡以及激子在超薄rubrene发光层中稳定性的复合平衡。     

基于接触势差法的表面功函数测试装置

利用接触势差法自行设计开发了一种新型的表面功函数测试装置。基本原理是参考电极与样品之间形成电容,计算流过参考电极与样品之间的电流,通过确定电流的零点来获得功函数。此测量仪器由函数发生、功率放大、振荡器等多个功能模块组成。能在空气环境中快速测量半导体、金属、金属氧化物薄膜的表面功函数。我们运用此装置成功地对有机电致发光的阳极氧化铟锡(ITO)薄膜、p型硅片的功函数进行了测量,得到了样品经过UV-Ozone处理前后功函数随时间变化的曲线,为器件的优化提供了依据。     

ITO阳极电阻对有机电致发光器件性能的影响

以不同方块电阻的ITO作为阳极,利用真空热蒸发的方法制备了双层结构有机电致发光器件ITO/TPD/Alq3/LiF/Al,定量研究了ITO阳极电阻对器件光电性能的影响。实验结果表明,具有较大阳极电阻的器件在一定的驱动电压下表现出较低的电流密度和亮度,我们认为主要原因是阳极电阻的分压导致用于载流子注入的有效驱动电压减少。扣除阳极电阻以后,我们发现用于载流子注入的有效驱动电压并不受阳极电阻的影响。另外,我们没有观察到阳极电阻对器件发光效率的明显影响。     

Optimization of microcavity OLED by varying the thickness of multi-layered mirror

We optimized the emission efficiency from a microcavity OLEDs consisting of widely used organic materials, N,N′-di(naphthalene-1-yl)-N,N′-diphenylbenzidine (NPB) as a hole transport layer and tris (8-hydroxyquinoline) (Alq₃) as emitting and electron transporting layer. LiF/Al was used as a cathode, while metallic Ag was used as an anode material. A LiF/NPB bi-layer or NPB layer on top of the cathode was considered to alter the optical properties of the top mirror. The electroluminescence emission spectra, electric field distribution inside the device, carrier density, recombination rate and exciton density were calculated as a function of the position of the emission layer. The results show that for optimal capping layers thicknesses, light output is enhanced as a result of the increase in both the reflectance and transmittance of the top mirror. Once the optimum structure has been determined, the microcavity OLED devices were fabricated and characterized. The experimental results have been compared to the simulations and the influence of the thickness of the mirror layers, emission region width and position on the performance of microcavity OLEDs was discussed.     

A New Conducting Polymer Electrode for Organic Electroluminescence Devices

Conducting polymer polydimethylsiloxane （PDMS） is studied for the high performance electrode of organic electroluminescence devices. A method to prepare the electrode consisting of a SiC thin film and PDMS is investigated. By using ultra thin SiC films with different thicknesses, the organic electroluminescence devices are obtained in an ultra vacuum system with the model device PDMS/SiC/PPV/Alq3, where PPV is poly para-phenylene vinylene and Alq3 is tris（S-hydroxyquinoline） aluminium. The capacitance voltage （C - V）, capacitance-frequency （C - F）, current-voltage （I - V）, radiation intensity-voltage （R - V） and luminance eFficiency-voltage （E - V） measurements are systematically studied to investigate the conductivity, Fermi alignment and devices properties in organic semiconductors. Scanning Kelvin probe measurement shows that the work function of PDMS/SiC anode with a 2.5-nm SiC over layer can be increased by as much as 0.28eV, compared to the conventional ITO anode. The result is attributed to the charge transfer effect and ohmic contacts at the interface.     

Improved performance of organic light-emitting devices with plasma treated ITO surface and plasma polymerized methyl methacrylate buffer layer

Transparent indium-tin-oxide (ITO) anode surface was modified using O₃ plasma and organic ultra-thin buffer layers were deposited on the ITO surface using 13.56 MHz rf plasma polymerization technique. A plasma polymerized methyl methacrylate (ppMMA) ultra-thin buffer layer was deposited between the ITO anode and hole transporting layer (HTL). The plasma polymerization of the buffer layer was carried out at a homemade capacitively coupled plasma (CCP) equipment. N,N′-Diphenyl-N,N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamine (TPD) as HTL, Tris(8-hydroxy-quinolinato)aluminum (Alq₃) as both emitting layer (EML)/electron transporting layer (ETL), and aluminum layer as cathode were deposited using thermal evaporation technique. Electroluminescence (EL) efficiency, operating voltage and stability of the organic light-emitting devices (OLEDs) were investigated in order to study the effect of the plasma surface treatment of the ITO anode and role of plasma polymerized methyl methacrylate as an organic ultra-thin buffer layer.     

具有Au/MoO_3空穴注入层的有机发光二极管

研究了单层MoO3(5nm)和复合Au(4nm)/MoO3(5nm)HILs对OLEDs器件性能的影响,器件结构为ITO/HIL/NPB(40nm)/Alq3(60nm)/LiF(1nm)/Al(100nm)。与单层MoO3HIL的器件相比,具有复合Au/MoO3HIL的器件具有较大的电流和亮度。这是由于Au的功函数介于ITO和MoO3之间,导致Au的引入提高了空穴的注入效率。     

有机异质结连接层C60/CuPc电荷产生能力研究

有机异质结连接层因其具有良好的透光性能、制备工艺和有机电致发光器件(Organic light-emitting diodes,OLEDs)完全兼容的优点,被广泛应用于叠层OLEDs中。在叠层OLEDs中,连接层可产生电荷,其工作性能是影响叠层OLEDs性能的关键因素之一。为了获得最佳性能的有机异质结连接层,本文制备了结构为glass/ITO/tris(8-hydroxyquinoline) aluminum(Alq_3)(60 nm)/C_(60)(x nm)/CuPc(y nm)/N,N′-bis(naphthalen-1-yl)-N,N′-bis (phenyl)-be-nzidine(NPB)(40 nm)/Al (100 nm)的有机器件,直接获得了有机异质结连接层C_(60)/CuPc产生的器件电流。通过结构优化发现,结构为C_(60)(30 nm)/CuPc(10 nm)的连接层具有最强的电荷产生能力,并对最优结构连接层形成的物理机制作了合理的解释.本文获得的结果可为理解有机异质结连接层工作机理以及制备高性能叠层OLEDs提供理论基础。     

硅片上顶发射的有机电致发光器件

为了更好地实现有机发光器件在硅片上的有源矩阵显示,有必要探讨在硅片上直接制作透明阴极的顶发射有机发光器件。在顶发射发光器件中,为了到达高的发光效率,底部阳极一般采用高反射率的金属。在通常所用的各种金属当中,金属银对可见光具有很高的反射率,然而由于其具有相当低的功函数,导致与有机材料间能级的不匹配,从而引起有机发光器件中阳极空穴注入的不理想而影响器件的性能。我们在硅片上制备顶发射的有机发光器件,用薄层QAD(quinacridone)作为发光层,表面修饰的银作为阳极,制备的有机发光器件的亮度在外加电压10V时达到13700cd／m^2,器件的最大电流效率在7V时达到4．3cd／A,是没有薄层QAD器件的2倍多,是由在器件中存在Alq3与QAD之间Foester能量转移机制引起的。