空穴传输层对有机电致发光器件性能的影响

制备了结构为ITO/MoO₃(40 nm)/空穴传输层/CBP:Ir(ppy)₂acac(8%)(30 nm)/BCP(10 nm)/Alq₃(40 nm)/LiF(1 nm)/Al(100 nm)的器件,其中Ir(ppy)₂acac为绿色磷光染料,空穴传输层分别为TAPC(50 nm)、TAPC(40 nm)/TCTA(10 nm)、NPB(50 nm)、NPB(40 nm)/TCTA(10 nm)。通过使用4种不同结构的空穴传输层,对器件的发光性能进行了研究。结果表明,空穴传输层对器件的发光性能有较大影响。在电压为6 V、电流密度为2 mA/cm²的条件下,4种结构的器件的电流效率分别为52.5,67.8,35.6,56.6 cd/A。其原因是TAPC/TCTA及NPB/TCTA能级结构更有利于空穴对发光层的注入而且TAPC拥有较高的空穴迁移率;另外,TAPC及TCTA拥有较高的LUMO和三线态能量,可以有效地将电子和三线态激子束缚在发光层内,增加绿光染料的复合发光几率。所制备的器件均表现出良好的色坐标稳定性。     

PVK空穴传输层对有机电致发光器件性能的影响

以聚乙烯基咔唑poly(N-vinylcarbazole)(PVK)旋涂层为空穴传输层,着重研究了PVK层厚度对双层器件氧化铟锡(ITO)/PVK/tris-(8-hydroxyquinoline)aluminum(Alq₃)/Mg:Ag/Al器件性能的影响。测试结果表明,当Alq₃层厚度一定时(50nm),只有PVK层为适当厚度(18nm)时双层器件才有最优良的器件性能,即最低的起亮电压,最高的发光亮度和效率。同时对比了不同PVK层厚度的PVK/Alq₃双层器件之间以及PVK/Alq₃与N,N′-bis-(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine(NPB)/Alq₃双层器件寿命的差异。测试结果表明,尽管越厚的PVK层对应的PVK/Alq₃双层器件发光性能并不是越好,但器件寿命越长。原因是器件Alq₃层内形成的Alq³⁺越少,因此器件稳定性越好;而PVK/Alq₃与NPB/Alq₃双层器件寿命的差异来自不同空穴传输层的制备工艺和能级结构的不同。     

富勒烯掺杂NPB空穴传输层的有机电致发光器件

报道了不同掺杂浓度NPB：C₆₀（富勒烯）作为空穴传输层对有机电致发光器件性能的影响.采用真空热蒸镀方法,制作了ITO/ NPB：C₆₀ （x % ）/Alq₃/LiF/Mg:Ag结构的四种有机电致发光器件.当NPB：C₆₀的掺杂浓度是15％时,器件的启亮电压是4 V,最大亮度是11000 cd/m².然而,当NPB：C₆₀的掺杂浓度是20％时,器件的最大亮度降     

基于PVK∶NPB掺杂体系的有机电致发光器件的性能

利用溶液旋涂的方法,通过改变复合功能层中poly(N-vinylcarbazole)(PVK)和N,N′-bis-(1-naph-thyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine(NPB)的质量比,制备结构为indium-tin-oxide(ITO)/PVK:NPB/2,9-dimenthyl-4,7-diphenyl-1,10-phenanthroline(BCP)/Mg:Ag的有机电致发光器件,并对器件的电致发光特性进行了表征。研究结果表明,当复合功能层中PVK和NPB的质量比为1:1时器件性能最好,在该器件的电致光谱中,除了NPB的本征谱峰外,在长波方向还出现了一个位于640nm处的谱峰,这是PVK和NPB产生的电致激基复合物发光,并且随着驱动电压的增加,电致激基复合物的发光强度也相对增强。     

ITO的表面处理对有机电致发光器件性能的影响

作为有机电致发光器件(OLEDs)的一个主要部分,ITO的表面形貌以及表面性能对整个器件的性能起着决定性的作用。介绍了对ITO的各种处理方法,包括O2Plasma和UV ozone等。这些方法可以改变ITO的表面化学成分以及结构,可以大幅度地提高器件的亮度、寿命以及稳定性,使OLEDs的实用化成为可能。     

利用NPB/MoO3/NpB作为空穴传输层的低驱动电压的有机发光器件

通过引入(NPB/MoO3)x/NPB作为空穴传输层,获得了低驱动电压的有机电致发光器件(OLEDs),(NPB/MoO3)x为多层结构(x为0,1和2).通过对比发现,在相同亮度下,x=1对应的器件具有最低的工作电压.这是由于在NPB和MoO3之间产生了电荷转移复合物(charge transfer,CT),这将会降低器件的空穴注入势垒,从而降低其工作电压,文中所研究器件为基于8-羟基喹啉铝(tris(8-hydroxyquino-line)aluminum,Alq3)的绿光器件.与x=0时的普通器件相比,在亮度为1 000 cd·m-2时,x=1时的工作电压降低了 0.8 V.     

空穴传输层掺杂SrF2的高效率蓝色磷光OLED器件

通过在OLED器件的空穴传输层中掺杂不同比例的SrF2制作出了高效率蓝色磷光OLED器件.这种器件能有效提高蓝色磷光OLED器件的空穴注入与传输特性,降低器件的的工作电压,提高流明效率(19.11m/W)、电流效率(26.9 cd/A)以及亮度(22 220 cd/m2),和未经掺杂的参比器件相比,分别提高了85.4％...     

空穴注入层对蓝色有机电致发光器件性能的影响

以DPVBi为发光层,NPB为空穴传输层,在阳极ITO和NPB之间分别插入不同的空穴注入层CuPc和PEDOT:PSS,制备了两种结构的蓝色有机电致发光器件(OLEDs):ITO/CuPc/NPB/DPVBi/BCP/Alq3/Al和ITO/PEDOT:PSS/NPB/DPVBi/BCP/Alq3/Al,研究了不同空穴注入材料对蓝色OLEDs发光性能的影响,并与没有空穴注入层的器件进行了比较.其中CuPc分别采用旋涂和真空蒸镀两种丁艺,比较了不同成膜工艺对器件发光特性的影响.结果表明:加入空穴注入层的器件比没有空穴注入层器件性能要好,其中插入水溶性CuPc的器件,其发光亮度和效率虽然比蒸镀CuPc器件要低,但比插入PEDOT:PSS 器件发光性能要好.又由于水溶性CuPc采用旋涂工艺成膜,与传统CuPc相比,制备工艺简单,所以为一种不错的空穴注入材料.     

超薄层BCP对有机电致发光器件性能的影响

采用真空热蒸镀的方法,在常规的双层器件结构的基础上,设计了三层双异质结有机电致发光器件(OLED):indium-tin oxide(ITO)/N,N′-diphenyl-N,N′-bis(1-naphthyl)(1,1′-biphenyl)-4,4′-diamine(NPB)/2,9-dimethyl-4,7-diphenyl-1,10-phenan throline(BCP)/8-hydroxyquinoline aluminum(Alq3)/Mg∶Ag。通过对器件的电致发光(EL)光谱及器件性能的表征,研究了不同超薄层BCP的厚度对OLED器件性能的影响。结果表明,当超薄层BCP的厚度从0.1nm逐渐增加到4.0nm时,器件的EL光谱实现了绿光→蓝绿光→蓝光的变化;BCP层有效地调节了载流子的复合区域,改变了器件的发光颜色,提高了器件的亮度和发光效率。     

PS-TPD空穴传输层的高亮度绿光有机电致发光器件的研究

研究了不同质量比的聚苯乙烯(PS)三苯基二胺(TPD)复合空穴传输层对有机电致发光器件(OLED)性能的影响。采用此掺杂体系作器件的空穴传输层,利用旋涂工艺制备了结构为indium-tin-oxide(ITO)/polystyrene(PS)∶N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine(TPD)/tris-(8-hydroxyquinoline)-aluminium(Alq3)/Mg∶Ag的双层有机电致发光器件。为便于比较,另直接蒸镀TPD薄膜做空穴传输层制备了相似结构的器件。利用飞行时间法对不同PS-TPD质量比例的薄膜的空穴迁移率进行了表征,并对器件的电致发光特性进行了测试。测试结果表明,掺杂薄膜的空穴迁移率比纯TPD膜的低1~2个数量级。当质量比为m(PS)∶m(TPD)=10∶90时,器件具有最高光亮度14280 cd/m2和最高流明效率1.2 l m/W。说明适当质量比PS的引入相对降低了薄膜的空穴迁移率,调节了TPD的空穴传输能力,更有效地平衡了复合区内正负载流子的数目,从而提高了器件的发光亮度和效率。     

Electroluminescence performance of organic light-emitting devices with KCl inside hole transport layer

A new multilayer organic light-emitting device (OLED) is fabricated by inserting kalium chloride (KCl) thin layer (1 nm) into hole transport layer (HTL). It has the configuration of ITO/NPB(15 nm)/KCl(1 nm)/NPB(25 nm)/Alq₃(60 nm)/KCl(1 nm)/Al. The electroluminescence (EL) result shows that the performance of the novel device has obviously improvement compared with the normal structure (ITO/NPB(40 nm)/Alq₃(60 nm)/KCl(1 nm)/Al). The EL and efficiency are about 1.4 and 1.3 times than that of conventional device. The suggested mechanism is that the KCl layer in N,N′-diphenyl-N,N′-bis(1-napthyl–phenyl)-1,1′-biphenyl-4,4′-diamine (NPB) can block the holes of NPB and then balance the holes and electrons. The better recombination of holes and electrons is beneficial to the enhancing properties of OLED.     

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 light-emitting devices (OLEDs). We found that the carrier mobility of the pentacene thin films could be efficiently improved after a critical annealing at temperature 120 °C. 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/m² at 12 V, which are reduced by 26% and improved by 50% compared with those of the control device.     

Performance improvement of GaN-based light-emitting diode with a p-InAlGaN hole injection layer

The characteristics of a blue light-emitting diode(LED)with a p-InAlGaN hole injection layer(HIL)is analyzed numerically.The simulation results indicate that the newly designed structure presents superior optical and electrical performance such as an increase in light output power,a reduction in current leakage and alleviation of efficiency droop.These improvements can be attributed to the p-InAlGaN serving as hole injection layers,which can alleviate the band bending induced by the polarization field,thereby improving both the hole injection efficiency and the electron blocking efficiency.     

Low driving voltage in organic light-emitting diode using MoO3/NPB multiple quantum well structure in hole transport layer

Driving voltage of organic light-emitting diode (OLED) is lowered by employing molybdenum trioxide (MoO₃)/N, N'-bis(naphthalene-1-yl)-N,N'-bis(phe-nyl)-benzidine (NPB) multiple quantum well (MQW) structure in hole transport layer. For the device with double quantum well (DQW) structure of ITO/ [MoO₃ (2.5 nm)/NPB (20 nm)]₂/Alq₃(50 nm)/LiF (0.8 nm)/Al (120 nm)], the turn-on voltage is reduced to 2.8 V, which is lowered by 0.4 V compared with that of the control device (without MQW structures), the driving voltage is 5.6 V, which is reduced by 1 V compared with that of the control device at the 1000 cd/m². In this work, the enhancement of the injection and transport ability for holes could reduce the driving voltage for the device with MQW structure, which is attributed not only to the reducing energy barrier between ITO and NPB, but also to the forming charge transfer complex between MoO₃ and NPB induced by the interfacial doping effect of MoO₃.     

Improving efficiency of organic light-emitting devices by optimizing the LiF interlayer in the hole transport layer

The efficiency of organic light-emitting devices (OLEDs) based on N,N'-bis(1-naphthyl)-N,N'-diphenyl-N,1'-biphenyl-4,4'-diamine (NPB) (the hole transport layer) and tris(8-hydroxyquinoline) aluminum (Alq₃) (both emission and electron transport layers) is improved remarkably by inserting a LiF interlayer into the hole transport layer. This thin LiF interlayer can effectively influence electrical performance and significantly improve the current efficiency of the device. A device with an optimum LiF layer thickness at the optimum position in NPB exhibits a maximum current efficiency of 5.96 cd/A at 215.79 mA/cm², which is about 86% higher than that of an ordinary device (without a LiF interlayer, 3.2 cd/A). An explanation can be put forward that LiF in the NPB layer can block holes and balance the recombination of holes and electrons. The results may provide some valuable references for improving OLED current efficiency.     

Enhanced luminance of white organic light-emitting diode with yellow nanophosphors-embedded blue polymer emitting layer

White organic light-emitting device was achieved through an incorporation of yellow YAG nanophosphors into blue polyfluorene emitting layer: electrode/YAG@polyfluorene/hole-transport/injection layers/ITO glass. The brightness of the proposed device (230 cd/m² at 30 V) was enhanced by a factor of about two in comparison with that of phosphor-free reference device. It is attributed to the increased local electric field caused by bumps of nanophophors on the emitting layer. With increase of voltage, the blue-green emission decreased whereas the yellow emission increased. It is due to the effective energy transfer from the blue-green to the yellow bands.     

发光层和空穴传输层对白色电致发光器件性能的影响

利用电子传输性能良好的苯并噻唑螯合锌(Zn(BTZ)₂)作为蓝光层，通过设计不同类型的空穴传输层并试验不同厚度的发光层后，制作了一种最佳厚度的双发光层白色电致发光器件：氧化铟锡(ITO)/N-N′-双(3-甲基苯基)-N-N′-二苯基-1-1′-二苯基-4-4′-二胺(TPD)∶N,N′-二(1-萘基)-N,N′-二苯基-1,1′-联苯-4-4′-二胺(NPB)(1∶0.0 关键词： 厚度 空穴传输层 白光 载流子     

Low driving voltage in an organic light-emitting diode using MoO3/NPB multiple quantum well structure in a hole transport layer

The driving voltage of an organic light-emitting diode(OLED) is lowered by employing molybdenum trioxide(MoO3)/N,N’-bis(naphthalene-1-yl)-N,N’-bis(phe-nyl)-benzidine(NPB) multiple quantum well(MQW) structure in the hole transport layer.For the device with double quantum well(DQW) structure of ITO/[MoO3(2.5 nm)/NPB(20 nm)]2/Alq3(50 nm)/LiF(0.8 nm)/Al(120 nm)],the turn-on voltage is reduced to 2.8 V,which is lowered by 0.4 V compared with that of the control device(without MQW structures),and the driving voltage is 5.6 V,which is reduced by 1 V compared with that of the control device at the 1000 cd/m2.In this work,the enhancement of the injection and transport ability for holes could reduce the driving voltage for the device with MQW structure,which is attributed not only to the reduced energy barrier between ITO and NPB,but also to the forming charge transfer complex between MoO3 and NPB induced by the interfacial doping effect of MoO3.     

Effects of hole injection layer thickness on the luminescent properties of white organic light-emitting diodes

This work investigates how the thickness of the hole injection layer (HIL) influences the luminescent characteristics of white organic light-emitting diodes (WOLED). Experimental results indicate that inserting a thin HIL (<200 Å) into a WOLED without an HIL reduces the brightness and clearly changes the chromaticity because the surface of the 4,4′,4″-tris{N,-(3-methylphenyl)-N-phenylamino}-triphenylamine) (m-MTDATA) film is extremely rough. In contrast, a dense film structure and the fine surface morphology of m-MTDATA of moderate thickness (350-650 Å) provides a uniform conducting path on which holes cross the indium tin oxide (ITO)/HIL interface, improving luminescent performance, associated with the relatively stable purity of the color of the emission, with Commission Internationale 1′Eclairage (CIE) coordinates of (x = 0.40, y = 0.40). However, inserting a thick HIL (>650 Å) reduces the luminescent performance and causes red-shift, because the holes and electrons in the effective emissive confinement region become less optimally balanced. Moreover, optimizing the device structure enables a bright WOLED with CIE coordinates of (x = 0.34, y = 0.33) to reach a luminance of 7685 cd/m² at a current density of 100 mA/cm², with a maximum luminous efficiency of 1.72 lm/W at 5.5 V.