基于连续性掺杂的高效全荧光白色有机电致发光器件的研究

利用荧光材料PT-01, PT-86, PT-05作为黄色荧光客体, 蓝色荧光客体以及荧光母体制备了一种基于连续性掺杂结构的全荧光白光有机电致发光器件. 其发光层为主体/客体薄层/主体/客体薄层···交替蒸镀的重复单元. 通过优化发光层中主体的厚度并检测发光层中单线态激子的分布, 将黄、蓝两种客体染料生长在发光层中适当的位置, 得到了高效且光谱稳定的全荧光白光器件. 其最大电流效率为11.2 cd/A, 亮度在159–20590 cd/m²范围内色坐标仅有(±0.004,±0.005)的改变. 基于这种连续性掺杂结构制备的器件, 其性能不但可以达到传统主-客体共掺结构所制备的器件的性能,而且具有较高的可重复性, 更适合产业化大批量生产. 关键词： 白色有机电致发光器件 连续性掺杂 能量转移 可重复性     

Highly efficient bipolar connecting layers for tandem organic light-emitting devices

A highly efficient tandem organic light-emitting device (OLED) has been fabricated by using an effective bipolar connecting layer structure. The connecting layers were made up of a layer of magnesium (Mg): 2,7-dipyrenyl-9,9-diphenyl fluorene (N-DPF) and a layer of tungsten trioxide (WO₃). Such a connecting layer structure permits efficient opposite holes and electrons flowing into two adjacent emitting units. The current efficiency of the two-unit tandem device can be dramatically enhanced by more than four times compared with that of the conventional single-unit device. At 60 mA/cm², the current efficiency of the tandem OLED using the connecting layers of Mg: N-DPF/WO₃ was about 8.15 cd/A. The results can be marked as a breakthrough approach to improve the current efficiency and brightness of OLEDs. Furthermore, a model of the carrier tunneling into light-emitting units is proposed based on carrier balance and field-assisted tunneling. It indicates that the connecting layer structure functions as the origin of high efficiency for the tandem OLEDs.     

Highly efficient white quantum dot light-emitting diode based on ZnO quantum dot

White quantum dot light-emitting diodes (QD-LEDs) have been a promising candidate for high-efficiency and color-saturated displays. Here, we report a simply solution-processed white QD-LED using ZnO QDs as emitters. The device is demonstrated with a maximum luminance of 300 cd/m², exhibiting the Commission Internationale de l’Enclairage coordinates of (0.33, 0.33). The unencapsulated white QD-LED has a long lifetime of 120 h. These results indicate that ZnO QDs provides an alternate and effective approach to achieve high-performance white QD-LEDs and also other optoelectronic devices.     

可调色红光有机电致发光器件

介绍了具有可调节发光光谱的高效红光有机发光二极管(OLED)器件,利用具有高三重态能量的9.9-螺二芴二苯基氧化磷(SPPO1)作为发光层的主体材料及空穴阻挡层,二(1-苯基异喹啉)(乙酰丙酮)合铱(III) (Ir(piq)2(acac))作为客体发光材料,在发光层内SPPO1的能量分别由福斯特和迪克斯特传递到Ir(piq)2(acac)的单重态和三重态从而发出红色磷光,通过调节磷光客体材料的比例得到最优器件结构,从而得到具有较好发光效率和发光亮度并可调节色纯的有机发光二极管器件。     

可调色红光有机电致发光器件

介绍了具有可调节发光光谱的高效红光有机发光二极管(OLED)器件,利用具有高三重态能量的9.9-螺二芴二苯基氧化磷(SPPO1)作为发光层的主体材料及空穴阻挡层,二(1-苯基异喹啉)(乙酰丙酮)合铱(III) (Ir(piq)2(acac))作为客体发光材料,在发光层内SPPO1的能量分别由福斯特和迪克斯特传递到Ir(piq)2(acac)的单重态和三重态从而发出红色磷光,通过调节磷光客体材料的比例得到最优器件结构,从而得到具有较好发光效率和发光亮度并可调节色纯的有机发光二极管器件。     

Solution-processed WOx hole injection layer for efficient fluorescent blue organic light-emitting diode

Solution-processed tungsten oxide (s-WO_x) interfacial layer for efficient hole injection in fluorescent blue organic light-emitting diode (OLED) is demonstrated. The OLED using 2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN) as emitter shows luminous efficiency of 3.3 cd/A, power efficiency of 2.5 lm/W and external quantum efficiency of 4.6% with Commission Internationale d'Eclairage (CIE) color coordinates of (0.154, 0.102). Using MADN doped 1-4-di-[4-(N,N-diphenyl)amino]styryl-benzene as emitter, luminous efficiency of 10.8 cd/A, power efficiency of 6.4 lm/W and external quantum efficiency of 7.2% with CIE color coordinates of (0.167, 0.283) are achieved. Atomic force microscopy and X-ray photoelectron spectroscopy show that s-WO_x features superior film morphology and non-stoichiometry with slight oxygen deficiency. Current-voltage characteristics and impedance spectroscopy analysis indicate that s-WO_x behaves slightly enhanced hole injection and accordingly contributes to improved device performance in comparison with conventional vacuum thermal evaporation WO_x. Our results pave an alternative way for broadening WO_x application with solution process and advancing fluorescent blue OLEDs.     

Highly flexible and efficient top-emitting organic light-emitting devices with ultrasmooth Ag anode

We demonstrate highly flexible and efficient top-emitting organic light-emitting devices (TOLEDs) by using an ultrasmooth Ag anode. A template-stripping process has been employed to create the ultrasmooth Ag anode on a photopolymer substrate. The flexible TOLEDs obtained by this method keep good electroluminescence properties under a small bending radius and after repeated bending. The efficiency of the flexible TOLEDs is improved by 60% compared with the conventional TOLEDs deposited on Si substrate due to the enhanced hole injection from the ultrasmooth anode.     

Efficiency of a blue organic light-emitting diode enhanced by inserting charge control layers into the emission region

We demonstrate high current efficiency of a blue fluorescent organic light-emitting diode (OLED) by using the charge control layers (CCLs) based on Alq3 . The CCLs that are inserted into the emitting layers (EMLs) could impede the hole injection and facilitate the electron transport, which can improve the carrier balance and further expand the exciton generation region. The maximal current efficiency of the optimal device is 5.89 cd/A at 1.81 mA/cm2 , which is about 2.19 times higher than that of the control device (CD) without the CCL, and the maximal luminance is 19.660 cd/m2 at 12V. The device shows a good color stability though the green light emitting material Alq3 is introduced as the CCL in the EML, but it has a poor lifetime due to the formation of cationic Alq3 species.     

Highly efficient blue organic light-emitting diodes using various hole and electron confinement layers

In this Letter, blue phosphorescence organic light-emitting diodes(PHOLEDs) employ structures for electron and/or hole confinement; 1,3,5-tris(N-phenylbenzimiazole-2-yl)benzene is used as a hole confinement layer and tris-(phenylpyrazole)iridium [IreppzT3] is utilized for an electron confinement layer(ECL). The electrical and optical properties of the fabricated blue PHOLEDs with various carrier-confinement structures are analyzed.Structures with a large energy offset between the carrier confinement and emitting layers enhance the charge-carrier balance in the emitting region, resulting from the effective carrier confinement. The maximum external quantum efficiency of the blue PHOLEDs with the double-ECLs is 24.02% at 1500 cd∕m2and its luminous efficiency is 43.76 cd∕A, which is 70.47% improved compared to the device without a carrier-confinement layer.     

Analytical model of drift and diffusion of charge carriers in organic light-emitting diodes in the presence of a space charge

A relatively simple analytical model taking into account energy disorder and space charge effects is proposed for calculating the current-voltage characteristics for the monopolar regime of charge transfer in thin layers of disordered organic materials. The dependence of the minimal energy barrier height for injection, for which the space charge effects can be disregarded, is determined as a function of the layer thickness and the Gaussian energy distribution width.     

Highly efficient all phosphorescent white organic light-emitting diodes for solid state lighting applications

We report highly efficient all phosphorescent white organic light-emitting diodes (OLEDs) with an exciton-confinement structure. By stacking two emissive layers (EMLs) with different charge transporting properties, effective charges as well as exciton confinements were achieved. Accordingly, efficient blue OLEDs with a peak external quantum efficiency (EQE) over 22% and power efficacy (PE) over 50 lm/W were developed by using iridium(III) bis(4,6-(difluorophenyl) pyridinato-N,C2′)picolinate (FIrpic) as an electro-phosphorescent dopant. When the optimized orange and red EMLs were sandwiched between the stacked two blue EMLs, white OLEDs with an EQE and PE of 24.3% and 45.9 lm/W at a luminance of 1000 cd/m² were obtained without the use of any out-coupling techniques. In addition, these white OLEDs exhibit a color rendering index (CRI) value of 84 with high efficacy.     

具有新型双空穴注入层的有机发光二极管

采用新型双空穴注入层N, N, N', N'-tetrakis(4-Methoxy-phenyl)benzidine/Copper phthalocyanine(MeO-TPD/CuPc)及器件结构:ITO/MeO-TPD(15 nm)/CuPc(15 nm)/ N, N'-Bis(naphthalen-1-yl)-N, N'-bis(phenyl)benzidine (NPB, 15 nm)/8-hydroxyquinoline (Alq₃, 50 nm)/LiF(1 nm)/Al(120 nm), 研制出高效有机发光二极管(器件D), 与其他器件(器件A, 没有空穴注入层的器件; 器件B, MeO-TPD单空穴注入层; 器件C, CuPc单空穴注入层)相比, 其性能得到明显改善. 器件D的起亮电压降至3.2 V, 比器件A, B, C的起亮电压分别降低了2, 0.3, 0.1 V. 器件D在10 V时, 其最大亮度为23893 cd/m², 最大功率效率为1.91 lm/W, 与器件A, B, C的最大功率效率相比, 分别提高了43% (1.34 lm/W), 22% (1.57 lm/W), 7% (1.79 lm/W). 性能改善的主要原因是由于空穴注入和传输性能得到了改善, 通过单空穴型器件的J-V 曲线对这一现象进行了分析. 关键词： 有机发光二极管 空穴注入层 功率效率 势垒     

Efficient red organic light-emitting diode sensitized by a phosphorescent Ir compound

The efficiencies of red organic light-emitting diode (OLED) using tris-(8-hydroxy-quinoline)aluminum (Alq₃) as host and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as dopant were greatly increased by adding a small amount (0.3 wt%) of Ir compound, iridium(III) bis(3-(2-benzothiazolyl)-7-(diethylamino)-2H-1-benzopyran-2-onato-N′,C⁴) (acetyl acetonate) (Ir(C6)₂(acac)), as a sensitizer. The device has a sandwiched structure of indium tin oxide (ITO)/4,4′,4″-tris(N-(2-naphthyl)-N-phenyl-amino)triphenylamine (T-NATA) (40 nm)/N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′ diamine (NPB) (40 nm)/Alq₃:DCJTB (0.7 wt%):Ir(C6)₂(acac) (0.3 wt%) (40 nm)/Alq₃ (40 nm)/LiF (1 nm)/Al (120 nm). It can be seen that the current efficiencies of this device remained almost (13.8±1) cd/A from 0.1 to 20,000 cd/m² and the Commission International d’Eclairage (CIE) coordinates at (0.60, 0.37) in the range of wide brightness. The significant improvement was attributed to the sensitization effect of the doped Ir(C6)₂(acac), thus the energy of singlet and triplet excitons is simultaneously transferred to the DCJTB.     

Improving organic light-emitting diode performance with patterned structures

The influence nano- and micro- structures on light extraction and carrier injection characteristics in organic light-emitting diodes (OLEDs) is examined. The results demonstrate device enhancement from two distinctive patterning scales: embedded microstructure arrays for improved light extraction and imprinted nanostructures for carrier injection enhancement. Further, based on these results, a two-level imprinting stamp is designed which simultaneously produces a micron-sized pattern for facilitating light extraction and a nanometer-sized pattern to improve carrier injection. Additionally, this scalable patterning technology circumvents imprinting misalignment while preserving its compatibility with rollto- roll technology.     

Numerical study of light-emitting diode with injected current modulated by designed electrode

Numerical model and procedure are developed to study the output optical performance of light-emitting diode (LED) in which injected current is spatially modulated by mesh-like top metal electrode. The mesh strips have rectangular crossection as in realistic LEDs. The finite element method is applied to obtain three-dimensional distributions of electric potential which are incorporated in the equations for total output power. The numerical procedure is applied to evaluate LED’s total output optical power at different geometric parameters of the electrode: the mesh pitch, the width, and the height of the top mesh-like electrodes. Modeling results demonstrate the effect of mesh pitch variation on the output optical power. In particular, at a certain value of the mesh pitch maximum total output optical power is revealed. The presented approach can be used in the optimization of the LEDs with designed metal electrodes.     

Highly efficient and stable organic light-emitting diodes employing MoO3-doped perylene-3, 4, 9, 10-tetracarboxylic dianhydride as hole injection layer

We report highly efficient and stable organic light-emitting diodes (OLEDs) with MoO₃-doped perylene-3, 4, 9, 10-tetracarboxylic dianhydride (PTCDA) as hole injection layer (HIL). A green OLED with structure of ITO/20 wt% MoO₃: PTCDA/NPB/Alq₃/LiF/Al shows a long lifetime of 1012 h at the initial luminance of 2000 cd/m², which is 1.3 times more stable than that of the device with MoO₃ as HIL. The current efficiency of 4.7 cd/A and power efficiency of 3.7 lm/W at about 100 cd/m² have been obtained. The charge transfer complex between PTCDA and MoO₃ plays a decisive role in improving the performance of OLEDs.     

轴对称真空二极管空间电荷限制流

基于ArcPIC代码采用PIC-MCC方法,模拟研究了轴对称真空二极管放电时电子密度和阴极表面场强分布情况,同时给出了二维空间电荷限制流的一阶和二阶拟合公式。研究发现,真空二极管放电时阴极表面电场会随阴极注入电流密度的增加而增加,而后出现振荡并趋于一个稳定状态;二维空间电荷限制流密度值随阴极发射半径的增大而减小,且阴极发射半径越大越接近一维空间电荷限制流值。     

Highly efficient flexible organic light-emitting devices utilizing F4-TCNQ/m-MTDATA multiple quantum well structures

Flexible organic light-emitting devices (FOLEDs) based on multiple quantum well (MQW) structures, which consist of alternate layers of 2,3,5,6-Tetrafluoro-7,7,8,8,-tetracyano-quinodimethane (F4-TCNQ) and 4,4′,4″-tris-(3-methylphenylphe-nylamino)tripheny-lamine (m-MTDATA) have been fabricated. The Alq₃-based device with double quantum well (DQW) structure exhibits the remarkable electroluminescent (EL) performances for the brightness of 23,500 cd/m² at 14 V and the maximum current efficiency of 7.0 cd/A at 300.3 mA/cm², respectively, which are greatly improved by 114% and 56% compared with the brightness of 10,958 cd/m² at 14 V and the maximum current efficiency of 4.5 cd/A at 174.0 mA/cm² for the conventional device without MQW structures. These results demonstrate that the EL performances of FOLEDs could be greatly improved by utilizing the novel MQW structures, and the reason for this improvement has also been explained by the effect of interfacial dipole and interfacial doping between F4-TCNQ and m-MTDATA in this article.     

Numerical investigations on the current conduction in bilayer organic light—emitting devices with ohmic injection of charge carriers

A numerical model for bilayer organic light-emitting diodes (OLEDs) has been developed on the basis of trappedcharge limited conduction. The dependences of the current density on the operation voltage, the thickness andtrap properties of the hole transport layer (HTL) and emission layer (EML) in bilayer OLEDs of the structure an-ode/HTL/EML/cathode have been numerically investigated. It has been found that, for given values of reduced trapdepth, total trap density, and carrier mobility of HTL and EML, there exists an optimum thickness ratio of HTL tothe sum of HTL and EML, by which a maximal current density, and hence maximal quantum efficiency and luminance,can be achieved. The current density decreases quickly with the mean trap density, and decreases nearly exponentiallywith the mean reduced trap depth.     

利用色彩转换法制备高色稳定性的柔性白色有机电致发光器件

本文利用色转换方法,将高效的蓝色柔性有机电致发光器件(flexible organic light emitting devices, FOLEDs)与色转换材料(color conversion material, CCM)相结合,制备了柔性白色有机电致发光器件(white organic light emitting devices, WOLEDs).首先利用2, 3, 5, 6-Tetrafluoro-7, 7, 8, 8-tetracyano-quinodimethane (F4-TCNQ)和4, 4', 4"-tris-(N-3-methylphenyl-N-phenylamino) tripheny-lamine (m-MTDATA)组成的多量子阱(multiple quantum well, MQW)结构作为空穴注入层(hole injection layer, HIL)结合新型蓝光材料N⁶, N⁶, N¹², N¹²-tetrap-tolylchrysene-6, 12-diamine (NCA)制备出高效的蓝光FOLEDs,然后将其与色转换材料4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) 结合,通过沉积不同厚度的CCM来优化白光器件的发光光谱,获得了色稳定性较高的白光. 实验结果表明:在驱动电压为7 V, DCJTB的厚度为120 nm时得到较接近白光等能点的色坐标 (0.33, 0.27),且当驱动电压由6 V升至11 V 时,器件的色坐标变化仅为(±0.02, ±0.02), 表现出高色稳定性.