Investigation of large-area OLED devices with various grid geometries

Luminance homogeneity is an important aspect for large-area (>1 cm²) organic light emitting diodes (OLED). Especially, high sheet resistances of transparent contacts lead to a significant brightness inhomogeneity caused by a drop of local potential difference. Therefore the implementation of thin low-resistance metallic grids onto transparent contacts is a crucial development aspect for large-area OLED design. We develop a finite-element electro-optical simulation for OLED using grid structures to optimize geometry, thickness and width of grid elements. We find an exponential relationship between luminance homogeneity and grid material volume, which leads to limitations of minimal grid line width and maximal emissive area for efficient development of large-area OLED.     

Optical and thermal properties of large-area OLED lightings with metallic grids

We investigate the effects of auxiliary metal electrodes on the optical and thermal properties of large-area (30 × 120 mm²) opaque and transparent white OLED lighting panels. Enlarging their emission area inevitably entails a non-uniform current distribution due to the limiting conductivity of transparent electrodes, causing local heat generation. To tackle it, we have used grid patterned Cr, Mo/Al/Mo, or Cu metal lines (0.15 mm in width) as auxiliary metal electrodes on an ITO anode. Among those, Cu metal grids exhibit the highest luminous efficacy with the least heat generation, and the most uniform light distribution by virtue of its lowest sheet resistance, followed by Mo/Al/Mo and then Cr metal grids. It is also found that local heat generation appears more seriously in large-area transparent OLED panels. With attempt to suppress it, we have also deposited Al metal lines (2 mm in width) on a semitransparent Al/Ag cathode by thermal evaporation, which brings in a highly uniform heat distribution. Furthermore, we study the effect of the shape of the light-emitting area on the luminance and heat distributions. A round-shaped OLED panel with a hexagonal metal grid exhibits highly homogeneous luminance and surface temperature distributions.     

照明用白光OLED技术的现状与挑战

有机电致发光二极管（OLED）具有制备工艺简单、抗震性能好、能耗较低,且能够在不同材质的基板上制造、柔韧、易弯曲等特点,是现代显示技术的重要研究方向,而其在照明领域的应用前景也被人们所看好。文章结合最新的研究成果,对OLED应用于照明的优势及遇到的问题与挑战做了简要讨论,并概括分析了解决这些问题的方法。     

Degradation of phosphorescent organic light-emitting diodes under pulsed current stressing

The electrical and optical degradation of green phosphorescent organic light-emitting diodes (OLEDs) stressed under 50 mA/cm² pulsed currents with 10–50% duty cycles was studied. The stressing resulted in significant increases in low-bias leakage current and operational voltage. The luminance evolution comprised an initial rapid decay regime and a subsequent slow decay regime, and only the latter was governed predominantly by electrical excitation. Compared to continuous-wave stressing, pulsed stressing with 10% duty cycle improved the effective half life by only ∼15%, indicating that self-heating plays a minor role in the performance degradation process. Adding a reverse bias component to the pulsed current led to suppressed low-bias leakage and current-induced luminance decay due to defect removal and alleviated charge build-up.     

光输出增强型微腔OLED器件研究

文章利用特制的玻璃作为OLED基板,一面为平整光滑的平面,另一面为具有规则凹凸形貌的粗化面。采用光输出增强型微腔OLED结构,器件结构为:玻璃基板(光面)/Al(15nm)/MoO3(40nm)/NPB(30nm)/Alq3(30nm):C545T(3%)/Alq3(20nm)/LiF(1nm)/Al(150nm),研究了器件的电流密度、亮度、发光效率、光致发光光谱等特性。结果表明,这种结构的器件相比于传统微腔型器件,相同电压下亮度约增加了40%,发光效率约提高了15%,具有更强的光萃取能力。     

多层结构红色OLED器件的制备与光电性能研究

采用真空热蒸镀的方法,在高精度膜厚控制仪的监控下,实现了有机薄膜功能材料的精确蒸镀,其中发光层采用三种材料的共蒸,制备了一种多层结构红色有机电致发光(OLED)器件:ITO/CuPc/α-NPD/Alq3∶Rubrene(10%)∶DCJTB(1%)/Alq3/LiF/Al.从实验结果分析可知:随着驱动电压的变化,其EL光谱有蓝移的现象,发射峰从638nm变到632nm,同时色坐标值也发生相应的变化;器件的发光效率在驱动电压较低时(5V),达到最大值5.77cd/A,随着驱动电压的增加,发光效率呈缓慢降低的趋势.     

半导体量子点集成有机发光二极管的光光转换器进展

介绍的光光转换器是新型红外光-可见光转换器件,红外光产生的光生载流子直接注入有机发光二极管产生可见光。以半导体红外探测与有机发光器件单片集成的光光转换器,直接实现了红外光到可见光的集成转换,在红外凝视技术中有极大的应用潜力。综述了无机红外探测与有机发光的光-光转换器的研究进展。     

高灰度级彩色OLED驱动电路的研究

介绍了OLED显示技术及相关市场信息，讨论了当前OLED的驱动技术、芯片和存在的问题，提出OLED高灰度级扫描实现方法和驱动芯片的设计，并进行了系统测试与验证。     

无氧溅射方法制备OLED的ITO透明电极

采用氧化铟锡(ITO)合金材料作为靶材,通过射频磁控溅射制备ITO膜.将获得的ITO膜应用于结构为ITO/m-MTDATA(30 nm)/NPB(20 nm)/Alq3(50 nm)LiF(0.8 nm)/Al(100 nm)的有机电致发光器件(OLED),得到了最大亮度为11560 cd/m2(电压为25V)、最大效率为2.52 cd/A(电压为14 V)的结果.为了获得双面发光,制作了结构为ITO/m-MTDATA(30 nm)/NPB(20 nm)/Alq3(50 nm)LiF(0.8 nm)/Al(20 nm)/ITO(50 nm)的器件,其阳极出光的最大亮度为14460 cd/m2(电压为18V)、最大效率为2.16 cd/A(电压为12V),阴极出光的最大亮度为1 263 cd/m2(电压为19 V)、最大效率为0.26 cd/A(电压为16V).     

基于PEN柔性衬底的顶发射微腔OLED性能研究

设计了结构为Ag/MoOx空穴注入层(HIL)/有机层/LiF/Al/Ag/Alq3的柔性有机电致发光器件(FOLED),研究通过改变HIL层的厚度改变腔长实现对微腔效应的调节,制备了性能优化的微腔FOLED。通过器件性能的对比,得到了可用Ag作为反射阳极的顶发射微腔FOLED全彩显示器件优化结构,即蓝、绿和红FOLED对应的优化HIL层厚度分别为100nm、120nm和160nm。     

蓝绿色磷光OLED的制备及发光性能研究

以mCP为主体发光材料,蓝绿色磷光染料BGIr1作 为掺杂剂,制备了6种不同BGIr1掺杂量的蓝绿色磷光有机电致发光器件(OLED),研究了不 同掺杂量对蓝绿色磷光OLED器件发光特性的影 响。制得器件的结构为ITO/MoO₃(20nm)/NPB(40nm)/mCP:BGIr1(x%,30nm)/BCP(10nm)/Alq₃(20 nm)/LiF/Al(100nm),其中x%为发光层中磷光染料BGIr1的掺杂量(质量分数)。结果表明,BGIr1掺杂量 为18%时,获得器件的发光性能最佳。18% BGIr 1掺杂器件在488nm和 512nm处获得两个主发射峰,当电 流密度为26.5mA/cm²时,获得最大发光效率为6.2cd/A;在15V驱动电压下,获得最大亮度为6970cd/cm², CIE坐标为(0.17,0.31)。这说明,BGI r1掺杂改善了器件的发光亮度和色纯度,提高了器件的发光效率。     

二维亚波长结构对OLED光抽出特性的FDTD模拟研究

有机发光二极管(OLED)发光效率很大程度上受到器件中高折射率材料(ITO/有机物)对导波光能量的制约.通过使用时域有限差分(FDTD)方法,对在OLED中的氧化铟与氧化锡复合透明阳极ITO结构上覆盖二维正方以及三角排列SiNx圆柱光子晶体厚膜(PCS)的结构进行了数值模拟,并对这种全新结构对于提高束缚于高折射率材料中的光的抽取效率的效果进行了分析,并给出了最优化的几何参数.     

城市配电网配电线路设计优化对策

本文基于中压配电网,深入分析配电线路优化设计,全面提升用电质量与用电安全,从根本上促进电力事业的发展.     

一种抑制关态漏电流和提高亮度稳定性的OLED微显示像素电路研究

OLED微显示像素驱动电路中,由于较小的存储电容和开关MOS管关态漏电流的影响,导致其存储电压和亮度不稳定.通过分析影响关态漏电流的主要因素,提出了一种多开关管串联和存储电容拆分相结合的办法以减小关态漏电流,并设计了一种含有两个开关管和两个存储电容的像素电路,该电路将关态漏电流由大于3 pA减小为0.4pA,存储电压和亮度稳定性得到了很大的改善,小亮度时一帧的亮度变化仅为0.18 cd/m2.电路可实现的最小OLED驱动电流为25 pA,像素亮度范围为1.82～217.37 cd/m2.     

微透镜阵列薄膜定向增强OLED耦合效率的研究

利用微透镜阵列(MLA)薄膜定向增强有机发光器件(OLED)耦合效率,采用光线追迹方法模拟了不同长短轴比的椭圆形MLA对OLED光的定向增强作用。采用数字微反射镜器件(DMD)并行光刻和热回流相结合的方法制作了MLA模版,经过电铸、压印得到MLA薄膜。理论模拟和实验结果表明,利用MLA可以定向提高OLED的出光效率,圆形MLA可提高垂直OLED基底表面方向的亮度42%;椭圆形MLA可实现OLED在长短轴方向上30°的半强度角度差,总的提取效率可提高30%以上。     

Increase of current density and luminance in organic light-emitting diode with reverse bias driving

When applying the voltage pulses (6 V) to the organic light-emitting diode based on tris(8-hydroxyquinolinato) aluminium (Alq₃) as the electron transporting layer, current density and luminance increased by 16% and 20%, respectively, by providing the reverse bias (−16 V) during the off-period. By using displacement current measurement, we can deduce that such an enhancement resulted from the interfacial positive charges trapped at the Alq₃/cathode interface, with the relaxation time ∼0.4 ms. By doping the organic material as the carrier trapping sites at Alq₃/cathode interface, such current density and luminance increase can be further enhanced. 25% and 36% increase in current density and luminance was demonstrated with such driving technique, respectively.     

Design of white tandem organic light-emitting diodes for full-color microdisplay with high current efficiency and high color gamut

Microdisplays based on organic light-emitting diodes (OLEDs) have a small form factor, and this can be a great advantage when applied to augmented reality and virtual reality devices. In addition, a high-resolution microdisplay of 3000 ppi or more can be achieved when applying a white OLED structure and a color filter. However, low luminance is the weakness of an OLED-based microdisplay as compared with other microdisplay technologies. By applying a tandem structure consisting of two separate emission layers, the efficiency of the OLED device is increased, and higher luminance can be achieved. The efficiency and white spectrum of the OLED device are affected by the position of the emitting layer in the tandem structure and calculated via optical simulation. Each white OLED device with optimized efficiency is fabricated according to the position of the emitting layer, and red, green, and blue spectrum and efficiency are confirmed after passing through color filters. The optimized white OLED device with color filters reaches 97.8% of the National Television Standards Committee standard.     

Threshold estimation of an organic laser diode using a rate-equation model validated experimentally with a microcavity OLED submitted to nanosecond electrical pulses

We propose a new model for the organic laser diode based on rate equations for polarons, singlet and triplet excitons for both host and guest molecules, and photon densities. The proposed model is validated experimentally by comparing calculated and measured optical responses in the context of pulsed nanosecond electrical excitation of high-speed μ-OLEDs in the limit of weak micro-cavity effects. We predict the laser threshold current density as a function of the micro-cavity quality factor, for two material gain and residual absorption values. We elucidate the crucial role played by the latter in setting the laser threshold and comment on the recently observed threshold value of ∼500 A/cm² by the group of Adachi [1]. Simulations predict that laser action under short electrical nanosecond pulse single-shot excitation is accompanied by damped relaxation oscillations in the GHz regime. The measured ultra-short experimental optical responses at 45 V are best reproduced numerically when the Langevin recombination rate is larger than usually observed in the literature as a consequence of the field dependence of the Poole-Frenkel law for the mobility.     

优化配电网网架,促进城市发展

通过对城市配电网网架的合理优化,不仅能够有效降低构建费与投资,同时也能够在很大程度上提升配电网系统的安全性,推动城市的快速发展.本文针对配电网网架的优化进行简单分析,以供日后参考.     

Simulation of OLEDs with a polar electron transport layer

Organic light-emitting diodes (OLEDs) rely on the use of functional materials with suitable energy levels and mobilities for selective charge carrier injection and transport of one species only at the respective electrode. Until recently, however, the dipolar nature of many organic semiconductors has been largely ignored in this context. In particular, electron transports layers (ETLs) often exhibit spontaneous orientation polarization leading to interfacial charges that modify the electrical potential landscape inside a hetero-layer device.Here we demonstrate that the effect of polar ETLs can be simulated using the well-established Poisson and drift-diffusion formalism, if these interfacial charges are taken into account. Impedance spectroscopy is used in order to validate our approach and to characterize the polarity of the material. Finally, simulations allow to quantify the impact of polar ETLs on device performance.