双层有机电致发光器件有机层厚度优化的数值研究

在陷阱电荷限制电流传导理论的基础上,提出了双层有机电致发光器件的数值模型,研究了结构为"阳极/空穴输运层(HTL)/发光层(EML)/阴极"的器件中电流密度和量子效率随有机层的特征陷阱能量、陷阱密度和载流子迁移率的依赖关系. 研究发现,对于给定的HTL和EML的特征陷阱能量、陷阱密度和载流子迁移率,存在一个最优的HTL和EML之间的厚度比率,在此最优厚度比下,器件的电流密度和量子效率达到最大.通过有机层厚度的优化,器件的电流密度和量子效率可提高多达两个数量级.另外,还研究了最优厚度比随有机层特征陷阱能量、总陷阱密度和载流子迁移率之间的定量关系.     

具有复合空穴传输层的高效低压有机电致发光器件

报道了用m-MTDATA掺杂NPB作复合空穴传输层(c-HTL)的高效率、低电压有机电致发光器件(OLED),器件的最高发光效率达到了5.3cd/A,比NPB作HTL的器件(3.4cd/A)提高了约50%.这是由于c-HTL具有较低的空穴迁移率,改善了发光层中两种载流子的平衡,从而提高了器件性能.进一步在ITO与c-H...     

具有双绝缘层的有机薄膜晶体管

为了提高SiO2单绝缘层器件的性能,在SiO2绝缘层的表面用旋涂的方法制备一层大约50 nm厚度的PMMA.实验结果表明用无机/有机双绝缘层可以有效的提高器件的性能同时降低器件的漏电流.计算出了载流子迁移率和开关电流比,基于PMMA/SiO2双绝缘层器件的载流子迁移率和开关电流比分别是4.0×10-3cm2/Vs和104.     

数值分析发光材料性质对OLED电流和亮度的影响

以具有指数分布的陷阱电荷限制电流为基础,用数值方法定量分析了单层有机电致发光器件(OLED)发光材料陷阱特性和发光层厚度对器件电流和亮度的影响。结果表明,电流密度和亮度随陷阱分布特征能级和有机层厚度的增大指数减小,并与总陷阱密度的1次方成反比,1为陷阱分布特征参数。     

数值分析发光材料性质对OLED电流和亮度的影响

以具有指数分布的陷阱电荷限制电流为基础，用数值方法定量分析了单层有机电致发光器件（OLED）发光材料陷阱特性和发光层厚度对器件电流和亮度的影响。结果表明，电流密度和亮度随陷阱分布特征能级和有机层厚度的增大指数减小，并与总陷阱密度的1次方成反比，1为陷阱分布特征参数。     

有机磷光电致发光器件中的复合宽度和外量子效率

从经验公式出发,基于T-T湮灭过程,建立了有机磷光电致发光器件中复合宽度和外量子效率的理论模型.结果表明:(1)随外加电压升高,器件的复合宽度减小,外量子效率增加;(2)随器件厚度的增加,复合宽度相应增加,但外量子效率在不同的电压下呈现不同的变化趋势;(3)外量子效率随复合电流密度的增大而显著降低.讨论了外加电压和器件厚度对复合宽度的影响,分析了外量子效率随外加电压、器件厚度及复合电流密度变化的原因.     

有机磷光电致发光器件中的复合宽度和外量子效率

从经验公式出发,基于T-T湮灭过程,建立了有机磷光电致发光器件中复合宽度和外量子效率的理论模型.结果表明:(1)随外加电压升高,器件的复合宽度减小,外量子效率增加;(2)随器件厚度的增加,复合宽度相应增加,但外量子效率在不同的电压下呈现不同的变化趋势;(3)外量子效率随复合电流密度的增大而显著降低.讨论了外加电压和器件厚度对复合宽度的影响,分析了外量子效率随外加电压、器件厚度及复合电流密度变化的原因.     

载流子平衡的低压高效有机发光器件

分别在ITO与NPB间加入高迁移率的m-MTDATA:x%4F-TCNQ来增强器件的空穴注入,在阴极和发光层之间加入高迁移率的Bphen:Liq层增强器件的电子注入,制备了结构为ITO/m-MTDATA:x%4F-TCNQ/NPB/Alq_3/Bphen:Liq/LiF/Al的有机发光器件.研究了传输层的单载流子器件行为,同时,由于注入的电子和空穴数量偏离平衡,器件的整体效率也会受到影响,在实验中通过调节4F-TCNQ的质量百分比,来调控空穴的注入和传输,使载流子达到了较好的平衡.器件的最大电流效率和流明效率分别达到了6.1 cd/A和5.2 lm/W.     

有机/聚合物异质结电致发光器件的光电性能

器件结构是影响有机发光器件(OLED)性能的重要因素之一.采用8-hydroxyquinoline-aluminum(AlQ)作为发光层(EML)和电子传输层(ETL),polyvinylcarbazole (PVK)作为空穴传输层(HTL),制备了具有有机小分子/聚合物异质结结构的OLED器件,通过其电压-电流-发光亮度(V-J-B)特性测试,研究了HTL的引入及其膜厚对器件性能的影响.实验结果表明,HTL的引入有效地改善了OLED的光电性能,同时HTL膜厚对器件性能具有显著影响,当HTL膜厚为20 nm时,所制备的OLED器件具有最小的驱动电压和启亮电压、最大的发光亮度和发光效率.

Abstract：

The device construction plays an important role in improving the optoelectronic performance of organic electroluminescence devices (OLEDs). Heterojunction OLEDs with a configuration of glass/ITO/PVK/AlQ/Mg/Al were fabricated by using 8-hydroxyquinoline-aluminum (AlQ) as the emission layer (EML) and electron transport layer (ETL) and polyvinylcarbazole (PVK) as the hole transport layer (HTL). The effect of the HTL thickness on the performance of OLEDs was investigated with respect to the driving voltage, turn-on voltage, electroluminescence brightness and efficiency of the devices. Experimental results demonstrate that the optical and electrical properies of OLEDs are closely related to the HTL thickness. The device fabricated with the HTL thickness of 20 nm possesses the best photoelectric properties such as the minimum driving voltage and turn-on voltage, and the maximum electroluminescence brightness and efficiency.     

聚合物/有机小分子异质结掺杂型电致发光二极管及其发射机制

为了提高有机电致发光器件的效率和稳定性,制作了聚合物/有机小分子异质结掺杂型电致发光二极管.它以新型PTPD(聚TPD)为空穴传输材料,高效荧光材料Rubrene为掺杂剂.异质结基本结构为PTPD/Alq3,双层掺杂时,器件电致发光的量子效率大约是未掺杂器件的两倍;与未掺杂器件和常用的TPD/Alq3二极管相比,掺杂器件的稳定性有了显著的提高.从电致发光光谱可知,掺杂器件的发射机制为载流子陷阱和Forster能量转换过程的共同作用.     

Doping-free hybrid white organic light-emitting diodes with fluorescent blue,phosphorescent green and red emission layers

Industrialized white organic light-emitting diodes (OLEDs) currently require host-guest doping, a complicated process necessitating precise control of the guest concentration to get high efficiency and stability. Two doping-free, hybrid white OLEDs with fluorescent blue, and phosphorescent green and red emissive layers (EMLs) are reported in this work. An ultra-thin red phosphorescent EML was situated in a blue-emitting electron transport layer (ETL), while the ultra-thin green phosphorescent EML was placed either in the ETL (Device 1), or the hole transport layer (HTL) (Device 2). Device 2 exhibits higher efficiency and more stable spectrum due to the enhanced utilization of excitons by ultra-thin green EML at the exciton generation zone within the HTL. Values of current efficiency (CE), power efficiency (PE), and CRI obtained for the optimized hybrid white OLEDs fabricated through a doping-free process were of 23.2 cd/A, 20.5 lm/W and 82 at 1000 cd/m², respectively.     

Numerical study on the short-circuit current in single layer organic solar cells with Schottkey contacts

The effects of the cathode operation voltage,the absorption coefficient,the carrier mobility,the temperature and the thickness of organic active layer on the short-circuit current density of single layer organic solar cells(OSCs) with Schottkey contacts are numerically studied.Quantitative dependences of the short-circuit current density on the respective parameters are obtained.The results show that a larger operation-voltage difference between the anode and the cathode,a higher carrier mobility as well as...     

Phosphorescent dye-doped hole transporting layer for organic light-emitting diodes

Hole transport materials are critical to the performance of organic light-emitting diodes (OLEDs). While 1,1-bis(di-4-tolylaminophenyl)cyclohexane (TAPC) with a high triplet energy is widely used for high efficiency phosphorescent OLEDs, devices using TAPC as a hole transport layer (HTL) have a short operating lifetime due to the build-up of trapped charges at the TAPC/emitting layer (EML) interface during device operation. In this work, to solve the operating stability problem, instead of using conventional HTLs, we use a(fac-tris(2-phenylpyridine)iridium (III))(Ir(ppy)₃) doped layer as an HTL to replace the conventional HTLs. Because of the hole injecting and transporting abilities of the phosphorescent dye, holes can be directly injected into the emitting layer without an injection barrier. OLEDs based on a phosphorescent dye-doped HTL show significant improvement in operational stability without loss of efficiency.     

超微OLED的制备及其光电特性的研究

为了实现高亮度有机电致发光器件(OLED)及其尺寸的微型化,采用接触式光刻技术,通过真空热蒸镀制备了具有不同掩膜版结构的OLED。器件的结构为玻璃衬底/ITO/LiF/空穴传输层(HTL,NPD)/发光层(EML,0.5-0.6vol%Rubrene:Alq3)/电子传输层(ETL,Alq3)/阴极,其中LiF作为绝缘层。分别制得发光面积为45μm×2mm的微细器件和直径为44μm的微小器件。实验研究了其光电特性,结果表明,4.5μm×2.0mm微细器件的最大电流密度为7A/cm2,为44μm微小器件的最大电流密度为40A/cm2。     

Numerical Analysis on Current Transport Characteristics in Single Layer Organic Electroluminescent Devices

A new model to describe I-V characteristics of organic light-emitting devices (OLEDs) is developed based on experimental results. The dependence of I-V characteristics on energy barrier, trap density and carrier mobility is analyzed. The result shows that this model combines the Fowler-Nordheim tunnel theory and the trap charge limited current theory with exponential trap distribution (TCL), and it describes the current transport characteristics of OLEDs more comprehensively. The I-V characteristics follow Fowler-Nordheim theory when the energy barrier is high, the trap density is small and the carrier mobility is large.In other cases they follow the TCL theory.     

加入激子阻挡层增强白色有机发光器件效率

通过在发光层（EBL）与电子注入层之间增加激子阻挡层（EBL）制备了新型白色有机发光器件（WOLED）。有EBL的新型器件效率和亮度均比传统结构器件高50％,在电流密度为4mA／cm^2时效率达到3．42cd／A,最大亮度为11000cd／m^2（16V）,色坐标为x=0．34、y=0．36;而具有相同EBL厚度的传统结构器件,在电流密度为4mA／cm^2时效率为2．15cd／A,最大亮度为6259cd／m^2（16V）。效率的提高是由于EBL的限制作用而提高了激子浓度。测量了器件的效率与电流密度关系,随电流密度增加电流效率的衰减缓慢,说明短寿命红色搀杂剂的激子-激子湮灭很弱。     

Improved efficiency in fluorescent blue organic light emitting diode with a carrier confining structure

A blue organic light emitting device (OLED) with improved efficiency and good color purity is reported. The highest occupied molecular orbital (HOMO) level of the hole transport layer (HTL) and that of the emissive layer (EML) differs by 0.3 eV. This energy level mismatch confines the carriers at the HTL/EML interface. Conventional devices have only one HTL/EML interface, with a current efficiency of 2.9 cd/A. Without adding a separate hole blocking layer, incorporating multi-layers of the same HTL and EML increases this efficiency to 5.8 cd/A, with only a small increase in operating voltage yielding increased power efficiency also. But, there are an optimum number of layers, beyond which efficiency loss results. Also, including the multilayer structure simultaneously improves the blue color co-ordinates. To gain insight into the role of multilayer structures in modifying charge transport and recombination zone a simulator was developed. The simulated results could qualitatively explain the experimental observations.     

Tandem organic light-emitting diodes with buffer- modified C60/pentacene as charge generation layer

Buffer-modified C60/pentacene as charge generation layer (CGL) is investigated to achieve effective performance of charge generation. Undoped green electroluminescent tandem organic light-emitting diodes (OLEDs) with multiple identical emissive units and using buffer-modified C60/pentacene organic semiconductor heterojunction (OHJ) as CGL are demonstrated to exhibit better current density and brightness, compared with conventional single-unit devices. The current density and brightness both can be significantly improved with increasing the thickness of Al. However, excessive thickness of Al seriously decreases the transmittance of films and damages the interface. As a result, the maximum current efficiency of 1.43 cd.A-1 at 30 mA.cm-2 can be achieved for tandem OLEDs with optimal thickness of Al. These results clearly demonstrate that Cs2CO3/Al is an effective buffer for C60/pentacene-based tandem OLEDs.