器件效应数值模拟中漂移扩散模型的误差分析

为了确定数值模拟过程中的误差来源,并针对误差来源改进软件,减小计算误差,对半导体器件数值模拟中的采用的漂移扩散模型进行了研究。结合自主开发的半导体器件效应软件GSRES,分析了软件中漂移扩散模型的理论近似,对计算模型中由于温度分布、载流子复合/产生率、载流子迁移率等项采取近似而导致的误差进行了分析。根据误差分析和数值模拟算例,认为误差主要来自于器件内部温度场分布和迁移率模型的近似,给出了软件的适用范围。结合半导体器件的研究热点和发展趋势,对该模型中需要进行改进的近似项进行了分析。     

器件效应数值模拟中漂移扩散模型的误差分析

为了确定数值模拟过程中的误差来源,并针对误差来源改进软件,减小计算误差,对半导体器件数值模拟中的采用的漂移扩散模型进行了研究。结合自主开发的半导体器件效应软件GSRES,分析了软件中漂移扩散模型的理论近似,对计算模型中由于温度分布、载流子复合/产生率、载流子迁移率等项采取近似而导致的误差进行了分析。根据误差分析和数值模拟算例,认为误差主要来自于器件内部温度场分布和迁移率模型的近似,给出了软件的适用范围。结合半导体器件的研究热点和发展趋势,对该模型中需要进行改进的近似项进行了分析。     

顶发射白光OLED器件制备及其色坐标漂移机制研究

采用了高反射率金属Al和电化学性能稳定的金属Mo,在硅基底上制备了多层结构的 Al/Mo/MoO₃阳极,并研究了不同MoO₃厚度下多层阳极的反射率。在此基础上,通过发光层共掺杂制备了顶部发光OLED器件,并对器件发光机制进行了系统研究和分析。实验结果表明：采用发光层共掺杂制备的顶部发光OLED器件的色坐标,随电流密度或电压的增加而发生漂移;OLED器件色坐标漂移的原因是三基色发光强度随电流密度的增加,逐渐偏离了形成白光(0.33, 0.33)所需三基色强度比例值,导致了OLED器件的色坐标发生了漂移,其机制是发光层中主-客之间能量转移和陷阱共同作用的结果。进一步研究发现,在不同电压下,红光发光强度随驱动电压(或电流密度)增大而线性地减小。     

双层有机EL器件ITO/PPV/Alq3/Al发光稳定性的研究

制备了一组由PPV和Alq3组成的双层有机EL器件ITO/PPV/Alq3/Al;比较了两个发光层厚度不同时器件发光性能的差异.测试和分析了温度、真空度、工作电压和存放时间对器件衰减规律的影响.     

新型蓝光OLED材料和器件

基于有机材料的电致发光技术可以应用于超薄平面显示和有机固体激光器等方面,在近20年来取得了飞速的发展,基本实现了红、绿、蓝三基色发光.绿色材料发展最快,基本达到了商业化实用阶段,而红色和蓝色材料的问题较多,特别是稳定、高效率的蓝光更具有挑战性.综述了近期我们对蓝光材料的分子设计与合成,以及蓝光器件的一些研究.主要包括金属络合物2,3-二甲基-8-羟基喹啉锂和聚芴衍生物树枝状的聚芴化合物的蓝光材料,以及利用基激复合态实现蓝光的电致发光器件.通过光致发光、电致发光光谱以及电压-电流-发光亮度特征曲线等研究了这些发光材料和器件的性质.现在蓝光器件的色纯度和工作寿命还有待提高.     

单层有机器件的电子传输特性的数值模拟

在漂移扩散模型的基础上建立了单层有机器件的模型,包括了电荷注入、传输、空间电荷效应和陷阱的影响.电荷注入考虑了热电子发射电流和隧道电流.模拟得到的结果和文献中报道的实验测试数据一致.模拟研究了各个因素对器件J-V曲线的影响,电流和器件长度成反比,电流随着空穴注入势垒的减小而增加.电子注入势垒从1.7 eV减少到0.5 eV时,电流随着电子注入势垒的减小而减小,这主要是因为有机材料中电子迁移率太小,电子注入电流的增加可以忽略,而电子注入势垒的减小使内建势增加,在同样的电压下,场强 关键词： 有机器件 传输特性 数值模拟     

通用二维半导体器件模拟软件的设计

介绍自行研制的通用二维半导体器件模拟软件CSS,该软件的求解器同时实现了漂移扩散模型和流体动力学模型,可对多种材料、不同结构的器件进行稳态和瞬态计算.作为算例,应用该软件对NPN三极管和MESFET管进行了数值模拟,给出了Ⅳ曲线、电子密度分布和温度变化等.     

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。     

ITO再生处理对有机电致发光器件特性的影响

分别采用Na OH和HCl溶液对废旧氧化铟锡(ITO)基板进行再生处理,用原子力显微镜(AFM)观测了处理后的ITO表面形貌,并基于再生处理过的ITO制备了有机电致发光器件(OLED),系统研究了器件的性能。结果表明,上述方法可以有效去除废旧ITO残留的铝电极并改变其表面的化学结构,提高了器件的特性,尤其以Na OH单次处理最为有效。以此制备的OLED器件电流效率达到12.08 cd/A,较之未回收利用的新ITO所制备的器件提高了14.7%;外量子效率达到5.23%,提高了11.7%。另外,经不同方法处理后,器件中生色团与生色团之间、生色团与助色团之间的空间位阻增大,器件发光光谱肩峰效应增强。     

颗粒湍流扩散的数值模拟

1引言颗粒湍流扩散是气固两相流中的一个重要的研究课题,近年来,国外有大量文献报道这方面的工作。因为颗粒的湍流扩散的研究的一个基本问题就是湍流的描述,它一方面可以来检验湍流描述的正确性;另一方面,该问题是气固两相流理论中,特别是颗粒群轨道模型中一个难点。描述湍流大体上可分为两种方法。一是直接数值模拟方法（DNS）,J．B．Mclaughlin对管流内颗粒沉降的研究就基于直接数值模拟山,K．D．squires和J．K．Eaton对颗粒扩散的研究也基于DNS［2］,DNS一般只适用于低Reynolds数。另一方面,用随机方法来模拟湍流,该…     

Light outcoupling efficiency enhancement in organic light emitting diodes using an organic scattering layer

Crystallized 4,7‐diphyenyl‐1,10‐phenanthroline (BPhen) films deposited by convenient vacuum thermal evaporation technique have been found to be an efficient means to extract the substrate wave guided light in organic light emitting diodes (OLEDs). The optimized BPhen film working as organic scattering layer was successfully used with OLEDs for light outcoupling efficiency improvement. Enhancement of 26%, 15% and 6% in efficiency of the blue, green and red OLEDs were obtained, respectively. The achievement was found to be advantageous in terms of simplicity of fabrication method and feasibility for large area OLED applications. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

ITO‐free top emitting organic light emitting diodes with enhanced light out‐coupling

Bottom emitting organic light emitting diodes (OLEDs) can suffer from lower external quantum efficiencies (EQE) due to inefficient out‐coupling of the generated light. Herein, it is demonstrated that the current efficiency and EQE of red, yellow, and blue fluorescent single layer polymer OLEDs is significantly enhanced when a MoO_x(5 nm)/Ag(10 nm)/MoO_x(40 nm) stack is used as the transparent anode in a top emitting OLED structure. A maximum current efficiency and EQE of 21.2 cd/A and 6.7%, respectively, was achieved for a yellow OLED, while a blue OLED achieved a maximum of 16.5 cd/A and 10.1%, respectively. The increase in light out‐coupling from the top‐emitting OLEDs led to increase in efficiency by a factor of up to 2.2 relative to the optimised bottom emitting devices, which is the best out‐coupling reported using solution processed polymers in a simple architecture and a significant step forward for their use in large area lighting and displays.     

3,4,9,10-Perylenetetracarboxylicdiimide as an interlayer for ultraviolet organic light emitting diodes

Ultraviolet organic light emitting diodes with 3,4,9,10-perylenetetracarboxylicdiimide (PTCDI) interlayer have been achieved. The emission spectrum and intensity were strongly dependent on the thickness of PTCDI interlayer, in spite of the fact that PTCDI has neither much lower HOMO nor much higher LUMO level, which is considered necessary for efficient charge blocking layers. The influence of PTCDI layer was investigated in three different device configurations and obtained results are discussed. For optimal device configuration, OLED with emission centered at 370 nm and turn-on voltage of 4.5 V is obtained.     

有机发光二极管光取出技术研究进展

有机发光二极管(OLED)在通信、信息、显示和照明等领域均显现出巨大的商业应用前景,十几年来一直是光电信息领域的研究热点之一.但是,OLED的外量子效率远低于内量子效率,极大程度地制约了其发展和应用.本文主要介绍了多种有效提高器件效率的光取出技术,对微透镜、光子晶体结构、纳米图案和纳米多孔膜以及微腔技术等多种OLED修饰方法进行了回顾和讨论.在此基础上,对一些光取出技术的研究做了展望.     

Thin film hexagonal gold grids as transparent conducting electrodes in organic light emitting diodes

Indium Tin Oxide (ITO) coated glass is currently the preferred transparent conducting electrode (TCE) for organic light emitting diodes (OLEDs). However, ITO has its drawbacks, not least the scarcity of Indium, high processing temperatures, and inflexibility. A number of technologies have been put forward as replacements for ITO. In this paper, an OLED based on a gold grid TCE is demonstrated, the light emission through the grid is examined, and luminance and current measurements are reported. The gold grid has a sheet resistance of 15 Ω□⁻¹ and a light transmission of 63% at 550 nm, comparable to ITO, but with advantages in terms of processing conditions and cost. The gold grid OLED has a lower turn‐on voltage (7.7 V versus 9.8 V) and achieves a luminance of 100 cdm⁻² at a lower voltage (10.9 V versus 12.4 V) than the reference ITO OLED. We discuss the lower turn‐on voltage and the uniformity of the light output through the gold grid TCE and examine the conduction mechanisms in the ITO and gold grid TCE OLEDs.     

Electrical and electroluminescence properties of ITO/PEDOT:PSS/TPD:Alq3:C60/Al organic light emitting diodes

Organic light emitting diodes (OLEDs) of ITO/PEDOT:PSS/TPD:Alq₃:C₆₀/Al with different C₆₀ concentrations (0-6.0 wt.%) have been fabricated. The physical parameters including electrical and optical properties of the samples have been measured by Luminance-current-voltage (L-I-V) characteristics and optical absorbance. The current-voltage characteristics indicate that field-emission tunneling injection dominates in the diodes at high applied voltages. It is found that with increasing the concentration of C₆₀, the injection barrier for holes slightly reduces and the hole’s mobility increases over two orders of magnitude. Also, electroluminescence enhances with the presence of C₆₀ in the blend; optimum current efficiency occurs at 3 wt% C₆₀. The method provides a simple way of increasing the efficiency of OLEDs.     

Organic light emitting diodes using magnesium doped organic acceptor as electron injection layer and silver as cathode

Organic light emitting diodes employing magnesium doped electron acceptor 3, 4, 9, 10 perylenetetracarboxylic dianhydride (Mg:PTCDA) as electron injection layer and silver as cathode were demonstrated. As compared to Mg:Ag cathode, the combination of the Mg:PTCDA layer and silver provided enhanced electron injection into tris (8-quinolinolato) aluminium. The device with 1:2 Mg:PTCDA and Ag showed an increase of about 12% in the maximum current efficiency, mainly due to the improved hole-electron balance, and an increase of about 28% in the maximum power efficiency, as compared to the control device using Mg:Ag cathode. The properties of Mg:PTCDA composites were studied as well.     

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).     

Direct observation of the potential distribution within organic light emitting diodes under operation

We show the first direct measurement of the potential distribution within organic light emitting diodes (OLEDs) under operation and hereby confirm existing hypotheses about charge transport and accumulation in the layer stack. Using a focused ion beam to mill holes in the diodes we gain access to the cross section of the devices and explore the spatially resolved potential distribution in situ by scanning Kelvin probe microscopy under different bias conditions. In bilayer OLEDs consisting of tris(hydroxyquinolinato) aluminum (Alq₃)/N, N ′‐bis(naphthalene‐1‐yl)‐N,N ′‐bis(phenyl) benzidine (NPB) the potential exclusively drops across the Alq₃ layer for applied bias between onset voltage and a given transition voltage. These findings are consistent with previously performed capacitance–voltage measurements. The behavior can be attributed to charge accumulation at the interface between the different organic materials. Furthermore, we show the potential distribution of devices with different cathode structures and degraded devices to identify the cathode interface as main culprit for decreased performance. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

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.