迁移率对单层有机发光器件中电场与载流子分布的影响

有机发光器件的宏观特性与有机层中的电场和载流子浓度分布密切相关。建立的有机电致发光器件模型是由两个金属电极中间夹一层有机发光薄膜材料组成的单层器件,金属与有机发光层之间为欧姆接触。模型以载流子运动的扩散-漂移理论为基础,利用数值方法研究了有机发光层中双极载流子注入时的电势、电场、载流子浓度和复合密度分布。分析结果表明:当两种载流子的迁移率相同时,电场强度、载流子浓度、复合密度的分布呈对称形式。而当电子和空穴的迁移率μn和μp相差比较大时,高迁移率的载流子不仅仅分布在注入端附近而且还有一小部分能够传输到另一端,而低迁移率的载流子只分布在其注入端附近;当μn、μp的大小相差不大时,载流子传输情况就介于两者之间。当μn/μp的比值变化时,电场强度的极大值向载流子迁移率小的注入端偏移。     

有机无机异质节中稀土配合物电致发光的研究

报道了有机无机异质节中稀土配合物的电致发光,器件结构为：ITO/PVK:Rare Earth Complex/无机材料/Al,其中无机材料可以选用ZnS,ZnSe,ZnO等。在这种结构的器件中,均获得了比较好的稀土离子的特征发射。以无机材料ZnS为例,讨论了异质节中稀土配合物的电致发光及优势。ZnS的电介质系数比PVK的电介质系数大3倍多,将有更大部分的电压降落在PVK层上,使PVK层内的电场强度增大,从而可以提高空穴在PVK层内的迁移速度,提高了空穴注入数目,有利于载流子的平衡。     

ZnO纳米棒的低温溶液法制备、光电特性研究及其在有机/无机复合电致发光中的应用

利用水热法制备了垂直于衬底的定向生长的ZnO纳米棒,利用扫描电子显微镜及光致发光的方法对其形貌及光学特性进行了表征,利用场发射性能测试装置对ZnO纳米棒的场发射性能进行了测试.结果表明:利用水热法在较低的温度(95 ℃) 下生长了具有较好形貌和结构的ZnO纳米棒,并表现出了较好的场发射特性,当电流密度为1 μA/cm²时,开启电场是2.8 V/μm,当电场为6.4 V/μm时,电流密度可以达到0.67 mA/cm²,场增强因子为3360.稳定性测试表明,在5 h内,4.5 V/μm的电场下,其波动不超过25%.将制备的ZnO纳米棒应用到有机/无机电致发光中,其中ZnO纳米棒为电子传输层,m-MTDATA(4,4',4″-tris{N,(3-methylphenyl)-N-phenylamino}-triphenylamine) 为空穴传输层,得到了ZnO的342 nm的紫外电致发光,此发光较ZnO纳米棒光致发光的紫外发射有约40 nm的蓝移. 关键词： ZnO纳米棒 场发射 水热法 有机/无机复合电致发光     

The effects of trap density on current bistability and negative differential resistance in organic bistable devices

Current bistable properties and negative differential resistance (NDR) behaviors of organic bistable devices (OBDs) with a single layer were simulated by using Shockley–Reed statistics for the trap population. The current–voltage (I–V) curves were calculated to investigate the effects of the trap density on the NDR characteristics of current bistabilities in the OBDs. The simulation results of the I–V curves showed that the current bistability and the NDR behavior of the OBDs were dominantly attributed to the trapped electrons in the organic layer. The NDR behavior of the I–V curve appeared with increasing trap density, and the increasing rate of the internal electric field caused by the trapped electrons became larger than that of the external electric field due to the applied voltage. This resulted in the appearance of NDR behavior in the I–V curves. These results can help improve understanding of the effects of the trap density on the current bistability and the origin of the NDR behavior in the I–V characteristic in OBDs.     

Novel Field Emission Organic Light Emitting Diodes with Dynode

This work presents novel field emission organic light emitting diodes(FEOLEDs) with dynode,in which an organic EL light-emitting layer is used instead of an inorganic phosphor thin film in the field emission display(FED).The proposed FEOLEDs introduce field emission electrons into organic light emitting diodes(OLEDs),which exhibit a higher luminous efficiency than conventional OLED.The field emission electrons emitted from the carbon nanotubes(CNTs) cathode and to be amplified by impact the dynode in vacuum.These field emission electrons are injected into the multi-layer organic materials of OLED to increase the electron density.Additionally,the proposed FEOLED increase the luminance of OLED from 10 820 cd/m2 to 24 782 cd/m2 by raising the current density of OLED from an external electron source.The role of FEOLED is to add the quantity of electrons-holes pairs in OLED,which increase the exciton and further increase the luminous efficiency of OLED.Under the same operating current density,the FEOLED exhibits a higher luminous efficiency than that of OLED.     

Highly-efficient solution-processed phosphorescent multi-layer organic light-emitting diodes investigated by electromodulation spectroscopy

We report on electromodulation (EM) spectroscopy studies of phosphorescent multi-layer organic light-emitting diodes (OLEDs) that are processed from solution. Compared to conventional single-layer OLEDs, they comprise an additional layer of a crosslinkable, oxetane-functionalized triphenylamine-dimer (XTPD) that is inserted between the PEDOT:PSS anode and the emissive layer. Devices with optimized stack architecture feature reduced operating voltages and reach a current efficiency approaching 40 cd/A—twice as much as the corresponding single-layer device. Using EM measurements, we quantify the electric field in the XTPD layer and the emissive layer of such a multi-layer OLED and also measure the average electric field in a single-layer reference device. By comparing the dependence of the internal field on the applied voltage for devices with and without the XTPD layer, we find that in the device containing the XTPD layer there is an increased accumulation of electrons at the anode side of the emissive layer. This accumulation enhances the recombination probability and supports the injection of holes into the emissive layer which explains the observed efficiency improvement and reduction in operating voltage compared to conventional single-layer OLEDs.     

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     

Performance improvement of rubrene-based organic light emitting devices with a mixed single layer

We have investigated the performance of organic light-emitting devices (OLEDs) with a rubrene-doped mixed single layer by using 4,4′-bis[N-(1-napthyl)-N-phenyl- amion] biphenyl (α-NPD) as hole transport layer. Comparing to a conventional heterostructure OLED, equal luminance vs. current density characteristics were obtained. In addition, maximum power efficiency was threefold improved, and the achieved value was 5.90 lm/W by optimizing a mixing ratio of hole and electron transport materials. By evaluating the temperature dependence of the J – V characteristics for electron-injection dominated device, the electron injection from Al/LiF to mixed organic layer is attributed to Schottky thermal emission model. And the barrier height of the electron injection from Al/LiF into mixed single layer was obtained to be 0.62 eV, which is lower than Al/Alq₃ interface. Meanwhile, the mixed single-layer device exhibited superior operational durability at a half-luminance of 2,250 h under a constant current operation mode. The reliability was improved with a factor of two compared to the heterostructure device due to the improvement of stability in mixed organic molecules and removal of the heterojunction interface in the mixed single-layer device.     

混合界面对溶液制备的磷光OLED器件性能的影响

利用混蒸的方法、将空穴阻挡材料2,9-Dimethyl-4,7-diphenyl-1,10-phenanhroline及电子传输材料Tris(8-hydroxy-quinolinato)aluminium混合,在电子传输层及空穴阻挡层之间制备了薄层的混合界面.在相同驱动电压下,采用混合界面的器件比常规器件的电流密度和亮...     

Effects of different buffer layers on the electro-luminescence performances in white organic light-emitting diodes

The effects of different hole injection materials as the buffer layer on the electro-luminescence (EL) performances of white organic light-emitting diodes (WOLEDs) are investigated in detail. It is found that the EL performances and electric properties were strongly dependent on the structure of the used hole injection materials with different thicknesses, which directly affected the injection and transport properties in devices, and thus the EL efficiency and lifetime. It can be seen that a hybrid buffer layer of 5 nm aluminum fluoride (AlF₃)/15 nm 4,4′,4″-tris(3-methylphenylphenylamino) (m-MTDATA) as the hole injection buffer layer shows the best EL performances in efficiency and lifetime, showing a promising hole injection material in WOLEDs. The mechanisms behind the enhanced performance of the hybrid buffer layer in WOLEDs are discussed based on X-ray photoelectron spectroscopy (XPS) measurement.     

Polymer solar cells based on a PEDOT:PSS layer spin-coated under the action of an electric field

In the process of fabrication of polymer photovoltaic(PV) devices,poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) thin film,acting as an anode buffer layer,is spin-coated under the action of an electric field.The PV devices with a PEDOT:PSS layer spin-coated under the action of a static electric field exhibit improved short-circuit current density(J sc) and power conversion efficiency(PCE).The investigation of morphology shows that the appropriate intensity of the electric field can increase the roughness of the surface of the PEDOT:PSS layer,which results in improved contact between the anode and hole transport layer and thus enhances the J sc of the devices.Chemical analysis is also provided by x-ray photoelectron spectroscopy(XPS) spectra.     

Improving the current efficiency of organic light-emitting device utilizing the well structure

We have demonstrated efficient organic electroluminescent (EL) devices with well Structure as the emitting layer. The well structure fabricated by alternating deposition of constituent tris-(8-hydroxyquinoline) aluminum (Alq₃) and 4,4-N,N-dicarbazole-biphenyl (CBP) layers improved the current efficiency. The enhanced efficiency can be attributed to the strong accumulation of electrons and holes in the thin Alq₃ layer, which leads to an increase of the exciton formation and exciton recombination probability. The single well device exhibits the highest current efficiency of 4.1 cd/A,which is more than twice than that of the conventional heterostructure device. It is an effective and simple way to improve the efficiency of EL devices by utilizing well structure as the emitting layer with proper well number.     

新型稀土铕配合物Eu(o-BBA)3(phen)电致发光研究

研究了一种新的稀土配合物邻苯甲酰苯甲酸-1,10-菲咯啉-铕(Eu(o-BBA)3(phen))的电致发光特性.采用不同的电子传输层材料,制备了多种结构的有机电致发光器件及有机无机复合器件.比较了单层电致发光器件A:ITO/PVK:Eu/Al与有机无机复合器件B:ITO/PVK:Eu/ZnS/Al发光性能的不同.分析了采用无机半导体材料ZnS作为电子传输层的优点.研究结果表明采用无机的电子传输层,能有效地避免激基复合物的形成,提高器件的亮度同时保持稀土离子发光的色纯性.     

固态阴极射线器件复合加速层的研究

固态阴极射线器件的加速层,是提高固态阴极射线性能的重要部分,它能够加大电子能量,倍增电子数量。其中增加注入电子从而提高过热电子的数量,是提高固态阴极射线器件性能的关键。为此 ,文章尝试将加速层复合,兼顾加速与电子注入性能。首先将SiO₂,ZnS和ZnO分别与有机聚合物MEH-PPV组合,确定较适合的复合加速层的组合：SiO₂/ZnS和 ZnO/SiO₂。然后将这两种复合加速层的性能对比,发现SiO₂/ZnS的性能更优越,因为电子注入性能ZnS和ZnO相当,而电子加速倍增性能ZnS明显优于ZnO,其中 SiO₂为主要的加速层,而ZnS起到降低注入势垒变成阶梯势垒的作用。最后又将复合加速层结构的固态阴极射线器件和传统的SiO₂夹层固态阴极射线器件对比,发现这种复合 加速层结构,尤其在高场下,可提高固态阴极射线的初电子源和过热电子的数目,从而提高其发光效率具有促进作用。     

不同加速层材料对固态阴极射线发光的影响

在固态阴极射线发光中,过热电子碰撞激发有机材料而发光,因此加速层对电子的加速能力是影响器件发光亮度的关键因素之一.分别以SiO2和ZnO作为加速层.制备出两种固态阴极射线发光器件A:ITO/MEH-PPV/SiO2/Al和B:ITO/MEH-PPV/ZnO/Al.通过理论计算比较了电子从电极注入到加速层的隧穿电流密度以及SiO2层与ZnO层的电场强度,计算结果表明:在相同驱动电压下,SiO2作为电子加速层时隧穿电流的密度要大于ZnO层的隧穿电流的密度,并且SiO2层的电场强度比ZnO层的电场强度大.实验结果表明:SiO2作为加速层的器件的发光强度高于以ZnO为电子加速层器件的发光强度.     

Effect of the external electric field on the kinetics of recombination of photoexcited carriers in a ZnSe/BeTe type II heterostructure

The kinetics of the radiative recombination of photoexcited electrons and holes for a spatially direct transition in a ZnSe/BeTe type II heterostructure in an external electric field has been analyzed. A strong decrease (more than two orders of magnitude) in the photoluminescence intensity, as well as a decrease in the duration of the relaxation of the direct transition, is observed when the electric field is applied. The energy levels and wavefunctions of electrons and holes in the ZnSe/BeTe heterostructure subjected to the electric field have been numerically calculated. It has been shown that the observed decrease in the photoluminescence intensity and duration of the relaxation of the direct transition is due to both an increase in the radiative recombination time and an increase in the rate of escape of photoexcited holes from the above-barrier level in the ZnSe layer to the BeTe layer.     

有机薄膜电致发光器件结构与发光特性的研究

从有机电致发光薄膜的发光机理出发，通过以Ａｌｑ薄膜器件、ＰＶＫ为空穴传输层和Ａｌｑ为发光层的双层 及ＰＶＫ掺荧光材料Ｐｅｒｙｌｅｎｅ的双层薄膜器件的研制，从器件的电致姚谱、电流密度－电压特性、亮度－电压特性的曲线的测试结果，计算分析了器件的流明效率、量子效率，并对有机薄膜电致发光器件的结构与发光特性之间的关系进行研究，利用能级理论分析了器件的姚特性随器件的结构不同所具有的规律。实验表明，加入ＰＶＫ     

互混型有机电致发光器件

通过共蒸镀空穴传输材料TPD和电子传输材料Alq₃,在普通双层器件的异质结界面引入了均匀互混层,并研究了互混层的厚度变化对器件光电性能的影响。互混层的引入在一定程度上改善了普通双层器件的异质结界面由于高浓度载流子积聚导致的高电场和界面缺陷对器件主要性能(效率和寿命)的负面影响。我们发现一定厚度的互混层使器件的性能有所提高。     

Strong amplification of an electric field and electro-optical response in ultrathin heterostructures ferroelectric-linear dielectric

An electroded heterostructure consisting of a dye layer sandwiched between two polymer ferroelectric layers is discussed. The dye layer plays a role of the probe of the electric field measured by an electroabsorption technique. Using this new method the electric field in ferroelectric and dielectric layers can be measured separately. When an a.c. voltage is applied to the heterostructure, the electric field in the dye layer increases 2.2 times (up to 0.55 GV/m), whereas the field in the ferroelectric decreases 2 times with respect to the average field in the entire structure. Moreover, the dye layer sandwiched between the ferroelectric layers may stand without breakdown the fields 5–7 times higher than a neat reference dye layer confined between metal electrodes. Therefore, the performance of electro-optical, electromechanical and other field controlled devices may be improved considerably when their functional materials are placed between ferroelectrics layers.     

高效率的有机电致发光器件

有机电致发光器件 (OL EDs)的发光机理包括电子和空穴从电极的注入、激子的形成及复合发光 ,其中 ,空穴和电子的注入平衡是非常重要的。为了平衡载流子的注入以得到高效率和稳定性好的器件 ,人们不仅使用了电子注入更为有效的 L i F/ Al[1] 和 Cs F/ Al[2 ] 等复合电极 ,同时也使用了空穴缓冲层 ,如 S.A.Van Slyke等 [3]在ITO和 NPB之间使用 Cu Pc,使得器件的稳定性得到了明显的提高 ;A.Gyoutoku等[4 ] 用碳膜使器件的半寿命超过 3 5 0 0小时 ;最近 ,Y.Kurosaka等 [5]和 Z.B.Deng[6 ]分别在 ITO和空穴传输层之间插入一薄层 Al…