Understanding the role of ultra-thin polymeric interlayers in improving efficiency of polymer light emitting diodes
Understanding the role of ultra-thin polymeric interlayers in improving efficiency of polymer light emitting diodes
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DOI：
10.1063/1.4879455
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发表时间：
2014-05-28
影响因子：
3.2
通讯作者：
Kim, Ji-Seon
中科院分区：
文献类型：
--
作者：
Bailey, Jim;Wright, Edward N.;Kim, Ji-Seon
在聚合物发光二极管（PLED）的聚（3，4-乙撑二氧噻吩）：聚苯乙烯磺酸盐空穴注入层和聚（9，9-二辛基芴-alt-苯并噻二唑）（F8 BT）发光层之间插入超薄聚合物夹层（IL）可以显著提高其效率。在本文中，我们实验研究了广泛的可能原因，这种增强与眼睛，以确定IL参数具有最显着的影响。空穴注入和电子阻挡的重要性进行了研究，通过改变IL材料（因此其电子能级）的PLED和空穴二极管结构。通过将IL材料与浓度为1重量%至7重量%的强电子接受小分子共混来引入不同水平的电荷转移掺杂，来检查IL导电性的作用。沉积厚度低于激子扩散长度的IL类似于15 nm，允许探测IL作为激子淬灭的物理屏障的作用。还用Lumation绿色系列1300（LG 1300）发光层制造了含IL的PLED。另一方面，使用3D多粒子动力学蒙特卡罗模拟与描述如何从PLED提取光的光学模型耦合来对PLED进行建模。该模型描述了电荷载流子传输和电子，空穴，单线态和三线态之间的相互作用，与电流密度，亮度和复合区（RZ）的位置计算每个PLED。该模型显示F8 BT PLED在阳极附近具有窄的电荷RZ，而LG 1300 PLED具有均匀分布在发光层上的宽电荷RZ。将发光层从F8 BT改变为Lumation绿色系列1300，因此，我们实验性地检查IL功能的依赖性，特别是关于阳极侧激子淬灭，对RZ的位置。我们发现F8 BT PLED亮度对发光聚合物和半导体聚合物IL之间的最高占据到最低未占据分子轨道能隙的差Δ的指数依赖性，因此d是决定效率的最重要参数。理解更宽的能隙IL材料对激子淬灭具有的指数效应可以允许δ用于更好地指导PLED结构设计。(C)2014 AIP出版有限责任公司。
Insertion of ultra-thin polymeric interlayers (ILs) between the poly(3,4-ethylenedioxythiophene): polystyrene sulphonate hole injection and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) light emission layers of polymer light emitting diodes (PLEDs) can significantly increase their efficiency. In this paper, we investigate experimentally a broad range of probable causes of this enhancement with an eye to determining which IL parameters have the most significant effects. The importance of hole injection and electron blocking was studied through varying the IL material (and consequently its electronic energy levels) for both PLED and hole-only diode structures. The role of IL conductivity was examined by introducing a varying level of charge-transfer doping through blending the IL materials with a strong electron-accepting small molecule in concentrations from 1% to 7% by weight. Depositing ILs with thicknesses below the exciton diffusion length of similar to 15nm allowed the role of the IL as a physical barrier to exciton quenching to be probed. IL containing PLEDs was also fabricated with Lumation Green Series 1300 (LG 1300) light emission layers. On the other hand, the PLEDs were modeled using a 3D multi-particle Kinetic Monte Carlo simulation coupled with an optical model describing how light is extracted from the PLED. The model describes charge carrier transport and interactions between electrons, holes, singlets, and triplets, with the current density, luminance, and recombination zone (RZ) locations calculated for each PLED. The model shows F8BT PLEDs have a narrow charge RZ adjacent to the anode, while LG 1300 PLEDs have a wide charge RZ that is evenly distributed across the light emitting layer. Varying the light emitting layer from F8BT to Lumation Green Series 1300, we therefore experimentally examine the dependence of the IL function, specifically in regard to anode-side exciton quenching, on the location of the RZ. We found an exponential dependence of F8BT PLED luminance on the difference, delta, in the highest occupied to lowest unoccupied molecular orbital energy gap between the light emitting polymer and a semiconducting polymeric IL, with d consequently the most important parameter determining efficiency. Understanding the exponential effect that wider energy gap IL materials have on exciton quenching may allow delta to be used to better guide PLED structure design. (C) 2014 AIP Publishing LLC.