【作者】 李璐；

【导师】 于军胜；

【作者基本信息】 电子科技大学 ， 光学工程， 2012， 博士

【摘要】 聚合物电致发光器件（polymer light-emitting diodes, PLEDs）作为新型的固体照明设备和显示器件具有更好的性能优势。与传统的发光照明和显示方式无机发光二极管（LED）、液晶显示器件（LCD）和等离子体显示器件（PDP）等比较，PLEDs具有自发光、快速响应、全固态器件、超薄体积、制备工艺简单、制作成本低，尤其是器件具有柔性和全溶液制备方法的特点，既适合大面积的生产从而降低成本，又适合在各种特殊表面和极端情况使用，PLEDs是公认为21世纪最理想和最有使用前景的照明和显示技术。但是目前在大尺寸的商业化应用上还存在一些问题需要解决，例如由于PLEDs内部电荷载流子的注入和传输不平衡导致的器件发光效率还不够理想，而且由于目前普遍使用的透明导电阳极氧化铟锡（ITO）使用了稀土元素铟（indium）导致ITO的成本和价格不断提高，所以控制整个PLEDs的生产成本越来越困难。针对这两方面的问题，我们通过使用新材料和界面修饰的方法改善器件的发光性能，同时通过使用新型纳米材料和纳米结构取代目前广泛使用的ITO透明导电阳极，制备高性能的三基色和基于三基色和两种互补色的白光磷光PLEDs，本论文在这两个方面进行了一系列的探索性和创新性的工作，具体包括：1．通过溶液旋涂的方法，在溶液中掺杂oligo(ethylene oxide)(PEO-DME)，从而制备了高效率蓝光磷光PLEDs，器件中使用poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)旋涂在透明导电阳极indium tin oxide (ITO)上作为空穴注入材料，氟化铯/铝作为电子注入电极。单层活性发光层使用poly(9-vinylcarbazole)(PVK)作为主体材料，bis[(4,6-difluorophenyl)-pyridinato-N,C2](picolinato)Ir(Ⅲ)(FIrpic)作为蓝光磷光掺杂染料，1,3-bis[(4-tert-butylphenyl)-1,3,4-oxidiazolyl]phenylene (OXD-7)作为电子传输材料。 PEO-DME的掺杂比例为5-10wt%时可以有效的降低电子和空穴的注入势垒。当发光亮度为2500cd/m2时，器件达到最大的电流效率为26.5cd/A。器件取得高性能的原因在于PEO-DME的掺杂会使这种材料与铝电极之间产生特殊的相互作用，从而改善了电荷载流子在界面的注入，另外PEO-DME的掺杂改变了器件内部的电场分布，从而导致电荷载流子的迁移率提高。2．通过在单层发光活性层中掺杂使用poly(ethylene glycol) dimethyl ether(PEG-DME)，制备了高性能白光磷光PLEDs。根据白光的颜色组成不同，器件的发光活性层中分别掺杂了PVK、OXD-7和两种互补色或者三基色的磷光染料。掺杂的PEG-DME可以有效的增强电子注入和传输，同时平衡电子和空穴的密度。基于两种互补色的白光PLEDs在正向观测亮度为1800cd/m~2时最大的电流效率为17.5cd/A，基于三基色的白光PLEDs在正向观测亮度为3000cd/m~2时最大的电流效率为35.7cd/A，即使发光亮度高达30000cd/m~2时，器件的电流效率仍然可以达到30cd/A以上。器件的高电流效率归因于提高了阴极向聚合物发光活性层的电子注入能力，电荷传输能力和PEG-DME对长波长发光峰的增强作用。另外，器件稳定的电流效率是由于单载流子器件中电荷载流子注入和传输的增强以及激子复合发光区域的移动导致的三重态激子-极化子湮灭和电场导致的三重态激子猝灭减弱。3．通过溶液法制备银纳米线（AgNW）和AgNW-聚合物复合电极基板，制备了蓝光、绿光和红光磷光PLEDs。基于这类金属纳米结构电极基板的发光器件获得了比传统ITO/玻璃基板上更高的发光效率。蓝光PLEDs在亮度为1400cd/m~2时，电流效率达到21.5cd/A，在发光亮度为450cd/m~2到5500cd/m~2时，器件的效率维持在20-21.5cd/A这个很小的范围之内，即使发光亮度达到10000cd/m~2时，效率仍然可以达到18.5cd/A。根据不同发光颜色，器件的结构略有不同，基于AgNW-聚合物复合电极基板的蓝光、绿光和红光器件的发光效率比基于ITO/玻璃基板的器件高20-50%。三种不同种颜色器件性能的提高归因于AgNW-聚合物复合电极基板具有比ITO/玻璃基板更高的透过率，尤其是在短波长区域和蓝光区域，同时复合电极基板中的AgNW是作为多光子散射中心存在，可以提高基板的出光率。另外，蓝光PLEDs器件可以经过10次到100次的反复弯曲，并且曲率直径只有1.5mm。进过计算，根据器件弯曲的方向不同，发光器件受到的内部压力或者表面张力可以达到5%，并且器件的发光性能变化不大，在器件反复弯曲100次后，电流效率可以保持在初始效率的87%。4．通过使用AgNW-聚合物复合电极基板制备了高性能磷光白光PLEDs，同时利用复合电极基板提高了白光器件的发光效率和光提取效率。基于两种互补色的白光PLEDs在正向观测亮度为4500cd/m~2时最大的电流效率为20.3cd/A，基于三基色的白光PLEDs在正向观测亮度为4000cd/m~2时最大的电流效率为42.3cd/A，相对于使用ITO/玻璃基板的传统器件，器件的发光效率分别提高了35%和41%。即使在发光亮度提高到10000cd/m~2以上，白光器件的发光效率依然分别保持在20cd/A和40cd/A。白光器件的高电流效率归因于AgNW-聚合物复合电极基板有效提取了传统器件中透明导电电极ITO中被陷阱的40-50%的光波导模式，大大提高了出光效率，另外复合电极基板表面和掩埋在聚合物主体材料内部的AgNW可以通过光散射的方式提取对比器件中玻璃基板中陷阱的光波导模式。此类白光器件同样具有性能优异的弯折性能，在反复弯折测试中，器件张力或者压力为5%的时候，器件的性能几乎不变。更多还原

【Abstract】 Polymer light-emitting diodes (PLEDs) as the solid lighting and display panel,compared with inorganic LED, liquid crystal display (LCD), have many advantages, e.g.self-emission, fast response, full solid device, super-thin thickness, low cost, especiallyflexible and solution processed. PLEDs are considered as the most ideal and potentiallighting technology in21stcentury. However, now there are also some problems toresolve from large scale commercial application such as low luminous efficiency andhigh fabrication cost due to the imbalance of charge carrier injection and transport andthe cost of commercial transport conductive anode indium-tin oxide (ITO) wasincreasing. Aiming at those problems, some new and systematic works have been doneto focus on the fabrication process to obtain high performance device usingmodification and novel nanostructure electrode to replace the ITO anode with highluminous efficiency for phosphorescent PLEDs.1. Solution processed blue electrophosphorescent PLEDs have been fabricatedcontaining an oligo(ethylene oxide)(PEO-DME) additive to enhance theelectroluminescence efficiency. The device uses poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) coated on indium tin oxide as the hole injectionelectrode, cesium fluoride/aluminum as the electron injection electrode. The singleemissive layer is a blend of poly(9-vinylcarbazole)(PVK) as the host,bis[(4,6-difluorophenyl)-pyridinato-N,C2](picolinato)Ir(III)(FIrpic) as thephosphorescent dopant, and1,3-bis[(4-tert-butylphenyl)-1,3,4-oxidiazolyl]phenylene(OXD-7) to enhance electron transporting. The addition of an oligo(ethylene oxide) at5-10wt%effectively lowers both the electron and hole injection barriers. The maximumcurrent efficiency obtained was26.5cd/A at an emission brightness of2500cd/m~2. Thehigh performance is due to (i) improved charge carrier injection at the interfaceresulting from specific interfacial interactions between PEO-DME and aluminum,(ii)improved charge carrier transporting ability and high electric field resulting fromPEO-DME doping.2. White polymer phosphorescent light-emitting diodes (WPLEDs) have been fabricated employing poly(ethylene glycol) dimethyl ether (PEG-DME) blended in thesingle active layer to enhance the emission efficiency. The devices have a simplesandwich architecture of ITO/PEDOT:PSS/emissive layer/CsF/Al. The emissive layeruses a blend of PVK, OXD-7, two or three phosphorescent dopants with complementarycolors. The addition of PEG-DME enhances electron injection, transport, and thebalance of densities of electrons and holes. The measured current efficiency in the frontviewing direction is17.5cd/A at1800cd/cm~2for the two complementary WPLEDs,and35.7cd/A at3000cd/m~2for the three complementary color WPLEDs. The currentefficiencies remain high even at brightness levels up to30,000cd/m~2. The high currentefficiency is ascribed to the improved electron injection ability from the metal cathode,the enhanced charge carrier transport ability and the enhanced red emitting intensity byblending with PEG-DME. Also the low roll-off of the current efficiency was due to thelower triplet-polaron annihilation and the electric field-induced triplet excitonquenching by increased charge carrier transport in unipolar device and movedrecombination zone. The improved charge carrier injection at the interface and theenhanced charge carrier transport were resulted from specific interfacial interactionsbetween PEG-DME and aluminum and higher electric field by blending withPEG-DME.3. We report the demonstration of blue, green, and red electrophosphorescentPLEDs fabricated on silver nanowire (AgNW) polymer composite electrode. Thecurrent efficiency of the ITO-free blue PLEDs falls in the narrow range of20.0-21.5cd/A in the brightness range of450-5500cd/m~2, and decreases slightly to18.5cd/A at10,000cd/m~2. The devices are20%-50%more efficient than control devices onITO/glass. The current efficiency of the green and red phosphorescent PLEDs was alsoenhanced by20-30%. The improved performance can be attributed to the highertransparency of the AgNW electrode than ITO/glass in the blue region, as well asphoton scattering on the surface of AgNWs in the composite electrode that enhanceslight out-coupling efficiency. The blue PLEDs can be repeatedly bent to1.5mm radiusconcave or convex with calculated strain in the emissive layer to be5%(tensile orcompressive).4. Phosphorescent WPLEDs have been fabricated employing AgNW-polymercomposite substrate to enhance the light out-coupling and emission efficiency. The current efficiency in the front viewing direction is20.3cd/A for the two complementarycolors devices and42.3cd/A at4000cd/cm~2for the three primary colors devices, theresults are35%and41%higher than that of a conventional WPLEDs used as acomparison, respectively. The high current efficiency is ascribed to the improved lightout-coupling and the waveguided light in ITO and glass substrate could extract in to airfrom light scattering of the AgNW network on the surface and embedded in the polymercomposite. The WPLEDs on the composite substrate are highly flexible and be bent to amaximum5%compressive strain with little decrease on device efficiency.更多还原