【作者】 吴清洋；

【导师】 赵毅；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2013， 博士

【摘要】 在全球能源短缺问题日益突出的背景下，有机电致发光器件(OLED)因其材料来源广泛、性能高、功耗低、色彩丰富、可实现大面积柔性显示、绿色环保等诸多优点，而深受学术界和产业界的广泛关注，被誉为二十一世纪最具发展前景的高科技领域之一。OLED历经二十多年来的迅速发展，已经逐渐从实验室研发阶段走向了产业化生产阶段。为了满足下一代平板显示及固态照明市场的应用要求，有机电致白光器件的综合性能还需要进一步提高。目前，白光有机电致发光器件的性能，如效率、寿命等已基本达到了商业化标准，但在实际应用中，无论是显示领域还是照明领域，还要求有机白光器件具有较好的色稳定性。然而，在器件的制备过程中，我们发现大部分的白光器件，无论采用单发光层结构还是多发光层结构，随着驱动电压或电流的增大，均存在色漂移问题。因此，本论文将以结构简单的互补色白光器件为研究基础，采用单发光层和多发光层这两种常用白光器件结构，从器件物理机制角度出发，研究制备高效率、色稳定的白光有机电致发光器件。论文主要内容包括以下几个方面：1、我们分析了引起白光器件色漂移的几个影响因素，并给出提高器件色稳定性的具体方法。引起白光器件色漂移的主要因素包括：载流子的捕获、激子湮灭以及复合区漂移。根据这些影响因素，我们提出具体解决方案。即：（1）合理利用能量转移机制，限制载流子捕获机制；当器件中不可避免的存在载流子捕获机制时，可利用降低染料掺杂浓度的方法来限制载流子捕获机制对光谱的影响；（2）利用增大激子复合区域、平衡载流子的注入与传输及减少有机层界面势垒等方法降低因激子湮灭引起的光色的改变；（3）选用载流子迁移率不依赖于电场变化或受电场影响较小的材料，来稳定激子复合区域，提高器件的色稳定性；（4）通过中间界面层对载流子、激子进行调控，使不同染料激子发射比例不随电压的变化而变化。同时，由于红光或黄光是合成白光的重要组成部分，而窄带隙的红、黄光普遍存在载流子捕获机制，我们通过具体实验更清晰地分析了在白光器件中，利用限制载流子捕获的方法可以稳定光谱。2、对于单发光层结构的互补色白光器件，我们选用PT系列专利材料分别制备了多掺杂结构和非掺杂结构的互补色全荧光白色有机电致发光器件。采用这两种方法制备的白光器件，电流效率均达到了11cd/A以上。且两器件在较宽的亮度范围内具有较好的色稳定性。我们分析其色稳定的原因为：（1）在单发光层染料共掺的多掺杂器件中，一般光谱的漂移主要是来自黄光或红光染料的浓度淬灭效应和载流子的陷阱作用，而在我们所制备的主客体染料共掺的全荧光白光器件中，由于黄光PT-01的掺杂浓度仅为0.5wt.%，在该器件中基本不存在由于浓度淬灭和载流子捕获机制引起的光谱的漂移；(2)在非掺杂器件中，由于染料是以薄层结构出现，必须考虑薄层的陷阱作用对器件色稳定性的影响。而在我们制备的非掺杂器件中，染料采用了超薄层结构，经分析器件并没有明显的载流子陷阱作用，这是非掺杂白光器件色稳定的原因之一；其次是由于激子复合区几乎不随电压的变化而改变，我们分析原因可能是由于PT-05这种荧光母体材料，其空穴、电子的迁移率受电场的影响较小。因此，非掺杂器件具有较好的色稳定性。在非掺杂器件中，我们通过分析单线态激子的分布及优化染料薄层间的母体厚度，将客体染料蒸镀在发光层适当位置处，得到了高效色稳定的WOLED。其效率可达多掺杂器件的水平，同时相对于多掺杂器件，非掺杂器件具有较高的可重复性和较低的制备成本，使其更适合产业化的批量生产。3、对于多发光层的互补色白光器件，我们首先研究了黄、蓝发光层间的界面层结构对器件电学特性和光学特性的影响。发现界面层Ir(ppz)3可以有效地调节载流子和激子的分布，使得在不同电压下，黄光、蓝光两发光层中的激子辐射复合发光比例基本保持不变，达到了稳定光谱的作用。为了进一步制备高效率、色稳定的白光器件，我们将蓝光层（DBFDPOPhCz：10wt.%FIrpic）与黄光层（CBP：6wt.%PO-01）结合，通过优化黄光层及界面层Ir(ppz)3的厚度，可以较容易地调节黄、蓝光的发光比例并稳定光谱。当黄光层的厚度为3nm，界面层Ir(ppz)3的厚度为1nm时，器件的最大电流效率及功率效率分别可达42.4cd/A和47.6lm/W。由于器件中采用MoOx及m-MTDATA：MoOx的结构，可有效的降低欧姆损失，使器件在较低的电压（3.5V）下,亮度可达1056cd/m2。当黄光层的厚度为5nm，界面层Ir(ppz)3的厚度为2nm时，器件在亮度范围为100-10000cd/m2时，色坐标仅由(0.333,0.436)变化到(0.330,0.434)。4、为了简化器件结构、降低成本，我们制备了单一母体多发光层结构的高效率、色稳定的全磷光互补色白光有机电致发光器件。由于宽带隙的母体材料不适合做红/黄染料的母体，为了解决这一问题，我们在mCP: PO-01的黄光层中掺入了一定浓度的FIrpic，发现黄光PO-01的发射效率得到了很大的提升。其主要原因是由于Firpic的引入，使得发光层中的三线态激子能量有效的通过FIrpic传递给PO-01，从而使得PO-01的发射效率增强。同时，由于FIrpic的引入，使得PO-01中大部分的激子发光来源于能量转移，仅有很少一部分是来源于PO-01的直接捕获载流子形成激子后辐射复合发光。因此，器件具有较稳定的白光发射。为了检验这一器件内部工作机理是否适用于其他宽带隙的母体材料，我们选用适合做FIrpic母体的TCTA做单一母体材料。经验证，在TCTA做母体时这种FIrpic向PO-01的能量转移依然存在。且由于母体材料及空穴传输层材料均为TCTA，减少了有机层间界面势垒对载流子传输性能的影响，有助于器件性能的提高。以TCTA做单一母体的多发光层结构器件，其最大电流效率，功率效率及外量子效率在电流密度为1mA/cm2时达到47.4cd/A，41.0lm/W，16.1%；在3.9V时，器件的亮度可达1000cd/cm2；亮度在67-5094cd/cm2时，色坐标仅从（0.401,0.473）变化到（0.404,0.474）。更多还原

【Abstract】 In the background of the global energy shortage, organic light-emitting diodes (OLEDs) hasbeen recognized as the most promising high-tech field in21th century because of their excellentproperties, such as wide material sources, high efficiency, low power consumption, rich colors,flexible display in large area and environmental friendliness etc. Over the rapid development inlast two decades, the activities on OLEDs turn to focus on the development of the commercialproducts, derived from the monotonously fundamental research. In order to satisfy therequirements of next generation of flat panel display and solid-state lighting, much more effortshould be made on the further improvements of OLEDs’ comprehensive performance.Currently, the performance of the white organic light-emitting diodes (WOLEDs), such asefficiency and lifetime has basically reached the commercial standards. In practical applications,both in the fields of lighting and display, a superior stability of WOLEDs is also required.However, in the process of fabricating devices, we found that most WOLEDs have the problemof color shift, regardless of a single emitting layer or multi emitting layer is applied. The varietyof the spectrum is the main factor of the color shift. In this paper, some mechanisms of theinfluences of color stability are revealed and WOLEDs based on complementary colors withhigh efficiency and color stability are fabricated via the structure of a single emitting layer ormulti emitting layer. The main contents involved in this dissertation are listed as follows.1. We firstly analyzed the influence of color shift, e.g., carrier trapping, exciton quenching andexciton recombination zone alternation. After that, some methods are put forward to improvethe color stability, such as (1) Rational utilizing of energy transfer mechanism, and limitingcarrier trapping mechanism. Low dopant concentration if there exist carrier trapping.(2)Employ the methods such as extending recombination zone, balancing the carrier injection andtransport, or reducing interface barrier potential of organic layer to decrease the color shiftcaused by exciton annihilation.(3) Select organic materials with carrier mobility independentelectric field to stable exciton recombination zone.(4) Regulate carriers and exciton through theinterface layer to balance various dye excitons. Red and yellow color are the basic colors of WOLEDs, whereas carriers trapping mechanism widely exists in red and yellow color withnarrow band gap. So we clearly analyzed that limit carriers trapping mechanism can stablizespectrum in WOLEDs through specific experiments.2. Highly efficient all fluorescent single emitting layer WOLEDs have been fabricated by themethod of co-doping and non-doping. WOLEDs fabricated in these two methods both have acurrent efficiency (CE) over11cd/A and superior color stability over a wide range ofluminance. The main reasons are as follows:(1) In co-doping system, the shift ofelectroluminescent (EL) spectra often occurs due to concentration quenching and carriertrapping of yellow or red dye. While in our WOLED based on the method of co-doping, theconcentration quenching and carrier trapping are almost non-exist because of the lowdoping concentration of PT-01(~0.5wt.%).(2) In non-doping system, the reason of colorstability not only due to the emission of ultrathin PT-01and PT-86from energy transfer notcarrier trapping, but also due to the carrier mobility of PT-05independent of electric field.From the analyses of the singlet exciton distribution and the influences of the thickness of thehost layer, PT-86and PT-01are evaporated at the proper location in the emitting layer andgetting a high efficiency and stable all fluorescent WOLEDs. The devices based on the methodof non-doping not only have similar performance as the co-doping one, but also have higherrepeatability, which makes them appropriate for a mass-production process.3. For the WOLEDs with multi emitting layer, the charge carriers and exciton were regulated byinserting the interlayer Ir(ppz)3between the two emissive zones based on two complementaryblue (DBFDPOPhCz:Firpic) and yellow (CBP:(Fbi)2Ir(acac) or PO-01) emitters. Theefficiencies and spectra of WOLEDs can be easily tuned by the thickness of the interlayer andthe yellow-EML (Y-EML). The device with1nm thick interlayer and3nm thick yellow emittinglayer obtains very high efficiencies of42.4cd/A and47.6lm/W and a luminance of1056cd/m2was realized at a low voltage of3.5V. In addition, another device with2nm thick interlayer and5nm thick Y-EML exhibited nearly voltage-independent EL spectra. Commission Internationalde L’Eclairage (CIE) coordinates of this device only changes from (0.333,0.436) at a luminanceof100cd/m2to (0.330,0.434) at that of10000cd/m2, nearly independent of the driving voltage.4. In order to simplify the device structure and reduce the production costs, high efficiency andcolor stability all phosphorescent WOLEDs were fabricated by the single host with multi emitting layer. External quantum efficiency (EQE) of the PO-01based yellow OLED issignificantly increased by co-doping FIrpic and PO-01into the common host of mCP. Detailedinvestigation indicates the enhancement is ascribed to effective triplet exciton gathering byFIrpic, then followed to PO-01by efficient energy transfer. A noticeable EQE enhancement isrealized in the WOLED according to this principle. At the same time, the spectra of WOLEDsare rather stability due to the emission of PO-01mostly from energy transfer not carrier trapping.This work makes it easier for a single host WOLED to simultaneously harvest high efficiencyand color stability. In order to test this mechanism whether suitable for other broadband gaphosts, we choose TCTA as host and find that the energy transfer from FIrpic to PO-01also exsit.The device with TCTA as host and hole transport layer shows high efficiency and color stability.A maximum EQE, PE and CE of16.1%,41.0lm/W and47.4cd/A at1mA/cm2, and a luminanceof1000cd/m2was realized at a low voltage of3.9V. In addition, The CIE coordinates only showa slightly shift from (0.401,0.473) to (0.404,0.474) as the luminance varied from67cd/m2to5094cd/m2.更多还原