【作者】 邹建华；

【导师】 彭俊彪； 吴宏滨；

【作者基本信息】 华南理工大学 ， 材料物理与化学， 2010， 博士

【摘要】 有机发光二极管(OLEDs)可分为有机小分子发光二极管(OLED)和聚合物发光二极管(PLED),因为他们在显示、照明、背光等领域的诱人的应用前景,而成为全世界学术界和工业界瞩目的焦点。经过二十年的研究,有机发光材料及器件已经逐渐从实验室走向市场,开始进入应用化阶段。然而,目前所有商业化的产品都是以小分子材料通过真空蒸镀工艺实现的,设备投资大、成品率低、材料浪费严重、不易实现大面积等。而聚合物发光二极管(PLED)可以通过溶液加工工艺(喷墨打印、旋涂、提拉等)恰好可以弥补以上真空蒸镀工艺的不足,受到越来越多学术界和工业界的关注。在显示方面, PLED技术分两种,一种是无源矩阵型PLED(PM-PLED),一种是有源矩阵型PLED(AMPLED)。未来全球PLED产业发展的趋势是在发展小尺寸PM-PLED产品的基础之上,向大尺寸AM-PLED产品发展。而薄膜晶体管(TFT)是有源显示中必不可少的组成部分之一。相比无机TFT,有机薄膜晶体管(OTFT)在很多方面都具有一定的优势,如可选择的材料丰富;可用柔软塑料做衬底,实现柔性显示;易于制备大面积薄膜;成本低,易于加工(如旋涂,印刷,蒸发等多种手段);可以在较低温度下制备薄膜等,因此基于有机薄膜晶体管驱动的有机电致发光(OTFT-PLED)即“全有机”显示器件,引起越来越广泛的关注。因此本文前一章从最基本的PLED有源显示原型器件着手,结合聚合物发光二极管的优点,采用丝网印刷技术,探讨了OTFT驱动聚合物发光二极管(OTFT-PLED)的可行性。除此之外,照明,背光领域也是未来PLED技术即白光聚合物发光二极管(WPLED)发展的重要应用方向。不过,基于高分子材料的发光器件,其性能尤其是功率效率和流明效率等重要性能参数,与小分子器件相比较,还大大落后,如要获得实际应用发光性能还需要进一步提高。白光PLED的实现及发光性能的提高涉及到新材料的开发、材料体系的匹配选择、器件结构的优化设计、发光光谱的稳定性及电荷的注入等。本文的其他内容就是对这些问题进行系统深入的研究,以期获得高性能的白光聚合物发光器件。首先,我们通过将3种含铱配合物FIrpic(蓝光发射配合物),Ir(mppy)3(绿光发射配合物)和Ir(piq)(红光发射配合物)掺杂到PVK和OXD-7主体材料中,随着掺杂浓度的不同,实现了高效的聚合物白光器件,其中,三元掺杂器件9.9 lm W-1,相当于20 lm W-1的总功率效率,最大前向电流效率达到了24.3 cd A-1 (相当于总电流功率达到48 cd A-1),最大外量子效率达到了14.4%。接着,我们用基于天蓝色发射磷光配合物FIrpic(~470 nm)与发光峰值在560-570 nm的黄光发射材料组成基于互补色方案的高效白光发光器件,获得的白光器件的前向电流效率达到42.9 cd/A(对应的总电流效率可达80 cd/A),功率效率达到20 lm/W(对应的总功率效率可达40 lm/W)。这些器件最突出的优点是采用简单的单层器件结构并且仅用了溶液加工方式,换句话说,没有通过真空蒸镀方式蒸镀空穴阻挡或者电子传输层,确保了聚合物光电器件的低成本。上述基于磷光材料的聚合物白光发光二级管器件取得了较高的效率,但是磷光白光发光二极管的效率随电流增加快速衰减,同时,它们一般包含一个天蓝色磷光染料Firpic,由于蓝光材料颜色不纯,导致白光的颜色质量一般都不是很好。另外,它们一般采用高三线态能级的PVK作为主体,而PVK主体材料本身的材料缺陷,导致器件稳定性差。为了解决上述问题,我们利用新合成的高效、深蓝色、稳定性的聚芴类材料作为主体和蓝光发射材料,调控掺杂浓度获得各种颜色平衡发射,通过不完全能量转移,掺杂绿光P-PPV,红光材料MEH-PPV,制备了器件结构十分简单的单层白光发射器件,器件的电流效率达到14.0 cd A-1,功率效率达到7.6 lm W-1,显色指数达79。发光光谱在很宽的电流强度范围内、长时间点亮以及不同温度处理情况下表现出良好的稳定性。最后,白光器件效率的提高,载流子平衡是关键。在阴极修饰方面,我们利用聚合物的不同溶解性,研究了用旋涂方法制备双层高分子白光二极管(WPLED)。通过在阴极界面插入水溶性的聚电介质层修饰,明显改善电子注入,改善发光器件的电子和空穴载流子注入平衡,使白光器件最大电流效率提高到5.0 cd/A,通过阴极修饰,使双层器件效率提高了一倍。在阳极修饰方面,提出对阳极缓冲层材料聚(3,4-二氧乙基噻吩)/聚(对苯乙烯磺酸)(PEDOT:PSS)进行改性,可将电致磷光器件的最大电流效率,功率效率和外量子效率大幅度提高50-90%。基于绿光发射体Ir(mppy)3的电致磷光器件的最大电流效率达到85 cd A-1,功率效率达到50 lm W-1,外量子效率超过22%,处于国际同类器件的先进水平。新型的阳极缓冲层既保持了能够很好地抑制漏电流,获得高效率的特性,还将其较低的电导率提高1-2个数量级。而我们将此结果将进一步应用在白光器件上,相信能得到良好的效果。更多还原

【Abstract】 Organic light-emitting diodes (OLEDs) include organic small molecule light-emitting diode (OLED) and polymer light-emitting diode (PLED), they have drawn great attentions by academic and industrial sectors because of the attractive prospect of application in the display, lighting, backlighting and other fields. After two decades of research, organic light-emitting materials and devices have come from the laboratory to the market, and begun to enter industrialization. However, all the commercial products are currently based on small molecule material by vacuum deposition process, which requires expensive equipment, and complicated the production of full color displays using traditional masking technologies. PLED base on solution-processes such as spin-coating, ink jet, and screen printing can overcome the disadvantagies and access full color and larger size display sizes at much lower costs, which attract more and more research specialist staff.In the area of display, the PLED technology include passive matrix PLED (PM-PLED) and active matrix PLED (AMPLED). In the future, at the PLED industrial development, the global trend is based on development of small-size PM-PLED and then to large-sized AM-PLED product. And the thin-film transistor (TFT) is essential in an active matrix display. Compared with inorganic TFT, organic thin film transistor (OTFT) have certain advantage in many respects, such as the diversity of material, to achieve flexible display on the flexisble substrate, easy to realize large area, and low-cost, simply processing ( such as spin coating, printing, evaporation and other means) and low temperature, so based on organic thin-film transistor driven organic electroluminescent (OTFT-PLED), namely so called "all organic display”, pay more widespread attention. Therefore, in the previous chapter of this article, we proceed from prototype device of active matrix PLED, combined with the advantages of polymer light-emitting diodes and using screen-printing technology, investigated the technology and related physical problems for integrating organic thin-film transistor (OTFT) and polymer light-emitting diode (PLED).In addition, the white polymer light-emitting diodes (WPLED) as lighting and backlighting are important applications for PLED technology in the future. However, white emission PLEDs are less efficient with respect to power efficiency (PE) and luminous efficiency(LE), when compared with devices fabricated using vacuumdeposition technologies, and are still far away from practical applications for solid-state lighting. In order to improve the performance of white PLED, which related to the development of new materials, matching options of material systems, optimization of device structure to balance charge injection. The other part content of this article focuses on these issues and in order to obtain high-performance white polymer light-emitting device.We report a single emission layer white PLEDs by triple doping of RGB iridium metal complexes or double doping of red and blue Ir complexes with appropriate ratio into poly(N-vinylcarbazole) (PVK) host in presence of electron transport material 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl] phenylene (OXD-7). After proper heat treatment, the triple-doped polymer WOLEDs have a peak PE of 9.53 lm W-1 (Device E) /9.95 lm W-1 (Device F) for forward viewing (corresponding to a total PE of 19/20 lm W-1) at 7.2/6.9 V, and a peak LE of 24.3 cd A-1 for forward viewing (corresponding to a total peak LE of 48 cd A-1), at 20.8 mA cm-2. Then, we use the sky-blue phosphor-based complexes emission FIrpic (~ 470 nm) and the yellow light emitting material with EL peak at 560-570 nm to compose complementary colors to obtain white light-emitting devices, and the current efficiency of the device achieved 42.9 cd / A for forward viewing (corresponding to the total current efficiency up to 80 cd / A), the power efficiency of 20 lm / W (corresponding to the total power efficiency up to 40 lm / W).An outstanding advantage of these polymer WOLEDs lies in very simple single emissive layer structure, only solution-processed technology is involved, that is no additive hole-blocking or electron transport layer was incorporated through extra vacuum-deposited technology, which ensures fully exploiting the potential of low-cost fabrication of polymer optoelectronic device.In most of the reported efficient WPLEDs, triplet emitter with sky-blue emission was used as a key component to fabricate phosphor-based device despite their relative poor color quality. Besides, unstable PVK was used as host material in these devices, which would degrade significantly during operation, thus limit their practiacal applications. In order to overcome this problem and obtain efficient WPLEDs with high color quality and long-term stability, an alternative approach is to use efficient deep-blue polymer as both host material and blue emitter to fabricate multiple dopants all-polymer WPLEDs. The polymers used here include, a newly synthesized efficient deep-blue emitting polyfluorene derivative named poly[(9,9-bis(4-(2-ethylhexyloxy)phenyl)fluorene)-co-(3,7-dibenziothiene-S,S-dioxide10)] (PPF-3,7SO10), a green light-emitting poly [2-(4-(3’,7’-dimethyloctyloxy) -phenyl) -p- phenylenevinylene] (P-PPV) and an orange-red light-emitting 2-methoxy-5- (2’-ethyl-hexyloxy)-1, 4-phenylenevinylene (MEH-PPV), respectively. Optimized device shows a peak luminous efficiency of 14.0 cd A?1 and a peak power efficiency of 7.6 lm W-1, with a CIE of (0.33, 0.35) at a current density of 10 mA cm-2.Finally, the balanced carrier is key to improve the efficiency of white device. For the modification of cathode, white polymer light-emitting diodes (WPLEDs) with bilayer structure were fabricated by spin coating method using different solubility of polymers. By inserting a layer of water-soluble electronic transporting material of PFN approaching to the cathode, the maximal luminance efficiencies of 5.3 cd/A is achieved with CIE coordinates of (0.34, 0.36). By modified the cathode, the LE of WPLED was enhanced by 100 %. And for modification of anode, influence of three types of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS), whose nominal conductivity varied in 5 orders in magnitude (~1 S cm-1, ~ 10?3 S cm-1, and 10?5 S cm-1, respectively), on the device performance of polymer-based phosphorescent organic light emitting diodes (PhOLEDs) were investigated. It was found that PEDOT:PSS (Baytron 8000) with the lowest conductivity resulted in superior device performance, in term of peak luminous efficiency (LE) and peak external quantum efficiency (EQE). When compared to that of devices with the routine PEDOT: PSS (Baytron P 4083) and the one with the highest conductivity (Baytron P), the device performance with PEDOT:PSS (Baytron 8000) as anode buffer layer was enhanced by 59 % and 91 %, respectively, in term of peak LE and peak EQE in PhOLEDs. It was found that improved manipulation of leakage current at small bias region, and more balanced charge carrier are responsible for the enhancement. Furthermore, novel glycerol modified PEDOT 8000 anode buffer layer whose conductivity increase as many as two orders of magnitude was developed to enhance overall device performance. These discoveries can potentially enable further improvement of the present efficiency of polymer light-emitting devices, indicating that polymer light-emitting devices (PLEDs) can achieve comparable device performance with vacuum-deposited small molecular devices.更多还原