【作者】 林楹；

【导师】 陈彧；

【作者基本信息】 华东理工大学 ， 先进材料与制备技术， 2011， 博士

【摘要】 新型有机及高分子光电材料的制备与器件设计是目前国际上一个十分活跃的领域。与液晶平面显示器相比,有机和高分子电致发光平面显示器(OLED和PLED)具有主动发光、无角度依赖性、对比度好、轻、薄、能耗低等显著特点,具有广阔的应用前景。红、绿、蓝三原色是实现有效全色显示的必备条件。与红光和绿光材料相比,蓝光材料的效率、稳定性和色纯度都与前两者相去甚远。开发好的蓝光材料不仅可以作为OLED或PLED中的发光层,还可作为主体来掺杂制备有效的绿光和白光光源。在蓝光材料中,基于芴的齐聚物和高分子拥有良好的热稳定性,高荧光量子效率和优异的电致发光特性,但其存在电荷注入与传输困难、易发生聚集、C-9位易被氧化等缺点,这些缺点正是导致器件效率低、色纯度低、光谱稳定性差等的原因。为了解决这些问题,本论文的主要研究内容是向基于芴的小分子和高分子结构中引入大体积的推电子和拉电子基团来增强材料的电荷注入与传输能力、抑制聚集效应和芴单元C-9位的氧化,从而改善器件性能。第一章综述了基于芴的蓝光小分子和高分子的研究进展,主要针对含有电子给体、受体的齐聚芴和聚芴的材料设计、合成及电致发光性能,发现：既含空穴传输又含电子传输片段的材料比相应的只含电子给体或受体的材料性能更佳。第二章利用Knoevenagel缩聚反应合成了一个主链含氰基、芴、三苯胺的共轭高分子(CNF-TPA)n。光动力学测试结果表明该高分子内存在从三苯胺到氰基芴的超快、高效的光诱导电荷转移,在苯腈中电荷分离态的寿命长达90μs。(CNF’-TPA’+)。的电荷复合过程比电荷分离慢得多。为进一步明确三苯胺单元的推电子特性,利用单体Yu0的Mcmurry缩聚反应制备了一个基于三苯胺的高分子Yul。在氩气饱和的甲苯中,Yul的荧光衰减曲线呈现出单指数的衰减,寿命为7.12 ns。第三章设计合成了一系列含不同比例氰基苯基-螺芴和咔唑-三苯胺的蓝光高分子PSF、PCC-1、PCC-2、PCC-3、PCF。向高分子骨架中引入氰基苯基-螺芴单元提高了材料的热稳定性和荧光量子效率,通过改变具有推-拉电子能力的聚合单体的比例,可有效调控高分子的HOMO、LUMO能级。当器件结构为ITO/PEDOT:PSS/高分子：PBD/CsF/Ca/Al时,基十PCC-2的器件性能最好,起亮电压为3.1 V,最高亮度为6369cd/m2,最大电流效率和功率效率分别为1.97 cd/A、1.40 lm/W。鉴于第三章中使用的氰基苯基-螺芴单体具有良好的电子传输、聚集抑制效应,保持这个单体不变,改变与三咔唑-三苯胺之间的投料比来和烷基芴发生聚合反应,在第四章制备了一系列蓝光高分子PTC-1、PTC-2、PTC-3、PTCF。高分子骨架中的电子给体三咔唑-三苯胺的存在可提高材料的HOMO、LUMO能级。当器件结构为ITO/PEDOT:PSS/高分子PBD/CsF/Ca/Al时,基于PTC-2的器件性能最好,起亮电压低至3.0 V,最高亮度为7257 cd/m2,最大电流效率为1.76 cd/A,电致发光峰值位于460 nm。第五章利用Suzuki偶联反应制得了一个带有氰基苯基芴和三苯胺双极性侧链的全芴主链高分子PTHCF。该高分子在薄膜中的紫外-可见吸收光谱比溶液中测得的光谱稍稍蓝移。结构为ITO/PEDOT:PSS/PTHCF770%+PBD3o%/CsF/Ca/Al的电致发光器件在电压驱动下发出来自全芴主链的深蓝色的光。将双极性侧链引入高分子结构中可以阻止分子间相互作用,增强电荷的注入与传导,增加电荷在主链中形成激子的几率,从而强化了高分子骨架的发光。第六章研究了一系列一端为氰基苯基、另一端为咔唑基的齐聚芴。双极性端基的存在可有效调变齐聚芴的能级。当器件结构为ITO/PEDOT:PSS/齐聚芴/TPBi/LiF/Al时,基于齐聚物F4的OLED器件表现出最好的性能：起亮电压为4.1 V,最高亮度为2180cd/m2,最大电流效率为1.17 cd/A。当采用蒸镀法得到优化器件结构ITO/MoO3/NPB/CBP:F4(1:4)/TPBi/LiF/Al时,最高亮度达5135 cd/m2,最高电流效率为1.76 cd/A,CIE色坐标为(0.16,0.09)。除了氰基外,喹啉基也具有良好的拉电子特性,因而我们在第七章选用二苯基喹啉基作为电子受体,将其与三苯胺基分别接在芴单元C-9位上的作为拉电子和推电子侧基制备两种聚合单体,按1：1的比例将两种单体与烷基芴的硼酸酯进行Suzuki偶联反应制备了蓝光高分子PTHD,与不含三苯胺侧基的高分子PHD相比,PTHD拥有更高的HOMO能级和更高的最大亮度。第八章采用拉电子的二苯基嗯二唑、推电子的三苯胺作为高分子主链中的部分片段,在三苯胺上接有1个或3个咔唑单元,制备了基于芴的高分子POFPA和POFCPA并比较二者性能。无论在稀甲苯溶液还是在薄膜中,咔唑含量较多的高分子POFCPA都比POFPA拥有更短波长的吸收或发射带,还有较高的荧光量子效率。当器件结构为ITO/PEDOT:PSS/高分子/TPBi/LiF/Al时,POFCPA器件内部各层的LUMO能级呈阶梯式,有利于高效的电子传输路径的形成,它的最大电流效率(1.79 cd/A)和功率效率(0.87lm/W)分别高于POFPA的器件效率(1.60 cd/A,0.83 lm/W)。发光层经掺杂优化后,POFCPA器件最高亮度达13613 cd/m2,最高电流效率达到3.38 cd/A,CIE色坐标为(0.15,0.24)。第九章系统总结了第二章至第八章的主要研究结果。更多还原

【Abstract】 Since the earliest reports of organic/polymeric light-emitting diodes (OLEDs/PLEDs), fabricating ultrathin, full-color, free-angle and large-area displays have stimulated intensive research interest around the world. To realize full-color displays, high performance red, green, and blue light-emitting materials are required. In contrast to red and green emitters, only a few blue emitters showed application potential but much inferior performance in efficiency, stability and color purity. The highly efficient blue light-emitting materials can be used as not only emissive layer in OLEDs/PLEDs, but also host materials for efficient blue and white light source. Among the promising blue emitters, fluorene-based oligomers and polymers have displayed excellent thermal stabilities, fluorescent quantum yields, and electroluminescent behaviors. However, the fluorene-based electroluminescent blue materials usually exhibited inferior electroluminescence efficiency, poor color purity and spectral stability caused by weak charge injection and transport, aggregation/excimer formation, and/or the fluorenone of photooxidized fluorene. To address these problems, covalently incorporating bulky electron-donating and-withdrawing groups onto the polymer backbone is an effective way to enhance the charge injection/transport and suppress aggregation/excimer formation. In addition, if the bulky groups were attached on the C-9 position of fluorene unit, the photooxidization could be inhibited.This thesis was divided into nine parts, as follows:The progress of the fluorene-based blue light-emitting compounds and polymers was reviewed in Chapter 1. The key point of the review was paid to the design, synthesis, and electroluminescent performance of oligofluorenes and polyfluorenes with electron-donors and/or acceptors. From the literatures reviewed, it was concluded that the materials containing both electron-donating and electron-withdrawing segments could have better performance than those corresponding "hole-only" or "electron-only" materials.In Chapter 2, aπ-conjugated copolymer (CNF-TPA)n was synthesized by Knoevenagel polycondensation. Fast and efficient photoinduced electron transfer from triphenylamine (TPA) to cyanofluorene (CNF) produced the long-lived charge-separated state (90 s) in benzonitrile. The charge-recombination process of (CNF·-TPA·+)n was much slower than the charge-separation in polar benzonitrile. To further confirm the electron-donating property of TPA units, a new blue-emitting polymer poly[5-(diphenylamino)-1,3-phenylenevinylene] (Yul) was prepared via McMurry condensation reaction of YuO. In Ar-saturated toluene, the fluorescence decay profile of this blue-emitting polymer exhibited single exponential decay with lifetime of 7.12 ns.Chapter 3 described a series of blue-light-emitting copolymers PSF, PCC-1, PCC-2, PCC-3, and PCF composed of different ratios of cyanophenyl-spirobifluorenes and carbazole-triphenylamines. Incorporation of the rigid spirobifluorene units substituted with cyanophenyl groups into the polymer backbone improved not only the thermal stabilities but also the photoluminescence efficiencies. With the device configuration of ITO/PEDOT:PSS/polymers:PBD/CsF/Ca/Al, PCC-2 showed the best performance with the lowest turn-on voltage of 3.1 V, the highest luminance of 6369 cd/m2, the highest current efficiency of 1.97 cd/A, and the best power efficiency of 1.40 lm/W.Since cyanophenyl-spirobifluorene is an excellent monomer with electron-transporting capability, in Chapter 4, we use it to polymerize with the electron-donating tricarbazole-triphenylamine and 9,9-dihexylfluorene-2,7-bis(trimethyleneborate). By tuning the feed ratio, a series of blue-light-emitting copolymers PTC-1, PTC-2, PTC-3, and PTCF were prepared. It was found that increasing the content of the donors raised both the HOMO and LUMO energy levels. With the device configuration of ITO/PEDOT:PSS/polymers:PBD/CsF/Ca/Al, PTC-2 showed the best performance with the turn-on voltage of 3.0 V, maximum brightness of 7257 cd/m2, maximum current efficiency of 1.76 cd/A, and EL emission peak at 460 nm.In Chapter 5, a novel bipolar copolymer PTHCF with triphenyamine and cyanophenylfluorene side chains was synthesized for studying the polymer backbone emission. In contrast to the electronic absorption spectrum in dilute solution, the absorbance of PTHCF in thin film was slightly, blue-shifted. An electroluminescence (EL) device with configuration of ITO/PEDOT:PSS/PTHCF70%+PBD30%/CsF/Ca/Al exhibited a deep-blue emission as result of excitons formed by the charges migrating along the full-fluorene mainchain. The incorporation of the bipolar side chains into the polymer structure prevented the inter-molecular interaction of the fluorene moieties, improved charge injection/transport, increased the yield of exciton formation in main chain, and thereby enhanced the polymer backbone emission.Chapter 6 innovatively reported a series of oligofluorenes with ambipolar cyanophenyl and carbazole end groups. The existence of the bipolar end groups could effectively tune the energy levels of the oligofluorenes. By using the device configuration of ITO/PEDOT:PSS/oligofluorenes/TPBi/LiF/Al, F4 with four fluorene spacers displayed the best performance:the lowest turn-on voltage (4.1 V),the highest maximum luminance (2180 cd/m2) and maximal current efficiency (1.17 cd/A). The optimized device of ITO/MoO3/NPB/CBP:F4(1:4)/TPBi/LiF/Al by vapor deposition showed highest brightness of 5135 cd/m2, current efficiency of 1.76 cd/A, and CIE coordinates of (0.16,0.09).Quinoline was also one of the outstanding electron acceptors. In Chapter 7 we synthesized a blue light-emitting copolymer PTHD containing electron-rich triphenylamine and electron-poor diphenylquinoline side chains in the C-9 positions of fluorene units. In contrast to the reference polymer poly{[9,9-dihexylfluorene]-alt-[9,9-di(2,4-diphenylquinoline)fluorene]} (PHD), PTHD exhibited higher HOMO energy level and maximum brightness.Besides cyano group and quinoline, another excellent electron-transporting candidate was oxadiazole. Thus, Chapter 8 introduced two copolymers POFPA and POFCPA, in which diphenyloxadiazole and carbazole/tricarbazole-triphenylamine were chosen as charge transport segments. Either in dilute toluene solution or in the thin film, the polymer with higher content of carbazole possessed shorter absorption and photoluminescence, as well as much higher fluorescent quantum yield, in comparison with the other polymer. With the device configuration of ITO/PEDOT:PSS/polymer/TPBi/LiF/Al, efficient graded LUMO route for electron injection and transport was obtained in the POFCPA device, leading to higher maximum current efficiency (1.79 cd/A) and power efficiency (0.87 lm/W) than the POFPA device (1.60 cd/A,0.83 lm/W). The doped device based on POFCPA showed maximum luminance of 13613 cd/m2, highest current efficiency of 3.38 cd/A with the CIE coordinates of (0.15,0.24).In Chapter 9, the research results from Chapter 2 to Chapter 8 were summarized. Keywords:electroluminescence; blue light-emitting materials; fluorene; electron-withdrawing groups; electron donating groups更多还原