有机电致磷光器件中高三重态能的新型聚合物类磷光主体材料研究

Due to easy fabrication and high efficiencies, the solution-processed phosphorescent organic light-emitting diodes (OLEDs) are established as most suitable for practical applications for flat-pannel displays and semiconductor lighting sources. In order to prevent concentration quenching and triplet-triplet annihilation, the phosphorescent OLEDs are typically fabricated by doping the phosphor into a certain host matrix. Most of the current phosphorescent host materials are organic small molecules. The exclusive polymeric host, polyvinylcarbazole (PVK), has been proved experimentally as excellent host only for red and green devices, rather than for blue ones, despite its high triplet energy of 3.0 eV. Therefore, it is highly desired to develop novel polymeric phosphorescent host materials that have high triplet energies of over 2.75 eV and be suitable for solution-processing. In present project, we propose to design and synthesize novel polymers with polyvinyl as main-chain and carbazole-containing moieties including N,N'-dicarbazolyl-3,5-benzene, N-phenylcarbazole, and 3,6-di(carbazole-9-yl)carbazole, as side-chain. The saturated polyvinyl is selected as main-chain and the side-chain is grafted to the main-chain by a non-conjugated way so that the conjugation extent within the side-chain is the exclusive factor to determine the overall triplet energy of the polymer. Then, some electron-transporting groups, such as pyridyl, triazolyl, diphenylphosphoryl and cyano are introduced into the side-chain to construct the bipolar polymeric host materials. Finally, the resultant polymers will be used as host materials to fabricate high-performance blue and white phosphorescent OLEDs by solution methods and dramatic performance improvements are expected. The target polymeric phosphorescent hosts have the following merits: (1) their solution-processible feature makes them be more suitable for large-scale industry application than traditional small molecule hosts, (2) their higher HOMO levels than PVK are favorable for more efficient hole injection in OLEDs, (3) some of the target polymers are possible to act as the universal hosts for the RGB primary color devices and white ones due to the high triplet energies, (4) in particular, the bipolar polymeric hosts are more capable of preventing efficiency roll-off in phosphorescent devices. In present project, for the first time we propose to develop polymeric derivatives of some traditional small molecular phosphorescent hosts, and put forward the strategy of bipolar polymeric hosts.

溶液加工的有机电致磷光器件因制备工艺简单、比荧光器件具有突出的效率优势而更有应用前景。磷光器件采用主体-客体掺杂体系，现有主体材料多数是有机小分子，仅有的聚合物主体材料PVK也只适合红光和绿光器件，并不是理想的蓝色磷光主体材料。本项目提出以聚乙烯为主链，以含咔唑的功能基团为侧链，设计、合成三重态能量大于2.75 eV、具有空穴传输能力的新型聚合物类蓝色磷光主体材料；并进一步在侧链引入电子传输基团，设计、合成双偶极的聚合物类磷光主体材料；利用溶液方法制备性能优良的蓝光、白光电致发光器件。预期目标材料具有适合溶液加工、比PVK具有更高的HOMO能级而更有利于空穴注入、部分聚合物还可能成为三基色和白色磷光器件的通用主体、尤其双偶极型聚合物更有利于解决磷光器件效率滚降问题等优点。项目亮点是首次将经典的小分子蓝色磷光主体材料衍生为聚合物类蓝色磷光主体材料，并提出双偶极的聚合物磷光主体材料这一新思路。

（1）首先按照项目计划开展工作，完成了预期的聚合物类磷光主体材料的制备和性质研究，并以这些聚合物为主体，利用溶液加工方法制备了蓝光和绿光磷光OLED器件，获得了理想的发光性能。所得聚合物均为未见报道的新材料，其中，共聚物类和均聚物类的双偶极聚合物都是首次报道；（2）其次，受以上聚合物主体材料发光性能的启发，研制了小分子类型的双偶极磷光主体材料，并提出“双n-型双偶极主体材料”的概念，发现这类材料区别于传统的双偶极分子，在拉低主体分子LUMO的同时不影响HOMO，从而在改善电子注入的同时不影响空穴注入，大幅改善载流子平衡能力，因此不仅有利于提高OLED器件发光效率，还有效减缓效率滚降；（3）同时，热致延迟荧光（TADF）材料已成为近年OLED领域的最大研究热门，根据这一最新趋势，对项目内容进行拓展，开发了新型的TADF发光材料和同样具有高效率优势的铱配合物类磷光材料，并制备了不同结构的单色光和白光OLED，都获得了优异的发光性能。该项目所得成果在Chemical Science、ACS Appl. Mater. Interfaces、J. Mater. Chem. C、Adv. Optical Mater.等高水平SCI期刊上发表学术论文19篇，另有发明专利、会议论文、硕士博士学位论文等成果10项，且后续研究成果将会在接下来的一两年内不断发表出来。总之，至今已圆满完成了项目任务，实现了项目目标。