【作者】 黄斌；

【导师】 孙岳明； 蒋伟；

【作者基本信息】 东南大学 ， 材料物理与化学， 2015， 博士

【摘要】 有机电致发光器件(OLEDs)是有机光电子领域的研究热点,在平板显示和固体照明领域有着广阔的应用前景。与传统的电致荧光器件(FOLEDs)相比,电致磷光器件(PhOLEDs)由于能充分利用器件中的单线态和三线态激子,器件的理论最大内量子效率达到100%。磷光主体材料的选择是影响PhOLEDs性能的关键因素。其中,双极磷光主体材料由于既能传输空穴又能传输电子,可以提高器件性能和简化器件结构,引起人们更多的关注。当双极磷光主体材料分子的单线态-三线态能级差(△EST)足够小(<0.5 eV)时,在分子自身的热运动作用下,分子内易发生反向隙间窜越(RISC),这类分子也就是所谓的热激活延迟荧光(TADF)材料。在TADF器件中,三线态激子可经过TADF材料分子内的反向隙间窜越,转变成单线态激子发光,也能充分利用100%的激子。这样,就能够用TADF材料代替有机贵金属配合物,从而大大降低有机电致发光器件的成本。因此,开发新型双极磷光主体材料及TADF材料具有重要意义。本文设计和合成了系列基于空穴传输基团咔唑、三苯胺和电子传输基团苯腈、2,4,6-三苯基-1,3,5-三嗪、二苯砜和二苯甲酮的双极磷光主体材料及TADF材料。研究了这些材料的构效关系,包括热稳定性、光物理性质、电化学性质及器件性能。主要研究内容如下：(1)合成了一种基于电子给体基团N-苯基咔唑和电子受体基团2,4,6-三苯基-1,3,5-三嗪基团的双极磷光主体材料TPCPZ,研究了其光物理、电化学和热稳定性,并湿法制备高效率的单层小分子绿光PhOLEDs。该单层绿光PhOLEDs的起亮电压为3.5 V,最大亮度达到18000 cd m-2,电流效率达到20.8 cdA-1。(2)通过电子给体基团3,6-二(叔丁基)咔唑分别在电子受体基团二苯砜的3-,3’,4-,4’-位发生取代,合成了一系列咔唑/砜衍生物,它们均可用作TADF材料。系统研究了分子结构对这些材料的光物理、电化学和热稳定性的影响。通过改变电子给体的数目和在电子受体上的取代位置,使五种化合物的△EsT从0.39 eV降到0.22 eV。(3)合成了一系列基于N-苯基咔唑/三苯胺取代苯腈/2,4,6-三苯基-1,3,5-三嗪的衍生物。系统研究了分子结构对它们的光物理、电化学和热稳定性的影响。通过控制电子给体和电子受体的连接方式,四种化合物的AEST从0.75 eV降到0.18 eV。其中,三苯胺/N-苯基咔唑取代2,4,6-三苯基-1,3,5-三嗪的衍生物的AEST仅为0.18 eV和0.37 eV,可作为TADF材料。(4)合成了以N-苯基咔唑基团作为空穴传输基团,通过在咔唑环的3,6-位或2,7-位分别引入电子传输基团二苯砜基,得到了两种新型双极主体材料(36DDPSPC和27DDPSPC),并系统研究了它们的光物理、电化学和热稳定性。36DDPSPC和27DDPSPC具有较好的热稳定性,有较高的三线态能级,分别为3.00和2.86 eV,可以用作蓝色磷光双极主体材料。(5)合成了基于电子给体基团3,6-二(叔丁基)咔唑、3,6-二(叔丁基)三咔唑和电子受体基团二苯甲酮的TADF材料t-BuCz2BP和t-BuTCz2BP,系统研究了它们的光物理、电化学和热稳定性。t-BuTCz2BP的三线态能级为2.59 eV, △EST仅为0.05 eV,基于t-BuTCz2BP湿法制得了不含贵金属的非掺杂高效TADF绿光OLEDs。该器件的起亮电压为4.5 V,最大亮度达到4200 cd m-2,电流效率达到9.2 cdA-1。更多还原

【Abstract】 Organic light emitting diodes (OLEDs) have gained tremendous attention due to their significant potential applications in flat-panel displays and solid state lighting. In contrast to traditional fluorescent OLEDs, the singlet exitions and trplet exitions can be utilized in PhOLEDs, leading to the limited internal quantum efficiency 100%. The choice of host materials for high-efficiency PhOLEDs is very important. Bipolar phosphorescent host materials have attracted major interest because not only they can transport holes and electrons, but also they are potent to improve the efficiency and simplify the structures of PhOLEDs. In principle, when the energy gap between singlet and triplet (△EST) of bipolar materials is small(<0.5 eV), the endothermic reverse intersystem crossing(RISC) can be overcome by the thermal motions of the molecule atoms. These materials are thermally activated delayed fluorescence (TADF) materials. As a result, the triplet excitons are transformed to singlet excitons via RISC in TADF materials, both triplet and singlet excitons can be harvested. On the basis of this concept, TADF materials can be used as substitutes of phosphors based on rare metals for high-efficiency and low-cost OLEDs. It is very important for us to develop novel bipolar phosphorescent host materials and TADF materials.In this thesis, we have designed and synthesized a series of novel bipolar materials based on electron-transporting groups such as 2,4,6-trisphenyl-l,3,5-triazine, diphenyl sulfone, benzonitrile, benzophenone and hole-transporting groups such as triphenylamine, carbazole. The structure-property relationships including their thermal, photophysical, electrochemical and electroluminescent properties have been systematically investigated. The main contents are described as follows:(1) A novel N-phenyl carbazole substituted 2,4,6-trisphenyl-1,3,5-triazine host material (TPCPZ) for solution processed green phosphorescent organic light-emitting devices (PhOLEDs) has been synthesized. The optical, electrochemical and thermal properties of TPCPZ have been characterized. The solution-processed single-layer device using TPCPZ as the host for fac-tris[2-(4-phenylpyridine)]iridium (Ir(ppy)3) exhibits a low turn-on voltage of 3.5 V, a maximum current efficiency of 20.8 cd A"1 and a maximum luminance of 18000 cd m-2.(2) A series of bipolar materials for TADF based on 3,6-di-tertbutyl-carbazole and diphenyl sulfone, have been synthesized. In these materials, the 3,6-di-tertbutyl-carbazole group is linked at the 3-,4-position or 3’-,4’-position of diphenyl sulfone. The effects of the conjugation connectivity on the electronic, photophysical and electrochemical properties of these materials have been systematically investigated. The △EST in these materials is tuned from 0.39 eV to 0.22 eV by manipulation of conjugation of the electron donor units.(3) A series of ambipolar compounds using triphenylamine/N-phenyl carbazole as electron donors and benzonitrile/2,4,6-trisphenyl-1,3,5-triazine as electron acceptors have been synthesized. The electronic, photophysical and electrochemical properties of these materials can be effectively tuned by manipulation the constitution of acceptor and donor units. The △EST in these materials is tuned from 0.75 eV to 0.18 eV by systematically changing the electron donor and acceptor units. Triphenylamine/N-phenyl carbazole substituted 2,4,6-trisphenyl-1,3,5-triazine exhibit small △EST (0.18 eV and 0.37 eV), and are potential for thermally activated delayed fluorescence materials.(4) A series of bipolar host materials (36DDPSPC and 27DDPSPC) based on N-phenyl carbazole and diphenyl sulfone for blue phosphorescent organic light-emitting devices (PhOLEDs) have been synthesized. Their optical, electrochemical and thermal properties have been characterized.36DDPSPC and 27DDPSPC exhibit high triplet energy of 3.00 eV and 2.86 eV, and can be used as blue phosphorescent host materials.(5) A series of benzophenone derivatives based on benzophenone and 3,6-ditert-butyl-carbazole/3,6-bis(3,6-ditert-butyl-carbazol-9-yl)-carbazole (t-BuCz2BP and t-BuTCz2BP) for TADF have been synthesized. The optical, electrochemical and thermal properties of t-BuCz2BP and t-BuTCz2BP have been characterized. In comparison with the reported benzophenone derivatives, t-BuCz2BP and t-BuTCz2BP exhibit better solubility and smaller △EST. t-BuTCz2BP exhibits a high Td(corresponding to 5% weight-loss)value of 489 ℃, a triplet energy of 2.59 eV, and a small △EST of 0.05 eV. The solution-processed non-metal green TADF OLED based on t-BuTCz2BP exhibits a low turn-on voltage of 4.5 V, a maximum current efficiency of 9.2 cd A"1 and a maximum luminance of 4200 cd m-2.更多还原