热激活延迟荧光材料在有机电致发光器件中的研究进展  

Research Progress on Thermal Activated Delayed Fluorescence Materials for Organic Light-emitting Diodes

作　　者：卢伶 张祥 赵青华[1] LU Ling;ZHANG Xiang;ZHAO Qinghua(The Key Laboratory for Functional Materials of Fujian Higher Education,College of Materials Science & Engineering,Huaqiao University,Xiamen 361021)

机构地区：[1]华侨大学材料科学与工程学院福建省高校功能材料重点实验室

出　　处：《材料导报》2019年第15期2589-2601,共13页Materials Reports

基　　金：国家自然科学基金(51202073);福建省自然科学基金面上项目(2016J01233);福建省石墨烯粉末及复合材料研究中心建设项目(2017H2001);华侨大学研究生科研创新基金资助项目~~

摘　　要：热激活延迟荧光(Thermally activated delayed fluorescence,TADF)材料的三重态激子能够反向系间窜越到单重态能级,发射延迟荧光,理论上内量子效率可以达到100%。与传统的磷光材料相比,一方面热激活延迟荧光材料避免了使用昂贵的重金属,成本较低,另一方面,使用更加稳定的荧光材料代替磷光材料,器件的效率和光谱稳定性均有所提高,因此热激活延迟荧光材料引起了人们的广泛关注,成为有机发光二极管(Organic light emitting diode,OLED)研究领域的热点方向。从分子设计的角度,不同类型的热激活延迟荧光材料已经被相继报道。小分子热激活延迟荧光材料设计要求选择合适的电子给体单元和受体单元,或者添加修饰基团来营造较大的空间位阻,以分离分子的HOMO和LUMO能级,减小其单重态和三重态能隙。同时为了提高荧光量子效率,可以通过增加小分子结构的刚性来削减分子内非辐射衰变。然而,小分子热激活延迟荧光材料通常作为掺杂剂被应用于荧光器件中,很难保证其不出现红移或蓝移情况,影响器件的色纯度。而树状和聚合物TADF材料的出现,可以适当解决这一难题。二者同属于高分子发光材料,都能够充分溶解于有机溶剂,可以通过溶液加工的工艺制作高效的非掺杂有机电致发光器件,克服了小分子只能真空蒸镀的不足。树状TADF材料因其较高的分子量、精确的分子结构、可调的能隙和颜色,已被广泛应用在有机光电器件中。树状化合物外围的树突,可以防止分子间相互作用引起的浓度猝灭和效率骤降。但是与核心发光分子共轭的树突结构会导致树状化合物的溶解度降低和发光颜色改变,所以非共轭结构是首选结构。此外,核心为双极性的树状化合物大多具有均衡的电子和空穴传输能力,内量子效率较高。聚合物因可溶液处理、具有柔性特点和可大面积、大规模生产而The triplet excitons of the thermally activated delayed fluorescence(TADF)materials can up-convert to the singlet level by the reverse intersystem crossing(RISC)process,emitting delayed fluorescence.TADF materials have attracted widespread attention,because they can reach 100%of theoretical internal quantum efficiency(IQE).Moreover,in contrast to phosphorescent materials,heavy metal-free TADF mate-rials are easier to realize the ultimate EL efficiency.On the base of the principle of molecular design,different types of TADF materials have been reported.The design of small molecule TADF materials requires to separate the HOMO and LUMO energy levels of the molecules,and result in reducing its singlet and triplet state energy gap,by selection of suitable electron donor and acceptor units,or the addition of modified groups to increase steric hindrance.Additionally,in order to improve the fluorescence quantum efficiency,the non-radiative decay needed to be reduced by increasing the rigidity of the small molecule structure.However,small-molecule TADF materials are usually used as dopants for fluorescent devices,and it is difficult to avoid appearing of red-shift or blue-shift of emission that affects color purity of devices.The dendritic and polymeric TADF emitters-macromolecular materials can be dissolved in organic solvents,and highly efficient non-doped organic electroluminescent devices can be fabricated by solution-processing,making up for the shortage of small molecules that can only be va-cuum evaporated.Dendritic TADF materials have been widely used in organic optoelectronic devices due to their high molecular weight,precise molecular structure,adjustable energy gap and color.The dendrites around the dendrimers can prevent concentration quenching and efficiency roll-off caused by intermolecular interactions.However,the dendritic structure conjugated to the core causes decreasing of solubility and changing of luminescent color,so a non-conjugated structure is preferred.In addition,most of bipolar dendritic cores

关 键 词：热激活延迟荧光 外量子效率 有机发光二极管 

分 类 号：O625.1[理学—有机化学] O6[理学—化学]