大扭曲弱给-受体结构的新型热激子荧光材料构筑及光电性能研究

The practical application of OLED solid-state lighting technology needs to solve the significant device efficiency roll-off caused by the accumulation of triplet states under high current density. At present, high efficiency phosphorescent and delayed fluorescence materials meet a bottleneck on achieving low efficiency roll-off device. However, hot exciton fluorescence materials with reverse intersystem crossing of high-lying triplet state can reduce the accumulation of triplet states, which are expected to achieve both high efficiency and low efficiency roll-off. A new strategy that is to design novel hot exciton fluorescent molecule with highly twisted moderate donor-acceptor（D-A）structure is developed. The highly twisted moderate D-A structure, which reduces the electronic coupling between D and A units, can realize iso-energetic charge-transfer singlet and triplet state, enhancement of reverse intersystem crossing rate, reduction of internal conversion rate from charge-transfer excited state to local excited state, and independent regulation of excited state properties of D or A units. Thus a more efficient reverse intersystem crossing channel between high-lying hot excitons can be obtained. The new series fluorescent molecules will be synthesized in this project. The photophysical properties of excited states will be adjusted by tailoring the D-A structure. The radiative decay of excitons during electrical injection process and the relationship between molecular structure, photophysical properties and electroluminescence mechanism will be investigated. The aim is to provide new material system and principle of molecular design to develop OLED with high efficiency and low efficiency roll-off, so the project has very important theoretical and practical application value.

OLED固态照明技术的实用化需解决高电流密度下三线态（T1）积累引起的显著器件效率滚降，目前高效率的磷光和延迟荧光材料在实现低效率滚降器件上遇到瓶颈，而利用高能量三线态反系间窜越的热激子荧光材料可降低T1积累，有望同时实现高效率和低效率滚降。本项目提出构筑大扭曲弱给-受体（D-A）新型热激子分子的新策略。通过大扭曲弱D-A结构降低D、A单元之间的电子耦合，可实现等能的电荷转移单线态和三线态、热激子反系间窜越速率的提高，电荷转移态向局域态内转换速率的降低以及D、A单元激发态特性的独立调控，从而获得更高效的热激子反系间窜越通道。本项目拟设计合成系列材料，通过裁剪D-A结构特征调控激发态光物理特性，研究电注入过程中激子的辐射衰减过程，建立分子结构-光物理特性-电致发光机制之间的关系，旨在为发展兼具高效率和低效率滚降的OLED提供新的材料体系和分子设计原则，因而具有十分重要的理论和实际应用价值。

照明用电超过了全球电力总消耗的20%以上，已经广泛应用于平板显示产品的有机电致发光二极管（OLEDs）技术具有色温可调节、轻薄面光源、柔性、低深蓝光成分的特点，可以和无机LEDs优势互补，在固态照明领域具有广泛的应用前景。相比于LEDs，OLEDs的功率效率仍然偏低，同时需要进一步降低OLEDs在高电流密度下的效率滚降。本项目设计合成联蒽类和非对称蒽类新型荧光分子，系统表征了相应荧光分子的化学结构和光物理性质；制备了相应的OLEDs器件，结合量化理论计算，结合建立分子结构-光物理特性-电致发光微观机制三者之间的关系；此外，综合考虑器件内量子效率和光提取，进一步探究极限器件功率效率的获得。基于本项目设计合成的新型荧光分子，实现了70%以上的高激子利用率和7.13%的外量子效率，在10000 cd m-2 高亮度下, 仍然保持7%以上的外量子效率，效率滚降仅为0.9%。基于本项目提出的超厚有机多异质结空穴传输层，制备了反型底发射白光OLEDs器件同时实现了高效的空穴注入和等离子体模式能量损失的抑制，实现了228.4 lm/W的峰值正向功率效率，同时，在1000 cd m-2的亮度下，实现了166.3 lm/W的正向功率效率，该结果经过第三方中科院苏州纳米研究所测试分析中心认证为165 lm/W，为目前国内外文献报道的最高值。上述研究成果为实现高效率、低效率滚降的OLEDs器件提供了重要的理论和技术基础。