单重态-单重态湮灭诱导蓝光热延迟荧光器件老化机理的探究及应用

The lack of efficient and stable blue emitter is a bottle-neck for the industry of organic light-emitting diodes (OLEDs). Blue OLEDs employing thermally activated delayed fluorescence (TADF) have garnered much attention in these years because of the advantages of highly efficiency and low-cost in comparison to the traditional fluorescent and phosphorescent OLEDs. Additionally, blue TADF OLEDs can be more stable than the blue phosphorescent OLEDs, and provide hope for the real application. One the basis of the long-term study on the blue TADF materials, the photoionization induced by singlet-singlet annihilation (SSA) rather than triplet-triplet or triplet-polaron annihilation process is found to dominate the degradation rate of the blue TADF OLEDs. Accordingly, we deduce that the half-lifetime of blue devices can be significantly improved by increasing the fluorescence rate of the TADF emitter, as well as controlling the synergistic oxidation processes in the device and improving the anti-oxidation ability of the emitter. This project will provide new insight into the degradation mechanism of blue TADF OLEDs and a practicable route for the design of efficient and stable blue materials.

缺少高效稳定的蓝光材料是有机发光二极管（OLED）产业发展的瓶颈。新出现的蓝光热延迟荧光（TADF）材料不但具有高效低成本的优点，并且表现出比传统蓝光磷光材料更好的稳定性，有望最终获得实际应用。本项目基于长期对蓝光TADF材料与器件的研究，提出单重态-单重态激子湮灭（SSA）上转换诱导氧化是导致蓝光TADF材料在器件中分解的主因，而不是通常认为的基于三重激发态的湮灭机制。提出通过提高与SSA竞争的荧光辐射过程的速率提高蓝光TADF材料稳定性的新思路。在抑制发光材料在器件中光氧化的同时进一步抑制光氧化与电化学氧化的协同作用，并提高材料的抗氧化分解能力，通过综合手段达到大幅度提高蓝光TADF器件寿命的目的。本项目的实施有助于进一步揭示蓝光TADF器件的老化机理，为实现高效稳定的蓝光OLED指明出路。

蓝光有机发光二极管（OLED）在效率与寿命上落后于绿光和红光OLED，成为限制OLED产业发展的短板，深入研究蓝光OLED老化机制以及开发新型高性能蓝光材料十分重要。本项目系统研究了系列蓝、绿光热活化延迟荧光（TADF）分子的光电特性对器件老化速率的影响，发现器件寿命与发光分子的TADF寿命、电化学稳定性、前线轨道能级关系较小，而与单重态激子的0−0能密切相关，老化反应动力学可用阿伦尼乌斯方程预测。由此提出通过窄化光谱和提高辐射速率来提高蓝光OLED稳定性的新思路。本项目设计并合成出具有极高辐射速率（1.5×108 s-1）的蓝光TADF分子和具有极窄半峰宽（13 nm）的蓝、绿光TADF分子，报道了蓝光和绿光OLED的最高性能。