蓝光磷光有机电致发光器件的激子调控及退化机理研究

Organic light-emitting devices (OLEDs) has emerged as a promising technology for displays and lightings with the advantages of high color quality, wide viewing angle and low power consumption. Being able to realizing a 100% of internal quantum efficiency in theory, phosphorescent OLEDs are being mostly used. However, due to the presence of exciton-polaron annihilation (EPA), phosphorescent OLEDs typically exhibit a poorer stability compared to their fluorescent counterpart. Among them, the blue phosphorescent OLEDs have the shortest lifetime. As a result, the current commercial portable devices such as mobile phone continue to use the less efficient fluorescent OLEDs as blue emitting, causing a limitation in performance improvement of OLED production. In this work, we conduct the studies on the degradation of blue phosphorescent OLEDs with regard to the EPA effects. In particular, blue phosphorescent dopants having stable molecular structures are proposed by revealing the roles of substitutes on the ligand of iridium complexes in their electro-chemical stabilities. The reasons behind the EPA effects due to the trapped charges are also differentiated by controlling the charge transport of emitting layers. Thus, optimized device structure with matched energy levels is built. Furthermore, we utilized thermally activated delayed fluorescent (TADF) materials as the host of blue phosphorescent emitters for exciton management in emitting layers. Due to the fast energy transfer between the TADF hosts and the blue emitters, the exciton density could be greatly reduced and guarantees a prolonged OLED lifetime. High-efficiency and long-lifetime blue phosphorescent OLEDs are therefore demonstrated based on optimized host/guest materials and device structure, which have the potential for realizing fully phosphorescent white OLEDs and paving the way of OLED production for wide applications.

有机电致发光器件（OLED）具有色彩好、视角宽和功耗低等突出优点，磷光发光材料可实现理论上100%的内量子效率，是制备高效率OLED的常用手段。然而，由于存在明显的激子-极化子湮灭效应，磷光OLED通常比荧光OLED具有更短的工作寿命，其中尤以蓝光磷光器件的寿命最短。尽管OLED目前在市场上已实现广泛的商业应用，但其所采用的蓝光发光体仍是低效率的荧光材料，从而限制了产品性能的提升。本项目拟采用不同分子结构的蓝光客体材料及不同电学传输性能的主体材料，分别研究配体取代基和极化子类型对蓝光磷光器件退化的影响，以确定合适的蓝光客体材料，构建能级匹配的器件结构，并采用热激活延迟荧光材料做主体，通过提高激子能量转移速率，改善蓝光磷光OLED的器件寿命。在此基础上，本项目旨在制备出具有高效率且长寿命的蓝光磷光器件，有望形成光色稳定的全磷光白光OLED，进一步提高OLED产品性能，并促进其商品化应用进程。

有机电致发光器件（OLED）在当今电子信息领域具有非常重要作用，然而其较低工作寿命仍是限制其发展的关键瓶颈之一，关于其老化机制仍存在争议。本项目通过器件结构设计，确定了导致OLED老化的关键复合界面，并利用混合连接层合理调控该复合界面处激子分布，从而有效提高了蓝光OLED工作寿命。更重要地，我们发现真空腔体杂质是引起OLED初始阶段快速衰退的主要外部原因之一，而蒸镀仪机械泵的返油蒸汽或是腔体杂质的主要来源，结合吸附阱和冷阱装置，成功抑制了返油蒸汽对OLED寿命的影响，从而为构建长寿命OLED制备了理想环境。另外，钙钛矿材料由于其优异的光电性能，在光电转化领域具有重要应用，但其环境敏感性使其具有较低器件稳定性。为此，我们设计了四甲基铵修饰苝衍生物、氨水修饰氧化石墨烯、氨水修饰PEDOT:PSS、咪唑修饰PCBM等系列电荷传输层，从增加疏水性和构建离子迁移陷阱的角度，有效提高了钙钛矿器件稳定性。通过咪唑或钐离子掺杂钙钛矿，我们同时调控了钙钛矿晶体生长和结构形貌，结合配位作用，掺杂剂还可起到钝化缺陷作用，最终导致钙钛矿器件在空气和加热条件都具有较好稳定性。综上，本项目深入研究了OLED和钙钛矿退化机理和稳定性改进方法，这些结果从器件结构和操作工艺上两方面都可为制备高效率、长寿命的器件提供指导帮助，通过优化寿命，进一步促进OLED和钙钛矿器件的产业化应用。