分子偶极矩取向调控蓝光OLED器件性能研究

The organic light emitting diodes (OLED) are expected to represent the next generation of flat-panel display and lighting technology for their features of surface lighting, super-thin flexible display, light, low cost and ease of integration, etc. However, the efficiency and stability of OLED are still low for now. Especially, the efficiency and stability of blue OLED needs to be improved more than that of red and green OLEDs for their wide band-gap. In this project, (1)the structure-activity relationship of the molecular orientation and the molecular structure will be researched by changing the electron-donating and electron-accepting of several series of blue emitting materials with thermally activated delayed fluorescence(TADF), such as DMAC-DPS, DMOC-DPS, Ac-RPM and so on, (2) angular-dependent polarization fluorescence spectra, nonlinear sum frequency spectroscopy, steady state and time resolved second harmonic generation technique will be used to study the relations between the molecular structure, host materials, device structure, fabrication conditions and the orientation of emitting molecular dipole moment, and to tune the emitting molecular dipole moment orientation, (3) the impacts of emitting molecular dipole moment orientation on the interface congestion and interface potential of charge, the arrangement of electrical energy level, the transportation of carriers of OLED will be investigated. We aim to make clear the impacts of emitting molecular dipole moment orientation on lighting performance of OLED, and to find the corresponding physical mechanism. The blue OLED with high efficiency would be obtained.

有机发光二极管（OLED）具有自主发光、色彩好、超薄、柔性可弯曲、成本低等优点，在信息显示和大面积照明等方面具有广阔的应用前景。但是其外量子效率较低、稳定性还有待于提高，特别是蓝光OLED，由于其较大的带隙，效率和稳定性较红绿光更需要提高和改善。本课题拟开展以下三个方面的研究：（1）改变DMAC-DPS、DMOC-DPS、Ac-RPM等3-4个系列具有热延迟荧光特性的蓝光OLED材料的供受电子基团,研究分子偶极矩取向与分子结构之间的构效关系；（2）采用角度依赖的偏振荧光、光学非线性和频、时间分辨的二次谐波产生光谱等技术和理论模拟来研究分子结构、主客体掺杂、制备条件、外加电场诱导、偏振紫外光照射等对分子偶极矩取向的影响与调控方法；（3）探索分子偶极矩取向对于OLED器件中界面的电荷聚集特性、界面势、电子能级排列、载流子传输和效率的影响规律和物理机制。制备出具有高外量子效率的蓝光OLED器件。

该项目通过优化分子偶极矩取向提高了蓝光OLED器件的性能。研究内容包括：理论上推导模拟角度依赖偏振荧光光谱与分子跃迁偶极矩取向角之间的关系；实验上，采用不同的制备方法、制备条件及后处理方式对载流子传输层、发光层等不同功能层中的分子偶极矩取向进行优化，利用角度依赖偏振荧光光谱、二次谐波产生等方法，对薄膜中的分子偶极矩取向进行分析，从而提高了OLED器件的性能，制备出具有较高外量子效率的蓝光OLED器件，并对其微观机理进行了分析。（1）研究了真空热蒸镀时基板温度、沉积速率、退火温度对发光层及载流子传输层分子取向的影响。当基板温度为60 °C 时，OLED 器件的最大亮度和外量子效率（EQE）分别达到 74320 cd/m2 和19.5%。高的沉积速率导致高比例的垂直取向的分子，有利于载流子的传输，优化后器件的最大亮度达到46670 cd/m2。（2）研究了退火温度对旋涂法制备的热活化延迟荧光OLED器件的性能。在最优退火温度时，发光分子的跃迁偶极取向和单载流子传输能力得到提高，从而提高了器件的性能。（3）制备并优化了PEDOT：PSS/GO和PEDOT：PSS/GO/AgNWs 透明复合电极，制备的复合电极的方块电阻最优为17 Ω/sq，在波长为550 nm处的透过率为88.7%。采用混合薄膜作为阳极的OLED器件的启亮电压降为2.1V，最大的电流效率和亮度分别增加到6.2cd/A和22894cd/m2。（4）制备了不同厚度的GO空穴注入层（GO-HIL），当GO-HIL为最佳厚度3.6 nm时，器件的最大电流效率和亮度分别为4.4cd/A和15770cd/m2。（5）制备了以热活化延迟荧光分子（DMAC-DPS）为主体，有机荧光分子BUBD-1为客体的混合发光层的发光特性与放大自发辐射特性。DMAC-DPS作为主体材料时，同时存在快速和延迟Förster能量传递过程，提高了主客体材料之间的能量传递效率，降低了混合发光层的放大自发辐射阈值，提高了其作为发光层时OLED的发光特性。（6）分别利用旋涂法和真空蒸镀法制备了BUBD-1薄膜，对其分子偶极矩取向进行了分析，水平分子取向有利于提高器件的输出耦合效率，而垂直取向分子更有利于边发射的放大自发辐射。