Witkowska Ewelina, Wiosna-Salyga Gabriela, Glowacki Ireneusz, Ke Tung-Huei, Malinowski Pawel, Heremans Paul
Department of Molecular Physics, Lodz University of Technology, Zeromskiego 116, 90-924 Lodz, Poland.
IMEC, Kapeldreef 75, B-3001 Leuven, Belgium.
Polymers (Basel). 2021 Apr 2;13(7):1148. doi: 10.3390/polym13071148.
Many methods have been proposed to increase the efficiency of organic electroluminescent materials applied as an emissive layer in organic light emitting diodes (OLEDs). Herein, we demonstrate enhancement of electroluminescence efficiency and operational stability solution processed OLEDs by employing thermally activated delayed fluorescence (TADF) molecules as assistant dopants in host-guest systems. The TADF assistant dopant (SpiroAC-TRZ) is used to facilitate efficient energy transfer from host material poly(-vinylcarbazole) (PVK) to a phosphorescent Ir(III) emitter. We present the analysis of energy transfer and charge trapping-two main processes playing a crucial role in light generation in host-guest structure OLEDs. The investigation of photo-, electro- and thermoluminescence for the double-dopant layer revealed that assistant dopant does not only harvest and transfer the electrically generated excitons to phosphorescent emitter molecules but also creates exciplexes. The triplet states of formed PVK:SpiroAC-TRZ exciplexes are involved in the transport process of charge carriers and promote long-range exciton energy transfer to the emitter, improving the efficiency of electroluminescence in a single emissive layer OLED, resulting in devices with luminance exceeding 18 000 cd/m with a luminous efficiency of 23 cd/A and external quantum efficiency (EQE) of 7.4%.
已经提出了许多方法来提高用作有机发光二极管（OLED）发光层的有机电致发光材料的效率。在此，我们展示了通过在主客体系统中使用热激活延迟荧光（TADF）分子作为辅助掺杂剂来提高溶液处理的OLED的电致发光效率和操作稳定性。TADF辅助掺杂剂（SpiroAC-TRZ）用于促进从主体材料聚（乙烯基咔唑）（PVK）到磷光Ir（III）发射体的有效能量转移。我们对能量转移和电荷俘获进行了分析，这是在主客体结构OLED中光产生过程中起关键作用的两个主要过程。对双掺杂层的光致发光、电致发光和热致发光的研究表明，辅助掺杂剂不仅收集并将电产生的激子转移到磷光发射体分子上，还形成了激基复合物。形成的PVK:SpiroAC-TRZ激基复合物的三重态参与电荷载流子的传输过程，并促进激子能量向发射体的长程转移，提高了单发光层OLED的电致发光效率，从而得到亮度超过18000 cd/m²、发光效率为23 cd/A且外量子效率（EQE）为7.4%的器件。
