Mao Hui-Ting, Zang Chun-Xiu, Shan Guo-Gang, Sun Hai-Zhu, Xie Wen-Fa, Su Zhong-Min
Institute of Functional Material Chemistry and National & Local United Engineering Lab for Power Battery, Faculty of Chemistry, Northeast Normal University , Changchun, Jilin 130024, P. R. China.
State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University , Changchun, Jilin 130012, P. R. China.
Inorg Chem. 2017 Aug 21;56(16):9979-9987. doi: 10.1021/acs.inorgchem.7b01516. Epub 2017 Aug 10.
Nondoped electroluminescent devices offer advantages over their doped counterparts such as good reproducibility, reduced phase separation between host and guest materials, and potential of lower-cost devices. However, low luminance efficiencies and significant roll-off values are longstanding issues for nondoped devices, and a rational design strategy for the preparation of efficient phosphors is highly desired. In this work, cyclometalated Ir(III) complexes 3CzIr(mtpy), 4CzIr(mtpy), 3POIr(mtpy), and 4POIr(mtpy) bearing carbazole (Cz) or diphenylphosphoryl (PhPO) groups substituted at different positions of 1,2-diphenyl-H-benzimidazole (HPBI) were designed and synthesized. Owing to the steric effects induced by these groups, a significant intermolecular interaction was avoided, thereby reducing self-quenching and triplet-triplet annihilation (TTA) at high brightness. Simultaneously, attached functional moieties manipulate the charge-carrier character and enhance the EL performance of the complexes. Device N3-10, based on 3POIr(mtpy), successfully realized excellent performance and improved efficiency stability, rendering a turn-on voltage of 2.5 V, a maximum current efficiency of 29.7 cd A, and a maximum power efficiency of 31.1 lm W, which are all almost 3-fold higher than that of the control device N-10 based on parent complex. Inspiringly, all of the devices showed reduced efficiency roll-off as luminance increased. To the best of our knowledge, these are good results for green-emitting PHOLEDs using vacuum evaporation techniques, and they provide fundamental insights into the future realization of efficient phosphorescent Ir(III) complexes and corresponding nondoped devices.
非掺杂电致发光器件相对于其掺杂对应物具有诸多优势，例如良好的可重复性、主体与客体材料之间减少的相分离以及低成本器件的潜力。然而，低发光效率和显著的效率滚降值一直是非掺杂器件长期存在的问题，因此非常需要一种合理的高效磷光体制备设计策略。在这项工作中，设计并合成了在1,2-二苯基-H-苯并咪唑（HPBI）的不同位置被咔唑（Cz）或二苯基磷酰基（PhPO）基团取代的环金属化Ir(III)配合物3CzIr(mtpy)、4CzIr(mtpy)、3POIr(mtpy)和4POIr(mtpy)。由于这些基团诱导的空间效应，避免了显著的分子间相互作用，从而减少了高亮度下的自猝灭和三重态-三重态湮灭（TTA）。同时，连接的功能部分控制电荷载流子特性并增强配合物的电致发光性能。基于3POIr(mtpy)的器件N3-10成功实现了优异的性能和提高的效率稳定性，开启电压为2.5 V，最大电流效率为29.7 cd A，最大功率效率为31.1 lm W，这些都几乎比基于母体配合物的对照器件N-10高出3倍。令人鼓舞的是，所有器件随着亮度增加效率滚降都有所降低。据我们所知，这些对于使用真空蒸发技术的绿色发射磷光有机发光二极管来说是很好的结果，并且它们为未来实现高效磷光Ir(III)配合物和相应的非掺杂器件提供了基本见解。
