Xie Jia-Xun, Lee Chih-Chien, Huang Lin-Ming, Lin Huang-Teng, Luo Dian, Hsieh Chung-Hung, Liu Shun-Wei, Chen Chih-Hsin
Organic Electronics Research Center, Ming Chi University of Technology, New Taipei City 24301, Taiwan.
Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 10617, Taiwan.
ACS Appl Mater Interfaces. 2023 Sep 20;15(37):44022-44032. doi: 10.1021/acsami.3c07430. Epub 2023 Aug 25.
Bis(2-phenylpyridine)(acetylacetonate)iridium, Ir(ppy)(acac), is a benchmark green emitter for phosphorescent organic light-emitting diodes (PhOLEDs). In this work, we reported three positional isomeric cyano-substituted Ir(ppy)(acac) complexes, i.e., Ir(3-CN), Ir(4-CN), and Ir(10-CN), with the emission in the yellow to red region (544-625 nm). Through theoretical investigation and single-crystal analysis, it was found that the introduction of cyano substitution at various positions of the ppy ligand allows for tuning the electron distribution and coordination bond length of Ir complexes. Therefore, the charge transfer property of Ir complexes is enhanced such that the energy gap of the cyano-substituted Ir(ppy)(acac) complexes was reduced. In addition, Ir(3-CN), Ir(4-CN), and Ir(10-CN) exhibited high PLQYs of 83, 54, and 75%, respectively, with the phosphorescence lifetime in the range of 0.79-2.08 μs. Notably, the device utilizing Ir(3-CN) as the emitter exhibited a maximum external quantum efficiency (EQE) of 25.4%, current efficiency of 56.9 cd A, power efficiency of 68.7 lm W, and brightness of 61,340 cd m at 8 V. The EQE of this device remained 24.3 and 19.9% at luminances of 1,000 and 10,000 cd m, corresponding to the efficiency roll-off of 4.3 and 21.7%, respectively. Comparing to the Ir complexes using the ligand with an extended conjugated structure, our results demonstrated a simple molecular design strategy for phosphorescence emitters with reduced molecular weight for efficient PhOLEDs in the yellow to red color region.
双（2-苯基吡啶）（乙酰丙酮）铱（Ir(ppy)(acac)）是用于磷光有机发光二极管（PhOLEDs）的一种基准绿色发光体。在这项工作中，我们报道了三种位置异构的氰基取代的Ir(ppy)(acac)配合物，即Ir(3-CN)、Ir(4-CN)和Ir(10-CN)，其发射波长在黄色到红色区域（544 - 625 nm）。通过理论研究和单晶分析发现，在ppy配体的不同位置引入氰基取代能够调节Ir配合物的电子分布和配位键长度。因此，Ir配合物的电荷转移性质得到增强，使得氰基取代的Ir(ppy)(acac)配合物的能隙减小。此外，Ir(3-CN)、Ir(4-CN)和Ir(10-CN)分别表现出83%、54%和75%的高PLQYs，磷光寿命在0.79 - 2.08 μs范围内。值得注意的是，以Ir(3-CN)作为发光体的器件在8 V时表现出25.4%的最大外量子效率（EQE）、56.9 cd A的电流效率、68.7 lm W的功率效率以及61,340 cd m的亮度。该器件在1,000和10,000 cd m的亮度下EQE分别保持在24.3%和19.9%，相应的效率滚降分别为4.3%和21.7%。与使用具有扩展共轭结构配体的Ir配合物相比，我们的结果展示了一种用于黄色到红色区域高效PhOLEDs的、具有降低分子量的磷光发光体的简单分子设计策略。
