2002120 (1 of 8) © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.advmat.de COMMUNICATION External Quantum Efciency Exceeding 24% with CIE y Value of 0.08 using a Novel Carbene-Based Iridium Complex in Deep-Blue Phosphorescent Organic Light-Emitting Diodes Ho-Yeol Park, Athithan Maheshwaran, Chang-Ki Moon, Hyuna Lee, Saripally Sudhaker Reddy, Vijaya Gopalan Sree, Jiyoung Yoon, Jeong Won Kim, Jang Hyuk Kwon, Jang-Joo Kim, and Sung-Ho Jin* H.-Y. Park, A. Maheshwaran, Dr. S. S. Reddy, Dr. V. G. Sree, Prof. S.-H. Jin Department of Chemistry Education Graduate Department of Chemical Materials Sustainable Utilization of Photovoltaic Energy Research Center Institute for Plastic Information and Energy Materials Pusan National University Busan 46241, Republic of Korea E-mail: shjin@pusan.ac.kr Dr. C.-K. Moon, Prof. J.-J. Kim Department of Materials Science and Engineering Seoul National University Seoul 151–744, Republic of Korea H. Lee, Prof. J. H. Kwon Organic Optoelectronic Device Laboratory (OODL) Department of Information Display Kyung Hee University Seoul 02447, Republic of Korea J. Yoon, Dr. J. W. Kim Division of Industrial Metrology Korea Research Institute of Standards and Science (KRISS) Daejeon 34113, Republic of Korea The ORCID identifcation number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202002120. DOI: 10.1002/adma.202002120 Research over the past decade has improved the efciencies of red, green, and blue phosphorescent organic light- emitting diodes (PHOLEDs) for solid- state lighting applications. A combination of red, green, and blue light is essen- tial for generating white light. Red and green triplet emitters have been devised that achieve high external quantum ef- ciencies (EQEs) and brightnesses in PHOLEDs. [1–4] However, the develop- ment of corresponding blue triplet emit- ters has been slower and as yet no device has been produced that meets high EQE along with color purity and high bright- ness. The National Television System Committee (NTSC) standard recommends Commission International de l’Éclairage (CIE) coordinates for blue of (0.14, 0.08), whereas the European Broadcast Union television recommends coordinates of (0.15, 0.06). [5] CIE (y) color coordinates of ≤ 0.10 are preferred and are considered the most important prerequisites for display applications. N-hetero- cyclic carbene (NHC) based ligands are among the most promi- sing deep-blue emission candidates. [6,7] These ligands typically form strong bonds with metal centers (e.g., with Ir(III) and Pt(II)), and thus, the complexes formed are more resistant to decomposition than conventional Ir(III) complexes. [8] How- ever, their EQE max values and maximum electroluminescent (EL) brightnesses are low. [9–16] Forrest et al. [11] successfully produced deep-blue PHOLEDs with an N-methylated pyri- dylimdiazole core and incorporating an additional exciton/ electron-blocking layer and graded doping structure with an EQE max of 10.1 ± 0.2% for fac-Ir(pmp) 3 with CIE(x, y) coordi- nates of (0.16, 0.09) and EQE max values of 14.4 ± 0.4% for mer- Ir(pmp) 3 with CIE(x, y) coordinates of (0.16, 0.15). In particular, fac-Ir(pmp) 3 exhibited high EL brightness with outstanding CIE color coordinates. Recently, Colman et al. [16] fabricated a deep- blue PHOLED device using an N-methylated imidazole core and a carbene-based Ir(III) complex as the exciton/electron- blocking layers with an EQE max of 13.4% and CIE(x, y) coordi- nates of (0.15, 0.05). However, it had a low EQE max as compared with red and green PHOLEDs. Overall, the carbene-based deep- blue device showed moderate PHOLED performance, despite Deep-blue triplet emitters remain far inferior to standard red and green triplet emitters in terms of exhibiting high-color-purity Commission International de l'Éclairage (CIE) y values of ≤0.1, external quantum efciencies (EQEs), and high electroluminescent brightnesses in phosphorescent organic light-emitting diodes. In fact, no deep-blue triplet emitter with color purity and high device performance has previously been reported. In this study, a deep-blue triplet emitter, mer-tris(N-phenyl, N-benzyl-pyridoimidazol-2-yl) iridium(III) (mer-Ir1) is developed, which meets the requirements of the National Television System Committee (NTSC) CIE(x, y) coordinates of (0.149, 0.085) with an extremely high EQE of 24.8% and maximum brightness (L max ) of 6453 cd m -2 , by a device with a 40 vol% doping ratio. Moreover, another device demonstrates an EQE max of 21.3%, an L max of 5247 cd m -2 , and CIE(x, y) coordinates of (0.151, 0.086) at a 30 vol% doping ratio. This is the frst report of a high-performance, deep-blue phosphor, carbene-based Ir(III) complex device with outstanding CIE(x, y) color coordinates and a high EQE. The results of this study indicate that the novel dopant mer-Ir1 is a promising candidate for reducing power consumption in display applications. Adv. Mater. 2020, 32, 2002120 15214095, 2020, 29, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/adma.202002120 by Kyung Hee University Library, Wiley Online Library on [23/11/2022]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License