Deep-blue phosphorescent organic light-emitting diodes (Ph-OLEDs) are essential for advanced full-color displays, yet developing efficient and stable deep-blue emitters remains a formidable challenge. In a new paper published in Light: Science & Applications, a team of scientists led by Prof. Feiyu Kang, Guodan Wei and Dr. Chengcheng Wu, from Tsinghua Shenzhen International Graduate School, together with collaborators Prof. Takuji Hatakeyama from Kyoto University and Prof. Chihaya Adachi from Kyushu University, has reported a breakthrough in molecular design strategy.
The researchers synthesized a novel class of asymmetric [3+2+1] coordinated iridium(III) complexes incorporating strongly electron-withdrawing trifluoromethyl and fluorine modified N-heterocyclic carbene ligands. This strategic ligand engineering enables precise modulation of excited-state characteristics, distinctly favoring charge-transfer or locally excited states for emission tuning. The CF3-substituted complexes exhibit pronounced charge-transfer character with significantly enhanced radiative decay rates, while the F-substituted complexes feature predominantly localized excitation.
Among these complexes, the CF3-substituted complex CF3-2 exhibits a remarkably high radiative decay rate of 1.28 million per second. Devices employing CF3-2 demonstrated an exceptional maximum external quantum efficiency of up to 29.0%, with emission centered at 443 nanometers and Commission Internationale de L'Eclairage coordinates of (0.147, 0.089), successfully fulfilling the National Television System Committee deep-blue standard for high-quality displays. Meanwhile, devices employing CF3-1 reached an EQE of 24.6% with a maximum luminance of 6542 candela per square meter.
Remarkably, the complex CF3-1 showed outstanding operational stability. A control device fabricated without sensitization exhibited a remarkable operational lifetime of 3875 hours at 100 candela per square meter. Furthermore, hyper-OLEDs using CF3-1 as a phosphorescent sensitizer and a thermally activated delayed fluorescence emitter achieved an impressive device lifetime of 2127 hours under the same luminance, representing a significant advancement in the practical stability of deep-blue OLEDs. In parallel, the CF3-2-sensitized hyper-OLED achieved deep-blue emission with CIE coordinates of (0.146, 0.067) and a lifetime of 373 hours.
The team also demonstrated the successful integration of these deep-blue emitters into thin-film transistor microdisplay technology, achieving a pixel resolution of 94 pixels per inch with a pixel size of 270 by 270 micrometers and programmable emission patterns. This innovative molecular coordination design strategy provides valuable insights into ligand engineering and exciton management, opening new pathways toward high-efficiency, long-lifetime deep-blue OLEDs for next-generation microdisplay and display technologies.
