High-efficiency and stable deep-blue iridium phosphorescent OLEDs with enhanced charge transfer dynamics

Deep-blue phosphorescent OLEDs (Ph-OLEDs) with high efficiency and stability are essential for advanced display technologies, ensuring sharp image quality and enhanced visibility. In this work, we report a novel class of asymmetric [3 + 2 + 1] coordinated iridium(III) complexes incorporate strongly electron-withdrawing trifluoromethyl (-CF₃) and fluorine (-F) modified N-heterocyclic carbene ligands. This strategic molecular design enables efficient deep-blue emission. Among these complexes, the CF₃-substituted Ir(III) complex (CF₃-2) exhibits pronounced charge-transfer (CT) characteristics and a significantly enhanced radiative decay rate ( $k_r$  = 1.28 ×10⁶ s^-1), enabling rapid and efficient phosphorescence at 443 nm. Devices employing CF₃-2 demonstrated exceptional maximum external quantum efficiency (EQE_max) of up to 29.0%, with emission centered at 443 nm and Commission Internationale de L'Éclairage (CIE) coordinates of (0.147, 0.089), fulfilling National Television System Committee (NTSC) blue standards for high-quality displays. Meanwhile, devices employing CF₃-1 reached an EQE_max of 24.6% with a maximum luminance of 6542 cd m^-2 and CIE_x,y of (0.152,0.126), demonstrating high color purity and efficiency. A control device fabricated without sensitization using CF₃-1 further confirms its intrinsic material stability by exhibiting a remarkable operational lifetime of LT₅₀ of 3875 h at L = 100 cd m^-2 with CIE_x,y of (0.132,0.131). Furthermore, hyper-OLEDs were developed using these complexes as phosphorescent sensitizers. The hyper-OLED incorporating CF₃-1 with the TADF emitter v-DABNA achieved an impressive device lifetime of LT₅₀ = 2127 h at 100 cd m^-2. In parallel, the CF₃-2-sensitized hyper-OLED using DOB2-DABNA-A achieved a deep-blue emission with CIE coordinates of (0.146, 0.067) and a lifetime of LT₅₀ = 373 h under the same luminance, representing a significant advancement in the practical stability of deep-blue OLEDs. Notably, we demonstrate the successful integration of these deep-blue Ph-OLEDs with OLED-on-TFT microdisplay technology, achieving a pixel resolution of 94 PPI (270 × 270 μm) with 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.