High-Performance Coemissive Blue Organic Light-Emitting Diodes Combining Phosphorescence and Multiresonance Fluorescence.

Phosphor-sensitized organic light-emitting diodes (PS-OLEDs) with coemissive narrow-spectrum Pt(II) complexes and multiresonance thermally activated delayed fluorescence (MR-TADF) emitters achieved efficient, durable, and deep blue emissions. This study systematically investigated the emission properties and energy transfer in PS-OLEDs by employing a series of phosphors and MR-TADF emitters. The tetradentate Pt(II)-based blue star phosphor (PtON-PTB) with a large van der Waals radius and the MR-TADF emitter 2,12-di-tert-butyl-5,9-bis(4-(tert-butyl)phenyl)-7-(methyl-d3)-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracene (M-t-DABNA-d) with stabilized deuterated methyl were newly developed. The performance of the PS-OLEDs, including efficiency, durability, and color purity, was significantly improved using PtON-PTB and M-t-DABNA-d. A bottom-emission PS-OLED synergistically using PtON-PTB and M-t-DABNA-d achieved a maximum external quantum efficiency (EQEmax) of 21.3% and a lifetime (LT90) of 55 h with Commission Internationale de l'Elcairage (CIE) coordinates of (0.14, 0.19) at 1000 cd m-2 and comprehensively outperformed the phosphorescent OLEDs (PHOLEDs) incorporating improved tetradentate Pt(II)-based blue phosphor (PtON-TBBI). A top-emission PS-OLED employing coemitters of PtON-PTB and t-DABNA achieved a maximum EQE of 24.2% and a lifetime (LT90) of 93 h with CIE coordinates of (0.12, 0.10) at a luminance of 1000 cd m-2. This study demonstrates the promising potential of high-performance blue PS-OLEDs with coemission properties by systematically integrating fluorescent and phosphorescent emitters in the OLED devices.