Efficient Deep‐Blue Organic Light‐Emitting Diodes Employing Doublet Sensitization

Abstract

AbstractFast and efficient exciton utilization is a crucial solution and highly desirable for achieving high‐performance blue organic light‐emitting diodes (OLEDs). However, the rate and efficiency of exciton utilization in traditional OLEDs, which employ fully closed‐shell materials as emitters, are inevitably limited by spin statistical limitations and transition prohibition. Herein, a new sensitization strategy, namely doublet‐sensitized fluorescence (DSF), is proposed to realize high‐performance deep‐blue electroluminescence. In the DSF‐OLED, a doublet‐emitting cerium(III) complex, Ce‐2, is utilized as sensitizer for multi‐resonance thermally activated delayed fluorescence emitter ν‐DABNA. Experimental results reveal that holes and electrons predominantly recombine on Ce‐2 to form doublet excitons, which subsequently transfer energy to the singlet state of ν‐DABNA via exceptionally fast (over 108 s−1) and efficient (≈100%) Förster resonance energy transfer for deep‐blue emission. Due to the circumvention of spin‐flip in the DSF mechanism, near‐unit exciton utilization efficiency and remarkably short exciton residence time of 1.36 µs are achieved in the proof‐of‐concept deep‐blue DSF‐OLED, which achieves a Commission Internationale de l'Eclairage coordinate of (0.13, 0.14), a high external quantum efficiency of 30.0%, and small efficiency roll‐off of 14.7% at a luminance of 1000 cd m−2. The DSF device exhibits significantly improved operational stability compared with unsensitized reference device.