Strategic Management of High‐Lying Triplet Excitons to Realize the Breakthrough in Efficiency of Blue Fluorescence OLEDs Based on AIE Emitter

Aggregation-induced emission (AIE) materials are attractive for the fabrication of high-efficiency organic light-emitting diodes (OLEDs) owing to the "hot exciton" process by reverse intersystem crossing (hRISC) and high photoluminescence quantum yields (PLQY). However, the internal conversion (IC) from the high-lying triplet excitation states (T-n, n >= 2) to the lower excited triplet state (Tn-1) is inevitable, resulting in severe exciton losses. Herein, an effective device structure is designed that reuses the lost triplet excitons caused by IC and realizes the breakthrough in the efficiency of blue fluorescence OLEDs based on AIE molecule as an emitter. The maximum external quantum efficiency reached as high as 14.8% and is kept at 14.4% at the luminance of 1000 cd m(-2). In the designed device, a triplet-triplet annihilation (TTA) up-conversion material 1-[2,5-dimethyl-4-(1-pyrenyl)phenyl]pyrene (DMPPP) is introduced into the AIE emitter as a triplet sensitizer to receive the lost triplet excitons, and a thin TTA up-conversion layer 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (CzPA) is introduced in the middle of the doped layer to form the emissive layer (EML). It is found that the hRISC process of iTPB-2AC greatly enhances the utilization efficiency of TTA intermediate state ([TT]*) excitons on CzPA to iTPB-2AC so that the utilization of the lost excitons is maximized. This work establishes physical insights into the AIE emission materials and device fabrication of high-efficiency blue fluorescence OLEDs.