Acceptor Interlocked Molecular Design for Solution-Processed Stable Deep- Blue TADF and Hyper Fluorescence Organic LED Enabling High-efficiency

Abstract

Solution processed deep-blue OLEDs with high external quantum efficiency and a long operational lifetime are constrained. In this context, we synthesized two TADF emitters utilizing new design strategy of twisted interlocked acceptor core integrated with carbazole (KCCz) and tert. butyl-carbazole (KCTBC) as donors for solution processed deep-blue TADF OLEDs. Twisting of acceptor core by two methyl groups resulted in complete separation of HOMO and LUMO along with cyanide group facilitate in generating low-lying triplet exited states as suggested by theoretical simulation. Combined effect of both resulted in tuning of emission in ultra-deep blue region through the efficient population of triplet excitons and concurrently RISC to produce highly efficient devices. A doped device based on KCTBC showed EQEmax of 9.0% along with low Efficiency roll-off with long operational device half lifetime of 72 minutes at initial brightness of 1,000 cd m-2, and CIE coordinates of (0.17, 0.13). In addition, with 12.5 wt% of 4CzFCN as assistant dopant/co-host to enhanced the performance of the KCTBC based device with an EQEmax of 13.9% and CIE coordinates of (0.18, 0.13). Further, a high-efficiency warm white OLED adopting the TADF hybrid approach is realized with EQEmax of 9.0 %.