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

摘要

Solution processed deep-blue organic light emitting diodes (OLEDs) withhigh external quantum efficiency (EQE) and a long operational lifetime arestill constrained. In this context, two thermally activated delayed fluorescence(TADF) emitters are synthesized utilizing a new design strategy of twistedinterlocked acceptor core integrated with carbazole (KCCz) and tert-butylcarbazole(KCTBC) as donors, respectively, for solution processed deep-blueTADF OLEDs. Twisting of the acceptor core by two methyl groups results incomplete separation of highest occupied molecular orbital and lowest unoccupiedmolecular orbital, along with cyanide group facilitating the generationof low-lying triplet excited states as suggested by theoretical simulation.The combined effect of both results in tuning of emission in ultradeep blueregion through the efficient population of triplet excitons and concurrentlyreverse intersystem crossing to produce highly efficient devices. A dopeddevice based on KCTBC shows EQE_(max) of 9.0 along with low efficiencyroll-off with long operational device half lifetime of 72 min at initial brightnessof 1000 cd m~(?2), and Commission Internationale de L’Eclairage (CIE)coordinates of (0.17, 0.13). In addition, with 12.5 wt of 4CzFCN as assistantdopant/cohost the performance of the KCTBC-based device is enhanced to anEQE_(max) of 13.9 and CIE coordinates of (0.18, 0.13). Further, a high-efficiencywarm white OLED adopting the TADF hybrid approach is realized withEQE_(max) of 9.0.