Suppressing Aggregation through a Rigid DOBNA‐Based Host for Ultralong‐Lifetime Red Solution‐Processed OLEDs

Abstract To address poor operational stability of solution‐processed organic light emitting diodes (s‐OLEDs), a key limitation compared to vacuum‐deposited device, the study proposes molecular design strategy that controls intramolecular rotational freedom for two indacene‐based host materials: 5,5,8,8‐tetramethyl‐14‐(4‐(4‐(triphenylsilyl)phenyl)quinazolin‐2‐yl)‐8,14‐dihydro‐5H‐indeno[1,2‐b]indeno[2',1':4,5]thieno [3,2‐g]indole ( DITI‐QSi ) and 14‐(2,12‐di‐tert‐butyl‐5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)‐5,5,8,8‐tetramethyl‐8,14‐dihydro‐5H‐indeno[1,2‐b]indeno[2',1':4,5]thieno [3,2‐g]indole ( DITI‐tDOBNA ). The bulky tetraphenylsilyl group in DITI‐QSi introduces rotational freedom to the quinazoline unit, increasing molecular flexibility and leading to severe molecular aggregation and a low photoluminescence quantum yield (PLQY). In contrast, the rigid DOBNA unit with steric hindrance from tert‐butyl groups in (tDOBNA) in DITI‐tDOBNA significantly suppresses such intramolecular rotation and aggregation, ensuring close host‐emitter proximity and improving PLQY, which thereby enhances both Förster and Dexter energy transfer processes. Additionally, an efficient electron‐withdrawing effect of DOBNA helps to improve the charge balance within the emitting layer. A red phosphorescent s‐OLED incorporating DITI‐tDOBNA achieves a high current efficiency of 25.1 cd/A and an external quantum efficiency (EQE) of 18.6%, with minimal efficiency roll‐off. Notably, the device demonstrates outstanding operational stability, with a half‐lifetime (LT 50 ) of 1400 h.