Boron-based thermally activated delayed fluorescence host materials as universal hosts for blue phosphorescent organic light-emitting diodes

Developing dopants and hosts is essential for enhancing the performance of blue phosphorescent organic light-emitting diodes (PhOLEDs). Herein, we developed host materials with thermally activated delayed fluorescence (TADF) characteristics—specifically, 9-(12-(3-(triphenylsilyl)phenyl)-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-11-yl)-9H-carbazole (BO-Cz-Si-1) and 9-(10-(3-(triphenylsilyl)phenyl)-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-11-yl)-9H-carbazole (BO-Cz-Si-2). These materials, derived from boron- and oxygen-based 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (DOBNA), are designed with TADF properties through a sterically modulated structure featuring one carbazole unit and one tetraphenylsilyl unit attached to the DOBNA core. These hosts exhibit a high triplet energy of 3.0 eV along with TADF characteristics, ensuring high efficiency and prolonged operational stability in blue PhOLEDs. The combination of BO-Cz-Si-1 (an electron transport-type host) and 9-(3-(triphenylsilyl)phenyl)-9H-3,9′-bicarbazole (a hole transport-type host) as a mixed host yields a maximum external quantum efficiency of 23.5 %, blue CIE color coordinates of (0.13, 0.18), and an improved device lifetime compared to the triazine-derived host. Notably, the DOBNA-derived hosts exhibit significantly longer device lifetimes than the triazine-derived host, irrespective of whether Ir or Pt phosphor is doped into the devices, suggesting the universal applicability of DOBNA-derived hosts for blue phosphors. These findings underscore the promising potential of DOBNA-based TADF hosts as n-type hosts, paving the way for highly stable and efficient blue PhOLEDs.