Efficiency enhancement in orange red thermally activated delayed fluorescence OLEDs by using a rigid di-indolocarbazole donor moiety

Abstract The development of orange-red thermally activated delayed fluorescence (TADF) materials with good optoelectronic and electroluminescence properties are full of challenges due to limited molecular designs. Herein, we investigated a series of materials using dimethylacridine (DMAC) and diindolocarbazole (DI) donor with dibenzo [a, c] phenazine (DBP) acceptor, and compared the characteristics of all synthesized materials as emitters. Due to lower singlet energy level, the rate constant of internal conversion (kIC) contribute to nonradiative decay cannot be ignored at the orange-red region. Therefore, employing rigid donor and acceptor moieties play a major role in suppressing kIC. We observed that employing a rigid donor of DI at β position enhanced the PLQY of 96.1% when compared to acridine based emitters. 5-(dibenzo [a, c] phenazin-11-yl)-10, 15-diphenyl-10, 15-dihydro-5H-diindolo [3, 2-a:3′, 2′-c] carbazole (β-DI-DBP) based OLED device showed better current efficiency (CEmax) of 47.1 cd/A and maximum external quantum efficiency (EQE) of 23.8%. This work demonstrates a better approach towards high PLQY orange red TADF material development.