Indolocarbazole-Based Hosts for Efficient Red Phosphorescent OLEDs

Two indolocarbazole-based host materials, namely, 5,7-di([1,1′:3′,1″-terphenyl]-5′-yl)-3,9-di-tert-butyl-5,7-dihydroindolo[2,3-b]carbazole (InCz-TP) and 4,4′-(3,9-di-tert-butylindolo[2,3-b]carbazole-5,7-diyl)bis(N,N-diphenylaniline) (InCz-TPA), were designed and synthesized for application in red phosphorescent organic light-emitting diodes (OLEDs). In these systems, bulky substituents possessing tailored electron-donating characteristics were incorporated into the indolocarbazole core. The triplet energy levels were experimentally determined to be 2.81 eV and 2.78 eV, indicating that both materials are appropriate host candidates for red phosphorescent OLEDs. Device evaluations revealed that InCz-TPA delivered superior performance compared to InCz-TP, reaching a maximum external quantum efficiency (EQE) of 8.50%, which corresponds to a 36% enhancement. Both devices exhibited an electroluminescence peak at 628 nm along with nearly identical CIE coordinates of (0.678, 0.317) and (0.680, 0.318), suggesting efficient energy transfer between host and dopant.