Boosting EQE to nearly 35% in Acridone-Based TADF Materials via HOMO Delocalization and Nonradiation Suppression

Abstract

As weak donors, carbazole (Cz) derivatives are particularly suitable for blue thermally activated delayed fluorescence (TADF) emitters. However, limited by the large singlet-triplet energy gap (ΔE ST ) and excessively weak charge transfer state, it is unfavorable for efficient TADF property. Herein, a series blue and sky-blue TADF materials, tCz-mPAO, BCz-mPAO and BCz-PAO, were developed by incorporating tert-butyl-carbazole (tCz) or 3,9'-bicarbazole (BCz) as donors and 10-pyridyl-acridone as acceptors. Focusing on simultaneously ensuring efficient reverse intersystem crossing (RISC) and increasing the photoluminescence quantum yields (PLQYs), two molecular design strategies relating to the donor and acceptor units separately, were deliberately employed. By varying donor from tCz to BCz, the HOMO distribution was significantly delocalized while maintaining minimal HOMO-LUMO overlap, resulting in an enhanced k r and optimal ΔE ST . Furthermore, strategic elimination of the flexible methyl group on the acceptor effectively suppresses energy dissipation thereby restricting non-radiative transition rate constant (k nr ). Combining these strategies, BCz-PAO demonstrated an optimal k r of 9.3×10 7 s -1 and a high PLQY of 98.2% in doped film. The sky-blue OLED achieved a remarkable maximum external quantum efficiency of 34.42% without light out-coupling enhancement or TADF-sensitized structure. These synergistic strategies establish a generalizable design paradigm for high-performance TADF emitters.