High-Performance Orange-Red Organic Light-Emitting Diodes with External Quantum Efficiencies Reaching 33.5% based on Carbonyl-Containing Delayed Fluorescence Molecules

Developing orange to red purely organic luminescent materials having external quantum efficiencies (eta(ext)s) exceeding 30% is challenging because it generally requires strong intramolecular charge transfer, efficient reverse intersystem crossing (RISC), high photoluminescence quantum yield (phi(PL)), and large optical outcoupling efficiency (phi(out)) simultaneously. Herein, by introducing benzoyl to dibenzo[a,c]phenazine acceptor, a stronger electron acceptor, dibenzo[a,c]phenazin-11-yl(phenyl)methanone, is created and employed for constructing orange-red delayed fluorescence molecules with various acridine-based electron donors. The incorporation of benzoyl leads to red-shifted photoluminescence with accelerated RISC, reduced delayed lifetimes, and increased phi(PL)s, and the adoption of spiro-structured acridine donors promotes horizontal dipole orientation and thus renders high phi(out)s. Consequently, the state-of-the-art orange-red organic light-emitting diodes are achieved, providing record-high electroluminescence (EL) efficiencies of 33.5%, 95.3 cd A(-1), and 93.5 lm W-1. By referring the control molecule without benzoyl, it is demonstrated that the presence of benzoyl can exert significant positive effect over improving delayed fluorescence and enhancing EL efficiencies, which can be a feasible design for robust organic luminescent materials.

Automated summary

This study successfully developed orange-red delayed fluorescence molecules with high efficiency organic light-emitting diodes by introducing a stronger electron acceptor benzoyl and utilizing spiral-structured acridine donors. The incorporation of benzoyl led to red-shifted photoluminescence, accelerated reverse intersystem crossing, reduced delayed lifetimes, increased photoluminescence quantum yield, and high optical outcoupling efficiency, resulting in record-high electroluminescence efficiencies.