Asymmetric steric-hindrance donor engineering enables ACQ-suppressed MR-TADF emitters for high-efficiency narrowband OLEDs

• An MR-TADF emitter mPhCz-QAO is developed using an asymmetric steric-hindrance donor strategy • The thermal, theoretical, photophysical, and electroluminescent properties of mPhCz-QAO are systematically investigated • Aggregation-caused quenching is effectively suppressed by the mPhCz-QAO molecular design • A narrow 31 nm emission bandwidth at 475 nm is achieved by mPhCz-QAO • Stable high EQE (∼22%) and narrow 38 nm EL spectra at elevated doping levels are maintained in mPhCz-QAO OLEDs A new organic emitter, m PhCz-QAO, was designed and synthesized through an asymmetric steric-hindrance donor strategy, establishing a distinctive molecular-engineering approach for achieving both high efficiency and narrowband emission in organic light-emitting materials. By introducing a meta -position asymmetric bulky donor, the strong intermolecular π-π interactions intrinsic to the QAO framework are effectively suppressed, thereby preventing aggregation-caused quenching (ACQ) in the solid state. This asymmetric donor simultaneously promotes a more delocalized distribution of the frontier molecular orbitals and strengthens the radiative transition process, leading to enhanced emission properties. Devices incorporating m PhCz-QAO exhibit exceptionally good performance at elevated doping levels, maintaining a maximum external quantum efficiency of approximately 22% as the doping concentration increases from 3 wt.% to 10 wt.%. The emission peak displays only a minimal shift (from 486 to 488 nm), while the narrow emission bandwidth of 38 nm remains fully preserved. These findings demonstrate the effectiveness of asymmetric donor engineering in overcoming concentration-related emission quenching and provide a powerful design framework for developing next-generation high-efficiency, high-color-purity organic emitters suitable for advanced display and lighting technologies.