Strategic Acceleration of Reverse Intersystem Crossing in Multi-Resonance TADF Emitters

Area of Science:

• Organic electronics
• Materials science
• Photophysics

Background:

• Advanced multi-resonance-induced thermally activated delayed fluorescence (MR-TADF) materials are key for next-generation organic light-emitting diodes (OLEDs) due to their narrowband emission and high efficiency.
• A major limitation is slow reverse intersystem crossing (RISC) rates, leading to efficiency roll-off at high brightness.

Purpose of the Study:

• To design novel blue MR-TADF molecules that enhance RISC rates while maintaining narrowband emission.
• To develop high-performance OLEDs with reduced efficiency roll-off.

Main Methods:

• Integration of a crumpled and asymmetric heptagonal dibenzodiazepine building block into MR-TADF molecules.
• Synthesis and characterization of a proof-of-concept emitter, AzBN2.
• Fabrication and testing of OLED devices utilizing the AzBN2 emitter.

Main Results:

• The AzBN2 emitter demonstrates deep-blue emission (462 nm) with a narrow spectral width (19 nm) and high color purity (CIE: (0.13, 0.067)).
• A more than twofold increase in the RISC rate was achieved compared to conventional designs.
• OLEDs fabricated with AzBN2 reached a record maximum external quantum efficiency (EQE) of 35.7% and maintained 29.8% EQE at 1000 cd m⁻².

Conclusions:

• The proposed molecular design strategy effectively enhances RISC rates in blue MR-TADF emitters.
• The crumpled dibenzodiazepine building block enables efficient deep-blue emission with suppressed efficiency roll-off.
• This work presents a significant advancement for high-performance MR-TADF OLED applications.