Achieving Efficient Blue Delayed Electrofluorescence by Shielding Acceptors with Carbazole Units.

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Developing efficient and stable blue emitters for organic light-emitting diodes (OLEDs) is crucial for advanced display and lighting applications.
• Thermally activated delayed fluorescence (TADF) materials offer a pathway to high efficiency, but achieving good performance in the blue spectrum remains challenging.
• Efficiency roll-off at high brightness levels is a significant limitation for current blue OLED technologies.

Purpose of the Study:

• To design and synthesize novel blue TADF emitters with high electroluminescence efficiency and reduced efficiency roll-off.
• To investigate the impact of shielding acceptor units with carbazole moieties on the photophysical properties and device performance.
• To demonstrate a facile and effective strategy for creating high-performance blue TADF materials.

Main Methods:

• Synthesis of two TADF emitters, DPAc-DCzBN and DPAc-DtCzBN, using benzonitrile as acceptor, 9,9-diphenylacridan as donor, and carbazole as a shielding unit.
• Fabrication and characterization of nondoped and doped OLED devices utilizing the synthesized TADF emitters.
• Evaluation of electroluminescence performance, including emission color, external quantum efficiency (EQE), and efficiency roll-off characteristics at various luminance levels.

Main Results:

• The nondoped DPAc-DCzBN emitter achieved sky-blue emission (CIE: (0.16, 0.26)) with a high EQE of 20.0% and excellent stability (EQEs of 19.5%, 16.1%, 12.6% at 100, 500, 1000 cd m⁻²).
• The doped DPAc-DtCzBN device exhibited pure blue emission (CIE: (0.16, 0.15)) with high EQEs of 23.1% (maxima), 18.3% (100 cd m⁻²), and 11.5% (500 cd m⁻²).
• The developed strategy of shielding acceptors with carbazole units proved effective in constructing high-performance blue TADF materials.

Conclusions:

• The carbazole-shielding strategy is a viable approach for developing high-performance blue TADF emitters.
• The synthesized DPAc-DCzBN and DPAc-DtCzBN materials represent significant advancements in blue TADF OLED technology, offering high efficiency and stability.
• This work provides a promising direction for the future design of efficient and stable electroluminescent materials for optoelectronic devices.