Noncovalent through-space charge transfer enables efficient and stable blue electroluminescence

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Donor-acceptor type thermally activated delayed fluorescence (TADF) materials are key for efficient organic light-emitting diodes (OLEDs).
• Achieving stable and efficient blue emission from TADF materials presents a significant challenge.
• Controlling electronic coupling in TADF molecules, via through-space or through-bond charge transfer, is essential for effective performance.

Purpose of the Study:

• To develop a novel strategy for designing high-performance blue TADF molecules.
• To leverage multichannel through-space charge transfer (TSCT) to enhance reverse intersystem crossing (RISC) and suppress bond cleavage.
• To investigate the performance of TSCT-based TADF molecules in OLED devices.

Main Methods:

• Design and synthesis of novel donor-acceptor TADF molecules utilizing a multichannel TSCT approach.
• Fabrication and characterization of OLED devices using the designed TADF molecules.
• Evaluation of device performance, including emission wavelength, external quantum efficiency (EQE), roll-off, and operational stability (T90).

Main Results:

• The designed molecule achieved blue emission at 468 nm with a high EQE of 32.3% and minimal roll-off.
• Exceptional operational stability was demonstrated with a T90 of 198.2 hours at 1000 cd/m².
• A TADF-sensitized fluorescent OLED using the molecule as a sensitizer achieved an EQE of 36.6% with narrowband emission and T90 exceeding 87.8 hours.

Conclusions:

• The multichannel TSCT strategy is effective for enhancing RISC and suppressing donor-acceptor bond cleavage in blue TADF materials.
• The developed molecules exhibit excellent performance and stability, addressing key challenges in blue OLEDs.
• This work establishes a robust framework for designing high-performance TSCT-based blue TADF emitters.