An Ultraviolet Thermally Activated Delayed Fluorescence OLED with Total External Quantum Efficiency over 9.

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Developing ultraviolet (UV) thermally activated delayed fluorescence (TADF) materials is difficult due to challenges in achieving high energy bandgaps and specific excited state properties.
• Existing deep-blue TADF emitters often struggle to achieve efficient UV emission.

Purpose of the Study:

• To design and synthesize a novel UV-emissive TADF compound.
• To investigate the potential of the new compound for high-performance UV organic light-emitting diodes (OLEDs).

Main Methods:

• Molecular engineering: Interlocking the diphenylsulfone (PS) acceptor unit of a known deep-blue TADF emitter (CZ-PS) with a dimethylmethylene bridge to create CZ-MPS.
• Characterization of photophysical properties, including emission spectra and energy levels.
• Fabrication and testing of OLED devices using CZ-MPS as a guest material.

Main Results:

• Successfully synthesized CZ-MPS, a novel UV-emissive TADF compound.
• CZ-MPS exhibits a shallower LUMO energy level and a more rigid structure compared to CZ-PS.
• OLED devices utilizing CZ-MPS achieved an emission maximum at 389 nm with a maximum total external quantum efficiency (EQEmax) of 9.3%.
• The achieved EQEmax is double the previous record for UV-OLEDs.

Conclusions:

• CZ-MPS is the first reported UV-emissive TADF compound.
• The molecular design strategy employed offers a promising pathway for developing high-performance UV-OLED materials.
• This work significantly advances the field of UV-emitting organic electronics.