Novel Robust Folded Thermally Activated Delayed Fluorescence Molecules for High-Performance OLEDs

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Folded thermally activated delayed fluorescence (TADF) molecules based on through-space charge transfer (TSCT) are of increasing interest.
• However, their electroluminescence (EL) efficiencies are often inferior, and their use as sensitizers for multi-resonance TADF (MR-TADF) emitters is underexplored.

Purpose of the Study:

• To design and synthesize novel isomeric folded TADF molecules (f-TRZ-1 and f-TRZ-2).
• To investigate their potential as emitters and sensitizers in organic light-emitting diodes (OLEDs).

Main Methods:

• Synthesis of f-TRZ-1 and f-TRZ-2 using 2,4,6-triphenyl-1,3,5-triazine (TRZ) as acceptor, 9-phenylcarbazole (PC) as donor, and 11,12-dihydroindolo[2,3-a]carbazole (HIC) as bridge.
• Fabrication and characterization of OLEDs using these molecules as emitters.
• Evaluation of their performance as sensitizers for a green MR-TADF emitter.

Main Results:

• The synthesized molecules exhibit effective TSCT, ultrahigh thermal stability, and balanced bipolar charge transport.
• OLEDs utilizing f-TRZ-1 and f-TRZ-2 as emitters achieved maximum external quantum efficiencies (η_ext,max) up to 28.9%.
• As sensitizers for a MR-TADF emitter, they improved η_ext,max to 37.8% and reduced efficiency roll-off in hyperfluorescence OLEDs.

Conclusions:

• The novel folded TADF molecules demonstrate excellent potential as high-performance emitters in OLEDs.
• Their application as sensitizers for MR-TADF emitters significantly enhances device performance, showcasing their versatility.