Highly Efficient Thermally Activated Delayed Fluorescence via J-Aggregates with Strong Intermolecular Charge Transfer

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Organic emissive materials face limitations from energy-gap law and spin statistics, especially for near-infrared (NIR) applications.
• Developing high-efficiency, low-cost organic light-emitting diodes (OLEDs) remains a significant challenge.

Purpose of the Study:

• To design and synthesize novel organic donor-acceptor molecules capable of forming J-aggregates.
• To achieve highly efficient thermally activated delayed fluorescence (TADF) in the yellow to NIR spectral range.
• To overcome intrinsic limitations in organic emissive materials for improved device performance.

Main Methods:

• Synthesis of two organic donor-acceptor molecules with strong, planar acceptors.
• Formation of J-aggregates with strong intermolecular charge transfer (CT) in solid states.
• Experimental and theoretical investigations of photophysical properties and exciton dynamics.
• Fabrication and characterization of organic light-emitting diodes (OLEDs).

Main Results:

• Synthesized molecules readily formed J-aggregates exhibiting strong intermolecular CT and tunable emission from yellow to NIR.
• J-aggregate formation mixed Frenkel and CT excitons, leading to high photoluminescence efficiency (>90%) in solid films.
• Achieved a reduced energy gap (≈0.3 eV) between singlet and triplet states, enabling efficient NIR TADF.
• Demonstrated OLEDs with external quantum efficiencies of 15.8% (red) and 14.1% (NIR).

Conclusions:

• The novel J-aggregate strategy effectively overcomes limitations in organic emissive materials, particularly for NIR applications.
• This approach enables high-efficiency TADF materials with tunable emission through molecular design and aggregate formation.
• The reported results represent a significant advancement for NIR OLEDs based on TADF materials, opening new avenues for molecular aggregate-based emitters.