Efficient and Bright Organic Radical Light-Emitting Diodes with Low Efficiency Roll-Off.

Area of Science:

• Organic electronics
• Materials science
• Photophysics

Background:

• Organic radicals offer potential for deep-red/near-infrared electroluminescence (EL) due to doublet fluorescence.
• Existing radical-based EL devices suffer from low carrier mobility, leading to efficiency roll-off at high current densities.

Purpose of the Study:

• To develop highly efficient and bright doublet electroluminescent devices using organic radicals.
• To address the efficiency roll-off issue in radical-based light-emitting devices.

Main Methods:

• Fabrication of electroluminescent devices combining a thermally activated delayed fluorescence (TADF) host with a tris(2,4,6-trichlorophenyl)methyl-based radical emitter.
• Steady-state and transient photophysical studies to investigate luminescence mechanisms.

Main Results:

• Achieved a high maximum external quantum efficiency (EQE) of 17.4% at 707 nm peak emission.
• Demonstrated significantly improved efficiency roll-off: 70% of max EQE maintained at 10 mA cm⁻², and 50% at 100 mA cm⁻².
• Confirmed doublet luminescence mechanisms through photophysical studies.

Conclusions:

• The developed host system facilitates balanced charge transport, crucial for high-performance radical-based EL devices.
• This work represents a significant advancement towards the practical application of organic radicals in near-infrared light-emitting devices.