Efficient thermally activated delayed fluorescence organic light-emitting device based on an exciplex

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Thermally activated delayed fluorescence (TADF) is crucial for high-efficiency organic light-emitting diodes (OLEDs).
• Designing exciplexes with optimized electronic properties is key to enhancing TADF performance.
• Minimizing efficiency roll-off in OLEDs remains a significant challenge for practical applications.

Purpose of the Study:

• To synthesize and characterize a novel donor-acceptor exciplex material.
• To investigate the photophysical properties, including singlet-triplet energy gap and reverse intersystem crossing rate.
• To fabricate and evaluate an organic light-emitting device (OLED) utilizing the developed exciplex.

Main Methods:

• Synthesis of a diphenylamine donor and a phosphine oxide-triazine acceptor.
• Characterization of the exciplex's photophysical properties using spectroscopy.
• Fabrication of an OLED device and measurement of its electroluminescence performance.
• Analysis of efficiency roll-off using transient electroluminescence and a triplet-triplet annihilation model.

Main Results:

• A novel exciplex was successfully synthesized, exhibiting significant TADF properties.
• Achieved a small singlet-triplet energy difference and a high reverse intersystem crossing rate.
• The fabricated OLED demonstrated high efficiencies (23.1 cd/A, 24.2 lm/W, 7.32% EQE) and high exciton utilization (54%).
• Exhibited minimal efficiency roll-off with a critical current density of 34.1 mA/cm².
• Attributed roll-off to triplet-triplet annihilation, supported by experimental data and modeling.
• Confirmed high exciton binding energy and charge confinement within the exciplex.

Conclusions:

• The developed exciplex is a promising material for high-efficiency, low-roll-off OLEDs.
• Simultaneous optimization of electronic properties is vital for efficient TADF emission.
• The study provides insights into managing efficiency roll-off mechanisms in OLED devices.