Acceptor-Donor-Acceptor-Type Orange-Red Thermally Activated Delayed Fluorescence Materials Realizing External Quantum...

Area of Science:

• Organic electronics
• Materials science
• Photophysics

Background:

• Thermally activated delayed fluorescence (TADF) materials are crucial for efficient organic light-emitting diodes (OLEDs).
• Achieving high photoluminescence quantum yield (PLQY) and minimizing efficiency roll-off at high brightness remain key challenges in OLED development.
• The acceptor-donor-acceptor (A-D-A) molecular design is a promising strategy for tuning optoelectronic properties.

Purpose of the Study:

• To synthesize and characterize two new orange-red TADF materials, PzTDBA and PzDBA.
• To investigate the structure-property relationships governing their photophysical and electroluminescent performance.
• To evaluate the potential of these materials for high-performance OLED applications.

Main Methods:

• Materials synthesis via established organic chemistry routes.
• Photophysical characterization including PLQY, ΔE_ST, and lifetime measurements.
• Fabrication and testing of OLED devices doped with PzTDBA and PzDBA.

Main Results:

• PzTDBA and PzDBA exhibit small ΔE_ST (0.05–0.06 eV) and near-unity PLQY.
• High reverse intersystem crossing rates (k_risc ~10⁶ s^-1) and short delayed exciton lifetimes (<2.63 µs) were observed.
• OLED devices achieved high external quantum efficiencies (EQE) of up to 30.3% with minimal roll-off (<3.6% at 1000 cd m^-2).
• Device operational lifetimes (LT₅₀) reached 159 h for PzTDBA and 193 h for PzDBA at 1000 cd m^-2.

Conclusions:

• The A-D-A configuration with rigid boron acceptors and dihydrophenazine donors effectively yields high-performance TADF materials.
• Fast k_risc and short delayed exciton lifetimes contribute to suppressed exciton annihilation and low roll-off.
• PzTDBA and PzDBA are promising candidates for efficient and stable orange-red OLEDs.