Accelerated Turn-On and High Performance in Light-Emitting Electrochemical Cells Using Highly Charged Iridium...

Area of Science:

• Materials Science
• Electrochemistry
• Photophysics

Background:

• Ionic transition metal complexes (iTMC) offer simple, solution-processed architectures for efficient electroluminescent devices.
• A key limitation in iridium-based iTMC LECs is slow response times due to low ionic conductivity of singly cationic complexes.
• Improving charge transport and device kinetics is crucial for practical applications.

Purpose of the Study:

• To synthesize and characterize novel triply cationic iridium complexes ([Ir]3+) for enhanced ionic conductivity in LECs.
• To investigate the impact of these [Ir]3+ complexes on the electroluminescence properties and response times of LECs.
• To explore strategies for optimizing LEC performance by combining singly and triply cationic iridium complexes.

Main Methods:

• Synthesis of triply cationic iridium complexes with alkylated bipyridine ligands (EPP, PPP) and varied ancillary ligands (bpy, meoxy).
• Fabrication of single-layer LEC devices using pristine films and blended films of cationic iridium complexes.
• Electroluminescence measurements, including turn-on time, luminance, and stability analysis.

Main Results:

• The synthesized [Ir]3+ complexes exhibited higher ionic conductivity and wider-bandgap emission compared to conventional [Ir]+ complexes.
• Pristine [Ir]3+ LECs showed 100-1000-fold faster electroluminescence but lower luminance and stability.
• Blending [Ir]+ and [Ir]3+ complexes, particularly a 10% EPP bpy [Ir]3+ device, achieved rapid turn-on (4 s) while retaining luminance and stability.

Conclusions:

• Triply cationic iridium complexes offer a viable strategy to enhance the DC response of iTMC LECs.
• Combining singly and triply cationic complexes allows for a synergistic improvement in LEC performance, balancing speed and stability.
• Further development of ionically conductive iridium emitters holds promise for advanced electroluminescent devices.