All-organic sulfonium salts acting as efficient solution processed electron injection layer for PLEDs

Area of Science:

• Organic electronics
• Materials science
• Device physics

Background:

• Polymer light-emitting diodes (PLEDs) often rely on unstable low work function metals for efficient charge injection.
• Achieving balanced charge transport and high electroluminescence efficiency in PLEDs remains a key challenge.
• Developing stable and efficient cathode interfacial layers (CILs) is crucial for PLED performance.

Purpose of the Study:

• To introduce all-organic triphenylsulfonium (TPS) salts as novel CILs for PLEDs.
• To demonstrate the replacement of unstable low work function metals with TPS salts.
• To investigate the impact of TPS salts on charge balance, electroluminescence efficiency, and device performance.

Main Methods:

• Deposition of TPS salts (TPS-triflate, TPS-nonaflate) from methanolic solutions as CILs.
• Fabrication and characterization of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-2,1',3-thiadiazole)] (F8BT)-based PLEDs.
• Analysis of device performance metrics including luminous efficiency, brightness, turn-on voltage, and operating voltage.
• Open-circuit voltage (Voc) measurements to assess electron injection barrier.
• Density functional theory (DFT) calculations to understand the electronic properties and stability of TPS salts.

Main Results:

• Incorporation of TPS salts significantly improved luminous efficiency (e.g., from 2.4 to 7.9 cd/A).
• Substantial increase in device brightness was observed (up to 4-fold increase).
• Reduced turn-on and operating voltages were achieved with TPS CILs.
• Favorable decrease in electron injection barrier was confirmed via Voc measurements.
• DFT calculations confirmed the stability of TPS salts upon electron transfer.

Conclusions:

• All-organic TPS salts provide a simple and effective strategy for high-performance PLEDs.
• TPS salts enable efficient electron injection and transport, leading to enhanced device efficiency and brightness.
• Morphology optimization of TPS-salt interlayers is critical for maximizing performance.
• This approach circumvents the need for unstable low work function metals in PLED fabrication.