Bright, stable, and efficient red light-emitting electrochemical cells using contorted nanographenes

Area of Science:

• Organic electronics
• Materials science
• Photophysics

Background:

• Small molecule light-emitting electrochemical cells (SM-LECs) are crucial for display and lighting technologies.
• Red-emitting materials with high stability and efficiency remain a challenge in SM-LEC development.

Purpose of the Study:

• To rationalize the electroluminescent behavior of a hexabenzoovalene derivative in SM-LECs.
• To investigate the stability and efficiency of red-emitting SM-LECs utilizing this novel nanographene emitter.
• To understand the relationship between electroluminescence band shape and electric field dependence.

Main Methods:

• Fabrication and characterization of SM-LECs using a contorted nanographene emitter.
• Performance evaluation including irradiance, external quantum efficiency (EQE), and operational stability.
• Dynamic electrochemical impedance spectroscopy to analyze electroluminescence properties.

Main Results:

• The nanographene emitter achieved irradiances of ~220 μW cm⁻² and EQEs of 0.78%.
• Initial device stability exceeded 200 hours, improving to 3600 hours (measured) and 13,000 hours (extrapolated) at high brightness after optimization.
• A unique electroluminescence behavior linked to electric field-dependent vibrational peak intensities was observed and rationalized.

Conclusions:

• The study presents a record-breaking stable and bright red-emitting SM-LEC.
• The rationalization of the electroluminescent behavior provides insights into the performance of contorted nanographene emitters.
• This work paves the way for advanced red-emitting materials in electrochemical cells.