Optical analysis of light-emitting electrochemical cells

Area of Science:

• Optoelectronics
• Materials Science
• Device Physics

Background:

• Light-emitting electrochemical cells (LECs) offer low-cost fabrication for emerging light applications.
• Understanding the impact of in-situ formed doped transport regions on LEC optical performance is crucial but limited.

Purpose of the Study:

• To investigate how the intricate doping structure of LECs influences their optical performance.
• To determine the optimal active layer thickness for maximizing emission intensity and efficiency in high-performance LECs.

Main Methods:

• Combined angle-dependent and doping-dependent optical measurements.
• Optical simulations to model light emission within the LEC structure.
• Analysis of exciton coupling and wave-guided modes as loss channels.

Main Results:

• The emission zone in high-performance LECs is centered at approximately 30% of the active layer thickness from the anode.
• Emission intensity and efficiency exhibit undulating behavior with varying active layer thickness.
• The first emission maximum (at ~100 nm) is limited by exciton coupling losses to doped regions.
• The second emission maximum (at ~300 nm) is primarily limited by wave-guided optical modes.

Conclusions:

• The optical performance of LECs is strongly dependent on active layer thickness and the interplay between doped regions and the emissive layer.
• Minimizing optical losses through careful device design, particularly active layer thickness, is key to achieving high-efficiency LECs.
• Understanding specific loss mechanisms, such as exciton coupling and wave-guiding, enables targeted optimization strategies for LECs.