Analysis and optimization of light outcoupling in OLEDs with external hierarchical textures

Area of Science:

• Materials Science
• Optoelectronics
• Nanotechnology

Background:

• Organic light-emitting diodes (OLEDs) are crucial for displays and lighting.
• Improving light outcoupling efficiency in OLEDs is essential for device performance.
• External outcoupling solutions are needed to overcome internal light loss mechanisms.

Purpose of the Study:

• To investigate hierarchical textures as an external outcoupling solution for OLEDs.
• To experimentally fabricate and optically simulate hierarchical textures.
• To evaluate the efficiency enhancement potential of hierarchical textures in large-area OLED devices.

Main Methods:

• Fabrication of hierarchical textures using laser-based methods and replication.
• Application of textured foils to OLED substrates.
• Optical simulations to model light outcoupling.
• Experimental characterization of OLED devices with and without textured foils.

Main Results:

• Hierarchical textures increased light outcoupling in red bottom-emitting OLEDs.
• Laboratory-scale devices showed smaller efficiency gains than predicted due to measurement limitations.
• Simulations predicted a potential 57% improvement in external quantum efficiency (EQE) for large-area devices.
• Optimized hierarchical textures achieved high efficiencies with less pronounced features than single textures.

Conclusions:

• Hierarchical textures are a promising approach for enhancing OLED light outcoupling.
• Device scale and measurement limitations affect observed efficiency gains.
• Parasitic absorption in the organic thin film stack is a key limiting factor for higher outcoupling.
• Further improvements are possible by addressing non-ideal reflections and optimizing substrate designs.