Soft holographic interference lithography microlens for enhanced organic light emitting diode light extraction

Area of Science:

• Optoelectronics
• Materials Science
• Nanotechnology

Background:

• Organic light-emitting diodes (OLEDs) are crucial for displays and lighting.
• Enhancing light extraction efficiency is key to improving OLED performance and reducing power consumption.
• Current light extraction methods often face limitations in efficiency and scalability.

Purpose of the Study:

• To investigate the use of large-area microlens arrays (μLAs) for significantly enhancing light extraction from OLEDs.
• To explore the relationship between μLA design, size, and OLED pixel dimensions on light extraction efficiency.
• To demonstrate a cost-effective fabrication method for μLAs suitable for OLED integration.

Main Methods:

• Fabrication of uniform 2 μm-pitch square μLAs using soft lithography with a polydimethylsiloxane (PDMS) mold.
• Embossing μLAs onto the indium-tin-oxide (ITO)-coated glass substrate of OLED devices.
• Characterization of electroluminescence (EL) enhancement in green and blue OLEDs with integrated μLAs.
• Optical simulations incorporating absorption effects in organic and ITO layers.

Main Results:

• Achieved approximately 100% enhancement in forward-direction electroluminescence (EL) using μLAs significantly larger than OLED pixels (~15 × 15 mm² μLA for ~3 × 3 mm² OLED).
• A 19 × 25 mm² μLA enhanced EL from a 3 × 3 array of OLED pixels by 96%.
• Experimental results align with simulations, which predict a ~140% enhancement with 0.7 mm thick glass.

Conclusions:

• Large-area μLAs fabricated via economical soft lithography offer a highly effective method for enhancing OLED light extraction.
• The relative size of the μLA to the OLED pixel is a critical factor for maximizing light extraction.
• Further improvements in OLED efficiency are achievable through optimized μLA integration and substrate thickness reduction.