Porous Scattering Layer Technology for Enhancing Light Extraction and Efficiency in Thin-Film Photonic Devices

Background

Thin-film photonic devices, such as organic light-emitting diodes (OLEDs), have become central to modern lighting and display technologies due to their ability to produce high-quality, energy-efficient light from compact, flexible form factors. These devices have achieved remarkable internal quantum efficiencies, approaching theoretical limits, thanks to advances in organic materials and device engineering. However, the practical utility of these devices is constrained by their limited ability to extract light generated within the device structure. This inefficiency arises primarily from the inherent planar geometry and the complex stack of materials with differing refractive indices, which cause a significant portion of the generated light to become trapped within the device layers through mechanisms such as total internal reflection and waveguiding. As a result, only a fraction of the produced light escapes to contribute to visible emission, limiting the overall energy efficiency and brightness of OLED-based products.

Current approaches to improving light extraction in thin-film photonic devices face several challenges. Conventional methods, such as micro-lens arrays, surface texturing, or low-index grids, often require complex fabrication processes that are difficult to scale and may not be compatible with flexible substrates or large-area manufacturing. Additionally, these techniques can introduce unwanted optical artifacts, degrade color stability across viewing angles, or add significant cost to the final device. Many existing solutions also fail to address the fundamental issue of refractive index mismatch within the device, resulting in persistent light trapping and suboptimal angular emission profiles. Consequently, there remains a pressing need for a scalable, cost-effective solution that can efficiently redirect trapped light into usable modes without compromising device integrity or display quality.

Technology

This technology centers on a specially engineered scattering layer designed to significantly enhance light extraction in thin-film photonic devices such as OLEDs and WOLEDs. The layer is constructed by laminating a porous film—composed of a high-refractive-index host medium like polyimide embedded with low-refractive-index voids (air pockets)—onto a substrate of glass or plastic. The large refractive index contrast (greater than 0.5) between the host medium and the voids creates efficient scattering centers that redirect light otherwise trapped within the device layers into extractable modes. The porous film can be fabricated via two scalable methods: a phase inversion process, where a polymer precursor is coated and then immersed in an antisolvent to induce phase separation and void formation, or by physically entrapping air bubbles in a polymer solution followed by curing. The resulting film, with thicknesses from 100 nm to 100 μm and voids ranging from nanometers to microns, exhibits high optical haze and minimal absorption, making it highly effective for light management.

What differentiates this technology is its ability to dramatically boost the external quantum efficiency and power efficiency of photonic devices without complex or costly modifications to the device architecture. By leveraging the strong refractive index contrast and hierarchical porous structure, the scattering layer efficiently converts substrate-trapped and waveguided light into useful emission, as demonstrated by up to 65% EQE and 77% power efficiency improvements in green OLEDs, and similar gains in WOLEDs. Additionally, the technology improves angular emission profiles to approach the ideal Lambertian distribution and stabilizes color output across viewing angles—both critical for premium lighting and display performance. Its compatibility with both rigid and flexible substrates, as well as solution-processed and quantum dot-based devices, underscores its versatility and scalability, offering a practical solution to the persistent challenge of light extraction in planar thin-film photonic devices.

Benefits

• Significantly increases external quantum efficiency (EQE) and power efficiency (PE) in OLEDs and WOLEDs (up to ~65% and ~78% improvements respectively)
• Enhances light extraction by redirecting trapped light into extractable modes through strong refractive index contrast scattering
• Improves angular emission profile toward a Lambertian distribution, providing more uniform viewing angles
• Enhances color stability and consistency across viewing angles, critical for lighting and display quality
• Employs scalable and versatile fabrication methods (phase inversion and air bubble entrapment) compatible with flexible or rigid substrates
• Maintains minimal optical absorption losses due to low extinction coefficients of the porous scattering layer
• Applicable to a wide range of thin-film photonic devices including OLEDs, WOLEDs, and quantum dot LEDs for lighting and display applications

Applications

• OLED display panels
• White OLED lighting panels
• Quantum dot LED lighting
• Flexible display devices

Additional info

A light extraction layer for thin-film photonic devices comprises a substrate supporting a porous film. This film features a high-refractive-index host medium embedded with low-index voids, creating a refractive index contrast exceeding 0.5. This structure effectively scatters trapped light, significantly boosting external quantum efficiency, power efficiency, and angular emission uniformity.