OLED Nanocomposite Gradient-Index Layer for Light Extraction

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Solution Overview

Problem

Current OLED lighting technologies suffer from low light extraction efficiency due to refractive index mismatches at various interfaces, leading to significant light loss through Fresnel reflection and total internal reflection, with external light extraction methods only addressing losses at the glass/air interface and not effectively addressing losses at other interfaces.

Innovation Solution

An internal light extraction scheme utilizing a nanocomposite gradient-index layer sparsely embedded with light scattering centers, achieved by varying the concentration of ZrO2 nanocrystals dispersed in an acrylic polymer, which suppresses Fresnel reflection and allows for targeted light scattering, enhancing light extraction efficiency without compromising surface quality or increasing processing complexity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If external light extraction structures (surface roughening or periodic structures) are applied to the substrate, then light extraction at the glass/air interface is improved, but light loss at the ITO/glass interface remains unaddressed and overall light extraction efficiency is limited to approximately 40%

Engineering Contradiction:

Improvelight extraction efficiencyVSAvoidinterface structure complexity

Core Design Contradiction:

Illumination intensityVSDevice complexity

Solution Approach 1:

The invention divides the light extraction problem into multiple interfaces by introducing intermediate layers with gradient refractive indices between the ITO electrode and glass substrate, and between the glass substrate and air. Each layer handles a specific interface's light extraction, transforming a single-interface problem into a multi-layer solution that addresses all light loss locations simultaneously.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces intermediate layers with refractive indices that are intermediate values between the adjacent layers (e.g., between ITO and glass, or between glass and air). These intermediary layers act as optical mediators that gradually transition the refractive index, reducing abrupt mismatches and enabling effective light extraction at multiple interfaces without requiring complex surface structures.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Illumination intensity

If high concentration of light scatters is used at the interface to generate sufficient light scattering events, then light extraction is improved, but unnecessary scattering of light within the acceptance cone occurs and surface quality deteriorates

Engineering Contradiction:

Improvelight extraction efficiencyVSAvoidsurface quality

Core Design Contradiction:

Illumination intensityVSManufacturing precision

Solution Approach 1:

The invention applies different light scattering characteristics to different regions and depths of the coating. The gradient-index layers provide controlled refraction at specific locations, while sparse light scatterers are distributed selectively to provide localized scattering only where needed. This local differentiation allows effective light extraction without excessive scattering throughout the entire structure, preserving surface quality.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the refractive index parameter continuously through gradient-index layers, transitioning from one material property to another in a controlled manner. This parameter change enables light to be guided and scattered at specific interfaces without requiring high concentrations of scattering particles, thereby maintaining surface quality while achieving effective light extraction.

Inventive Principle:

Principle #35Parameter changes

3Illumination intensity

If a high refractive index coating is applied to enhance light extraction, then Fresnel reflection is suppressed, but the coating thickness and material composition become more complex

Engineering Contradiction:

Improvelight extraction efficiencyVSAvoidcoating structure complexity

Core Design Contradiction:

Illumination intensityVSDevice complexity

Solution Approach 1:

Instead of using a single abrupt high refractive index layer, the patent employs gradient-index layers where the refractive index changes continuously or in gradual steps. This parameter transition achieves the same light extraction benefit as a abrupt high-RI coating while distributing the optical effect across multiple thinner layers, reducing overall structural complexity and enabling better integration with existing OLED manufacturing processes.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention uses composite structures combining gradient-index polymer layers with sparsely distributed light-scattering particles. This composite approach achieves effective light extraction through the combination of refractive index gradient (suppressing Fresnel reflection) and controlled scattering (redirecting light), while avoiding the need for thick or complex single-material coatings.

Inventive Principle:

Principle #40Composite materials

4Illumination intensity

If light scatterers are introduced at the interface to extract light, then light extraction is improved, but processing complexity increases due to the need for additional smoothing layers to prevent current leakage

Engineering Contradiction:

Improvelight extraction efficiencyVSAvoidmanufacturing process simplicity

Core Design Contradiction:

Illumination intensityVSEase of manufacture

Solution Approach 1:

The patent merges the light extraction function with the existing encapsulation coating layers. The gradient-index layers and light scatterers are incorporated into the encapsulation structure itself, combining multiple functions (protection, light extraction, and electrical isolation) into a single integrated layer system. This eliminates the need for separate smoothing layers and reduces the number of processing steps while maintaining surface quality and preventing current leakage.

Inventive Principle:

Principle #5Merging (Combining)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The gradient-index layer effectively increases light extraction efficiency by bending light rays outside the acceptance cone back into the device, reducing unnecessary scattering and improving the overall performance of OLED lighting devices while maintaining high refractive index and transparency.

Implementation Method 1

a gradient-refractive index profile (or a discreet approximation, i.e. thin layers with small index changes) can significantly suppress Fresnel reflection

Methodology Applied

Scientific EffectFresnel reflection: Reflection

Implementation Method 2

Incorporating a gradient-index offers two main benefits: First, a gradient-refractive index profile (or a discreet approximation, i.e. thin layers with small index changes) can significantly suppress Fresnel reflection

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 3

the concentration of the light scatters has to be large at the interface, which scatters light indiscriminately, resulting in the unnecessary scattering of the light that is within the cone of acceptance

Methodology Applied

Scientific EffectLight scattering: Scattering