OLED Passivation Layer Nanoparticles for Light Extraction

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Solution Overview

Problem

The existing organic light emitting diode (OLED) display devices suffer from low external quantum efficiency due to light loss caused by total reflection at interfaces with different refractive indices, resulting in only about 20% of emitted light being extracted for image display, with approximately 40% being dissipated in the waveguide mode.

Innovation Solution

Incorporating a passivation layer with polymeric nanoparticles having a refractive index that decreases towards the center, specifically a double-layer structure with a silica nucleus and a polystyrene shell, to refract light emitted from the emission layer and improve external light extraction efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a conventional passivation layer with uniform refractive index is used, then the device structure is simple, but light extraction efficiency is low due to total reflection at interfaces

Engineering Contradiction:

Improvestructure simplicityVSAvoidlight extraction efficiency

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The passivation layer is divided into multiple regions with different refractive indices: a first region with refractive index n1, a second region with refractive index n2 (where n1 < n2), and a third region with refractive index n3 (where n2 < n3). This local variation in refractive index allows different parts of the light to be extracted through different regions, significantly improving overall light extraction efficiency while maintaining a relatively simple layered structure.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The passivation layer uses a composite structure combining materials with different refractive indices in a layered arrangement. This composite approach creates multiple refraction interfaces that work together to extract light more effectively than a single uniform material could achieve, resolving the contradiction between structural simplicity and light extraction performance.

Inventive Principle:

Principle #40Composite materials

2Ease of manufacture

If the refractive index is uniform throughout the passivation layer, then manufacturing is easier, but approximately 40% of light is dissipated in waveguide mode

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidwaveguide mode loss

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

By creating local variations in refractive index through the layered structure (n1 < n2 < n3), the patent prevents waveguide mode formation that occurs with uniform refractive indices. Each layer with different refractive index acts to scatter and redirect light that would otherwise be trapped in waveguide modes, reducing the 40% loss while keeping the manufacturing process relatively straightforward.

Inventive Principle:

Principle #3Local quality

3Loss of energy

If a multi-layer passivation structure with varying refractive indices is implemented, then light extraction efficiency increases to 50% or more, but device complexity increases

Engineering Contradiction:

Improvelight extraction efficiencyVSAvoidpassivation layer structure

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The passivation layer is segmented into three distinct regions with progressively increasing refractive indices. This segmentation allows each region to perform a specific function in light extraction, achieving over 50% light extraction efficiency. The segmented structure is more complex than a uniform layer but remains manageable through systematic material selection and layering.

Inventive Principle:

Principle #1Segmentation

4Loss of energy

If all light paths including total reflection paths are utilized, then external quantum efficiency is maximized, but color clarity may be compromised

Engineering Contradiction:

Improveexternal quantum efficiencyVSAvoidcolor clarity

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

Different regions of the passivation layer extract light at different angles and through different optical paths. The layered structure with varying refractive indices allows for controlled light extraction that maximizes external quantum efficiency while the systematic arrangement helps maintain color clarity by preventing excessive mixing of light paths.

Inventive Principle:

Principle #3Local quality

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

This approach enhances the extraction efficiency of external light to 50% or more by utilizing all light paths, including those previously lost to total reflection, thereby improving luminance and reducing color clarity issues.

Implementation Method 1

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentEP3136464B1Organic light emitting diode display device and method of fabricating the same

Publication Date: 2022.02.16 LG DISPLAY CO LTD

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AI summary

An organic light emitting diode display device includes a first substrate, a thin film transistor on the first substrate, a protection layer on the thin film transistor, a light emitting diode on the protection layer, a passivation layer on the light emitting diode, a second substrate on the passivation layer, and a plurality of polymeric nanoparticles disposed within at least one of the protection layer or the passivation layer , wherein at least one of the polymeric nanoparticles comprises a structure having multiple layers, and wherein a refractive index decreases toward a center of the structure.