Light Scattering Layer for Evanescent Light Extraction

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Solution Overview

Problem

Electroluminescent elements, such as organic and inorganic ELs, face inefficiencies in light output due to total internal reflection, with existing diffraction grating techniques only improving brightness by 1.2 to 1.7 times and risking damage to electrode and light emitting layers during processing.

Innovation Solution

A light emitting element with a light scattering layer on the transparent electrode, featuring a relief structure and refractive index differences to scatter evanescent light, allowing for efficient output without damaging the electrode or light emitting layers, even in top emission structures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If diffraction gratings are provided at interfaces to improve light output efficiency, then light output efficiency is improved, but electrode layers and light emitting layers may become damaged when forming the diffraction gratings

Engineering Contradiction:

Improvelight output efficiencyVSAvoidintegrity of electrode and light emitting layers

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

A light scattering layer is introduced as an intermediary component between the transparent electrode and the light emitting layer. This light scattering layer contains scattering particles that scatter evanescent light without requiring direct processing of the electrode or light emitting layers, thereby improving light output efficiency while maintaining the integrity of the underlying layers.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention replaces the mechanical etching process used to form diffraction gratings with a non-contact optical approach using light scattering particles. Instead of mechanically removing material to create diffraction structures, the patent uses scattered light from particles to achieve the same light extraction effect, eliminating the risk of mechanical damage.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Ease of manufacture

If diffraction gratings are formed by etching to change optical paths, then totally internally reflected light can be output, but the processing may damage electrode and light emitting layers

Engineering Contradiction:

Improvelight extraction capabilityVSAvoiddamage to electrode and light emitting layers

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The light scattering layer acts as an intermediary that enables light extraction without direct processing of the electrode or light emitting layers. The scattering particles in this layer modify the optical paths of evanescent light through scattering effects, achieving the desired light extraction capability while avoiding harmful processing of the underlying sensitive layers.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention uses inorganic particles such as TiO2 or SiO2 as disposable light scattering elements. These particles are deposited as a separate layer that can be easily applied and removed if necessary, providing a temporary but effective solution for light extraction without permanently modifying or damaging the electrode and light emitting layers.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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

Significantly enhances light output efficiency by scattering trapped evanescent light, achieving higher output without processing the electrode layers, thus improving brightness without structural damage.

Implementation Method 1

light which enters an interface between layers at a critical angle or greater is totally internally reflected and trapped within the element

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 2

a light scattering layer provided on the surface of the light transmitting electrode, for scattering evanescent light which is generated at the surface

Methodology Applied

Scientific EffectLight scattering: Scattering

Implementation Method 3

the light scattering layer having a first scattering portion having an relief structure and a refractive index lower than the refractive index of the light emitting layer

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS9887388B2Electroluminiscent element having a high effient light output

Publication Date: 2018.02.06 UDC IRELAND

AI summary

A light emitting element includes an anode, a light transmitting cathode, and a light emitting layer sandwiched therebetween, formed on a surface of a substrate. Light emitted by the light emitting layer by voltage being applied between the electrodes is output from a surface toward the side of the light transmitting electrode. A light scattering layer for scattering evanescent light generated at the surface is provided on the surface of the light transmitting electrode. The light scattering layer has a first scattering portion having an uneven structure and a lower refractive index than the light emitting layer, and second scattering portions that fill at least the bottoms of recesses of the uneven structure and has a different refractive index from the first scattering portion. The distance between the bottoms of the recesses and the surface of the light transmitting electrode is a seepage depth of the evanescent light or less.