Organic Electroluminescence Element Light Extraction Layer Design

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Solution Overview

Problem

Existing organic electroluminescence elements face low light-outcoupling efficiency due to total reflection at interfaces with different refractive indices and absorption, leading to poor luminance and short lifespan, especially when dealing with multiple light emitting layers and broad spectrum emissions, which cause chromaticity deviations and view angle dependence issues.

Innovation Solution

The organic electroluminescence element incorporates a substrate with a light diffusion layer, a light transmissive electrode, a light reflective electrode, and multiple light emitting layers, where the light emitting layers are optimized with specific phase shifts and refractive indices to enhance light extraction, using a weighted average emission wavelength and phase shift expression to position the light emitting layers for maximum light interference and reduced view angle dependence.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If multiple light emitting layers are stacked to increase luminance and efficiency, then luminance and lifespan are improved, but light-outcoupling efficiency deteriorates due to increased total reflection loss at multiple interfaces

Engineering Contradiction:

ImproveluminanceVSAvoidlight-outcoupling efficiency

Core Design Contradiction:

Illumination intensityVSLoss of energy

Solution Approach 1:

A light extraction layer is introduced as an intermediary between the light emitting layers and the substrate. This layer has a refractive index that is lower than the light emitting layer and higher than the substrate, creating a gradient that reduces total reflection loss and improves light extraction efficiency while maintaining high luminance from multiple stacked layers

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of energy

If diffraction gratings are used to extract more light, then light-outcoupling efficiency is improved for specific wavelengths and directions, but chromaticity deviation and view angle dependence worsen for broad spectrum emissions

Engineering Contradiction:

Improvetotal reflection lossVSAvoidchromaticity uniformity

Core Design Contradiction:

Loss of energyVSEase of manufacture

Solution Approach 1:

Instead of using diffraction gratings that work for specific wavelengths, the invention changes the refractive index parameter by introducing a light extraction layer with intermediate refractive index. This approach works effectively across the broad spectrum without causing chromaticity deviation or view angle dependence issues

Inventive Principle:

Principle #35Parameter changes

3Illumination intensity

If interference is used to maximize light component in frontal direction, then light extraction is improved for specific angles, but overall light-outcoupling efficiency worsens because not all rays are extracted

Engineering Contradiction:

Improvefrontal light componentVSAvoidoverall light extraction

Core Design Contradiction:

Illumination intensityVSLoss of energy

Solution Approach 1:

The light extraction layer provides localized refractive index optimization at each interface between light emitting layers and the substrate. This creates favorable conditions for light extraction at multiple locations and angles simultaneously, not just in the frontal direction, thereby improving overall light-outcoupling efficiency

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 configuration significantly increases light extraction efficiency and reduces view angle dependence, resulting in improved luminance and extended lifespan of the organic electroluminescence elements by effectively managing light interference and refractive index differences.

Implementation Method 1

a light diffusion layer on a surface of the substrate

Methodology Applied

Scientific EffectLight scattering: Scattering

Implementation Method 2

a light reflective electrode paired with the light transmissive electrode

Methodology Applied

Scientific EffectLight reflection: Reflection

Implementation Method 3

light is produced in an organic light emitting layer in response to application of voltage between the anode and the cathode, and the produced light passes through the transparent electrode and the transparent substrate and emerges outside

Methodology Applied

Scientific EffectLight transmission: Refraction

Data Source

PatentUS9379359B2Organic electroluminescence element and lighting device using same

Publication Date: 2016.06.28 SAMSUNG DISPLAY CO LTD

AI summary

The present disclosure relates to an organic electroluminescence element including: a substrate having a light transmissive property; a light diffusion layer; a light transmissive electrode; a light reflective electrode; and a light emitting layer. With regard to the first light emitting layer being the first closest light emitting layer to the light reflective electrode, the relation defined by following expression (2) is satisfied,⁢[FORMULA⁢⁢1]ϕ⁡(λm)×λm4⁢π+l+0.12⁢λm≤nm⁡(λm)×dm≤ϕ⁡(λm)×λm4⁢π+l+0.52⁢λm(2)wherein, λm represents the weighted average emission wavelength, Ø(λm) represents the phase shift, nm(λm) represents the average refractive index of a medium filling a space between the light reflective electrode and the first light emitting layer, and dm represents the distance from the light reflective electrode to the first light emitting layer. m is equal to 1.1 is an integer equal to or more than 0.