Electroluminescent Device Light-Scattering Layer
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Solution Overview
Problem
Electroluminescent (EL) devices suffer from inefficiencies in extracting photons generated by electron-hole recombination due to high optical indices of materials, leading to significant light trapping and absorption, resulting in reduced light output and contrast, especially under diffuse illumination.
Innovation Solution
Incorporating a light-scattering layer with a volume ratio of light-scattering particles between 0.55 and 0.75 between the substrate and cover, comprising transparent particles with a higher refractive index than the surrounding layers, to scatter trapped high-angle light and enhance light extraction without affecting color or luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional EL device structure is used with high optical index materials, then the device structure is simple and manufacturing is easier, but light extraction efficiency is poor due to light trapping and absorption
Solution Approach 1:
A light-scattering layer is introduced as an intermediary component between the EL unit and the cover. This layer contains transparent light-scattering particles with a refractive index higher than surrounding layers, which mediate the light extraction process by scattering trapped high-angle light and redirecting it toward extraction paths, thereby improving light extraction efficiency without complicating the overall device structure
Solution Approach 2:
The patent optimizes the volume ratio of light-scattering particles in the light-scattering layer to be between 0.55 and 0.75. This parameter change ensures sufficient light scattering effect while maintaining appropriate optical properties. Additionally, the refractive index of the scattering particles is specifically selected to be higher than surrounding layers to maximize the scattering effect and improve light extraction
2Illumination intensity
If a light-scattering layer with high particle volume ratio is used to improve light extraction, then light output increases, but absorption losses may increase and sharpness in pixellated applications may deteriorate
Solution Approach 1:
The patent precisely optimizes the volume ratio of light-scattering particles to be between 0.55 and 0.75. This parameter optimization achieves the right balance: sufficient scattering to extract trapped light and improve overall light output, while avoiding excessive scattering that would cause image degradation and loss of sharpness in pixellated displays
Solution Approach 2:
The light-scattering layer is positioned specifically between the EL unit and the cover, creating a localized scattering region. The scattering particles are transparent and have higher refractive index than surrounding layers, which allows selective scattering of trapped light while maintaining optical quality and sharpness in the displayed image
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 solution significantly increases light output and maintains sharpness in pixellated applications by effectively redirecting trapped light, improving brightness and contrast while minimizing absorption losses.
Implementation Method 1
a light-scattering layer is located between the substrate and cover. The light-scattering layer includes transparent, light-scattering particles, wherein the ratio of the volume of light-scattering particles to the volume of the light-scattering layer is between 0.55 and 0.75
Implementation Method 2
comprising transparent particles with a higher refractive index than the surrounding layers, to scatter trapped high-angle light
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
An electroluminescent (EL) device that includes a light-emitting area formed over a substrate ( 10). First (12) and second electrodes (16) and one or more EL unit(s) (14) are included along with at least one light-emitting layer formed between the electrodes, wherein at least one electrode is transparent. A cover (20) is located oyer the light-emitting area, and a light-scattering layer (22) is located between the substrate and cover. The light-scattering layer includes transparent, light-scattering particles (23), wherein the ratio of the volume of light-scattering particles to the volume of the light-scattering layer is greater than 0.55 over a majority of the light-emitting area, wherein either the substrate or cover is transparent and transmits light emitted from the EL unit(s).