Light Extraction Sheet Refractive Index Bridge
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Solution Overview
Problem
Conventional organic electroluminescence (EL) devices suffer from limited light extraction efficiency due to total reflection and light absorption at interfaces with high refractive indices, resulting in significant loss of emitted light, which is also a challenge for other light-emitting diodes and illuminators.
Innovation Solution
A light extraction sheet with a low-refractive index layer and a high-refractive index layer having a bump-dent structure is implemented between the light-emitting element and the transparent substrate, combined with a diffusing layer or microlens array on the external surface to enhance light transmission and extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a high refractive index material is used in the light emission layer and surrounding structures, then the light emission intensity is enhanced, but total reflection occurs at interfaces causing significant light loss
Solution Approach 1:
A low refractive index layer (refractive index 1.3-1.6) is introduced as an intermediary between the high refractive index light emission layer (refractive index 1.7-2.0) and the transparent substrate. This intermediate layer acts as a refractive index bridge, reducing the abrupt refractive index difference at interfaces and thereby suppressing total reflection while maintaining the light emission enhancement benefits of high refractive index materials.
Solution Approach 2:
The patent optimizes the thickness of the low refractive index layer to be in the range of 50-500 nm, and controls the refractive index difference between layers. By adjusting these parameters (thickness and refractive index values), the patent achieves optimal balance between suppressing total reflection and maintaining light emission intensity, demonstrating parameter optimization to resolve the contradiction.
2Loss of energy
If conventional light extraction structures are added to improve light extraction efficiency, then light extraction efficiency is enhanced, but the device structure becomes more complex
Solution Approach 1:
The patent combines the low refractive index layer with the transparent substrate to form an integrated light extraction sheet structure. This merging approach integrates the light extraction function directly into the substrate, eliminating the need for separate, complex light extraction components while achieving improved light extraction efficiency through the refractive index gradient design.
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 improves light extraction efficiency by reducing total reflection and enhancing light transmission, particularly for light incident at angles between 60 degrees and 80 degrees, leading to higher luminance and longer lifespan of light-emitting devices.
Implementation Method 1
total reflection may occur at interfaces between different refractive indices and light may be absorbed by the material(s)
Implementation Method 2
The light extraction sheet includes a low-refractive index layer and a high-refractive index layer having a higher refractive index than does the low-refractive index layer
Implementation Method 3
a first light extraction structure on the first face side of the light-transmitting substrate, the first light extraction structure including a low-refractive index layer and a high-refractive index layer having a higher refractive index than does the low-refractive index layer, the low-refractive index layer being between the light-transmitting substrate and the high-refractive index layer, and an interface between the high-refractive index layer and the low-refractive index layer having bump-dent features
Data Source
AI summary
An illuminator includes a light-emitting element and a light extraction sheet which transmits light occurring from the light-emitting element. The light-emitting element includes a first electrode having a light transmitting property, a second electrode, and an emission layer between the first and second electrodes. The light extraction sheet includes a light-transmitting substrate having a first face and a second face, a first light extraction structure on the first face side of the light-transmitting substrate, and a second light extraction structure on the second face side of the light-transmitting substrate. The first light extraction structure includes a low-refractive index layer and a high-refractive index layer having a higher refractive index than the low-refractive index layer. The second light extraction structure is arranged so that light which is transmitted through the light-transmitting substrate and arrives at an incident angle of 60 to 80 degrees has an average transmittance of 20% or more.