Light-Emitting Device With Intermediate Layer And Concavo-Convex Pattern
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Solution Overview
Problem
Light-emitting devices face low light-extraction efficiency due to total reflection at interfaces with significant refractive index differences, limiting the extraction of light emitted from high-refractive-index media to low-refractive-index media.
Innovation Solution
A light-emitting device structure featuring a light-emitting layer, an intermediate layer with a refractive index close to the light-emitting layer, and a fine concavo-convex pattern that reflects light emitted from the intermediate layer back into the light-emitting layer, reducing total reflection and enhancing light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a flat interface is used between layers with different refractive indices, then the device structure is simple, but total reflection occurs at interfaces with large refractive index differences, reducing light-extraction efficiency
Solution Approach 1:
The patent applies curvature by introducing a fine concavo-convex pattern on the interface between the light-emitting layer and intermediate layer. This curved/rough interface structure modifies light propagation paths, enabling light that would normally undergo total reflection at a flat interface to be scattered and extracted, thereby resolving the contradiction between structural simplicity and light-extraction efficiency.
Solution Approach 2:
The patent applies local quality by creating a non-uniform interface structure where only specific regions have concavo-convex patterns. This localized modification allows light extraction enhancement at critical interfaces without requiring complete structural redesign, balancing complexity and performance.
2Illumination intensity
If the refractive index difference between adjacent layers is large, then the optical contrast is high, but total reflection increases, reducing light extraction
Solution Approach 1:
The patent introduces an intermediate layer with refractive index n4 that acts as an optical intermediary between the light-emitting layer (n3) and the seal layer (n2). This intermediate layer reduces the abrupt refractive index difference, minimizing total reflection while maintaining optical contrast through the fine concavo-convex pattern that enhances light extraction at the n3-n4 interface.
3Device complexity
If conventional light extraction structures are used, then the device structure is simple, but light emitted at angles greater than the critical angle is totally reflected, limiting light extraction efficiency
Solution Approach 1:
The fine concavo-convex pattern creates multiple local interfaces with varying angles, allowing light emitted at various angles (including those greater than the critical angle for flat interfaces) to find extraction paths. This curved interface structure converts angular-dependent total reflection into angle-independent scattering and extraction.
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 proposed structure significantly improves light-extraction efficiency by minimizing total reflection and allowing more light to be emitted from the device, as demonstrated by the examples showing increased light quantity ratios compared to devices without the fine concavo-convex pattern.
Implementation Method 1
Light-emitting devices in which light is totally reflected when being emitted from a high-refractive-index medium to a low-refractive-index medium pose a problem in that the light-extraction efficiency is low
Implementation Method 2
when the interface is flat, the reflectivity depends on the incident angle of the light and the difference in refractive index between media which share the interface
Data Source
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AI summary
The present invention provides a light-emitting device which includes, in the order mentioned, a light-emitting layer containing a light-emitting portion, an intermediate layer, and a fine concavo-convex pattern, wherein the intermediate layer is disposed over a second surface of the light-emitting layer which surface is opposite to a first surface of the light-emitting layer, wherein the fine concavo-convex pattern has a cross-sectional shape which has portions projected and recessed with respect to the light-emitting layer, and reflects light emitted from the light-emitting layer, and wherein at least part of the intermediate layer has a refractive index of 0.9n to 1.1n, where n denotes a refractive index of the light-emitting portion with respect to light which has a main light-emitting wavelength.