Organic Electroluminescence Element Light Extraction
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Solution Overview
Problem
Organic electroluminescence elements suffer from low light extraction efficiency due to the non-directive nature of light emission from the light emission layer, resulting in insufficient light output and dark images, as only 15-20% of emitted light can be extracted due to total internal reflection and scattering, with existing methods like concavity on substrates or diffraction gratings being costly and prone to defects.
Innovation Solution
Employing a transparent resin film with hard coat layers on both sides, where the refractive indices of the hard coat layers are balanced to minimize reflections, and incorporating light scattering fillers to enhance light extraction efficiency while maintaining film properties like abrasion resistance and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a transparent substrate with conventional structure is used, then the element structure is simple, but the light extraction efficiency is low (only 15-20% of light can be extracted)
Solution Approach 1:
The patent introduces a transparent resin film as an intermediary layer between the substrate and the light emission layer. This resin film has a refractive index (1.3-1.6) lower than both the substrate (1.5-1.7) and the light emission layer (1.7-2.1), acting as a mediator to reduce total internal reflection and improve light extraction efficiency to 30% or more while maintaining structural simplicity
Solution Approach 2:
The patent changes the refractive index parameter of the substrate system by using a transparent resin film with specifically controlled refractive index (1.3-1.6). This parameter change creates optimal conditions for reducing total internal reflection at interfaces, thereby improving light extraction efficiency without complicating the overall structure
2Illumination intensity
If the refractive index of the light emission layer is high (1.7-2.1), then the light emission intensity is high, but the light extraction efficiency decreases due to total internal reflection
Solution Approach 1:
The transparent resin film serves as an intermediary layer with refractive index (1.3-1.6) lower than the light emission layer (1.7-2.1). This intermediary structure reduces the refractive index difference at the interface, minimizing total internal reflection and enabling more light to escape while preserving the high emission intensity characteristics of the light emission layer
3Reliability
If a transparent resin film with hard coat layers is used to improve durability, then the abrasion resistance and adhesion are improved, but the refractive index matching becomes more complex
Solution Approach 1:
The patent segments the protective structure into distinct functional layers: a transparent resin film base layer and hard coat layers applied on its surfaces. This segmentation allows the base layer to provide optical functions (refractive index matching) while the hard coat layers provide mechanical protection, with each layer optimized for its specific function
Solution Approach 2:
The patent creates a composite structure combining the transparent resin film with hard coat layers. The transparent resin film provides optimal refractive index (1.3-1.6) for light extraction, while the hard coat layers provide enhanced abrasion resistance and adhesion. The composite structure achieves both optical performance and mechanical durability
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 improves light extraction efficiency and film properties, allowing for higher luminance with reduced power consumption and improved durability of the organic electroluminescence element.
Implementation Method 1
each refractive index of the hard coat layers satisfies Expressions (1)-(4)... the transparent substrate has a function to scatter aa light to the light emission side
Implementation Method 2
only 15 to 20% of the light emitted in the light emission layer can be extracted. This is because light which enters a boundary (a boundary between a transparent substrate and the atmosphere) at an angle θ larger than a critical angle is totally reflected
Implementation Method 3
the transparent substrate has a function to scatter aa light to the light emission side with respect to the organic electroluminescence layer
Implementation Method 4
an electron and a hole were injected into the light emission layer and recombined to form an exciton. The element emits light, utilizing light (fluorescent light or phosphorescent light) generated by inactivation of the exciton
Data Source
AI summary
Disclosed are an organic electroluminescence element with significantly improved light extraction efficiency and improved film properties and an illumination device that uses said element. The organic electroluminescence element has a transparent electrode, an organic electroluminescence layer, and a cathode sequentially stacked on a transparent base material. The element is characterized in that the transparent base material is a transparent resin film, there is a hard coat layer on both sides, the respective refractive indices satisfy the expressions (1)-(4), and there is a function to scatter light to the light emission side with respect to the organic electroluminescence layer. Expression (1): −0.2≦n(H1)−n(A)≦0.2, Expression (2): −0.1≦n(H1)−n(B)≦0.1, Expression (3): −0.1≦n(H2)−n(B)≦0.1, Expression (4): −0.1≦n(H1)−n(H2)≦0.1. In the expressions, n(A) is the refractive index of the transparent electrode; n(H1) is the refractive index of the hard coat layer (on the transparent electrode side); n(H2) is the refractive index of the hard coat layer (on the side opposite the transparent electrode); and n(B) is the refractive index of the transparent resin film.