EL Element Microrelief Structure for Light Extraction
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Solution Overview
Problem
Conventional EL elements suffer from low light extraction efficiency due to total reflection at the interface with air, with existing uneven patterns not optimizing light extraction efficiency and causing anisotropic light dispersion.
Innovation Solution
A microstructure with convex or concave parts of specific shapes is applied to the EL element, featuring a circular bottom surface with a generatrix that monotonically reduces or increases in height, optimizing light extraction efficiency by improving the light extraction efficiency and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat light emission plane is used, then the device structure is simple, but the light extraction efficiency is low (less than 20%) due to total reflection at the interface with air
Solution Approach 1:
The patent applies curvature by forming convex parts with spherical caps or hemispherical shapes on the light emission plane. This curvature modifies the interface geometry between the EL element and air, enabling light rays that would otherwise undergo total reflection to be redirected at angles that allow extraction. The spherical/hemispherical geometry creates gradual refraction transitions that reduce the abrupt refractive index mismatch, thereby improving light extraction efficiency while maintaining manufacturing feasibility through molding or embossing techniques.
2Illumination intensity
If stripe-shaped uneven patterns are formed on the light emission plane, then the front direction luminance is improved, but the light dispersion becomes anisotropic causing unevenness of light reflection
Solution Approach 1:
The patent transitions from uniform stripe patterns to a hybrid structure where spherical caps are selectively positioned on certain stripes while other stripes remain flat or have different configurations. This local differentiation allows specific regions to optimize for forward luminance enhancement while other regions maintain uniform light distribution. The selective application of convex structures on individual stripes creates localized light extraction enhancement without imposing global anisotropic dispersion patterns.
Solution Approach 2:
The patent introduces asymmetry by varying the stripe configurations - some stripes have convex parts with spherical caps while others have different profiles or spacing. This asymmetric arrangement within the periodic stripe structure breaks the uniformity that causes anisotropic dispersion, allowing light to be extracted more uniformly in lateral directions while still maintaining enhanced forward luminance through the convex structures on selected stripes.
3Loss of energy
If convex parts with triangular or semicircular cross sections are used, then the light extraction efficiency is improved compared to flat surfaces, but these shapes are not optimal for maximizing light extraction efficiency
Solution Approach 1:
The patent systematically varies geometric parameters of the convex parts, specifically exploring different cross-sectional profiles (triangular, semicircular, and spherical cap shapes) and their dimensions. By changing the shape parameters and comparing light extraction efficiency for each configuration, the patent identifies that spherical caps provide superior performance. The parameter optimization includes adjusting the radius of the spherical cap, the base diameter, and the height to maximize light extraction while considering manufacturing constraints.
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 microstructure enhances light extraction efficiency by 2.26 times or more compared to conventional flat light emission planes, with convex parts showing excellent extraction efficiency and concave parts offering improved durability.
Implementation Method 1
The members constituting the EL element have a higher refractive index than air. Thus, although having the advantages as described above, the EL element has a problem in which total reflection easily occurs at an interface between the EL element and an air layer
Implementation Method 2
the EL element has a problem in which total reflection easily occurs at an interface between the EL element and an air layer when the emitted light exits from the EL element
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3(a)~3(b)
AI summary
Provided is a microstructure for electroluminescent (EL) elements which has superior light extraction efficiency. The microstructure for EL elements comprises a plurality of microconvexities (a) having circular bottom surfaces (p). Each microconvexity (a) has a peak (q) on a perpendicular line from the centre of the circular bottom surface (p), and is defined by a generatrix dropped from the peak (q) to the circumference of the bottom surface (p). The height of the generatrix of each convexity (a) is monotonically reduced from the peak (q) to the circumference of the bottom surface (p). The height of the peaks (q) of the convexities (a) is 0.67-1.15 times the radius of the bottom surfaces (p). The height of the convexities (a) at the position on the radius of the bottom surface (p) 3/4 away from the centre of the bottom surface (p) is 0.21-0.65 times the radius of the bottom surface (p). The height of the convexities (a) at the position on the radius of the bottom surface (p) 9/10 away from the centre of the bottom surface (p) is 0.04-0.38 times the radius of the bottom surface (p).