Light Emitting Device Transparent Sheet Surface Structure
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Solution Overview
Problem
Conventional light emitting devices employing organic electroluminescence elements face limitations in light extraction efficiency, with maximum efficiency capped at 1−cos θc, and suffer from issues like total reflection, ambient light reflection, and color imbalance due to diffraction grating and projection-based techniques.
Innovation Solution
A transparent sheet with a surface structure comprising minute regions of varying heights and depths, where the diameter of the largest inscribed circle ranges from 0.2 μm to 1.5 μm, randomly arranged to prevent total reflection and enhance light extraction efficiency, and a light emitting device incorporating this sheet to improve light extraction and reduce ambient light reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a diffraction grating or projection structure is used to improve light extraction efficiency, then light extraction efficiency is improved, but color imbalance and ambient light reflection occur
Solution Approach 1:
The patent divides the transparent substrate surface into multiple minute regions (0.2-1.5 μm diameter) with different heights and depths. This segmentation creates multiple scattering centers that randomize light extraction paths, preventing the directional bias and color imbalance associated with diffraction gratings while maintaining high extraction efficiency.
Solution Approach 2:
The patent employs asymmetric surface structures where minute regions have varying heights and depths rather than uniform projections. This asymmetry disrupts the periodicity required for diffraction, thereby eliminating color imbalance and ambient light reflection issues while still achieving enhanced light extraction through multiple scattering events.
2Illumination intensity
If the refractive index of the transparent substrate is increased to improve light emission, then light emission is enhanced, but total reflection occurs at larger incident angles
Solution Approach 1:
The patent transitions from a planar interface to a three-dimensional surface structure with minute regions of varying heights and depths. This dimensional change creates multiple extraction pathways at different angles and positions, allowing light that would normally undergo total reflection at the planar interface to escape through the elevated minute regions, thereby resolving the trade-off between emission intensity and total reflection.
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 enhances light extraction efficiency by preventing total reflection and ambient light reflection, while maintaining uniform light intensity and color across directions, thereby improving the overall performance of light emitting devices.
Implementation Method 1
When the incident angle θ exceeds a critical angle θc=sin−1(1/n′1), total reflection occurs. The minute region δ1 projects toward a position above the second surface... the minute region δ2 dents toward a position below the second surface
Implementation Method 2
light which enters a point P on a surface of the transparent substrate 105 at an angle θ from the surface normal to the surface, and is diffracted at this point and emitted into an air layer 106
Data Source
AI summary
A sheet and a light emitting device are provided which also emit light having an incident angle larger than or equal to a critical angle to significantly increase light extraction efficiency, prevent ambient light reflection, and suppress the occurrence of a distribution of light intensity varying depending on the direction and an imbalance in color. The light emitting device has a surface structure (13) in a surface adjacent to a light emitting element of a transparent substrate (5). The surface of the transparent substrate (5) is virtually divided into minute regions without a gap, the diameter of a largest circle inscribed in the minute region being 0.2 μm or more and 1.5 μm or less. Each minute region has a convex or concave shape in the surface of the transparent substrate 5. The proportions of the convex shapes and the concave shapes are P and 1−P, respectively, where P is within the range of 0.4 to 0.98.