Light Extraction Sheet With Stepped Projections
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Solution Overview
Problem
Conventional light-emitting devices suffer from low light extraction efficiency due to total reflection, leading to decreased luminance and increased power consumption, and existing light extraction structures do not effectively account for light absorption, which further reduces overall efficiency.
Innovation Solution
A sheet for light-emitting devices featuring a first layer with projecting portions and a second layer formed on the top surfaces of these steps, where the effective refractive indices of the first and second layers are higher than that of the air, allowing for efficient extraction of light incident at critical angles and reducing absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional transparent substrate is used in a light-emitting device, then the device structure is simple, but light extraction efficiency is low due to total reflection at critical angles
Solution Approach 1:
The transparent substrate surface is segmented into multiple regions with different refractive indices by forming recesses and projections. This segmentation allows light at different angles to be extracted efficiently - light at critical angles is extracted through the projection portions while light at other angles passes through the recess portions, thereby resolving the total reflection problem without complicating the overall device structure
Solution Approach 2:
Different regions of the substrate surface are given different optical properties - the projection portions have higher refractive index to extract light at critical angles, while the recess portions have lower refractive index to transmit light at other angles. This local differentiation of optical quality enables efficient light extraction across all angles while maintaining overall structural simplicity
2Productivity
If existing light extraction structures are used, then some light extraction is improved, but light absorption is not effectively accounted for, reducing overall efficiency
Solution Approach 1:
The invention changes the optical parameters of the substrate surface by creating a microstructured pattern of recesses and projections with specific depth and width ratios. This parameter optimization ensures that light extraction efficiency is maximized while minimizing the path length of light within the substrate, thereby reducing absorption losses and improving overall device efficiency
3Productivity
If the refractive index of the transparent substrate is increased to improve light extraction, then light extraction efficiency improves, but absorption of light increases
Solution Approach 1:
Rather than uniformly increasing the refractive index throughout the substrate, the invention segments the surface into high refractive index projection portions and low refractive index recess portions. This allows light extraction to be enhanced at critical angles through the high index regions while the low index recess regions minimize absorption paths for other light angles, thus improving extraction efficiency without proportionally increasing absorption
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 enhances light extraction efficiency by minimizing absorption and improving luminance while reducing power consumption and extending the life of light-emitting device elements.
Implementation Method 1
This light is refracted at this point P at a refraction angle θ0 and outputted to an air layer 20
Implementation Method 2
when the incidence angle θ1 becomes greater than a critical angle θc=sin−1 (1/n), total reflection occurs
Data Source
AI summary
A sheet for use in a light-emitting device including layers including a light-emitting layer was invented. The sheet includes: a first layer including a plurality of projecting portions; and a second layer on the first layer, in which the projecting portions each include at least two steps, the second layer is formed on top at least surfaces of the steps, and when an effective refractive index of the first layer is n1, an effective refractive index of the second layer is n2, and an effective refractive index of the air above the second layer is n0, a relationship n1>n2>n0 is satisfied.