Light Extraction Sheet for Organic EL Devices
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Solution Overview
Problem
Conventional organic electroluminescence (EL) devices suffer from limited light extraction efficiency due to high refractive indices and light absorption at interfaces, resulting in significant total reflection and absorption, which hinders effective light propagation and emission.
Innovation Solution
A light extraction sheet with a low-refractive index layer and a high-refractive index layer, featuring a bump-dent structure, is introduced between the light-transmitting substrate and the high-refractive index layer, along with a microlens array on the opposite side to enhance light transmission and extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional organic EL devices use standard interface structures, then device simplicity is maintained, but light extraction efficiency is limited due to total reflection and absorption at interfaces
Solution Approach 1:
The interface structure is segmented into multiple distinct layers: a low-refractive index layer (first extraction layer) and a high-refractive index layer (second extraction layer) with bump-dent features. This segmentation allows each layer to perform specific optical functions - the low-refractive index layer reduces total reflection, while the high-refractive index layer with bump-dent features enhances light extraction, thereby resolving the contradiction between structural simplicity and light extraction efficiency
Solution Approach 2:
The low-refractive index layer acts as an intermediary layer between the organic emission layer and the high-refractive index layer. This intermediary structure mediates the optical interaction by reducing total reflection at interfaces and facilitating more efficient light propagation, thus improving light extraction efficiency without significantly complicating the overall device structure
2Illumination intensity
If high refractive index materials are used at light emission interfaces, then light confinement is improved, but total reflection increases and light extraction efficiency decreases
Solution Approach 1:
The patent applies local quality by creating spatial variation in refractive index properties. The low-refractive index layer is positioned specifically at the interface where total reflection occurs, while the high-refractive index layer with bump-dent features is positioned to enhance extraction. This localized optimization allows light confinement where needed while minimizing total reflection losses, resolving the contradiction between light confinement and extraction efficiency
Solution Approach 2:
The bump-dent features introduce curved surfaces at the interface between the low-refractive index layer and the high-refractive index layer. These curved surfaces modify light propagation paths, reducing total reflection and enhancing light extraction efficiency while maintaining appropriate light confinement, thus resolving the contradiction between light confinement and extraction efficiency
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 significantly improves light extraction efficiency by reducing total reflection and absorption, allowing for higher transmittance of light at incident angles between 40 degrees and 60 degrees, thereby enhancing the overall luminance and efficiency of organic EL devices.
Implementation Method 1
total reflection may occur at interfaces between different refractive indices and light may be absorbed by the material(s), thus hindering effective light propagation to the exterior
Implementation Method 2
a low-refractive index layer having a lower refractive index than does the light-transmitting substrate and a high-refractive index layer having a higher refractive index than does the low-refractive index layer
Implementation Method 3
a microlens array on the opposite side to enhance light transmission and extraction efficiency
Data Source
AI summary
An illuminator includes a light-emitting element and a light extraction sheet which transmits light occurring from the light-emitting element. The light-emitting element includes a first electrode having a light transmitting property, a second electrode, and an emission layer between the first and second electrodes. The light extraction sheet includes a light-transmitting substrate having a first principal face and a second principal face, a first light extraction structure on the first principal face side of the light-transmitting substrate, and a second light extraction structure on the second principal face side of the light-transmitting substrate. The first light extraction structure includes a low-refractive index layer and a high-refractive index layer. The second light extraction structure is arranged so that light which is transmitted through the light-transmitting substrate and arrives at an incident angle of 40 degrees to 60 degrees has an average transmittance of 42% or more.