OLED Light-Transmitting Layer Refractive Index Engineering
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Solution Overview
Problem
Organic light-emitting display apparatuses suffer from reduced light efficiency and color shift at side viewing angles due to non-directive light emission and external moisture/oxygen sensitivity, which current thin film encapsulation methods fail to adequately address.
Innovation Solution
An organic light-emitting display apparatus with a light-transmitting layer comprising alternating inorganic and organic films, where the organic films include a first material with a refractive index greater than 1.5, dispersed in a second material, to redirect and enhance light emission, and a protective layer to prevent moisture and oxygen ingress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thin film encapsulation is used to seal OLED, then protection from moisture and oxygen is achieved, but color shift is generated at side viewing angles
Solution Approach 1:
The encapsulation structure is divided into multiple thin films (first encapsulation layer, second encapsulation layer, third encapsulation layer) with different refractive indices, arranged in alternating sequence. This segmentation allows each layer to contribute differently to light management while collectively providing protection against moisture and oxygen.
Solution Approach 2:
Different encapsulation layers are assigned different local optical properties (refractive indices) to perform specific functions. The first encapsulation layer has higher refractive index than the second, while the third has higher refractive index than the second, creating localized optical characteristics that control light propagation paths and reduce color shift at side viewing angles.
2Adaptability or versatility
If organic emission layer emits light without directivity, then light is emitted in all directions, but light efficiency is reduced due to total reflection
Solution Approach 1:
The refractive index parameter is strategically varied across different encapsulation layers to control light emission. By setting the first encapsulation layer's refractive index higher than the second, and the third encapsulation layer's refractive index higher than the second, the structure modifies light propagation parameters to reduce total internal reflection and improve light extraction efficiency.
Solution Approach 2:
The alternating encapsulation layers with different refractive indices act as optical intermediaries between the organic emission layer and the external environment. These intermediate layers gradually transition the refractive index, enabling more efficient light extraction by reducing the abrupt refractive index mismatch that causes total internal 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
The solution effectively reduces color shift at side viewing angles and increases light efficiency by scattering and redirecting non-directive light, while also protecting the OLED from external contaminants.
Implementation Method 1
at least two of the organic films each include a first material having a first refractive index and a second material having a second refractive index, wherein the first refractive index is greater than the second refractive index
Implementation Method 2
The solution effectively reduces color shift at side viewing angles and increases light efficiency by scattering and redirecting non-directive light
Implementation Method 3
since light emitted from an organic emission layer does not have directivity, and since some of the emitted light does not exit externally due to total reflection
Data Source
AI summary
An organic light-emitting display apparatus includes: a substrate; a pixel electrode disposed on the substrate; a counter electrode disposed on the pixel electrode and capable of transmitting light; an organic emission layer disposed between the pixel electrode and the counter electrode so as to emit light toward at least the counter electrode; and a light-transmitting layer disposed on the counter electrode along a path of light emitted from the organic emission layer and including at least one inorganic film and organic films separated by the inorganic film. At least two of the organic films each include a first material having a first refractive index and a second material having a second refractive index. The first refractive index is greater than the second refractive index, and the first material is dispersed in the second material in the form of plurality of particles.