Photonic Crystal Layer Light Extraction Organic EL Display
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Solution Overview
Problem
Conventional organic electroluminescent (EL) display devices face reduced light coupling efficiency due to refractive index differences between layers, leading to light reflection and decreased external efficiency, which complicates manufacturing and affects durability and reliability.
Innovation Solution
A photonic crystal layer is formed directly on the stack of an organic EL display device, with protrusions or piercing holes, and a refractive layer is interposed between the photonic crystal layer and the stack, using a thermal transfer donor film for precise manufacturing, eliminating the need for spatial layers and enhancing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional organic EL display device structure is used with standard layering, then the device is simple to manufacture, but light coupling efficiency is reduced due to refractive index differences causing reflection
Solution Approach 1:
The patent introduces a photonic crystal layer as an intermediary structure between the organic light-emitting layer and the encapsulation layer. This photonic crystal layer acts as a mediator that gradually transitions the refractive index from the organic layer to the encapsulation layer, reducing reflection and improving light coupling efficiency without complicating the manufacturing process
Solution Approach 2:
The patent modifies the refractive index parameter by introducing a photonic crystal layer with specific optical properties. The photonic crystal layer has a refractive index that is intermediate between the organic light-emitting layer and the encapsulation layer, creating a gradual transition that reduces reflection. The pitch and depth of the photonic crystal structure are optimized to control light extraction at different wavelengths
2Reliability
If spatial layers are used between the photonic crystal layer and the stack, then light extraction can be optimized, but the manufacturing process becomes more complex and time-consuming
Solution Approach 1:
The patent merges the photonic crystal layer directly with the encapsulation layer, eliminating the need for separate spatial layers. The photonic crystal structure is formed as an integral part of the encapsulation process, combining the light extraction function with the protective encapsulation function in a single integrated structure
Solution Approach 2:
The photonic crystal structure is prepared in advance on a separate substrate and then transferred to the final device structure. This preliminary preparation allows the complex photonic crystal pattern to be formed using optimized processes independent of the main device fabrication, thereby improving overall manufacturing efficiency
3Reliability
If multiple layers including spatial layers are used to improve light coupling, then light extraction efficiency increases, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies the photonic crystal structure only in specific locations where light extraction is most critical, such as at the interfaces between layers with different refractive indices. The pitch and depth of the photonic crystal features are locally optimized for different wavelength ranges, creating a simplified structure that targets specific optical problems without requiring complex multi-layer designs throughout the entire device
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 improves light extraction efficiency, simplifies the manufacturing process, reduces costs and time, and enhances the durability and reliability of organic EL display devices by eliminating the need for spatial layers and optimizing light coupling for different wavelengths of colored light.
Implementation Method 1
A problem is that external efficiency is reduced when light emitted from the organic light-emitting layer has an outgoing angle greater than a critical angle of one of the layers. When this happens, reflection occurs at the surface of the layer.
Implementation Method 2
a laser induced thermal transfer donor film for the EL display device is used to form the photonic crystal layer on the stack
Data Source
AI summary
The invention is directed to an organic electroluminescent (EL) display device having an improved light extracting efficiency due to a photonic crystal layer formed proximate one side of a stack. Among other elements, the stack may include a first electrode formed on a substrate, an organic light emitting layer formed above the first electrode, and a second electrode formed above the organic light emitting layer. Additionally, the photonic crystal layer may be configured to correspond to a wavelength of colored light. An organic EL display device having an improved light extracting efficiency may be manufactured using a thermal transfer donor film to adhere the photonic crystal layer to the stack.