Encapsulation Layer Refractive Index Matching for OLED Displays
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Solution Overview
Problem
Existing display devices using self-luminous materials face vulnerability to external environments such as oxygen and moisture, necessitating an encapsulation layer that maintains high light transmittance while effectively sealing the light-emitting elements.
Innovation Solution
An encapsulation layer is designed with alternating layers of inorganic films and organic films, where the refractive index difference between adjacent layers is minimized to enhance light transmittance, using specific copolymers like epoxy-based copolymers with substituents, and optimized thicknesses to achieve a transmittance of 85-95% for wavelengths between 380 nm and 500 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an encapsulation layer with alternating inorganic and organic films is used to seal the light-emitting element, then the barrier properties against oxygen and moisture are improved, but the light transmittance deteriorates due to refractive index differences at interfaces
Solution Approach 1:
The patent changes the refractive index parameter of the organic film by selecting specific materials (epoxy-based copolymers with substituents like hydroxy ketone, carboxyl, thioether, sulfone, cyclic thiophene, thiadiazole, or thianthrene groups) to achieve a refractive index between 1.65 and 1.75 at 450 nm, minimizing the refractive index difference with adjacent inorganic films and thereby reducing light reflection at interfaces
Solution Approach 2:
The patent uses composite material structures where the organic film is composed of specific copolymer materials with controlled composition ratios. The epoxy-based copolymer includes specific substituents that tune both the refractive index and barrier properties, creating a multi-functional composite layer that simultaneously achieves high light transmittance and effective sealing
2Illumination intensity
If the refractive index difference between adjacent films is reduced to improve light transmittance, then the light emission efficiency is improved, but the material selection and manufacturing precision requirements increase
Solution Approach 1:
The patent specifies precise refractive index ranges (1.65-1.75 at 450 nm for organic film, 1.70-1.80 for inorganic film) and controls film thickness parameters (organic film: 50-200 nm, inorganic film: 10-50 nm) to achieve optimal light transmittance while maintaining manufacturability through defined parameter windows
Solution Approach 2:
The patent applies different material compositions and refractive index characteristics to specific layers within the encapsulation structure. The organic film uses epoxy-based copolymers with specific substituents positioned at controlled concentrations to create local optical property optimization at each interface without compromising overall barrier performance
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 encapsulation layer improves light emission efficiency by reducing light reflectance at interfaces, maintaining barrier properties, and enhancing the overall transmittance and emission efficiency of the display device.
Implementation Method 1
The encapsulation layer includes a first inorganic film having a first refractive index at a wavelength between about 380 nm and about 500 nm, the first refractive index being between about 1.5 and about 1.7; a second inorganic film disposed on the first inorganic film and having a second refractive index at a wavelength between about 380 nm and about 500 nm, the second refractive index being between about 1.5 and about 1.7; and an organic film disposed between the first inorganic film and the second inorganic film, and having a third refractive index at a wavelength between about 380 nm and about 500 nm, the third refractive index being between about 1.5 and about 1.7
Data Source
AI summary
A display device includes a light-emitting element layer and an encapsulation layer disposed on the light-emitting element layer. The encapsulation layer includes a first inorganic film having a first refractive index at a wavelength between about 380 nm and about 500 nm, the first refractive index being between about 1.5 and about 1.7, a second inorganic film disposed on the first inorganic film and having a second refractive index at a wavelength between about 380 nm and about 500 nm, the second refractive index being between about 1.5 and about 1.7, and an organic film disposed between the first inorganic film and the second inorganic film, and having a third refractive index at a wavelength between about 380 nm and about 500 nm, the third refractive index being between about 1.5 and about 1.7. Accordingly, the display device including the encapsulation layer with the high light transmittance may have the high light emission efficiency.