OLED Capping Layer Wavelength-Dependent Refractive Index
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Solution Overview
Problem
Existing organic light-emitting display apparatuses face challenges in achieving high light efficiency and minimizing color deviation as a function of viewing angles, particularly due to low reflectivity of the opposite electrode and unsuitable refractive index profiles of the capping layer.
Innovation Solution
The organic light-emitting display apparatus incorporates a capping layer with varying refractive indices as a function of wavelength, disposed over the opposite electrode, and a thin-film encapsulation layer, ensuring a refractive index of 1.9 to 2.3 at 530 nm, with a higher index at 460 nm and lower index at 620 nm, and a uniform thickness of 600 Å to 750 Å, to enhance light extraction efficiency and direct color deviation away from user perception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional capping layer with uniform refractive index is used, then the structure is simple, but light extraction efficiency is low and color deviation is significant in side viewing angles
Solution Approach 1:
The capping layer is designed with spatially varying refractive index characteristics through wavelength-selective optical resonance. Different wavelength ranges (color channels) experience different effective refractive indices, allowing optimized light extraction for each color while managing color deviation independently. This resolves the contradiction by making the optical properties location/wavelength-dependent rather than uniform.
Solution Approach 2:
The patent introduces dynamic optical resonance characteristics that can be tuned by adjusting the thickness and material composition of the capping layer. The resonant frequency of the microcavity can be adjusted to optimize light extraction at different viewing angles and wavelengths, providing adaptive optical performance without changing the physical structure.
2Illumination intensity
If the opposite electrode has low reflectivity, then the device structure is simpler, but resonance efficiency and light extraction are reduced
Solution Approach 1:
The patent optimizes the optical parameters of the opposite electrode by adjusting its reflectivity characteristics to create an effective microcavity resonance system. By carefully selecting the reflectivity parameter of the electrode and combining it with the capping layer's optical properties, the system achieves enhanced light extraction efficiency without requiring complex multi-layer electrode structures.
3Ease of manufacture
If a standard capping layer is used, then manufacturing is easier, but color deviation in side viewing angles is significant and easily detected by users
Solution Approach 1:
The capping layer is designed with specific thickness parameters (e.g., 50-150 nm) that create wavelength-dependent optical resonance. This local optimization of thickness and material properties ensures that color deviation is directed toward wavelength ranges less sensitive to human vision in side viewing angles, making the deviation less detectable while maintaining manufacturability.
Solution Approach 2:
The patent converts the potentially harmful effect of color deviation into a beneficial outcome by strategically directing the deviation toward blue wavelengths in side viewing angles. Since human vision is less sensitive to color changes in the blue region at oblique angles, the deviation becomes less noticeable to users, effectively turning a defect into an acceptable or even advantageous characteristic.
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
This configuration significantly increases resonance efficiency of the blue sub-pixel and reduces color deviation in side viewing angles, making it less noticeable to users while maintaining high light efficiency, thereby improving the display's overall performance.
Implementation Method 1
a capping layer over the opposite electrode and having a refractive index with respect to the first wavelength that is higher than a refractive index with respect to the second wavelength by at least 7%
Implementation Method 2
having a refractive index with respect to the first wavelength that is higher than a refractive index with respect to the second wavelength by at least 7%
Implementation Method 3
having a refractive index with respect to the first wavelength that is higher than a refractive index with respect to the second wavelength by at least 7%; A refractive index of the capping layer with respect to the third wavelength may be less than the refractive index with respect to the second wavelength by at least 3%
Data Source
AI summary
An organic light-emitting display apparatus includes a first sub-pixel, a second sub-pixel, and a third sub-pixel configured to emit different colors of light. The organic light-emitting display apparatus includes: a substrate; first through third pixel electrodes; a first organic emission layer configured to emit light having a first wavelength; a second organic emission layer configured to emit light having a second wavelength; a third organic emission layer configured to emit light having a third wavelength; an opposite electrode; a capping layer over the opposite electrode and having a refractive index with respect to the first wavelength that is higher than a refractive index with respect to the second wavelength by at least 7%; and a thin-film encapsulation layer over the capping layer.