QD-LED Pixel with Uniform Layer Thickness and Refractive Index Bridge
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Solution Overview
Problem
Conventional Quantum Dot Light Emitting Diode (QLED) displays face challenges in achieving efficient light extraction, reducing color shift, and maintaining on-axis brightness while keeping sub-pixel layer thicknesses constant, especially due to issues with total internal reflection and the complexity of modifying cavity structures.
Innovation Solution
A light emitting structure with a substrate, sub-pixel stacks, a bank, and filler materials of varying refractive indices, where the sub-pixel stacks have a uniform distance between the emissive layer and the electrode layer, optimized for on-axis emission and off-axis light reflection to minimize color shift and enhance brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a thick top filler layer with high refractive index is used to reduce Fresnel reflections and increase transmissivity, then light extraction efficiency is improved, but light is mostly trapped by total internal reflection
Solution Approach 1:
A low refractive index layer is introduced as an intermediary between the high refractive index filler material and the surrounding medium. This intermediate layer acts as a refractive index bridge, gradually transitioning the optical impedance and enabling trapped light to escape by reducing the abrupt refractive index mismatch that causes total internal reflection.
Solution Approach 2:
The refractive index parameter is spatially varied by introducing a gradient structure - a low refractive index layer is placed strategically within the filler material. This parameter change creates optimal conditions for light extraction by positioning a material with intermediate optical properties at the critical interface where light needs to escape.
2Productivity
If different thicknesses of organic layers are used for different sub-pixels to maximize light output, then luminance efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
Instead of varying the thickness of organic layers across different sub-pixels, the patent applies local quality by varying the refractive index of the filler material at specific locations. The low refractive index layer is strategically positioned to provide local optical enhancement where needed, while maintaining uniform physical layer thicknesses throughout the device structure.
Solution Approach 2:
The filler material is segmented into regions with different refractive indices - a high refractive index bulk filler material and a low refractive index layer. This segmentation allows independent optimization of optical properties in different spatial zones without requiring complex variations in the organic layer structure.
3Loss of energy
If cavity structures are modified to improve light emission, then extraction efficiency is improved, but device complexity and fabrication difficulty increase
Solution Approach 1:
Instead of modifying the complex cavity structure itself, the patent introduces a simpler optical element - a low refractive index layer within the filler material. This copied approach achieves light extraction enhancement through a less complex means, replicating the optical function without the structural complexity of modified cavities.
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 achieves balanced color distribution and reduced color shift across different viewing angles by maximizing on-axis brightness and optimizing light extraction through the use of filler materials and bank structures, while simplifying the fabrication process by maintaining uniform layer thicknesses across sub-pixels.
Implementation Method 1
a first filler material in the interior space and having a first refraction index; a second filler material over the first filler material and having a second refractive index lower than the first refractive index
Implementation Method 2
the light in a high index layer may be mostly trapped by total internal reflection (TIR). To extract the trapped light, reflective and/or scattering banks surrounding the filler layer are used to out-couple light that is trapped by TIR
Implementation Method 3
reflective and/or scattering banks surrounding the filler layer are used to out-couple light that is trapped by TIR
Implementation Method 4
reflective and/or scattering banks surrounding the filler layer are used to out-couple light that is trapped by TIR
Implementation Method 5
Quantum Dot Light Emitting Diode (QLED) displays
Data Source
AI summary
A light emitting structure comprises a substrate, a plurality of sub-pixel stacks over the substrate emitting different colors, a bank surrounding the sub-pixel stacks and forming an interior space above the sub-pixel stacks, a first filler material in the interior space, a second filler material over the first filler material, and an interface between the first filler material and the second filler material. Each of the sub-pixel stacks including an emissive layer between a first transport layer and a second transport layer, a first electrode layer coupled to the first transport layer, and a second electrode layer coupled to the second transport layer. The sub-pixel stacks each have a substantially uniform distance between the emissive layer and the first electrode layer. Each of the sub-pixel stacks emits a main emission peak at one direction normal to a top surface of each of the sub-pixel stacks through the interface.