LED Contrast Enhancement via Segmented Reflective Electrode
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Solution Overview
Problem
LED devices face challenges in maximizing light output and ambient contrast ratio due to reflective back electrodes that reflect ambient light, with existing solutions like circular polarizers being expensive and scattering layers not effectively absorbing ambient light.
Innovation Solution
A light-emitting diode (LED) device structure featuring a reflective electrode, a transparent electrode with light-emitting layers in between, a contrast-enhancement element with a reflected-light absorbing layer and a patterned light-scattering layer, which enhances light output and ambient contrast by selectively absorbing ambient light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a highly reflective back electrode is used to enhance light output, then light output is improved, but ambient contrast ratio deteriorates due to reflection of ambient light
Solution Approach 1:
The back electrode is segmented into reflective regions and non-reflective regions. The reflective regions enhance light output while the non-reflective regions (covered by black matrix) absorb ambient light to maintain contrast ratio. This segmentation allows simultaneous optimization of both light output and ambient contrast ratio.
Solution Approach 2:
Different regions of the back electrode are assigned different optical properties. Areas corresponding to light-emitting pixels have high reflectivity to enhance light output, while areas corresponding to non-emitting regions have low reflectivity (black matrix) to absorb ambient light and maintain contrast ratio.
2Duration of action of stationary object
If the light-emitting area is maximized to reduce current density and extend lifetime, then device lifetime is improved, but the area available for black matrix is reduced, increasing ambient light reflection and reducing contrast
Solution Approach 1:
The black matrix is applied selectively only in non-emitting regions rather than uniformly across the entire back electrode. This partial application maintains contrast ratio in critical areas while preserving maximum light-emitting area in pixel regions, thus extending device lifetime without sacrificing contrast performance.
3Object-affected harmful factors
If circular polarizers are used to reduce reflected ambient light, then ambient contrast ratio is improved, but device cost increases significantly
Solution Approach 1:
The patent replaces expensive circular polarizers with a much cheaper black matrix material that can be applied through standard deposition techniques. While the black matrix absorbs both ambient and emitted light, the overall system cost is dramatically reduced, making the solution economically viable despite the trade-off in optical efficiency.
Solution Approach 2:
The patent extracts the contrast enhancement function from the expensive circular polarizer and implements it through a simpler black matrix structure combined with selective positioning. This extraction allows using inexpensive materials and manufacturing processes while achieving the essential contrast improvement function.
4Illumination intensity
If scattering layers are used to improve light emission, then light output is improved, but effectiveness of circular polarizers is inhibited and ambient light is not selectively absorbed
Solution Approach 1:
The patent converts the potentially harmful effect of ambient light reflection into a beneficial contrast enhancement mechanism. By strategically placing black matrix in non-emitting regions, the reflected ambient light is absorbed where it would otherwise degrade contrast, while emitted light from pixel regions remains largely unaffected, thus improving contrast without significantly compromising light output.
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 proposed structure effectively increases light output and ambient contrast by efficiently absorbing ambient light while allowing emitted light to escape, improving the overall performance of LED devices.
Implementation Method 1
The reflected-light absorbing layer absorbs the reflected ambient light
Implementation Method 2
Light emitted from the OLED device at higher than the critical angle that would have otherwise been trapped can penetrate into the scattering layer and be scattered out of the device
Data Source
AI summary
A light-emitting diode (LED) device includes a reflective electrode and a transparent electrode having one or more light-emitting layers formed there-between. A contrast-enhancement element is located on a side of the transparent electrode opposite the light-emitting layer. The contrast-enhancement element has a first reflected-light absorbing layer and a second layer including transparent areas and reflective areas. The second layer is between the first reflected-light absorbing layer and the reflective electrode. A patterned light-scattering layer is located between the reflective areas of the second layer and the reflective electrode.