Emissive Display Contrast via Scattering Layer and Polarizer
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Solution Overview
Problem
Emissive displays face challenges in achieving suitable contrast ratios across varying ambient lighting conditions due to reflective metals used in OLEDs, which reflect ambient light, and existing solutions like circular polarizers or absorptive layers either absorb too much light or reduce luminance.
Innovation Solution
Incorporating a reflective electrode and a transparent electrode with one or more light-emitting layers, a scattering layer to scatter trapped light, and a circular polarizer positioned opposite the reflective electrode, along with a contrast-enhancement layer comprising alternating light-absorbing and light-transmissive portions, to enhance both luminance and ambient contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If reflective metals are used in OLED displays to provide current to emissive layers, then electrical conductivity is improved, but ambient light reflectance increases making display difficult to view
Solution Approach 1:
The display surface is segmented into light-emitting areas and non-light-emitting areas. The non-light-emitting areas use transparent electrodes with circuitry, while light-emitting areas use reflective electrodes. This segmentation allows different regions to have different optical properties, reducing overall ambient light reflectance while maintaining electrical functionality.
Solution Approach 2:
Different electrode materials are used in different locations: transparent electrodes in non-light-emitting areas to minimize reflectance, and reflective electrodes in light-emitting areas to enhance light output. This local differentiation optimizes both electrical conductivity and optical performance in各自 appropriate regions.
2Object-affected harmful factors
If circular polarizer is used to improve contrast by absorbing reflected ambient light, then ambient contrast ratio is improved, but luminance is reduced due to light absorption
Solution Approach 1:
The display system dynamically adapts to different ambient lighting conditions. In bright outdoor conditions, the circular polarizer effectively reduces reflectance. In darker indoor conditions, the system can adjust to prioritize luminance output, providing optimized performance for different viewing environments.
Solution Approach 2:
The optical properties of the display are adjusted by changing the polarization state of light through the circular polarizer. This parameter change allows selective absorption of reflected ambient light while maintaining forward-emitted light, improving contrast without completely sacrificing luminance.
3Object-affected harmful factors
If absorptive layer is placed at back of device to absorb ambient light, then ambient light reflectance is reduced, but light emitted from emissive layer is lost reducing luminance
Solution Approach 1:
The harmful function of the back electrode is extracted and separated from the light extraction path. The back electrode's primary function of providing electrical current is maintained, while its light-reflecting function is removed by making it transparent, preventing interference with forward-emitted light.
Solution Approach 2:
A transparent electrode serves as an intermediary between the back electrode and the light-emitting layers. This intermediary allows electrical current to pass through while being optically transparent to the emitted light, preventing the back electrode from absorbing or reflecting forward-emitted light.
4Object-affected harmful factors
If black matrix is provided between light emitting elements to reduce reflectance, then ambient light reflectance is reduced, but light transmission is blocked reducing luminance
Solution Approach 1:
The display is segmented into light-emitting areas and non-light-emitting areas separated by transparent spacers. This segmentation provides structural definition and reduces ambient light reflectance at pixel boundaries without using light-absorbing black matrices that would block emitted light and reduce luminance.
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 increases luminance and ambient contrast, with the scattering layer effectively scattering trapped light and the circular polarizer maintaining polarization, while the contrast-enhancement layer absorbs ambient light at high angles, reducing reflectance and improving the ambient contrast ratio.
Implementation Method 1
A scattering layer is positioned in the emissive display device to scatter light trapped in the one or more light-emitting layers
Implementation Method 2
The polarizer polarizes ambient light falling on the display, and the quarter wave plate circularly polarizes the linearly polarized light by 45 degrees
Implementation Method 3
The absorptive layer absorbs the ambient light in addition to any light emitted from the emissive layer of organic materials
Implementation Method 4
a reflective electrode... One or more light-emitting layers are formed between the reflective and transparent electrodes
Data Source
AI summary
An emissive display device, including: a reflective electrode and a transparent electrode. One or more light-emitting layers are formed between the reflective and transparent electrodes. A scattering layer is positioned in the emissive display device to scatter light trapped in the one or more light-emitting layers; and a circular polarizer is located on the side of the scattering layer opposite the reflective electrode.