Light-emitting display device with light-scattering layer
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Solution Overview
Problem
Inorganic LED display devices face inefficiencies due to light trapping within the device structure, resulting in significant loss of emitted photons, primarily due to total internal reflection caused by the high optical indices of materials used.
Innovation Solution
A light-emissive device structure is implemented with a substrate, a first electrode, a colloidal light-emitting layer of inorganic particles, and a second electrode, where at least one electrode is transparent with a refractive index equal to or greater than the colloidal layer, and a light-scattering layer is added on the transparent electrode to redirect trapped light, enhancing light output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high optical index materials are used in the LED structure, then the device achieves high brightness and good environmental stability, but light is trapped within the device due to total internal reflection, resulting in significant loss of emitted photons
Solution Approach 1:
A transparent electrode with refractive index matching or greater than the colloidal light-emitting layer is introduced as an intermediary component. This electrode serves as an optical mediator that prevents total internal reflection at the interface between the high-index light-emitting layer and lower-index surrounding media, thereby extracting trapped light while maintaining the brightness benefits of high optical index materials.
Solution Approach 2:
The refractive index parameter of the transparent electrode is specifically selected to be equal to or greater than that of the colloidal light-emitting layer. This parameter change resolves the optical impedance mismatch that causes total internal reflection, enabling efficient light extraction without sacrificing the brightness advantages of the high-index emitting materials.
2Loss of energy
If a transparent electrode with refractive index equal to or greater than the colloidal layer is used, then light extraction is improved, but the device structure becomes more complex
Solution Approach 1:
The transparent electrode performs multiple functions simultaneously: it serves as an electrical contact for charge injection/extraction and as an optical element for light extraction. By combining electrical and optical functions in a single component, the design avoids adding separate extraction structures, thereby improving light output efficiency without proportionally increasing device complexity.
3Duration of action of stationary object
If inorganic light-emitting particles are used, then the device achieves long lifetime and high brightness, but the manufacturing cost increases due to high-vacuum techniques and sapphire substrates
Solution Approach 1:
The substrate material parameter is changed from expensive sapphire to cost-effective alternatives such as glass or plastic. This parameter change maintains the long lifetime and high brightness characteristics of inorganic light-emitting particles while significantly reducing manufacturing costs by eliminating the need for expensive sapphire substrates and high-vacuum deposition techniques.
Solution Approach 2:
The design accepts the use of cheaper, non-sapphire substrates that may have shorter individual lifetimes but can be easily replaced. This approach reduces manufacturing costs while maintaining overall system performance, as the expensive inorganic light-emitting particle layer remains intact and functional.
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 significantly improves light output by scattering trapped light, increasing the efficiency of the light-emissive display device and reducing light loss, thereby enhancing the overall performance of the inorganic LED display.
Implementation Method 1
a light-scattering layer is formed on a side of the transparent electrode opposite the colloidal light-emitting layer
Implementation Method 2
The transparent electrode preferably has a refractive index substantially equal to or greater than the refractive index of the colloidal light-emitting layer
Implementation Method 3
total internal reflection caused by the high optical indices of materials used
Data Source
AI summary
A light-emissive device includes a substrate having a first electrode formed on the substrate. A colloidal light-emitting layer comprising inorganic, light-emissive particles is formed over the first electrode. A second electrode is formed over the light-emitting layer. At least one of the first and second electrodes is transparent. The transparent electrode preferably has a refractive index substantially equal to or greater than the refractive index of the colloidal light-emitting layer. Finally, a light-scattering layer is formed on a side of the transparent electrode opposite the colloidal light-emitting layer.