Stepped Electrode Reflects Oblique Light in OLED Pixels
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Solution Overview
Problem
Organic electroluminescent display devices face low light extraction efficiency due to light being totally reflected at interfaces with different refractive indices, resulting in waveguide light being absorbed or emitted from the end surface, and leakage light causes color mixture issues, reducing the effective use of emitted light.
Innovation Solution
The introduction of a second electrode with a stepped portion and a light-reflecting surface that extends from the first electrode to the insulating layer, allowing light emitted parallel or obliquely to be reflected and directed towards the light-emitting area, increasing extraction efficiency and reducing color mixture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a light shielding layer is provided to partition adjacent pixels, then color mixture is reduced, but the numerical aperture of pixels is decreased and light extraction efficiency is reduced
Solution Approach 1:
A light-reflecting layer is introduced as an intermediary component between adjacent pixels. This layer reflects oblique light back into the pixel, preventing color mixture while maintaining light extraction efficiency. The light-reflecting layer acts as a mediator that redirects light rather than blocking it, solving the contradiction between preventing color mixture and maintaining high light extraction efficiency.
Solution Approach 2:
The patent converts the harmful effect of oblique light (which causes color mixture) into a beneficial effect by reflecting it back into the pixel. Instead of blocking oblique light with a light shielding layer, the light-reflecting layer redirects it to contribute to light extraction, thereby converting a harmful factor into a useful resource that enhances display quality.
2Object-affected harmful factors
If the width of the light shielding layer is increased to reduce color mixture, then color mixture is reduced, but the numerical aperture is decreased
Solution Approach 1:
The light-reflecting layer serves as an intermediary that allows the light shielding layer to be thinner while still preventing color mixture. By reflecting oblique light back into the pixel, the light-reflecting layer compensates for the reduced shielding width, maintaining color isolation while preserving a larger numerical aperture for efficient light extraction.
3Illumination intensity
If light is emitted parallel to the film surface, then light propagation occurs, but total internal reflection occurs at interfaces and light is lost
Solution Approach 1:
The light-reflecting layer converts the harmful effect of total internal reflection (which causes light loss) into a beneficial effect by reflecting oblique light back into the pixel. This redirected light would otherwise be lost but now contributes to the emitted light, thereby converting energy loss into useful light output and improving overall light extraction efficiency.
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 enhances light extraction efficiency by reflecting parallel and oblique light components, increasing the amount of usable light emitted from the pixel and reducing color mixture, thereby improving the overall performance of the organic electroluminescent display device.
Implementation Method 1
a second electrode contacting the first electrode in the opening of the first insulating layer and extending from the upper surface of the first electrode to the upper surface of the first insulating layer; a second insulating layer covering a peripheral portion of the second electrode; an organic electroluminescence layer extending from a top surface of the second electrode to a top surface of the second insulating layer
Data Source
AI summary
An organic electroluminescent display device includes a first insulating layer that buries a peripheral portion of a first electrode and has an opening exposing an area of the first electrode inner to the peripheral portion thereof; a second electrode that is in contact with the first electrode in the opening and is provided continuously on a top surface of the first electrode and onto a top surface of the first insulating layer; a second insulating layer covering a peripheral portion of the second electrode; an organic EL layer; and a third electrode. The second electrode includes a stepped portion. An area where the stepped portion is included and the second electrode, the organic electroluminescence layer and the third electrode overlap each other is a light emitting area. Light emitted by the organic EL layer is reflected by the stepped portion.