Convexo-Concave Electrode Structure for OLED Light Extraction
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Solution Overview
Problem
Organic electroluminescence devices face significant light loss due to trapping in substrate, thin film, and surface plasmon modes, particularly the surface plasmon mode, which hinders the achievement of high external quantum efficiency and directional light radiation.
Innovation Solution
An organic electroluminescence device with a convexo-concave structure at the interface between electrodes and the organic compound layer, where the distance between convex portions matches the peak wavelength of radiated light and the propagation distance of surface plasmons, facilitates the extraction of light in the surface plasmon mode by scattering it into propagation light, reducing directionality and enhancing external quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a convexo-concave structure with small pitch is used to extract surface plasmon light, then light extraction efficiency improves, but wavelength selectivity and directional radiation increase excessively
Solution Approach 1:
The patent changes the pitch parameter of the convexo-concave structure to be equal to or more than the peak wavelength of radiated light. This parameter modification allows the structure to extract surface plasmon light effectively while reducing excessive wavelength selectivity and directional radiation, thereby resolving the technical contradiction between light extraction efficiency and wavelength adaptability
Solution Approach 2:
The patent applies a convexo-concave structure that provides partial extraction of surface plasmon light rather than complete extraction. By using a pitch equal to or more than the peak wavelength, the structure achieves sufficient light extraction efficiency while avoiding excessive directional radiation and wavelength selectivity that would occur with smaller pitch structures
2Productivity
If the pitch of convexo-concave structure is reduced to increase light extraction, then more surface plasmon light is converted, but radiation becomes highly directional
Solution Approach 1:
The patent modifies the pitch parameter of the convexo-concave structure to be equal to or more than the peak wavelength of radiated light. This parameter change enables the structure to convert surface plasmon light effectively while maintaining diffuse radiation patterns, thus resolving the contradiction between productivity and radiation shape
3Loss of energy
If Bragg diffraction is used to extract surface plasmon light, then light radiation is enhanced, but strong wavelength and angle dependency is introduced
Solution Approach 1:
The patent changes the pitch parameter from being smaller than the wavelength (Bragg diffraction condition) to being equal to or more than the peak wavelength. This parameter modification enables surface plasmon light extraction while reducing strong wavelength and angle dependency, thereby resolving the technical contradiction between energy loss reduction and adaptability
Solution Approach 2:
The patent converts the harmful effect of strong wavelength and angle dependency into a benefit by using a convexo-concave structure with pitch equal to or more than the peak wavelength. This approach maintains effective surface plasmon light extraction while producing more diffuse and less selective radiation, turning the limitation into an advantage for broader applicability
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 increases light extraction efficiency, lowers radiation directionality, and improves external quantum efficiency by converting surface plasmon light into propagating light, while also enhancing light extraction in thin-film and substrate modes.
Implementation Method 1
the light in the surface plasmon mode can be a useful radiation in a form of Bragg scattering with use of Bragg diffraction
Implementation Method 2
the light in the surface plasmon mode can be a useful radiation in a form of Bragg scattering with use of Bragg diffraction
Implementation Method 3
emits light using exciton energy generated in the organic compound layer by a recombination of holes injected into the emitting layer from the anode and electrons injected into the emitting layer from the cathode
Implementation Method 4
adjustment of an optical interference distance and the like are conducted in order to improve a luminous efficiency
Data Source
AI summary
The first electrode has a convexo-concave structure including a plurality of convex portions and a plurality of concave portions at an interface with the organic compound layer. The convexo-concave structure has at least one cross section in a thickness direction of the light-transmissive substrate, the cross section being shaped in a sine-wave curve or a curve represented by a sum of a plurality of sine waves having different amplitudes or angles. A distance between a convex portion and an adjacent convex portion forming the convexo-concave structure is equal to or more than a peak wavelength of light radiated from the emitting layer and is equal to or less than a propagation distance (Lsp) of surface plasmon at the interface between the first electrode having the convexo-concave structure and the organic compound layer.