OLED Cathode Microstructure for Plasmon Extraction
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Solution Overview
Problem
Existing organic light emitting diodes (OLEDs) face low light extraction efficiency due to the conversion of near-field light into surface plasmons on metal cathodes, which are not effectively converted back into propagating light, and lack of optimal parameters for periodic microstructures to enhance this efficiency.
Innovation Solution
A two-dimensional periodic microstructure is formed on the cathodic conductive layer with specific parameters, including a range of extraction wavelengths and distances between concave or convex portions, to improve light extraction efficiency by converting surface plasmons into propagating light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a periodic microstructure is provided on the cathode surface to extract surface plasmons, then light extraction efficiency is improved, but the conversion efficiency from surface plasmon to propagation light remains insufficient due to lack of optimal parameters
Solution Approach 1:
The patent applies parameter changes by establishing specific relationships between the period of the microstructure and the wavelength of surface plasmons. The period is set to satisfy the condition: λ_sp/2 < period < λ_sp, where λ_sp is the wavelength of surface plasmons. This parameter optimization enables efficient conversion of surface plasmons into propagation light, resolving the contradiction between improving light extraction efficiency and achieving manufacturable precision.
Solution Approach 2:
The patent introduces a periodic microstructure dimension on the cathode surface, transforming a flat two-dimensional surface into a three-dimensional structured surface. This dimensional change creates diffraction gratings that couple surface plasmons with propagation light modes, enabling the conversion process and improving light extraction efficiency.
2Illumination intensity
If light is emitted in all directions from the light emitting layer, then complete light coverage is achieved, but most light enters waveguide mode and undergoes total reflection, reducing extraction efficiency
Solution Approach 1:
The patent introduces a periodic microstructure dimension on the cathode surface, transforming a flat two-dimensional surface into a three-dimensional structured surface. This dimensional change creates diffraction gratings that couple surface plasmons with propagation light modes, enabling the conversion process and improving light extraction efficiency.
Solution Approach 2:
The patent employs periodic action by creating a periodic microstructure on the cathode surface with a specific period ranging from λ_sp/2 to λ_sp. This periodic structure acts as a diffraction grating that systematically converts surface plasmons into propagation light at regular intervals, enabling efficient and continuous light extraction throughout the emission process.
3Length of stationary object
If the light emitting layer is positioned close to the metal cathode, then device thickness is reduced, but near-field light is converted to surface plasmons that disappear, decreasing light extraction efficiency
Solution Approach 1:
The patent converts the harmful effect of near-field light conversion into a beneficial process. Instead of allowing surface plasmons to disappear, the periodic microstructure on the cathode surface captures these surface plasmons and converts them into propagation light. This transforms the previously harmful energy loss into a useful light extraction mechanism, improving overall light extraction efficiency while maintaining thin device structure.
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
Significantly enhances light extraction efficiency by converting surface plasmons into directional radiant light, improving the brightness of OLEDs and related devices.
Implementation Method 1
a method of using surface plasmon resonance is suggested. For example, PTL 1 to PTL 4 disclose a method of providing a one-directional or two-directional periodic microstructure on a surface of a metallic layer (cathode). In this method, the periodic microstructure functions as a diffraction lattice. Due to this, energy, which disappears as the surface plasmon on the surface of the cathode is extracted as light
Implementation Method 2
the periodic microstructure functions as a diffraction lattice. Due to this, energy, which disappears as the surface plasmon on the surface of the cathode is extracted as light
Data Source
AI summary
An organic light emitting diode includes an anodic conductive layer, an organic EL layer, and a cathodic conductive layer formed from Ag or an alloy of Ag, or the like, sequentially laminated on a substrate, such that a two-dimensional lattice structure is provided on a surface of the cathodic conductive layer on an organic EL layer side, an extraction wavelength and a distance between centers of concave portions or convex portions in the two-dimensional lattice structure are within a region surrounded by specific coordinates in a graph illustrating a relationship between the light extraction wavelength and the distance, and the depth of the concave portions or a height of the convex portions is 12 nm to 180 nm.