OLED Dielectric Capping Layer for Light Outcoupling
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Solution Overview
Problem
Conventional organic light-emitting diodes (OLEDs) face challenges in achieving high luminous intensity and contrast ratio, with complex production methods due to the need for varying thicknesses of refractive dielectric layers for different colors, and low contrast ratios despite enhanced light output.
Innovation Solution
A multilayer OLED structure with a dielectric capping layer that reduces reflectance and increases outcoupling of light, allowing for a uniform capping layer thickness across different colors, utilizing materials with anomalous dispersion or ferroelectric/liquid crystalline materials to control refractive index and optical pathlength, thereby simplifying production and enhancing luminous intensity and contrast ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If varying thicknesses of refractive dielectric layers are used for different colors, then light output is enhanced, but production complexity increases
Solution Approach 1:
The patent changes the optical parameters of a single dielectric layer by adjusting its thickness and refractive index to achieve wavelength-independent light extraction enhancement. This allows the same layer structure to work for all colors (red, green, blue) without requiring different thicknesses for each wavelength, thus simplifying production while maintaining enhanced light output.
Solution Approach 2:
The dielectric layer is designed to perform multiple functions simultaneously: it serves as both the extraction enhancement layer and the protective capping layer for the cathode. Moreover, a single uniform thickness design makes the structure universal for all color emissions, eliminating the need for color-specific thickness variations and simplifying the manufacturing process.
2Illumination intensity
If refractive dielectric layers are used to enhance light output, then luminous intensity increases, but contrast ratio remains low
Solution Approach 1:
The patent introduces a low-refractive-index dielectric material as an intermediary layer between the high-refractive-index organic emitting layer and the external environment. This intermediary layer creates a larger refractive index gradient, enhancing light extraction while the low refractive index reduces parasitic reflections, thereby improving both luminous intensity and contrast ratio simultaneously.
Solution Approach 2:
By selecting dielectric materials with low refractive indices (lower than conventional materials), the patent changes the optical parameters to achieve dual benefits: enhanced light extraction efficiency (increasing luminous intensity) and reduced reflectance (improving contrast ratio). This parameter change resolves the contradiction between brightness and contrast.
3Adaptability or versatility
If multiple layers with different thicknesses are used for different colors, then color-specific optimization is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs a homogeneous dielectric layer with uniform thickness across all color regions (red, green, blue). This homogeneous structure eliminates the need for precise thickness variations for different colors, significantly reducing manufacturing precision requirements while still achieving optimal light extraction through the unified low-refractive-index material design.
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 results in a simplified production method for OLED arrays with increased luminous intensity and contrast ratio, reducing reflectance and improving light output while maintaining a uniform capping layer thickness across different colors.
Implementation Method 1
The capping layer is selected to have the effect that the reflectance of external light is reduced whereas outcoupling of the light generated in the at least one layer of organic material through the capping layer is increased
Implementation Method 2
The basic feature of the organic LED is the electroluminescence of specific organic materials. The excitons decay radiatively into the ground state by generating light
Implementation Method 3
The anode layer 102 and the cathode layer 104 inject charge carriers, i.e. electrons and holes, into the emitting layer 103
Implementation Method 4
In the emitting layer 103 the charge carriers are transported and the charge carriers of opposite charge form so called excitons
Data Source
AI summary
The present invention is directed to an organic light emitting device (OLED) including a first electrode, a second electrode, at least one layer of organic material arranged between the first electrode and the second electrode, and a dielectric capping layer arranged on the second electrode opposite to the first electrode, wherein the capping layer comprises an outer surface, opposite to the second electrode, for emission of light generated in the at least one layer of organic material. The capping layer has the effect that a reflectance of external light is reduced whereas outcoupling of the light generated in the at least one layer of organic material through the capping layer is increased.