OLED Microcavity Light Out-Coupling via High-Index Interlayers
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Solution Overview
Problem
Organic electroluminescent devices suffer from low light escape efficiency due to scattering, internal reflection, and absorption, leading to poor image quality and color purity, and existing solutions like Quarter Wave Stacks (QWS) result in strong microcavities that trap light, causing narrow viewing angles and increased complexity.
Innovation Solution
Incorporating intermediate layers with a refractive index greater than 1.8 or metal materials between the substrate and the first electrode to form a semi-transparent mirror, creating a microcavity with the reflective second electrode, which enhances light out-coupling and color purity without altering the electrodes' electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a strong microcavity is formed using Quarter Wave Stack (QWS), then light out-coupling is enhanced, but light is trapped causing narrow viewing angles and increased device complexity
Solution Approach 1:
The patent changes the optical parameters of the device by introducing intermediate layers with high refractive index (greater than 1.8) between the substrate and the first electrode. These layers form a semi-transparent mirror that creates a microcavity with intermediate strength, enhancing light out-coupling without the extreme trapping effects of strong microcavities. The refractive index parameter of the intermediate layers is specifically selected to achieve the desired balance between light extraction and viewing angle maintenance.
Solution Approach 2:
The patent introduces intermediate layers as intermediary elements between the substrate and the first electrode. These intermediate layers with high refractive index act as mediators that form a semi-transparent mirror, creating a microcavity structure that moderates the interaction between light and the device layers. This intermediary structure provides a balanced microcavity effect that avoids the extremes of strong light trapping while still enhancing light out-coupling effectively.
2Illumination intensity
If a strong microcavity is formed using Quarter Wave Stack (QWS), then light out-coupling is enhanced, but viewing angle becomes narrow
Solution Approach 1:
The patent modifies the optical parameters by using intermediate layers with high refractive index (greater than 1.8) to create a microcavity with intermediate strength. This parameter change in the refractive index and layer configuration produces a balanced optical field distribution that enhances light out-coupling while maintaining wider viewing angles compared to strong microcavity structures.
Solution Approach 2:
The patent applies local quality by positioning intermediate layers with high refractive index at specific locations (between the substrate and the first electrode) rather than throughout the entire device. This localized application of high refractive index material creates the semi-transparent mirror and microcavity effect precisely where needed, affecting light extraction without overly constraining the viewing angle across the entire device structure.
3Ease of manufacture
If standard device structure with ITO anode is used, then manufacturing is simple, but microcavity effect is weak and color purity is poor
Solution Approach 1:
The patent introduces intermediate layers with high refractive index as intermediary elements between the substrate and the ITO anode. These intermediate layers form a semi-transparent mirror that creates a microcavity structure, enhancing the optical performance and color purity without replacing the standard ITO anode or significantly complicating the manufacturing process. The intermediate layers act as mediators that improve optical properties while maintaining manufacturing simplicity.
Solution Approach 2:
The patent employs composite material structure by combining the standard ITO anode with intermediate layers of high refractive index dielectric or metal materials. This composite structure at the substrate-anode interface creates the semi-transparent mirror and microcavity effect, enhancing color purity and light out-coupling while maintaining compatibility with existing manufacturing processes for OLED devices.
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 approach increases light out-coupling, improves color purity, and maintains consistent color with viewing angle, while avoiding the absorption issues of QWS, resulting in a microcavity of intermediate strength that enhances the overall light output and spectral enhancement.
Implementation Method 1
one or more intermediate layers of dielectric material with a refractive index greater than 1.8 or a metal material disposed between the substrate and the first electrode forming a semi-transparent mirror whereby a microcavity is provided between the reflective second electrode and the semi-transparent mirror
Implementation Method 2
The provision of intermediate layers disposed between the substrate and the first electrode all of which have a surface nearest the organic light-emitting layer not more than 150 nm from a surface of the first electrode nearest the organic light-emitting layer results in an increase in out-coupling of light from the device
Implementation Method 3
The photon density of states is modified such that only certain wavelengths, which correspond to allowed cavity modes, are emitted with emission intensity being enhanced in a direction perpendicular to the layers of the device
Implementation Method 4
one or more intermediate layers of dielectric material with a refractive index greater than 1.8 disposed between the substrate and the first electrode
Data Source
AI summary
An organic electroluminescent device comprising: a transparent substrate; a first electrode disposed over the substrate for injecting charge of a first polarity; a second electrode disposed over the first electrode for injecting charge of a second polarity opposite to said first polarity; an organic light-emitting layer disposed between the first and the second electrode, wherein the second electrode is reflective, the first electrode is transparent or semi-transparent, and one or more intermediate layers of dielectric material with a refractive index greater than 1.8 or a metal material is disposed between the substrate and the first electrode forming a semi-transparent mirror whereby a microcavity is provided between the reflective second electrode and the semi-transparent mirror, all the intermediate layers disposed between the substrate and the first electrode having a surface nearest the organic light-emitting layer not more than 150 nm from a surface of the first electrode nearest the organic light-emitting layer.