OLED Nano-Grating Light Extraction via Refractive Index Modulation
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Solution Overview
Problem
Conventional OLEDs suffer from low light extraction efficiency due to total internal reflection and light trapping in high-index organic materials, with existing methods to improve this efficiency being limited and often associated with reduced electrical efficiency, decreased lifetime, and increased costs.
Innovation Solution
A method of fabricating OLEDs with a nano-structured grating pattern in the photo-sensitive organic electroluminescent layer, using a Mach-Zehnder interferometer to create a periodic refractive index change, which enhances light extraction by modifying the refractive index and providing a Fresnel lens structure for improved light focusing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional OLED structure with transparent anode and reflecting cathode is used, then device simplicity and ease of manufacture are maintained, but light extraction efficiency is limited due to total internal reflection and light trapping in high-index organic materials
Solution Approach 1:
The patent applies parameter changes by modifying the refractive index of the organic electroluminescent layer through photo-sensitive material composition adjustments. By controlling the refractive index parameter, the device achieves improved light extraction efficiency without complicating the manufacturing process, directly resolving the contradiction between ease of manufacture and light extraction efficiency
Solution Approach 2:
The patent introduces a nano-structured grating pattern that creates periodic refractive index variations in the organic layer. This dimensional structuring at the nanoscale enables light extraction enhancement through diffraction and scattering effects, overcoming total internal reflection without requiring complex device architecture changes
2Loss of energy
If nano-structured grating pattern with periodic refractive index change is introduced, then light extraction efficiency is significantly increased, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical or structural modifications with optical field-based solutions. By using a Mach-Zehnder interferometer to create periodic refractive index patterns through light interference, the device achieves nano-structuring without mechanical complexity, resolving the contradiction between light extraction efficiency and device complexity
Solution Approach 2:
The patent achieves complex nano-structuring by simply changing the refractive index parameter of the photo-sensitive organic material. This parameter modification, controlled through exposure to interference patterns, creates the desired grating structure without adding device complexity, as the same material layer serves both functional and structural purposes
3Loss of energy
If refractive index of organic electroluminescent layer is modified to improve light extraction, then output coupling efficiency is enhanced, but electrical efficiency may be reduced
Solution Approach 1:
The patent applies local quality by creating periodic refractive index variations only in specific regions of the organic electroluminescent layer through selective photo-exposure. This localized modification enhances light extraction at the grating pattern locations while preserving the electrical properties of the bulk material, resolving the contradiction between output coupling efficiency and electrical efficiency
Solution Approach 2:
The patent uses composite material approach by combining photo-sensitive organic electroluminescent material with specific refractive index properties. This composite formulation allows simultaneous optimization of optical extraction and electrical performance, as the material exhibits both photorefractive and electroluminescent properties, resolving the efficiency contradiction
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 nano-structured grating pattern significantly increases light extraction efficiency across various wavelengths and angles, offering improved output coupling while maintaining electrical efficiency and reducing costs, with tunable refractive index for optimized performance.
Implementation Method 1
Illuminating the UV-sensitive organic layer with an intensity-dependent-interference fringe using a Mach-Zehnder interferometer
Implementation Method 2
The refractive index of the electroluminescent layer is dependent on an intensity of the UV-laser radiation
Implementation Method 3
light generated within a high-index organic material has difficulty propagating into the surrounding lower-index Anode/Glass substrate owing to total internal refection (TIR) at the glass/air interface
Implementation Method 4
A method of fabricating a nano-structured grating pattern in a photo-sensitive organic electroluminescent layer
Implementation Method 5
providing a Fresnel lens structure for improved light focusing
Implementation Method 6
the electroluminescent organic semiconductor material emits light when a voltage is applied across the anode and cathode electrodes
Data Source
Figure 1~3
Figure 4a~4c
Figure 5a~6b
AI summary
There is provided an organic light emitting diode (OLED) comprising an organic electroluminescent layer formed between a first electrode and a second electrode, characterised in that organic electroluminescent layer comprises a nano-structured grating pattern provided therein, wherein the grating is configured to modify the refractive index of the electroluminescent layer.