OLED Refractive Layer for Light Extraction and Current Flow
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Solution Overview
Problem
Conventional organic light emitting diode (OLED) displays face challenges in manufacturing large-sized top emission type displays due to surface resistivity issues with the second electrode, leading to inefficient current flow, and bottom emission type displays suffer from reduced light emission efficiency and color reproduction.
Innovation Solution
Incorporating a refractive layer with a higher refractive index than the first electrode, made of materials like TiO2, ZnO2, or ZrO2, between the substrate and the first electrode, which enhances light emission efficiency and color reproduction by refracting and reflecting light under a micro-cavity effect, while allowing the first and second electrodes to differ in thickness and transparency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If top emission type structure is used, then light emission efficiency is improved, but surface resistivity of the second electrode increases with device enlargement causing inefficient current flow
Solution Approach 1:
The patent inverts the conventional top emission structure to a bottom emission structure, where the first electrode becomes the light-emitting side and the second electrode becomes the reflective back electrode. This inversion allows the second electrode to be made thicker for better current flow while still achieving efficient light emission through the first electrode.
Solution Approach 2:
The patent introduces a refractive layer with high refractive index (2.2-3.0) between the substrate and the first electrode to enhance light extraction efficiency. This parameter change compensates for the reduced light emission efficiency that would otherwise result from the bottom emission configuration.
2Reliability
If bottom emission type structure is used, then current flow efficiency is improved by allowing sufficient electrode thickness, but light emission efficiency and color reproduction are deteriorated
Solution Approach 1:
The patent introduces a refractive layer as an intermediary between the substrate and the first electrode. This layer has a high refractive index (2.2-3.0) that creates a larger refractive index difference with the surrounding media, thereby enhancing light extraction efficiency and color reproduction in the bottom emission structure.
Solution Approach 2:
By changing the refractive index parameter of the layer adjacent to the first electrode, the patent optimizes light extraction efficiency. The refractive layer with index 2.2-3.0 creates optimal conditions for light emission while maintaining the benefits of the bottom emission structure.
3Ease of manufacture
If a single-layer second electrode is used for large area coverage, then manufacturing simplicity is maintained, but surface resistivity increases causing poor current flow
Solution Approach 1:
By inverting the emission structure, the patent allows the second electrode to be positioned at the back where it can be made thicker for better current flow. The first electrode remains thin and transparent for light emission, while the second electrode provides robust electrical connection across the entire large area.
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 configuration improves light emission efficiency and color reproduction in OLED displays, making them suitable for larger sizes by optimizing the refractive index and layer thicknesses, and maintaining efficient current flow.
Implementation Method 1
a refractive layer disposed between the substrate and the first electrode, where the refractive layer has a refractive index that is greater than the refractive index of the first electrode
Implementation Method 2
refracting and reflecting light under a micro-cavity effect
Implementation Method 3
refracting and reflecting light under a micro-cavity effect
Data Source
AI summary
An organic light emitting diode display is disclosed. The display includes a substrate, a first electrode placed on the substrate, an organic emissive layer placed on the first electrode, a second electrode placed on the organic emissive layer, and a refractive layer disposed between the substrate and the first electrode. The refractive layer is greater in refractive index than the first electrode.