OLED Hole Injecting Layer Wettability via Hydrophilic Wall
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Solution Overview
Problem
Passive matrix OLEDs experience decreased hole injecting efficiency due to de-wetting phenomena around hydrophobic polymer walls, leading to reduced brightness, especially in larger display applications.
Innovation Solution
A display device with a hydrophilic wall made of silicon oxide, where the combined thickness of the first electrode and hole injecting layer exceeds the hydrophilic wall thickness, ensuring continuous formation and improved wettability, and using PEDOT and PSS in the hole injecting layer, along with amorphous silicon TFTs, to enhance hole injecting efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hydrophobic polymer wall is used to separate pixel areas, then the wall provides effective electrical isolation, but de-wetting phenomenon occurs causing non-uniform hole injecting layer thickness and reduced brightness
Solution Approach 1:
The patent changes the surface energy parameter of the wall by switching from a hydrophobic polymer material to a hydrophilic material (silicon oxide, silicon nitride, or indium tin oxide). This parameter change eliminates the de-wetting phenomenon that occurs with hydrophobic materials, ensuring uniform hole injecting layer formation while maintaining electrical isolation functionality.
Solution Approach 2:
The patent employs composite material structure where the wall is formed from inorganic hydrophilic materials (silicon oxide, silicon nitride, or indium tin oxide) rather than organic polymer materials. This material substitution resolves the contradiction by providing both electrical isolation and hydrophilic surface properties for uniform layer deposition.
2Ease of manufacture
If the hole injecting layer is formed by ink-jetting on pixel area, then the manufacturing process is simple, but de-wetting around hydrophobic walls causes thinning and reduced hole injecting efficiency
Solution Approach 1:
By changing the surface energy parameter of the wall from hydrophobic to hydrophilic, the patent ensures that the ink-jetted hole injecting layer maintains uniform thickness during the drying process. The hydrophilic surface prevents de-wetting, allowing the simple ink-jetting process to achieve both ease of manufacture and manufacturing precision.
3Ease of manufacture
If passive matrix OLED structure is used, then manufacturing is simple, but power consumption increases rapidly with display size and resolution
Solution Approach 1:
The patent applies segmentation by dividing the display into independently controllable pixel areas, each with its own TFT switch and organic light emitting layer. This active matrix structure allows individual pixel control, enabling high resolution displays while maintaining reasonable power consumption through selective pixel activation.
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 improves hole injecting efficiency and brightness by ensuring uniform thickness and coverage of the hole injecting layer, addressing the de-wetting issues and enhancing manufacturing simplicity.
Implementation Method 1
a hydrophilic wall between the first electrode and an adjacent electrode that is adjacent to the first electrode... ensuring continuous formation and improved wettability
Data Source
AI summary
An organic light emitting diode (OLED) display device with improved hole injection efficiency is presented, along with a method of making the display device. A thin film transistor (TFT) is formed on an insulating substrate. A pixel electrode is electrically connected to the TFT, and a hydrophilic wall is formed between the pixel electrode and an adjacent pixel electrode. A hole injecting layer and a first organic light emitting layer covering the pixel electrode and the hydrophilic wall and formed. Then, a second organic light emitting layer and a third organic light emitting layer are formed to partly cover the first organic light emitting layer.