Hydrophilic Expansion Layer for Uniform OLED Ink-Jet Printing
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Solution Overview
Problem
Ink-jet printing for OLEDs faces issues with uneven film formation due to fixed thickness of pixel definition layers, leading to arched films with thicker centers and thinner edges, which affects light emission uniformity and the service life of display devices.
Innovation Solution
A display substrate with a two-layer pixel definition layer structure, where the first layer is made of a hydrophilic material with an expansion layer that can adjust its thickness, and the second layer is hydrophobic, ensuring the ink spreads uniformly and preventing overflow, thereby maintaining film thickness uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a fixed thickness pixel definition layer is used in ink-jet printing, then the manufacturing process is simple, but the film formation becomes uneven with arched shapes affecting light emission uniformity
Solution Approach 1:
The pixel definition layer is divided into multiple sub-layers with different functions: a first definition layer made of hydrophilic material that attracts ink solution, a second definition layer made of hydrophobic material that repels ink solution, and an expansion layer that adjusts thickness. This segmentation allows each layer to perform its specific function, solving the film thickness uniformity problem while maintaining manageable manufacturing complexity.
Solution Approach 2:
The invention changes the thickness parameter of the pixel definition layer dynamically by introducing an expansion layer that can expand to different degrees based on material properties and processing conditions. This allows the thickness to be adjusted to match the ink film thickness, ensuring uniform film formation without creating arched shapes that would affect light emission uniformity.
2Reliability
If the pixel definition layer thickness is increased to prevent ink overflow, then ink containment is improved, but film thickness uniformity deteriorates due to arched formation
Solution Approach 1:
Different regions of the pixel definition layer are given different properties: the first definition layer has hydrophilic properties to attract and spread ink solution uniformly, while the second definition layer has hydrophobic properties to prevent overflow at the edges. The expansion layer provides localized thickness adjustment. This local differentiation of properties allows the structure to simultaneously achieve good ink containment and uniform film thickness.
3Reliability
If a single-layer pixel definition structure is used, then the manufacturing process is simple, but the ability to control ink spreading and prevent overflow is insufficient
Solution Approach 1:
The pixel definition layer is segmented into functionally distinct layers: a hydrophilic first definition layer that promotes ink spreading, a hydrophobic second definition layer that prevents overflow, and an expansion layer for thickness control. This segmentation enables precise control over ink spreading behavior that cannot be achieved with a single-layer structure.
Solution Approach 2:
The pixel definition layer uses composite material structure combining hydrophilic materials (such as polyisoprene, polystyrene, or epoxy resin) and hydrophobic materials (such as fluorinated polymers) in specific configurations. This composite approach allows the structure to exhibit both ink-attracting and ink-repelling properties simultaneously, achieving superior ink spreading control.
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 adjustable thickness of the first definition layer ensures uniform pixel film formation, improving light emission consistency and extending the service life of display devices by preventing uneven film formation.
Implementation Method 1
the first definition layer includes an expansion layer capable of changing a thickness of the first definition layer
Implementation Method 2
the negative thermal expansion material includes Mn3XN or ZrW2O8
Implementation Method 3
the hydrophilic material is a material having attraction to a solution in which an organic electroluminescent material is dissolved
Implementation Method 4
the hydrophobic material is a material having repellency to ink in which an organic electroluminescent material is dissolved
Data Source
AI summary
A display substrate, an ink-jet printing method thereof and a display apparatus are provided. The display substrate includes a base substrate. A plurality of pixel definition layers is disposed on the base substrate, and a sub-pixel region is formed between pixel definition layers. A pixel definition layer includes a first definition layer disposed on the base substrate, and the first definition layer adopts a hydrophilic material. The first definition layer includes an expansion layer capable of changing the thickness of the first definition layer.