OLED Display Two-Stage Bank Structure for Uniform Emission
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Solution Overview
Problem
The existing organic light emitting diode display devices face issues with non-uniform organic emission layers formed using solution processes, leading to luminance deviations, reduced image quality, and shortened device lifespan due to the pile-up phenomenon, especially when large-sized masks sag, causing thickness variations in the emission layers.
Innovation Solution
A two-stage bank structure is implemented, where a hydrophilic first bank and a hydrophobic second bank are used to define emission areas, with the second bank extending in a direction to expose parts of the first electrode, ensuring uniform organic emission layer formation and preventing material mixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a large-sized mask is used for patterning in vacuum deposition, then large-sized display devices can be manufactured, but the mask sags causing non-uniform organic emission layers and deposition errors
Solution Approach 1:
The patent divides the single large mask into multiple smaller masks arranged in a matrix pattern. Each mask has a size that prevents sagging while collectively covering the entire large display area. This segmentation allows vacuum deposition to be performed across large areas without the precision loss caused by mask sagging.
Solution Approach 2:
The patent employs a multi-layer bank structure where first banks and second banks are positioned at different heights and depths. The second banks are nested within the regions defined by first banks, creating a hierarchical arrangement that guides material deposition precisely into pixel regions while preventing pile-up at edges.
2Productivity
If solution process is used for large area patterning, then material reuse rate increases and thermal stability improves, but pile-up phenomenon occurs causing non-uniform emission layers
Solution Approach 1:
The patent creates different surface properties at different locations by implementing two-stage banks with distinct heights and hydrophobicity levels. First banks have one surface property while second banks have different properties, causing the organic emission material to spread differently in different regions. This local differentiation prevents pile-up at edges while ensuring complete coverage in central regions.
Solution Approach 2:
The patent transitions from two-dimensional planar patterning to three-dimensional hierarchical structuring with banks at different heights and depths. This vertical dimensionality addition creates depth-guided material flow that prevents lateral pile-up while maintaining complete pixel coverage, solving the uniformity issue inherent in flat solution processing.
3Device complexity
If single-stage bank structure is used, then device structure is simpler, but emission layer uniformity cannot be controlled
Solution Approach 1:
The banking structure is segmented into multiple functional stages: first banks that provide initial material confinement and second banks that provide refined edge control. Each stage performs a specific function in the material deposition sequence, allowing precise control over emission layer uniformity through divided functional responsibilities.
Solution Approach 2:
The first banks are formed in advance to establish the basic pixel region boundaries and provide initial material confinement. Subsequently, second banks are formed to refine the edges and control final material distribution. This preliminary action sequence ensures that each banking stage builds upon the previous one to achieve cumulative precision 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
This configuration ensures a uniform thickness of the organic emission layer, enhancing display quality, reducing the likelihood of dark spots, and extending the device's lifespan by minimizing the pile-up phenomenon and maintaining a sufficient aperture ratio.
Implementation Method 1
The solution process enables large area patterning with inkjet printing or nozzle printing
Implementation Method 2
The coated organic emission materials have a thickness deviation at each location due to difference in a hardening rate
Implementation Method 3
a hydrophilic first bank and a hydrophobic second bank are used to define emission areas
Implementation Method 4
a hydrophilic first bank and a hydrophobic second bank are used to define emission areas
Data Source
AI summary
An organic light emitting diode display device includes a substrate having pixel areas which are defined in a matrix form in first and second directions intersecting each other; a plurality of first electrodes each arranged in the corresponding pixel areas; a first bank having at least one first opening through which at least part of the first electrode is exposed; a second bank covering a part of the first bank and having at least one second opening through which at least part of the first electrode is exposed; and an organic emission layer disposed in the first opening. The second opening extends in the first direction so that the plurality of first electrodes arranged in the first direction is exposed through the second opening.