Organic EL Bank Structure Reduces Leakage Current
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Solution Overview
Problem
Existing methods for producing organic electroluminescent display devices face challenges such as non-uniform thickness of layers, increased leakage current, and reduced productivity due to issues like material adherence to bank surfaces and local electric field concentration, which affect light-emission efficiency and device reliability.
Innovation Solution
The solution involves forming a bank on top of the organic layer to prevent material adherence and ensure uniform thickness, using a configuration where the organic layer is positioned below the light-emitting layer, and employing a production method that includes spin coating and ink-jet processing to simplify the process and improve cost-effectiveness for large-sized displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the hole injecting layer is applied in a larger region than the light-emitting layer, then the light-emitting layer can be fully covered, but leakage current is generated due to exposed conductive material
Solution Approach 1:
The patent introduces a third layer (encapsulation layer) above the existing two-layer structure (hole injecting layer and light-emitting layer) to vertically contain the conductive material within the pixel region. This dimensional addition allows the hole injecting layer to extend beyond the light-emitting layer for adequate coverage while the encapsulation layer prevents lateral spreading, thus eliminating leakage current without compromising light-emission efficiency.
Solution Approach 2:
The encapsulation layer acts as an intermediary barrier between the conductive hole injecting layer and the surrounding regions. This intermediate layer prevents direct contact between the exposed conductive material and adjacent pixels, thereby blocking leakage current paths while maintaining the electrical functionality of the hole injecting layer for charge injection into the light-emitting layer.
2Object-generated harmful factors
If the light-emitting layer area is made equal to or greater than the hole injecting layer area, then leakage current is suppressed, but the hole injecting layer cannot be fully covered and thickness uniformity is reduced
Solution Approach 1:
By adding the encapsulation layer in the vertical dimension, the patent enables the hole injecting layer to extend beyond the light-emitting layer boundaries without causing leakage. The encapsulation layer confines the conductive material laterally, allowing adequate coverage for uniform thickness formation while preventing exposure that would cause leakage current.
Solution Approach 2:
The encapsulation layer provides localized containment specifically at the boundaries where the hole injecting layer extends beyond the light-emitting layer. This local quality control allows different regions to have different functions: the central region maintains uniform thickness for optimal performance, while the extended regions are contained to prevent leakage without disrupting the overall thickness uniformity.
3Manufacturing precision
If vacuum deposition with mask is used to form light-emitting layers in respective pixels, then precise layer formation is achieved, but productivity and cost effectiveness are reduced
Solution Approach 1:
The patent extracts the patterning function from the vacuum deposition process itself and relocates it to the encapsulation layer formation step. By using ink-jet printing to deposit the encapsulation layer material only in required regions, the process achieves precise layer formation without requiring complex masks during vacuum deposition, thereby simplifying the overall manufacturing process and improving productivity.
Solution Approach 2:
The patent replaces the mechanical mask-based patterning system with a digital printing system (ink-jet process) for forming the encapsulation layer. This substitution eliminates the need for physical masks and complex alignment mechanisms, enabling more flexible and efficient production while maintaining precise layer formation through digital patterning control.
4Productivity
If ink-jet process is used to apply organic materials, then productivity and cost effectiveness are improved, but material spreading between pixels occurs
Solution Approach 1:
The encapsulation layer serves as an intermediary barrier that prevents material spreading between pixels. By forming this confining layer through ink-jet printing, the process maintains the productivity and cost advantages of ink-jet technology while the encapsulation layer acts as a physical barrier that stops material migration, thereby achieving both high productivity and precise material placement.
Solution Approach 2:
The encapsulation layer is formed preliminarily to establish material containment boundaries before final material deposition. This preliminary action creates predefined regions that guide subsequent material placement, preventing spreading while allowing the use of ink-jet process for its productivity and cost benefits.
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 approach effectively reduces leakage current, enhances light-emitting efficiency, and extends the lifespan of the organic electroluminescent display devices by ensuring uniform layer thickness and preventing material spreading, thereby improving overall device performance and manufacturing efficiency.
Implementation Method 1
a multi-layer of a hole injecting layer and a light-emitting layer, which constitutes an organic EL element, is applied in a region between banks
Implementation Method 2
employing a production method that includes spin coating and ink-jet processing
Data Source
AI summary
The present invention provides an organic electroluminescent display device including an electroluminescent element with a reduced leakage current and also provides a production method thereof. The present invention is an organic electroluminescent display device including an electroluminescent element, the electroluminescent element comprising a lower electrode, an organic layer, a light-emitting layer, and an upper electrode, stacked one above the other on and above a substrate in this order, wherein the organic electroluminescent display device further includes a bank formed on the organic layer.