Top Emission Organic EL Lower Electrode Thickness Control
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Solution Overview
Problem
In top emission organic EL elements, the center area of the lower electrode often has low packing density and thickness due to drying process flows and contact angle effects, leading to reduced light reflection efficiency and overall light extracting efficiency.
Innovation Solution
A top emission organic EL element design where the lower electrode thickness increases from the boundary portion towards the center area, ensuring a sufficient thickness of 150 nm or more at the center, and a manufacturing method involving an insulating layer with a hole portion and a bank to prevent nanoparticle flow, ensuring uniform packing density and light reflectance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If liquid-phase coating technique is used to manufacture the lower electrode, then mass productiveness is enhanced, but the center area of the electrode film becomes thin with low packing density
Solution Approach 1:
The patent applies a preliminary anti-flow action by using a dispersant containing surfactant before the drying process begins. This prevents the nanoparticle flow that would otherwise occur during drying, ensuring uniform distribution of nanoparticles across the electrode film including the center area, while still allowing the use of liquid-phase coating for mass production
2Ease of manufacture
If the solution is coated and dried, then the electrode film is formed, but the nanoparticles move toward the edge portion causing non-uniform density
Solution Approach 1:
The patent introduces a dispersant containing surfactant as an intermediary substance between the nanoparticle solution and the substrate. This dispersant adsorbs onto the nanoparticle surfaces and provides steric or electrostatic repulsion that prevents nanoparticle aggregation and flow during drying, maintaining uniform packing density across the entire electrode film
3Ease of manufacture
If the bank surface has high affinity with ink, then the solution is drawn toward the bank, but the center area of the film has even lower packing density
Solution Approach 1:
The dispersant acts as an intermediary that modifies the interaction between the nanoparticle solution and the bank surface. By providing steric or electrostatic repulsion through surfactant adsorption, it counteracts the capillary action that would draw solution toward the bank, ensuring the center area maintains sufficient nanoparticle concentration and packing density
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 design enhances light reflectance uniformity and increases the light extracting efficiency of the organic EL element by maintaining adequate thickness and packing density across the lower electrode, particularly at the center area.
Implementation Method 1
the lower electrode on the substrate side is required to have high light reflectivity in order to enhance light extracting efficiency
Implementation Method 2
a flow heading from the center area toward an edge portion is generated during a process in which drying advances. The nanoparticles within the solution move together with the flow toward the edge portion
Data Source
AI summary
A top emission organic EL element includes a substrate, an insulating layer including a hole portion, a lower electrode, a light emitting layer, a bank surrounding the lower electrode and the light emitting layer, and an upper transparent electrode. The insulating layer, the lower electrode, the light emitting layer, the bank, and the upper transparent electrode are disposed above the substrate. The bank is arranged on the insulating layer so as to surround the hole portion. The lower electrode is configured to cover an inner side of the hole portion and an area, where the bank is not arranged, of an upper surface of the insulating layer, and a thickness at a center area of the lower electrode is 150 nm or more.