Organic Light Emitting Element Ink Viscosity Control
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Solution Overview
Problem
The ink application method for organic electroluminescent devices faces challenges in achieving both excellent ejectability and flatness of the functional layer, as low viscosity is required for good ejectability but high viscosity is needed for flatness, and existing inks struggle to balance these opposing characteristics.
Innovation Solution
An ink composition comprising a functional material, a first solvent, a second solvent with a diester skeleton, and a third aliphatic alcohol solvent, where the boiling points are carefully managed to maintain low viscosity for ejectability and increase viscosity for flatness, with the third solvent evaporating after ejection to enhance layer flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the ink viscosity is lowered to improve ejectability, then the ejectability is improved, but the flatness of the functional layer deteriorates
Solution Approach 1:
The ink viscosity is made dynamic rather than static by using a solvent mixture where the third solvent (aliphatic alcohol) evaporates after ejection, causing the viscosity to increase from a lower initial value to a higher final value. This dynamic viscosity change allows the ink to exhibit low viscosity during ejection for good ejectability, then transitions to high viscosity after ejection to provide excellent flatness.
Solution Approach 2:
The physical parameter of viscosity is changed over time through controlled evaporation of the third solvent. The ink composition is designed with specific solvents (first solvent: high boiling point, second solvent: diester with moderate boiling point, third solvent: aliphatic alcohol with lowest boiling point) that create a time-dependent viscosity profile, transitioning from low to high viscosity as the third solvent evaporates.
2Manufacturing precision
If the ink viscosity is increased to improve flatness, then the flatness is improved, but the ejectability deteriorates
Solution Approach 1:
The third solvent is incorporated into the ink composition in advance to suppress the viscosity of the second solvent before ejection. This preliminary action ensures low viscosity during the ejection process, and the third solvent is designed to evaporate after ejection, automatically providing the high viscosity needed for flatness without compromising initial ejectability.
Solution Approach 2:
The third solvent (aliphatic alcohol) acts as an intermediary substance that temporarily modifies the viscosity characteristics of the ink. It mediates between the conflicting requirements of low viscosity for ejection and high viscosity for flatness by being present during ejection to lower viscosity, then evaporating to allow the second solvent to provide high viscosity for flatness.
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 ink achieves both high ejectability before ejection and improved flatness after ejection, resulting in a uniform functional layer thickness and excellent light-emitting characteristics for organic electroluminescent devices.
Implementation Method 1
After the third solvent evaporates, the viscosity of the second solvent returns to the predetermined viscosity and the ink becomes higher in viscosity
Data Source
Figure 1~2B
Figure 3~4
Figure 5
AI summary
An ink for an organic electroluminescent device that is excellent in both the ejectability and the flatness is provided. The ink is the ink 7a for use in an organic electroluminescent device. The ink 7a includes the functional material 7b and the first, second, and third solvents. The functional material 7b constitutes the functional layer 7 of the organic electroluminescent device 111. The first solvent dissolves the functional material 7b. The second solvent has the diester backbone and is equal to or lower than the first solvent in boiling point, or higher than the first solvent in boiling point by a difference of 20°C or less. The third solvent is an aliphatic alcohol and is lower than the first and second solvents in boiling point.