Ink Composition for Organic EL Functional Layers
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Solution Overview
Problem
Existing ink compositions for forming functional layers in organic electroluminescence (EL) elements face issues with nozzle clogging, uneven application, and poor wettability due to solvent properties, leading to suboptimal film formation and electrical properties.
Innovation Solution
An ink composition combining a first aromatic solvent with a boiling point between 250°C and 350°C and a second aliphatic solvent with a boiling point above 200°C, where the second solvent has a lower surface tension and higher volume fraction, preventing nozzle clogging and ensuring even application and wettability on conductive films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an alcohol compound with high boiling point is used as a solvent, then the ink is suitable for ink jet method, but the organic material is easily aggregated during drying process
Solution Approach 1:
The patent uses a mixed solvent system comprising an alcohol compound (first solvent) and a carboxylic acid compound (second solvent) instead of a single solvent. This composite solvent system allows the alcohol compound to provide stable nozzle discharge while the carboxylic acid compound suppresses organic material aggregation during drying, resolving the contradiction between discharge stability and material stability.
Solution Approach 2:
The patent specifies precise parameter ranges: the alcohol compound has a boiling point of 120°C or higher (preferably 140-200°C), the carboxylic acid compound has a boiling point of 100-180°C, and their volume ratios are controlled (first solvent: 10-70 vol%, second solvent: 30-90 vol%). These parameter optimizations ensure both stable discharge and prevention of aggregation.
2Reliability
If aromatic compounds are used as solvents, then nozzle clogging is prevented, but wetting spread is difficult and uneven application occurs
Solution Approach 1:
The patent combines aromatic compounds (providing nozzle discharge stability and clogging prevention) with carboxylic acid compounds (providing excellent wetting properties). This composite solvent system integrates the advantages of both solvent types, achieving both stable discharge and uniform application on conductive films.
Solution Approach 2:
The carboxylic acid compound specifically addresses the wetting issue at the liquid-substrate interface, while the aromatic compound maintains overall discharge stability. Each solvent component performs its specialized function locally, achieving both nozzle reliability and application uniformity.
3Speed
If a low boiling point solvent is used, then evaporation is fast, but wettability deteriorates when remaining solvent is present
Solution Approach 1:
The patent uses a mixed solvent system where the carboxylic acid compound (with moderate boiling point of 100-180°C) provides sustained wettability during the drying process, while the alcohol compound (boiling point 120°C or higher) ensures fast enough evaporation. The synergistic effect maintains both evaporation speed and wettability throughout the drying process.
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 composition effectively prevents nozzle clogging and ensures even film formation, enhancing the stability and uniformity of functional layers in organic EL elements, thereby improving the yield and display quality of light-emitting devices.
Implementation Method 1
the second solvent has a lower surface tension and higher volume fraction, preventing nozzle clogging and ensuring even application and wettability on conductive films
Implementation Method 2
a first aromatic solvent with a boiling point between 250°C and 350°C... a second aliphatic solvent with a boiling point above 200°C
Data Source
AI summary
An ink for forming a functional layer includes a first component that contains at least one kind of aromatic solvent of which a boiling point is higher than or equal to 250° C. and lower than or equal to 350° C., a second component that contains at least one kind of aliphatic solvent of which a boiling point is higher than or equal to 200° C., and a third component for forming a positive hole injection layer, in which a solubility of the third component in the first component is higher than the solubility of the third component in the second component, a mixing ratio of the second component is 30 vol %, the boiling point of the first component is higher than the boiling point of the second component, and a difference between the boiling points thereof is higher than or equal to 30° C.