Aromatic Solvent Inkjet Fluid for OLED Organic Layers
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Solution Overview
Problem
Inkjet printing of small molecule materials for organic light emitting devices (OLEDs) faces challenges due to rapid drying of conventional solvents, leading to nozzle clogging and inferior film morphology, while higher boiling point solvents are difficult to remove and can cause heat degradation, resulting in solvent residue that interferes with device performance.
Innovation Solution
A liquid composition comprising a small molecule organic semiconductor material mixed with an aromatic solvent having a melting point of 25° C. or lower, which facilitates charge carrier transport and reduces solvent residue, allowing for improved inkjet printing of organic layers in OLEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional solvents (toluene or xylene) are used for inkjet printing of small molecule materials, then the solvent can be easily removed, but the solvent dries too fast causing nozzle clogging and inferior film morphology
Solution Approach 1:
The patent changes the physical parameters of the solvent by selecting aromatic solvents with higher boiling points (e.g., o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, mesitylene, 1,2,4-trimethylbenzene) compared to conventional solvents like toluene or xylene. This parameter change slows down the evaporation rate, preventing nozzle clogging and improving film morphology while still allowing solvent removal through controlled drying processes.
Solution Approach 2:
The patent uses composite solvent systems comprising aromatic solvents combined with specific small molecule organic semiconductor materials. The aromatic solvent acts as a carrier that provides optimal drying characteristics and film formation properties, creating a composite inkjet formulation that resolves the contradiction between easy removal and controlled evaporation.
2Reliability
If higher boiling point solvents are used to prevent rapid drying, then nozzle clogging and film morphology are improved, but the solvent is difficult to remove and can cause heat degradation
Solution Approach 1:
The patent carefully selects aromatic solvents with boiling points in a specific range (higher than toluene/xylene but not excessively high) to optimize the balance between preventing rapid drying and enabling solvent removal. The controlled boiling point parameter allows sufficient time for proper film formation during deposition while still permitting complete evaporation during subsequent drying or device operation.
3Reliability
If higher boiling point solvents are used to prevent rapid drying, then nozzle clogging is reduced, but solvent residue remains in the deposited organic layer interfering with device performance
Solution Approach 1:
The patent selects aromatic solvents with specific boiling point parameters that enable complete evaporation during the device fabrication process. The chosen solvents have volatility characteristics that allow them to remain in the liquid state during inkjet deposition (preventing clogging) but evaporate completely during subsequent drying or initial device operation, leaving no residue to interfere with electronic device performance.
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 use of aromatic solvents with specific properties enhances the performance of organic electronic devices by reducing electrical resistance and minimizing solvent residue, leading to improved device performance and extended operational lifetimes.
Implementation Method 1
an aromatic solvent that will create less resistance to the transport of charge carriers, such as electrons
Implementation Method 2
drying the liquid composition to form the organic layer on the surface
Data Source
AI summary
A liquid composition (e.g., inkjet fluid) for forming an organic layer of an organic electronic device (e.g., an OLED). The liquid composition comprises a small molecule organic semiconductor material mixed in an aromatic solvent. The aromatic solvent, when left as a residue in the organic layer, is capable of presenting relatively reduced resistivity to charge transport or facilitating charge transport in the organic layer that is deposited, as compared to other conventional solvents. In certain embodiments, the aromatic solvent compound has the following formula: wherein R represents one or more optional substituents on the benzene ring, wherein each R is independently an aliphatic group containing from 1-15 carbon atoms; and wherein X is a substitution group that contains an electron-withdrawing group selected from nitrile, sulfonyl, or trifluoromethyl.