Ester-based solvent systems for printable organic light-emitting diode ink formulations
View Patent ↗Ink compositions for forming active layers in an organic light-emitting diode are provided. Also provided are methods of forming active layers of an OLED using the ink compositions. The ink compositions comprise a solvent system in which a substantial majority of the solvent is comprised of one or more ester compounds.
1. An ink composition comprising a conductive hole injection material dissolved in an ester-based solvent system, the ester-based solvent system having a boiling point of at least 300° C. and a surface tension at 23° C. in the range from about 25 dyne/cm to about 33 dyne/cm and comprising at least one ester, wherein at least 90 weight percent of the ester-based solvent system comprises the at least one ester, and wherein the at least one ester comprises an alkyl octanoate.
2. The ink composition of claim 1 , wherein the ester-based solvent system comprises at least 99 weight percent esters.
3. The ink composition of claim 1 , wherein the ester-based solvent system comprises at least 90 weight percent of the alkyl octanoate.
4. The ink composition of claim 1 , wherein the ester-based solvent system further comprises an alkyl sebacate.
5. The ink composition of claim 1 , wherein the ester-based solvent system comprises two or more alkyl octanoates.
6. The ink composition of claim 5 , wherein the ester-based solvent system comprises diethyl octanoate and octyl octanoate.
7. The ink composition of claim 5 , wherein the ester-based solvent system consists essentially of diethyl octanoate and octyl octanoate.
8. The ink composition of claim 1 , wherein the hole injection material is selected from phenylamines, starburst-type amines, phthalocyanines, and polyaniline.
9. A method of forming a hole injection layer for an organic light-emitting diode, the method comprising:
forming a layer of an ink composition in a pixel cell of an organic light-emitting diode pixel bank, the ink composition comprising a conductive hole injection material dissolved in an ester-based solvent system, the ester-based solvent system having a boiling point of at least 300° C. and a surface tension at 23° C. in the range from about 25 dyne/cm to about 33 dyne/cm and comprising at least one ester, wherein at least 90 weight percent of the ester-based solvent system comprises the at least one ester, and wherein the at least one ester comprises an alkyl octanoate; and
allowing the solvent from the solvent system to evaporate, whereby the hole injection layer is formed.
10. The method of claim 9 , wherein forming a layer of an ink composition in a pixel cell of an organic light-emitting diode pixel bank comprising inkjet printing the ink composition into the pixel cell of the organic light-emitting diode pixel bank.
11. The method of claim 9 , wherein the ester-based solvent system comprises at least 99 weight percent esters.
12. The method of claim 9 , wherein the ester-based solvent system comprises two or more alkyl octanoates.
13. The method of claim 12 , wherein the ester-based solvent system comprises diethyl octanoate and octyl octanoate.
14. The method of claim 9 , wherein the hole injection material is selected from phenylamines, starburst-type amines, phthalocyanines, and polyaniline.