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. A method of forming a light-emitting layer for an organic light-emitting diode, the method comprising:
forming a layer of an ink composition in a pixel cell of a organic light-emitting diode pixel bank, the pixel cell comprising an emission region defined by a pixel bank, the ink composition comprising an organic electroluminescent material dissolved in an ester-based solvent system comprising at least one ester, 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 26 dyne/cm to about 33 dyne/cm; and
allowing the solvent from the solvent system to evaporate, whereby the light-emitting layer is formed.
2. The method of claim 1 , wherein the ester-based solvent system comprises an ester selected from alkyl octanoates, alkyl sebacates or combinations thereof.
3. The method of claim 1 , wherein the ester-based solvent system comprises diethyl sebacate.
4. The method of claim 1 , wherein the ester-based solvent system consists essentially of diethyl sebacate.
5. The method of claim 1 , wherein the ester-based solvent system comprises an alkyl octanoate.
6. The method of claim 5 , wherein the ester-based solvent system comprises octyl octanoate.
7. The method of claim 6 , wherein the ester-based solvent system consists essentially of octyl octanoate.
8. The method of claim 6 , wherein the ester-based solvent system comprises at least one additional ester, and further wherein the ester-based solvent system comprises at least 50 weight percent octyl octanoate, based on the total weight of the solvents in the ester-based solvent system.
9. The method of claim 8 , wherein the at least one additional ester comprises diallyl phthalate, isononyl isononate or a mixture thereof.
10. The method of claim 1 , wherein the thickness of the light-emitting layer varies by no more than 10% across the width of the pixel cell.
11. The method of claim 1 , wherein the ester-based solvent system comprises at least 99 weight percent ester, based on the total weight of the solvents in the ester-based solvent system.
12. The method of claim 11 , wherein the ester-based solvent system consists essentially of esters.
13. The method of claim 1 , wherein the at least one ester has a boiling point of at least 300° C. and a surface tension at 23° C. in the range from about 26 dyne/cm to about 33 dyne/cm.
14. The method of claim 1 , wherein the ester-based solvent system comprises at least 90 weight percent ester, based on the total weight of the solvents in the ester-based solvent system.
15. A method of forming a hole transporting layer for an organic light-emitting diode, the method comprising:
forming a layer of an ink composition in a pixel cell of a organic light-emitting diode pixel bank, the pixel cell comprising an emission region defined by a pixel bank, the ink composition comprising an hole transporting material comprising a crosslinking polymer, wherein the hole transporting material is dissolved in an ester-based solvent system comprising at least one ester, 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 32 dyne/cm; and
allowing the solvent from the solvent system to evaporate, whereby the hole transporting layer is formed.
16. The method of claim 15 , wherein the ester-based solvent system comprises an alkyl octanoate.
17. The method of claim 16 , wherein the ester-based solvent system comprises two or more alkyl octanoates.
18. The method of claim 17 , wherein the ester-based solvent system comprises diethyl octanoate and octyl octanoate.
19. The method of claim 18 , wherein the ester-based solvent system consists essentially of diethyl octanoate and octyl octanoate.
20. The method of claim 15 , wherein the thickness of the hole transporting layer varies by no more than 10% across the width of the pixel cell.
21. A method of forming a hole transport layer and a light-emitting layer for an organic light-emitting diode, the method comprising:
forming a layer of an ink composition in a pixel cell of a organic light-emitting diode pixel bank, the pixel cell comprising an emission region defined by a pixel bank, the ink composition comprising an hole transporting material comprising a crosslinking polymer, wherein the hole transporting material is dissolved in an ester-based solvent system comprising at least one ester, 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 32 dyne/cm;
allowing the solvent from the solvent system to evaporate, whereby the hole transporting layer is formed;
forming a layer of an ink composition on the hole transporting layer, the ink composition comprising an organic electroluminescent material dissolved in an ester-based solvent system comprising at least one ester, 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 26 dyne/cm to about 33 dyne/cm; and
allowing the solvent from the solvent system to evaporate, whereby the light-emitting layer is formed.
22. The method of claim 21 , wherein the crosslinking polymer of the hole transporting layer is not fully crosslinked.
23. A method of forming a hole transporting layer and a light-emitting layer for an organic light-emitting diode, the method comprising:
forming a layer of a first ink composition in a pixel cell of a organic light-emitting diode pixel bank, the first ink composition comprising a hole transporting material comprising a crosslinking polymer, wherein the hole transporting material is dissolved in a first ester-based solvent system comprising a mixture of diethyl octanoate and octyl octanoate;
allowing the solvent from the first ester-based solvent system to evaporate, whereby the hole transporting layer is formed;
forming a layer of a second ink composition in the pixel cell on the hole transporting layer, the second ink composition comprising an organic electroluminescent material dissolved in a second ester-based solvent system comprising diethyl sebacate; and
allowing the solvent from the second ester-based solvent system to evaporate, whereby the light-emitting layer is formed.
24. The method of claim 15 , wherein the ester-based solvent system comprises at least 99 weight percent ester, based on the total weight of the solvents in the ester-based solvent system.
25. The method of claim 24 , wherein the ester-based solvent system consists essentially of esters.
26. The method of claim 15 , wherein the at least one ester has 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 32 dyne/cm.
27. The method of claim 15 , wherein
the ester-based solvent system comprises at least 90 weight percent ester, based on the total weight of the solvents in the ester-based solvent system.