Fluorosurfactant-containing ink compositions for inkjet printing
Ink compositions formulated for inkjet printing the hole injecting layer (HIL) or hole transporting layer (HTL) of an organic light emitting diode (OLED) are provided. The ink compositions comprise fluorosurfactants that prevent uncontrolled spreading of the printed ink compositions. Also provided are methods of inkjet printing the HILs or HTLs using the ink compositions.
1. An ink composition comprising:
at least 40 wt. % of an electrically conductive polythiophene;
at least 5 wt. % of an aprotic organic solvent having a boiling point of at least 240 ° C., a viscosity of no greater than 15 cPs at 25 ° C. and a surface tension of no greater than 55 dyne/cm at 25 ° C.; and
water.
2. The ink composition of claim 1 comprising at least 50 wt. % of the electrically conductive polythiophene and at least 10 wt. % of the aprotic organic solvent.
3. The ink composition of claim 1 , wherein the aprotic organic solvent has a viscosity of no greater than 10 cPs at 25 ° C.
4. The ink composition of claim 1 further comprising a propylene glycol methyl ether co-solvent, wherein the aprotic organic solvent is the majority organic solvent in the ink composition.
5. The ink composition of claim 1 , wherein the aprotic organic solvent is sulfolane.
6. The ink composition of claim 5 , wherein the electrically conductive polythiophene is poly(3,4-ethylenedioxythiophene).
7. The ink composition of claim 6 comprising at least 55 wt. % of the poly(3,4-ethylenedioxythiophene).
8. The ink composition of claim 6 further comprising a propylene glycol methyl ether co-solvent, wherein the sulfolane is the majority organic solvent in the ink composition, and further wherein the ink composition comprises 50 wt. % to 70 wt. % of the poly(3,4-ethylenedioxythiophene) and 5 wt. % to 15 wt. % of the sulfolane.
9. The ink composition of claim 5 further comprising a propylene glycol methyl ether co-solvent, wherein the sulfolane is the majority organic solvent in the ink composition.
10. The ink composition of claim 1 , wherein the aprotic organic solvent is propylene carbonate.
11. The ink composition of claim 1 , wherein the aprotic organic solvent is dimethylpropylene urea.
12. A method of forming a hole injecting layer for an organic light emitting diode, the method comprising:
inkjet printing a droplet of an ink composition over an electrode layer in a pixel cell of an organic light emitting diode pixel bank, the ink composition comprising:
at least 40 wt. % of an electrically conductive polythiophene;
at least 5 wt. % of an aprotic organic solvent having a boiling point of at least 240 ° C., a viscosity of no greater than 15 cPs at the printing temperature and a surface tension of no greater than 55 dyne/cm at the printing temperature; and water; and
allowing the volatile components of the ink composition to evaporate, whereby the hole injecting layer is formed.
13. The method of claim 12 , wherein the ink composition comprises at least 50 wt. % of the electrically conductive polythiophene and at least 10 wt. % of the aprotic organic solvent.
14. The method of claim 12 , wherein the aprotic organic solvent has a viscosity of no greater than 10 cPs at the printing temperature.
15. The method of claim 12 , wherein the ink composition further comprises a propylene glycol methyl ether co-solvent, wherein the aprotic organic solvent is the majority organic solvent in the ink composition.
16. The method of claim 12 , wherein the aprotic organic solvent is sulfolane.
17. The method of claim 16 , wherein the electrically conductive polythiophene is poly(3,4-ethylenedioxythiophene).
18. The method of claim 17 , wherein the ink composition comprises at least 55 wt. % of the poly(3,4-ethylenedioxythiophene).
19. The method of claim 17 , wherein the ink composition further comprises a propylene glycol methyl ether co-solvent, wherein the sulfolane is the majority organic solvent in the ink composition, and further wherein the ink composition comprises 50 wt. % to 70 wt. % of the poly(3,4-ethylenedioxythiophene) and 5 wt. % to 15 wt. % of the sulfolane.
20. The method of claim 16 , wherein the ink composition further comprises a propylene glycol methyl ether co-solvent, wherein the sulfolane is the majority organic solvent in the ink composition.
21. The method of claim 12 , wherein the aprotic organic solvent is propylene carbonate.
22. The method of claim 12 , wherein the aprotic organic solvent is dimethylpropylene urea.