Ester-based solvent systems for printable organic light-emitting diode ink formulations

1. A method of forming a hole transporting layer, a hole injection layer, or a light-emitting layer for an organic light-emitting diode, the method comprising:

inkjet printing a layer of an ink composition in a pixel cell of an organic light-emitting diode pixel bank, the ink composition comprising a first component selected from a hole transporting material comprising a crosslinkable polymer, a conductive hole injection material, and an organic electroluminescent material, wherein the first component is dissolved in a solvent system, the solvent system comprising at least one ester, and further wherein the ink composition comprises from 0.1 to 5 weight percent of the first component and has a viscosity of 100 cPs or lower at 23° C.; and

drying the layer of the ink composition under vacuum.

2. The method of claim 1 , further comprising heating the layer of the ink composition.

3. The method of claim 1 , wherein the ink composition comprises the organic electroluminescent material and the organic electroluminescent material is an organic polymer selected from polyparaphenylene vinylene derivatives, polythiophene derivatives, polyparaphenylene derivatives, polysilane derivatives, polyacetylene derivatives, and polyfluorene derivatives.

4. The method of claim 3 , wherein the light-emitting layer emits luminescence with a coefficient of variation of no greater than 20%.

5. The method of claim 1 , wherein the ink composition comprises the hole transporting material and the hole transporting material is selected from polysilanes, polysilane derivatives, polysiloxane derivatives having an aromatic amine at the side chain or the main chain, pyrazoline derivatives, polythiophene, polythiophene derivatives, polypyrroles, polypyrrole derivatives, poly(2,5 thienylene vinylene), and poly(2,5 thienylene vinylene) derivatives.

6. The method of claim 1 , wherein the ink composition comprises the conductive hole injection material and the conductive hole injection material is selected from phenylamines, starburst-type amines, phthalocyanines, and polyaniline.

7. The method of claim 1 , wherein the pixel cell comprises a floor and a wall that defines the perimeter of the pixel cell, and further wherein the pixel cell and the wall are coated with surfactant.

8. The method of claim 1 , wherein the hole transporting layer, the hole injection layer, or the light-emitting layer has a thickness that varies by no more than 10%.

9. A method of forming a hole transporting layer and a light-emitting layer for an organic light-emitting diode, the method comprising:

inkjet printing a layer of a first ink composition in a pixel cell of an organic light-emitting diode pixel bank, the first ink composition comprising a hole transporting material comprising a crosslinkable polymer, wherein the hole transporting material is dissolved in a solvent system, the solvent system comprising at least one ester, wherein the first ink composition comprises from 0.1 to 5 weight percent of the hole transporting material and has a viscosity of 100 cPs or lower at 23° C.;

drying the layer of the first ink composition under vacuum;

inkjet printing a layer of a second ink composition in the pixel cell, the second ink composition comprising an organic electroluminescent material dissolved in a second solvent system, the second solvent system comprising least one ester, wherein the second ink composition comprises from 0.1 to 5 weight percent of the organic electroluminescent material and has a viscosity of 100 cPs or lower at 23° C.; and

drying the layer of the second ink composition under vacuum.

10. The method of claim 9 , further comprising heating the layer of the first ink composition, whereby a hole transporting layer that is at least partially crosslinked is formed and heating the layer of the second ink composition, whereby a light emitting layer is formed.

11. The method of claim 10 , wherein the crosslinkable polymer of the hole transporting layer is not fully crosslinked.

12. The method of claim 9 , wherein the at least one ester of the first solvent system and the at least one ester of the second solvent system are the same ester.

13. The method of claim 9 , further comprising inkjet printing a third ink composition comprising a conductive hole injection material dissolved in a solvent system in the pixel cell, the solvent system comprising at least one ester, and drying the layer of the third ink composition under vacuum.

14. The method of claim 13 , further comprising heating the layer of the third ink composition, whereby a hole injection layer is formed.