Organic light emitting diodes
This invention relates to organic light emitting diodes (OLEDs) and to methods for their manufacture. The invention provides an OLED element or display which enables contrast to be produced in an image. In accordance with the invention a layer of ink is patterned as a blocking layer between two OLED layers. The ink reduces or prevents conduction, i.e. movement of charge, between the two OLED layers in that area of the device. The ink may be dark in color, e.g. black, to increase the contrast ratio of the OLED. The blocking layer is provided between any two layers in the OLED and blocks the charge movement in these areas. The blocking layer may comprise a multiplicity of ink dots, the density of which determines the extent to which conduction is hindered. The blocking layer may be produced as a “grey-scale” pattern wherein the density of dots is varied across the pattern.
1. A method of forming an OLED element or display having two or more OLED layers, one of which is an electroluminescent layer, which method comprises providing a blocking layer that prevents conduction and movement of any charge into the electroluminescent layer by printing with an ink that prevents conduction and movement of any charge into the electroluminescent layer in a desired pattern between two of the OLED layers wherein one of the layers is the electroluminescent layer and the other layer is a hole-injection or hole-transport layer, whereby, in use, conduction across the OLED element or display is reduced in the area of the pattern.
2. A method of forming an OLED element or display as claimed in claim 1 wherein the ink is coloured to increase contrast.
3. A method of forming an OLED element or display as claimed in claim 1 wherein the blocking layer pattern comprises a multiplicity of discrete points of ink.
4. A method of forming an OLED element or display as claimed in claim 3 wherein the discrete points of ink are less than about 100 μm in size.
5. A method of forming an OLED element or display as claimed in claim 3 or 4 wherein the pattern comprises regions with different densities of the discrete points.
6. A method of forming an OLED element or display as claimed in claim 1 wherein the ink is insoluble in the medium used to deposit underlying and/or overlying OLED layers.
7. A method of forming an OLED element or display as claimed in claim 1 wherein the ink comprises a medium which is a liquid which does not dissolve the layer on which the ink is printed.
8. A method of forming an OLED element or display as claimed in claim 1 wherein the ink further comprises a colorant, a polymeric binder and/or functional additives.
9. A method of forming an OLED element or display as claimed in claim 1 wherein the ink is deposited by a direct printing technique selected from ink-jet printing, screen printing, microcontact printing, stamping, soft lithography or electrophotographic printing using a liquid or solid toner.
10. A method of forming an OLED element or display as claimed in claim 9 wherein the ink is deposited by ink-jet printing.
11. A method of forming an OLED element or display as claimed in claim 1 wherein the ink blocking layer is thicker than the OLED layer(s) subsequently deposited onto it.
12. A method of forming an OLED element or display as claimed in claim 1 wherein the ink blocking layer thickness is from 100 nm to 100 μm thick.
13. A method of forming an OLED element or display as claimed in claim 1 wherein the OLED layer(s) to be deposited are independently applied by a coating or printing technique selected from solution-, spin-, spray-, dip-, web-, die- or evaporation coating: electroless deposition and ink-jet printing, screen printing, microcontact printing, stamping or soft lithography.
14. A method of forming an OLED element or display as claimed in claim 1 wherein the wetting of the ink includes a surface treatment of the layer on which the ink is deposited.
15. An OLED element or display obtainable by a method as claimed in claim 1 .
16. An OLED display as claimed in claim 15 which, in use, produces a pseudo 3-D image.