Organic light-emitting diode display with structured electrode
A display may have an array of organic light-emitting diode (OLED) pixels that each have OLED layers interposed between a cathode and an anode. Voltage may be applied to the anode of each pixel to control the magnitude of emitted light. The conductivity of the OLED layers may allow leakage current to pass between neighboring anodes in the display. To reduce leakage current and cross-talk, the thickness of at least one of the OLED layers may be reduced. To maintain the optical cavity of the pixels, transparent optical spacer structures may be inserted. Alternatively, the thickness of the anodes can be increased. To accommodate a common prime layer within the OLED layers, the optical spacers or anodes may be separately patterned to have different thicknesses. Grating structures and photonic crystal structures may be embedded as part of the optical spacers to help control emission at selected viewing angles.
1. A display comprising:
a cathode;
an anode;
organic light-emitting diode (OLED) layers formed between the cathode and the anode, wherein the organic light-emitting diode layers comprise electron layers having a first thickness and a hole transport layer having a second thickness less than the first thickness and minimized, directly over the anode, to reduce leakage current in the display;
a reflector layer, wherein the anode has a top surface facing the cathode and a bottom surface facing the reflector layer;
an additional anode; and
an additional reflector layer, wherein the anode and the additional anode have different thicknesses.
2. The display of claim 1 , wherein the hole transport layer has a minimum thickness allowed by a process used to manufacture the display.
3. The display of claim 2 , wherein the organic light-emitting diode layers further comprise a hole injection layer having a minimum thickness allowed by the manufacturing process or an electron blocking layer having a minimum thickness allowed by the manufacturing process.
4. The display of claim 1 , further comprising:
a Distributed Bragg Reflector (DBR) structure interposed between the reflector layer and the anode, wherein the DBR structure is configured to enhance the reflectivity of the reflector layer, and wherein the thickness and material of the anode is selected as part of the DBR structure.
5. The display of claim 1 , wherein the thickness of the anode is selected to provide a predetermined optical cavity distance for the display.
6. The display of claim 1 , wherein the anode is part of a first pixel and wherein the additional anode is part of a second pixel, further comprising:
a common electron blocking layer that is formed over the anode in the first pixel and the additional anode in the second pixel;
a first emissive layer formed as part of the first pixel; and
a second emissive layer formed as part of the second pixel.
7. A method of forming a display, comprising:
obtaining a substrate;
forming a reflector layer on the substrate;
forming a cathode;
forming an anode having a top surface facing the cathode and a bottom surface facing the reflector layer;
forming an additional anode having a different thickness than the anode;
forming an additional reflector layer under the additional anode; and
forming organic layers between the cathode and the anode, wherein forming the organic layers comprises:
forming electron layers having a first thickness; and
forming a hole transport layer having a second thickness less than the first thickness and minimized, directly over the anode, to reduce lateral leakage current.
8. The method of claim 7 , wherein the anode is part of a first pixel and wherein the additional anode is part of a second pixel, the method further comprising:
simultaneously forming a common electron blocking layer over the anode of the first pixel and the additional anode of the second pixel.
9. The method of claim 7 , wherein the anode is part of a first pixel, wherein the additional anode is part of a second pixel, and wherein the anode of the first pixel and the additional anode of the second pixel are separately patterned using different anode masks.
10. The method of claim 7 , wherein the anode is part of a first pixel and wherein the additional anode is part of a second pixel, the method further comprising:
forming a plurality of organic layers simultaneously over the anode in the first pixel and the additional anode in the second pixel.
11. An electronic device, comprising:
control circuitry; and
a display, wherein the display comprises:
a cathode;
an anode;
a reflector; and
a hole transport layer between the anode and the cathode, wherein the hole transport layer has a minimal thickness, directly over the anode, optimized to reduce leakage current in the display; and
transparent optical spacers sandwiched between the anode and the reflector and having different thicknesses in adjacent pixels of the display.
12. The electronic device of claim 11 , wherein the display further comprises a common electron blocking layer formed over the adjacent pixels.
13. The electronic device of claim 11 , wherein the display further comprises:
organic layers formed between the cathode and the anode, wherein all of the organic layers are simultaneously formed over the adjacent pixels.