Philips OLED Technology

This is a document provided by Philips describing their research efforts towards OLED technology.

http://docs.google.com/present/edit?id=0AXkRihIwaG7XZDc4d3Z2c18xNTRkNGs2OXNkNQ&hl=en

An organic light emitting diode is a solid-state semiconductor device that is around 200 times smaller than a human hair.

They can either two or three layers or organic material.

In a two layer design the layers consist of:

• substrate layer which supports the OLED - this layer is made of clear plastic, glass or foil
• an anode which removes electrons when a current flows through the device. The removal of electrons adds electrons "holes".
• the organic layers which are made of organic molecules or polymers.
  

- the conducting layer is made of organic plastic molecules that transport the holes from the anode . An example of a conducting polymer used in OLED's is polyaniline.
- the emissive layer is made of organic plastic molecules that transport electrons from the cathode. The light is made at this point. An example of a polymer used in the emissive layer is polyfluorene.

• a cathode injects electron when a current flows through the device.

The process is as follows:

1. The battery or power supply of the device containing the OLED applies a voltage across the OLED.
2. An electrical current flows from the cathode to the anode through the organic layers (an electrical current is a flow of electrons).
   • The cathode gives electrons to the emissive layer of organic molecules.
   • The anode removes electrons from the conductive layer of organic molecules. (This is the equivalent to giving electron holes to the conductive layer.)
3. At the boundary between the emissive and the conductive layers, electrons find electron holes.
   • When an electron finds an electron hole, the electron fills the hole (it falls into an energy level of the atom that's missing an electron).
   • When this happens, the electron gives up energy in the form of a photon of light.
4. The OLED emits light.
5. The color of the light depends on the type of organic molecule in the emissive layer. Manufacturers place several types of organic films on the same OLED to make color displays.
6. The intensity or brightness of the light depends on the amount of electrical current applied: the more current, the brighter the light.

Types of OLED's:

• passive matrix
• active matrix
• transparent
• top-emitting
• foldable
• white

Each type has its own specific use.

OLED Advantages and Disadvantages
The LCD is currently the display of choice in small devices and is also popular in large-screen TVs. Regular LEDs often form the digits on digital clocks and other electronic devices. OLEDs offer many advantages over both LCDs and LEDs:

* The plastic, organic layers of an OLED are thinner, lighter and more flexible than the crystalline layers in an LED or LCD.
* Because the light-emitting layers of an OLED are lighter, the substrate of an OLED can be flexible instead of rigid. OLED substrates can be plastic rather than the glass used for LEDs and LCDs.
* OLEDs are brighter than LEDs. Because the organic layers of an OLED are much thinner than the corresponding inorganic crystal layers of an LED, the conductive and emissive layers of an OLED can be multi-layered. Also, LEDs and LCDs require glass for support, and glass absorbs some light. OLEDs do not require glass.
* OLEDs do not require backlighting like LCDs (see How LCDs Work). LCDs work by selectively blocking areas of the backlight to make the images that you see, while OLEDs generate light themselves. Because OLEDs do not require backlighting, they consume much less power than LCDs (most of the LCD power goes to the backlighting). This is especially important for battery-operated devices such as cell phones.
* OLEDs are easier to produce and can be made to larger sizes. Because OLEDs are essentially plastics, they can be made into large, thin sheets. It is much more difficult to grow and lay down so many liquid crystals.
* OLEDs have large fields of view, about 170 degrees. Because LCDs work by blocking light, they have an inherent viewing obstacle from certain angles. OLEDs produce their own light, so they have a much wider viewing range.

Problems with OLED
OLED seems to be the perfect technology for all types of displays, but it also has some problems:

* Lifetime - While red and green OLED films have longer lifetimes (46,000 to 230,000 hours), blue organics currently have much shorter lifetimes (up to around 14,000 hours[source: OLED-Info.com]).
* Manufacturing - Manufacturing processes are expensive right now.
* Water - Water can easily damage OLEDs.

OLED seems to be the perfect technology for all types of displays, but it also has some problems:

• Lifetime - While red and green OLED films have longer lifetimes (46,000 to 230,000 hours), blue organics currently have much shorter lifetimes (up to around 14,000 hours[source: OLED-Info.com]).
• Manufacturing - Manufacturing processes are expensive right now.
• Water - Water can easily damage OLEDs.

How can OLED's be used?

General Electric has been developing OLED architectural lighting. They are developing products that may be as thin as wall paper and able to be applied in the same way.

Please refer to the Cool Links section on the right side of the blog for more information.