TECHNOVA
OLEDs -A Flexible Future
In the not so distant future we could be having newspapers with OLED displays, which could refresh information to keep up with the latest news, could be folded like a regular newspaper, and you wouldn’t even have to buy one everyday! There could be "heads up" displays in cars. Display monitors could be built into one’s clothing. All this can be made possible only due to OLEDs(Organic Light-Emitting Diodes).
An organic light-emitting diode (OLED) is an LED having a thin-film of organic compound. The emissive electroluminescent layer can include a polymeric substance that allows the deposition of suitable organic compounds, in rows and columns on a flat carrier by using a simple "printing" method to create a matrix of pixels which can emit different colored light.
Working of OLEDs
OLEDs emit light in a similar manner to LEDs, through a process called electrophosphorescence. The power supply of the device applies a voltage across the OLED. An electrical current flows from the cathode to the anode through the organic layers. The cathode gives electrons to the emissive layer of organic molecules. The anode removes electrons from the conductive layer of organic molecules. At the boundary between the emissive and the conductive layers, combination of electrons and holes takes place. When this happens, the electron gives up energy in the form of light. The color of light emitted depends on the type of organic molecules in the emissive layer. Manufacturers place several types of organic films on the same OLED to make color displays. The intensity or brightness of the light depends on the amount of electrical current applied.
OLED Advantages
The radically different manufacturing process of OLEDs lends itself to many advantages over flat panel displays made with LCD technology. Since OLEDs can be printed onto any suitable substrate using inkjet printer technology, they have a significantly lower cost than LCDs or plasma displays. The fact that OLEDs can be printed onto flexible substrates opens the door to new applications such as roll-up displays or even displays embedded in clothing.
The range of colors, brightness, and viewing angle possible with OLEDs are greater than that of LCDs because OLED pixels directly emit light. Because of this, OLED pixel colors appear correct and unshifted, even as the viewing angle approaches 90 degrees from the axis perpendicular to the display. LCDs employ a backlight and are incapable of showing true black, while an "off" OLED element produces no light and consumes no power. In LCDs, energy is wasted because of polarizers. Additionally, in color LCDs the color filters filter out two-thirds of the light output, such that for an otherwise ideal color LCD panel, the maximum light output is only one-sixth of the input
Disadvantages
OLED seems to be the perfect technology for all types of displays, but they also have some problems:
- Lifetime - While red and green OLED films have long lifetimes (10,000 to 40,000 hours), blue organics have much shorter lifetimes (only about 1,000 hours).
- Manufacturing - Manufacturing processes are expensive.
- Water - Water can easily damage OLEDs.
Current and Future OLED Applications
OLEDs are used in small-screen devices such as cell phones, PDAs and digital cameras. Kodak uses OLED displays in several of its digital-camera models. Several companies have already built prototype computer monitors and large screen TVs. In May 2005, Samsung Electronics announced that it had developed the first 40-inch, OLED-based, ultra-slim TV.
Sony showcased a pair of large-format widescreen OLED panels it is developing for future TVs, in the Consumer Electronics Show, held in January, 2007.
Thus, commercial production of large–format OLED displays is just a matter of time, due to the various advantages offered by it over conventional displays.