How Things Work: Organic LEDs

A new technology is poised to shake up the multimedia display industry. While CRT and LCD monitors control the market now, the days of their dominance may be numbered.

The new technology, known as OLED, or Organic Light Emitting Diode, may form the basis of an entirely new line of displays in consumer electronics. Current LCDs utilize traditional silicon-based transistors and capacitors to energize each pixel on the screen. OLED displays use special polymers made from organic materials to produce the picture you see on your computer screen, cell phone, mp3 player, or PDA. The use of organic materials in this way is quite a departure from existing display technologies, which have been a presence for so long that the LCD and CRT are now household names along with the likes of Teflon and Styrofoam.

Ironically, this ?new? technology has been around for over twenty years. The process by which organic polymers emit light, called electro-luminescence, was first discovered by scientists at Eastman Kodak in the 1970s. In their work at the photography giant, researchers Dr. Ching Tang and Steven Van Slyke discovered that applying an electrical current to certain carbon compounds produced a green glow. Since then, engineers at companies like Kodak, DuPont, and Samsung have turned a curious phenomenon into a marketable, mass-producible consumer product.

Current OLED displays are a mixture of old and new technology. It would be easy for one to mistake an OLED display for a LCD display, as both are flat screens. Even on the inside, similarities exist. Both methods produce a picture by applying voltage to individual red, green, and blue elements that make up each pixel on the screen. By varying the intensity of the voltage applied, the 255 hues of each sub-pixel can be produced, giving us the 16 million colors we?re familiar with in today?s monitors.

The similarities end there. OLED displays, unlike LCDs, actually emit their own light. Recalling some high school chemistry, one may recall that an electron dropping from a higher to a lower energy state gives off its excess energy in the form of a photon. In the case of an OLED, the emitted photons have wavelengths in the visible spectrum. Liquid crystals, in contrast (no pun intended), actually block light. Take a look at a calculator or cheap digital watch. The digits on the screen are black. LCDs rely on either ambient light reflecting off the display or backlighting to compensate for this.

OLED displays exploit these atomic emissions by sandwiching layers of positively and negatively charged organic materials into a grid of pixels, where applied charge causes each tiny diode to emit light. This complex microstructure is manufactured using the same principle as a common inkjet printer: tiny jets of ?color? ? in this case, various chemical dopants ? can be applied with accuracy as precise as one micrometer. The resulting LEDs are essentially analogous to the silicon-based big brothers one might see blinking to hard drive activity or lighting one?s alarm clock at night, only they are made of polymeric materials and are much, much smaller.

So what could be so revolutionary about OLEDs that could usurp today?s king of multimedia displays, the LCD flatscreen? After all, a picture is a picture, right? Wrong. Proponents of the new technology say OLED displays hold several advantages over the LCD. Because OLED displays directly produce light, they are more vibrant than traditional LCDs. The liquid crystals present in LCDs slightly distort light passing through it, lowering fidelity. Additionally, OLEDs have wider viewing angles than LCDs because LCDs polarize light passing through, which limits viewing to positions directly in front of the screen. LEDs emit light omnidirectionally.

Perhaps the most important advantage OLED displays have over their competition is that of size. Since they require no backlighting, their profile is reduced and power consumption is lowered. They don?t even need glass in front of the screen. Philips has developed fully functional prototype OLED displays only 1 mm thick. Compare that to the average depth of a 17? LCD monitor at 200 mm or even 400 mm for a 17? CRT. With a potential for production of OLEDs being cheaper than LCDs, there has even been speculation by members of the industry that the displays could see widespread use in areas outside of consumer electronics. They imagine large-dimensioned paper-thin displays able to display information to motorists, commuters, and passersby. If OLED technology becomes this versatile in the future, it will be something to keep an eye on.