About OLED

An OLED (organic light-emitting diode) is a LED (light-emitting diode) in which the emissive electroluminescent layer is a film of organic compound that emits light in response to an electric current. This layer of organic semiconductor is situated between two electrodes. Typically, at least one of these electrodes is transparent. Large sized OLEDs are used to create digital displays in devices such as television screens and computer monitors. Small sized OLEDs are mainly used in wearable devices, portable systems such as mobile phones, handheld game consoles and PDAs. A major area of research is the development of white OLED devices for use in solid-state lighting applications.

Hong Kong-born American physical chemist Ching W. Tang and his co-worker Steven Van Slyke at Eastman Kodak built the first practical OLED device in 1987. This was a revolution for the technology.

OLED displays can use either passive-matrix (PMOLED) or active-matrix (AMOLED) addressing schemes. Passive matrix OLEDs (PMOLED) uses a simple control scheme in which you control each line in the display sequentially whereas active-matrix OLEDs (AMOLED) require a thin-film transistor backplane to switch each individual pixel on or off, but allow for higher resolution and larger display sizes.

An OLED display works without a backlight, thus, it can display deep black levels and can be thinner and lighter than a liquid crystal display (LCD). In low ambient light conditions (such as a dark room), an OLED screen can achieve a higher contrast ratio than an LCD, regardless of whether the LCD uses cold cathode fluorescent lamps or an LED backlight.

Advantages

Lower Cost

OLEDs can be printed onto any suitable substrate by an inkjet printer or even by screen printing, theoretically making them cheaper to produce than LCD or plasma displays during mass production.

Better Picture Quality

OLEDs enable a greater contrast ratio and wider viewing angle compared to LCDs, because OLED pixels emit light directly. Furthermore, OLED pixel colors appear correct and unshifted, even as the viewing angle approaches 90° from the normal

Better Power Efficiency and Thickness

LCDs filter the light emitted from a backlight, allowing a small fraction of light through. Thus, they cannot show true black. However, an inactive OLED element does not produce light or consume power, allowing true blacks. Removing the backlight also makes OLEDs lighter because some substrates are not needed.

Faster Response Time

OLEDs also have a much faster response time than LCD. According to LG, OLED response times are up to 1,000 times faster than LCD.

 

Disadvantages

Lifetime

The biggest technical problem for OLEDs was the limited lifetime of the organic materials. A 2008 technical report on an OLED TV panel reported that "After 1,000 hours the blue luminance degraded by 12%, the red by 7% and the green by 8%." In particular, blue OLEDs historically have had a lifetime of around 14,000 hours to half original brightness (five years at 8 hours a day) when used for flat-panel displays. This is lower than the typical lifetime of LCD, LED or PDP technology. Each currently is rated for about 25,000–40,000 hours to half brightness, depending on manufacturer and model.

Color Balance

Additionally, as the OLED material used to produce blue light degrades significantly more rapidly than the materials that produce other colors. Blue light output will decrease relative to the other colors of light. This variation in the differential color output will change the color balance of the display and is much more noticeable than a decrease in overall luminance.

Water Damage

Water can instantly damage the organic materials of the displays. Therefore, improved sealing processes are important for practical manufacturing.

Outdoor Performance

As an emissive display technology, OLEDs rely completely upon converting electricity to light, unlike most LCDs which are to some extent reflective. The metallic cathode in an OLED acts as a mirror, with reflectance approaching 80%, leading to poor readability in bright ambient light such as outdoors.

Power Consumption

While an OLED will consume around 40% of the power of an LCD displaying an image that is primarily black, for the majority of images it will consume 60–80% of the power of an LCD. However, an OLED can use more than three times as much power to display an image with a white background, such as a document or web site. This can lead to reduced battery life in mobile devices, when white backgrounds are used.