altRecent years have been moved to the display technology. We move from plasma to LCD, now the boom is for LED screens, while still gaining market began development of its replacement: the OLED.

By Beatriz Pineda *

 

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As the acronym defines it, OLED (Organic Light Emitting Diode) is an emitter organic light emitting diode containing films of organic compounds (chemical compounds in gaseous, liquid or solid whose molecules contain carbon) which when electrically stimulated emits light itself.

Such films, depending on the type of construction, may be formed of small molecules or polymers. The first are composed of at least two atoms while polymers or macromolecules are composed of structural units repeat.
 
One of the great advantages of OLEDs is that they can create sharper and brighter images, consuming less energy than conventional light-emitting diodes LED or liquid crystal displays.

A little history
Until a few years ago only to organic materials were considered as insulators, but in the years 50 laboratory tests showed that certain organic components could carry current.

In this same decade they saw the first observations of electroluminescence in organic materials Bernanose A. et al., In the Nancy University in France.

In 1977 Heeger, Mac Diarmid and Shirakawa discovered a high conductivity in iodine-doped polyacetylene, who later in the year 2000 were awarded the Nobel Prize in Chemistry for "the discovery and development of conductive polymers in organic".

The first diode device was reported in 1987 by Tang et al., Eastman Kodak Company who developed based on molecular devices bilayer films deposited vapor, consisting of a layer of hole transporting and emissive layer generating electroluminescence.

Finally in 1990 Burroughes JH et al., In the Cavendish Laboratory in Cambridge, they reported a high efficiency green light emitting polymers using sheets 100 nanometers thick.

OLED structure
The basic OLED structure consists of several extremely thin layers of different materials. The 6 basic layers are described below:

Substratum
This layer may be transparent glass or plastic and is responsible for supporting the device.

Anode
The anode extracts electrons (holes inserted) when a current flows through the device.

Hole transport layer (HTL)
This layer is responsible for transport of gaps (or holes) from the anode.

Emission layer (EML)
When electrons and holes recombine, energy transfer molecules who emission layer emitting light excited the characteristic color of its component.

Electron transport layer (ETL)
Its function is similar to that of the HTL layer and is responsible for transporting electrons from the cathode.

Cathode
The cathode may be transparent or not depending on the type of OLED, this injects electrons when a current flows through the device.

Types OLED
Passive matrix OLED (PMOLED)
In this type of OLED cathode and anode they are formed by perpendicular strips. Since the organic layer is between said stripes, the light is emitted at intersections (pixels), by applying voltage in the horizontal and vertical matrix points.

This type of OLED is easy to manufacture but consumes more energy than the alternative system, for this reason are ideal for small screens (1 "to 3") and Alphanumeric.

Active Matrix OLED (AMOLED)
Complete anode and cathode layers are used, the matrix TFT (Thin Film Transistor) is on the anode. In this arrangement the TFTs are responsible for determining which pixels should be turned on or off.


One of its great advantages is that it consumes less energy than PMOLEDs and have higher rates of cooling, for this reason it is used in the manufacture of large screens (TVs, PC monitors, electronic signs, billboards).

Transparent OLED (TOLED)
In these devices all layers are composed of transparent materials or semi-transparent, allowing bidirectional light emission through the cathode and anode

folding or flexible OLED (PLED)
Thanks to the properties of OLED components in their manufacture can be used plastic substrates or flexible sheets and ultra-thin, which make them lighter, more durable.
Sony has been working in this area to develop screens that can be used in a number of applications such as televisions, cellular manufacturing, etc.

soled
It is formed by stacking stations OLED layers to achieve the desired color light. This type of OLED allow us to replace conventional lighting systems such as fluorescent lamps may be generated as brighter lights in a more efficient and uniform manner, greatly reducing energy consumption.

OLED types of structures
Lower emission OLED
The light generated by the emitter layer, travels conversely toward the TFT circuitry, which partially blocks the light output. Its manufacture is relatively simple and economical result for this reason conventional designs bottom emission OLED use.

OLED top emission
Unlike the previous case in this structure the cathode is formed of a transparent material and the anode may be opaque and / or refractive allowing light to travel frontally drastically increasing the luminous area. The design of Sony uses this type of structure because it maximizes thus the brightness of the image as energy efficiency.

In addition to adopting the top emission OLED Sony developed its own technology Super Top Emission ™ that incorporates a set of technologies such as micro cavities and the color filters in the OLED structure.

At present there are several products on the market that incorporate OLED screens, some of them: TV (XEL-1) and in the area of ​​professional monitoring the 740 PVM. In addition to the new Broadcast monitors and 25 17 inches (BVM-E250 and BVM-E170) manufactured by Sony.

Many are the advantages of OLED technology, thanks to the characteristics of its components each pixel can be turned off completely allowing the reproduction of extremely deep blacks, plus the contrast ratio of an OLED it is excellent.

The switching time of the OLED is so fast that are no longer necessary frequencies Hz refresh 120 or 240 Hz to suppress blur in motion. For these and many other reasons is the future OLED technology display screens.

OLED technology will certainly become the next generation of flat screens and is the key in developing a wide variety of applications with ultra thin and flexible displays such as the development of smart clothing, lighting, cars windshield allow the display of speed controls, GPS, phone, etc., this and much more is possible thanks to the great qualities of OLED technology.


*Product manager
Sony Broadcast & Professional Latin America (BPLA)

Richard St.
Author: Richard St.
Editor
Journalist from the University of Antioquia (2010), with experience in technology and economics. Editor of the magazines TVyVideo + Radio and AVI Latin America. Academic Coordinator of TecnoTelevisión & Radio.

Comments

Jorge Alberto FERREYRA
# Jorge Alberto FERREYRA 27-05-2011 03:29
Excellent explanation, instructs us to continue hearing the new changes that have been
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