Centaurus Technologies and Innovations, Inc

ORGANIC LIGHT EMITTING DIODES (OLED)

By Ulugbek Akhmedov
January 11, 2007

Traditional Light Emitting Diodes or LED work on the following principle: there are two types of semiconductors that carry opposite electric charges. Negative charges are carried by well-known electrons and positive charges are carried by particles called “holes” which are electrons’ rivals. Holes carry positive charge and thought to be a vacancy in the semiconductor. If an electron fills in such vacancy there is no excessive change remaining in place. As electrons fill in the holes in the boundary layer they produce energy. One can also think of analogy of electrons falling instead of the water in the Niagara waterfall, which energy is harnessed by the hydroelectric power station. If you like a more fancy analogy, think of annihilation of particles and antiparticles which produces pure energy: light.

As this light can be emitted only through this very thin boundary layer it makes the light beam coming out of it very narrow and also very bright. As virtually very little heat is produced in the process of mixing positive and negative charges, LEDs are very efficient. They can convert over 90% of electricity into light. Miniature size and efficiency make LEDs an attractive light source that can be shaped according to the needs. LEDs are also used in flat TVs as, unlike LCD screen, they do not require additional backlight.

However there are certain disadvantages of LEDs that impedes faster implementation of this technology in various lighting and imagery applications. Here they are:

• • higher initial cost per lumen of the emitted light – semiconductor technologies, despite significant progress made, remain quite costly;
• • even if a tiny LED bulb may last over 50000 hours, bigger screens are more prone to failure due to the sealing issues – the greater the area the greater the chance that water and air will gradually destabilize LED performance due to corrosive effects;
• • circuitry for LED must have heat dissipation technology inbuilt in it; this is not because LED will overheat, but because LED performance is sensitive to the surrounding temperatures;
• • LEDs require complex power supply setups the eats into their genuine efficiency.

Along with inorganic LEDs, which are called just LEDs, there are Organic LEDs or OLEDs. The major difference between LED and OLED is the role of a semiconductor is played by an organic compound that may have less costly technology of production and processing. OLEDs generally give off less lumen per unit area. Their technological advantage is that big TV screen can be literally printed on the carrying substrate and sealed.

OLEDs have their disadvantages as well. The major disadvantage is the chemical instability of the organic matter used as light source. Over time they transform into chemicals that cannot be used as light source. This drawback is mainly due to water and air penetration though the minor breaks in the sealant. Scientists are currently working on water soluble chemicals that would be less prone to moisture and oxygen coming from air. At the present moment, the progress is slow, and major difficulty is not likely to be overcome any soon as it involves chemically aggressive behavior of oxygen towards metals – the key light emitting element in OLEDs.

In any case, the lifetime of LED and OLED screens must be well in 100,000 hours to make them suitable for TV and PC screen applications.

There are scientists who are working in a completely different field but trying to solve similar problem: how to create the most energy efficient light source. They are studying fireflies. But this is a different story…

New York City, NY