Organic light emitting diode (OLED) is a light-emitting diode (LED) whose emissive electroluminescent layer is composed of a film of organic compounds.
The first diode device was reported at Eastman Kodak by Dr. Ching W Tang and Steven Van Slyke in 19871. This device used a novel two-layer structure with separate hole transporting and electron transporting layers such that recombination and light emission occurred in the middle of the organic layer. This resulted in a reduction in operating voltage and improvements in
efficiency and led to the current area of OLED research and device production.

There are two main families of OLED: those based on small molecules and those employing polymers. Research into polymer electroluminescence culminated in 1990 with J. H. Burroughes et al. at the Cavendish Laboratory in Cambridge reporting a high efficiency green light-emitting polymer based device using 100 nm thick films of poly(p-phenylene vinylene). However multilayer OLEDs can be fabricated with two or more layers in order to improve device efficiency.
Another highly efficient white OLED device is to produce laminated structure. Kido believes that contains a structural unit N brightness white OLED can achieve a single OLED, N times, thus substantially increase the efficiency of the device.

Advantages of OLED:

1. Much faster response time.
2. Consume significantly less energy.
3. Able to display "True Black" picture.
4. Wider viewing angles.
5. Thinner display.
6. Better contrast ratio.
7. Safer for the environment.
8. Has potential to be mass produced inexpensively.

Recently, researchers from Kyushu University that led by Chihaya Adachi developed one kind of new OLED light-emitting fluorescent materials with 100% internal quantum efficiency. They have established light emission principle called thermally activated delayed fluorescence (TDAF) and worked on designing a material to increase its luminous efficiency. TADF OLEDs are free from the heavy metals used in phosphorescent emitters and so they could be cheaper and better for the environment. It can expect that will be great development in the future.

OLED systems can be used in television screens, computer monitors, small portable system screens such as cell phones and PDAs, advertising, information and indication. OLEDs can also be used in light sources for general space illumination, and large area light-emitting elements.

1. C. W. Tang, S. A. VanSlyke, Appl. Phys. Lett. 1987, 51, 913.

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