organic light-emitting diode (rus. светодиод, органический abbr., OLED) — LED whose emitting electroluminescent layer is composed of organic compounds.

Description

The function principle and emission mechanism of organic LEDs are similar to those of other types of LEDs. Organic LEDs are comprised of the following elements:

-a substrate (plastic, glass, foil);

-a cathode that injects electrons into the emitting layer when electric current flows;

-layers of organic materials one of which carries holes injected into the anode (usually composed of polyaniline) and the other carries electrons injected into the cathode (this is where radiative recombination of the charge carriers occurs);

-a transparent anode which injects holes when exposed to electric current.

The most commonly used materials for this application are tin-doped indium oxide (ITO) (as anode) and metals such as aluminium and calcium (as cathode), as well as light-emitting materials – low molecular weight organic materials and polymers.

The main application for organic light emitting diodes is in data display units called OLED displays. Colour displays are used most commonly.

By the types of their matrices, OLED displays are categorised into passive-matrix displays (PMOLED) whose picture elements are formed at points of intersection of mutually perpendicular anode and cathode strips and controlled by an external circuit, and active-matrix displays (AMOLED) which are controlled by thin-film field-effect transistors arranged into a matrix placed under anode film.

There are three alternative designs of colour OLED displays. In the first design option every element of the screen uses three separate colour emitters i.e. the three organic materials emit light in primary colours: red, green and blue. In the second option the scheme consists of three identical white emitters that emit light through colour filters. The third option applies blue emitters and specially selected fluorescent materials to convert short-wave blue light into longer wavelengths: green and red.

Illustrations

Organic LED structure.

Author

  • Zaitsev Dmitry D.

Sources

  1. OLED // Wikipedia, the free Encyclopedia. — http://en.wikipedia.org/wiki/Organic_light-emitting_diode (reference date: 12.12.2011).
  2. Majjskaja V. OLEDs. Amazing things near us (in Russian)//Ehlektronika: NTB. 2007. №5. P. 39–46.

Contact us