Organic light-emitting diode
An OLED is a light-emitting diode
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...

 (LED) in which the emissive electroluminescent
Electroluminescence is an optical phenomenon and electrical phenomenon in which a material emits light in response to the passage of an electric current or to a strong electric field...

 layer is a film of organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

s which emit light in response to an electric current. This layer of organic semiconductor
Organic semiconductor
An organic semiconductor is an organic material with semiconductor properties. Single molecules, short chain and organic polymers can be semiconductive. Semiconducting small molecules include the polycyclic aromatic compounds pentacene, anthracene, and rubrene...

 material is situated between two electrodes. Generally, at least one of these electrodes is transparent.

There are two main families of OLEDs: those based on small molecules and those employing polymers. Adding mobile ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s to an OLED creates a Light-emitting Electrochemical Cell
Light-emitting Electrochemical Cell
A light-emitting electrochemical cell is a solid-state device that generates light from an electric current . LEC's are usually composed of two metal electrodes connected by an organic semiconductor containing mobile ions...

 or LEC, which has a slightly different mode of operation.