A light-emitting electrochemical cell (LEC or LEEC) is a solid-state device that generates light from an electric current (electroluminescence

Electroluminescence

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...

). LEC's are usually composed of two metal electrodes connected by (e.g. sandwiching) an 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...

 containing mobile ions. Aside from the mobile ions, their structure is very similar to that of an organic light-emitting diode

Organic light-emitting diode

An OLED is a light-emitting diode in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes...

 (OLED).

LECs have most of the advantages of OLEDs, as well as additional ones:

• The device does not depend on the difference in work function
  Work function
  In solid-state physics, the work function is the minimum energy needed to remove an electron from a solid to a point immediately outside the solid surface...
  
   of the electrodes. Consequently, the electrodes can be made of the same material (e.g., gold). Similarly, the device can still be operated at low voltages.
  • Recently developed materials such as graphene
    Graphene
    Graphene is an allotrope of carbon, whose structure is one-atom-thick planar sheets of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The term graphene was coined as a combination of graphite and the suffix -ene by Hanns-Peter Boehm, who described single-layer...
    
     or a blend of carbon nanotube
    Carbon nanotube
    Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...
    
    s and polymers have been used as electrodes, eliminating the need for using indium tin oxide
    Indium tin oxide
    Indium tin oxide is a solid solution of indium oxide and tin oxide , typically 90% In2O3, 10% SnO2 by weight. It is transparent and colorless in thin layers while in bulk form it is yellowish to grey...
    
    for a transparent electrode.
• The thickness of the active electroluminescent layer is not critical for the device to operate. This means that:
  • LECs can be printed with relatively inexpensive printing processes (where control over film thicknesses can be difficult).
  • Internal device operation can be observed directly.

History

While electroluminescence had been seen previously in similar devices, the invention of the polymer LEC is attributed to Pei et al. Since then, numerous research groups, and even a few companies, have worked on improving and commercializing the devices.