Understanding the operation of light-emitting electrochemical cells

The ionic concentration (c(ion)) is demonstrated to play a critical role for the operation of wide-gap light-emitting electrochemical cells. p-type and n-type doped regions are observed to grow from the anode and cathode, respectively, and form a light-emitting p-n junction when c(ion)>= 0.1 ions/conjugated-polymer repeat unit. For lower c(ion), the doped regions come to a full stop before making contact and forming a p-n junction due to an ion-depletion effect. Finally, the n-type doped polymer is observed to be unstable over time under inert conditions, suggesting that a chemical side reaction between the n-type doped polymer and the electrolyte takes place. (C) 2008 American Institute of Physics.