The performance of polymer light-emitting diodes (LEDs) having the configuration Al/MEH–PPV/ITO, whereMEH–PPV=poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene)has been improved by light iodine doping of the emissive MEH–PPV polymer layer whereby the turn-on voltage is reduced and the external quantum efficiency is increased by an order of magnitude. It differs from nondoped MEH–PPV LEDs in that light emission is observed in both forward and reverse bias modes. It is believed that the mobility of theI3−anions in the(MEH–PPV)x+y(I3)xy−species formed on doping the MEH–PPV compensate for injected charges at the electrodes, thus reducing the electron and hole injection barriers. ©1997 American Institute of Physics.