Light-emitting electrochemical cells from a blend of p- and n-type luminescent conjugated polymers

We demonstrate polymer light-emitting electrochemical cells (LECs) made of a blend of p- and n-type luminescent conjugated polymers. These two polymers, poly[9-(3,6,9-trioxadecyl)-carbazole-3,6-diyl] (TOD-PC, a p-type polymer) and poly[2,3-di(p-tolyl)-quinoxaline-5,8-diyl] (DT-PQX, a n-type polymer), are blue and blue-green emission polymers, respectively, both with high photoluminescent quantum efficiency. However, the photoluminescence of the polymer blend is completely quenched, due to the charge transfer between the two polymers. A new and faint orange-yellow photoluminescence emission, which has photonic energy consistent with the energy difference of the pi band of TOD-PC and the pi* and of DT-PQX, has been observed. LECs fabricated from this polymer blend show strong current injection and bright electroluminescence at this new emission color, which is believed to be due to the interpolymer radiative recombination of the electrons from the n-type polymer and holes from the p-type polymer. Such an independent p doping of TOD-PC and n doping of DT-PQX in the blend and interpolymer radiative recombination provide an interesting way of generating new emission colors in the LEC system. (C) 1997 American Institute of Physics.