Temperature-dependent recombination in polymer composite light-emitting diodes

We study the temperature dependence of the current-voltage and radiance-voltage curves in double-carrier injected polymer light-emitting devices comprised of poly(2-methoxy,5-(2'-ethyl-hexoxy)-p-phenylene vinylene) (MEHPPV) and MEH-PPV/SiO2 as the active layer. The quantum efficiency increases significantly as the temperature is decreased in agreement with an increase in the recombination efficiency with decreasing temperature. Moreover, the bimolecular recombination efficiency saturates at low temperatures and high currents to a very high value for both the composite and plain MEH-PPV devices with the nanoparticles serving as charge traps only at moderately low current densities. Finally, we find that the order of magnitude improvement in radiance observed in some polymer/nanoparticle composites is due to an increase in the effective electric field across the device. (C) 1998 American Institute of Physics. [S0003-6951(98)02952-0].