Temperature-dependent recombination in polymer composite light-emitting diodes

We study the temperature dependence of the current-voltage and radiance-vol tage curves in double-carrier injected polymer light-emitting devices compr ised of poly(2-methoxy,5-(2'-ethyl-hexoxy)-p-phenylene vinylene) (MEHPPV) a nd MEH-PPV/SiO2 as the active layer. The quantum efficiency increases signi ficantly as the temperature is decreased in agreement with an increase in t he recombination efficiency with decreasing temperature. Moreover, the bimo lecular recombination efficiency saturates at low temperatures and high cur rents 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 curr ent densities. Finally, we find that the order of magnitude improvement in radiance observed in some polymer/nanoparticle composites is due to an incr ease in the effective electric field across the device. (C) 1998 American I nstitute of Physics. [S0003-6951(98)02952-0].