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].